Bulletin 627

BuREu OF MiNS

FLAMMABILITY CHARACTERISTICSOF COMBUSTIBLE GASES AND VAPORS

By Michael G. Zabetacis

Bulletin 627BUREAU OF MINES

FLAMMABILITY CHARACTERISTICSOF COMBUSTIBLE GASES AND VAPORS

By Michael G. Zabetakis

0

This publication has been cataloged as follows:

Zabetakis, Michael George, 1924-Flanunability (haraeteristics of combu.tilhe gases and

vapors. rWashingtonj U.S. Dept of the Interior, lureati ofMines 11965)

121 p. Illus., tables. (U.S. Bureau of Mines. Bulletin 627)Includes bibliography.1. Combustion gases. 2. Gases. 3. Vapors. 1. Title. II. Title:

Combustible gases. (Series)TN23.U4 no. 627 622.06173U.S. Dept. of the Int. Library.

For sale by the Superintendent of Documents, U.S. Government Printing OfficeWashington, D.C., 20402 Price 75 cents

CONTENTS

Page Flammability characteristics-Continued PapeAbstract -------------------------------------- Aromatic hydrocarbons- ContinuedIntroduction---------------------------------- I Limits in other atmospheres---------------- 60Definitions and theory ------------------------- 2 Autoignition ------------------------------ 62

Limits of flammability ----------------------- 2 Burning rate ----------------------------- 62Ignition ------------------------------------ 3 Alicyclic hydrocarbons ---------------------- 63Formation of flammiable mixtures -------------- 4 Limits in air ----------------------------- 63

Presentation of data ---------------------- ----- 9 Limits in other atmospheres ---------------- 64Deflagration and detonation processes..----------- 15 Alcohols----------------------------------- 65

Deflagration ------------------------------- 15 Limits in air ----------------------------- 65Detonation -------------------------------- 16 Limits in other atmospheres ---------------- 66Blast pressore ------------------------------ 16 Autoignition ------------------------------ 67

Preventive measures -------------------------- 18 Burning rate ------------------------------ 68Inerting ------------------------------------ 1 Ethers ------------------------------------- 69Flame arrestors and relief diaphragms-------- 18 Limits in air ------------------------------ 69

Flammability characteristics ------- ------------ 20 Limits in other atmospheres ----------- -- ---- 69Paraffin hydrocarbons ------------------------ 20 Autoignition ---- ------------------------- 70

Limits in air----------------------------- 20 Esters ------------------------------------- 70Limits in other atmospheres ---------------- 27 Aldehydes and ketones ---------------------- 73Autoignition ----------------------------- 32 Sulfur compounds --------------------------- 74Burning rate ----------------------------- 42 Fuels and fuel blends ----------------------- 74

Unsaturated hydrocarbons ------------------- 47 aimmonia and related compounds ---------- 74Limits in air---------------------------- 47 Boron hydrides---------------------------- 82Limits in other atmospheres ----------------- 50 Gasolines, diesel and jet fuels --------------- 82Autoignition ----------------------------- 50 Hydrogen ------------------------------- 89Burning rate ------------------------------ 51 Hydraulic fluids and engin) , oils -------------- 95Stability --------------------------- -- ---- 51 Miscellaneous ------------------------------ 97

Acetylenic hydrocarbons------- ------------- 653 Acknowledgments-------------------------- --- 106Limits in air ------------------------------ 3 Bibliography ------------------- -------------- 107Limits in other attmospheres ------- --------- 55Autoignition ------------------------------ 0 Appendix A. Siirnmary limits of flammability- 114Burni~ng rate ----------------------------- 56 pnix.-oihoticom ston---17Stability-- - - ---------------------------- 57 Appendix C. -11eat contents of gases ----------- 118

Aromictic hydrocarbons.--------------------- 59 Appendix 1). -Definitions of principal symbols- 119Limrits in air -------------------------- 59 Subject index--------------------------------120

ILLUSTRATONS

Fig. Page1 . Ignitibility curve and limits of flammiability for methane-air mixtures at atmosphieric pressure and 26* C- 22. FfI~tv of tempe-rature onl limits of flinniatdlity of a conmbustibile vapor in air at a constant initial pins-

'i. ini d ilay I aforv ignition of N PN ini air at 1 000)1 pa ig in the tem pira ture range from 1 510* to 21 0* C, . 5,.1 Logar i ini of time delay bewfore ign itijon of NJi N in air at 1,0001 psig iinitial pressur---------------- ---- 6

..Simiplified nixer----------------------------------------- ------------------ ------ 76. Comnposition of gas in chamlber 2, figure 5 (instantaneous muixing)- - - ---------------------- ------- 77, Coiiiposition of gas in chambher 2, figure 5 (delayed mixing) ----------------------------------------- 7

.. Variation in, lower limits oft tlaininatilitv of various comibustibles in air Ps a function of droplet diameter 7FVnn i in ahi lit 3 di agrain for the systveiIin i(t Ii ate-oxy g(il-nit rogetYi atI at I nospli e pressure and 26' C -

10 n.FlanmiiaI ilitY v (i 5grin for t he syst iiii iii(-ithaoi'(-oxy'geni- nitrogeni at at n osph eric pressure and~ 2110 C fi. F; icrt o f iuiitia i en I per it uri on liit s of flai iiiability of it coin hust ii d vapor- iii rt-a ir syst lii itt atmnos-

lpheric pr(-&ur-- -- -- ----------- I------- -------------- ------------------ -- ---- - - -----12. Ictrict oif initial pressure on liimits of' flaiinahility of JP-4 in air at 26' C ------------ -1

Iv CONTENTrS

13. Effect of temperature and pressure on limits of flammability of a combustible vapor lin a specifiedoxident ----------------------------------------------------------------------------------- 12

14. Flammability diagram for the system gasoline vapor-water vapor-air at 700 F and at 2120 F anid atinlos-pherio pressure----------------------------------- ---------I -I----------- ------- 13

15. Pressure produced by Ignition of a 9,6 volumec-percent mietbanie-air mixture in a 9-liter cylinld(r ------ 1516. D~etonation velocity I, V'; 9tatic pressure, 11,; and reflected pressure, I',, dleveloped b)'Y a detonation

wave rating through byxd ogen-oxygen mixtures in at cylindrical tube at atmzosphieric pressureand X 0 F a9-a I ----- --- --- --- ---- --- --- --- -- - -- - --- --- --- -- - --- --- --- -- - - 16

17. Pressure variation following ignition of a flanimiable mixtu re ini unp)rotected arid prot;ect ei eiielosures~ 18 i18. P~ressure produced by Ignition of at flamninal le mixture in a vonted oven .-- -- -- ------------- it919. Effect of molecular weight onl lower limits or flammnability of paraffin hydrocarbons at 250 C ----------- 2020. Effect of temperature onl lower limit of flainniability of mnethane in Peir tit atmniperic presilr-------2221. Effect of temperature onl lower limits of flamnmability of it0 pairaffin hydrocarbons init ir ait atmlospheric

pressure. . . - - - - - ------- - - -------- 2:322. Effect of temperature on lower limits of flamnnialnility of 10 parailin liydi darhoiis init;, ti a i )nopl-rie

pressure by wveight----------------- -------- ----------------------------- 2423. Effect of temperature on L,1/ 2 ,,- ratio of paraffin hydrocarbons lin tir tit atinoplicric pressure --. 2524. Effect of temperature onl (71 7/U.s- raitio of liaril hydrocarbons ini air at atmnospheric pressure in the

absence of cool flames----------------------------------------------------------- 2625. Effect of pressure on limits of flammnability of pentane, hexane, and hept aite tin air ait 260 (C------------- 2626. Effect of pressure on limits of flammnability of natural gas in air tit 280 C ----------------------------- 2727. Effect of pressure onl lower temperature limits Of flammiability of pent'ane, blexance, beptanle. and octanle

litair ------------------------------ ------------------------------------------ _ - --- --- 2828. Limits of flammability of various methane-inert gas-mnir mixtures ait 250 C and attmiospheric pressure_.- 2929. Limits of flamnmability of ethano-carbon dioxide-air anni cthaine-nitrogen-air mixtures ait 250 C and

atmospheric pressure------------------------------------------------------------------------ 3030. Limits of flammability of propane-carboni ioxitie-air and propaoc-nitrogen-air mixtures at 25' C and

atmospheric pressuire-------------------------------------3131. Limits of flammabilityofbtn-rbndoiearadbt 1 -nton-rmiuest25Cad

atmospheric pressure ----------------------------------------------------------------------- 3232. Limits of flammability of various n-pentane-inert gas-air nmixtu- i a tt 250 C and atmospheric pressure- 3333. Limits of flammability of various n-hexane-inert gas-air mixtur -s ait 250 C anid atmospheric pressure- 3434. Limits of flammability of n-heptane-water vapor-air mixtures at 1000 and 2000 C and atmospheric

pressure ---------- f------------------------------------------------------------------------ 353.Approxiate limits offlammability of higher paraffin hydrocarbons (C.112 ,+2, n2!5) in carbon dioxide-

air and nitrogen-air mixtures at 250 C and atmospheric pressuire---------------------------------- 3636. Effect of pressure upon limits of flammability of natural gats-nitrogen-air mixtures at 260 C ------------ 3737. Effect of pressure onl limits of flammability of ethane-carbon dioxide-air mixtures at 260 C ------------ 3838. Effect of pressure on limits of flammability of ethane-nitrogen-air mixtures at 260 C----------------- 3939. Effect of pressure onl limits of flammiability of propane-carbon flioxide-air mixtures--------------------4040. Effect of pressure onl limits of flammiability of propanie-nitrogen-air mixtures -------------------------- 4141. Effect of pressure on minimum oxygen requirements for flame propagation through natural gas-nlitrogen-

air, ethane-nitrogen-air, and propanie-nitrogen-air mixtures at 260 C ------------------------------ 4242. Low-temperature limit of flammiability of decane-air, dodecane-air, anid mecan-dodecane-air mixtures-43. Minimum autoignition temperatures of paraffin hydrocarbons in air ats at function of average carbon

chain length------------------------------------------------------------------------------- 4444. Burning velocities of miethane-, ethane-, propane-, and n-hceptane vapor-air mixtures at atmospheric

pressure and room temperature - --------------------------------------------------------- 445. Burning velocities of methane-, ethanne-, and propane-oxygen mixtures ait atmospheric pressure and room

temperature -------- ---------------------------------------------------------------------- 4646. Variation in horning v'elocity of stoichiometric methane-aiir and propane-air mixtures with pressuii: at

260 C--------------------------------------------------------- ------------------ -------- 4747. Variation in burning velocity of stoichiornetric methane- andl ethyl cne-oxygen mixtures with presstire 4

a t 26 ' C - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 448. Effect of temperature on burning velocities of four paraffin hydrocarbons in air at atmospheric pressure- 4949. Detoiation velocities of mnethane-air mixtures ait atmospheric pressure------------------------------ 4950. D)etonation velocities of methane-, ethane-, propane-, butane-, and hexane-oxygen mixtures at atmos-

pheric pressure -------------------------------- ------------------------------------------ 451. D~etonation velocities of n-heptatne vapor in WFNA (white funming nitric acid) -nitrogen gas mixtures at

atmospheric pressure arnd 4000 K ---------------------------------------------------------- 50)52. Relation between liquid-burning rate. (large-pool diameter) and ratio of net heat of combustion to

sensible heat of vaporization----------------------------------------------------------------- 5053. Effect of temperature on lower limit of flammnability of ethylene in air at atmospheric pressure..-----5054. Limits of flammability of ethylene-carbon (lioxide-air and ethylene-nitrogeni-air mixtures at atmospheric

pressure andl 26'0 C--------------------------------------------------------------- 555. Limits of flammability of propylene-carboni dioxide-air and propylene-nitrogen-air mixtures at atmos-

phieric ressure and 26' C-------- ------------ ---------------------------------------------- 51.56. Limits of flainmability of inobutylerie-carbori dioxide-air and isobutylene-nitrogenl-air mlixtures lit

5 a ttmnlosp ieric pressurremandl26' C -------------------------------------------------------------- 5257 . Limits of flammnability of isobuitylene-water vapor-oxygen inixtures at I 5)O C and atmospheric pressumre- 53

58. Limits of flaminmibility of bmtene- I-carbon dioxide-air 1111d bUteme- I-nitrogen-air mixtures ait atniospl(briCpressure and 26* --- ---------------- ---------------------------------------------------- 54

5 9. Limits of flammnability of 3 miethyl butemie-l-carbom dioxide-,dr and 3 miethyl-buiteie- I-nitrogeni-airmixtures at atmospheric pressure and 260 C--------------------------------------------------- 54

CONTrENTrS V

Fig. Prg60). ,imyits of flatnmabilit 'y of butudlenc-ccirbon dioxide-cur find btitadlene-nitrogon-air mixtures at atmos-

phteric pressure and 260 C - -- -- - -- - - - - - - - - - - - - - - - - - - - - - 5561. Effect of tube dliame'ter onl initial pressure requirements for propagation of dleflagration aind detonation

through acetylene gas --------------------- --------- _--------62. Range of flammiable mixtures for me(tbylatctylene-propcii(liene-propylenie system at 120' C find at 50

find 100psig-- - ---------------------------------------------- ------- -------------- ------_63. Quenched limitsi of flammiability of acetylene-carbon dioxide-air and acetylene-nitrogen-air mixtures

at atmosp~heric pressure find 2t1 C otinced in at 2-inch tube ------------------------------------- 5864. Mini ccci autoigi iio temperatures of aceetylene-air aind acctylcne-oxygcn mixtures at atmospheric

and elevated pressures----------------------------------------------------------------------- 5865. Burning velocity of acetylene-air mixtures ait atmospheric pressure and room temperature -------------- 5966. Maximumn LID ratio required for transition of at defl agration to a detonation fin acetylene vapor at 600

F and froto 10 to 70 psia -------------- ----------------------------------------------------- 59#17. Ficcal-to-initial pressure ratios4 developed by acetylene with (letonatijn initiation at various points

aloncgcatube--------------------------------------------------------------------- - - 6068. Limits of fihinicriability of benzver-niethyl bromide-air mixtures at 25' C and benizene-carbon dioxide-air

aind henzene-nitrogen-air mnixtures at 250 aind 15(0' C aind atmospheric pressure ----------------- _ - 6169. Lilits Of flammablttiility Of ll 2()2 -C 6lI 4 .(Cl13)h-ll 2O ait 1540 C aind 1 atmosphere pressure ---------------- 6270. Limits of flammnability of 90-weight-perceet llY0 2-C6 114.( Clf 3 )2-lCOOiI at 154V C and 1 atmosphere

pressure-.---------------------------------------------------------------------------------- 6371. Nliniinuin autoignition temperatures of aroinatic hydrocarbons in air as a function of correlation

paramieter L --------- ----------------------------------------------- 6472. Limits of flammllInabili ty of cyclopropan-cacrhon dioxide-air, cyclopropane-nitrogen-air, and cyclopropane-

heliumn-air miixtures ait 250 C aind atmospheric pressure ------------------------------------------ 6573. Limits of flammi iability of cyclopropatne-hiutni-oxygen aind cyclopropane-nitrous oxide-oxygen mixtures

ait 25' C and atmospheric pressure ------------------------------------------ ------------------ 6674. Limits of flaninability of cyclopropitne,-he(liumt-niitrotus oxide mixtures at 250 C and atmospheric pressure- 6675. Limits of flammability of methyl alcohiol-carbon dioxide-air and methyl alcohol-nitrogen-air mixtures at

25' C and atmospheric pressure -------------------------------------------------- ------------ 6676. Limits of Flammability of methyl alcohol-water vapor-air mixtures at 1000, 2000, and 4000 C and

alnospheric pressure ----------------------------------------------------------------------- 6777. Limits Of flammability of ethy) alcohiol-carbon dioxide-air and ethyl alcohol-nitrogen-air mixtures at

251 C and atmospheric pressure ------------------------------------------------------------- 6878. Limits of flatmmnability of ethyl alcohiol-wt, vapor-air mixtumres at 1000 C and atmospheric pressure- 6879). Limits of flammnability of terf-bcctyl alcohol-water vapor-air mixtures at 1500 C and atmospheric pressure- 6880. Limits of flanmmability of terl-butyl alcohiol-carbon dioxide-oxygen mixtures at 1500 C and atmospheric

pressure --------------------------------------------------------- ------------------------- 6881. Limits of flammability of 2-ethiylbtantol-niitrogeni-oxygeni mixtures at 1500 C and atmospheric pressure- 6982. Limits of flamniability of dimethyl ether-carbon dioxide-air aind dimethyl ether-nitrogen-air mixtures at

25' C anid atmnospheric presstire------- ------------------------------------------------------ 6983. Limits of flammability of dilethyl ether-carbon dioxide-air aind diethyl ether-nitrogen-air mixtures at 250

Cafidatilloqpheric pr'ssccre-------- ------------------------------------------------------ - -6984. Limits of flamnability of diethyl ether-helium-oxygen aind diethyl ether-nitrous oxide-oxygen mixtures

ait 25' Canid atmospheric pressuire.-------- --------------------------------------------------- 70S5. Limits of flammability of diethvl ether-nitrous oxide-heliumn mixtures ait 25' C and atmospheric pressure- 7080i. Limlits of flammnabilit y of mnet hcyl formcvite-cccrbon dioxide,-air aind miethyl formate-iiitrogen-air mixtures- 7187. Limits of taimicabilit y of isobut'vi forinate-ecarbon dioxide-air aind isobutyl formate-n1itrogen -air mixtures- 7288. Limlits of flitInfilbilit y of flet hI' acetate-carboci dioxide-air aind methyl aetate-nitrogvci-air mnixtumres-- 7289). Effu-ct, of temperature onl lower limits of flamomability of MEK-tolumene mixtures in air itt atmosp~heric4 ressiirc'------------- ---- ---------------------------------------------------------------- 7390. ICetof teiperattire on lower limits of flammability of TIIF..toluiene mixtures in air at atmospheric

pressur ------- ------------------ ----- ---------------------------------------------------- 7491. Effect of liquid composition on lower finciti of flammability of MIEK-tolice mixtures in air at 300 alid

20010 C ------------------------ ---------------------------------------------------------- 7502. Effec I of liquid composition onl lower limits of flammability of TIIF-toluene mixtures in air at 30* and

2001 C..---------- ----------- -------------------- -------------- ----------------------- --- 769:3. Limits of fliamomcilbili~y of acetomie-carboci dioxide-air and acetone-iiitrogeni-air mixtures ---------------- 7794. Limiits of flamumnalilit v of mocthtil Othyl ktocie (NI EK)-chilorobromomecthlace (CBM)-air, MIEK-carbon

dioxide-air acnd NI F'IK-ctitrog(.ci-itir'tiixtiires at 250 C aid atmospheric p~ressure -------------------- 7995. Limcit s of launiibilit y of carboci distilfide-etirbon dioxide-air, ccarbon dioxide-nitrogen-air mixtures cit 25'

C andi cit cmslieric pressure, aid carboni discilfide-water vapor-air ait 1000 C and atmospheric pressure. 7996. Limits of fl Icucictabilit y of liydropemi sclfidvearboci dioxide-air mixtures ait 250 C amid atmnosp~heric

pressuir--------------------- ------------------------------------- -------- 7997. Licoits of flit titcatdlit Nof ethiyl moerecptaci-F'-12-air aid ethyl mercaptaic-F-22-air mixtures ait atmos.

phiiric priesurvandul27' C_----_------ ---- ------------- ---- -- - - 71)98. 1 am its of fil c cI) 1hlil y of ium nioc iii, U I) N Il NI NI I, anicd hydrazice cit at mosphieric pressure icc satcurated

acid ieur-saurited vapor-dir inixtcri--------------------------------091)I. Flu iinnable mcix tiure cocinpositioc s of It razici -hept ccc -air cit 1250 C acid approximcatel y atmospheric

,pressutre _--_ _ . - -. - - -- - - - - - - - - - - - - - - - -- - - - - - - 81100. 'N tiniiui Spout anieous igncition tcinpurat ores of liquid hydrazine, MINI1, and U I) I I at sil incit ial

ucciprau o of 250 C ici cocctact wit" N02)*-air mcixtucrus cit 740(10 mt cin Hg as a funct ion of No,*coiiecctratioc------------------1-------------------- ---- -------------- 82

101 . N ilci iciucci spoict it a olis ign it ioc t ciiipi rcto ris of l iquiiid hcydcraz inc at various initial tecI puwrat ores illNO2 *-air mixtures at 740 1 1t) mmi fig as at function of NOJ,* coccntration --------------------- 1

V1 CONTENTS

rig. P84e102. Minimum spontaneous ignition tomperatures of liquid MMH at various initial temperatures in NO,*-

air mixtures at 740 ± 10 mm Hg as a function of NO?* concentration --------------------------. 84103. Minimum spontaneous ignition temperatures of liquid UI)MH at various initial temperatures in

NO,*-air mixtures at 740 ± 10 mm Hg as a function of NO,* concentration ..-------------------- 85104. Minimum spontaneous ignition teirperatures of 0.05 cc of liquid UDMH in tle-OrNO,* atmospheres

at 1 atmosphere for various He/Os ratios-- ----- ----------------------------------------- 80105, Minimum spontaneous ignition temperatures of 0.05 cc of liquid UDMH in NO,e-air mixtures at 15

and 45 pas as a function of NO,* concentratioc ....... 87106. Minimum spontaneous Ignition temperatures of vaporized UDMH-air mixtures in contact with 100

pet NO,* at 250 C and 740± 10 mm Hg as a tunetion of UDMH concentration in air ------------- 87107. Limits of flammability of diborane-ethane-air mixtures at laboratory temperatures and 300 mm Hg

initial pressure ------------------------------------------------------------------------------- 88108. ASTM distillation curves for, A aviation gasoline, grade 100/130; B, aviation gasoline, grade 115/145;

C aviation jet fuel, grade JP-I; D, aviation jet fuel, grade JP--3; and, B, aviation jet fuel, gradeJP-4 ..................................... ................................... 88

109. Limits of flammability of aviation gasoline, grades 115/145 vapor-carbon dioxide-air vad 115/145vapor-nitrogen-air, at 270 C and atmospheric pressure ----------------------------------------- 88

110. Limits of flammability of JP-4 vapor-carbon dioxide-air and JP-4 vapor-nitrogen-air mixtures at 270 Cand atmospheric presure --------------------------------------------------------------- - 88

Ill. Limits of flprnmabi9t" nf hydrogen-carbon dioxide-air and hydrogen-nitrogen-air mixtures at 250 Cand atmospheric pressure -----------.-----------.------------------------------------- 89

112. Limits of flammability of IHrNO-NjO at approximately 280 C and I atmosphuee ------------------ A113. Limits of flammability of HrNO-air at approximately 280 C and I atmosphere -------------------- 91114. Limits of flammability of Hi-NO-air at approximately 280 C and I atmosphere -----................. 92115. Rate of vaporisation of liquid hydrogen from paraffin in a 2.8-inch l)ewar flask: Initial liquid depth-

6.7 inches ------------------------------------------.----------------------------------- 93116. Theoretical liquid regression rates following spillage of liquid hydrogen onto, A, an average soil; B, moist

sandy soil; and C, dry sandy soil --------------------------.-------------------------------- 93117. Theoretical decrease in liquid hydrogen level following spillage onto, A, dry sandy soil; B, moist sandy

soil; and C, an average soil ---------------------------------------------------------------- 94118. Extent of flammable mixtures and height of v(sible cloud formed after rapid s illage of 3 liters of liquid

hydrogen on a dry macadam surface in a quiescent air atmosphere at 15'C ---------------------- 94119. Motion picture sequence of visible clouds and flames resulting fron, rapid spi~lage of 7.8 liters of liquid

hydrogen on a gravel surface at 180 C ------------------------------------------------------ 95120. Maximum flame height and width produced by ignition of vapor-air mixtures formed by sudden spil-

lage of 2.8 to 89 liters of liquid hydrogen --------- --------------------------------------- 96121. Burning rates of liquid hydrogen and of liquid methane at the boiling points in 6-inch-Pyrex Dewar

flaks --------------------------------------------------------------------------- 96122. Variation in minimum autoignition temperature with pressure of commercial phosphate ester and

mineral oil lubricantd in air in r 450-cc-stainless steel bomb ---------------------------------- 98123. Logarithm of initial pressure-AIT ratio of seven fluids in air for various reciprocal temperatures ------ 99124. Variation in TnT, of air with V,/Vf and with Pf/P, in an adiabatic compression process .------------- 100125. Variation in air temperature with P,/Pj in an adiabatic compression process for five initial air tem-

peratures ----------------------------------------------------------------------- 101126. Limits of flammability of carbon monoxide-carbon dioxide-air and carbon monoxide-nitrogen-air

mixtures at atmospheric pressure and 26 C --------------------------------------------- 102127. Lower limits of flammability of NPN vapor-air mixtures over the pressure range from 0 to 1,000 psig

at 750 1250 1500 and 1700 C -------------------------------------------------------------- 102128. Flammable NPN vapor-air mixtures formed over the pressure range from 0 to 1,000 psig at 500 and

1250 C --------------------------.---------------------.-------------------------------- 103129. Variation of explosion pressure following spontaneous ignition with NPN concentration- -----.. -- 104130. Minimum spontaneous ignition and decomposition temperatures of n-propyl nitrate in air as a func-

tion of pressure ------------------------------------------------------------------------- 104131. Flammability of trichloroethylene-air mixtures .-------------------------------------------- 105

TABLES

Page1. Conditions of failure of peak overpressure-sensitive elements ------------------------------------- 172. Properties of paraffin hydrocarbons ---- -.---------- ---.-------.------------.------------------ 213. Upper flammability limits of methane-air mixtures at 15 psig _... ...------------------------- 244. Lower temperature limits and autoignition temperatures of paraffin hydrocarbons at atmospheric

pressure -----------------.--------------------------- -------------------------------- 255. Limits of flammability of methane in chlorine- . ...............---------------------------- 276. Limits of flammability of ethane in chlorine- ---.--------- ----------------------------------- 287. Properties of unsaturated hydrocarbons .... ..--------------------------------------------------- 488. Limits of flammability of unsaturated hydrocarbons at atmospheric pressure and room temperature, in

volume-percent combustible vapor -----------.-------------------------------------------- 529. Minimum autoignition temperatures of unsaturated hydrocarbons at atmospheric pressure ----------... 52

10. Heats of formation of unsaturated hydrocarbons at 250 C ---------------------------------------- 53II. Properties of selected aromatic hydrocarbons --------------------------------------------------- 60

CONT 7N'rS VIU

Pageo12. Prop ,rties of aelected alicyclic hydrocarbons ------------------------------------------------------- 6413. Properties of selected simple alcohols ---------------------------------------------------------- 6714. Propertie of selected ethers ---------------------.------------------------------------------------ 7015. Properties of selected esters --------------------------------------------------------------- - -- 7116. Properties of selected aldehydes and ketones ---------------------------------------------------- 7317. Properties of selected sulfur compounds ------------------------------------------------------- 7418. Properties of selected fuels and fuel blends ------------------------------------------------------ 7719. Limits of flammability of ammonia at room temperature and near atmospheric pressure --------------- 7820. Autoignition temperature values of various fuels in air at I atmosphere ----------------------------- 8821. Limits of flammability of hydrogen in various oxidants at 250 C and atmospheric pressure .------------ 89A-I. Summary of limits of flammability, lower temperature limits, and minimum autoignition temperatures

of individual gases and vapors in air at atmospheric preuure -------------------------------- 114

FLAMMABILITY CHARACTERISTICS OF COM-BUSTIBLE GASES AND VAPORS

Acu I A Zxketakiqi

A bstract3 HIS is a summiary of the available limit of flammiability, autoignition,and burning-rate (lata for more than 200 combustible gases ancd vaporsin air and other oxidants, its well as of empirical rules and graphs that

c'an be used to predict similar dta for thousands of other combustibles unidera variety of environmental conditions. Specific data are presented on theparaffinic, unsaturated, aromatic, arid alivNycl ic hydrocarbons, alcohols, ethers,aldehydes, ketones, and sulfur vomnpoundls, and" an assortment of fuels, fuelblends, hydraulic fluids, engine oils, and miscellaneous combustible gases andvapors.

Introduction

Prevention of unwanted fires andl gas4 explosion disasters requirei aknowledge of flamimability chlaracteristics (limits of flamnimabdity, ignition

Mrequirements, and burning rates) of pertinent combustible gases and vaporslky to be enicountered under various conditions oif use (or misuse). Available

data maly not always be adequate for use in at particular application since theymnay have been obtained at, tt lower temperature and pressure than is encounteredin practice. For example, tile quantity of air that is required to diecrease thecomlbustible vapor concentration to at safe level in in. particular proem"; Carriedout at 200 'Cj should be based onl flammiability data obtained at this temperature.When these are not, available, suitable approximations can be made to permit arealistic evaluation of the hazards associated with the process b)eing considered;such approxiniat ions can serve as the basis for dezsi;7;tng suitable safety devicesfor the protection of personnel and equipment.

Tile purpose of this bulletin is to present a general review of the subjectof flammability, and to supply select expe-rimiental data and empirical rules onthe flainiabillty characteristices of various famiilies of combustible gases aridvapors iii air and other oxidizing atmospheres. It contains what, are believedto be the latest and molst reliable dlata for more than 200 combustibles ofinterest to those concerned with the prevention of dishstrous gas explosions.In addition, the emipirical rules and graphs presenlted here can be used topreti ict similar data for other com bustiles tunder a variety of conditions.

This b~ulletin sup plemients Bureau bulletins (40)" andh other pub~lications (158).Basic knowledge of coimihust ion is (desirable for I- thorough understanding

of thie material, which can be found in numierous publications (69, 19.9, eoe).Therefore, only t hose aspects requiiredl for anl understanding, of flammabilityare considered here; even these are considered from a fairly elemnentaryviewpoint.

lhrii hernlst. project coordinator, Otxi ~ Explosi wilves Reeh center, numeu of Mines. Pittsburgh, Naitl idntumbers in parenthes reer to Items In the bibiloi phy at toand of titl report

Work on manumoript oompleted May 19N.

2 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

DEFINITIONS AND THEORYLUMil1S OF FLAMM AIIT I ' ' I I

combustible gas-air mixture can be burned ILimits of __

over a wile range of concentiations-when F f lammabilityeither subjected to elevated temperatures orexposed to a catalytic surface at ordinary E 4-temperatures. However, homogeneoug corn- >:bustible gas-air mixtures are flammable, that, is, I.,g2 blitthey can propagate flame freelyv within a W 2- r lmt

- ~ Z Xlimnlted range of compositionts. F~or examplke, Wtrace amounts of methane in air can be readily Xoxidized on a heated surfaee, but a flame wipropagate from an ignition source at amirbient .8

tmetures and pressures only if the sur- 'n .6ronigmixture contains at least 5 but less A

than 15 volume-percent methane. The more X--dilute mixture is known as the lower limit, orcombustible-lean, limit, mixture; the more .concentrated mixture is known as the upper 2 4 6 8 10 12- 14 16 18limit, or combustible-rich limit, mixture. In METHANE, volume-percentpractice, thle limits of flammability of at par-ticular system of gases aire affected by the Fiouau .- Ignitihility Curve and Limits of Fiamn-temperature, pressure, direction offan rp- inability for Methane-Air Mixtures at Atmospheric

gation, gravitational field strength, and sur- Prsuead2'Croundings. The limits are obtained experi-mentally by determining thle limiting mixture ignition of meothane-air mixtures (75). Forcompositions between flammable and nion- example, at 0.2-millijoule (mij) spark is inade-flammable mixtures (244). That is, quate to ignite even a stoichiometric mixture at

atmospheric pressure and 260 C; a 1-mj sparkLT. 11[C,+C~1,(1) can ignite mixtures containing between 6 and

and 11.5 volume-percent methane, etc. Such limit-UTT.p= 1/2[(,,+ C1.], (2) mixture compositions that depend on the igni-

tion source strength may be d~efined ats limits ofwhere L,.P and U7 .P are the lower andl uppe.r ignitibiity or more simply ignitibility limits;limits of flmmability, respectively, at at speci- th'ey are thus indicative ot the ignitin'g abilityfled temperature and pressure, C,,, and C, are of the energy source. Limit mixtures that tirethe greatest and least concentrations of fuel in essentially independent of the ignition sourceoxidant that are nonflammnable, and ('if and strength and that give a measure of the ability(?gf are the least and greatest concentrations of of at flamie to propagate iaay from the ignitionfiiel in oxidant that aire flamimable. Tile rate source mnay be defined ats lim'its of flammability.at which a flamie propagates through it flamn- Considerably greater spark energies aire requiredmable mixture depends on at number of factors, to establish limits of flammability than tireincluding temperature, pressure, amnd mnixture required for limits of ignitibility (218); further,composition. It is at minimui ait thle limits of more energy is usually required to establish tileflunmnuabifity and at maximumi at near' stoichio- upper limit thani is requiredl to establish thlemetric mixtures (130). lower limit. !n general, when the sour-ce

The Bureau of Mlines has adop)ted at st andaird strength is adlequate, mixtures just, outside the-apparatus for limit -of-flammiability doeteininail- range of flammnable comp11 ositionls Yield flaimetions (40). Originally designed for use ait caps when ignitedl. These flaiiie caps prop~agateatmospheric pre'ssu~re and roo~m t emplera ture, on Iv at short, (listaunce fromn the ignitioni sourceit, wats later mnodified for use t.t rediuced preg- illit auniifor in iixture. The reason for t his;tire, 1wIcloa mgasar-a gl il a e seenii i figure 2 which shows (,he effec't of

tile hase, of thme 2-inch, glass, flaine-propagation temp~erature oil limits of flaimmnlability at attube. T i riodifiCat io1 iintr0otlueVi' I ihCullt r ('on1sUta inlitil pressurem. As the temperat tirethat wats not inmiiediatelY apparenlt, as thle is increased, t he lower limit delec(ases and1( tilespark energ 'v was lill alwalys adiequate for uise ill upper limiit jecretses, Thus, since at localizedhliit-of 'I* mniiv(etmiutos F'i'ure energy somirc(. elevates' the ternpermit tire ofillmusita , tihle effit oif miixtur'e conmpositionl on nlemimby gases, even at nonflaniiale mixture vall

hle electrical spark energy reqjuiremlenits fora propaigate llaiiie at shorit distance fromin lhe

DiEFINIT'IONS AND THEORY 3

Saturated vapr- limits of flammability has been questioned.aurmxtur Upper After a thorough study, Linnett and Simpson

z limit concluded that while fundamental limits mayexist there is no experimental evidence toindicate that such limits have been measured

Auto- (18). In a more recent publication, Mullinsi t Fignition reached the same conclusion (154). Accord-Mist Flammable ingly, the limits of flammability obtained in an

apparatus of suitable sise and with a satis-' 9factory ignition source should not be termed

8 fundamental or absolute limits until the exist-ence of such limits has been established.

A limit However, as long as experimentally determinedlimits are obtained under conditions similar tothose found in practice, they may be used to

I I AlT design installations that are safe and to assessrt u AIT potential gas-explosion hazards.

TEMPERATURE- Industrially, heterogeneous single-phase (gas)Fiouis 2.--Effect of Temperature on Limits of and multi-phase (gas, liquid, and solid). flaa.

Flammability of a Combustible Vapor in Air at a mable mixtures are probably even more impor-Constant Initial Pressure. tant than homogeneous gas mixtures. Un-

fortunately, our knowledge of such mixturessource. That is, a nonflammable mixture (for is rather limited. It is important to recognire,example, com )osition-temperature point A, however, that heterogeneous mixtures canfig. 2) may become flammable for a time, if its ignite at concentrations that would normallytemperature is elevated sufficiently (composi- be nonflammable if the mixture were homoge-tion-temperature point B). neous. For example, I liter of methane can

Flammable mixtures considered in figure 2 form a flammable mixture with air near the topfall in one of three regions. The first isleft of of a 100-liter container, although a nonflam-the saturated vapor-air mixtures curve, in the mable (1.0 volume-percent) mixture wouldregion labeled "Mist". Such mixtures consist, result if complete mixing occurred at roomof droplets suspended in a vapor-air mixture; temperature. This is an importa:t concept,they are discussed in greater detail in the section since layering can occur with any combustibleon formation of flammable mixtures. The second gas or vapor in both stationary and flowinglies along the curve for saturated vapor-air mixtures. Roberts, Pursall and Sellers (176-mixtures; the last and most common region lies 180) have presented an excelent series of reviewto the right of this curve. Compositions in the articles on the layering and dispersion ofsecond and third regions make up the saturated methane in coal mines.and unsaturated flammable mixtures of a The subject of flammable sprays, mists, andcombustible-oxidant system at a specified foams is well-documented (5, 18, £, £7, 76,pressure. £05, 215, £45). Again, where such hetero-

In practice, complications may arise when geneous mixtures exist, flame propagation canflame propagation and flammability limit deter- occur at so-called average concentrations wellminations are made in small tubes. Since heat below the lower limit of flammability (86);is transferred to the tube walis from the flame thus, the term "average" may be meaninglessfront by radiation, conduction, and convection, when used to define mixture composition ina flame may be quenched by the surrounding heterogeneous systems.walls. Accordingly, limit determinations mustbe made in apparatus of such a size that. wall IGNrONquenching is minimized. A 2-inch-ID verticaltube is suitable for use with the paraffin Lewis and von Elbe (130). Mullins (153,154)hydrocarbons (methane, ethane, etc.) at at- and Belles and Swett (156) have prepareAmospheric pressure and room temperature. excellent reviews of the processes associatedlowever, such a tube is neither satisfactory with spark-ignition and spontaneous-ignitionunder these conditions for memny halogenated of a flammable mixture. In general, manyand other compounds nor for paraffin hydro- flammable mixtures can be ignited by sparkscarbons at. very low temperatures and pressures having a relatively small energy content (1 to(1,97, 2, /N). 100 mj) but a large power density (greater

Because of the many difficulties associated than 1 megawatt/cm). However, when thewith choosing suitable apparatus, it is not source energy is diffuse, as in a sheet discharge,surprising to find that the very existence of the even the total energy requirements for ignition

4 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE OASES AND VAPORS

may be extremely large (79, 82, 85, IeS, 181, 1950 C; another equation must be used for28). There is still much to be learned in this data at higher temperatures. The solid lines

field, however, since electrical discharges are in figure 4 define an 8 C' band that includesnot normally as well defined in practice as the experimental points in the temperaturethey are in the laboratory. range from 1700 to 1950 C.

When a flammable mixture is heated to anelevated temperature, a reaction is initiated that FORMATION OF FLAMMABLEmay proceed with sufficient rapidity to ignite MIXTUESthe mixture. The time that elapses between theinstant the mixture temperature is raised and In practice, heterogeneous mixtures arethat in which a flame appears is loosely called always formed when two gases or vapors arethe time lag or time delay before ignition. In first'brought together. Before discussing thegeneral, this time delay decreases as the tem- formation of such mixtures in detail, a simpli-perature increases. According to Semenov fled mixer such as that shown in figure 5 will be(193), these quantities are related by the considered briefly. This mixer consists ofexpression chambers I and 2 containing gases A and B,

0.22E respectively; chamber 2, which contains alog r=---+B, (3) stirrer, is separated from chamber 1 and piston

3 by a partition with a small hole, H. At timewhere T is the time delay before ignition in te, a force F applied to piston 3 drives gas Aseconds; E is an apparent activation energy for into chamber 2 at a constant rate. If gas Athe rate controing reaction in calories per is distributed instantaneously throughout cham-mole; T is the absolute temperature, expressed ber 2 as soon as it asses through H, a coupo-in degrees, Kelvin; and B is a constant. Two sition diagram such as a given in figure 6types of ignition temperature data are found in results; the (uniform) piston motion starts at

urrent literature. In the first, the effect of t. and stops at t,. However, if a time intervaltemperature on time delay is considered for de- At is required to distribute a samll volume fromlays of less than 1 second (127, 158). Such data chamber 1 throughout chamber 2, then at anyare applicable to systems in which the contact instant between t. and t, + At, a variety oftime between the heated surface and a flowing mixture compositions exists in chamber 2.flammable mixture is very short; they are not This situation is represented schematically insatisfactory when the contact time is indefinite. figure 7. The interval of time during whichFrt hefactr e n (3)contatti e is of de i se heterogeneous gas mixtures would exist in the

Further,second case is determined in part by the rateit gives only the time delay for a range of tem- at which gas A is added to chamber 2, by theperatures at which autoignition occurs; if the size of the two chambers, and by the efficiencytemperature is reduced sufficiently, ignition does of the tirrer.not occur. From the standpoint of safety, it of the stirrer.is the lowest temperature at which ignition can In practice, flammable mixtures may formoccur that is of interest. This is called the either by accident, or design. When they areminimum spontaneous-ignition, or autoignition, formed by accident, it is usually desirable totemperature (AIT) and is determined in a uni- reduce the combustible coicentration quicklyformly heated apparatus that is sufficiently nona b mirr n erta n con-large to minimize wall quenching effects (194, nonflammable mixtures. Under certain con-287). Figures 3 and 4 illustrate typical auto- ditions, it may be possible to increase the con-ignition-temperature data. In figure 3 the bustible concentration so as to produce anonflammable mixture. Such procedures areminimum autoignition-temperature or AIT discussed in greater detail in the followingvalue for n-propyl nitrate is 1700 C at an section.initial pressure of 1,000 psig (243). Data in Fectinbthis figure may be used to construct a log T Flammable mixtures are encountered in

I production of many chemicals and in certainversus , plot such as that in figure 4. Such physical operations. These include gasfreeing

ic tank containing a combustible gas (232),graphs illustrate the applicability of equation drying plastic-wire coating, and recovering(3) to autoignition temperature data. The solvent fromt solvent-air mixture. Whenequation of the broken line in figure 4 is layering can occur, as in drying operations, it

is not enough to add air at such a rate that thelog 12.3 10 25 ( verall mixture composition is below the lowerogr -25T. . (4) limit of flammability (assuming that uniform

mixtures result). Special precautions must, beIn 'his specific case, equation (4) is applicable taken to assure the rapid formation of non-only in the temperature range from 1700 to flammable mixtures (235). When a batch

DEFINITIONS AND THEORY5

4o 1* 1 I I i

360 SampleA vol, cc

y 0.5032 0.75

320- 1.00X 1.500 1.75C 0 2.00

28 0 2.25A 2.50v 2.75

Q 240 - A 3000- 0 325

0 0w 2000

m. Region of

160- au toignitionLLI

0 120I

w

80--

K 00 JAT I 1 %150 160 170 180 190 200 210 220

TEMPERATURE, OC

FIOURE 3.-Time l)elay Before Ignition of NPN in Air at 1,000 Psig it, the Temperature Range From1500 to 2100 C. (1-33 apparatus; type-347, stainless steel test chamber.)

rocess is involved, an added precaution must tures that are initially above the upper limit ofCe taken; a constituent at a partial pressure flammability may become flammable. A simi-near its vapor pressure value may condense lar effect must be considered when mixtures arewhen it is momentarily compressed by addition sampled with equipment that is cooler thanof other gases or vapors. Accordingly, mix- the original sample; if vapor condenses in the

6 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

TEMPERATURE, OC

210 200 190 I80 170600 1 |

AWT

400 V

° l:I/8Co

'0200-0

80- Region of-- outoignition

w 60°_ 0tLco 40-

°/oU020 A

I- 20 A

10 0

8-

EI IIII02.05 2.10 2.15 2.20 2.2 2.0

RECIPROCAL TEMPERATURE,

15r.

Fzouits 4,-Logarithm of Time Delay Before Ignition of NPN in Air at 1,000 Paig Initial Pressure.(Data from figure 3.)

sampling line, the test sample will not yield mists and sprays (particle sizes below 10 mi-accurate data. A flammable mixture sampled crons) the combustible concentration at thein this manner may appear to be nonflammable lower fimit is about the same as that in uniformand thus create a hazardous situation (236). vapor-air mixtures (17, 18, 22, £4, 76, 245).

A flammable mixture can also form at tern- However, a. the droplet diameter increases, theperatures below the flash point of the liquid lower limit appears to decrease. In studyingcombustible either if the latter i6 sprayed into this problem, Burgoyne found that coarse drop-the air, or if a mist or foam forms. With fine lets tend to fail towards the flame front in an

DEFINITIONS AND THEORY 7

Chamber I Chamber 2 100oo-

- fl3 Gas AGs8

Figure 5.-Simplified mixer. 1 0100

FIGURE 5.-Simplified Mixer. ELAPSED TIME

Z~ 10 - FIGURE 7.-Compo ition of Gas in Chamber 2, Figure5 (Delayed Mixing).

16 of fine droplets and vapors (24). With sprays,1 0E the motion of the droplets also affects the limit0 composition, so that the resultant behavior is

rather complex. The effect of mist and sprayQi 5 7 droplet size on the apparent lower limit isillus-

S trated in figure 8. Kerosine vapor and mist0 0- 1 100 0 data were obtained by Zabetakis and Rosen

10 If (2045); tetralin mist data, by Burgoyne andELAPSED TIME Cohen (24); kerosine spray data, by Anson

(5); and the methylene bistearamide data, byFIGURE 6.-Composition of Gas in Chamber 2, Figure Browning, Tyler, and Krall (18).

5 (Instantaneous Mixing). Flammable mist-vapor-air mixtures mayoccur as the foam on a flammable liquid col-

upward propagating flame, and as a result the lapses. Thus, when ignited, many foams canconcentration at the flame front actually ap- propagate flame. Bartkowiak, Lambiris, andproaches the value found in lower limit mixtures Zabetaki found that the pressure rise AP pro-

100

-0.07----- Stoichiometric

B .L 80 - mixture (decane-air)£17 - .06

Kerosine spray

0 0 -. 05.aZU 60 Kerosine vapor

E and mist .-. 04 E

0 0

00

.- MethyleneZ bistearamide spray

20.0o -

retaln is -Tetralin mist .01 8

0 20 40 60 80 100 120 140 160DROP'.ET DIAMETER, miictonv

FiouRJF 8.-Variatioi i" Lower Limits of FlanitabilIity of Various Combustibles in Air m~ a Function of D~roplIetAiame£ter.

8 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

duced in an enclosure by the complete combus- enriched air at reduced pressures (215). Airtion of a layer of foam of thickness A, is proper- can become oxygen-enriched as the pressure istional to h, and inversely proportional to hA, reduced, because oxygen is more soluble thanthe height of the air space above the liquid nitrogen in most liquids (83). Thus the pres-before foaming (7). That is ence of foams on combustible liquids are a po-

tential explosion hazard.A flammable foam can also form on nonflam-

ha mable liquid if the foam is generated bi a flam-unable gas mixture instead of air. urgoyne

Pressures in excess of 30 psi were produced by and Steel, who studied this problem, found thatthe ignition of foams in small containers, the flammability of methane-air mixtures in

Thomas found that an additional hazard water-base foanis was affected by both the wet-could arise from production of foams by oxygen- ness of the foam and the bubble size (28).

PRESENTATION OF DATALimit-of-flammability data that have been With either type of presentation, addition of

obtained at a specified temperature and pressure methane, oxygen, or nitrogen to a particularwith a particular combustible-oxidant-inert mixture results in formation of a series of mix-system may be presented on either a triangular tures that fall along the line between the com-or a rectangular plot. For example, figure 9 position point (for example, Mi in figures 9 andshows a triangular flammability diagram for 10) and the vertices of the bounding triangle.the system methane-oxygen-nitrogen. This For example, addition of methane (+CH,) tomethod of presentation is frequently used mixture M1 yields initially all mixture corn-because all mixture components are included positions between Mi and C (100 pct CH4).in the diagram. However, as the sum of all After a homogeneous mixture is produced, amixture compositions at, any point on the tri- new mixture composition point, such as M2, isangular plot is constant (100 pct) the diagram obtained. Similarly, if oxygen is added (+02)can be simplified by use of a rectangular plot to the mixture represented by point Mi, all(24.). For example, the flammable area of compositions between M1 and 0 (100 pct O)figure 9 may be presented as illustrated in are obtained initially; if nitrogen is added, allfigure 10. As noted, the oxygen concentration compositions between MI and N (100 pct N2 )at any point is obtained by subtracting the are obtained initially. If more than one gas ismethane and nitrogen concentrations at the added to M1, for example, methane and oxy-point of interest from 100 as follows: gen, the resultant composition point may be

Pet 02=100 pet-pct CH 4-pct N2. (6) obtained by considering that the mixing process

00

+ +CH4 06io o MI -02J 4

M3~ +N2 Air/ -

Flammable 0S mixtures

//

/O /7

,Min 02

r1gz::aticol C/N 0'100 90 so 70 60 50 40 30 2 0 i0 00 OXYGEN, volume-percent

FIGURE 9.--Flammability Diagram for the Syatem Methane-Oxygen-Nitrogen at Atmospherilo Pressure and 200 C.9

L ______

10 FLAMLABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

100

- L % 02 -100%-% CH4 -% N2

80-

C

160 02 +CH4E

-N-N 1 N 2

zA

I

40 6

44- ! /4

Fla mmaoble20- mixtures-

Lriticl C/NL MiN

0 20 40 60 Aso 100

NITROGEN, volurne-percent

Fioulz 10.-Flammability Diagram for the System Methano-Oxygen- Nitrogen at Atmospheric Pressure and W6 C.(Data from fig. 9).

occurs in two steps. First,, the methane is added composition point (for example, M1 in figures 9 andto Mi and the gases are mixed thoroughly to 10) shifts away from the vertices C, 0, and Ngive M2. Oxygen is then added to Af2 with along tile extensions to the lines MI-C, Mimixing to give a new (flammable) mixture, M3. -O and Mi -N, indicated in figures 9 and 10If the methane and oxygen were added to a by the minus signs. The final composition isfixed volume at constant pressure, some of M 1 determined by the percentage of each component,and then of M2 would escape and mix with the removed from the initial mixture.surrounding atmosphere. In many instances Mixtures with constant oxygen-to-nitrogenthis is an important consideration because the ratio (as in air), are obtained in figures 9 and 10resulting mixtures may be flammable. For by joining the apex, C, with the appropriateexample, even if an inert gas is added to a mixture composition along the baselne, ON.constant-volume tank filled with methane, Thus, the Air line, CA, (fig. 10) is formed byflamnmable mixtures (-an form outside the tank joining C with the mixture A (21 percent 0as the displaced methane escapes into the +79 percent N2). Using this latter point, A,atmosphere. If the inethant, is not dissipated one can readily determine the mixture cornposi-quickly, a dangerous situation1 can arise. tions that are formed when mixture M1 is

When a mixttire compoment is removed by displaced from an enclosure and mixed with air.condensation or absorption, the corresponding Initially, all mixture compositions between Af I

ie

PRESENTATION OF DATA 11

and A would form. Since these would pass %oir 100 % combustible vapor-% inertthrough the flammable mixture zone, a hazard- rous condition would be created. Similarly, ifpure combustible CH, were dumped into theatmosphere (air) all mixtures between C and Awould form. These would include the flam-mable mixtures along CA so that a hazardouscondition would again be created, unless thec)mbustible were dissipated quickly.

Mixtures with constant oxidant content areobtained by constructing straight lines parallelto zero oxidant line- such mixtures also have a iconstant combustible-plus-inert content. Oneparticular constant oxidant line is of specialimportance-the minimum constant oxidantline that is tangent to the flammability diagramor, in some cases, the one that passes throughthe extreme upper-limit-of-flammability value.This line gives the minimum oxidant (air, INERT, volume-Percentoxygen, chlorine, etc.) concentration needed to FIouRm ll.-Effect of Initial Temperature on Limit.support combustion of a particular combustible of Flammability of a Combustible Vapor-Inert-Airat a specified temperature and pressure. In System at Atmospheric Pressure.figures 9 and 10, the tangent line gives the 9 -

minimuin oxygen value (Min 01, 12 volume- % air 100 % % J P4 vaporpercent) required for flame propagation through 8 Vmethane-oxygen-nitrogen mixtures at 260 C 1Eand 1 atmosphere. . 7

Another important construction line is thatwhich gives the maximum nonflammable com- 0bustible-to-inert ratio (critical C/N). Mixtures *along and below this line form nonflammable 2mixtures upon addition of oxidant. The critical / FlammableC/N ratio is the slope of the tangent line from mixturesthe origin (Figs. 9 and 10), 100 percent oxidant, 4-to the lean side of the flammable mixtures acurve. The reciprocal of this slope gives the > 3minimum ratio of inert-to-combustible at which .r

nonflammable mixtures form upon addition of a 2 -oxidant. It is of interest in fire extinguishing. -

An increase in temperature or pressure iLusually widens the flammable range of aparticular combustible-oxidant system. The Ieffect of temperature is shown in figure 11; 0 200 400 600 800two flammable areas, T, and T,, are defined fora combustible-inert-oxidant system at constant INITIAL PRESSURE, mm Hgpresure. The effect of temperature on the Frouaz 12.-Effect of Initial Presure on Limita oflimi!ts of flammability of a combustible in a Flammability of JP-4 (Jet Fuel Vapor) in Air atspecified oxidant was previously shown in 269 C.figure 2. This type of graph is especiallyuseful since it gives the vapor pressure of the downward propagation of flame is used. Sincecombustible, the lower and upper temperature T, is the intersection of the lower-limit andlimits of flammability (T, and Tv), the Ham- vapor-pressure curves, a relationship can bemable region for a range of ten eratures, and developed between Tl,, or the flash point, andthe autoignition temperature (AlT). Nearly the constants defining the vapor pressure of a20 of these graphs were presented by Van combustible liquid. An excellent summary ofDolah and coworkers for a group of corn- such relationships has been presented by M ullinsbustibles used in flight vehicles (218). for simple fuels and fuel blends (154).

The lower temperature limit, TL, is essentially At constant temperature, the flammablethe flash point of a combustible in which up- range of a combustible in a specified oxidant canward propagation of flame is use4 ; in general, it be represented as in figure 12. Here the flam-is somewhat lower than the flash point, in which mable range of JP-4 vapor-air mixturm is given

12 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

rL1-~ L"II

_ p

S -- -- - _IT 2

Pvapor hp

Fiouns 13.-Effect of Temperature and Pressure on Limits of Flammability of a Combustible Vapor in a SpecifiedOxidant.

as a function of pressure (241). A more The flammable range is the same as that de-generalized flammability diagram of a particular picted in figure 2. At constant temperaturecombustible-oxidant system can be presented (for example, T), the flammable range isin a three dimensional plot of temperature, pres- bounded by the lower limit curve LIPLI and thesure, and combustible content-as illustrated upper limit curve U1Pc,; the broken curvein figure 13 (244). Here, composition is given PLIPUI represents the low pressure (quenched)as the ratio of partial pressure of the combustible limit. The flammable range is the same asvapor, pVAPOR, to the total pressure P. For any that depicted in figure 12. A similar range isvalue of P, the limitis of flammabiity ar given defined at temperatures T,, T3, and T# whichas a function of the temperature. For example, are less than T,. However, at T3 and T, theat I atmosphere (P= 1), the flammable range is upper limit curves intersect the vapor pressurebounded by the lower limit curve L4LL", and curves, so that, no upper limits are found abovethe upper limit curve UU2; all mixtures along U. and U,. In other words, all compositionsthe vapor pressure curve L4 U,' U are flammable. along U.U. and U.L4 are flamuable. The curve

PRESENTATION OF DATA 13

28 -T

A

24

X air =100 - % gasoline vapor - %water vapor

20

C

4 Nonflammablemmixture

0B 10 20 30 40 50 60 70 80 90 100WATER VAPOR, volumtu-percent

70 100 120 140 150 160 ]70 180 190 200 210 212-I I I I I .. I = i I I IL

CORRESPONDING AIR-SATURAT!ON TEMPERATURE. "F.

Fionw 14.- Flammability Diagram for the System Gasoline Vapor-Water Vapor-Air at 700 F (2i ° C) and at2120 F (iO0 ° C) and At :u spheric Pressure.

L4 'LUJ UZU defines the range of limit mixtures percent-water-vapor point. If water vapor iswhich are saturated with fuel vapor. Further, removed by condensation or absorbtion, thesince L4 is the saturated lower limit mixture at~ composition point will move along the extensionone atmosphere, TW is the flash point, to the line drawn from A to the 100-percent-

Some of the points considered in this and the water-vapor point. The same applies to theprex ious ,ectioni are illustrated in figure 14 other components, air and gasoline, as indicated(A73). This is the flammability diagram for earlier. .Moreover, if more than one componentthe system gasoline v-apor-wWterr vapor-air at is involved, the final composition point can be700 F(2 10 () and 2120F (100 °C) and atnos- found by considering the effect of each cor-pheric pres.ure. The air saturation tempera- ponent separately. poture, that is, the temperature at which saturated Figure 14 is of special interest since it can beair contains the quantity of water given on the used to evaluate the hazards associated with awater vapor axis, is t1ls included. For precise gas-freeing operation. For example, mixturework, a much larger graph or an enlargement represents a saturated gasoline vapor-air-of the region from 0 to 8 percent gasoline vapor water vapor mixture at 700 F. A more volatileand from 0 to 30 percent water vapor ould gasoline than the one used here would give abe used. However, figure 14 is adequate here. saturated mixture with more gasoline vaporIf water vapor is added to a particular mixture and less air in a closed tank, a less volatileA, all mixture compositions between t and gasoline would give less gasoline vapor and

pure water vapor will form as noted (if the more air. In any event, if a continuous supplytemperature is at least 2120 F), and the corn- of air saturated with water vapor is added to aposition point will shift towards the 100- tank containing mixture A, all compositions

14 FLAMMABILIT1 CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

between A and B (air plus water vapor) will be between points along AE and B. Again, asformed until all the gasoline vapor is flushed the water vapor in these mixtures condens ifrom the tank, and mixturv B alone remains. outside the tank, the composition of the result-If steam is used to flush mixture A from the ant mixtures will shift away from the 100-tank, all compositions between A and C will percent-water-vapor point, C. The mixture inform until all the gasoline vapor has beer the tank will remain at E unless air is used toflushed from the tank and only steam remains flush the tank, in which case mixture composi-(at 2120 F or higher). If the tank is permitted tons between E and B will form. Again, ifto cool, the steam will condense and air will be the water vapor within the tank condenses, thedrawn into the tank giving mixtures along mixture composition will shift away from C.C-B. At 700 F, only air plus a small amount In any event, at this temperature (175 ° F), theof water vapor will remain.

If hot water and water vapor at 1750 F are addition of air to mixture E will lead to forma-used to flush mixture A from the tank, the tion of flammable mixtures. Thus, mixture Amixture composition can only shift along AC to cannot be flushed from a tank without form ingE. Mixtures between A andE that are flushed flammable mixtures, anless steam or some otherfrom the tank mix with air to give mixtures inert vapor or gas is used.

L.A

DEFLAGRATION AND DETONATION PROCESSESOnce a flammable mixture is ignited, the weight, of the burned gases, and T is the final

resulting flame, if not extinguished, will either (16, ',mttic) temperature of the products. Withattach itself to the ignition source or propagate otle 1 eCloisurem, or with noncentral ignition,tra)m it. If it propagates from the source, the the flame front is disturbed by the walls beforepropagation rate will be either subsonic (de- ,orihuntion is completed, so that calculatedilagration) or supersonic (detonation) relative pressure cannot be expected to approximateto the unburned gas. If it is subsonic, the pres- actual pressure. Even with spherical enclosures,sure will equalize at the speed of sound through- the flame front is not actually spherical, so thatout the enclosure in which combustion is taking the walls tend to disturb the flame before corn-place so that the pressure drop across the flame hustion is complete (118, 130). A graph of the(reaction) front will be relatively small. If the pressure developed by the combustion of arate is supersonic, the rate of pressure equaliza- stoichiometric methane-air mixture (centraltion will be less than the propagation rate and ignition) in a 19.7 cm diameter, 9-liter cylinder,hire will be an appreciable pressure drop across is given in figure 15. The calculated pressurethe flame front. Moreover, with most con- for a 9-liter sphere is included for comparison;butible-air mixtures, at ordinary temperatures, K in equation (7) was evaluated from thethe ratio of the peak-to-initial pressure within experimental curve at 70 milliseconds. Thethe enclosure will seldom exceed about 8:1 in calculated curve follows the experimental curvethe former, but may be more than 40:1 in the closely about 75 milliseconds, when the latterlatter case. The pressure buildup is especially curve has a break. This suggests that thegreat when detonation follows a large pressure flame front was affected by tbe cylinder wallsrise due to deflagration. The distance required in such a way that the rate of pressure risefor a deflagration to transit to a detonation decreased, and the experimental curve fell belowdepends on the flammable mixture, temperature, the calculated curve. Further, since the com-pessure, the enclosure, and the ignition source. bustion gases were being cooled, the maximum

ith a sufficiently powerful ignition sourbe,detonation may occur immediately upon igni- 00tion, even in the open. However, the ignitionenergy required to initiate a detonation is Calculated Iusually many orders of magnitude greater than (9-liter sphre)--, 11that required to initiate a deflagration (3, 249). 80 I I Experimental

DEFLAGRATION t (9-liter cylinder)

Where a deflagration occurs in a spherical L 60

enclosuire of volume V with central ignition, the ci)approximate pressure rise AP at aLv instant t &itter ignition is given by the expressions: W

c/n 40-APA7 _]P= (7) Wu)

and 0.

1" = A- _.'- (I) 20

where K is a constant. S. is the burning velocity,', is the initial pressure, 1'm is the maximum [

pressure, '1 is the initial temperlture, it, is the 0 40 80 120 160number of inoles of gas in the initial mixture, ELAPSED TIME, millisecondsn, is the nU'nl)er of moles of gas in the hurnedgases, Al7 is the average molecular weight of the Fiuar 15.---Pr(wssure Produced by Ignition of a 9.6Volum(",Percent Methane-Air Mixture in H 9-Literinitial mixture, -Ifb is the average molecular Cylinder (E-xperimental).

15

16 FLAMMABILITY CHARAC*TERISTICS OF COMBUSTIBLE GASES AND VAPORS

pressure fell below the calculated value. The Wolfson and Dunn have developed generalizedminimum elapsed time (in milliseconds) re- charts that simplify the operations involved inquired to reach the maximum pressure appears obtaining the pressure ratio as well as the den-to be about 75 iV for the paraffin hydrocarbons sity and temperature/molecular weight ratiosand fuel blends such as gasoline; V is the across the detonation wave and the energyvolume in cubic feet in this case. release in the detonation wave.

Many investigators have measured and cal-culated detonation and reflected pressures

DETONATION resulting from detonation waves (54 57, 204).Figure 16 from the data of Stoner and Bleakney

Wolfson and Dunn (52, 230) have expressed (204) gives the detonation velocity, the staticthe pressure ratio P2/P1 across a detonation or detonation pressure, and the reflected pres-front as sure developed by a detonation wave propa-

P2 I gating through hydrogen-oxy en mixtures at(,,M, 2+ 1), (9) atmospheric pressure and 180 C.

where %, is the specific heat ratio of the burned BLAST PRESSUREgases, y is the specific heat ratio of the initialmixture, and £ is the Mach ntunber of thediretatond wv ithe respct tomber the The pressures produced by a deflagration ordetonation wave with respect to the initial a detonation are often sufficient to demolish anmixture. M, is given in terms of the tempera- enclosure (reactor, building, etc.). As noted, atures T and molecular weights W of the initial deflagration can produce pressure rises in excessand final mixtures by the expression: of 8:1, and pressure rises of 40:1 (reflected

pressure) can accompany a detonation. As( 1M'+l)' (ya±)TW (10) ordinary structures can be demolished by pres-

"n 1' 7 'Y2T,W 2 sure differentials of 2 or 3 psi, it is not surprising

3,500 50

P ( theoretical) 45

40

/ 35

30

2,500 25 EE Ps (experimental)0

-20

152,000

10

5

1,500 I 1 1 I I I 020 30 40 50 60 70 80 90

H2 , volume - percent

FIoUsZ 1.Detonation Velocity, V; Static Presure P.; and Reflected Pressure, P,, Developed by a DetonationWave Propagating Through Hydrogen-Oxygen Miziures in a Cylindrical TuIbe at Atmospheric Pressure and180 C.

DEFLAGRATION AND DETONATION PROCESSES 17

that even reinforced concrete structures have must be taken to protect the personnel andbeen completely demolished by explosions of equipment from blast and missiles. Browne,near-limit, flammable mixtures. Hileman, and Weger (16) have reviewed the

Jacobs and coworkers have studied the dam- design criteria for suitable barricades. Otherage potential of detonation waves in great detail authors have considered the design of suitable(91, 170). They have considered the principlcs laboratories and structures to prevent frag-involved in rupturing of pipes and vessels by ment damage to surrounding ar-9,s (44, 174,detonations and the relevance of engineering 203, 20).and metallurgical data to explosions. Morerecently, Randall and Ginsburg (171) have in- TABLE 1.-Conditions of failure of peak over-vestigated bursting of tubular specimens at pressure-sensitive dements (217)ordinary and reduced temperatures. Theyfound that the detonation pressure required to Approx-burst such specimens was, in general, slightly iniatehigher than the corresponding static-bursting incidentpressure. Ductility of the test specimen ap- Structural element Failure blastpeared to have little effect on the bursting pressurepressure, but ductility increased the strength (psi)of pipes containing notches or other stressraisers. Glass windows, large Usually shattering, 0. 5-1.0

When a detonation causes an enclosure to and small. occasional framefail, a shock wave may propagate outward at a failure.rate determined by characteristics of the Corrugated Asbestos Sh ittering. 1.0-2. 0medium through which it is transmitted, and Aidiug.the available energy. hi the shock velocity, , Corrigattd steel or Conneclion failure, 1.0-2. 0

aluninumrr panel- followed by buck-is known, the resulting overpressure, (P-P,), ing. Iih Iis given by the expression (20.1) Wood siding panels, Usually failure oc- 1.0-2. 0

standard house curs at main con-construction. nections, allowing

PP~l~ (11)a whole panel tobe blown in.

Concrete or cinder- Shattering of the 2. 0-3.0where, is the ratio of specific heats, and a is the block wall panels, wall.velocity of sound in the medium through which 8 or 12 inchesthe shock wave passes. The approximate thick (not rein-damage potential can be assessed from the data forced).

Brick wall panel, 8 Shearing and flexure 7. 0-8.0in table 1 (217). or 12 irches thick failures.

In conducting experiments in which blast (not reinforced).pressures may be generated, special precautions

K

PREVENTIVE MEASURESINERTING1

In principle, a gas explosion hazard can beeliminated by removing either all flammablemixtures or all ignition sources (23, 240). UnprotectedHowever this is not always practical, as manyindustrial operations require the vresence offlammable mixtures, and actual or potentialignition sources. Accordingly special pre- Ccautions must be taken to minimize the damagethat would result if an accidental ignition were Coto occur. One such precaution involves the Wuse of explosive actuators which attempt to a.add inert, material at such a rate that an Protectedexplosive reaction is quenohi d before structuraldamage occurs (70, 72). Figure 17 shows howthe pressure varies with and without suchprotection. In the latter case, the pressure tirise is approximately a cubic function of time, ELAPSED TIMEas noted earlier. In the former case, inert is FIGURE 1-Pressure Variation Following Ignition ofadded when the pressure or the rate of pressure a Flammable Mixture in Unprotected and Protectedrise exceeds a predetermined value. This Enclosures.occurs at the time t, in figure 17 when theexplosive actuators function to add the inert.As noted, the pressure increases momentarily where k is the thermal conductivity of the gas;aboe the value found in the unprotected m is the mesh width; T is the mean bulk tern-case and then falls rapidly as the combustion perature of the flame gases through the arrestor;reaction is quenched by the inert. T. is the initial temperature of the arrestor; Q is

the heat lost by unit area of flame; x, is theFLAME ARRESTORS AND RELIEF thickness of the flame propagating at the burn-

DIAPHRAGMS ing velocity, S; d is the diameter of an aperture;A is the area of a hole in unit area of the

Inert atmospheres must be used when not arrestor face; and t is the arrestor thickness.even a small explosive reaction can be tolerated. Equations (12) and (13) can be used toHowever, when the ignition of a flammable determine the mesh width or aperture diam-mixture would create little hazard if the burning eter needed to stop a flame having a particulurmixture were vented, flame arrestors and relief approach velocity. In practice, application ofdiaphragms could be used effectively. The these equations assumes a knowledge of thedesign of such systems is determined by the flame speed in the system of interest. Somesize and strength of the confining vessels, ducts, useful data have been made available byetc. Palmer and Rasbash and Rogowski (172, 173),

In recent studies of the efficiency of wire as well as by Jost (118) and Lewis and von Elbegauze and perforated block arrestors (161, 162), (130).

almer found the velocity of approach of the Tube bundles also may be used in place offlame to be the major factor in determining wire scraens. SC3tt found that these permitwhether flame passed through an arrestor. For increased aperture diametera for a given ap-these two types of arrestors, lie found the proach velocity (192).critical approach velocity to be In practice, it may be desirable to install

pressure relief vents tu imit damage to ductS1.75k(2-T.), systems where fli me may propafate. Rasbash

0 1,(12) and Rogowski (173) found that with propane-and and pentane-air mixtures, the maximum pres-

andT sure PM (pounds per square inch) developed inV9"6kA"(T-T°), (3 an open-ended duct, having a cross section of

dQ/13) 1 ft- is:18

p

PREVENTIVE MEASURES 19

L L and it is thus proportional to K. For smallPM--O.7 ,and6< <48, (14) values of K it, was found that

where is the ratio of duct length to diameter. PS=K.D As with ducts, larger pressures wvr6 obtained

However, the presence of an obstacle (bend, whea obstructions were placed in the oven.constriction, etc.) in the path of escapinggases increased the pressure due to resistanceto fluid flow by the obstacle. Location of arelief vent near the ignition source decreased P2the maximum pressure as well as the flamespeed. For values of K (cross-section area 4of duct/area of vent) greater than 1, these Iauthors found

O.8K<P, _i.8K, (15) P1L 0Wwhere 2_5K<32, and 6 <5T__.30. To keep the c

pressure at a minimum either many smallvents or a continuous slot was recommendedrather than a few large vents. In addition,vents should be located at positions whereignition is likely to occur and should open ELAPSED TIME-before the flame has traveled more than 2 feet.

When possible, relief vents should be used F iouE 18--Pressure Produced by Ignition of awith flame arrestors. The vents tend not only Fiammable Mixture in a Vented Oven.to reduce the pressure within a system followingignition but also to reduce the flame speed, In designing explosion reliefs for ovens, Sim-thus making all arrestors more effective. Un- monds ubbage pointcd out that (1) thefortunately, in certain large applications (for reliefs should be c,.astrueted in such a way thatexample, drying ovens), it is difficult to use they do not form dangerous missiles if an explo-flame arrestors effectively. In such cases, sion occurs; (2) the weight of the relief must bcgreater reliance minst Ie placed on the proper small so that it, opens before the pressure buildsfue ,tioning of relief vents. Siesmonds and up to a dangerous level: (3) the areas and posi-Cubbage (42, 43, 195) have investigated the tions of relief openings must be such that thedesign of affective vents for industrial ovens, explosion pressure is not excessive; (4) sufficientThey found two peaks in the pressure re-ords free space must be utilized around the oven toobtained during the vnting of cubical ovens pterrmit satisfactory operation of the relief and(fig. 18). The first peak, Pi; the oven volume, minimize risk of burns to personnel; and (5)I"; the factor, K; and the weight per unit oven doors should be fastened securely so thatarea (lb/ft) of relief, w, were related as follows they do not open in the event of an explosion.for -t 25 percent town gas -air mixture: Burgoyne and Wilson have presented the

results of an experimental study of pentanevapor-air explosions in vessels of 60- and 200-

More generally, cubic-foot volume (30). They found the ratesof pressure rise greater than could be predicted

Po(O.3Kw+0.4), (17) from laminar burning velocity data, so that theeffect of a relief area in lowering the peakwhere S, is the burning velocity of the mixture pressure was less than expected. All experi-

tit the oven temperature. ments were conducted at an initial pressure ofThe first, pressure pulse was ascribed to the I atmosphere. Vent data for use at higher

release and mIotion o tAe relief vent following initial press,.res are summarized in an articleigniton; the sec('ond pulse, to (ontitue(d jurn- by Block (10); a code for designing pressureing at an inrcased rate. 'Phe secord pulse relief systems has been proposed in this article.represents thip pressure drop across the vent, Other authors have considered the effects of

temperature and characteristics of the flare-, Town US epetmane; pproxalnely 52 the hyroon 17 ICt cprtn mable mixture on vent requirements (14, 35,,OWnogien, IS pet i ,thane; the i ,Uali ; i o" nr 8ydrc4u5I 46ns, 3 pet1

Otrot~i mmpet;ca~on ioaiieS pt; nd o~en 38 45,46,134 14., 18, 21)

FLAMMABILITY CHARACTERISTICSThe flammability data (limits of flamma- bustible vapor per liter of air at standard con-

bility, flash point, ignition temperature and ditions, that is, 00 C and 760 mm Hg (0.045 toburning velocity) of the various chemical farn- 0.050 oz combustible vapor per cubic foot ofilies exhibit many similarities. Accordingly, air) (247). This is illustrated in figure 19 inthe data presented here are grouped under the which some lower limits of flammability arevarious commercially important families, blends, plotted against molecular weight; except forand miscellaneous combustibles. methane, ethane, and propane all limit values

fall in a band between concentrations of approx-PARAFFIN HYDROCARBONS imately 45 and 50 mg/r.

(C.H The following expression may be used toR2n 2) convert from a lower lirrit L in volume-percentLimits in Air of vapor in the vapor-air mixture to one in

Lower and upper limits of flammability at milligrams of combustible, per liter of air at250 C (or at the temperature noted) and 1 standard conditions:atmosphere (L25 and U25) for many members of lmg\ L (vol pct)the paraffin hydrocarbon series are given in L (mg) 0 L(volpct)table 2, together with the molecular weight, M, 1 1vapor specific gravity, sp gr, stoichiometrict[ volmgcomposition in air, C., (appendix B) and heatof combustion, AH, (188). At room tempera- specific volume being volume of combustibleture and atmospheric or reduced pressure, the vapor per milligram of combustible. At stand-lower limits of flammability of most of this ard conditions (00 C and 760 mm Hg) this isseries fall in the range from 45 to 50 mg com- about 22.414/1,OOOM, where M is the molecular

6

5 Xi50mg/I

.4

L 45 mg/I

0 2240-

0

FLAMMABILITY CHARACTERISTICS 21

TABLE 2.-Properties of parafin hydrocarbons

Lower limit i air Upper limit in airNet AH.Pr I.n (W a U N Ur

Combustible Formula M (A -1) (n pr ol Rf (Vol g) R

p( ot) , pot) ((vol pot) / )(vol ( ef t)vl) Ref.

Methane ............... CH, ----------- 16.04 0.65 9.48 191.8 5.0 0. 3 8 40 1.0 1.6 126 (40)Ethane --------------- CaH .---------- 30.07 1.04 8.65 341.3 3.0 .53 1 4 12.4 2.2 190 4,Propane ................. CsH .--------- 44.09 1.52 4.02 488. 5 2. A .52 42 (116) 9.6 2.4 210 (41n-Butane...----.------ C4H0 --------- 88,12 2.01 3.12 635.4 1.8 .58 48 (11) 84 2.7 240 41n-Pentane ------------ C all - - - - - - - - - - 72.15 2. 49 2.55 782.0 1.4 .85 4 J40 7.8 3 1 270 (40)n-Hexane ............. . --- C-- -........... 88.17 2.96 2.16 928.9 1.2 .56 47 (546 7. 4 8.4 810 401n-Heptane ................ C,Ha ........... 10020 3.46 1.87 107.8 1.05 . W 47 (546 6.7 8.6 820n-Octane ----.---------- Call, --------- 114.23 3.94 1.65 1222.8 .96 .58 49 (56 .......... -..................n-No,,ane ----------.--- Cll, .--------- 1. . 28 443 147 169.7 . .6 48 ,146) .... 49.(546)n-Decane -- _----------- Colin --------- 142.28 4.91 1.33 1516.6 '.75 .6 48 (4) '5.6 4.2 880.n- Undecane ----------- --- C -........... 1 .30 5.40 1.22 1663.6 .68 .6 8 (4 __n-Dodecane ....... C- - ..----_---- 170.33 5. 88 1.12 1810.5 .60 .84 46 (4 - -n-Tridecane------Ciallsa,.........184.36 6.37 1.04 1957.4 .85 .3 40 (').........................-----n-Tetradecane ............ Cills0 . . . . . . . . . .. 198.38 7.8 97 2104.3 b. 0 .62 44 )n.1'entadecane --------- C::la............212 41 7:33 90 2231. .4 5.1 40 1( ---'---n-llexadecane----------C 11 - - - - - - - - - 22644 7 82 85 2398. 51 44 (I

1 t-43' C. 4 Calculated value extrapolated to 25" C at Explosives Re. Center,Uj.53 C. Federal Bureau of Mlnes.t-86 C.

weight of the combustible. Since L (vol pct) Combining this equation with equation (21),of most members of this series is much less than we have100 percent, the lower limit can be expressed L2 o(mg/1) -48 mg/i, (27)as (for paraffin hydrocarbons, except methane,

L -0.45ML (vol pet). (20) ethane, and propane. Substitution of thisvalue into equation (20) gives

At any specified temperature, the ratio of 107the lower limit to the amount of combustible L2olO t (28)needed for complete combustion, C,,, also isapproximately constant. This was first notedby Jones (95) and later by Lloyd (138), who The following expression may be used tofound that for paraffin hydrocarbons at about convert a lower limit value in volume-percent250 C, to a fuel-air (weight) ratio:

L21. ru0.55C,,. (21) ! L (Vol pet)

For the complete combustion of the paraffin L(F .96/A)0_0-L (vol pt)jhydrocarbons, we have:

The reciprocal expression gives the air-fuelCaH2 .+2 + (1.5n + 0.5)O--*nCO2+ (n-+ 1)H 20, (weight) ratio:

so that in air (22). 7NF-- -- (30)50 * 00 -~* (30

100 vo (Al LL (vol pct) jC,=I+4.73(.5n 0.5 vo pet, (23)1+4.773(1.5n+0.5) pAs noted, the lower limits given in figure 19

were determined at room temperature and at-where 4.773 is the reciprocal of 0.2095, the mospheric or reduced pressure. Lower limitsmolar concentration of oxygen in dry air. The vary with temperature as shown for methane invalues of C,, (appendix B) are included in table figure 20. The limit values obtained with up-2. By weight these become ward propagation of flame (R1) fall fairly close

to a straight line that passes through the lower1,000[12.01n+ 1.008(2n±2)) ing limit value at 250 C and the flame temperature

( 22.414X4.773(1.5n±0.5) 1- (24) (12250 C). This is in accordance with theor White criterion that the flame temperature is

14.03n+2.021 g. constant at' the lower limit (RO2). The data(,9.34 1 l _.n+0.5 J 1 (25) obtained by White with downward propagation

of flame fall along a line parallel to the lineThus, through the limit values obtained with upward

C,,-87 mg/l, n>4. (26) propagation. Taking the value 1,300' C as

22 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

air 100%-% methane

5-Flammable mixtures

-- Vapor pressure4 curve Downward propagation of flame

E

r AITz qc Upward propagation of flame

1 -

-200 0 200 400 600 800 1,000 1,200 1,400TEMPERATURE, ° C

Fiouim 20.-Effect of Temperature on Lower Limit of Flammability of Methane in Air at Atmospheric Pressure.

the approximate flame temperature for the plot of L,/L 25. against the temperature (fig. 23,paraffin hydrocarbon series (5), and using the solid line).lower limit values at room temperature in table These data are also correlated fairly well with2, the limits of the first 10 paraffin hydrocar- the modified Burgess-Wheeler Law suggestedbons are represented as in figures 21 and 22. by Zabetakis, Lambiris, and Scott (.42):Figure 21 ives the lower limits in volume-per-07cent and figure 22 in milligrams per liter. By 0"75 (t-25'), (33)weight, the lower limits of most members ofthis series again fall in a fairly narrow band("higher hydrocarbons" region). Individual where t is the temperature in 'C and AM, is theadiabatic flame temperatures can be determined net heat of combustion in kilocalories per mole.for lower limit mixtures using the data in table Then,2 and appendix C (55). L, = 0.75

The straight lines of figures 21 and 22 are L 2 - So- (t-25). (34)given by: L2 o tL Substituting the value 1,040 for L 25.AH, ob-

Li 2& - (t-250 ), (31) tained by Spakowski (R01), we have(1,3000--250)or L

L,- 1-0.000784(t-25*). (32) L2 *-- 1-0.000721(t-250), (35)

which is also given in figure 23 for a limitedThey are described in more general terms by a temperature range with the broken line.

FLAMMABILITY CHARACTERISTICS 23

6 f I

% air = 100%-% combustible

5

Flammable mixtures

-

4 MetPrpn

C,

9.

0> Ethane AITL" 3 -

j PropaneDButane

CD)022- AIT-

PentaneHexane. -'" .

1 HeptaneOctane ,,Deane AIT

-200 0 200 400 600 800 1,000 1,200 1,400TEMPERATURE, C

FIGURE 21.-Effect of Temperature on Lower Limits of Flammabilty of 10 Paraffin Hydrocarbons in Air atAtmospheric Pressure.

Only the lower limit at 250 C and atmospheric flames (87, 88), the upper limit also increasespressure is needed to use figure 23. For exam- linearly with temperature. The effect ofpie, assuming a constant flame temperature, the temperature appears to be fairly well correlatedratio L tL23 . at 6000 C is 0.55. The calculated by the modified Burgess-Wheeler law:lower limit of methane at 6000 C therefore is5.0X0.55, or 2.75 volume-percent. The same 0.75value can be obtained directly from figure 21. U- + y- (t-250 ). (36)From the modified Burgess-Wheeler Law curve,L/L 25.=0.585 at 6000 C, so that L4o.=2.92 If we assume that the heat release at the uppervolume-percent. limit is equal to that at the lower limit, th en

Limit-of-flammability measurements are corn-plicated by surface and vapor-phase reactionsthat occur at temperatures above the auto- U = 0 0 ( )ignition temperature. For example, Burgoyne - 1+0.000721(t-25). (37)and Hirsch (25) have shown that methane'airmixtures containing up to 5 percent methane A plot of Ui Un. against temperature fig. 24)burn readily at 1,000' C. E'xperinments were was used to corn are recent experimental valuesconducted with mixtures containing as lit le as of Rolingson and coworkers (18.e) for methane-0.5 percent methane; figure 20 predicts that a air mixtures at 15 psig with those predicted bYflame would not propagate through such a the modified Burgess-Wheeler law. The expen-rmixture, mental and calculated upper limits are givenx in

Flammability experiments at elevated ten- table 3 together with tlie difference U,,-peratures indicate that in the absence of cool U..r, In each case, the difference is iess than

24 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE aASES AND VAPORS

60

50 Higherhydro-

carbons

Propane40- Ethane0 Methane

I3O20- I

10

-200 0 200 400 600 800 1,000 1,200 1,400TEMPERATURE, ° C

Fouau 22.-Effect of Temperature on Lower Limits of Flammability of 10 Paraffin Hydrocarbons in Air atAtmospheric Pressure by Weight.

4 percent of the experimental value, which is point. The lower temperature limits of paraffinapproximately within the limit of experimental hydrocarbon at atmospheric pressure are givenerror. Earlier experiments of White (222) at in table 4.temperatures to 4000 C, with downward flamepropagation, also are represented quite ade- TABLE 3.-Upper flammability limits, U, ofquately by equation (37). For example, White methane-air mixtures at 15 psigfound that the upper limit of pentane in air(downward propagation) increased linearly from4.50 volume-percent at about 170 C to 5.35 Temperature U,.p,, (vol U.,1. (vol Uo.I -Uo. .volume-percent at 300' C. The ratio of 5.35: (C) perceLt) percent) (vol percent)4.50 is 1.17, which compares quite well withUW./U&. =l.20 obtained from figure 24. 25 ---------- 15.5 15.5 0

Given the vapor pressure curve and the lower 100 -------- 16. 3 16. 4 .1limit of flammability, the low " temperature 200 -------- 17.0 17. 5 .5limit or approximate lash point of a combustible 30. 17. 9 18. 6 .7can be calculated from either equation (32) or(35) (.018). Approximate flash points were (J8I.obtained previously, using only the vaporpressure curve and the lower linit at ordinary Moderate changes in pressure do not ordi-or elevated temperatures (1,54). The values narily affect the limits of flammability of theobtained with this procedure are somewhat paraffins in air, as shown in figure 25 for pen-low because the lower limit at any temperature tane, hexane, and heptane in air (241) in aabove the flash point is less than at the flash range from 75 to 760 mm Hg. The lower limits

FLAMMABILITY CHARACTERISTICS 25

TABLE 4.-Lower temperature limits and autoignltion temperatures oJ paraffln hAdrocarbonw atatmospheric pressure

Autoignition temperatureLower temperature limit

In airIn air In oxygen

C oF Ref. C 0 F Ref. o C F Ref.

Methane ----------------- 187 -305 (1) 537 999 (158) -------- ...........Ethane ------------------ 130 -202 (1) 515 959 (937) 506 943 (94)Propane ----------------- -102 -152 (1) 466 871 (158) ----................n-Butane ------------------ 72 -96 (1) 405 761 (2,17) 283 542 (191)Isobutane-----------------81 -114 (1) 462 864 (158) 319 606 (94)n-Pentane- ----.-------- -48 -54 (1) 258 496 (194) 258 496 (144)n-Hexane ----------------- 26 -15 (159) 223 433 (194) 225 437 (94)n-Heptane --------------- 4 25 (169) 223 433 (237) 209 408 (94)n-Octane ---------------- 13 56 (159) 220 428 (*37) 208 406 (191)n-Nonane ---------------- 31 88 (159) 206 403 (2,37) - - --------n-Decane ---------------- 46 115 (159) 208 406 (237) 202 396 (94)n-l)odecane -------------- 74 165 (159) 204 399 (237) ........................n-1(exadecane ------------- 126 259 (1) 205 401 (237) .........................

Caculated value.

1.2 7 7 p 7 I

N2

.8 -N

Modified Burgess-Wheeler Low

" .6 -N.4

.4 -

Constant flame temperature

.2

01 1

-200 0 200 400 600 800 1,000 1,200 1,400

TEMPERATURE, -C

Fiounz 23.-Effect of Temperature on L,/LNo Ratio of Paraffin Hydrocarbons in Air at Atmospheric Pressure.

26 FLAMMABILITY CHARACTERISTICS OF' COMBUSTIBLE GASES AND VAPORS

1.4 Neither expression is applicable when coolflames are obtained. Substitution of equation(21) for Lw. into equation (39) gives

1.3 U.=4.8 (40)

The limits of flammability of natural gas1.2 - (85-95 pct methane and 15-5 pct ethane)

have been determined over an extended pres-sure range by Jones and coworkers (78, 105).They are given in figure 26 for pressures from1 to 680 atmnos heres (10,000 psig). Ananalysis of these Sata shows tile limits varylinearly with the logarithm of the initial

1% , pressure. That is,10 100 200 300 400 300

TEMPERATURE,'C L (vol pet) =4.9-0.71 log I' (atm), (41)

Fioum 24.-Effect of Temperature on U,/U. Ratio andof Paraffin Hydrocarbons in Air at AtmosphericPressure in the Absence of Cool Flames. U (vol pet) =14.1 +20.4 log P (atm), (42)

coincide, but the upper limits, by weight, with a standard error of estimate of 0.53 volincrease with increasing molecular weight. pet for L and 1.51 vol pet, for U.

Be volume, at atmospheric pressure and 250 Although the limits of flammability are notC, Spakowski (201) found that the upper and taffected significantly by moderate changes inlower limits were related by the exprcs~sion: pressure, the temperature limits are pressure

dependent. As the total pressure is lowered,U26. =-7.1L5'. (38) the partial pressure of the combustible must

also be lowered to maintain a constant corn-However, the data presented here are correlated bustible concentration. The effect of pressuremore precisely by a somewhat simpler expres- on the lower temperature limit of the normalsion: paraffins pentane, hexane, heptane, and octane

U26.=6.5 421n. (39) in air, for pressures from 0.2 to 2 atmospheres,

400~Heptane

z0

! 300

z HexaneUj. Pentane

0 2000-,", Flammable mixturesW W

= 100o0

0 100 200 300 400 500 600 700 800INITIAL PRESSURE, mm Hg

FIuu'aE 25.-Effect of Presure on Limits of Flammability of Pentare, Ilexane, and lieptane in Air at 26' C.

FLAMMABILITY CHARACTERISTICS 27

60

% air = 100%-% natural gas

50

C® 40

E.2 Flammable mixtures9 30

20

z

10

0 100 200 300 400 500 600 700 800INITIAL PRESSURE, atmospheres

FJGuRE 26-Effect of Pressure on Limits of Flammability of Natural Gas in Air at 280 C.

is shown in figure 27. '[ire tepn erature limits TABLE 5.-Limits of flammability of methane inwere calculated from the L,,. values, the vapor chcrinepressure curves, and the data of figure 23. (volume-pecnt)

Limits in Other Atmospheres Temperature, 0 CPrevmre, Limits

Liim its of fla aininbility of soine paraffin y- p sig L5_100drocarbots hav-e been determined in oxygen, 25 100 200c h ,lo rin e , a n d o x id e s o f n itr o g e n , .' w e ll 'a s in . . . .. .m ixtures of air id various inerts. The l wer ' fLowr 5.63 0.6li ,its ill o x y g e n a l ( in a w id e v a r ie t y o f t [. . U p p e r -- -- 7 0 6 6 -. -- 0 .-Ox g n-imtrogen iixtures are essentially the 100 ... . . .-Lower- ------ .---- 2.4 6sliw its those ill air at the smniiie temperatire tUppcr - "- 72 76 77a n d p r e s s u r e (fig . 1 0 ) . L i m ii -o i-I ttlan .. a b ilit y 2 0(0 .. . . .-L o w ,r . .. ..-- - - - - - - - - - - - -Iileasurements by Bartkowirik and Zabetaki.; pjwr 73 72 75for mrthiane aii eliaic iii clilrinte at 1, 7.8, -

wid i 4.6 atio spheres, riuiiiiig from 2 5 to 200 °

i nre , miniliarized in tab vs 5 ad 6( (S). atiiiosphere with wich tie combustible is('oard ad , Joles (,;0) have Iresiit vd lixed. ''hie cimrrposit ion of i poitnt oi such a

gi'allhicall v t e liimi of fla inahbilit vof the first diagrani, exc pt one that represents only conl-six INVIIiii*'s of lie paralnfihi series in air con- bustible a)d air, cannot be read directly.tainig various ii rts, based mi a repivse nita- I list ead, one mnust determinie he co mipositiontion foiund useful ill som 111i1iig applitations of the atillosphere, add the combustible con-aid treating inert gas or vapor as part oif the tent, and then compute the total mixture coin-

28 FLAMMAL4ITY C1-L.IACTERISTICS OF COMBUST'IBLE GASES AND VAPORS

40 - Unfortunately, the methane-methyl bromide-air data were obtained in a 17-inch tube.Although satsfactory for methane and otherhydrocarbons,, th.3 tube is apparently notsatisfactory for miany of the halogenated ydro

20- carbons. Thus a recent industrial explosion0~n. involvitig methvi b~romide prompted Hill toOctane reconsider the f i-immabiity of methyl bromide

itL air (84), He found that methyl bromide wasnot ,nly iiammable in air but that, it formed

:3 flananable mixtures 4t 1 atmosphere wits awider variety of eoncentrations than Jones had

Heptanereportad (96). This would sug,-e&, that, thereis no justification for the assumption thatJones' flammabii r data for methyl bromidewere influenced bsy the presence of mercury

0Hexanepressure aire included in figure '8 amid are usedto form the approximate, brokeon, flammabilitycurves for the methane-methyl bromide-airsystem.

-40- Data of Moran. and Bertschy for pentane-prnoropropane-air, pentane-sulfur hexafluo-

Pentan ~ rie-air and peintane-perfiuoromethiane-air mix-ture aeicuded in figure 32 (147). Data by

-60 IBurgoyne and Williams-Leir for hexane-methyl-60 - 71 1bromnide-air and hexane-Freon-12 I (F-12;

0.2 0.4 0.6 1 2 CF2 Cl2)-air mixtures have been included inPRESSURE, atmospheres figure 33. These data were all obtained in

1'%-inch-diameter tubes. An investigation ofFIGURE 27.-Effect of Pressure on Lower Temperature flamm~biity of hexane-methyl bromide-air

Limits of Flammability of Pentane, Ilexane, lleptane, mixtures in a 4-inch tube indicated that an in-and ctan in ir.crease in tube size (from 17 %-inclies to 4-inches-

ID) resulted in a narrowing of the flammableTABLE 6.-Limits of flammability of ethane in range; the uipper limit decreased from 7.5 to

ch.,o ine 5.7 volume-percent. n-hexane vapor in air whilethe lower linmit remained constant. The

(volume-percent) amount of methyl bromide required for extinc-tion decreased from 7.05 volume-percent in the

Prsur, Liis Temperature, C13a'-inch tube to ti.0 volume-percent in the 4-Pssure Liis____ inch tube. However, again this is not in line

25 100 200 with the results obtained by Hill with meth vI

______ ____bromide-air mixtures (84). Accordingly, winklthe data obtained in approximately 2-inch tubes

9------------ {9wer-- 6. 1 2. 5 2.5 ' eeue ocnsc iue3,the Hill data,Lppe ---- 58 58 - - - -

100 --------- JLowr-- 3.5 1 .0 1 . 0 obtained in *t larger apparatus, tire also used toUlpper_ __ 63 75 82 form the approximate, broken, flammability

200 --------- Lower.------------- ------- ----------- curves for the hiexane-inethyl bromide-air~Upper~. -- (6 73 76 system.

______________________________ -- The limits of flammability diagrams for thesystemi n-hieptane-w.ater vapor-air tit 100' and

position. This 'oas been done for methane 2000 C (fig. 34) show the effects of temperaturethrough hexane (figs. 28-33). C onmpositionis on it systemi that, pro~iuces both nornial anidaire determined directly fromi the abscissas (inert Cool flu~nes at atm~osphieric pressure (192). In-conicent ration) amnd orintes (comnbust ible eonl- terestinigly enough, the mininima o xygen re-centration-); the air in tany mixture is thle differ- quirernent for flaine propagation (Mii 002 temice between~ 100 percent and the sum of inert 200- C is thc samie for the (coo1 and normnaland coinbuitible. Data of 13urgoyne amid flame regions in this instance. Further, theXWiIliainr-. Leir for inethane-miethmyl bromide decrease in zninimnuni oxygen requirements(.MeBr)-air an~d niethane-carbori tetrachlloride- 11 Trade names are Used for leniificatiol (only; this does not implyatir mixtures aire included in figure 28 (29). endorseinent by the Bfureau of Wines.

FLAMMABILITY CHAP ACTERISTICS 29

16 -1- -- 1

%air =100%--% methane.-% inert

14

12

MeBrU~10

CCI4

E C02

Lj Flammable H0H

0 10 20 30 40 50ADDED INERT, volume-percent

FioUnt 28. -Limits of Flammability of Various Methane-Irer, '*ts.Air Mixii rs at 250 C and AtmosphericPressure.

(fromn 1:3.5±0.3 vourne-percent tt 1000 C to extinction (peak values) at 250 C and atmos-12.8±0.3 volutre-pereent kit, 200' C) is wit' in pheric pressure tire about 28 and 42 volurne-the range predicted by the miodified Burgess- percent, respectively. Ti. 7utio of these valuesWheeler law (equation 35 and fig. 231), HIow- is appro:, ,dtely inversel y proportional to theever, the a~'iiable data ve14)' to mear-r ait ratio of tfieii nieat capacities at the temnperaturepresent to permit at realistic evaluation of the ait which co .bustion occurs. Accordingly,vaitidity of this latw, genieralized flammability diagramns of the type

N'Spection of the liinit-of-flaniuability curves given in figure 35 can be constructed for thein figures 28 to 33 reveals that c cept for higher Itydr -arbons, ignoring Lhe presence ofmiethatn( and ethane, Clio miinium amounts Of cool flamies. 31uch diagralms do not appear tocarbon dioxide and nitrogen required for flame be applicable to the Maogenated hydrocabons

30 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

14

%air =100%-% ethane-% inert

12

10-

-

E Flammable

La N2z 6

4-

2-

0 10 20 30 40 50ADDED INERT, volume-percent

FicUE 29.-Limits of Flammability of Ethane-Carbon Dioxide-Air and Ethane-Nitrogen-Air Mixtures at 25* Cand Atmospheric Pres8ire.

since these materials tend to decompose even Similar dtai atre given for ethane-carbonin flames of limnit-mixture composition and, ats dioxide-atir (fig. :37) and ethie-nitrogen-atirnoted, may themselves propagate flamne. Cole- (fig. 318) (121), andl for propane-carbon dlioxideC-man (37) hats found that time ratios of the peak air (fig. :19) and propaine-nitrogen-air (fig. 40)values of a hialogenated hydrocarbon tire not (122). Miiii oxygen reqluiremuents forconstant but are proportional to the heats of flame propagation (inin 02) through naturalcombustion of the combustibles to which the gas-nitrogen-air, ethane-nitrogen-alir, and pro-halogenated ht'ydrocarbon is added. Jpane-nitrogen-itir att atmospheric and elevated

Few data aire available for the effects of pressures and 260 C are summarized in figure 4 1.pressure on the limits of flammability of coin- [he inininmum 02 values in v'oluie-Vpi-rcent

b ustible-inert-air mixtures. One such set of are related to pressure ats follows:data is sumnmairized in figur 36, which givesthe limits of flammability of natural gas for natural gas:(85 pct nethane+15 pet ethane) nitrogen-airat 260 C and 0, 500, 1,000 and 2,000 psig (106). Miil. 02= 13.98-1.68 log P;, (4:3)

FLAMMABILITY CHARACTERISTICS 31

10

% air = 100%-% propane-% inert

8

4,-a)

) 6- FlammableE N2= mixtures

CL

0

0

2-

II I I

0 10 20 30 40 50ADDED INERT, volume-percent

FIouRE 30.-Limits of Flammability of Propane-Carbon Dioxide-Air and Propane-Nitrogen-Air Mixtures at 250 Cand Atmospheric Pressure.

for ethane: mixture containing 80 volume-percent methane,15 volume-percent ethane and 5 volume-percent

Min. (=12,60-.36 log P; and (44) propane has a lower limit in air at 250 C andfor propane: atmospheric pressure of:

Min. O=13.29-1.52 log P; (45) 100 vwhere I' is the initial pressure in paia. 80 5 5

The lower limit of flammability of any 5.0+3.0 - 2.1mixture of the paraffin hydrocarbons can becalculated by Le Chatelier's law (40, 12.9, 235): Liquid mixtures can be treated in the same way

if tie relative escaping tendencies of the various300 ", components are known. Since the paraffin

L . _- X-, 100 (46) hydrocarbons obey Raoult's law (143), theI I partial pressure of each component can be-, calculated as follows:

where C, and L, are the percentage composition p=paNj (48)and lower limit, respectively, of the -tb com-bustible in the mixture. For example, a where p, is the vapor pressure of the i' com-

32 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

10 - 1

% air = 100%-% butane-% inert

8

6- ,N24-.

E Flammable> mixtures

z 4-/Cst C02

2-

SI I

0 10 20 30 40 50ADDED INERT, volume-percent

FIGURE 31.-Limits of Flammability of Butane-Carbon Dioxide-Air and Butane-Nitrogen-Air Mixtures at 250 Cand Atmospheric Pressure.

ponent in the blend, po is the vapor pressure Ashman and Biichler (6), and Kuchta, Lam-of the pure com ponent and N, is its mole biris, and Zabetakis (127). These are notfraction in the solution. This procedure has normally used for safety purposes, unless therebeen used to calculate the lower temperature is some assurance that the contact time oflimits of decane-dodecane blends in air (fig. 42). combustible and air is less than the ignitionThe vapor pressures of decane and dodecane delay at the temperature of the hot zone. Theand the calculated low temperature limits are minimum autoignition temperature (AIT) isgiven by solid lines and four experimental usually the quantity of interest in safety work,values by circles, especially when combustible and air can remain

in contact for an indefinite period.Autoignition Some AIT values for paraffin hydrocarbons in

air obtained by Setchkin in a 1-liter sphericalTwo types (,f autoignition data are obtained Pyrex flask (194) and by Zabetakis, Furno, and

depending upon whether the objective is to Jones in a 200 cc Pyrex Erlenmeyer flaskcause or to prevent the ignition of a combustible (237) are given in table 4. Interestinglyin air. The first type are usually obtained at enough, experiments conducted in these andhigh temperatures, where the ignition delay is other flasks generally indicate that flask shaperelatively short. Typical of these are the data and size are important in determining the AIT.of Mullins (153), Brokaw and Jackson (15, 90), The AIT data obtained in the 200 ce flask may

FLAMMABILITY CHARACTERISTICS 33

8

% air =100%-% n-pentane-%00 inert

7

6-

4-

0

3--N

zL&J

0 10 20 30 40 50ADDED INERT, volume-percent

FIGURE 32.-Limits of Flammability of Various n-Pentanc-Inert Gas-Air Mixtures at 250 C and AtmosphericPressure.

34 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

8-11

% air =100%-% n-hexane-% inert

7

6

4-'

E

MeBr

zj F-12

3- C02

2N

117

0 10 20 30 40 50ADDED INERT, volume-percent

FIOURE 33.-Limits of Flammability of Various n-I Iexane-Iiiert (ias-Air Mixtures at 25 C and AtmosphericPressure.

FLAMMABILITY CHARACTERISTICS 35

30

%air =100%-% n- heptane-% water

25--

~20

E~c \200' C

Cool flamez

5-Normal flame

1000 CCs

0 10 20 30 40 50WATER VAPOR, volume-percent

FtouiE 34.-Limits of Flammability of n-llcptane-Water Vnpor-Air Mixtumres at 1000 and 2000 C and AtmosphericPressu re.

36 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

4 F I 1 1% air = 100%-% combustible-% inert

-,

E.2_30

46

C0

N2FlammableIJmixtures

Cst

0C-, L

0 10 20 30 40 50ADDED INERT, volume-percent

FIGuRE 35.-Approximate Limits of Flammability of Higher Paraffin Hydrocarbons (C.H2 .+3, n>5) in CarbonDioxide-Air and Nitrogen-Air Mixtures at 230 C and Atmospheric Pressure.

FLAMMABILITY CH{ARACTERISTICS 37

%air =100%-% nitrogen-% natural gas56

1 4w 4 2,000 psigE

32 -100pi

U 500 psig24 24:D Flammable!ZC mixtures

Z 16-Atm ospheric

8-

0 8 16 24 32 40 48 56 64ADDED NITROGEN, volume-percent

Fi' tiE 36.-Effect of Pressure on Limits of Flammability of Natural Gans-Nitrogen-Air Mixtures at 260 C.

38 FLAMMIABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

56-

go air =100%0-%0 ethane-% 00 O2

48-

40900 psig

~32

R 500 psig

Ld 24- 250 psigz

16-

8-

0 s 16 24 32 40 48 56CARBON DIOXIDE, volume-percent

IIG(LkL Ig.-L(1ect of IPrcsiiri oil Ljimit- of Ihirnriinality of Ethancj-('nrbon Jioxio-Air Nhytire'. at 26' C

FLAMMABILITY CH{ARACTERISTICS 39

561

%0 air =100%7-10% ethane-%07 N2

48

40

a) 900 psig

0

>24z

w 16-Atmospheric

8

0 8 16 24 32 40 48 56ADDED NITROGEN, volume-percent

Fmumn. 3s".- iI-rof I'russire on Limits of FIaimability of Ethaict-Nitrogen-Air Mixtures at 26 ' C.

40 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

40 1 I I

% air = 100%-% propane-% C02

32

C0)

9-24-4)E

> 200 psigLdzg 16- 100 psig0

..,,,,,,.,. At mos phe ric

8

0 8 lb 24 32 40 48CARBON DIOXIDE, volume-percent

FIGuRE 39.-Effect of Pressu.-c on Limits of Flammability of Propane-Carbon Dioxide-Air Mixtures.

FLAMMABILITY CHARACTERISTICS 41

4U [ I I I I

% air = i00%-% propane-% N2

32-

24-L

d24E0 ,/200 psig

L

S16 100 psig0

,, I I I I I

0 8 16 24 32 40 48 56ADDED NITROGEN, volume-percent

FIOURE 40.-Effect of Pressure on Limits of Flammability of Propane-Nitrogen-Air Mixtures.

be correlated with molecular structure by length as abscissa (fig. 43). The data fall intop lotting them against the average carbon chain two regions-a high-temperature region inlength defined as which the AIT is greater than 4000 Cand a

low temperature region in which the AIT is less2 gjiN, than 3000 C. These regions coincide with those

La~ (49) of Mtilcahy who found that oxidation proceedsLay.- 4('-(4)) by one of two different mechanisms (162), and

by Frank, Blackham, and Swarts (60). Thewhere g, is the number of possible chains each AIT values of combustibles in the first, regioncontaining N, carbon atoms and 31 is the tIum- are normally much more sensitive to the oxy-her of methyl (--('113) groups. For example, gen concentration of the oxidizing atmospheren-nonane and 2,2,3,3-tetraniethyl pent e each and to the spray injection pressure than are thehave 9 carbon atoms, but the former has 2 combustibles in the second region. Unfortu-methyl groups and the latter ha 6. The former nately, the available consistent AIT data abouthas only one chain of 9 carbon atoms with a the effec's of oxygen concentration and in-methyl group on each eml, and the latter has jection pressure are too meager to permit aLI maximnuni of 4 chains with : carblon at oms, 8 detailed comparison.chains witi 4 carbon atoms, and 3 chains with 5 The physical processes (206) and reactionscarbon at oms. Thus, n-nomanc has an average that lead "to autoignition are of interest in anychain length of and 2,2,3,3-tei ramnethvl detailed st uidy of this ignition process. Saloojapentame has am average of 3.9. 'The more highly (18.J), Terao (207), Affens, Johnson and Carhartbranched e combustible is, the higher its (1, 2), and others have studied the autoignitionignition temperature will be. .ininium auto- of various hydrocarbons in an effort to deter-ignition temperatures of 20 paraflins were mine the mechanisms that lead to the ignitionplotted as ordinate against the average chain reaction.

42 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

4,000

2,000

1,000800--

600

La 400-1A

L

U' 200 -U)LiJin0-

100 - Natural gas80 Propane80-

60-

40 Ethane

20-

10 I6 8 10 12 14

OXYGEN, volume-percent

FIoURE 41.--Effect of Pressure on Minimum Oxygen Requirements for Flame Propagation Through Natural Gas-Nitrogen-Air, Ethane-Nitrogen-Air, and Propane.Nitrogen-Air Nlixtures at 26' C.

An increase in pressure generally decreases where T is the AIT at in initial pressure P, andthe AlT of a .n )If ustible in a given oxidant. A and B are constants. Accordingly, the & ITFor example, the AIT of a nat undl ga-; il air v'almes obtained at atmospheric pressure shoulddecreased front 530 (C at I atmosphere to 240' not he used to assess ignition hazards at high(' at 610 atmospheres (9,000 psig) (7S). The pressures.AIT's of several hydrocarbons were found toobey Semnenoiv's eq uation over a limited pressurerange (248): The burning velocities, S., of various hydro-

carbons have been measured by numerous in-P A" 'log / A +B (50) vestigators in air and other oxidants (68, 131).

At one atmosphere and 26' C, the burning

-P

FLAMMABILITY CHARACXERISTIC13 43

TEMPERATURE, 0F

32 68 104 140 176 212 248I f I

t'O 101.32 CL7_Flammable 1.05 6E EE Calculated,.. .79 _

W., .39 0

0- Decane .26

0 C

.5-

0 20 40 60 80 100 120TEMPERATURE, 0C

FIGURE 42.-Low-Temperature Limit of Flammability of Decane-Air, Dodecane-Air and Decane-Dodecane-AirMixtures (Experimental Points 0).

velocities of paraffin hydrocarbons in air range from 0.2 to 2 atmospheres (fig. 47). The effectfrom a few centimeters a second near the limits of temperature is more consistent. For a givento about 45 cm/sec near the stoichiomietric pressure and mixture composition, an increasemixture composition; much higher values are in temperature raises S.. In general:obtained with paraffin hydrocarbon-oxygen miix-tures. Figure 44 gives results obtained by (51)BT,Gtibbs and Calcote for four paraffin hydrocar-bon-air mixtures at atmospheric pressure and where A and B are constants, T is the tempera-roomi iemperature (68). The datta are ex- ture and n is; a constant for a particular mixturepressed in t.?ris of the stoichio)letric composi- composition. Dugger, Heimel, and Weastlion. C,,; burning velocities aire given for the (50, 51, 81) obtained a value of 2.0 for n forcomposition range front 0.7 to 1.4 (',,. These some of the paraffin hydrocarbons (fig. 48).nut hors hanve presented1 similar dtai for comn- The burning velocity of the stoichionietricbiistibles ait 25' and 100' C. Figure 45 gives inethane-air and mietthane-oxygen miixtures givenresults ob~tained by Singer, Giuner, and Cook in figures 44 and 45 (10 not, agree with the valuesfor three paraffin hydroearbon-oxygen mnixt ures given in figures- 46 to 48 but, in each catse, theait at mospheric p1 essure and roolin temperatuire burning velocity data are internally consistent.'in thle range from 0.3i to 1 .4 (",, (198) . Buirning The actualil flamle speed relative to at fixedx'elecities range front !t low of 125 ('il/sec to at observer maty be much greater than S. sincehigh of 425 i/s& e; th~ese vluies aire coI nsider- the burned gases, if not vented, will expand andably greater thait those obtainmed in akir. A impart it inot ion to~ thle flamne zone. If detona-chllge in eithber temperatuare or pre11suret will t ion occurs, thle reacetioni speed increases nmark-ailter S,, for at particulari t Pie For. exam ple, edly. For example, figure 40 gives t hi KogarkoA~gnew aind ( iaifi (3) found t hat an inicrease in data oil velocities; wit li which at dot onattiomi waveJpressure caus~es S,, of si oichiioietri n nlt hane-air piropagat es t hroumgh various miet hane-air inix-andl propatne-atir mixtuares to~ decrease in thle t ares ait atmnosphieric pressure iii a 310.5 CII-pr.isim range from 0.5 to 20 atimospheres (fig. diamieter pipe (12;5). Similar results hatve been46l)) S, of stoichioniet vie nmetillne-uxygeii mix- obtained b y (en:t cim, (Ct arlson, and Hill t lowtunes, however, increasedi in the pressure range pressuires with natural gas-air mixtures (67).

44 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

550 -CH4 I i I I I 1 I

C2 H6

500-C3 H8, o ---C-C-C.- .

9 C-C-C-C-C

6 96m 400- C-C-C-C.C- C-C-C-C tC CI-. /~~-z 6

n-C4 H1 0 1z 350-

C

300-z n-C5H12 C

n-C 2 /n-C10H22

250n n-C6 H1 4 - 7.C8 H18 n-CI 2 H2 6 n-C16H34

n-CH - nC14H30

2001' 1 1 11 3 5 7 9 11 13 15 17

AVERAGE CARBON CHAIN I ENGTH, Lovg

FIGURE 43.-Minimum Autoignition I rqnperaturc, of Pi "9flin Ifydrocart, ijq ii Air as a Function of AverageCarbon Chin oingth,

In each case, powerful initiators were required is s,. reait t'mt pre., rq ,vaves are net sent ottto obtain a detonation in relat,velv large ip'-. ahea of the :lctnati,,n frwit Thus, pressureTheenergyrequiremanausforignitioii srere uce, detect j- that are 'sef 1 -1 e.\plosion preven-if oxygen is used as the oxidant in place of air. tion witi loflagrati i i'ovi ire useless withFurther, the detonation velocity incre ,s as de 'fnatiojthe oxygan content of the atmosphere in- With liqi i fuels,, t bthriiing rote dependscreased. Detonation velocities ,,tained k , r),rt ,i tI et o P *r zktiol ,id on theMorrison for methane, ethane, propa;.i, I,'itaie, poI size [3(;rges Stia. er itnd ("runer (20)and hexane in oxygen are given in Ifi. 1 50 , .'0 siowi that tho liqu, .. rcision ate ' Ls(150); similar data obtained by Wayint, tid gi, byPotter are given in figure 51 for n-hepLau.o- v=v=(!-e ', (52)nitrogen-white fuming nitric acid . ipors (219).Of principal interest ere is the ii gnitude of wh.'r, i is the vdue of v _,l iargr pour, IT isthe detonation velocity; even in air, ti is velocity a ca Aa.tt, and d is the pool d;auetter 'iery

FLAMMABILITY CHARACTERISTICS 45

r-r-

" .Ethane

40 -

,-/ / n-Heptane-

. \ "PropaneE 30- /*'Methane

o/

20

10

0 _ I I I

0.6 0.8 1.0 1.2 1.4 1.6COMBUSTIBLE, fraction of stoichiometric

FIGuRE 44.--Burning Velocities of Miethane-, Ethane-, Propane-, and n-fleptane Vapor-Air Mixtures at Atimos-pheric Pressure and Room Temperature.

46 FLAMMABIUTY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

5 0 0 - - - T I ' I I I 1 I

450-

400

N" 350E

0 300- rpn

CDz

250

200

150

100 1I I I I I I0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

COMBUSTIBLE CONCENTRATION, fraction of stoichiometric

J"'unIE 45.-Burning Velocitfi of N ethane-, E'tha ,-, aniid Propntrie-Oxygen Nfixtur.. tt Atmo t vhric 1PrvssurranOd Room "l'ipI eraturtv.

mp

FLAMMABILITY CHARACTERISTICS 47_ 50 - -T - I I '

4o -

E30

Propane

020zMethane-

106

10

0.2 0.4 0.6 1 2 4 6 10 20 40PRESSURE, atmospheres

FIGURE 46.-Variation in Burning Velocity of Stoichiometric Methane-Air and Propane-Air Mixtures WithPressure at 26" C.

expressed v_ as: lower limits of flammabilit of the olefins((Iv,) excluding ethylene fall in the range

0 0076 ( net heat of combustion, AIh" from 46 to 48 ng combustible vapor per liter- sensible heat of vaporization, Aif! of air (0.046 to 0.048 oz combustible vapor per

cubic foot of air).em/mai. (53) The effect of temperature on the lower limit

Figure 52 gives a summary of the r,, values for of flammability of ethvlene in air at atmospiericit number of cojubustibles, including several prsure. assunilng a (onstant limit flametemperature, is sh own by (he curve labeledp~araffin hydlroarbos (21). Of special igiifi- "U pwird propagation of flane" in figure 53.calce here is tlat Al J.All is niearliv cipnsti t 1 ifirtunatlel, ml downward Ilate pro paga-(about 100) for the paraffin liydrovarbons, s tion dta art, available over an extended tern-tliat their linar bitrnlinl[ rate,' t lre . lare tir l i per ininrate perat"ure range (2,22); these are included in

figure 53. As in the case of similar data ob-

tained with i nellane, tliese define a straightUNSATURATED HYDROCARBONS line parilhl tip t ll' "(',,istant flame t:emipera-,,, )ur, . pward pro I pagation of flari)'" line.Again, the nodifiel Burgess-Wiheler law,

equation (33), give., a variation in lower limitLimits in Air with temperature that Is ('lose tip t iot given I)y

The iniecilar weight, .pecific gravity, iiid t he ( 'ntnt flauin temiperature" line. so that1the.- properties of tile 3I"rmlr'aimouin, cosid- either u he il eI lit temllp)erat Uires below tileered here ire inluded in' table 7. At roonm AlT (of ethylere (-|ttf)' ('. .I*,:,The ", C)as tilepeniperat ure and atmospheric pressure, tit lilnit Hlati' te nperatniras of ohclins are no t toot

48 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

TABLE 7.-Properties of unsaturated hydrocarbons

Lower limit In air Upper limit In air

Combustible Formula A4 (Air In air /e L, L u(vol pct) \till) ( -(Vol Ref. (vol e---- ef.

pet) C pet) ,

Ethylene... . ............ C-----------28.05 0.97 6.53 316.2 2.7 0.41 35 (115) 36 5.5 700 (26)Propylene--....-- . C sla ............ 42.08 1.45 4.45 460.4 2.4 .54 46 (102) II 2. f 210 (40)Butene.l -------- -------- Coils .---- .---- 56. 1 1.194 3.37 17.7 1.7 .50 44 () 9.7 2.9 270 (1)ite-Butene-2-------------Cdl,------------'6.10 I 1.94 3.37 (a6,0 !.8 .i 46 (40) 9.7 2.9 270 (40)

lobutylene .............. lC,- ......... 56.10 1.94 3.37 (04. i 1.8 .53 46 (40) 9.6 2.8 260 (26)3-M ethyl-butene-I ... .. . l---- .. ...-------- 70.13 2.42 2.72 752.3 1.5 .5,5 1 48 (40) 9.1 3.3 310 (40)

P adiene............-- -40.06 1.3 4.97 443.7 2.6 53 48 (2)---1,3- Nutadiene............--C if............ 54.09 1.87 3.67 576.3 10 .54 491 (10P) 12e 3.3 320 ())

I Figures compiled at Explosive Res. Center, Federal Bureau of Mines.ICalculated value.

800

700

41)

E Ethylene

0

-J

E 500 -

w

4 00

0.2 0.4 0.6 1 2 4

PRESSURE, atmospheres

IIOUFtE 47.-Variation in Burning Velocity of Stoi-chiomntric Methane- and Etltylcne-Oxygen MixturesWith Presaure at 26°C.

FLAM3ABILITY CHARACTERISTICS 49

200 I

KEY0 Methane* Propane150- o n -eptaneA iso-octane

0 100o

>0Az S -, 10 + 0.000342 r 2

z a=50-0ca

0200 300 400 500 600 700 800

TEMPERATURE, a K

FGuRz. 48.-Effect of Temperature on Burning Velocities of Four Paraffin Hydrocarbons in Air at AtmosphericPressure.

,000 - 3.000

1,500 0 2.500

0100 EE

L 1,000 - : 2,000z0 o

z

o I500- -i 9 1,00

z

KEY0A Hexane

c1 1,000- A Butane -6 8 10 12 14 03 Propane

METHANE, votume-percent * Ethane0 Methane

F'ww rip; 49 -- letoratiolt Velocjtis of ),ttiume-kir 500Mixtres at At liospheric I'ressuire. (Initintor: 50 70 0 10 20 30 40grams of armitol exlloive. Pipe diiietcr 30.5 er.) COMBUSTIBLE, volume percent

different froin those of p[araflili hNI(II'(W1L1)orIs, ')etoyjti Vejociiies of \letrharl-,he generalized pralph fir IL,,'L (fig. 23) (an 14- Ethanet*-, l'rolpar e-, Butane-, ald Ilexrie-()xgr'l

used for these un iaturated hydfocalbOmls. Nlixture- at .itmospheric PtI.-.i.ure.

50 FLAMMABILITY CIIARAC'rERISr01CS OF COMBUSTIBLE GASER AND) VAPORIS

".001- T II I

V 3 -Downward proplagationl

9,400of flame

E2 Modified Burge'ss Wheeler Law

*WFNA0 z~aUpward propagation

ui 2.000 - Constant flame temperature- " of flame

WFNA N2z(Mole fraction N12 =0.5) i 0_

t~1,500-- 0 ?l'0 400 600 800 1,000 i1200

oTEMPERATURE, C

FIGURE 53.-Effect of Temperature on Lower Limit of

1,000Flammability of Ethylene in Air at AtmosphericlOOC I I Pressure.

0 5 10 15 20 40 ------n-HEPTANE, mole-percent %air =100%-% ethylene-% inert

FIGURE 51.-Detonation Velocities of n-Heptane Vapor-in WFNA (White Fuming Nitric Acid)-NitrogenGas Mixtures at Atmospheric P'ressure and 400' K. 30

1.42

1.0z

S.8 C41-11 2 0 10 20 30 40 50\1 C61 11-O ADDED INERT, volume-percent

4 LNG

.6 - C8 1-10 -0 -Cg 6 ,, FIGURE 54.-Limits of Flamm~bility, ef -Hthylenie-Carbon 1)ioxide-Air anid Ethylene-Nitrogen-AirMixtures at Atmnospheric Pressure and 26' C.

.4 UDMHO -i (100, 1101, 103), (figs. 154-60). The first twofigures are modifications of the limit-of-

.2 CT flainniability diagramns given in (.40); the thirdC C 0 is essentilly the same ITs that viven in the earlier

Cf130H Publication hut include., the experimental

points. The oither curves were constructed10 50' 100 150 200 250 300 Irom originail, unpublished data obtained t

He /N Hthe Explosives Res. Center, Federal Bureau ofMines.

Firo;i 52-Relation Between Litrnid-Butrning Rate Other liniit-of-flarnm-ability determinations(LarV r- Pool Diameter) and Rtatio of Net Heat of have been made in oxygen and nitrous oxide.Comb -ltion to Sensible Heat of Vaporization. These data are included in table 8 (40, 100,1007).

Limiis in Other Atmospheres Autoignition

Th~e limits of flammability (if ethylene, propy- There have been few determinations of AIT'slene, isobutylene, but ene- I, :3 methyl butene-1I, of the unsat orated liyplrocarbonus in air or otherand butadienie in various inert-air atniosphleres oxidants; the available data (9./j, 116, 191) arehii've been determined by Jones and coworkers summarized in table 9.

FLAMMABILITY CHARACTERISTIC435

12 -1-

%air =100%-% propylene-% Inert

10

-%

EFlammable

>6 mixturesLAS N2zW

-j

a>, IctCO 20.42

2-

0 10 20 30 40 50ADDED INERT, volume-percent

FI"ouRE 55-Lrnits of Flammability of Propylene-Carbon IDioxide-Air and Propylene-Nitrogen. Air Mixe CatAtmospheric Pressure and 26' C. itla

fill?-ina rliiz, 110 ' I itk '-f 9i .lbustib e,; have positive heUL, of formiation,The burning velocity of ethylene has been AJI, (table 10) iunri Would therefore it~erat-a(leterinined in air, oxygen), and o)xygen-nitrogen heat if (iecomiposed to thle elements carbon andatmiospheres by numerous investi .gators (8, 7, hydrogen. Even miore heat would be liber-P/, O'S, 131). In generatl, it is higher than the ateol if gases with it negative heat of for-

b rning velocities of the paraffin hydrocurbons nation -~ for example, inetane-form froin thleunder the samne comiditionls (fig. 47). Simmnilar elenments. In practice, at mixture of productsresults tire to Ibe expectedl for other unisaturatedl results ulpon decoinposition of such conibusti-hydrocarbonis, although thie available datat are bles. F~or examlple, at propagating decompo-rather mneager. sition reaction can be initiated -ill pure ethyleneStability in at 2-inch-iD tube at 230 C an dlpressures as

low as 750 psig, using 2 gramso guncottoll.Many unmsaturated hydrocarbon vapors can A reaction can lbe initiated at 2 1 'C and pro;;-propagate flame in the absence of air at, elevatedl sures ats low as 975 psig with I grain oftemperatures and pressures; that is, they have guncotton. 'IFie decomuposition products are

52 FLAMMAB.LI'Y CHARACTEREISTICS OF COMBUSTIBLE GASES AND VAPORS

80

.4- N2 -

02 C02

Ljd FlammableUj mixtures

4-

0 10 20 ZG 40 50ADDED INERT, volume-percent

FIGURE 56.--Imits of Flammability of Iobutylfne-Carbon Dioxide-Air and Irobutylen -Nitrogon-Afr Mixturre atAmosphcrio Prewure and 26* C.

TABLE 8.---Limit qfflammability of unsaturate'] TAimL 0.-M.finimum autoignition temperatureshydrocarbons at atmospheric pre sure and room oj unsaturated hydrocarbons at atmospherictemperature, in 2olume-percent combustible prtssurevapor

.......L Autoignition temperature

In ai: In oxygen In nitrous - .................oxide Combustible In W'r In oaygenCombustibleI .. .

0 ~ ~ 0 C 0f 'C F Ref.SL 1 UIL IU L IU oC 0 F Ref. -O °FRf

Ethylere ------- 2. 7 36 2. 9 80 1.9 40 Ethylene --------- 490 914 (116) 485 9 (116)Fropylene ---- 2. 0 11 2. 1 53 1.4 29 Propylene ------- 458 156 (9) 423 793 (1)Butene-i_-.----- 1.6 10 1.7 i 58 ----- .. Butene-l -------- 394 723 (I) 310 590 (1)Butene-2- ----- 1.7 9.7 1.71 55 i '3261Butene5 (1 )

1,2J•utadiene 418 784 (19 33 " 35 ( 91)

I Figures oompiled by Explosives es. Canter, Federal Bureau oxprinarily carbon, methane, and hydrogen: Mte.

approximately 30 Kcal are reieased per iwole ofethylene decmposed. Propylene yielded si i- Propadiene and buiadiene also decomposelar products followig explosive decimposition readily under the action of powerful igijitors.during compression to 4,860 atmospheres (34). Propadiene vapor has beon decomposed in a

FLAMMAI3ILITY CHARiACTERIBTICS 53

60

% oxygen 100% -% isobutylene -% water vapor

50

2~Min 02(1)40 16%

E-5030a-

Flammablem~ixtures

w

0CC)

024060 80 100WATER VAPOR, volume-percent

FIGURE 57.-Limits of Flammability of Isobutylene-Water Vapor-Oxygen Mixture at 150* C and AtmosperiePressure.

~-,,wh ;1be at 120' C an(' 0 psig using a ACETEN Nihl~hQCARBONSpiatir'umn wire ignitor. Decomposition of buta- ( Rdiene in an industrial accidJent resulted in aitpopcorn" polymer; the reaction was a pparently Afinitiated by an unstable peroxide (.4).Lnt i i

TAHLE lO.-Heats ol formation (Kcal/miole) of Acetylene forms flammuble mixtures in airunsaturated hydrocarbons at 25' C. at atmospheric pressure and 250 C, in a range

Combustible: all/ from 2.5 to 100 volume-percent acety'lene.Acetylene ----------------------------- ~ 54. Quenched and apparatus limited upper limitsPropadvne -_-----------_-- 45. 9 have been obtained in 1-, and 2-, and 3-inch-1-3, laetadjene.- - --------------- 4,3 diameter tubes (40), but pure acetylene can1-, thyene----------------- ---------- 6. propagate flame at atmospheric pressure inPropylene -------------------------- ---~ 4. tubes with diameters of at least 5 inches.1-Butce -----------------------------. 3 Sargent has summarized availablo data on

I Refs. (114,18P), initial pressure requirements for deflagration and

54 FLAMMABIITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

10( 1 1 1 detonation through acetylene in horizontalair 100%-% butene-I-% Iner, tubes of about .02 to 6 inches ID at 600 F. (89,

185). His curves are given in figure 61, which8 also includes an experimental point from the

data of Jones and coworkers obtained in a.vertical 2-inch-diameter tube. The existence

N2 of this point, at a pressure below that given bySargent's curve for a 2-inch tube, indicates that

E C02 this curve should be used only for horizontalsystems. The point labeled "Industrial explo-

SFlar.am bl sion" was reported by Miller and Penny (144)W 4 and presumably refers to a deflagration. The..j third experimental point is discussed, along

with the detonation curve, in the section onto 2- stability.21 The effect of temperature on the lower limit

of flammability was determined by White in a2.5-cm tube with downward propagation of

Iflame (2). Although the actual limit values0 10 20 30 40 50 tire not satisfactory for our purposes, they can

ADDED INERT, volume-percent be used to check the applicability of the fL-/'2 5ratio data presented in figure 23. The WhiteFiouaz. 58.-Limits of Flammability of Butene-l- ratio of lower limits at 3000 and 200 C. is

Carbon Dioxide-Air and Butene-l-.Nitrogen-AirMixtures at Atmospheric Pressure and 260 C. 2.19/2.90=0.76; the corresponding ratio from

10 I% air = l00%-% 3 methyl butene.l-% inert

8

430.

E _6--N

FiGuRE 59.-Limits of Flamma- N2bility of 3 Methyl Butene-1- " L-Carbon Dioxide-Air and 3 zMethyl-Butene-l-Nitrogen-AirMixtures at Atmospheric Pre. M Flammablesure and 260 C. 01 4- mixtures

-2

10 20 30 40 50ADDED INERT, volume.percent

FLAMMABILiTY CHARACTERISTICS 55

12 1% air = 100%-% butadiene -% inert

10I

EFGuRE 60.-Limits of Flamma- .

bility of Butadiene-Carbon > 6-Dioxide-Air and Butadiene-Nitrogen-Air Mixtures at At- z Flammble NZmospheric Pressure and 260 C. W mixtures

t C 0 2

24

SI I I0 10 20 30 40 50

ADDED INERT, volurtie-percent

"Constant flame temperature" curve in figure The quantities of propylene required to23 is 0.78. Accordingly,, this figure should be prevent flame propagation through methyl-satisfactory for use wit i acetylene at tempera- acetylene-propadiene-propylene mixtures attures in the range from 20' to 3006 C. 120' C and 50 and 100 psig have been deter-

The lower limit of flammability of methyl- mined in 1-, 2-, 4-, and 12-inch tubes (fig. 62),acetylene (propyne) in air at' atmospheric and at 120' C and 100 psig in a 24-inch sphere.pressure is 1.7 volume-percent, equal to 0.34 C,, As noted, the propylene requirements arewhich compares favorably with the value for strongly affected by temperature, pressure, andacetylene (0.32 0,,). Upper limit investiga- container size. As the tube diameter increases,tions have been conducted bv Fitzgerald (59) the quantity of propylene required to preventin a 2-inch tube at 20' and 1200 C to determine flame propagation increases; this effec, is lessthe low-pressure limits or lowest pressures at pronounced in the larger vessels (diameterwhich a flame will propagate through methyl- greater than 4 inches) than in the smalleracetylene vapor at these temperatures. He vessels (diameter less than 4 inches). Thefouwd these to be 50 and 30 psig at 20' and results obtained in the 24-inch sphere were120' C, respectively. In a 4-inch tube, Hall similar to those in the 12-inch tube.and Straker (77) obtained a low-pressure limitof 43 psig at. 20' C. This indicates that the Limits in Other Atmospheresupper limit of flammability of methylacetylenein air is probably less than 100 percent at 200 C Gliwitzky (71), and Jones and coworkersand 1 atmosphere. determined the effects of carbon dio.-ide and

56 FLAMMABILTY CHARACTERISTICS OF COMBUSTIBLE GASEE AND VAPORS

400 ---- , I 1 i I 11I

200 -Deflagration

100-80

C,,

60CLJ

= 40

Sargent20 0 Miller and Penny (Extrapolated)

0 Industrial explosionA Jones and others

10- NN

0.02 0.04 0.06 0.1 0.2 0.4 0.6 1 2 4 6 10DIAMETER, inches

FiouRI 61.-Effect of Tube Diameter on Initial Pressure Requirements for Propagation of Deflagration andDetonation Through Acetylene Gas.

nitrogen, on the limits of acetylene in air at gel, or charcoal lowered the pipe temperatureatmospheric pressure and room temperature. required for ignition to a 280 ° to 300' C range.Unfortunately, all measurements were made in The presence of 1 gram of potassium hydroxidetubes that were too narrow to give actual upper lowered tile pipe temperature still further tolimit data. Nevertheless, the resulting 170' C. The impact of a 0.25-inch steel ballquenched-limit data are summarized in figure falling from a height of 15 inches against a63, because they show the relative effects of fragment of copper acetylide produced a hotadding two inert diluents to- acetylene-air spot that ignited the surrounding gaseous acety-mixtures in a 2-inch-ID tube. lene at room temperature and 3 atmospheres.

Autoignition Burning RateA summary of available autoignition tem- The burning velocity data for acetylene in

perature data for acetylene, acetylene-air, and air obtained by Manton and Milliken at 1acetylene-oxygen mixtures in clean systems is atmosphere and room temperature are given ingiven in figure 64. They are based on measure- figure 65 (158). The burning velocity rangesments by Jones and Miller (110), by Jones and from a low of a few centimeters per second nearKennedy in quartz tubes (99), and by Miller the lower limit to a high of about 160 cm/secand Penny in a 0.5-inch steel pipe, 15 inches on the rich side of the stoichiometric composi-long (14). Jones and Miller found minimum tion. Parker and Wolfhard (164) have foundautoignition temperatures of 3050 and 2960 C considerable variation in the burning velocityfor a variety of acetylene-air and acetylene- of acetylene in various oxidants. The burningoxygen mixtures, respectively, at atmospheric velocities in stoichionetric mixtures with oxy-pressure. Miller and Penny report little waria- gen, nitrous oxide, nitric oxide, and nitrogention in the autoignition temperature of acety- tetroxide were found to be 900, 160, 87, and 135lene in a clean pipe at 4 to 26 atmospheres initial cm/sec, respectively; for comparison, the burn-pressure. However, the presence of I gram of ing velocity in a stoichiometric acetylene-airpowdered rust, scale, kieselguhr, alumina, silica mixture (fig. 65) is 130 cm/sec.

FLAMNMAIILTTY C'I I AltA(Tl.Ei1STICS 57

'000

,Z

\Flammable mixtures -

12-inch-I D bomb,l0O psi

2-inch-I D bomb,IO0psig '\ \-"2-inch~-i D

~~0 I~~-inch-ID bomb,IO0psig \ \obs~i

00 90 80 70 60 50 4 00 1PROPYLENE, volume- percent

FIGURE 62.-Itange of Flamnmable Mixtures for Mc(thy-lacety.lene-Propadienc-Propylenie System at 1200 C and at50 an~d 100 Psig.

The burning velocities of acetylene-air m1ix- required for propagation ait subsonic (deflagra-lures were found to ibe indlependcit, of pressure tion) and supersonic rotes (detonation) intob~et ween 0.1 and 1.0 atmnosphlere (138). Sint- the unhurijod gats tire giveni for ai range of pipeibrly, A 'new andt( 'raiffl (3) and Parker andi~ (I. -41er.s i!, ''',ure 61 (185). D~eflagration isWVofhard (164~) found U'h, 1urninq, velocities LIscussed briefly under Liniits of Flan-iniability;of stoicliioietric, acetylene-oxygen and1( acety- dletonatio : 1s dfiscussed in this section.lene-nitrous oxide inixt tires wereo independent (of The cuirse labeled ''Detonation'' in figurep)ressure bet ween approxiimately 0,5 and 2 61 gives thle iniimui pressure required foratmuospheires and~ 0.03 and I atniospliere, re- propagation (of it (detonalt ion, once initiated, inlspectively. Th'le b~urning velocities (if st ojchio- tuibes of 0.3 to 1(0 inches (liv ieter. In ipraw-Inetric 1cctylene-mitiic ox'ide and( acetyliene- live, at (detonat ion inay be initiated directl

11i rogen let rt xide iiixtures incrca:~ed slightly front it defla grittion t hat hias lpropaglited throu lo vern thiis pressurme range 0.03 tot I at mospier'e at rat, her ill -definied distance, know itsi Its

(1 ((.4). pedletInait) 0n or run-up) distanimce. This (us-Stabfitytanlce depends ontc itemneritutre, pressure. tuhbe'Staili~r Ijittiieter, conidition iof tube watls, and onl

As noted, iicetyleiie canil propagatte fltiie inl igilit ion-s( urce streligtbI. Fori exampiJle, usingthe absence (if air (39, 165). The pressures it fulsed p~itiiui wir-e ignit(Ir, Miller anid P~enny

58 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

100 (144) found the predetonation distance for% air 100%-% acetylene-% Inert acetylene in a 1-inch tube to be t1 feet at 51.4

psia, 22 feet at 55.9 psia, 12 feet ot 73.5 psia,and 2.8 to 3.2 feet at 294 psia initial pressure.

80 Extrapolation of these data yields the pointin figure 61 for a very large predetonationdistance. This point (44 psia and1-inch diam-eter) lies fairly close to the detonation curveestablished by Sargent (185). The maximum

A, lenth-to-diameter ratios (LID) given by Sargentfor establishing detonation in acetylene is

9plotted against intial pressure in figure 66.Z In tubes, Fa ving ta diameter greater than those

40 - given along the top of the figure and havingL mixtures powerful ignitors, the LID ratio will be less than

that given by the curve. Nevertheless, thisfigure should be of use in giving the outer

20 N2bound of LID and the approximate quenchingC02 - diameter; a better value for the quenching

est diameter can be obtained directly from figure~61.Although predetonation distances are diffi-

o 20 40 80 cult to measure and experimental data oftenADDED INERT, voiurre-percent exhibit much scatter, they are of interest in

safety work because they can be used to evalu-

FIUnt 63.-Quenched Limits of Flammability of ate the maximum pressures likely to occur inAcetylene-Carbon Dioxide-Air and Acetylene- a system due to cascading or pressure piling.Nitrogen-Air Mix~'rcs at Atmospheric Pressure and -'bis phenomenon presents a sp..-:-ial problem26' C, Obtained in a 2-Inch Tube. because the final pressure achieved in a detona-

700 1 1 IKEY

Oxidant Pressure Tube* Air 1 atm 131 cc quartz0 Air 1 atm 200 cc quartz600-.L Air 2 atrm 200 cc quartz0 Oxygen 1 atm 131 cc quartz

None 4-26 atm !-inch steel pipe

500-

FiGURa 64-Minimumn Autoigni- ztion Temperatures of Acety- 9lene-Air and Acetylene-oxygenmixtures at atmospheric and Zelevated pressures. 4 00 - Region of autoigntion

300I-

2000 20 40 60 80 100

ACETYLENE, volume-percent

FLAMMABILITY CHARACTERISiTICS 59

2001g to be expected from a detonAtion is about50 times the initial pressure. As the pre-sureequalizes at the speed of sound in a deflrgra-tion, the maximum initial pre3sure to be ex-pected upon tranisiticn from deflagration to a

00 150- detonation is approximately 1i times the frac-N. tion of acetylene that has been burned times

E the initial precombustion pressure. Fifty timesU this pressure is -.ho ap'proximate maximum

pressure that rould be o ;ained when a detona-- tion occur-. '.Lo illustrate this, Sargent has

3 100 r-plotted the final-to-initial pressure ratio (P,/Pj)W ~against the predetonation distance-to -tube

> length for acetylene. A siniliar graph is givenz/ in figure 67. To use this graph, the maximum

z redetonation distance to be expected must-s be deemndfo figure 66. Tb.-n'z

maximum final-to-initial pressure ratio.

____ ____ ____ ____(C.H 2 . ,)

0 5 10 1s LiMitS inaAirACETYLEJE, volume-percent

Fso.-s, 65.-Burning VnIocity of Acetylcnc-Air Nfx The combustibles considered in this sectiontures at Atmospl.cric k'ressurc and Room Tempera- are listed in table 11, with pertinent properties.ture. At atmospheric pressure and room temperature,

the lower limits of flariimabilit ofte aromatiction depends on the initial pressure at the onset hdoabn arap oately 50±2 mg/lof detonation. F, r example, the maximum (0.050± 0.002 oz combtustible vapor per cubicpressure to be expected from the deflagration foot of air).of Lcetylene at moderatc pressures is about 11 The lower limit of toluene was determinedtimes the initial pressure (144); the maximum by Zabetakis and coworkers in air at 300,

QUENCHING DIAMETER, inches

0128 421 0.5

FIOURE 66.-Mlaxiimum LID ratio .SRea uired for Transition of aDeflgration to a Detonation *:. 40-in Acetylene Vapor at '*01 F Cand from 10 to 70 Psia. .

10 20 30 40 50 60 70INITIAL PRESSURE. psia

60 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

TABLE 1 1.-Properties o selected aromatic hydrocarbons

Lower limit in air ' Upper limit in air IC, in net Ali .....

('ombustihlm Formula M Sp gr air (vol /Kcal -Wr ) pt(volle 110 m1 j00 (L o I I.. [Ii

PCtI pet)

Blzeee ('1,1 78. 11 2.,69) 2. 72 757. 5 1, 31 0. 48 47 7. 9 2. 9 300"IhUe(_( (... l711, 92. 13 3. is 2.27 101. 5 1.2 . 53 50 7. 1 3. 1 310IE'thl ihmnzene - (!e C 116. 16 63.17 1.96 104s. 5 1. 1) 51 48 6. 7 3. 4 341)omI-X'vn. ..... (l10 106.t 16 . 7 1.96 1045., 9 1. 1 56 53 6. 4 3. 3 320rn-Xvmmmle ----- cjl 106. 1 6 :3. 67 1, 96 1045. 5 1.- 1 .56 53 6. 4 3. 31 321)p-Xl.n_-- C---- 106. 16 3. 67 1.96 1145. 7 1 1 56 53 6. 6 . 4 340(IIinmI----------C 1 2 120. 19 4. 15 1. 72 111,.2 .8,8 .1 4S 6 .5 3. 8 3170p-Cym--en--.....--Co11, 4 134.21 4.63 1. 53 1341.8 . 85 56 51 t.5 3.6 350

I Re. (147).

400 -- ---.--------... T ....... T

300 j

FiorRaE 67.--Final-lo-Initial Pres -

sunr Ratios Decvvopied y Acet- 200yeime With I),olitiol l 1litim-tion at Various Points Along a

Tube.

100 ,--

0 0.2 0.4 0.6 0.8 1 0PREDETONATION DISTANCE/ TUBE LENGTH

1000, and 200' (i (235, 247); the varintion in Their values rmiuge f'rin 8.8 percent (ctiinieiielower limit with tonipertlikre is given by eqaui- (80' (' aid a) tii pherie pres,.re) (if 10.8 per-tions (31) and (33') derived for parafflin h 'dro- (,ett ctiiniiei (I4i' (' kiind 11) psig pressutire).carbons, aid the vorresponding curves of filgure23. For example, jImp, rIL.3, ,. vwits folund to he Limits in Other Atmospheres1.07/1.24 or 0.86; the ratio predicted by thecurve in figtire 23 is 0.87. The !iniit ,,if flhininititilitl ,dtgiiumed hv ir.

Ihe u )p(er litijts of tie irminiics (iin.idered g(li. (;29) mrid lhv r.1,i (.t[)) f iur zlmc'l-

here it 1000 ( nire inchded in t able 11 (270. miirl)lml di~xhNle-iir and eli? 'mi.-iitrmigeu-nuliThese were otlaiiied it ntnisl)lierii' fpreslr mixilt tires at tit Iiimmli'n jtreslilre nllml a 25 ° (' mieiii it 2-incl-diwnietr Itihe, oiin ait line eid. glixen in igtre WS , ; simiillir dall mire :ivlii firBlier nind W~elbb 4lobtiL Ined uppier iliii n miatit i the last two Ililiires t 1it n111, m1hwric pes~olrtR mtmilinrciil grade m'iieriv (9;.1 prt riiiet-e) 1i11ml I 1 (' The iiertint rpqtltrm'liieit tit 2i;ii nir tit elevated tenimer ires anm iiimmmtheic t ire liprixhlihitek lile silmie 1 tihfse if It-milld 'el'vtted pressures Ii it chim1ed b1 1111 (I ). Ilexine (fig. 33). Agnili, it sloi le hi II l!

FLAMMABILiTY CHARACTERXSTJCO 6

10. . ......

%air =100%-97o benzene - qV inert

8

150

6,25

>Ee~

z 4Zir-WN

0 10 20 30 40 50ADDED INERT, volume-percent

Fioiunw 6S.'--Limila of Flarnmabilitv of Benzene-Methyl Bromide-Air Mixttures at 250 C and Benzene.-CarbonDioxide-Air and Bnzene-Ntrogen-Air Mixtures at 250 and 1500 C and Atmospheric Pressure.

that the methyl lbromide datta aire not consistent expressed in mole-percent as in the ori~iawith those obtained by Hlill (rompare figs. 28 presentation. 'Plur system has no lower mit

an3), Tjhese lattter (lain (80) were used to, mixtures, as a flamie can be initiated in hydrogenconstruct. thle approxitnate (broken) flaninma- peroxide vapors (186). As a 90-weight-percent,hility curves for the benzene-iriethyl bromide- hydrog en peroxide was actually used to obtainitir system,. these flawinability data, all compositions were

Tlhe decrease in the minimium oxyNgen require- cailculated to) yield values based on a 10-cercent,mnents for flaine p~ropatgationi (fronti 14.2±+0.3 hydrogen per(')xidle co nten t. This co~uld be donevohiinw-percent ait 250' C to 1:3 1 ±013 volumve- here because only three cemiponients are consid-[)ere~ont ait 150t' in it carbon dioxidle-air atnmrs- Pred. Where four components aire considered,phere; fromt ! 1.4 ±0.3 voluine-jiercent at 250 the flumnahiiity 6ata can be presented in aC to 10.1 -f.0.3 v'ohiine-percemit fit I 50, in) at tiiree-itnenginn plot ; if two of the cornpo -initri pgcm-air tttJ11iO~jpher'e) iS withilin(fhe Irange mient 11 ppear in fixed proportions, at triangularpredic ted lv (flie miodified ilurgess4-Whepeler plot (,an Ce used wit It the two compnets (forlakw (equialion (05), fig. 23). exaniple, 90-weight. Iercemit hydrogen peroxide)

Tlhe limlits of 1f1ilnifilalitY of ort Iioxvknle C40mnsid ered ats a sinigle c~npinemlt. Such a(( df11 (('i,) 2)-water-h' dogemi peroxide hu- plIot is presented in figure 70 for 00-weight-I wres were dri crmin ed tit I 54' C and I titimu14- percent hydroigen 1)eroxidle-4 rthoxyvilenie-forinicl'ohere rs'weby Matrt iiidill, Lang, atid acid (HMUMO~) at 1540 C and I 'atmnosphere.4itbem skis (1T).hle (lait tire pretiented iii rhit; was considered to) he at plane in a regularit triangular plot. in figure t19; emflposiionS are tetrahedIron in the original article and is there-

.-- -.- --- -. ......,-......

62 FLAMMABMI1TY CHARACTERISTICS ul, COMBUSTIBLE GASES AND VAPOUIS

100 0

80 20Composition line formed with

82.6 mole % (go wt %) H202

600

200 2 aoe eseo

g p d Flammbblemixtures l co

Decmpsitonof hepeoxideloers th upe eaadpr-oitos epciey.T'

100 so 60 40 20 0H202, mole-percent

FimuRi 69.--Limits of Fladsmabity of HiOrCH4 (CH3)rHO at 154i C and I Atmosphere Prature.

fore not a regular triangle. As before, onl~y an -CHa group (24 1). When the benzene ringupper limit curve is given because 90-weight- contains two side groups, L, is determinedpercent hydrogen peroxide is flammable. In first for the side roup that yieds the largestaddition, a calculated curve based on Le Chate- average value and d to this is added l, , orlier's rule is given, as is the upper liait curve of the average chain length of the second sideobtained with decomposed hydrogen peroxide group; (a, p, and correspond to the ortho-,Decomposition of the ide lowers the upper meta-, and para-positions, respectively). T-limit appreciably ane o ields a system wLch data again fal into high- and low-temperaturehas a lower limit of flammability (not deter- regions (fig. 43).mined in this study).

Autoignition Burning Rate

Burning rates and detonation velocities ofThe minimum autoignition temperatures of benzene in air and oxygen appear to be ap-

a series of aromatic hydrocarbons in air at proximately the same as those of the higheratmospheric pressure are given in figure 71 as paraffin hydrocarbons. For example, the re-a fntion oF the correlation parameter L ... sults of Golovina and lFyodorov (211) showThis parameter was determined by use of that the maximum burning velocities of benzeneequation (49), treating the benzene ring as a in nitrogen-oxygen mixtures range from about

6Ao

FLAMMABILITY CHARACTERISTICS 6

100 0

80 20

.60 4

00

Oxtdant; ecompose

0 VaV100100 so 60 40 20 0

90 weight-percent H 202. mole-percent

Fioun. 70-Limitaof Flammability of 90-Weight-Paeent IIOrCH# .(CH3)rlICOOH at 1540 C and I AtmnospherePressure.

295 cm/sec in oxygen to 45 cm/sec in air; the table 12. The lower limits of flammability inmaximum burning velocities of haxane in air at atmospheric press ire and room tempera-various nitrogen-oxygen mixtures range from ture fall in the range from 48 ±3mg/i (.048abouit 260 cm/sec in oxygen to 40 cm/sec in ±.003 oz combustible per cubic foot of air).air. Similarly, Fraser (0!) found the maximum By volume, this is equivalent to approximatelydetonation velocities of benzene and n-octane 0.55 02,,, which is the same as for paraffiniiii oxygen to be 2,510 and 2,540 rn/see, hydrocarbons. The ratio of the upper limitrespectively, to C,, appears to increase with molecular

weight.ALICYCLIC HYDROCARBONS According to Jones (40), the lower limit of

(CA.,,) cyclohexane in air at atmospheric pressure and260 C determined in a 2.0-inch tube is 1.26

Limita in Air voluine-percent. Under thea same conditions,Burgoyne and Neale (26) found the lower limit

A summary of the pertinent properti&; of to be 1.34 volume-percent, using a 2.5-inchsome of the members of the series is given in tube. Matson and Dufour (141) found the

64 FlAML4DIITY CHARACTER18TICS OF COMBUSTiBLE GAGES AND VAPORS

57- -1

~~CH 52 CHH-HICH

a-wH C 3 CCH3

02475 -F- 0H CH3 -CH-CH3

S425

CH3-H 3-H3-C 22H37 - CH

375 1 C2H5 10 12 3 4 5 6

L avg

Fiaunu 71.-Minimum Autoignition Temperatures of Aromatic Hydrocarbons in Air as a Function of CorrelationParameter L.,..

TABLE 12.-Properties; of selected alicyclic hydrocarbons

Net A J....... limit In air Upper limit in airS9 !r, C.0 k.0l

Combustible Formula M (Au) inair mole ) L. LM L U,, U(Vol pet) (Vol * ~(mg) Ref. (vol Un mg) Rat,

pe) T pot) C.,

C corpn ------- Cas.. 4208 1.48 4.45 465 2,4 1 0.54 46 (107) 10.4 2.3 220 (107)Cy lb(ae- ----- 11. .-- ----- .10 A'94 3.37 1'600 1,8 .5 46 (1) ---- - ---- -- -C eoAnse_.----- lo - -- _I... - 70.13 2 42 2.72 740.8 1.'5 .M 48 (I)6 -i

C coeae---- --- - (:11------ 84.16 2.91 2.27 81. 7 1. .6 :7 49 (40) -7.8 3.4 32 0Eflif1eycobutane-- --- lhg. 84. 10 2. l '2.27 MW) 1.2 .53 41 (40) 7. 7 3.4 310 (40

lower limit to be 1.12 volume-percent, tit 21' C cordingly, the data of Jones and of Burgoynein a 12-inch diamieter chamber about 15 inches and Neale are used here.long: however, there is evidence that they didnot use the same criteria of flammability am did Limits in Other Atmospheresthe other authors; only one observation windowwas provided at the to p of a rather squatty The limits of flammability of cyclopropane-chamber, whereas with the glas's tubes used by carbon dioxide-air, cyclopropaiie-nitrogen-air,Jones and by Burgoyne and Neole the flame and cyclopropanc-helium-air mixtures at 250 C~could be observed along the entire tube. Ac- and atmospheric pressure are given in figure

LI

FLAW&ADILITY CHARACTERISTICS 0

% air 100O%-% cyclopropane-% inert

10-

EFiGUaRE 72.-Liits of Flamma- Flmae

bility of Cy clopropane- Carbon FlmalIDioxide-Air, Cyclopropane-Ni- U36 mixturestrugen-Air, and Cyclopropane- z1Iihum-Air Mixturcs at 250

and Atniospheric Pressurc 0

-

01020 30 40 50ADDED INERT, volume-percent

72 (106). The first two curves are similar to ALICOHOLS (05 H2.+10H)those obtained with naraffin hydrocarbons (fig.35).LiisiAr

& ~~~Thp limits of flainmability of cyclopropane-LiisiArheliumn-oxygen and cyclopropane-nitrous oxide- The alcohols considered here are listed inoxygen mixtuires at 25' C and atmospheric pres- table 13 together with L~s. and U26.. Thesare are given in figure 731 (106). The latter ratios Lzso/C., are approximately 0,5. How-clurvn diffctrs from the former, as both additives ever, the L (mg/i) values decrease with increaseare oxidants (oxygen andl nitrous oxide). in molecular weight. If L* is taken to be the

The limits o! flammability of cyclopro pane- weight of combustible material (exclusive of thelielirnt-ii~itrons oxide initires at 25' C and oxygen in the molecule) per liter of air, then foratinospherie. pressure are giren in figure 74 (106). the simple alcohols:Hlere the minimum oxidant, concentration *LM- 16 (4(nitrous oxide) required for flame propagation L*~ M.(4is approximately twice the corresponding con-centration of oxygen in the systems cyclo- This eqkuation gives the value,; listed in paren-propane.-heliumi-air (fig. 7-2) and ('yclopropane- theses in the mg/I coluimn; these are in fairhelium-oxygen (fig. 73). agreement with the values obtained for the

66 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

-- p on eo2 corresponding L*. from figure 19 for ethyloxygen -100c-% lopropne-( He, or N20) alcohol (M=-46) is 2.2 volume-percent. Then,

from equation (54), L is 3.4 volume-percent; the50 - iN 2 0 measured value is 3.3 volume-porcent.

The lower limits of methyl alcohol have beendetermined by Scott and coworkars at 25', 100',and 2000 C (192). The values at these three

40 temperatures are 6.7, 6.5, and 5.9 volume-per-cent, respectively. rhe calculated values ob-4tained from the modified Burgess-Wheeler law

Flammable He (fig. 23) at 1000 and 2000 C are 6.4 and 5.8I3 mxtue volme-percent, respectively.

Limits in Other Atmospheres

20- C5 1 (in 02 + N20) The limits of flammability of methyl alcohol-carbon dioxide-air and metnyl alcohol-nitrogen-air mixtures at atmospheric pressure and 25'

o cal (in 02 and 50' C are given in figure 75; flammabilitydeterminations on mixtures containing moreI than 15 percent methyl alcohol vapor wereI conducted at 50 ° C. The maximum amountsS 20 40 60 1 of carbon dioxide and nitrogen required to20 40 6o s loo prevent flame propagation in these inixtures

NITROGEN OR NITROUS OXIDE, volume-percent

40FIGuRa 73.-Limits of Flammability of Cyclopropane- % ] = i tHelium-Oxygen and Cyclopropane-Nitrous Oxide- X air 100%-% methyl alcohol-% inertOxygen Mixtures at 250 C and Atmospheric Pressure.

40 I I35

% N2 0 = 100%-% cyclopropane-% He

30-30 V\k

E2 Min N20 6= 25-\

21\ \uz 20-

o Flammable > 20\10 i smixturesSz Flammable \ XSaturated at

10! mixtures 25' C and 1 atm.

C s.COC02

10-0 20 40 60 80

HELIUM, volume-percent

FiGURE 74.-Limits of Flammability of C clo ropane- 5flelium-Nitrous Oxide Mixtures at 250 JandAtmos-pherio Pressure.

saturated hydrocarbons. Approximate L (mg/ i 0 3 4I) values can be obtained from the higher DE10 20 30 40 50hydrocarbon values given in figure 22 by ADDED INERT, voiume-percentmultiplying these by the ratio M/(M-16).Further, figure 19 can be used to obtain L* and FIGURE 75.-Limits of Flammability of Methyl Alcohol-

Carbon Dioxide-Air and Methyl Alcohol-Nitrogen-values in volume-percent. For example, at Air Mixtures at 25* C and Atmospheric Pressure.250 C, L" is about 47 mg/1 from figure 22; the (Broken curve at 500 C and atmospheric pressure.)

i

FLAMMABILITY CHARACTERISTICS 67

TABLE 13.-Propertes oj 8elected simple akohols

Lower limit In air Upper limit In airNetalHe

Combustible Formula Al (AirI in ai jj uLu, U(Vol pct) (vol . ,g Ref. (Vol Ref

pet) C., / pct)

Methyl alcohol----- S....... oH _-- 82.04 1.11 12.25 IN1 8.7 0.65 1103 (40) '31 2.0 , f5

Ethyl alcohol ............. CH OH ........ 46.07 1.59 6.58 306 3.3 .5 70 (40) '11 2. 9 1 )(086)

n-Propylalcohol ........ CHF O- ........ 60.09 2.07 4.48 448 '2.2 .49 1460 (40) 814 3.2 420 j (4

n-Butyi alcohol --------- CiHoOH ........ 74.12 2. M 3.37 e 41.7 .50 87 I (S) 412 -------------- ()

pri-n-Amyl alcohol -... C&IIIsOH ----- 83.15 3.04 2.72 742 '1.4 .51 { VO (6) 10 .................

n.-..exyl alcohol.-- ------ - 102.17 3.53 2.27 888 1.2 .53 ............

t L.. L- . t-100e C.M*Fgures compied by Explosivu Re. Center, Federal Bureau of

it -60'. Min o.At saturation temperature. I Calculated value.

were compared with the corresponding maxima 60 Tfor paraffin hydrocarbons (figs. 28-35); it was a ir -100%-% methyl alcohol-% wa \found that appreciably more inert is required tomake mixtures containing methyl alcohol non- soflammable. Conversely, methyl alcohol re- 400 Cquires less oxygen to form flammable mixtures, 2W Cat a given temperature and pressure, than paraf- 40fin hydrocarboni do. This may be due in partto the oxygen of the alcohol molecule. For the -simple alcohols, we have: 30

C.H,,OH+ 1.5nO2--*nCO3+ (n + I )H 20. (55) C

20 - Flamrmable

Thus, the ratio of oxygen required for complete mixturescombustion of an alcohol to that for complete rzcombustion of the corresponding paraffin, 10

equation (22), is:

(56) 0 L 20 30 40 5O 60

WATER VAPOR, volume.percent

When n-- 1, this ratio is 0.75. The correspond- FIGURE 76.-Limits of Flammability of Methyl Alcohol-ing ratios of the experimental minimum oxygen Water Vapor-Air Mixtures at 1000, 2000, and 4000 Cvalues from figures 75 and 28 are 0.82 with and Atmospheric Pressure.carbon dioxide and 0.85 with nitrogen as inert.

The limits of flammability of methyl alcohol- ity data for the systems tert-butyl alcohol-water vapor-air were obtained by Scott (192) carbon dioxide-oxygen and 2-ethylbutanol-in a 2-inch-ID cylindrical tube at 1000 and nitrogen-oxygen are given in figures 79-81.200' C and in a '4.9-liter cylindrical bomb at4000 C and I atmosphere (fig. 76). Similar Autoignitiondata were obtained by Dvorak and Reiser in a2.2-liter apparatus at 1000 C (58). The minimum autoignition temperatures in

The limits of flammability of ethyi alcohol- air and oxygen of a number of alcohols atcarbon dioxide-air and ethyl alcohol.nitrogen- atmospheric pressure are given in appendix A.air mixtures were obtained at 25' C and Comparison of these values with those of theatmospheric, or one-half atmosphere, pressure as corresponding paraffins (methyl alcohol andnoted (fig. 77). Additional flammability data, methane; ethyl alcohol and ethane, etc.),obtained for ethyl alcohol at 100' C 'and I shows that the AlT values of the alcohols areatmosphere are given in figure 78. Flammabil- generally lower.

68 FLAMMABILITY CHARACTrERISTICS OF COMBUSTIBLE GIASES AND VAPORS

15It air m 100%-% ethyl alcohcl-% Inr air an l00%-% alcohol-% water vapor

vkq"2- '13.8%10- Flammable8

Flammable 0C02 mixtures

0 10 20 30L 40 so 0 8 Cs,ADDED INERT, volume-percent _

Fiounia 77.-Limits of Flammability of Ethyl Alcohol- 0Carbon Dioxide-Air and Ethyl Alcohol-Nitrogen-Air t 24Mixtures at 250 C and Atmospheric Pressure. P(Broken curves at one-half atmosphere.)

251 III% air -100%-% ethyl alcohol-% water 0 10 20 30 40

WATER VAPOR, volume-percent

*20Fioumz 79.-Limits of Flammability of ter-Butyl

Alcohol-Water Vapor-Air Mixtures at 1500 C andAtmospheric Pressure.

E iO 60115Mi 2.3 % oxygen 100% -% 1\alcohol-% C02

50-

0 Flammable nmlbe 0

400

WaX Vao-i Mixure at100CadAmop2i5r sre

and Cacote or a rnge o mixtue comositios Alchol-Cros Dixd-xge itrs t10

ate 5 apC;-the mxmmturni 00 n veloispwereinctoshrcPrsuefosutre 5. n 14c/e 1 rsetvl

(8.Thes rinvesotiaos o otland th hlt 00 CRO the IDE aximumves were 72.

burning velocities of methyl and n-propyl alco- and 64.8 cm/sec, respectively. These values

Lik

FLAMMtABILU/Y CHARCTERISTICS 89

60 ----- - 40 T "I Xygsk'plt a le•i tenoI-.% n % air 100%-% ether-% Inert

Cool flames

40- t 20 \ 0 2 30 5

400

0 FlammF oble 8 - t o\ a i o D m h N2Ner.1mixtures 9.3%9

920-

C-st ADDED INERT, volume-percent

10- FiauaE 82.-imxits of Flammability of Dimethyl Ether-Carbon Dioxide-Air and Dimethyl Ether-Nitrogen-

*Air Mixtures at 250 C and Atmospheric Pressure.

0 20 40 60 80 100 40 [ I 1 iNITROGEN, volume-percent air - 100%-% ether-% inrt

FiOuRs 81.-Limits of Flammability of 2-Ethyl- §butanol-Nitrogen-Oxygen Mixtures at 1500 C and KAtmospheric Pressure. 4 30 Cool flames

are in fair agreement with the corresponding -values of the paraffin hydrocarbons. Q:

The methyl alcohol liquid-burning rate ob- 20-tained from equation (53) is in fair agreement awith that obtained experimentalir (fig. 52). FlammbIe N2The relatively low AHeIL JJ. ratios .or the alco- mixtureshols indicates that they should be characterized o 0C02by low-burning rates in large pools. t

ETHO S (CUH,.,.OCAj) 0iit 1n0i 20 30 40 50Liitsn r ADDED INERT, volume-percent

The properties of a few common ethers are FIGURE 83.--Limits of Flammability of Diethyl Ether-listed in table 14. Unfortunately, the limits Carbon Dioxide-Air and Diethyl Ether-Nitrogen-Airdata show appreciable scatter, so it is difficult Mixtures at 250 C and Atmospheric Pressure.to establish any general rules with the givendata. However, as a first approximation, the limit of the cool flame region in air is 48.4 vol-L/C,, is about 0.5 for the simple ethers. ume-percent, according to Burgoyne and Neale

(26). The limits of the systems diethyl ether-Limits in Other Atmosphereo helium-oxygen and diethyl ether-nitrous oxide-

oxygen are given in figure 84 and the limits ofBecause of the importance of ethers as anes- diethyl ether-helium-nitrous oxide are given inthetics, limits of flammability were determined figure 85 (106). Again, as with the alcohols,in several atmospheres. The limits of the sys- more inert is needed to assure the formation oftems dimethyl ether-Freon-12 (CCI2 F2)-air nonflammable mixtures than is needed for thedimethyl ether-carbon dioxide-air, and dimethyl corresponding paraffin hydrocarbons. Also,ether-nitrogen-air obtained by Jones and co- cool flames are encountered at lower tempera-workers are given in figure 82 (114); the tures and pressures.limits of the systems diethyl ether-carbon di- Comparison of curves in figures 84 and 85oxide-air and diethyl ether-nitrogen-air are shows that the minimum oxidant requirementgiven in figure 83 (26, 166, 108), Cool flames for the formation of flammable diethyl ether-exist above the upper limit as noted; the upper helium-oxidant mixtures is approximately twice

70 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

TABLE 14.-Properties Of 8elected ethers

- -Lower limit in aW Upper limit ill air

orml, is Ls L Tin UsComba~lbe Fomula M ~ (Vol pct) moe (vol C. ) /,\ elf. (vol K)ig Ref.

pet) pet) 0

Dimetllyl ether ......... C~igOCH .... 4&. 07 1. 50 6. 83 0.16 3.4 0.562 { 7 1 1 4.1 760 (114)

Dletliyl ether----------Cils- 74. 12 2. N6 3.37 608 1.9 . 56 ( 4 (40) g 36 11 1,880 (40)

Eth~yl propyl ether---- CiHsOCa,, - 88. .8&15 3. 28 2. 72 5 760 1.7 .62 68 } (3.) M0 (8)

Dl-t-propyi ether-....C~I1,OCI,?--102.17 3.53 2.27 '900 1.4 .87 1 501 (40) 7.9 3. 291) (40)

Dlvtnyl ether----------...CillOCifla ... 70.00 2.42 4. 02 31,770 1.7 .42 54 11) 2 6. 7 1,160 (97)

IVLM-16 I Calculated value.V--- 'cool fiames: Ua.'>16 vol pot.

'Cool flsmes: tVag-53 vol pot. I Ref. (165).

100 30 10%- dity ete-%H o 2)3

% 02= 10%-%diehyl lhe- 1 % e o N20 ~ 100%-% diethy! ether-% He

',

20

E 0

K Flammable Min N20E6

wmixtures22

401

5 ~N20

Csf~n 02+ N0) H HELUMvolume-percent

Csj in 2) 2 ,, FioTTasE 85.-Limits of Flammability of Diethyl Ether-- Nitrous Oxide-Helium Mixtures at 250 C and At-

0 20 40 60 80 100 mospheric Pressure.HELIUM OR NITROUS OXIDE, volume-percent

Fzouaai 84.-imits of Flammability of Diethyl Ether- Since the ethers tend to formn peroxides underHelium-Oxygen and Diethyl Ether-Nitrou's Oxide- a -variety of conditions, they inay appear to beOxygen Mixtures at 25' C and Atmospheric Pressure, unstable at room temperature (238).

as great with nitrous oxide as with oxygen.ES RS(n n_0 CH.IHowever, if .1 mole of nitrous oxide furnishes The properties of several esters are listed inone-half mole of oxygen during combustion, table 15. The ratio of the lower limit at 25' Cthen the minimum oxygen contents in the two to the stoichiometric concentration is about 0.55cases are otearly equa. Unfortunately, the for many of these compounds. This is tileavailable data are too meager to permit a more same ratio as in equation (21) for paraffindetailed comparison, hydrocarbons. The lower limit values ex-

pressed in terms of the weight of combustibleAutclinitioper liter of air (see section about alcohols) areAuFistetdo in parei.these,3 under L(mng/1). These ore

In genere.l, ethers are readily ignited by hot larger than thle corresponding values for thesurfaces. These combustibles usually hlave a hydrocarbons and alcohols. The inert require-lower ignition temperature in air and in oxygen nients and minimum oxygen requirements forthan do the corresponding paraffin,; and the firs,.t member of the series, methyl formate,alcohols. The available at'toigraion temipera- tire neI4 rly the same as for mnethyl alcohol andture data are included in app-ndix A. diniethyl' ether (figs. 76, 82, 86). This is not

FLAMMABILrITY CHARACTERISTICS 71

TABLE 15.-Properties of selected esters

Lower limit in air Upper limit in air

Sp. gr. C., Net ll,(omlunstibh" Formula M (Air-1) in air ( Kcal L2 & L U., [ U

(vol pct) \i0 )(vol ( g Re. (vol (ng\ Ref.pet) I. .T pet) \I

Methyl formate-...... II('OOCJI ... 60.05 2.07 9,48 219 5.0 0.53 142 1(,,,) 23.0 2.4 800 t111)

Ethyl foruate. ......... |COO(',ii .... 74.08 2. b0 5,65 307 2.8 .50 { M (40) 16.0 2.8 630 (40)

n-Buty1 forniate ......... COOCI,n..... 102.13 3.53 3.12 2650 1.7 .M 1 7 (40) 8.2 2.6 410 (40)

Methyl acetoe-......... CIICOOCIh, .. 74.08 2,50 L.65 358 3.2 .57 (146 40) 16.0 2.8 630 (40)

Ethyl acetate ......... CICOOC11,.. 88.10 3.04 4.02 504 2.2 .55 I M (40) 11.0 510 (176)n-Propyl acetato ...... CII3COOCsII?.. 102.13 3.53 3.12 1650 1.6 .58 ( 57 (40) 8.0 2.6 400 (40)

n-Butyl acetate ......... ('1COOC4lt,.. 116.16 4.01 2.55 ........... '14 .55 {73 (') '8.0 3.1 450 (6)

n-Amyl acetate ......... CIICOOC,1j . 130,18 4.50 2.16 ---- 1.0 .51 1 40 5 ) ' 7.1 3.3 440 (')

Methyl proplonate ...... CHCOOCIIs.. 88.10 3.04 4.02 ........ 2.4 .60 7 (0) 13.0 '5.2 580 (40)

Ethyl propionate ....... C 11COOC,21. 102.13 3 53 3.12 2650 1.8 .58 { (40) 11.0 3.5 510 (4())

L- LM -32 4 1=100 C.M L-- a Figures eompled by Explosives Res. Center, Federal Bureau of Mines.

Calculated value. 6 P-0.5 atm.t=90' C.

true of the othei' members for which data The autoignition temperatures of many esterscompiled at the Explosives Research Center are in air and oxygen at atmospheric pressure areavaialable--.isobutyl formate and methyl acetate given in appendix A. In general, the AIT(figs. 87, 88). Accordingly, it is rather difficult values of the esters are lower than are those ofto make additional generalizations for this series, the corresponding paraffins.

25 -n1--- I

5% air = 100%-% methyl formate-% inert

20

FIGURE 86.-Limits of Flamma- 0 Fbility of Methyl Formate-Carbon FDioxide-Air and Methyl Formate- W mixturesNitrogen-Air Mixtures.

5-

0 10 20 30 40 50ADDED INERT, volume-percent

FLAMMABWLITY niiRACTXHISTIC3 or COMBUSTIBLE GAOVI AND VAPORA

10T

air m 100%-% isobutyl formate

aH81C02

Fioun. 87.--LUmite of Flimrabfl- tj Flammable N2ity of Isobutyl Formato'-Carbon C mixturesDioldde-Air and lonbutyl For- aia 4eNltrogn-.AIr Mixtures. 0 4&¥

0 10 20 30 40 50ADDED INERT, volume-percent

20T ""I

air 100%,-% methyl acetate-% inert

U 10- FlammableFsolua 88.-ALmlit o! Flamnmabil- t M2

Ity of Methyl Aoetate-Carbon t mixturesDioxide-Air and Methyl Aoetate- !Nitrogen-Air Mixture. -j C C0

0 10 20 30 40 50ADDED INERT, volume-percent

IP

FLAMMABILITY CHIARACTERISTICS 7320~ ~ -n- I~- -- i - ------- r r~

____ Flammable mixtures

E 70.5 mole MEK + 29.5 mole %u toene

0C')

AtmospericiPessure

Fgive i tablEe 1.Thto of Teprte Lower Limits on, Famity sown M -tat he sytues MnEK- a

atDHY E 250 KEO E (C. airO timi the s1ici0n-ri Ccpsto aosen ahd THFo en oe vlue Chitler

is approximately 0.5. law, equation (46). Calculated and experi-Zabe takis, Cooper, and Furno found that the mental values for the preceding systems in air

lower limits of wethyl ethyl ketone (MEK) and are iven in figures 91 and 92.MEK-toluene mixtures vary linearly with Te limitsoth systems acetone-carboDtemperature between room temperature and dioxide-air, acetone-nitrogen-air, MEK-chlorc-20 0 C (36. A summary of these data is bromomethane (CBM) -air, MEK-carbon di-given in figure 89; broken curves in this figure oxide-air, and MEK-nitrogen-air are given inwere obtained from the modified Burgess- figures 93 and 94. The data in these ftgurcsWheeler law, equation (33), taking the lower were obtained by Jones and coworkers (2588).

TABLE I 6.-Pro pertim of 8e.ected aldehydes and kcet ones

NLA. Lower limit lo air Upper limit In air

Combustible Formula Ai (Ag - 1) inA ai 14 LIDU Umole) ( 4 IL ) . U(Vol pet) (Vol !E/g\ Ref. (voi C,, /f-g\ Rof.pet) 'kJ pet) k.

Aretaldehyde.......... .I1aCIIO. . 44.051 L.62 7.73 264 4 40 0.52 82 (M9) ' 36 4.7 1,100 (961)Pmopionuidehyde. .- CS1tCHO. . &S. 08 2.01 497 409 2.9 .69 7 (9) *14 2.8 420 (96)1'mraidehy~de ..... (CIIiCHO)s,_.132.16 4.%8 2.72 .. 1.3 .49 78 (40)_ j _iAcetone (lC I, 8.08 2.01 4.97 403 2.6 .52 70 (98) Ii 2.6Niethyl ethyl ketone. C 113CC . ,c- 72.10 2,49 3 67 648 1.9 .52 62 (U3) 10 2.7 360 (19#3hiethyl prcpyl ketone M.sC C~I 813 2.97 2.90 692 1.6 .55 63 (40) 8.2 2.8 340 (40,

a(011CCVI PA. 13 2.'J 2 90 592 I'6 .65 63 (1) - . .Nfethyl butyl ketone CII,3COC,1it 100.16 3 4A 2,40 840 '1. 4 .58 64 (40) '8.0 3.3 390 (40)

I Cool flameL: U-f0 Vol pet.' Cool Barnes: Via-17 vol pot.I CalculatA~ t'Clue.*f-60 C.I -100 C.

74 A 1 A ~ ~ cR CVT~ 1 I S M S CO USSTI L r, G X~ S VI ND VA ?O BS

2.0 Flammable Mixt'Ures

THEGD

1.8

6 70.5 mote-% HE+ 29.5 mo~e% toluen~e

'14 35.6 mol% ~l-lV * 6 .4m e% toluenle

00

204

1.2U 20 40 60IA .TEMP~ailt of T Fo ue n MlitureB in Air at

T h eec i ati T e r r P e r t e s o f v a i u Sfi L S A N D n m E L E O

de und 'kili u no onrd i

teme rtre s of endIO . Fuis used for not co eedaatigpOiS lowe an inad d here(tble1

aldehy ~ ~ ~ a5ueaeg~e n ln those t e nIaae O P

at os hei vr alues are low r at e e t~ f5 r

of r-1 h '- para us. A m o iy n ,( I ) ~ .' a

of sulfu copud adusnlren

pCflb0 4 ,I7 This theytyl havei

T h eM n d I S e rzin e ( N2') ' m o n

arerie give infu tapo zse N,9 di mNle

A)ti en I aegni- theoyi formCS)S flammable ixtuire s

es ppae 7 1 , g l i , ,l o carb o n an o h r M .i i a v r I o f co flcen tr ia

a n tab~t A8 anedr water ti o f, Vht e and

an lv l r n e ase xi at s in . a n i ncae ( n

wide tel am uerp en i -. fr carboan an m o ra . doa be 19 N ~ widn

disk d~ ~% t m r a d a r' aon O v n ton a noted in t a n, us ,(1) re o

Fl ar n s 4 with car bo 4dair ( f 9 5) ; that Fue - .. hy r crbo s r,1 a ie ns

vicarbo nl diodfor in t an droge 7)fi e- (lor m g*an ethe rfa m b e ~ t fa l tem F rt er r iniia

d] meeapanwit chorl ,, (17 (fg. 7) thet trie 1ne raige. axrre in

with chlo inar

,Eich lO% j oet an e in th t it shows not press

t a h In e us n wth er ifoun

qguof car11bon disulfd e essentially c

th 'a2. flarnt l rang fcr.ie

topetthe guatj:e of inert requr teperature.

t~~ o p r e v e n t T A 1L t 1 7 . - P r O P e ' " 6 oJ .e te c te d s n tjflr v n ~ n d p e o t i

-P

-3 0213 231

FLAMMABILM' Y' CIHARACTERISTICS 75

2.0-r------- --- -

0 Experimental points

1.8 - Calculated

300C0

9.0 Flammable mixtures

E~1.6-

0CL

LU

0

0 20 4 08 0MEK, mole-percent

FioUREI 91.-Effect of Liquid Composition on Lower Limits of Flammability of MIEK-Toluene Mixture-s in Airat 300 and 2000 C.

76 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

2.0 I

0 Experimental points- Calculated

Flammable mixtures

E0~1.6-

0

U0

~1.4-

C,,

1.00 20 40 60 8 0

THF, mole-percentFioug, 92.-Effect of Liquid Composition on Lower Limits of Flammability of THF-Toluexte Mixtures in Air

at 300 and 2000 C.

FLAMMABILY CLARACTERISTICS 77

14 1 f

a air - 100%-% acetone-% inert

12

10

a-

E.- Flammable Fiovas 9&.-Limita of Flammabil-

mixtures N2 ity of Aoetone-Carbon Dioxide-ti Air and Aeetone-Nitrogen-Airz Mixtures.

Cs,, C02

4- -

2 I

0 10 20 30 40 50ADDED INERT, volume-percent

TABLE 18.-Properties of selected fue. and fuel blend.

Not Aem limit In air Upper limit In air

I ., / .8aCombustible Formula AV (22i) iNCS AH -MOWG -- -a (Lu-U(oPa)(Vol C I (o ~ ( j\ Ia

Pet) IS pot)19'"

Ammonia ------------.-.-- --..- 7.. 17.08 0.0 21.58 .......... 1 0.0 134 (16, 2 1.8 800 (181)

Hydrasine ............... N-.-'".- - 2 06 I 17.32- ......... 4.7 .27 70 -88 10- .3 (... .?eonomtyl b draem NuCi.:: 46.07 1.:80 7.73------4 .82 so (18)_!----5'.

Unspunmetrl NH*(CHs)s. 60.10 2%OR 4.07..... .2 .40 .6 5 10.1....Monmtylyn ln.. N E a....4 0 .0i ?? ..... mn ........

Ddioa... ..........D ...... .27.09 ... 88 478 .8 .12 10 (11 8. 1..I ........ 16)Tetra .......... ..... . 1 4 & 67 4 1........ .---- 10----Pentaborane ............ B ........... 17 2,18 8 308 0 . .12 12 ............

Deosorae........Da.u . 12.: 4.2 ..--------- 2 .11 It IS ............. U ..... ..... . 7 2 ........ ..... . . ........ ........Aviation Be lP- ... ............................. (141)....38Aviation let fuel .1P-I ........................ ............ ........... 1.4............."1 71 -Aviation etfuelJ P-4.... .1.2 ......... . ? 8 .Aviation jet tuel J P-4.........................-.---..-............,...... ... .. .

Aydron ............. Ht ............ 2.0 0 298 87.3 4.-- ---- 8. 7 (40) 7 .84 270.

Calculated value. I-u100. 0.'t-30 0.

78 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

12 1 I I I

, air = 100%-% methyl ethyl ketone-% inert

10

EN2

Fiovaa 94.-Limits of Flammabil- L CBMit of Methyl Ethyl Ketone z(E K) - Chlorobromemethane 6(CBM)-Air, MEK-Carbon Diox-ide Dioxide-Air and MEK-Nitro- " Flammableoen- Mr Mixtures at 250 C and -. mixturesAtmospheric Pressure.

-j 4- C02/

XI ,CstIT

2q

0 10 20 30 40 50ADDED INERT, volume-percent

TABLE 19.-Limits of flammability of ammonia following quantities of hydrocarbon vapor wereat room temperature and near atmospheric needed to inhibit flame propagation in apressure lY-inch glass tube ' at 1250 C and atmospheric

pressure: 39.8 pct benzene; 35.0 pct toluene;Oxidant C.o L U Ref. 27.3 pct m-xylene; 23.8 pct cumene; 21.0 pct

_ n-heptane. On this same basis, 95.3 pct air isneeded to prevent flame propa ation (188); this

Air O-e------------. 21.8 15 28 (167, 18) corresponds to a lower limit of flammability ofOxygen ---------------- 57. 1 15 79 ( $25)Nitrous oxide -------- 40. 0 2. 2 72 (109) 4.7 pct hydrazine vapor. The flammable range

in air at atmospheric pressure is presentedraphically in figure 98, which also gives the

Hydrazine vapor burns in the absence of an fammable ranges of monomethylhydrazine,oxidizer, so that it has no upper limit and can unsymmetrical dimethylhydrazine, and ammon-therefore be used as a monopropellant. The ia for comparison (218). The flammabilitydeomposition flame yields hydrogen, nitrogen, diagram for the system hydrazine-n-heptane-and ammonia (64, 78). However, hydrazine air at 125 ° C and atmospheric pressure is givenvapor can be rendered nonflammable by addi- in figure 99. These data were also obtainedtion of stable diluents or inhibitors. The in a 0l4-inch glass tube.amount of diluent required at any temperature A summary of the autoignition temperatureand pressure appears to be governed in part by data obtained by Perlee, lmhof, and ZabetakisthA ignition source strength. With a 0.25-inch (166) for hydrazine, MMH, and UDMH in airspark gap and a 15,000-volt, 60-ma-luminous- and nitrogen dioxide (actually, the equilibriumtube transformer as the energy source, Furno,Martindill, and Zabetakis (68) found that the I Comparble results were partialy obtained ina 2-nch tube.

i-

Fp

FLAMMABILITY CHARACTERISTICS 79507 20- 1

air - 100%-% carbon disulfide-% Inert air = 100%-% ethyl mcrcaptan-% inert

40 - 1SF-22 (CH CI 172)

6 .. CHcCl 172)

3 0 \oI- Flammablemixtures

= Flammable \ M 0mixtures min 02 C

10- C02

0 0 5 10 15 20ADDED INERT, volume-percent

Fioumm 97.-Limits of Flammability of Ethyl Mereap-0 20 40 60 80 tan-F-12-Air and Ethyl Mercaptan-F-22-Air Mixtures

ADDED INERT, volume.percent at Atmospheric Pressure and 270 C.

FiouRE 95.-Limits of Flammability of Carbon Disul- mixture NO2*-NO 2 NO 4 ) is given in figurefide-Carbon Dioxide-Air, Carbon Dioxide-Nitrogen- 100; short horizontal lines indicate th un-Air Mixtures at 250 C and Atmospheric Pressure, andCarbon Disulfide-Water Vapor-Air at 1000 C and certainty in N0 2 * concentrations. These ma-Atmospheric Pressure. terials may ignite spontaneously at room

temperature with relatively small NO2 * con-50 1 centrations in the air; at 250 C, liquid UDMH

% air 1009-% hydrogen sulfid. -% C02 ignites in N02*-air atmospheres that containmore than about 8 volume-percent NOa*; MMHI and hydrazine ignite in atmospheres that

contain more than about 11 and 14 volume-40- - percent NO 2 *, respectively. In general, evensmaller concentrations of N0 2 * produce spon-

taneous ignition of these combustibles athigher initial combustible liquid temperatures.

30-- Mi 02 The effect of the hydrazine liquid temperature11.6% on the spontaneous ignition temperature in* , NO2 *-air atmospheres is illustrated in figure 101.

0_ Similar data are given in figures 102 and 103J FlammableFlmmatue for MMH and UDMH; there is an apparentu' 20 mixtures

Zanomal* in the data obtained with ivi1il at0 36' 55 , and 67' C.0= 0 The use of various helium-oxygen atmos-

pheres in place of air results in the spontaneousS10- Igniton temperature curves given in figure 104for UDMH. Comparison of curve B of this set

with curve A of figure 100 indicates that thespontaneous ignition temperature of UDMH in

S I I NO2 *-He-O. atmospheres is the same as that0 10 20 30 40 obtained in N 2 -air atmospheres.Ignition temperature data obtained withCARBON DIOXIDE, volumepercent tTDMH in NO2 *-air mixtures at 15 and 45 psia

FIwRE 96.--Limits of Flammability of Hydrogen Sul- are summarized in figure 105. These indicatefide-Carbon I)ioxide-Air Mixtures at 25' C and that although the spontaneous ignition tem-Atmospheric Pressure. perature of UDMII in air is not affected ap-

80 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

760 1 1 1 100600 -Ammonia Upper -78.9

- ~limit400- -DH52.6 .

EE 200 -Flammable- 26.3 E

-d Cs, mixtures 0

Flovitz 9S.-ljznits of FlamIna- CO 100: 1.t 7 of Ammonia UD MH, CO0.MMIH, and Hydrazine at At- W8 so

niOSPheric Presaure in Saturated crand Near-Saturated vapor.Akr 0. 60 Cst -7.9 >Mixtures. C51 - w

40- Lower -5. Jt

-limit - I~

20- Hydrazine -2.6 20

MMH

10L 1. 3150O -100 -50 0 50 100 150 200

TEMPERATURE, OC

FLAMMABILITY CHARACTERISTICS 81

100

10 90

20 00

0

30 0 00 70

%304000 60o

0KEY

mFlammable &50 mixtures 50

0168 0 4!

60 4

X70 30

0 KEY80 ~0 Flammable 2

HEPTANE-VAPOR, volume-percent

F URN 99.-oFlammable Mixture Compositions of 20ydrazine-Heptane-Air at 125* C and

Approximately Atmospheric Pressure.

82 FLAMMABILITY CHARACTP.RISTICS OF COMBUSTIBLE GASES AN) VAPORS

300 I Boron Hydrides

This series includes diborane (B2H,), tetra-a UOMH borane (B4Ho), pentaborane (B '), and deca-b MMH borane (B1oH 4). However, reliable tipper andc Hydrazine lower limit data are available only on the first

250 member of this series at the present time.These were obtained by Parker and Wclfhard(168) who determined the limits of flammabilityof diborane in air in a 5-cm-diameter tube at aninitial pressure of 300 mm Hg; this combustible

200 forms flammable mixtures in air in the rangeRegion of spontaneous ignition from 0.8 to 87.5 volume-percent. A pale blueegogflame propagated throughout the tube at, the

upper limit; luminous iltmes were not visibleabove 79 volume-perccnt. Limit of flamma-bility curves for the system diborrnie-ethane-air

S150 are presented in rectangular coordinates in figure107. Except for the slight dip to the ethine-axis (zero diborane) in the area in which ethaneforms flammable mixtures in air, these curves

E are rather similar to those obtained with other100. combustible-oxidant-inert systems. Burning

velocities in excess of 500 cm/sec were measuredin this same study for fuel-rich diborane-airmixtures.

Berl and Renich have prepared a summaryreport about boron hydrides (9). It includes

50 -data obtained by these and other authors; they

a h C 25* C found the lower limit of pentaborane in air tobe 0.42 volume-percent.

The autoignition temperature of diborane inDew point line of NO* air is apparently quite low. Price obtained a

0 - value of 135' C at 16.1 mm Hg (169); that ofpentaborane is 30' C at about 8 mm Hg (9).

0 5 10 is 20 25 30 Gasolines, Diesel and Jet FuelsNOI CONCENTRATION, volume-percent

Fuels considered in this section are blendsFicVRu 100.-Minimum Spontaneous Ignition Tern- that contain a wide variety of hydrocarbons

peratures of Liquid Hydrazine, MMH, and UDMH and additives. Accordingly, their flammabilityat an Initirl Temperature of 25* C in Contact With characteristics arc governed by the method usedNO,*-Air Mixtures at 740± 10 mm Hg as a Functionof NO,* Concentration. to extract a vapor sample as well as by the

history of the liquid. For example, since thepreciably by this pressure change, it is affected lower limit of flammability, expressed inin a range of NO,*-air mixtures. volume-percent, is inversely proportional to

The data presented in figures 100 to 105 were the molecular weight of the combustible vap(,r,obtained with liquid fuel in contact with apor- equation (28), the first vapors to come from aized NO* ;n air. Similar data obtained with blend, such as gasoline, give a higher lowervaporized UDMH-air in contact with NO* limit value than the completely vaporit.sdare given in figure 106. This figure indicates sample. Conversely, the heavy fractions orthat LTDMH-air mixtures that contain more residue give a smaller lower linit value. Forthan 9 volume-percent UDMH will ignite spon- this reason, there is some disagreement aboutItaneously on contact with NO*; UDMH-air the limits of flammability of blends such asmixtures that contain more than approximately gasoline and the diesel and jet fuels. These2 volume-percent UDMH can be ignited by an fuels are, in general, characterized by a wideignition source under the same conditions (166). distillation range; the ASTM distillation curves

FLAMMABILITY CHARACTERISTICS~ 83

300 I

200

Lj

M Region of spontaneous ignition

000

100-

36*770

670

Ix

0 0 15 20

NO CONCENTRATION, volume-percent

FiGuRE 101.-Miniiui Spontaneous Ignition Temperatures of Liquid Il:3drazine at Vafious Initial Temperaturesin NO,*-Air Mixtures at 740± 10 mmn lg as a Fuikction of N0 2 * Concentration.

84 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

200 .................

x

,.* / 67"

C100 -"36 Region of spontaneous ignition

0o

/ -105 10 15 20 25

NO* CONCENTRATION, volume-percent

FhG'RE 102.- Miiniml 111 Spontneous lgniitioii Tiperaturv of Liqih' \IN1\ :t a trius Initil] " tih-ir trciiil N( ) -Air M[ixtizrtus at 740 10 min lig as a Iwt otion of N02* 'onceittratioth.

FLAMMABILITY CHARACTERISTICS 85

200

S

SRegion of spontaneous ignition

wD

x

36* and 55* - "

x

0 5 10 15 20

NO* CONCENTRATiON, volume-percent

FIGURE 103.-Minimum Spontaneous lgtition Temperatures of Liquid UDMlf at Various Initial Temperaturesin N)3*-Air Mixtures at 740:_ 10 mm lig as a Function of N0* Concentration.

86 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

400 - I

Curve He/0 2

a 0.0/100b 100/25C 100/6.50d 100/1.70

300 U 100/0.30f 100/0.00

P

V Region of spontaneous ignition

-200 -we Vcc

FIGURE 104.-Minimum Spon- %taneous Ignition TemperaturesRatios. 100 - 'iof 0.05 cc of Liquid UD MNH inAtmosphere for Various He/O2

-a ob line of N* 2 ~ .

- - - -

-- _ __ - -

0 5 10 15 20 25NO* CONCENTRATION, volume-percent

22

FLAMMABILrTY CHARACTERISTI( 5 87

300 . . . - . . 250 ---T-T T -T-----T-- i F

a 15 psiab 45 psia

_ 200

200-Region of spontaneous ignition

Region of spontaneous ;gnitioni

0 150

I J100 1100

Lower limit of flammabilityof UDMH in air

I ] ] 50I0 5 10 15 20

NO* CONCENTRATION, volume-percent Dew point line

FiouRx 105.-Minimum Spontaneous Ignition Tern- ""peraturep of 0.05 cc of Linuid UDNIH in NO,*-AirMixtures at 15 and 45 Psia as a Function of NO,* I I I IConcentration. 0 4 8 12 16 20

of two gasolines and three jet fuels considered UDMH CONCENTRATION, volume-percent

here are given in figure 108. Unfortunately, FIGURE 106.-Minimum Spontaneous Ignition Tem-such curves give only an approximate measure peratures of Vaporized UDMH-Air Mixtures in Con-of the volatile constituents in the liquid blend. tact With 100 pct NO; at 250 C and 740± 10 mmEven relatively nonvolatile high-flashpoint, oils Hg as a Iunction of UDMH Concentration in Air.

may liberate flammable vapors at such a slowrate that the closed vapor space above the grade JP-4 (fig. 110). Combustible vapor-air-liquid may be made flammable at reduced carbon dioxide and vapor-air-nitrogen mixturestemperatures. Gasolines can produce flam- at about 25' C and atmospheric pressure aremable saturated vapor-air mixture at tempera- considered for each. Similar data are given intures below -65' C (241), although the flash figure 14 for the gasoline vapor-air-water vaporpoints of such fuels are considered to be about system at 21' and 100' C; the effect of pressure-45' C (158). An apparent discrepancy thus on limits of flammability of volatile constituentsexists if flashpoint data are used to predict of JP-4 vapor in air are discussed in connectionthe lowest temperature at which flammable with figure 12.mixtures can be formed in a closed vapor space Minimum autoignition temperatures of gaso-above a blend in long-term storage. lines and jet fuels considered here are given in

As noted earlier, the limits of flammability of compilations by Zabetakis, Kuchta, and co-hydrocarbon fuels are not strongly dependent workers (126, 237). These data are includedon molecular weight when the limits are ex- in table 20.pressed by weight. However, since results Setchkin (194) determined the AIT values ofmeasured by a volume are perhaps more widely four diesel fuels with cetane numbers of 41, 55,used than those measured by weight, typical 60 and 68. These data are included in table 20.flammability curves are presented by volume Johnson, Crellin, and Carhart (92, 93) obtainedfor the light fractions from aviation' gasoline, values that. were larger than those obtained bygrade 115/145 (fig. 109), and aviation jet fuel, Setchkin, using a smaller apparatus.

88 FLAMMAI3ILIT CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

100

S air 100 -% diban@-X ethane S air 100X- X psolIne- S inert

lmF lammable

wimm~ mixtures 0

Luminous20- flame(cltio\\a 0 to 20 3 40 0,I i I

ADDED INERT. volume-percent

0 20 40 60 so 1W. Fzoaui 109.-Limit. of Flammability of AviationETHANE. volume-percent Gasoline Grades 115/145 Vapor-Carbon Dioxide-Air

and 115/145 Vapor-Nitrogen-Air, at 27" C and At-Fnouzz 107.-Limits of Flammability of Diborane- mospherlc Pressure.

Ethane-Air Mixtures at Laboratory Temperaturesand 300 mm Hg Initial Pressure. 10 1

460- % i r00%-% JP4- inert

- 6-

420 -/ !" I8

380- -

// N2

340 /4- Flammable3407 It mixtureCL C02"

02

--

S260-, " 0 10 20 30 40 50

l'- ADDED INERT,. volume-percent

220- Fiouaz 110.-Limits of Flammability of JP-4 Vapor-Carbon Dioxide-Air and JP-4 Vapor-Nitrogen-Air/ -Mixtures at 270 C and Atmospheric Pressure.

180-/ , " TABLE 20.-Autoignition temperature ialues of

various fuels in air at 1 atmosphereFuel:

140 Aviation gasoline: AlT, -c100/130 -------------------------- 440115/145 -------------------------- 471

Aviation jet fuel:I00 I I JP-1 ---------------------------- 228

0 20 40 60 80 100 JP-3 -------------------------- 238DISTILLED, percent JP-4 ---------------------------- 242

JS-6 n----------------------.------ 232FJouaz 108.-ASTM Distillation Curves for, A, Avis- )iesel fuel:

tion Gasoline, Grade 100/130; B, Aviation Gasoline, 41 eetane ----------- ------------ 233Grade 115/145; C, Aviation Jet Fuel, Grade JP-I; 55 cetane ------------------------ 230D, Aviation Jet Fuel, Grade JP-3; and F, Aviation 00 cetane------------------ 225Jet Fuel, Grade JP-4. 68 cetane -------- _---------------- 226

FLAMMABILITY CHARACTERISTICS 89

Burning velocities of the fuels considered 80here are in the same range as those of the ir= 1bo%-% hydrogen-% inerthydrocarbons considered earlier. Values forvarious fuels have been tabulated by Barnett Mn 02and Hibbard (156). o -%

Hydroqen I 22

Numerous flammability characteristicsstudies have been conducted with hydrogen in 0recent years. Drell and Belles have prepared ,an excellent survey of these characteristics (48). Cs5This survey includes all but the most recent .work of interest.

The low pressure limits of flame propagation 20 Famab_-for stnichiometric hydrogen-air mixtures are mixtres C02somewhat lower than those for stoichiometricethylene-air mixtures (197) in cylindrical tubes.In the range from 6 to 130 mm Hg, the limit Ifor stoichiometric hydrogen-air mixtureS is 0 20 40 60 80

given by the expression: ADDED INERT, volume-p.rnent

log P=3.19-1.19 log D, (57) Fiuaz III.-Limits of Flammability of Hydrogen.Carbon Dioxide-Air and Hydrogen-Nitrogen-Air

where P is the low-pressure limit in millimeters Mixtures at 250 C and Atmospheric Pressure.of Hg, and D is the tube diameter in milli-meters.

Hydrogen forms flammable mixtures at curves were found to deviate from the resultsambient temperatures and pressures with oxy- obtained from the Le Chatelier law, brokengen, air, chlorine, and the oxides of nitrogen, curves; additional data are given in the originalLimits of flammability in these oxidants at article.approximately 250 C and I atmosphere are The burning velocity of hydrogen in air atlisted in table 21. 25' C and one atmosphere range from a low

of a few centimeters per second to 325 cm/secTABLE 21 -Limits of mmability of hydrogen (68). When liquefied, it, vaporizes and burns

T i variouoiatfs a 5la a o an d oen in air at a rate that is determined by the ratein various o)xidants at 25'C and atmosp~ric at which heat enters the liquid. Heat ispressure abstracted from the surroundings and, where aflame exists, from the flame itself. Figure 115

Oxidant L3 (t Ref. gives the results obtained from vaporizing.liquid hydrogen from paraffin cast in a Dewar

4.flask; epe ental points were obtained fromOxygen -------- exper5imentalAir -----------------. . 0 75 (40) gas evolto measurements. The solid curveChlorine -------------- 4. 1 89 (em, ike) (theoretical) was obtained by Zabetakis andS---------------------3. 0 84 (189) Burgess by assuming the heat influx rate to beNO ------------------- 6.8 66 (189) conduction limited (234); the initial flash

vaporization rates are probably film- andnucleate boiling-limited. The theoretical liquid

Flammability diagrams of the syatems hydro- regression rates following spillage of liquidgen-air-carbon dioxide and hydrogen-air-niitro- hydrogen onto three soils are presented ingen obtained by Jones and Perrott (112) are figure 116, the corresponding decrease in liquidgiven in figure 111. Lines that establish level is given in figure 117. Because of itsminimum oxygen values for each system are low temperature, the vaporized hydrogenalso included. Note that although the mini- forms a vapor trail as it. leaves the liquid.mum value occurs near the "nose" of the However, the position of this trail or visiblehydrogen-air-nitrogen curve, the corresponding cloud does not necessarily coincide with thatvalue occurs atr the upper limit of the hydrogen- of the flammable zones formed above the liqui,air-carbon dioxide curve. pool. This is illustrated in figure 118, in which

Flammability diagrams obtained by Scott, the positions of the flammable zones and visibleVan Dolah, and Zabetakis for the systems clouds are defined in a height-elapsed timehydrogen-nitric oxide-nitrous oxide, hydrogen- graph. Two flammable zones are defined here.nitrous oxide-air, and hydrogen-nitric oxide-air These are also seen in the motion picturearegivenin figures 112-114 (189). Upperlimit sequence (fig. 119) of the visible clou 6 and

g0 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE OASES AND VAPORS

100 0

KEY* Flammable mixture

0 Nonflammable mixture so 20

40 NO, mleecen

Fiouiaz 112.-Limits of Flammability of HrNt).';2 at Approximately 280 C ane I Atmosphere,

A..AMMABILITY CHARACTERISTICS 91

100 0

KEY

* Flammable mixtureo Nonflammable mixture 80 20A Coward and Jones,

Bureau of Mines

o3 Smith and Linnett,JCS (London),1953, pp. 37-43

20 80

0 100100 80 60 40 20 0N2 0, mole-percent

FIGURE 113.-Limits of Flammaubility of Ilr-N20-Air at Approximately 280 C and 1 Atmosphere.

92 FLAMIMABILIT CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPOR$

100 0

KEY* Flammable mixture* Nonflammable mixture 80 20A Coward and Jones,

Bureau of MinesBull. 503

60 40 1

00

0 -10010 80 60 40 20 0

AIR, mole-percent

FIOL'Rz 114.-Limits of Flammability Of HrNO..Air at Approximately 280 C and I Atmosphere.

FLAM"MABILITY CHARACTERISTICS 93

Start of liquid transfer to Dewar

10 1----T - -T - T - '

a-

. .- (Film and nucleate boiling limited)E

I: Theoretical(conduction limited)

IAI

2 -

Region i_of vilent

boiling F--1- Quiet vaporization

0 1I I I I 1 1 1 1 1 1 1

-20 0 20 40 60 80 100 120 140 160ELAPSED TIME, seconds

FxoUiuE 115.-Rate of Vaporization of Liquid Hydrogen From Parafin in a 2.8-Inch Dewar Flask: Initial LiquidDepth-6.7 Inches.

0.4 I I I I

.3

2

• 040 60 80 100 120 140 1'60

ELAPSED TIME, seconds

FiOURs 116.-Theoretical Liquid Regression Rates Following Spillage of Liquid Hydrogen Onto, A, an A\'trage,oil; B, Moist Sandy Soil (8 Pet. Moisture); and C, Dry Sandy Soil,

94 FLAMMABILITY CWARMcIERISTICS OF CO)MBUSTIBLE~ GASES AND VAPORS

4-

0 20 ~ 40 60 8 0 2 4 6ELAPSED TIME, seconds

Fzonn 17.TheretcalDeceas inLiquid Hydrogen Level Folowing Spillage Onto, A, Dry Sandy Soil; B,Fioitz117-Thoreica Merist San Sol (S Pet. Moisture); and C, and Average Soil.

14-

KEY0 Loer-limit mixture

12 Nonflammable

10 Nonflammable

FIGURE I I.-Extent of Flamma- 8-ble Mixtures and Height ofVisible Cloud Formed After -Height of visible cloudRapid Spillage of 3 Liters ofLiquid Hydrogen on a Dry Mac-~adam Surface in a Quiescent X 6 -Air Atznoephere at 150 C. .

""N

4LPE T-E sNod

FLAMMABILITY CHARACTERISTICS 95

flames that resulted following spillage of 7.8liters of liquid hydrogen and subsequentignition of vapors above the spill area. Theheight and width of fireballs that resulted fromignition of vapors produced by rapid vaporiza-tion of about 3 to 90 liters o? liquid hydrogenare given in figure 120. The data are repre-sented fairly well by the equation

Hm.= Wym,= 7./)V feet= 17.8V!M feet, (56)

where H.. and W. are the maximum flameheight and width, respectively, V1 is the volumeof liquid hydrogen in liters, and M is the massof this volume in pounds.

The burning rate of a 6-inch pool of liquidhydrogen in air is given as the regression of the

.375 liquid level in figure 121; burning rate data forliquid methane are included for comparison.An extrapolated value of burning rate for largepools of liquid hydrogen is included in figure 52.

Approximate quantity-distance relationshipscan be established for the storage of liquid hy-&-ogen near inhabited buildings and other stor-age sites f certain assumptions are made (83,

2o0- 160, ,34). Additional work is required toestablish such distances for very large quantities

15- of liquid.The detonation velocity and the static and10- W reflected pressures developed by a detonation

3 . wave propagating through hydrogen-oxygenV) mixtures are given in figure i6. The predeto-

0-1 nation distance in horizontal pipes is reportedlyproportional to the square root of the pipediameter (229); this is presamably applicableto results obtained with a mild ignition source,since a shock front can establish a detonationat essentially zero runup distance. Numerousinvestigators have examined this and relatedproblems in recent years (11--8, 65, 155-137,k '161).

.3 HYDRAULIC FLUIDS AND ENGINEOILS

Both mineral oil derivad and synthetic hy-draulic fluids and engine oils are presently incommon use (148). These materials are oftenused at elevated temperatures and pressuresand contain additives designed to improve qta-bility, viscosity, load-bearing characteristics,etc. Such additives affect flammability char-acteristics of the base fluid. However, the base

.364 2 Floun ll.-Motion Picture Sequence (16 Frames perSecond) of Visible Clouds and Flames ResultingFrom Rapid Spillage of 7.8 Liters of Liquid Hydrogenon a Gravel Surface at 180 C. Ignition Source: 20Inches Above Gravel.

96 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASE4' AND VAPOJ%3

100-r-T--r-F--F-r I I ,1F- i1-

60- Flame height - -I- Flame width 0

ME0

2 20

FiounE 120.-Maimurn rianeheight and widtk. pitcd-c'd byIgnitioni U vapor-air mixtures0formed by sudden spillage of 10 1 II I I L I I I IL

2.8 to 89 liters of liquid hy- 2 4 6 8 10 20 40 60 80 100drogen (VI). VI, liters

5-U

.4-

00 Hydrogen

0z Methane0 2

FG URE 121.-Burning rates of wliquid hydrogun %nd of liquid 0methane at the boiling points in W6-inch-Pyrex Dear flasks. 1i

10 20 30 40 50 60

ELAPSED TIME, minutes

FLAMMABILiTY CHARACrERISTIL"S 97

fluid generally plays a predominant role iii de- ambient temperatures can lead to the auto-ternining limits of flammability and ignition ignition oi ,t mineral oil lubricant (curve 5) iftAmperaturo of a particular fluid. For exam- sufficient vapo' or mist is in the system. In thepie, many of the oil-based fluids have lover same pressure range, only elevated initiallimits of flammability that fall in the ranges temperatures could lead to the autoignition of agiven in figure 22 for paraffin hydrocarbons. phosphate ester (curve 4). If the initial pressureFurther, those that have minimumn autoignition is increased to 10 atmospheres, autoignitiontemperatures in the lower temperature ranges cin oo-ur at, lower air-intake temperatures inconsidered in fiugres 43 and 71 are not affected every case (248).appreciably by oxygen concentration of theatmotsphere and by ambient and fluid-injec'ion M C] M OUSpressures; those that, have minimum autoigni-tion temperatures in the higher temperature The flammability characteristics of a numberranges do not follow these generblizat ions (287). of miscellaneous combustibles not consideredSince these fluids are designed for use at ele- elsewhere, are discussed in this section. Thesevated temperatures and pressures, they are nor- include carbon monoxide, n-propyl nitrate, andmally made up of high -molecular weight mate- the halogenated hydrocarbons. The propertiestials. Accordingly, they are flammable at of these and a geat variety of other materialsordinary temperatures and ressures as mists are included in Appendix A.and foams. Burgoyne and his coworkers (27) The limits of flammability of the systems car-found that, lubricating-oi mists were flrmma- bon monoxide-carbon dioxide-air and carbonble in air but not in carbon dioxide-air mix- monoxide-nitrogen-air are presented in figureture,: that contained about 28 ,volume-percent 126. These curves were constructed from thecarbon dioxide (fig. 1i5). At elevated temper- flammability data obtained by Jones in a 2-inchOtnre4, the ,A!, vapors cracked Rnd produced vertical glass tube with upward flame propaga-acetylene and hydrogen, which affected the tion (11); other representations may be foundflarmmability of the resultant mixture; the va- in the original reference and in the compilationpors are often unstable at elevated tempera- prepared by Coward and Jones (40).tures. Chiantella, Affens. and Johnson have Materials that are oxidized or decomposeddetermined the effect of elevated temperatures readily may yield erratic flammability dataon the stability and ignition properties of three under certain conditions. This effect i illus-commercial triaryl phosphate fluids (36). trated in figure 127 which summarizes the

Zabetakis, Scott, and Kennedy have deter- lower-limits data obtained by Zabetakis, Masonmined the effect of pressure on the autoignition and Van Dolah with n-propyl nitrate (NPN) intemperatures of commercial lubricants (248). air at various temperatures and pressures (248).Figure 122 gives the minimunm autoignition An increase in temperature from 750 to 1250 Ctemperatures for four commercial phosphate is accompanied by a decrease in the lower-limitester-base fluids (curves 1-4) and three values; a further increase in temperature tomineral oils (curves 5-7). In each case, the 1500 C results in a further lowering of the lowerminimum autoignition temperature was found limit at pressures below 100 psig, but not at theto decrease with increase in pressure over most higher pressures. An increase in the tempera-of the pressure range considered. A plot of the ture to 1700 C results in an apparent increase inlogarithm of the initial pressure to temperature the lower-limit value because of the slow oxida-ratio versus the reciprocal of the temperature tion of NPN. A complete flammability dia-is given for curves 1 to 7 in figure 123. The gram has been constructed for the NPN vaporresultant curves are linear over P limited tern- system in figure 128; a single lower limit curveperature range. and two upper limit curves are given here tc

The ratio of the final temperature attained by show the effect of pressure on the flammableair in an adiabatic compression process to the range of a vapor-air system.initial temperature is given in figure 124 as a The spontaneous ignition of NPN in air wasfunction of both the final-to-initial pressure considered earlier at 1,000 psig (figs. 3, 4). Theratio and initial-to-final volume ratio. If a explosion pressures obtained at this initial pres-lubricating oil is exposed to high temperatures sure in air and in a 10 volume-percent oxygenduring a compression process, autoignition may +90-volume-percent nitrogen atmosphere atoccur if the residence or contact time is ade- various NPN concentrations are presented inquate. Such high temperatures do occur in figure 129. A summary of the minimum spon-practice and have been kLown to cause disas- taneous ignition and decomposition tempera-trous explosions (68, 146, 149, 27, 2 1). The tures obtained with NPN in air and nitrogencurves ii ligure 125 show that in the compression respectively are given in figure 130. The datapressure range 1 to 10 atmospheres (initial given in this figure exhibit a behavior that ispraesure=l atmosphere), a wide range of typical of that found with other combustibles

98 FLAMMABILITY CHARACTIEISTICS OF COMBUSTIBLE. GASES AND) tAPORS

6.50 .T- .. ............ -T-- r - - -T-T T -TT -1

00

C0autignti1

IV~0:500

£0. 80 20 416810 0 0

INT2450SSR, t

FIUR 12.Vrai4i0i0umAtintoiTmeaur ihPesr t(omnrh hsht sa2 Miea viiurcnsi i na40-cSaiesSellonj

FLAMMABILrrY CHARACTERISTICS 9

TEMPERATURE, -C

650 550 450 400 350 300 250 200 175

.6 - M n e ra l

Phosphate 3 ol

.4 esters0

A -X

Regioo ofoutoignition

.10.08

0D60

be .04-FIGUIC~ 123.-togarithm of Ini- I-,

tial Prpe~ura-AIT Ratio of ESeven Fluids in Air for VariousReciproca~lTemperatureb. Data. -

from Figure 122. .02-

.0i-.008-

.006-

.004

.002 V11 VI

I. .40I 1.8

100 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

2.4

2.2-

V,

2.0- v-

1.8-Pf

FiouUm 124.-Variation in T,/T, i -of Air With V4/Vt and WithPIPi in an Adiabatic Corn- 1.6-preaion Procen.

1.4

1.2

1 2 3 4 5 6 7 8 9 10

vi Pfvf P,

LAs

FLAMM4ABILITY CHARACTERISTICS 101

500 O tm Re(!ion of500- autoignition

Fiouaa 125.-Variation In Air 11A;rIemperature With P,/P, in anAdiabatic Compnression Proces3

Tepea 30 -/I-tfor Five Initial Air Tepr <~~0P ttures (00, 250, 5O*, 750, and MAIT1000 C). Regions of autoignl-tion for lubricants TV and Vat CL 0.P,/P, Between 1 and 10 Atmos- 2phere and P, of Between 1 and W10 Atmospheres. 20 -P-1

t

P,,i100

102 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

80 at elevated pressures; the minimum spontaneousignition temperature first decreases with ini-

air - 1009- carbon monoxide- Inert tial increase in pressure and then increases asthe pressure is increased still further (120,

60 248).Burning velocities were found to range fromI20 cm/sec to 110 cm/sec in NPN-air mixtures

containing 3.0 to 7.2 volume-percent NPN.id Flammable Detonations were obtained in saturated NPN0 40- mixtures vapor-air mixtures from 300 to 650 C and 1

atmosphere pressure; the detonation velocito0 _,, 'st C02/ was from 1,500 to 2,000 meters per secondS N2Stable detonations were obtained with liquidz NPN at 900 C; the detonation velocity was

cc - from 4,700 to 5,100 meters per second.5Although many of the halogenated hydro-

carbons are known to be flammable (40) stillothers such as methyl bromide, methyleneF chloride, and trichloroethylene (TCE) have

0 20 40 60 80 been considered to be nonflammable or essential-ADDED INERT, volume-percent ly nonflammable in air. As noted in connection

witb the methyl bromide data given in figureFrounn 126.-Limits of Flammability of Carbon Mo- 28 Hill found methyl bromide to be flammable

novide-Carbon Dioxide-Air and Carbon Monoxide- . HNitrogen-Air Mixtures at Atmospheric Pressure and in air at 1 atmosphere pressure (84); the re-2W' C. ported limits of flammability were from 10 to

5

Flammable mixtures

00 2 -- 1700C (3 hr heating time) -

> /75C /170C (2 hr heating time)

0 - - - - - - - - - -z 1.500C .1250CZ I I

0 100 200 300 400 500 600 700 800 900 1,000PRESSURE, psig

FIGUaz 127.-Lower Linitq of Flammability of NPN Vapor-Air Mixtures river the l'r,ssijrv Range I.-roi 0 t1,000 Psig at 75', 125', 150

o, and 170" C.

FLAMMABILrrY CHARACTERISTICS 103

100 15 volume-percent methyl bromide. At aninitial pressure of 100 psig, the flammable rangewas found to extend from 6 to 25 volume-per-

90 -- cent. Similarly, methylene chloride and tri-chloroethane were found to be flammable in airat ambient temperatures although the flam-mable ranges were not determined. In general,

so - much higher source energies are required withImpossible vapor-air these combustibles than are required to ignitemixtures at T &I25 "C methane-air mixtures.

70 An approximate flammability diagram wasprepared by Scott for trich oroethylene-air

60 mixtures (190); a modification is reproduced in60 .figure 131. The lower limit data were obtained

in a vertical 7-inch-diameter flammabil~ty tubeand the upper limit data in an 8-inch-diameter

0 50- glass sphere with upward propagation of flame.lammable mixtures of TCE and air were also

0 obtained between 10.5 and 41 volume-percenta40 TCE at, I atmosphere and 1000 C in an 8-inch-> diameter glass sphere. Under the same con-Z ditions, flammable mixtures of TCE andz oxygen were obtained between 7.5 and 90

30 volume-percent TCE. However, additionalwork must be conducted with this and theother halogenated hydrocarbons to determine

20 Saturated vapor-oir the effect of vessel size, ignition source strength,mixtures T 1250C temperature and pressure on their flammability

characteristics.1 o Other useful flammability data may be found

T-50o6C for various miscellaneous combustibles in many.. Flammable of the publications listed in the bibliography" , ,(40, 154, 200, 208-214, 118). These include

0 200 400 600 800 1,000 data on the gases produced when metals reactPRESSURE, psig with water (56) and sulfur reacts with various

hydrocarbons (62). Still other references con-1"1OURE 128.-Flammable NPN Vapor-Air Mixtures sider the hazards associated with the production

Formed Over the l'ressure Range From 0 to 1,000 of unstable peroxides (142, 157, 187, 238) ,andPsig at 50° and 1250 C. other reactive materials (66, 74, 80, 139).

,.S

104 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

5,000--

Inct 4,000-

o3,000-

a-

z 2,000-

0

Q. 1,000-0 AiX ~0-10% 02 + 90% N2

0 0.3 0.6 0.9 1.2 1.5 1.8 2.1

NPN VAPOR, volume-percent

FIOURZ 129.-Variation of Explosion Pressure Following Spontaneous Ignition With NPN Concentration, Initial

Pressure 1,000 Psig.

2 4 0C 11T _ T

Regions of spontaneous ignition and

220- spontaneous decomposition

~ Dcoposition in N2 0

0 400 800 1,200 1,600 2,000 2,400 2,800 3,200 3,600 4,000

INITIAL PRESSURE, psig

FIGURE 130.-Minimum Spontaneous Ignition and Decomposition Temporatures of n-Propyl Nitrate in Air as a

Function ofPressure, Type 347) Stainless Steel Test Chamber,

FLAMMABILITY CHARACTERISTICS 105TEMPERATURE. "C

0 10 20 30 40 50 60 70 80 90 1001,o000 , r , , I T -F.. .

800 -- 1O

-90600 L80

- 60/400 5

30 Upper limit 4 E300 - -440 "

Impossible mixtures 0 >

200 Flammable mixtures EE

i, i0 __-e,/,r ower limit 420

60-

40-1030- Nonflammable mixtures

u

10 I 0 I,

0 50 100 150 200 250TEMPERATURE, "F

FIouRE 131.-Flammability of Trichloroethylene-Air Mixtures.

ACKNOWLEDGMENTSMany of the unpublished data reported here Burgess 6 and Robert W. Van Dolah for many

were obtained by the predecessor of the author, fruitful discussions of the material contained inthe late G. W. Jones, former chief of the gas the sections on Definitions and Theory, De-explosions branch. Other data were obtained flagration and Detonation Processes, and Pre-by the author and his coworkers, particularly ventive Measures.Messrs. George S. Scott, Joseph M. Kuchta,Aldo L. Furno and Henry E. Perlee. In I Presently with Reaction Motors Division, Thiokol Chemical corpo-

addition, the author is indebted to Drs. David ration, Denville, New Jersey.

106

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108 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND 'VAPORS

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I!5 WI 1,il)lr). 4t0A - 4 2A. tu 1 ).ios 69. viniI.0 ofad h nlr

15Richiard soni, E . C ., and C. It . Stilton. Explosive 196 Simos R. 1', a~U fN nd If Gur (I'on lfham. Th 'fanPropt rt it of I acq ji r-Sotlv cut Vsapors.- Iin. I lneo hieth . .51 ,rid 1955 p. ts 1ra211

T"o I 1rig. ('hem., v-. 20, 19289, pp. 197-- 190. FrdvSvv 1 95 ) 21

7l;. Itobvrts, A-., B3. It. Ptirsall, drid J1. B3. Sellers. 197. Sireo'r, I )orothl M ., Frank I Belle~s, andl AdolphNIt t io it Lav t ririg ii M in e A irwa vs. (Coil, E. SpI tktwski . Ir vtsigi on iiand Initerlrtt a-Guiard., v . 205, ( )t'tober ')62, pp.53-4 timu tof i ll(, Fl:mrir iiailit 'v Region ftor Somt Letarn

177 Mlelhant la,ring in Milne Air- II vdrocarun-Air MNtuirts. 4th Srnv. (Intcr-MovsPr 1 h liryo avi.(ol lint.)A oil (itribisitin, Williamrus & W'ilkins Co.,t stiai., v.tr 205, 1ii 91jIto ofBa'Iig ('~ ltnimore, Md., 1953, Ill. 1241-1314.

'- 05 92, Pl) 59 53Id. Methlarne ayvtrin g in MIin e Air- I104. Sinitger, J. M. , J ,ose ph i rutnvr, an rd IE. 11, Cook.

Ulits. Part Ill. Thet Theorv otf Layering Burrnin g ',,eloc itis hv by h Buni~~i-I Inrn r('ouitintd t. C'oll. ( uard., v. 205, 1 962, jpp Method. 1. 11 vearbori-Oxvygtri Mixtures at':10-636. I ii, Atinoie~tre. 11.11 v.Ndroca rm- nAi r \f ix-

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1962, pp. 723 -732. 199. Sutill., Marion L., and Karl W.- St inson.- Fuels;

112 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

and Combustion. McGraw-Hill Book Co., 220. Weber, J. P., J. Savitt, and K. Krc. DetonationNew York, 1952, 340 pp. Tets lvaluate lligh Pressure Cells. Ind. and

200. Solov'ev, N. V., and A. N. Baratov. Dependence Eng. Chem., v. 53, 1961, pp. 128A-131A.of the Lower Limit of Flammability on Molecu- 221. Well, N. A. Rupture Characteristics of Safetylar Structure. Russian J. Phys. Chem. (Zhur. Diaphragms. J. Appl. Phys., 1959, pp. 621-Fiz. Khim.), v. 34, 1960, pp. 1661-1670. 624.

201. Spakowski, A. E. Pressure Limit of Flame Prop- 222. White, A. G. Limits for the Propagation ofagation of Pure Hydrocarbon-Air Mixtures at Flame in Inflammable Gas-Air Mixtures.Reduced Pressures. Not. Advisory Committee I1. The Effect of Temperature on the Limits.for Aeronautics Res. Memo. E52H 15, 1952, J. Chem. Soe., v. 127, 1925, pp. 672-68.33 pp. 223. . imits for the Propagatiol of Flame

202. Spalding, I). B. Some Fundamentals of Combus- in Vapor-Air Mixtures. Part 1. Mixtures oftion. Butterworths Sct. Pub. (London), 1955, Air and One Vapour at the Ordinary Tempera-250 pp. ture and Pressure. J. Chem. Soc., v. 121, 1922,

203. Stenberg, John F., and Edward G. Coffey. De- pp. 1244-1270.signing a High-Pressure Laboratory. Chem. 224. . Limits for the Propagation of FlameEng., 1962, pp. 115-118. in Inflammable Gas-Air Mixtures. Part 1.

204. Stoner, R. G., and W. Bleakney. The Attenua- Mixtures of Air and One Gas at the Ordinarytion of Spherical Shock Waves in Air. J. Appl. Temperature and Pressure. J. Chem. Soc., v.Phys., v. 19, 1948, pp. 670--678. 125, 1924, pp. 2387-2396.

205. Sullivan, M. V., J. K. Wolfe, and W. A. Zisman. 225. . Limitg for the Propagation of FlameFlammability of the Higher-Boiling Liquids and at Various Temperatures in Mixtures of Am-Their Mists. Ind. and Eng. Chem., v. 39, 1947, monia With Air and Oxygen. J. Chem. Soc.,p. 1607. v. 121, 1922, pp. 1688-1695.

206. Tamura, Z., and Y. Tanasawa. Evaporation and 226. White, A. G., and T. W. Price. The Ignition ofCombustion of Drop Contacting With a Hot Ether-Alcohol-Air and Acetone-Air Mixtures inSurface. 7th Symp. (Internat.) on Combus- Contact With Heated Surfaces. J. Chem. Soc.,tion, Butterworths Sci. Pub. (London), 1959, v. 115. 1919, pp. 1462-1505.pp. 509-522. 227. White, Douglas F. The Unintentional Ignition207. Terao, Kunio. Selbstzunung von Kohlenwas- of Hydraulic Fluids Inside High Pressureserstoff-Luftgemischen in Stoss'ellen. J. Phys. Pneumatic Systems. ASNE J., 1960, pp. 405-Soc. of Japan, v. 15, 1960, pp. 2086-2092. 413.

208. The Combustion Institute. Combustion and 228. Winter, E. F. The Electrostatic Problem inFlame. Butterworths Sci. Pub. (London), v. Aircraft Fueling. J. Royal Aeronautical Soc.,1-7, 1957-63. v. 66, 1962, pp. 429-446.

209. - . 4th Symposium (International) on 229. Wolfson, Bernard T. Harnessing Explosions.Combustion. The Williams & Wilkins Co., Office of Aerospace Res. Rept. No. 17, 1962,Baltimore, Md., 1953, 926 pp. pp. 3-4.

210. . 5th Symposium (International) on 230. Wolfson, Bernard T., and Robert G. Dunn.Combustion. Reinhold Pub. Corp., New York, GCineralized Charts of Detonation Parameters1955, 802 pp. for Gaseous Mixtures. J. Chem. Eng. Data,211. . 6th Symposium (International) on v. 1, 1956 pp. 77-82.Combustion. Reiphold Pub. Corp., New York, 231. Zabetakis, Nfichael G. Explosion of Dephliegmator1957, 943 pp. at Cities Service Oil Company Refinery, Ponca212. - . 7th Symposium (International) on City, Okla., 1959. BuMines Rept. of Inv. 5645,Combustion. Butterworths Sci. Pub. (London), 1960, 16 pp.1959, 959 pp. 232. . Gasfreeing of Cargo Tanks. Bu-

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218. Van Dolah, Robert W., Michael G. Zabetakis, Minimum Spontancous I fition TemperaturesDavid S. Burgess, and George S. Scott. Re- of Combustibles in Air. fnd. and Eng. Chem.,vie' . of Fire and Explosion 1lazards of Flight v. 46, 1954, pp. 2173-2179.Vehicle Combustibles. BuMines Inf. Circ. 238. Zabetakis, M. G., P. M, (ossey, and G. S. Scott.8137, 1962, 8 pp. Limits Of Fla ouinability of Methyl Ethyl Ketone219. Wayman, D. H1., and R. L, Potter. Detonations nd Methyl Isobutyl Ketone in Broniochloro-in Gaseous Fuming Nitric Acid-Hydrocarbon methane-Air Mixtures. BuMines Rept. of Inv.Mixtures. Combustion and Flame, Butter- 5680 1960, 12 pp.worth. Sol. Pub. (London), 1957, v. 1, pp. 239. Zabetakis, M. G., and G. W. Jones. Flammability321-329. of Carbon Disulfide in Mixtures of Air and

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241. Zabetakis, Michael G., George W. Jones, George tions Involved in Handling Kerosine. Proc.S. Soctt, and Aldo L. Furno. Research on the Am. Petrol. Inst., sec. 3 v. 37, 1957, p. 296.Flammability Characteristics of Aircraft Fuels. 246. Zabetakis, M. G., G. S. 9cott, and G. W. Jones.Wright Air Development Center, Tech. Rept. Limits of Flammabilityr of Paraffin Hydrocar-52-35, supp. 4, 1956, 85 pp. bans in Air. Ind. and Eng. Chem., v. 43, 1951,

242. Zabetakis, M. G., S. Lambiris, and G. S. Scott. pp. 2120-2124.Flame Temperatures of Limit Mixtures. 7th 247. - -. The Flammability CharacteristicsSymip. (Internat.) on Combustion, ilutterworths of the C,.H2.-s Aromatic Series. BuMinesSci. Publ. (London), 1959, pp. 484-487. Rept. of Inv. 4824, 1951, 9 pp.

243. Zebatakia, M. G., C. M. Mason, anid It. W. Van 248. Zabetakis, M. G., G. S. Scott, and R. E. Kennedy.Dolah. The Safety Characteristics of Normal Autoignition of Lubricants at Elevated Pres-Propyl Nitrate. BuMies Rept. of Inv. 6058, sures. Bu Mines Rept. of Inv. 6112, 1962, 10 pp.1962, 26 pp. 249. Zeldovich, Ia. B., S. M. Koarko, and N. N.

244. Zabetakis, M. C., and J. K. Richmond. The Simonov. Ali ExperimntalI Investigation ofDetermination and Graphic Representation of Spherical Detonation of Gases. Zhurnal Tekh.the Limits of Flammability of Complex Hydro- Fiziki (J. Tech. Phys. (USSR)), v. 26,1956, p. 1744.

APPENDIX ATALILE A-I. Summary o limits offlammability,

lower temperature limits (TL), aml miniMm Limits of flam-autoignition temperatures (AiT) of inditidual mtibility (vohnme-gases and vapors in air at atmospheric pressure Combustible percent) Ti. AIT

Limits of flam- Lis Us&mability (volume-1

Combustible percent) T1, AIT_. (0 C) (0 C) ,ec-Butyl benzene -- 1 0..77 1 5. 420

ler-Butyl benzene ---- 1 .77 I 5. 8-------- 450U 1 n-Butyl bromide- - ---- 2. 5 -------- - -- 265

Butyl cellosolve ------ 8 1. 1 10 - --------- 245n-Butyl chloride ----- 1.8 1 10 .

Acetal --------------- 1.6 10 37 230 n-Butyl formate ----- 1. 7 8. 2Acetaldehyde --------- -. 0 60 ------. 175 n-Butyl stearate ----- . - ------ 35

,

Acetic acid ---------- 2 5.4 ----- 40 465 Butyric acid --------- 2. 1 - ---- -......-. 450Acetic anhydride-----2 2. 7 8 10 47 390 a-Butryolactone -------- 2.0 0----------------_ __Acetanilide ---------- 1.0 .............. 545 Carbon disulfide ...-... 1.3 50 90Acetone ------------- 2.6 I 13 . 465 Carbon monoxide .- 12. 5 74 ...

Acetophenone ------- 1. 1 --------------. 570 Chlorolhnzn ---------- 1.4 --------- 211Acetylacetone ....... 1. 7 ---- ....------ 340 rn-Crosol- _.--.--- - 1. 1 ...... - -.. ..Acetyl chloride ... . - 5. 0 -------- ------ --- 390 Crotonaldehyde . 2. 1 1 10 .

Acetylene--- -------- 2. 5 100 305 Cumene ------------ 1. 8 ' 6.5 ... 425Acrolein..-.-...... 2.8 31 ---- 235 Cyanogen ------------ 6.6 -------Acrylonitrile --------- 3. 0 ------- - -6 Cycloheptane. ------ -- 1. 1 .6 .7....Acetone Cyanohydrin. 2. 2 12 ------ ----- Cyclohexane --------- 1.3 7. 8 . 245Adipic acid ---------- -1. 6 -------- - 420 Cyclohexanol ---------- 1. 2 ----- - 300Aldol- .-------------- '2.0 -------- 250 Cyclohexene- -------- 1.2Allyl alcohol --------- 2.5 18 22 --- Cyclohexyl acetate _ 1.0 -. 33"Allyl amine ---------- 2. 2 22 --- 375 Cyclopropane- -------- 2. 4 10. 5 0 0Allyl bromHe --------- 2. 7 -----------. 295 Cyniene.... .. . 85 )5 415Allyl chlorid ---------- 2. 9-......... -32 485 .D,,aborate-------- 2o-?kminodiphenyl ... 66 4. 1 I--------450 Decalin- - -........ --- 74 1 1 .1. 57 25iAmmonia ----------- 15 28 --- -- n---ecane- n----- -1 2 75 3 5. -16 [ 210n-Amyl acetate- 1. 0 1 7. 1 I 25 36 ).iutrium ---------- 4. 1 75 -............

n-Arnyl alcohol ------ 1 1. 4 1 10 r 38 00) l)iborat -.-----.--.. - • - .8 88tert-Amyl alcohol __._ - 1.4 --------------- *135 Dies fuel (6)ce ahz) . _ .. [ "2,

n-Ainyl chloride..- .. - 1. 6 1 8. 6 260 l)icth I :,ri- -.- . 8 Iten-Amyl chloride. -.. '1. 570 2 l34l5vl ,, A t 1 - _ 8 .130

0 ' y yll - 1 75 - - 1430Amyl nitrite_ 1 0 1- . _- xI2 ( -lyl y7 . .. .- '7 24160n-Amyl propionae- 0. 7)ie hy] (,t(hr-Anylene----------- 1. 4 7 275 1) l)h.0 p3l i)eot 7 .------- 290Aniline- .---------- 7 2 .3 615 I), 'hy' 1 ,"_ . ; 450Anthracene ---------- 4 .65 ..... . 5,10 Di , , ht c) .i,,ol__ t ., o i, I .

n,-Amyl nitrate- ... 1.1 . .. !)5 l)s,, ,utyl ki'-. G .Benzene ------------ - 1.3 7 . . 5l' 2-4, 1 ,.eyvit, .... 1-'20Benzyl benzoate_.. . 4 .... ... J * - 4Si l)uisop , x x 1h.r- _Benzvl chloride-------' 1.2 ,.. l)wthyi ,, I - -11)Bicyclohe-xyl---------- 65 5. 1 24,5 2 )i't-hc *ln- I 2 _.1 2Bilihenyl-------- -----. 70 --- . I 110 .4 .;3-0inethy. . ie o j

2fiielini d4. 8 1-- CIO im-I by) hIe- d 2: 15Promobnzen --------- 1. 6 - ,h. , :,.

Butadiene (1,3) ... . 2, 0 12 42o iWO..n-Butae-- ----------- 1.8 8.4 I 40 ..iii 1hy ,1-r 3. 35)1,3-Butandiol- ---------- 1 9 J 1 p , )irn (lhvi or.t-Butene-I ....... ...- 1. 6 1" 0 " - ---- 1.. s , .135Butene-2 ----- -- .... I ,7 9. 1 . . . 2,3-1) i !all, v 1. 1 :35n-Butyl acetate ....... 5 4 8. . 25 2, 2-,D31 Ipro),i l .I 151n-Butyl alcohol ....... 1. 7 ' 12 I " l), t a a liule - . 0 :05see-Butyl alcohol -. 1. 7 9.8 21 4)5 )imt I1-ulfoxid . .-- - - -tert-Butyl alcohol ' 1. 9 9. 0 1I 4SO J)ioxi , - -. . .. . 1 2 . .,)

tert-Butyl amine 1. 7 8. 9 3s0 1

N l)i , . .5 6. 1 - . 7

n-Butyl benze! -----. 82 1 5.8 _-- .110 I)tei.la,,ii. . ' 7

See tootnotem at end of table.

114

APPENDIX A 115

Limits of flam- Limits of flam-Imability (volume- inability (volume-

Combustible percent) TL AIT Combustible peicent) TL AIT(00C) (0 C) I__ T_- (_ (0 C)( ) (0 C)Los Ulf Lot U.

Dip henyl ether ....... 40.8 ......... 620 Methyl chloride ------- 4 7 - ----- ------Diphenyl methane . 7---------------- 485 Methyl cyclohexane_ 1. 1 6.7 ------- 250DiN~ yl ether -------- -1.7 27---------- Methyl cyclopenta-n-Do( ecane ---------- . .60--------- 74 205 diene -------------- 1.1..3 1 7.6 49 445Ethan --------------- 30 12.4 -130 515 Methyl ethyl ketone. 1.9 10 .............Ethyl acetate --------- 2 11 ------------ Methyl ethyl ketoneEthyl alcohol --------- 3. 3 1119 .. 365 peroxide ----------------------- -- 40 390Ethyl amine --------- -3.5.--------------- 385 Methyl formate ...... 5.0 23 ------ 465Ethyl benzene ------ '1. 0 1 6. 7 ------ 430 Methyl cyclohexanok_ ' 1.0 -------- ------ 295Ethyl 12hloride ------- 3. 8 -------- ---- " ----- Methyl isobutyl car-Ethyl cyclobatane --- 1. 2 7. 7.--------210 binol------------ -- 1. 2-------- 4 40 -Ethyi yclohexane_. 142. 0 146. 6 ------ 260 Methyl isopropenylE thyl cyclopertane_. 1. 1 6.7 ..--- 260 ketone ------------- 1.8 '9. 0 -----------Ethyl formate ------- -2.8 16 ------ 455 Methyl lactate --------- 1 2. 2 - -----------Ethyl lactate- --------- 1.5 ---------. 400 a-Methyl naphthalee '.8 -......-.....-- 530Ethyl met captan .... 2. 8 18 I--.. 300 2, Methyl pentane_--_ 41.2 -------------------Ethyl nitrate ---------- 4 0 --------- I Methyl propionate.--- 2. 4 13 -----------Elhyl nitrite- .. 3. 0 50 ---------- Methyl propyl ketone-, 1.6 8-2 ----------Ethyl propionate - - 1.8 11 ... 440 Methyl .tyrene ------- 41.0 -------- / 49 495

Ethyl propyl ether - - 1 7 1 9 - ----- Methyl vinyl ether. __ 2. 6 39 ------Ethylele ......---- 2. 7 36 - 490 Methylene chloride--- -------- --------- ------ 615Ethyleneimine --------- 3. 6 46 -- .320 Monoisopropyl bicy-Ethylene glycol- . 3.5 -------------- 400 clohexy- - - ,52 " 4. 1 124 230.2hylene oxide ------- 3. 6 100 ----- ----- 2-MonoisopropylFurfural alcohol-----, -1.8 in 16 72 390 biphenyl --------- 1) 53 3. 2 141 435Gasoline- Monoinethylhydra-

100/130------------1.3 7. 1 ------. 440 zinc------------------115/145 --------- 1. 2 7. 1 ------. 470 Naphthalene ------- 1 88 20 5.9

lycei.------- ---- -------- -------------- -- 370 Nicotine --------------- 1,751 --.. " -----------n-itcIptane --------- 1.05 6. 7 -- 4 215 Nitroethaie ------------ 3. 4 --------- 307-1leXIlecalI-- ----- - . 43 ------ 126 205 Nitro nethane -----------. 3 --------- - 33 -

-llexatle -- ---------- 1.2 7.4 -26 225 1-Nitropropane ----- 2. 2 --- 34n-llexvI alcohol ---. -I 1. 2 .............. 2-Nitropropane ------- 2. 5 --- 27,-ll l ether . . .6 .4. 185 n-,oan --- - 21. .5 ----------- 3 2051llyhazie. .4. 7 100 -----------4: n-Octane ------------ 0. 95 --------- - 13 220l ,drogil........ 4. 0 5 400 l'araldehyde ------------ 1. 3 --- - --.... --

llvdrogen cyaii(ie___ 5.6 46 -- - -Pentahorane -....... 42 --------- -- -- ....... .4 4- -.... ... . 1.4 7. 8 -A8 260

lsa-It anl (ti't 1. 1 1 7. 1 25 360 'entaon.tilene I- Ilsoialn ii(tl] I ,. I .I 350 eol-.....-------- 335lolta. ,.. -- 81 401 Plitlalic aiodridc . 2 2Is(ohilvi llvolol . 1. 7 '11 .........- 3-Picoline ------------ 4 1.4 ------- ---------- 5t0[SlAt vl hiW llo( -6 9, 43 - - - 0 .i l.l.allt -- ------------------ 2 3 . 74 23 7. 2Iulit vi fu-lia, 2. 0 S. 9 - 'ropadicniw, . 1- 2. 16Isb vi', . , 1. 8 1. . . . .. . l'ro _ ... ... . . . 2. 1 .,5 1 )2 450lsfn-r,- I. 4 . . . . 1,2-1'ropanditl I - ' 2.5 . - - . 410

--- -- ---.. .. . .. . .-U l /-}'ropiolaetoie 2. ii4,, .7 .I r i tlhhyd. 2. 9 17

:dd l . 2 .. .t-I yl acetiate._ 1. 1I,. 'pr()o 'l tdhilil iyl 4 . j It .. . . t 1 -Prop~y l' , h l _l 1.2 2. '2 ' 1.1 - ' w o.1.vI fi l: l'rp It ttiine ,

ii i.: , _ - 210 l'rj, yl ,hlori,ic-_ 2. 4_6ii _ - -230 t-Kj,'l nitrate- I . 8 100 21 175

K i .,si . . - . 2111 i'r,+ l!1h11 . " . 1 .4 I 460M' i ,1. ii 1 5 187 54 0 rou; I. 1], hi 3. 1\h-!110 v,.All 3. 1 f; 44_ .'ri,, nl i. Ityol : 2. 4i

Nio 'li v,',' Ir. l. .. III Ou I i' ..-l', - i ,. . '1 .0 ;7 . . .N11" 11 tI i hIA t- C 0 NA 1 , 2 17

,h0 ;N-1' U..,~ ,.u 1 12

M cI i i : t1111w 4- . 2 1! - I -2 - - .. . .. 2..N(l' It- i i - ._ t(------ 2 , t ~ .- E{( 'p1 t]L-IV I -lc-)ht . '. 53. . 5Q it rtii 1- . ... 1 (I........3- M ,vI vl I )[ ,I .. on I~ I 1 5 1 St , v I,.- , " 2 I. 1 . .1. , %1 l' ,ut kelm w), 1. l 2 0 S.1 . . illfi," l '2. 0 - 2.17

, jj c ,'i )1\,, 7 ' 2. 5 "2( ... 3"'11 ,-T ,.orl~ ,\I _ I v. ) I. . ... M ; ,,.L 'I vIo ).l l ', )" v - it, kt -tr ll.,. . : *.5 . _. 2

i 1 I ' . . . . 1. 7 -.. . 46I

11 % l'' , \,1h',,filralc . . 2 (0

.,ithi IthYl ,th.r _ 2. 2 . ------. rait........... ... - 5. o 71 315s,, iii I/tntes ti t end of table.

116 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

TABLE A-I. Summary of limits of flamma-bility, lower temperature limits (TL) andminimum autoignition temperatures (AIT) ofindividual gaves and vapors rn air at atmosphericpressure- Contiaued

Limits of flam-mability (volume-

Combusible percent) T, AIT(0C) ( 0 C)

L,.. U,__ ,

,2,3,3-Tetrmnethylpentane ----------- 0. 8 --------------- 430

Tetramethylene gly-col ... --------- ------ 390

Toluene ------------ 1.2 '.7.1 ------- 480Trichloro~thane ------ ---------I ----------- 500Trichlo=oethylene -_-- 24 12 26 40 30 420Triethyl amine ------ 1.2 8. 0 ....--Triethylene glycol. . 9 2 9.2 ------------2,2,3-Trimethyl bu-

tane ...------------ 1.0 -------------- 420Trimeth;yl amine .... 2. 0 12 -----------2,2,4-Trimethyl pen-

tane -------------- .95 -------------- 415Trimethylene glycol - 1.7 -------------- 400Trioxane ------------ 3.2 --------------- -----Turpentine ------.. '.7 ............Unsymmetrical di-

methylhydrazine_- 2. 0 95 -----------Vinyl acetate -------- 2. 6 -------------------Viniyl chloride ------- & 6 33 ..----......m-Xylene ----------- 1.1 3.4 ------- 530o-Xyene------------ 11.1 16.4------ 465p-Xylene ----------- ' 1.1 '6.6 ------- 530

1 t:100* C, 1:1-0: C. : t-:43* C.i-47* C. 12g.-530 C. Ug195* C.8 tm75* C. C. t~ (- 1 m60

o C.

4 Calclated. . t-130 C. 2 4-96 C.t-60* C. 1 1-72* C. Ist70O C.

4 t-850 C. Is t-117o

C. U 9 -29 C.1- 140. C. 9T - 125o C. C .- 247

o C.

'1-160O0 C. "t-2000 C. "-0 C.

t-110. C. "-78o C. 1 '-203° C.

"t-17*6 C. t-122* C.

APPENDIX BSTOICHIOMETRIC COMPOSITION

N, 0 0.25 0.50 0.75The stoichiometric composition (C,,) of a .. - -

combustible vapor CnH.O\Fk in air may be ------------ 1. 87 1. 83 1. 79 1. 75obtained from the equation 12 ------------- 1. 72 1. 68 1. 65 1.62

13 1.59 1,56 1.53 1.50m k2X14 --------------- 1. 47 1,45 1.42 1.40

CH OxFFk±+ .+ - A 2 O--CCO2 15------ 1. 38 1.36 1.33 1. 3116 ------------- 1.29 1.27 1.25 1. 2417 ------------- 1. 22 1.20 1.18 1. 17

rn-k 18 -------------- 1. 15 1. 13 1.12 1. 10H2O+kHF. 19 ....------------ 1. 09 1. 08 1. 06 1. 0520 ------------- 1.04 1.02 1.01 1.0021 -------------. 99 .98 .97 . 9522 -------------. 94 .93 .92 .91

100 23 -------------. 90 .89 .88 .87Thus, C,,= - - volume-per- 24 -------------. 87 .86 .85 .841_ A.73 jn -k-2X') 25 ------------- 83 .82 .81 .81

1+4.773 4 26 --------------. 80 .79 .78 .7827 ------------- .77 .76 .76 75cent, where 4,773 is the reciprocal of 0.2095, 28 -----------. 74 .74 .73 72

the molar concentration of oxygen in dry air. 29 -------------. 72 .71 .71 .70The following table lists the values of C,, for 30 ------------- . 69 .69 .68 68a range of ( m-k-2X) values from 0.5 to m-k-2 I I I Ihe

30.75: 4 1 N-n+ 4 ; where n, m, X, and k are thenumber of carbon, hydrogen, oxygen, and halogen atoms,

N 1 0 0.25 0.50 respectively, in the combustible.

___-- -For example, the stoichiometric mixture com------------------- 29.53 121.83 position of acetyl chloride (C 2H 3 0CI) in air

1--------------17. 32 14. 35 12. 25 10. 69 may be found by noting that2 -------------- 9.48 8.52 7. 73 7.083 -------------- 6.53 6.05 5.65 5.29 nm -k-2X 3-1-24 -------------- 4.97 4. 70 4.45 4.22 N=n+. 205 -------------- 4.02 3.84 3.67 3.51 2=46 -------------- 3. 37 3. 24 3.12 3.017 -------------- 2. 90 2. 81 2. 72 2. 63 The entry for N=2.0 in the preceding table is8 -------------- 2.55 2. 48 2.40 2. 349--------------2. 27 2. 21 2. 16 2. 10 9.48 volume-percent, which is the value of C,,10 .------------- 2. 05 2. 00 1.96 1.91 for this combustible in air.

117

APPENDIX CHEAT CONTENTS OF GASES

(Kcalimole I)

T, - K CO, H,O O, N,

298. 16 0 0 0 0300 .017 .014 .013 .013400 .941 .823 .723 .709500 1.986 1.653 1.4541 1.412600 3. 085 2. 508 2. 2094 2. 125700 4. 244 3. 389 2. 9873 2, 852800 5. 452 4. 298 3. 7849 3. 595900 6.700 . 238 4.5990 4.354

1,000 7. 983 6. 208 5. 4265 5. 1291,100 9.293 7.208 6.265 5.9171,200 10.630 8 238 7. 114 6.7171,300 11.987 9.297 7.970 7.5291.400 lM 360 10. 382 & 834 8. 3491,500 14.749 11.494 9.705 9. 1781,600 16. 150 12.627 10.582 10.0141,700 17. 563 13. 785 11.464 10. 8571,800 1& 985 14. 962 12. 353 11. 7051,900 20. 416 16. 157 13. 248 12. 5592,000 21. 855 17. 372 14. 148 13. 4172,100 23. 301 18. 600 15. 053 14. 2782,200 24. 753 19. 843 15. 965 15. 1442,300 26.210 21. 101 16. 881 16.0122. 400 27. 672 22. 371 17. 803 16. 8842.500 29. 140 23. 652 18. 731 17. 758

I Gordon, J. S. Thermodynamics of High Temperature Gas Mix-tuuan-d Application to Combustion Problemn. WADC TechnicalReport 57-33, 3anuary 1967, 172 pp.

118

APPENDIX DDEFINITIONS OF PRINCIPAL Symbol: filcua eigtiUof

SYMBOLS M-----Mach number.No,--,----Equilibrium mixture of NO 2 and

Symbol: Definition NO at a specified temperature*A--------Constant. and pressure.*'--------Avea. n ---------- Number of moles.a ---------- Velocity of sound. P----lresmire.B--------- Constant. P --------- Maximum pressure.C., ------- tStoichiometric composition. n~P-------Pressure rise.

-H------Heat of combustion. p ---------- Partial pressure.K --------- Ratio of duct area to vent area.S----- Burning velocity.k -------- T hermal conductivity. T -------- Absolute temperature.L -------- Lower limit of flammability. t----------T- emperature.

-*-----Modified lower limit value. r- -- -- - -- Tme delay before ignition.LA-------Average carbon chain length for U -------- Upper limit of flammability.

paraffin hydrocarbons arnd correla- U -------- Upper limit of flammability at P0 C.tion parameter for aromatic hy- V -------- Volume.drocarbons. V'--------Critical approach velocity.

------ Lowe(r limit of flammability at io C. v ---------- Liquid regression rate./ID ------ Length to diameter ratio. ------- Specific heat ratio.

119

SUBJECT INDEXA PaeHPg

Acetaldehyde --------------------------- 73 Hlalogenated hydrocarbons -------------- 102AkaietIIIV hydrocarbons ------------------------ 53 He~at of formation-_ - -- ------------------ 51Airf1'1!_ ratio--------------------------------- 21 Pi-lleptane ------------------------------ 21.25, 35Alcohols----------------------- ------------- 6(5 Heterogeneous mixtures---------- ------------- 3Aldehydes ------------------- ----------------- 73 n-llexadecanm-------------------------------21, 25Ammonia------------------------------------ 77 Yi-llexano ------------------------------- 21, 25.,34n-Ainyl alcohol ------------------------------- 6 7 n-ll&'Xy.l floo------------------7Aromatic hydrocarbons------------------------ 511 Hydraulic fluids --------------------------- 9Autoignitlon------------------------------ 4,32,41 Hiydrogen ---------------------------------- 77, 89)

B Hydrogen peroxide.---------------------------1Barrcades----------------------------------- 17 1Blast pressure --------- ----------------------- 16 Ignition ----------------------------------Burgess-Wheeler law ------------------ -------- 22 Ignition. temperature -------------- ------------ 4Burnling velocity.--------------- - -- - - -4), 45 Ignitihility limits -------------------------------Butadiwne --------------------------------- 48,53 Inertial is------------------1n-Butane ------------------------------- 21, 25, 32 Isobutylene----------------------------------- 48Butene-1-------------------------------48,50,52n-Butyl alcohol ------------------------------- 671tert-Butyl alcohol ----------------------------- 68 JP-4 ------------------------------------- 11,88

o KCarbon chain--------------------------------- 41 Kerosine -------------------------------------- 7Carbon monoxide ---------------------------- 97 Ketones------------------------------------- 73Combustion equations-------------------- 21, 117Contact time_---------------------------------4 LCool flames ---------- ------------------------ 28 Layering ------- ------------------------------ 3Copper acetylide ------------------------------ 56 Le Chatelier's law ----------------------------- 31Critical CIN----------------------------------11 Limits of flammability ------------------------- 2Cyclopropane --------------------------------- 64 Liquid mixtures ------------------------------- 31

Lower limit ---------------------------------- 2D Low pressure limits ------------------------- 12,89n-Decane---------------------------------- 21,25Decane-dodecane blends --------------------- 32, 43 MDeco.nposition-------------------------------- 5A Methane ------------- ---------------------- 9,21Deflagration --------------------------------- 15 Methyl acetylene --- _--------------------------5)Detonation -------------------------------- 16, 57 Methyl alcohol --------------------------- - 6i)7Dimethyl ether ------------------------------- 70 Methyl bromide ------------------------- --- 21N, 61n-Dodccane ------------------------------- 21,25 3-Methyl butene-1 ---------------------------- 48

E Mehyl formate ------------------------------ 71JE Methylene bistearamide ------------------------ 7Enigine oils ----------------------------------- 95 Mlethylene chloride-------------------------- 102Esters - - ------------------------------------ 70 Minimum oxygen value-------_.- --.- -- ------ 1Ethane -------------------------------- 21, 25, 28 Mists -------------------------------------- 3, 6Ethers-------------------------------------- 69 MIixer-------------------------------------- 4,7

Eth' alcohol --------------------------------- 672-Ethyl butanol ------------------------------ 67 NEthylene----------------------------------- 48, 52 Natural gas------------- ------------------- 27, 30

F n-Nonane --------------------------------- 21, 25Flame arrestors ------------------------------- 18 0Flame caps ----------------------------------- 2 n-Octane ---------------------------------- 21, 25Flame extinction ------------- _----------------29Flammability characteristics ------------------- 20Foam --------- ------------------------------- Paraffin hydrocarbons ----------------------- 2(0, 3Formic acid ------------ ---------------------- 61 n-Pentadecane ---------- ---------------------- 21Freon-12------------------------------------ 69 ?entane----------------------- -------------- 24Fuel-air ratio --------------------------------- 21 n-Pentane ------------------------------ 21, 25, 33Fuel blends ---------------------------------- 74 Perfluo-ometha--- -------------------------- 28

Perfluoropropane ----------------------------- 28G Peroxides------------------------------- 53, 70, 103Gas freeing--------------------------------- 13 Predetonation distance---------------------- 57Gas mixtures --------------------------------- 3 Pressure piling - - - ---------------------------- 58Gasoline ---------------------------------- 13, 82 Propadiene -------------- -------------------- 48

120

SUBJECT INDEX 121

Page PagePropane .......................... ------- 21, 25, 31 Sulfw compounds -----. . . . . . 74Isopropyl alcohol ----------........ .......... 115 Sulfur hexafluoride -------...................... 28n-irropyl alcohiol ----------------------------- 67n-Propyl nitrate -------.--------------------- 97 TPropylene ----------.------------------------ 48,51 Temperature limit --------------------------- 11

n-Tctradecane ----------------------....- ---- 21Q Tetralin ------------------------------------ 7

Time delay- ........ ..-------- 4Quantity-distance relationships --------------- 95 Town gas --------------.------------------ 19Triangular diagram -------------------------- 9

Trlchloroethylene ----------------------------- 102R n-Tridecane --------------------------------- 21

Raoult's law -----------.-------------------- 31 Tube diameter ------------------------- 3,53,57Rectangular diagra ------------------------ 9Rc.gression rate- -..------.-------------------- 44 URelief diaphragms -------------------------- 18 n- Undecane ------------------------------ 21

Unsaturated hydrocarbons ...--------------- 47S Upper limit --------------------------- 2, 23, 26

Shock wave ------------------------------- 17 WSpark-energy requirements ------------------- 3 Wall quenching ----------------------------- 3Spontaneous ignition -------------------------- 3Spray injection ----------------------------- 97 XSprays ..--------------------------- ------ 6 o-Xylene ----------------------------------- 60

* U.S. GOVERNMLNT PRINTING OFICE. 1965 O-761 .-