Report of the Committee on

Handling and Conveying of Dusts, Vapors, and Gases

Murray A. Cappers, Jr., Chair J&H MArsh & McLennan Inc., NJ [I]

Joe IL Barton, Indianapolis, IN [U] Krls Chatrmhi, Fike Corp., MO [M] John M. Cholin, J M Cholin Consultants Inc., NJ [SE] David G. Clark, The DuPont Co., DE [U] Ralph E. Collins, R E Collins Assoc., MA [SE] C. James Dahn, Safety Consulting Engineers Inc., IL [SE] Vahld Ebadat, Chilworth Technology Inc., NJ [SE] Walter L. Frank, EQE Int'l Inc., DE [U] Henry W. Garzia, Fenwal Safety Systems/Williams Holdings, MA [M] RayE. George, The Chemithon Corp., WA [M] JRoseph P. Gillis, Westboro, MA [SE]

ay Hunter, Ray Hunter & Assoc. Inc., AL [M] Rep. American Air Filter

JBeavr~ldJ. Jennett, Georgia Gulf Sulfur Corp., GA [M] C. Kirby, Union Carbide Corp., WV [M]

James E. Maness, Bunge Corp., MO [U] Rep. Grain Elevator & Processing Society

Guillermo A. Navas, Sheet Metal & Air Conditioning Contractors' Nat'l Assn., VA [M]

Robert W. Nelson, Pocasset, MA [I] Rep. HSB Industrial Risk Insurers

Gary A. Page, American Home Products, NJ [M] mes L. Roberts, Fluor Daniel, Inc., SC [SE] chard F. Schwab, AlliedSignal Inc., NJ [U]

William J. Stevenson, Cv Technology, Inc., FL [M] Lynn IL Underwood, Wausau HPR Engineering, WI [I] John Vallulls, Factory Mutual Research Corp., MA [I] Harold H. Weber, Jr., The Sulphur Inst., DC [U]

(Vote Ltd. to 655) W. H. White, White Consulting Services, OH [SE]

Rep. TC on Finishing Processes

Alternates

Ted Brown, Int'l Sulphur, Inc., TX [M] (Alt. to J. J. Jennett)

Henry L. Febo, Jr., Factory Mutual Research Corp., MA[I ] (Ait. toJ. Valiulis)

Paul F. Hart, HSB Industrial Risk Insurers, IL [I] (Alt. to R. W. Nelson)

Gregory I. Hurst, Nat'l Starch & Chemical Co., IN [U] (Alt. to J. IL Barton)

Robert A. Koebler, Wausau HPR Engineering, TX [I] (Alt. to L. IL Underwood)

Bernadette N. Reyes, Safety Consulting Engineers, Inc., IL [SE] (Alt. to C.J. Dahn)

John H. Stratton, Sheet Metal & Air Conditioning Contractors' Nat'l Assn., VA [M] (Ah. to G. A. Navas)

Nonvoting

Harry Verakls, U.S. Dept. of Labor, Mine Safety & Health Admin., WV

Staff Liaison: Guy It. Colonna

Committee Scope: This Committee shall have primary responsibility for documents on the prevention, control, and extanguishment of fires and explosions in the design, construction, installation, operation and maintenance of facilities and systems processing or conveying flammable or combustible dusts, gases, vapors and mists.

This list represents the membership at the time the Committee was balloted on the text of this edition. Since that time, changes in the membership may have occurred. A key to dasxificatio~s is found at the front of this book.

The Technical Committee on Handling and Conveying of Dusts, Vapors, and Gases is presenting two Reports for adoption, as follows:

Report I: The Technical Committee proposes for adoption a withdrawal of NFPA 650-1998, Standard for Pneumatic Conveying Systems for Handling Combustible Particulate Solids. NFPA 650- 1998 is published in Volume 7 of the 1999 National Fire Codes and in separate pamphlet form.

NFPA 650 has been submitted to letter ballot of the Technical Committee on Handling and Conveying of Dusts, Vapors, and Gases, which consists of 25 voting members; of whom 22 voted affirmatively, and 3 ballots were not returned (Messrs. Dahn, Maness, and Valiulis).

Report lh The Technical Committee proposes for adoption a complete revision of NFPA 654-1997, Standard for the Prevention of F'we and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. NFPA 654-1997 is published in Volume 7 of the 1999 National Fire Codes and in separate pamphlet form.

NFPA 654 has been submitted to letter ballot of the Technical Committee on Handling and Conveying of Dusts, Vapors, and Gases, which consists of 25 voting members. The results of the balloting, after circulation of any negative votes, can be found in the report.

118

N F P A 6 5 0 / 6 5 4 - - M A Y 2 0 0 0 R O P

NFPA 650 (Log #CP1)

650- 1 - (Entire Documen t ) : Accept SUBMITTER: Technica l Commi t t ee on Hand l ing and Conveying of Dusts, Vapors, and Gases

I RECOMMENDATION: The Commi t t ee proposes to withdraw NFPA 650, S tandard for Pneumat i c Conveying Systems Hand l ing Combust ib le Particulate Solids. SUBSTANTIATION: Portions of NFPA 650 have been incorpora ted into th~ p roposed comple te revision of NFPA 654, Standard for the Prevent ion of Fire and Dust Explosions f rom the Manufac tur ing , Processing, and Hand l ing of Combust ib le Particulate Solids. COMMITTEE ACTION: Accept.

NFPA 654

(Log #CP1) 654- 1 - (Entire d o c u m e n t ) : Accept SURMITTER: Technica l Commi t t ee on Hand l ing and Conveying of Dusts, Vapors and Gases

] RECOMMENDATION: T he Commi t t ee proposes a complete I revision of NFPA 654, S tandard for the Prevention of Fire and Dust I Explosions f rom the Manufactur ing , Processing, and Handl ing of I Combust ib le Particulate Solids, to inc lude por t ions of NFPA 650, [ S tandard for Pnuema t i c Conveying Systems for Handl ing I Combust ib le Particulate Solids, which is be ing withdrawn. The I revised d o c u m e n t is shown at the end of this report.

SUBSTANTIATION: T h e combina t ion of NFPA 650 and 654 el iminates r e d u n d a n c y between two similar s tandards. It provides a uni f ied approach for pro tec t ing facilities tha t hand le mos t combus t ib le par t iculate solids.

The p roposed revision adds specific criteria related to fire protect ion in addi t ion to the existing explosion protect ion requ i rements . COMMITTEE ACTION: Accept. NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 25 VOTE ON C O M M I T T E E ACTION:

AFFIRMATIVE: 21 NEGATIVE: 1 NOT RETURNED: 3 Cappers, Hunter , Roberts

EXPLANATION OF NEGATIVE: MANESS: Most of the s tandard is good, however, some is too

theoretical and may no t be achievable by industry. For this reason, and those listed below, I am voting negative on these proposals.

1. 1-1.3 - Shall no t apply to facilities covered by NFPA 36. Can this be changed editorially?

2. 2-2.3.1 and related append ix material and 2-4.1. This material is theoretical and may no t be achievable in many situations. The material does consider dus t that becomes wet and sticks to surfaces. Further, it suggests tha t 50 pe rcen t of a 1 /32 inch layer (.015 inches) over 5 percen t of the surface is sufficient for an explosion to propagate or occur. This criteria is very theoretical and will only put operators at risk for authori t ies having jur isdic t ion ru l ing that they have violated the s tandard. In reality, when dus t explosions occur due to poor housekeep ing , the levels far exceed those sugges ted in these provisions. In some facilities, this level of cleanliness may be considered good u n d e r some condit ions. Requi r ing vent ing to be placed on rooms or buildings for these same reasons is also excessive. This whole issue needs to be recons idered by the commit tee .

3. 2-3.2, 2-3.3, 3-2.4. T he re are many port ions of a bui lding such as a built in surge bin or receiving h o p p e r tha t canno t and do not need to be c leaned of dus t accumulat ions . They may be too small to en ter and are des igned to hold dus t or bulk powdered products , therefore they should no t be requi red to be c leaned of dus t accumulat ions . This, too, is a theoretical s tandard that may not be achievable in many cases.

4. 3-2.1, 3-2.6. It shou ld be made clear tha t these provisions do no t apply to scale or surge bins used to feed processes with materials.

5. 3-2.7. Such vent ing requ i rements are no t practical to be m a n d a t e d in large s t ructures with a large he igh t to d iameter ratio. This material shou ld be advisory a n d placed m the appendix . COMMENT ON AFFIRMATIVE:

NAVAS: It seems conflict ing to list in Section 9-1, NFPA Publications, a n u m b e r of d o c u m e n t s also listed as exclusions in Section 1-1.3. [9-1 indicates: "The following d o c u m e n t s or por t ions the reof are re ferenced within this s t anda rd as manda to ry ...," while 1-1.3 indicates "This s tandard (NFPA 654) shall no t

ol~lAY to materials covered by the following:", t hen lists various d o c u m e n t s also found in Section 9-1, a m o n g o ther

d o c u m e n t s which are properly referenced.] The following is an up-to-date list of various SMACNA

documen t s listed in the Appendix: Sheet Metal and Air Condi t ion ing Contractors ' National

Association, Inc., P.O. Box 221230, Chantilly, VA 20153-1230. • SMACNA. Accepted Indust ry Practice for Industr ial Duct

Construct ion, First Edition, Shee t Metal and Air Condi t ion ing Contractors ' National Association, Inc., Cbantilly, VA. 1975.

• SMACNA. R o u n d Industrial Duct Cons t ruc t ion Standards, First Edition, ibid. 1977.

• SMACNA. Rectangular Industrial Duct Const ruct ion Standards, First Edition, ibid. 1980.

• SMACNA. Thermoplas t i c Duct (PVC) Const ruc t ion Manual , Second Edition, ibid. 1995.

• SMACNA. T h e r m o s e t FRP Duct Cons t ruc t ion Manual , First Edition, ibid. 1997.

NELSON: With regard to the draft of NFPA 654 dated 1 / 2 8 / 9 9 the following are s o m e c o m m e n t s for considerat ion.

1. The most major c o m m e n t is the change in the defini t ion of "deflagration." The addi t ion of the phrase "or radiant flux per uni t of time" has m u d d i e d the use o f the words "deflagration: an d explosion." For example, in 2-2.2.2 the phrase "dust def lagrat ion hazard" is used while in 2-2.3.1 the phrase "dust explosion hazard" is used. The only appa ren t d i f ference is the radiant flux condi t ion which is a n o t h e r word for fire and is, in my opinion, confus ing to the user. This is bu t one example of the mixed usage of the two words in the s tandard . I believe the def ini t ion of def lagrat ion should be b rough t up at the nex t NFPA 68 mee t ing and resolved so tha t we can editorially correct NFPA fi54.

2. I f ind 2-1.4 to be r e d u n d a n t with 6-6.1 and suggest its e l iminat ion.

3. In 2-4.2 the t e rm "vent closure" is used. The re is a d e f l a t i o n for this t e rm in NFPA 68 which I feel shou ld be added to the NFPA 654 definitions.

4. In 3-3.3.1 the phrase "dilute phase pneuma t i c conveying systems" is used. This system type has no t been def ined and shou ld be in order to make clear to which systems the subsequen t sections apply.

5. In 3-5, LFL is no t descr ibed nor is the re a def ini t ion for LFL. Similarly MEC shou ld have the words " m i n i m u m explosible concent ra t ion" used.

6. In 3-10.9 the "or" between tempera tu re and vibration should be an "and."

7. In 3-13.1.7 recirculafion of air hand l ing hybrid systems is permit ted. This will allow for the bui ldup of the percentage of f l ammable vapor in the system. The commit tee needs to a m e n d dais sect ion to prohib i t recycling of f l ammable vapors.

8. In 3-13.2.3.5 explosion pressure and its symbol are used but are no t defined. Suggest that the defini t ion f rom NFPA 68 be added to the def ln iuons section.

9. In 3-18.2~ Exception, there needs to be an exclusion for materials that liberate a f l ammable vapor or gas. In this case the drying med ia shou ld not be recycled.

10. In the defini t ions section, 1-5, the following defini t ions do no t appear to be used in the s tandard and shou ld be removed:

Booster Fan Detonat ion F lammable limits t%, Relay Fan Replacement- in-kind Wall protector

(Log #CP3) 654- 2 - (1-5 Deflagrat ion): Accept SUBMITTER: Technical Commi t t ee on Hand l ing and Conveying of Dusts, Vapors and Gases RECOMMENDATION: Revise the defini t ion of Deflagration to read as follows:

"Propagat ion of a combus t ion zone th rough a pre-mixed fue l /oxid izer mix ture at a rate that is less than the speed of so u n d in the unreac ted m e d i u m , p roduc ing a significant increase in pressure or radiant flux per uni t of time."

119

N F P A 654 - - MAY 2 0 0 0 R O P

SUBSTANTIATION: The existing definition had no lower limit for combustion propagat ion which limited its usefulness. The proposed definit ion addresses that issue by including criteria for overpressure and radiant flux, making it useful for the entire fire

rotect ion community. OMMI'I ' rEE ACTION: Accept.

NUMBER OF COMMr['rEE MEMBERS ELIGIBLE TO VOTE: 25 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 20 NEGATIVE: 2 NOT RETURNED: 3 Cappers, Hunter , Roberts

EXPLANATION OF NEGATIVE: GILLIS: The definit ion of Deflagration r e c o m m e n d e d in

Proposal 654-2 (Log #CP3) does no t establish a lower limit for combustion propagat ion as claimed in the substantiation. A wood crib fire in a closed volume or the effect of puffing on a l ighted cigarette would qualify as deflagrations under this definition. Also, the word "significant" is a vague qualifier and cannot be measured.

I r e c o m m e n d the following definition: Deflagration: Propagation of a combustion zone through a pre-

mixed fuel /oxidizer suspension at a rate that is less than the speed of sound in the unreacted medium.

NELSON: See items 1 through 10 in my comments on affirmative ballot on Proposal 654-1 (Log #CP1).

(Log #CP4) 654- 3 - (1-5 Hybrid Mixture): Accept SUBMITTER: Technical Commit tee on Handl ing and Conveying of Dusts, Vapors and Gases RECOMMENDATION: Revise the definition of Hybrid Mixture to read as follows:

"A mixture of air and combustibles, that contains combustibles of different physical states." SUBSTANTIATION: The proposed definit ion is a broader, more inclusive description which includes hybrid mixtures as covered by this s~.ndard as well as those covered by o ther NFPA Standards (e.g., NFPA 68 and 69). In addition, it provides consistency with both existing a n d p r o p o s e d European standards. COMMITTEE ACTION: Accept. NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 25 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 22 NOT RETURNED: 3 Cappers, Hunter , Roberts

(Log #CP2) 654- 4 - (1-5 Wall Protector (Shield)): Accept SUBMITTER: Technical Commit tee on Handling and Conveying of Dusts, Vapors and Gases RECOMMENDATION: Revise the definition of Wall Protector (Shield) to read as follows:

"Noncombust ible surfacing applied to a wall area for the purpose of reducing the clearance requirements between the wall and a heat-producing appliance." SUBSTANTIATION: Editorial. The word "requirements" was added to clarify what was being reduced. COMMITTEE ACTION: Accept. NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 25 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 22 NOT RETURNED: 3 Cappers, Hunter, Roberts

COMMENT ON AFFIRMATIVE: DAHN: Not clear. NELSON: See items 1 through 10 in my comments on affirmative

ballot on Proposal 654-1 (Log #CP1).

(Log #1) 654- 5 - (3-1.2.1 Exception No. 3 (New)): Accept in Principle in Part SUBMITrER: John Valiulis, Factory Mutual Research Corp. RECOMMENDATION: Add a third exception to Section 3-1.2.1 as follows:

Exception No. 3: Isolation devices are no t required if an analysis is conducted of the extent and direction of expected explosion propagation, and the following three conditions are met:

(a) The analysis concludes that explosion propagat ion between nonisolated equipment would not increase the life safety hazard, and

(b) The analysis concludes that the cost of providing the explosion isolation would exceed 1/10 of the increase in property damage due to the propagation, and

(c) The study is documen ted and is acceptable to the authority having jurisdiction. SUBSTANTIATION: There are many cases when the lack of explosion isolation between two pieces of equ ipment would not increase the life safety hazard nor significantly increase property damage, for instance in cases where appropriate explosion protect ion is provided on all equipment . The standard should recognize such cases and exempt them from the need for isolation. The ratio of $1 spent on explosion isolation to save $10 of property damage is proposed as only one way to def ine a costzjustified protect ion feature. Other ways p roposed by your committee to define cost-effective improvements could be adop ted in plaize of the $1/$10 ra t ioproposed. COMMITTEE ACTION: Accept in Principle in Part.

Revise the proposed new third exception to Section 3-1.2.1 as follows:

Exception No. 3: Isolation devices are no t required if an analysis is conducted, that is documen ted and is acceptable to the authority having jurisdiction, and concludes that:

(a) Deflagration propagat ion between nonisolated equ ipment would not increase the life safety hazard, and

(b) Deflagration propagat ion between nonisolated equipment would no t cause unacceptable property damage or unacceptable interrupt ion of operations. COMMITTEE STATEMENT: This revision includes the intent of the submitter, but dele ted in item (b) the arbitrary limit for an acceptable level of property damage. Other changes were editorial. NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 25 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 22 NOT RETURNED: 3 Cappers, Hunter , Roberts

COMMENT ON AFFIRMATIVE: GARZIA: Should be 3-1.3.1, Exception No. 3. NELSON: 3-1.2.1 has no exceptions. I believe the item should

be numbered 3-1.3.1.

120

N F P A 654 ~ MAY 2 0 0 0 R O P

NFPA 654

Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling o f Combustible

Particulate Solids

2000 Edition

NOTICE: An asterisk (*) following the number or letter designating a paragraph indicates that explanatory material on the paragraph can be found in Appendix A.

Information on referenced publications can be found in Chapter 9 and Appendix D.

Chapter 1 General

1-1 Scope.

1-1.1" This standard shall apply to all phases of the manufacture, processing, blending, pneumat ic conveying, repackaging, and handl ing of combustible particulate solids or hybrid mixtures, regardless of concentrat ion or particle size, where the materials present a fire or explosion hazard.

1-1.2 This standard shall apply to systems that convey combustible particulate solids that are p roduced as a result of a principal or

deemed to reflect situations and the state of the art prevalent at the time the s tandard was issued.

Unless otherwise noted, the provisions of this documen t shall not apply to facilities, equipment , structures, or installations that were existing or approved for construction or installation pr ior to the effective date of the document , except in those cases where it is de te rmined by the authority having jurisdiction that the existing situation involves a distinct hazard to life or adjacent property.

1-4.2 This standard shall apply to facilities on which construction is begun subsequent to the date of publication of the standard. When major replacement or renovation of existing facilities is planned, provisions of this s tandard shall apply.

1-5 Definitions. For the purposes of this standard, the following terms and definitions shall apply.

Abort Gate/Abort Damper. A device for the quick diversion of material or air to the exterior o f the building or other safe location in the event of a fire.

Air-Material Separator (AMS). Any device designed to separate the conveying air f rom the material being conveyed. Examples include cyclones, bag filter houses, and electrostatic precipitators.

Air-Material Separator, Primary. A collector that removes the bulk of the product or material f rom the conveying air stream.

incidental activity, regardless of concentrat ion or particle size, where the materials present a fire or explosion hazard. Air-Material ~ . t o r , Secondary. A device for removing the

residual dust .~"p ' ro~Jct remaining in the air stream after the 1-1.3 This standard shall no t apply to materials covered by the primary a i r ~ r i a l separator following: .~i!: ~.:.=~ .... "

. . . . . . . . . . . . . . . . . . . . . . . . A i r - M . ~ . ~ D e ~ . ~ A M D ) . * A power-driven fan, blower, or l) r~rret ooD, t~oae jor me lvianujacrure and Storage oj ,tieroso~ o t h ~ t h a t e ~ i J s h ~ s an airflow bv movin~ a volume of air

Products p ~.:"~] nit d '~e. ':%.'-i'!~::.: ';=" (2) NFPA 61, Standard for the Prevention of Fires and Dust ~-.:::~.".:" ~-'.-. .:~i::"

Explosions in Agricultural and Food Products Facilities -~-:'i;/=:<~ro~* Acceptable to the authority having jurisdiction. (3) NFPA 120, Standard for Coal Preparation Plants "~".:iii.,..~ =• ~:. (4) NFPA 432, Code for the Storage of Organic Peroxide Formulations A u ~ Havin~lur isdic t ion * The ort, anization office or (5) N~..A 480,.Standard for the Storage, Handlin~ and Processing:~i..::~;=~== .... i n d i ~ " ~ o n ~ l l ~ l e for approving equipment , materialsl an

oj ~v.la.gne~um ~o~,aL~ - a n a rowaers . . . . . . . . %!i'iii~iii~!:.i!:=:=.~nstallatio)~:::'or a procedure. {.O) NIq'A 4~51., ~'tanaara. flor the rroaucrion, rrocessing, t~anatin~ "::-'==..:::.: ":':==..':=:::::=:=:::=~,-=========....====..:=======....:.,.;i=',-

and Storage of Titan,urn ":?:.::- "~4:"]ff~'r Fan See Relay Fan (7) NFPA 482 Standard or the Production, Processing, Hat~.~.n~ "~:L-:::-:-':~;=:" :~; . . . . . : '

and Storage of Zirconium fl :.':!!'~:::~!ii~. "~-i=. combus t ib le Dust.* Any finely divided solid material that is 420 • (8) NF.PA 485, Standard for the Storage, Handling, ~(~essin~i~nd '~iiii-=::~icrons or smaller in d iameter (material passing a U S No 40 t~seoj~a~n*umjwe~t . . . . . . . . ..-=~'~'=..-'.-:ii~'~ . . . . . . "i!::?:i:!~!~!i~::.... %.:#!~::"Standard Sieve) and presents a fire or explosion hazard when

! ~ ) N~y,~A4~5, l~plostveMat~ats,Code.. , ~ ' . . "'%=, .~i~i~i# ~:- ....... ~i::iiii::iii::i~.~ # " dispersed and ignited in air. kio) t,~rre~ oai, ~tanaara jor me 2vlacatmng ana rmtsatft~i~i.Og:. ":':':':"

Aluminum and the Production and Hand. ling ~ m i ~ .~.:.::. Combustible Particulate Solid.* Any combustible solid material, (11 ) NFPA 655, Standard for Preventwn ,.~.."Sulfur"~i;..and =::i!i#'::" composed of distinct particles or pieces, regardless of size, shape,

Explosions ~==-. ~:'-:!--"-'::'!-'. :=-:i -=':::" or chemical composiuon. Combustible particulate solids include • (12) NFPA 664, Standard for the P r ~ ! ! g f F i r e s aCi~ii~xplbsions dusts, fibers, fines, chips, chunks, flakes, or mixtures of these. m Wood Processing and Woodworking Facilit~.~::, ~!?? ( 1 3 ) N FPA 1124, Code far the.Manufacture, ~ . . ~ p o ~ ' o n , and Compartmentat ion. The interposing of a physical barrier that is 5"torage oj rtrewore.s, and Pyrotechnic Articles "~==.~4;==" no t required to be fire or .explosion resistant in order to limit

(14) NFPA 1125, Code for the Manufacture of Mdf.~•Rocka and combustible particulate solid migration and hence to control the High Power Rocket Motors size of a hazard area.

(15) NFPA 8503, Standard for Pulverized Fuel Systems

I-1.4 In the event of a conflict between this s tandard and a specific occupancy standard, the specific occupancy standard requirements shall apply•

1-2 Purpose . The purpose of this s tandard shall be to prescribe technical requirements for safety to life and property from fire and explosion and to minimize the resulting damage from a fire or explosion.

1-3 Equivalency. Nothing in this s tandard shall be interpreted as preventing the use of systems, methods, or devices of equivalent or superior quality, strength, fire resistance, effectiveness, durability, and safety over those prescribed by this standard, provided technical documenta t ion is submit ted to the authority having jurisdiction to demonst ra te equivalency and the system, method, or device is approved for the in tended purpose.

1-4 Retroactivity.

1-4.1 The provisions of this documen t shall be considered necessary in order to provide a reasonable level of protect ion from loss of life and proper ty from fire and explosion. They shall be

Deflagration. Propagation of a combustion zone th rough a pre- mixed fuel-oxidizer mixture at a rate that is less than the speed of sound in the unreacted medium, producing a significant increase in pressure or radiant flux per unit of time.

Detachment. The locating of a combustible particulate solid process in the open air or in a separate building.

Detonation. Propagation of a combustion zone at a velocity that is greater than the speed of sound in the unreac ted medium.

Dryer. A piece of processing equ ipment using tempera ture or pressure change to reduce the moisture or volatile content of the material being handled.

Duct. Pipes, tubes, or o ther enclosures used for the purpose of pneumatically conveying materials.

Dust Collector. See Air-Material Separator.

Explosion. The bursting or rupture of an enclosure or a container due to the deve lopment of internal pressure f rom a deflagration.

121

N ~ A 654 1 MAY 2000 R O P

Fire Barrier Wall. A wall separa t ing bui ldings or subdividing a bui ld ing to prevent the spread of fire a n d having a fire resistance rat ing and structural stability.

Fire Wall. A wall separa t ing bui ldings or subdividing a bui ld ing to prevent the spread of fire a n d having a fire resistance rating and structural stability.

F lammable Limits. T he m i n i m u m and m a x i m u m concent ra t ions of vapor in air below and above which propaga t ion of f lame does no t occur, usually expressed in te rms of percen t by volume of the vapor or gas in mr.

Hybrid Mixture.* A mixture of air and combust ibles that contains combust ib les of d i f ferent physical states.

Ksr The index of dus t explosibility def ined as

Kst=(dP//dt ) V 1/3 where V is the volume o f t h e test vessel and max

the value of (dP/dt)m= will be a m a x i m u m for a part icular dus t concent ra t ion , referred to as the "op t imum" concent ra t ion as de t e rmined in accordance with ASTM E 1226, Test Method for Pressure and Rate of Pressure Rise for Combustible Dusts.

Labeled. Equ ipmen t or materials to which has been a t tached a label, symbol, or o ther identifying mark of an organizat ion that is acceptable to the au thor i ty having jur isdic t ion and conce rned with p roduc t evaluation, that main ta ins periodic inspect ion of p roduc t ion of labeled e q u i p m e n t or materials, and by whose labeling the m a n u f a c t u r e r indicates compl iance with appropr ia te

Segregation. The in te rpos ing o f a fire and explosion-resistant barrier between the combus t ib le part iculate solid process an d o ther operat ions .

Separation. The in terpos ing of dis tance between the combust ib le part iculate solid process and o ther operat ions tha t are in the same room.

Shall. Indicates a manda to ry requ i rement .

Should . Indicates a r e c o m m e n d a t i o n or tha t which is advised but no t reqnired.

Spark. A moving particle of solid material that emits radiant energy due ei ther to its t empera tu re or the process of combust ion on its surface.

Standard. A documen t , the main text of which contains only manda to ry provisions us ing the word "shall" to indicate r equ i rements and which is in a fo rm general ly suitable for manda to ry re ference by ano the r s t andard or code or for adopt ion into law. N o n m a n d a t o r y provisions shall be located in an appendix , footnote , or f ine-print no te and are no t to be considered a part of the r equ i rements of a s tandard.

Wall Pro tec tor (Shield). Noncombus t ib le surfacing appl ied to a wall a rea for the purpose of r educ ing the clearance requ i rements between the wall a n d a hea t -p roduc ing appliance.

Water-Compatible .* A material that is ne i ther reactive with water nor i n c o m p a t i b i . . ~ t h water and consequen t ly can be ext inguished s tandards or pe r fo rmance in a specified manne r . with a wa te r -b . .~ i l : : :~ngu i sh ing system.

Listed.* Equ ipmen t materials, or services inc luded n a list .... #i!::ii!::, " publ ished by an organizat ion that is acceptable to the author i ty W a t e r - I ~ . b l e . * A material that does no t chemically react having jur isdic t ion and conce rned with evaluation of products or with w ' 4 t ~ ~ g o e s a change of phase or state u p o n mixture services, tha t main ta ins periodic inspect ion of p roduc t ion of listed with ~ ( " ~ a a t r e / i ~ , it pe rmanen t ly changed or incompat ible

. . . . . . . ~ : , / : ? . ' 5 2 ¥ ; : - ~ . . ' , : . : : . . ,:-:-: : :: ~

e q m p m e n t or matermls or pe rmthc eva luauon of servaces, and w ~ i : ~ e "f'~naander ~ - f ~ r o c e s s . whose listing: states that ei ther the e q u i o m e n t material or service ~::!?: ,.,. ~i~ ~::" meets appro~priate des ignated standa~rd~or has been tested and .... ~!i!i~gter- ,~.'~.a.ctive.* A:~a te r ia l tha t chemically reacts with water, found suitable for a specified purpose . " : : " p ' ~ " ~ ' ~ m e o ther c o m p o u n d that can represen t a different set

of i! otection concerns. Min imum Explosible Concent ra t ion (MEC).* T he m i n i m u m ~,. ~.:!::, ~.

concent ra t ion of combust ib le dus t s u s p e n d e d in air, m e a s u r e d in~:':.~..::'~::::,... "::~'..:.:":::'Chapter 2 Facility and Systems Design mass per un i t volume, tha t will suppor t a def lagrat ion as def ined '~f:!.:!~:..::,.., ,:ii:, !::" by the test p rocedure in ASTM E 1515, Standard Test Method for "!~i:. "':.ili~!ii"."i~ i'al. The provisions of this section shall apply to the Minimum Explosible Concentration of Combustible Dusts . . . . . ::~.:,.,.::s."is:'bve'i:i~'design of systems that hand le combust ib le part iculate

::.'.:~.~::':~.':'~ii:. "-~!:'.:;" liltS. Noncombustible Material. A material that, in the f ~ " in " ~ c h "%....:~,,:-

it is used and u n d e r the condi t ions anticipated, wil[.:~..t,.ignit¢.'~:. . . . . . . :. :ii~#:~-l.l* Systems tha t hand le combust ib le part iculate solids shall be suppor t combus t ion , burn , or release f lammable ~'~i~.~4~::!~iiii::::ii~::.. "~:::':!::" des igned by and installed u n d e r the supervision of qualified subjected to fire or heat. Materials tha t are r e p o r t e ~ g ============================== engineers who are knowledgeable o f these systems an d their passed ASTM E 136, Standard Test M e t h o d f o r : : ~ r o f ~ , a l s ' associated hazards. in a Vertical Tube Furnace at 750°C. shall b ~ : ; . ' ~ . ' ~ : , "::i~.~ii!-i...:i!!~::' noncombus t ib l e materials. For the p u r ~ e s of this::!~dard.~iii ':: 2-1.2 The design of systems a n d facilities tha t handle combust ible noncombus t i b l e cons t ruc t ion and l i m ~ ' ~ ' : ~ m b u s t i b l ~ i i i -:" part iculate solids shall consider the physical and chemical cons t ruc t ion are both cons idered to be n ~ . . m b u s t i b l ~ ; proper t ies and hazardous characteristics of the materials being

x::::::::::.. .::::.- conveyed. Pneumatic Conveying System. A p n e u m a t i ~ . v ~ . ' ~ g system

consists of a material feeder, an a i r -mater ia l s e p ~ ' r , an 2-1.2.1 Those por t ions of the process a n d facility where dus t enclosed ductwork system, and an air-moving de.~"~e in which a explosion hazards exist shall be protec ted f rom the effects of dus t combust ib le part iculate solid is conveyed f rom one poin t to ano the r with a s t ream of air or o ther gases. Pneumat ic conveying systems inc ludes dus t collection systems.

Pneumatic Conveying System, Negative-Pressure. Negative- pressure-type systems t ranspor t material by utilizing gas at less than a tmospher i c pressure. These systems consist of a s equence of an air intake, a material feeder, an a i r -mater ia l separator, an air- moving device, and in te rconnec t ing ducts.

Pneumatic Conveying System, Positive-Pressure. Positive pressure-type systems t ranspor t material by utilizing gas at grea ter than a tmospher ic pressure. Such systems consist of a s equence of an air-moving device, a feeder for in t roduc ing materials into the system, an a i r -mater ia l separator, and in t e rconnec t ing ducts.

explosions in accordafice with Sections 2-2, 2-3, 2-4, and Chapter 3.

2-1.2.2 Those port ions of the process and facility where a combust ib le part iculate solid presents a fire hazard shall be protec ted in accordance with Chap te r 6.

2-1.3 Recycling of a i r -mater ia l separa tor exhaus t to buildings shall be permi t ted i f the system is des igned to prevent both re turn of dus t with an efficiency of 99.9 pe rcen t at 10 microns an d t ransmiss ion of energy f rom a fire or explosion to the building.

Exception No. 1: Recycling of air-material separator exhaust to the building shall not be permitted under any circumstances when combustible gases or vapors or hybrid mixtures are involved.

Relay Fan. A fan or a blower installed in-line to overcome the pressure drop due to frictional losses in the conveying stream.

Replace-in-Kind. To furn i sh with new parts or equ ipment , as applied to e q u i p m e n t and facilities, of the same type but no t necessarily of identical design.

Exception No. 2: Recycling of air-material separator exhaust to the building shall not be permitted when the recycled stream would reduce the concentration of oxygen below 19.5 volume percent in the work area.

2-1.4 Ext inguishing agents shall be compatible with the const ruct ion a n d process materials with which they migh t come into contact.

122

N F P A 654 ~ M A Y 2 0 0 0 R O P

2-1.5 Where a pneumatic conveying system or any part of such systems operates as a positive-pressure-type system and the air- moving device's gauge discharge pressure is 15 psi (103 kPa) or greater, the system shall be des igned in accordance with Section VIII of the ASME Boiler and Pressure Vessel Code, or ASME B31.3, Process Piping.

2-1.6" The design and its basis shall be documen ted and shall include the propert ies that define the hazards of the material being processed.

2-1.7 All components of pneumat ic conveying systems that handle combustible particulate solids shall be des igned to be dusttlght.

Exception: Openings designed for intake and discharge of air and material.

2-2 Segregation, Separation, or Detachment o f Combustible Dust Handling and Process ing Areas.

2-2.1 General. Areas in which combustible dusts are produced, processed, handled, or collected shall be detached, segregated, or separated from other occupancies in order to minimize damage from a fire or explosion.

2-2.2 Use o f Segregation.

2-2.2.1 Physical barriers that are erected to segregate dust hazards shall have all penetra t ions of floors, walls, ceilings, or partitions sealed dusttight, and, where structural assemblies have a fire

des igned in accordance with NFPA 221, Standard for Fire Walls and Fire Barrier Walls.

2-3.5 Openings in fire walls and in fire barrier walls shall be protected by self-closing fire doors that have a fire resistance rating equivalent to the wall design. Fire doors shall be installed according to NFPA 80, Standard for Fire Doors and Fire Windows, and shall normally be in the closed position.

2-3.6 Means of egress shall comply with NFPA 101 ®, Life Safety Code ® .

2-3.7 All penetra t ions of floors, walls, ceilings, and partit ions shall be dusttight, and, where structural assemblies have a fire endurance rating, the seal shall maintain that rating.

Exception: Sealing of penetrations shall not be required when the penetrated barrier is provided for reasons other than to limit the migration of dusts or to control the spread of fire or explosion.

2-3.8 Interior stairs, elevators, and manlifts shall be enclosed in dusttight shafts that have a minimum fire resistance rating of 1 hour. Doors that are the automatic-closing or self-closing type and have a fire resistance rating of 1 hour shall be provided at each landing.

Exception: Stairs, elevators, and manlifls that serve only open-deck floors, mezzanines, and platforms need not be enclosed.

2-3.9* Floors and load-bearing walls that are exposed to dust endurance rating, the seal shall maintain that rating, explosion hazar~i:$...hall be designed so as to preclude failure

during an e x ~ ...... 2-2.2.2 Physical barriers that are erected to segregate dust .::i!#ii:, ~" deflagration hazards shal) be designed to preclude failure of these 2-4* D e ~ ' t t ~ Venting. barriers before the deflagration pressure can be safely vented to the ':i::i::::::i::: ="=?=========}h== outside. (For deflagration venting, see Section 2-4.) 2-4.1"A!~.t~ ~ o o m ~ ! ~ i l d i n g contains a dust explosion hazard that

is e.~'~::~liiii~" prote~::-.. .~, tSipment, as defined in 2-2.3.1, such 2-2.3 Use of Separation. ~ a s s]..~.ll be provide~ii~th deflagration venting to a safe outside

...-t~".v.atiodi~-i.-:.. : .... 2-2.3.1" When separation is used to limit the fire or dust explosion ........... !i::::i::iii!~::....:~!)i!iiii!i~::. hazardous area, the hazardous area shall include areas where dust 2-4.~::iiiii:.W.ent closures shall be directed toward a restricted area, and accumulations exceed 1/3~ in. (0.8 mm) or where dust clouds o fa . the ve:~i~ps .uge shall not be a missile hazard. The fireball and hazardous concentra t ion exist. :-~--~:~::.:,. blast p r d : ~ " t h a t are created by the venting process shall not

"%":::~-~.~p.inge ~ o n unrestr icted personnel pathways. Exception: For dust accumulations with a bulk density less than 75 "% "i~iiiii!i~i~iiiii::i~?!:~:::-i ....... lb/fF (33.75 kg/m 3 ), the allowable thickness can be prorated up.ward by ::::-!:.....:-~!ii'::'2-5*i'::iii-~elief Valves. Relief valves shall not be vented to a dust the following equation: ~-'gii-::~'i:. "-iiii:" hazl'i~d area as defined by 2-2.3.1.

.... ¢::" -~::~iii ~::::::~ ......... (1/ \tv~\ ~ii~i~. :iill i:' :.:. :iiiiiii:,!~-6 Equip.ment Arrangement . Equipment shall be located or

Allowa hickness i "nches V321~ "! .=:.:i::"'-'::'='i~:':'~i~i::.. ..::¢:i:!4="=%~:i::... "-~::'.'i;:" arranged in a manner that mxmm~zes combustthle dust ble I n * = ~ "::::":::: ":" :::" "::::::::::::"::: . . . . . es bulkdensit lib" ~3~ %.'-:!U!':.. ":'::~:~!~i~i::" accumulanons on not surtac . y ~ / J..!....:.=]... ....... "::i.~.-'ii~:

-..::!f~::::':'::~:iiii::::i::i!ii!}~ .... ==========?=?====}====:===;==== 2-7 Electrical Equipment. 2-2.3.2 The required separation d i s t a n ~ e t w e e n ~ '~ i i~ar~4~ 's area identified in 2-2.3.1 and surroundii~//~::~osures s l ~ l b e de te rmined by an engineer ing evaluation tP/~i::~dresses!i~3e propert ies of the materials, the type of opecaff~::..the ~ o u n t of material likely to be present outside the proces~::i~t~fiaent, the building design, and the nature of sur rounding e~6su res . In no case shall the distance be less than 30 ft (9 m). ':-:"

2-2.3.3 When separation is used, housekeeping, fixed dust collection systems employed at points of release, and compar tmenta t lon shall be permit ted to be used in order to limit the extent of the hazardous area.

2-3 Building Construction.

2-3.1 All buildings shall be of Type I or Type II construction, as def ined in NFPA 220, Standard on Types of Building Construction. Where local, state, and national building codes require, modifications shall be permit ted for conformance to these codes.

2-3.2* Interior surfaces where dust accumulations can occur shall be designed and constructed so as to facilitate cleaning and to minimize combustible dust accumulations.

2-3.3 Spaces inaccessible to housekeeping shall be sealed in order to prevent dust accumulation.

2-3.4 Interior walls erected for the purpose of limiting fire spread shall have a min imum 1-hour fire resistance rating and shall be

2-7.1 All electrical equ ipment and installations shall comply with the requirements of NFPA 70, National Electrical Code e, or NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment.

2-7.2* In local areas of a plant where a hazardous quantity of dust accumulates or is suspended in air, the area shall be classified and all electrical equ ipment and installations in those local areas shall comply with Article 502 or Article 503 of NFPA 70, National Electrical Code, as applicable.

2-7.3 Hazardous (classified) areas that are identified in accordance with 2-7.2 shall be documented , and such documenta t ion shall be permanent ly maintained on file for the life of the facility.

2-8 Management of Change. Written procedures to manage change to process materials, technology, equipment , p rocedures , and facilities shall be established and implemented. The requirements of 2-8.1 through 2-8.2 shall be appl ied retroactively.

2-8.1 The management-of-change procedures shall ensure that the following issues are addressed prior to any change:

(1) The technical basis for the proposed change (2) Thi: safety and health implications (3) Whether the change is pe rmanen t or temporary (4) Modifications to operat ing and maintenance procedures

123

N F P A 654 ~ MAY 2 0 0 0 R O P

(5) Employee training requirements (6) Authorization requirements for the proposed change

Exception: Implementation of the management-of-change procedures shall not be required for replaceme'nts-in-kind.

2-8.2 Design documentation, as required by 2-1.6, shall be updated to incorporate the change.

Chapter 3 Process Equipment

3-1 General. Methods of fire and explosion protection for specific equipment shall be in accordance with this section.

Exception:* A documented risk evaluation acceptable to the authority having jurisdiction shall be permitted to be conducted to determine the level of protection to be provided.

3-1,1 Explosion Protection for Equipment. The design of explosion protection for equipment shall incorporate one or more of the following methods of protection.

(1) Oxidant concentration reduction in accordance with NFPA 69, Standard on Explosion Prevention Systems

a. Where oxygen monitoring is used, it shall be installed in accordance with ISA $84.01, Application of Safety Instrumented Systems for the Process Industries.

b.* When the chemical properties of the material being conveyed require a minimum concentration of oxygen to control pyrophoricity, that level of concentration shall be maintained.

(2)* Deflagration venting (3) Deflagration pressure containment in accordance with NFPA

69, Standard on Explosion Prevention Systems (4) Deflagration suppression systems in accordance with NFPA

69, Standard on Explosion Prevention Systems (5) Dilution with a noncombustible dust to render the mixture

noncombustible, ff this method is used, test data for specific dust and diluent combinations shall be provided and shall be acceptable to the authority having jurisdiction.

(6) Deflagration venting through a Iisted dust retention and fame arresting device.

3-1.2 Fire Protection for Equipment. Equipment fire protection ~iili shall be designed in accordance with Chapter 6. ':':

3-1.3" Isolation of Equipment.

3-1.3.1 Where an explosion hazard exists, isolation d~es ~ l be provided to prevent deflagration propagation betwe....~i~ieces:~t=

connected by ductwork. I s o l a t i o n d e ~ ' ~ = ~ u . ~ ! i ~ : ~ : . . . . . . ¢~ -~,, equipment are not limited, to the following: "::?:-~.::...:.~ ".':-'.'$i

~:.~i!~:: "::::::::~:::""!~i~i::. (1)* Chokes ~" (2)* Rotary valves /!i "#~J~ (3)* Automatic fast-acting valve syst~!~.~.~.accordatJi~:witl~ : ; : : ' ' ' ' ' " ":~':::":::- ~

NFPA 69, Standard on Explosion P r e v e n ~ i o d ~ s ~ (4)* Flame front diverters in accordance ~ .~FPA. . : .~ , Standard

on Explosion Prevention Systems "~'.<2".::.'.~:, ..:~:" (5)* Flame front extinguishing systems in a c o ~ i c e with NFPA

69, Standard on Explosion Prevention Systems .¢'::"

Exception No. 1: Isolation devices are not required when oxidant concentration has been reduced or when the dust has been rendered noncombustible in accordance with 3-1.1(1) or (5).

Exception No. 2:* Isolation devices are not required i f a documented risk evaluation that is acceptable to the authority having jurisdiction determines that deflagration propagation will not occur.

3-1.3.2" Where an explosion hazard exists, isolation devices shall be provided to prevent defiagration propagation from air-material separators upstream to the work areas. Isolation devices include, but are not limited to, those listed in 3-1.3.1(1) through (5).

Exception: Isolation devices are not required i f a documented risk evaluation that is acceptable to the authority having jurisidiction determines that deflagration propagation will not occur.

3-1.3.3 Where a fire propagation hazard exists, the requirements of Chapter 6 shall apply.

3-2 Bulk Storage Enclosures.

3-2.1 General. For the purposes of this section, bulk storage shall include such items as bins, tanks, hoppers, and silos.

Exception:* The requirements of this section do not apply to containers that are used for transportation of the material.

3-2.2 Construction. Bulk storage containers, whether located inside or outside of buildings, shall be constructed of noncombustible material.

3-2.3 Explosion Hazards.

3-2.3.1 Where an explosion hazard exists, there shall be no intermnk or interbin venting.

3-2.3.2 Where an explosion hazard exists, fixed bulk storage containers shall be located outside of buildings.

Exception No. I: Those f ixed bulk storage containers that are protected in accordance with 3-1.1(I), (3), (4), (5), or (6).

Exception No. 2:* Those fixed bulk storage containers that are located within 20 f l (6 m) of an exterior wall and equip[~ed with deflagration vents that are vented through ducts to the outside and where the reglu~d venting efficiency due to the duct has been accounted for. The ducts shall be designed to withstand the effects of the deflagration.

Exception No. 3:* Fixed bulk storage containers of 8 f l 3 (0.2 rr~ ) or less.

3-2.3.3 Where an containers shall ..1~

hazard exists, fixed bulk storage t in accordance with 3-1.1.

Exception 1 outside o(..t

ixed bulk storage containers that are located risk evaluation shall be permitted to be conducted explosion protection to be provided.

be omitted (0. 2 m3 )?

protection requirements per 3-1.1 shall be volume of the fixed bulk storage container is

3: The requirements of this section shall not appO to ~iving containers that are used for transportation of the

~'.:~:'-:~aterior Surfaces. Interior surfaces shall be designed and ~ucted to facilitate cleaning and to minimize combustible accumulation.

Access Doors and Openings.

3-2.5.1 Access doors or openings shall be provided to permit inspection, cleaning, and maintenance.

3-2.5.2 Access doors or openings shall be designed to prevent dust leaks.

3-2.5.3 Access doors or openings that are not specifically designed for deflagration venting shall not be considered as providing that function.

3-2.5.4 Access doors shall be properly bonded and grounded.

3-3 Material Transfer System.

3-3.1 General

3-3.1.1 Where more than one material is to be handled bya system, compatibility tests shall be run. Where incompatibility is found, provisions shall be made for cleaning the system prior to transporting a new material.

3-3.1.2 Where the materials being conveyed are corrosive, the system shall be constructed of corrosion-resistant materials.

3-3.1.3 Where the atmosphere surrounding the conveying system is corrosive, the conveying system shall be constructed of corrosion- resistant materials.

3-3.2 Pneumatic Conveying Systems

3-3.2.1 Additions of branch linesshall not be made to an exisdng system without redesigning the entire system. Branch lines shall

124

N F P A 654 ~ MAY 2 0 0 0 R O P

not be d isconnected nor shall unused port ions of the system be blanked off without providing a means to maintain required and balanced airflow.

3-3.2.2 The rate of airflow at each hood or o ther pickup point shall be des igned so as to convey and control the material.

3-3.2.3 All ductwork shall be sized so as to provide the air volume and air velocity necessary to keep the duct interior clean and free of residual material.

3-3.2.4 The design of the pneumatic conveyance system shall be documented . The documenta t ion shall include data on the range of particulate size, concentrat ion in conveyance air stream, potential for reaction between the t ransported particulate and extinguishing media used to protect process equipment , conductivity of the particulate, and other physical and chemical propert ies that affect the fire protection of the process.

3-3.2.5 Pneumatic conveying systems that remove material from operations that generate flames, sparks, or ho t material shall no t be in terconnected with pneumat ic conveying systems that t ransport combustible particulate solids or hybrid mixtures.

3-3.3 Operations

3-3.3.1 Sequence of Operat ion. Dilute phase pneumat ic conveying systems shall be designed with the operat ing logic, sequencing, and t iming outl ined in 3-3.3.2 and 3-3-3.3.

3-3,3.2* Start-Up. Pneumatic conveying systems shall be designed such that, upon start-up, the system will achieve and maintain design air velocity prior to the admission of material to the system.

3-3.3.3 Shutdown. Pneumatic conveying systems shall be designed such that, upon shutdown of the process, the system will maintain design air velocity until material is purged from the system.

3-4 Specific Requirements for Systems That Convey Metal Particulates.

3-6.2 Flexible hose and connect ions shall be permit ted to be used for material "pickup and isolation. Bellows shall be permit ted to be used for the free movement of weigh bins if the bellows are conductive and the equ ipmen t is bonded and grounded.

3-6.3* Changes in duct sizes shall be designed so as to prevent the accumulat ion of material by utilizing a tapered transformation piece; the included angle of the taper shall be not more than 30 degrees.

3-6.4* When ducts pass through a physical barrier that is erected to segregate dust deflagration hazards, physical isolation protect ion shall be provided to prevent propagation of deflagrations between segregated spaces.

3-7 Sight Glasses.

3-7.1 Sight glasses shall be of a material that is impact- and erosion-resistant. Sight glass assemblies shall have a pressure rating equal to or greater than that of the ductwork.

37.2 Ductwork shall be suppor ted on each side of the sight glass so that the sight glass does no t carry any of the system weight and is no t subject to stress or strain.

3-7.3 The mechanical s t rength of the sight glass mount ing mechanism shall be equal to the adjoining ductwork.

3-7.4 The inside diameter of a sight glass shall no t cause a restriction of flow.

.~:ii!'.-:. 3-7.5 The c o ~ ' ~ . . . s between the sight glass and the ductwork shall be s q u ~ f f , butl~[d and sealed so as to be both airtight and du sttight..::.:iii~: ,::~::'~*r'ii:::-%."

. . ~ ! ~ e c t r i ~ ! ~ n d i n g across the length of the sight glass 3-7.6 sh~i~ '&~: f i~nuous " ~ : : ~ v e a resistance of no more than 1 ohm.

.... - ~ i : : P r e ~ r e Protect~i~'n Systems.

3 ~ c u u ' m Breakers. Vacuum breakers shall be installed on 3-4.1 General. This section shall apply to facilities that operate . . . . nega f f~ . e s . s . o r e systems if that system is not des igned for the pneumat ic conveying systems for metallic particulates. ~:~.,:.....:,.. m a x i m ~ u u m attainable.

3-4.1.1" Unless otherwise determined, metallic particulates shall :':!ii- " ' ~ . : : - . ~ u r e Relief Devices. Pressure relief devices for relief of be deemed water-reactive, and water-based extinguishing agents ::i~i,.~i-:'::.pne~ttic overpressure shall be installed on positive-pressure shall not be used. ,~i~ii~i~i!~!!!~!i~. "%:" s y s t ~ s . [For information on deflagration "pressure relief see A-i-

x.'..'#" "-'-:.-".-:-':iii" ":ii!i!::....:../,, 1 (2). l Exception No. 1: Specially engineered high-density wat~i~ray s ~ ~.::.. ~,.:ii'~:;:" approved by the authority having jurisdiction shall be ~ . to'~iii~'i!i:i::.~.. ":i~i: '':'y Exception No. 1: Systems that are designed for less than a gauge use"& --x'i{~':':':-i~ii~i. ~ "::!i:'~::iiiiiii::! y press'ure of 15 psi (104 kPa) and are provided with safety interlocks

x:~:-~a::,'~:":::':"" "::"i.-'.:i:~ :.....::::i:!:i::. ... designed in accordance with ISA $84. 01, App licalion of Safety Exception No. 2: This requirement shall not .~Ty tt":~:.?:'.~..llectid~..~iiy" Instrumented Systems for the Process Industries. iron dusts from shot blasting. ,::ff . . . . ~-~i:, ~i!~:'."::"

~i-":::, "%i~. 4 .... Exception No. 2: Systems that are designed for less than a gauge 3-4.1.2 Systems that convey alloys that'exli~":'~fire or e ~ o s i o n pressure of 15 psi (104 hPa) and are capable of containing the maximum characteristics similar to those of the base ffi:~.~!~hall .l#" provided pressure attainable. with the same protect ion as systems that c o n v ~ ' ~ , . ~ e metal.

"::~.-:.':~i~iY" 3-8.3 Airflow Control Valves. 3-4.2 Iron, Nickel, Copper , and Other Transitio#."~letal Particulates. Transition metal combustible partii:ulates shall be 3-8.3.1 Airflow control valves that are installed in pneumatic classified as water-compatible, water-incompatible, or water- reactive based on the available chemical and physical data and in conjunct ion with the authority having jurisdiction.

3-5 Systems That Convey Hybrid Mixtures. The percentage of the lower f lammable limit (LFL) of f lammable vapors and the percentage of the min imum explosible concentrat ion (MEC) of combustible dusts, when combined, shall not exceed 25 percent within the airstream.

Exception: Systems protected in accordance with 3-1.1(1), (2), (3), and (4).

systems shall be of both airtight and dustt ight construction.

3-8.3.2 Airflow control valves shall be sized so as to allow passage of the total airflow of the system when the damper is fully open.

3-8.3.3 The position of airflow control valves shall be visually indicated.

3-8.3.4 Manually adjusted airflow control valves, dampers, gates, or orifice plates shall have a means of securing them to prevent subsequent adjustment or manipulat ion once the system is balanced.

3-6 Duct Systems.

3-6.1 Ducts that handle combustible particulate solids shall conform to the requirements of NFPA 91, Standard for Exhaust S3stems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids, except as amended by the requirements of this chapter.

3-8.3.5 Diverter valves shall effect a positive diversion of the material and shall mechanically seal all o ther directions from air or material leakage.

3-9 Material Feeding Devices.

3-9.1 Mechanical Feeding Devices. Mechanical feeding devices shall be equipped with a shear pin or overload detect ion device and alarm. The alarm shall sound at the operator control station.

125

N F P A 654 - - MAY 2000 R O P

3-9.2 Drives. All drives used in conjunct ion with feeders, air locks, and other material feeding devices shall be directly connected.

Exception: Belt, chain and sprocket, or other indirect drives that are designed to stall the driving forces without slipping and to provide for the removal of static electric charges shall be permitted to be used.

3-10" Bucket Elevators.

3-10.1" Where an explosion hazard exists, bucket elevators shall be provided with deflagration venting. When bucket elevators are located within the building, deflagration vents shall be ducted to the outside.

Exception: As an alternative to deflagration venting, bucket elevators shall be permitted to be protected in accordance with 3-1.1(1), (3), (4), (5), (6) or 3-1.3.1(5).

3-10.2 Elevator casings, head and boot sections, and connect ing ducts shall be dustt ight and shall be constructed of noncombust ib le materials.

3-10.3 Where provided, inlet and discharge hoppers shall be designed to be accessible for cleaning and inspection.

3-10.4 Belt-driven bucket elevators shall be provided with a detector that will cut off the power to the drive motor if the motor speed drops below 80 percent of normal operating speed. Feed to the elevator leg shall be s topped or diverted.

3-12.2 Where an explosion hazard exists, systems shall be designed in such a manne r that combustible material does not pass through an air-moving device.

Exception No. I:* Those systems designed to operate at a combustible particulate solids concentration or hybrid mixture concentration of less than 0.0003 oz/fl ~ (0.3 gm/mZ ).

Exception No. 2:* Those systems operating at a combustible particulate" solids concentration or hybrid mixture concentration equal to or greater than 0.0003 oz/fl ~ (0.3 grn/m ~ ) and protected by an approved explosion prevention or isolation system to prevent the propagation of the flame front from the f an to other equipment in accordance with any of the following: 3-1.1(1), (4), (5), or 3-1.3.1(3), (4), or (5).

3-12.3 Where a fire hazard exists and where combustible particulate solids pass th rough an air-moving device, provisions shall be made to prevent igmted material f rom entering processes downstream, in accordance with Chapter 6.

3-13 Air-Material Separators (Air-Separation Devices).

3-13.1 General.

3-13.'1.1 Where an explosion hazard exists, air-material separators shall be located outside of buildings.

Exception No. 1: Those air-material separators that are protected in accordance with 3-1.1(I), (3), (4), (5), or (6).

3-10.5 Belt-driven bucket elevators shall have a nonslip material (lagging) installed on the head pulle)~ to minimize slippage. Belts and lagging shall have a surface resisuvity not greater than 100 meg- ohms per square and be fire resistant and oil resistant.

3-10.6 No bearings shall be located within the bucket elevator casing.

Exception No. 2"...::::::::::..:..*.-:~::iT..hose air-material separators that are located within 20 f l (6 m) of . ~ ' : " ~ wall and are equipped with deflagration vents that are ven t~hroug '~duc t s to the outst'de and where the reduced venting e f ~ ' ~ e ' t o the duct has been accounted for. The ducts shall be ~ e d % l ~ t h s t a n d the effects of the deflagration.

.~"~i~::.:.:" '~:::" - - - - - - ~ : . ~i~i~.-'.-'::, ., Exc.~3~t:'::tg..O".:" 3: Th~". '~gbments of this sectwn shall be permitted to be o#fflted.~ the volume of ~ air-raaterial separator is less than 8 f l" (0.2

3-10.7" Head and boot sections shall be provided with openings "~ ~.~...:!'~:~::::::~:i~:i.. to allow for clean-out, inspection, and a l ignment of the pulley and 3 - 1 $ ~ . . W h e r e both an explosion hazard and a fire hazard exist in belt. ,, an a i r '~ .er i . .~l separator, provisions for protect ion for each type

~'~:~:..:,.. of haza(~i~.~]l be provided. 3-10.8" The bucket elevator shall be driven by a motor and drive '"::.~:..-Y"::!~ii~'::.~i~!~:i::.:. .:~i:: train that is capable of handl ing the full rated capacity of the % "':.~i~i~-~!,.~-::~:%r-material separators shall be protected in accordance elevator without overloading. The drive shall be capable q.f..,,.. ::~i~:...::#.:::wit~i::i~|.l. starting the unchoked elevator under full (100 p e r c e n t ) ~ i i : . , '~i: ::-'"

..::#" ":::':~i~i "%...~xception: For air-material separators that are located outside of 3-10.9 Elevators shall have monitors at head and ta~!!~.!leys ~ t . . . . . . . . . :.iiiiii;:'~uildings, a risk evaluation shall be permitted to be conducted to indicate high bearing temperature or vibration det~i~ik~ii::..h.=¢.~i~:~:~.ii::iiiii~:~::.:...'~i~ ~;': determine the level of explosion protection to be provided. pulley alignment, and belt alignment. Abnormal c o n d ~ shall~:~:~::!!!!!!!i! ~::" actuate an alarm requiring corrective action..,..-:T-.'h'~:~larm ~ ~ . " 3-13.1.4 Manifolding of dust collection ducts to air-material sound at the operator control station. .~:¢.:::::::'":::~i~i~i~::, ~:~i~::i!~i::.::i-~;:' separators shall not be permit ted.

Exception: This requirement does not a ~ a t o r s th~iSave~belt Exception No. 1: Dust collection ducts from a single piece of equipment s~e~s bely. w 500 f l /mrn (2.5 m/sec) or capac~ti~ii~s.s than ~ 0 j'P / h r or from multiple pieces of equipment interconnected on the same process (100 m'/~r). ======================. ...:~':: stream shall be permitted to be manifolded.

..... -~3~i~::, ~.-:;;-":" 3-10.10 All bins into which material is directly d ~ i - g e d from the bucket elevator and that are not designed with a~.~/~'matic overflow systems shall be equipped with devices to shut down equ ipment or with high-level indicating devices with visual or audible alarms. The alarm shall sound at the opera tor control station.

3-11" Enclosed Conveyors.

3-11.1 Housings for enclosed conveyors (e.g., screw, drag) shall be of metal construction and shall be des igned so as to prevent escape of combustible dusts. Coverings on clean-out, inspection, and other openings shall be securely fastened.

3-11.2 All conveyors shall be equipped with a device that shuts off the power to the drive motor and sounds an alarm in the event the conveyor plugs. The alarm shall sound at the operator control station. Feed to the conveyor shall be s topped or diverted.

3-12 Air-Moving Devices (Fans and Blowers).

3-12.1 Air-movlng devices shall conform to the requirements of NFPA 91, Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists and Noncombustible Particulate Solids, except as amended by the requirements of this chapter.

Exception No. 2: Dust collection ducts from nonassociated pieces of equipment shall be permitted to be manifolded i f each of the ducts is equipped with an isolation device prior to manifolding in accordance with 3-1.3.

Exception No. 3: Dust collection ducts for centralized vacuum cleaning systems shall be permitted to be manifolded.

3-13.1.5" Isolation devices shall be provided for air-material separators in accordance with 3-1.3.

5-13.1.6 Where l ightning protect ion is provided, it shall be installed in accordance with NTPA 780, Standard for the Installation of Lightning Protection Systems.

3-13.1.7 Exhaust air from the final air-material separator shall be discharged outside to a restricted area and away from air intakes.

Exception No. 1: Air from air-material separators shall be permitted to be recirculated directly back to the pneumatic conveying system.

Exception No~ 2: Air from air-material separators shall be permitted to be returned to the building when in compliance with the requirements of 2-1.3.

126

N F P A 6 5 4 ~ M A Y 2 0 0 0 R O P

3-13.1.8 Where more than one material is to be handled by a system and are known to be incompatible, provisions shall be made for cleaning the system prior to handl ing a new material.

3-13.2 Construction.

3-13.2.1 Air-material separators shall be conswucted of noncombust ib le materials.

Exception: Filter media shall be permitted to be of combustible maten'al.

3-13.2.2 Air-material separators shall be constructed so as to minimize internal ledges or o ther points of dust accumulation. Hopper bot toms shall be sloped, and the discharge conveying system shall be designed to handle the maximum material flow attainable from the system.

3-13.2.3 Access doors.

3-13.2.3.1 Access doors or openings shall be provided to permit inspection, cleaning, and maintenance.

3-13.2.3.2 Access doors or openings shall be designed to prevent dust leaks.

3-13.2.3.3 Access doors shall be permi t ted to be used as deflagration vents if they are specifically designed for both purposes.

3-13.2.3.4 Access doors shall be properly bonded and grounded.

3-13.2.3.5" Access doors shall be designed to withstand the vented explosion pressure ( P ~ ) .

3-14 Abort Gates/Abort Dampers.

3-14.1 Construction. Abort gates and abort dampers shall be constructed of noncombust ib le materials. Abort gates and abort dampers that are installed after January 1, 2004, shall be listed for the purpose.

3-17.1 Mixers and blenders shall be dusttight.

3-17.2 Foreign materials shall be removed as required by 5-1.1.

3-17.3 Where an explosion hazard exists, protection shall be provided as specified in 3-1.1.

3-17.4 Where a fire hazard exists, protect ion shall be in accordance with Chapter 6.

3-17.5 Mixers and blenders shall be made of metal or other noncombust ib le material.

3-18" Dryers.

3-18.1 Heating systems shall be in accordance with Section 5-6.

3-18.2 Drying media that come into contact with material being processed shall no t be recycled to rooms or buildings.

Exception: Drying media shall be permitted to be recycled to the drying process i f passed through a filter, dust separator, or equivalent means of dust removal

3-18.3 Dryers shall be constructed of noncombust ib le materials.

3-18.4 Interior surfaces of dryers shall be designed so that accumulations of material are minimized and cleaning is facilitated.

3-18.5 Access d ~ or openings shall be provided in all parts of the dryer a n d . ~ ' ~ . $ ~ n g conveyors to permit inspection, cleaning, malntenanc~i~.<.: . ~ " d th~:'effective use of portable extinguishers or hose s t r e asta~. >::-:-'.:.::~-.~

3-18.6<~i'i~:'~e an : ~ o . s i o n hazard exists, protection shall be p r ~ " ~:~.' ::~p e cifi e ~1~i~!~:1.1.

:.:...~8.:7 ' ~ . e r e a fire ff~'~rd exists, protect ion shall be in "" a ~ i ~ i . w i t h Chapter 6.

. - - : : - : : : : : :~

Exception: This requirement shall not apply to replacement components . . . . 3-18.8"~iiil".i~.¢at...e.d dryers shall have operat ing controls arranged so as for abort gates or abort dampers that are installed on or before January/~'~'.:".:!?.:~'.<:::....... to main~!!hXle temperature of the drying chamber within the 2004. ':~'..'~'::-"~ ~i~i~i~i~':.':~g.: ¢ s c r i b e~::t im its.

. : . :~ : . : - : . : . : . : . : . : . :+ : . : . . - . .+ : , -

3-14.2 Opera t ion . . :'iii~...::#iiiii~i:'~ii~eated dryers shall comply with NFPA 86, Standard for ...-:!!~'::~-!!!!-.:- %!::" O v ~ and Furnaces.

3-14.2.1 The abort gate or abort damper shall be ins .t~. "~d s~'i~at %:. ...... it diverts airflow to a restricted area. ..~ii:.'-".~:.. #:" ~, "~:-:i;~18.10 Heated dryers and their auxiliary equipment shall be

:.':!!::'%~iliiii~::....::ii#i:?"~iiiii~:..-.~i3i!. '':~'::" equipped with separate excess temperature-l imit controls that are 3-14.2.2 The abort gate or abort damper shall be provf~i.Z'.~th a<":~-"-"" arranged to supervise the following: manual reset such that subse uent to opera.tJ ,~:: . i~an o "!ii.~.e , q .................... ...~ .... ~ . . . . . . . . . re turned to the closed position at the ~ ' i ~ (~ i?~ i i~ : . .Auto~Y' (1) Heated air supply to the drying chamber or remote reset provisions shall not be ~ w e d . "<%~i~!:: ,iiiiiii:: (2) Airstream at the discharge of the drying chamber

3-15" Size Reduction. "":" ":":'i-~iiiii~::.. ":~iiiil

3-15.1 Before material is processed by size r ~ o n - . . ~ t u i p m e n t , foreign materials shall be removed as required b ~ : ~ ] .

3-15.2 Where an explosion hazard exists, protect'~on shall be provided as specified in 3-1.1.

3-15.3 Where a fire hazard exists, protect ion shall be provided in accordance with Chapter 6.

3-16" Particle Size Separation.

3-16.1 Particle-separation devices shall be in dustt ight enclosures.

3-16.2 Connect ion ducts shall be in conformance with 3-5.

3-16.3" Where an explosion hazard exists, protect ion shall be provided as specified in 3-1.1.

Exception:* Screens and sieves shall not be required to have explosion protection.

3-16.4 Where a fire hazard exists, protect ion shall be in accordance with Chapter 6.

3-17 Mixers and Blenders.

Chapter 4 Fugitive Dust Control and Housekeeping

4-1 Fugitive Dust Control. Continuous suction shall be provided for processes where combustible dust is l iberated in normal operation so as to minimize the escape of dust. The dust shall be conveyed to dust collectors.

4-2 Housekeeping. The requirements of 4-2.1 through 4-2.3 shall be applied retroactively.

4-2.1" Equipment shall be maintained and operated in a manner that minimizes the escape of dust. Regular cleaning frequencies shall be established for floors and horizontal surfaces, such as ducts, pipes, hoods, ledges, and beams, to minimize dust accumulations within operat ing areas of the facility.

4-2.2* Surfaces shall be cleaned in a manne r that minimizes the generat ion of dust clouds. Vigorous sweeping or blowing down with steam or compressed air produces dust clouds and shall be permit ted only if the following requirements are met:

(1) Area and equ ipment shall be vacuumed prior to blowdown. (2) Electrical power and other sources of ignition shall be shut

down or removed from the area. (3) Only low gauge pressure [15 psi (103 kPa)] steam or

compressed air shall be used. (4) There shall be no hot surfaces in an area that is capable of

igniting a dust cloud or layer.

127

N F P A 654 - - MAY 2 0 0 0 R O P

4-2.3 Vacuum cleaners shall be listed for use in Class II hazardous locations or shall be a fixed-pipe suction system with remotely located exhauster and dust collector installed in conformance with Section 3-13.

Exception: Where flammable vapors or gases are present, vacuum cleaners shall be listed for Class I and Class I I hazardous locations.

Chapter 5 Ignition Sources

5-1 Heat from Mechanical Sparks and Friction.

5-1.1 Foreign Materials.

5-1.1.1 Means shall be provided to prevent foreign material from entering the system when such foreign material presents an ignition hazard.

5-1.1.2 Floor sweepings shall not be returned to any machine.

5-1.1.3" Where the process is configured such that the pneumatic conveying system conveys materials that can act as an ignition source, means shall be provided to minimize the hazard. These means shall be permitted to include protection measures identified in 3-1.1 and Section 6-1, as appropriate.

5-1.1.4" Foreign materials (such as tramp metal) that are capable of igniting combustible material being processed shall be removed from the process stream by one of the following methods:

(1) Magnetic separators of the permanent or electromagnetic type. Where electromagnetic separators are used, provisions shall be made to indicate the loss of power to the electromagnetic separators.

(2) Pneumatic separators (3) Grates or other separation devices

5-1.2" Belt Drives. Belt drives shall be designed to stall without the belt's slipping, or a safety device shall be provided to shut down the equipment if slippage occurs.

5-1.3" Bearings. Roller or ball bearings shall be used on all processing and transfer equipment. Lubrication shall be ~!i i performed in accordance with the manufacturer 's recommendations.

Exception: Bushings shall be permitted to be used when a d ~ ' . . ~ . engineering evaluation shows that mechanical loads and..:~.~eds f i ~ u d e ignition due to frictional heating. .#...:~i~i'iii,i:~...~

5-1.4 Equipment. Equipment with moving parts shall ~- i i i~tal l :~ i i ' "~'";~""'~" and maintained so that true alignment is m a . . ~ . . : . . a n a ~ ~ e is provided to minimize friction. ....:~(..:.:::.'.. "-.'::.:-:~-.::, ":":":"::::::""::~iii;":

5-2 Electrical Equipment. All e l e c t r i c . ~ : ~ i p m e n t ":*~li- J

installations shall comply with the r e q i l i r e ~ of Seo~ln 2-7.

5-3* Static Electricity. The requirements of" ':"::~"':: 5::i. ~ -~.~. .;i i-'3.3 be applied retroactively. ~ : " ~

shall ,::#w

5-3.1" All system components shall be conductive. Bonding and

grounding with a resistance of less than 1.0 X 10 6 ohms to ground shall be provided.

Exception: Where the use of conductive components is not practical, nonconductive equipment shall be permitted when either (a) or (b) are followed:

(a) A documented engin~rlng analysis that is acceptable to the authority having jurisdiction has deterrained that no electrostatic ignition potential exists.

(b) Where materials being conveyed are not compatible with metal ductwork and other means of explosion protection are provided in accordance with 3-1.1(I), (3). (4), or (5).

5-3.2 Where belt drives are used, the belts shall be electrically

conductive and have a resistance of less than 1.0 X 106 ohms to ground.

5-3.3 Portable nonconductive bulk containers such as flexible intermediate bulk containers (FIBCs) shall not be permitted to

discharge material into equipment where flammable vapor atmospheres or ignition-sensitive dust atmospheres are present.

Exception:* FIBCs that are listed or tested by a recognized testing organization and are shown not to ignite flammable atmospheres during transfer shall be permitted to be used. Documentation of test results shall be made available to the authority having jurisdiction.

5-3.4 Particulate solids shall not be manually dumped directly into vessels containing flammable atmospheres (gases or vapors at a flammable concentration with an oxidant) or where displacement might cause a flammable atmosphere external to the vessel.

5-4 Cartridge-Actuated Tools. The requirements of 5-4.1 through 5-4.3 shall be applied retroactively.

5-4.1 Cartridge-actuated tools shall not be used in areas where combustible material is produced, processed, or present unless all machinery is shut down and the area is thoroughly cleaned and inspected to ensure the removal of all accumulations of combustible material. Accepted lock-out/tag-out procedures shall be followed for the shutdown of machinery.

5-4.2 The use of cartridge-actuated tools shall be in accordance with 5-5.2.

5-4.3 An inspection shall be made after the work is completed to ensure that no cartridges or charges are left in the area where they can enter equipment or be accidentally discharged after operation of the dust-producing or handling machinery is resumed.

5-5 Open F l a ~ Sparks. The requirements of 5-5.1 through 5-5.3 shall i~p l i ed :~e t roac t ive ly .

5-5.1 C t i ~ g ~i:.:M...elding shall comply with the applicable requi~'~'~t~s of 7 4 51B, Standard for Fire Prevention During W~,"~'}:~in~ anent'Hot Work. • ~,~:."~2 ".:~ . . . . . :¢'::~

. ~ . ~ G ~ d i n g , chlpl~ng, and other operataons that produce : " e i ~ , ~ $ ~ . or open flame ignition sources shall be controlled by a h ~ i ~ r k permit system in accordance with NFPA 51B, Standard for F i i ' ~ t . i o n During Welding, Cutting, and Other Hot Work.

i.-'.:..gl~..:3 Sm.'~]'ug shall be permitted only in designated areas.

;:"~-~eess.,,... and Comfort Heating Systems.

; ~ . 1 " In areas containing combustible dust, process and comfort eating shall be provided by indirect means.

5-6.2 Fired equipment shall be located outdoors or in a separate, dust-free room or building.

5-6.3 Air for combustion shall be taken from a clean outside source.

5-6.4 Comfort air systems for processing areas containing combustible dust shall not be recirculated.

Exception: Recirculating systems shall be permitted to be used i f all of the following are provided:

(a) Only fresh makeup air is heated. (b) The return air is filtered to prevent accumulations of dust in the

recirculating s3stem. (c) The exhaust flow is balanced with flesh air intake.

5-6.5 Comfort air shall not be permitted to flow from hazardous to nonhazardous areas.

5-7* Hot Surfaces. The temperature of surfaces external to process equipment, such as compressors; steam, water, process piping; ducts; and process equipment, within an area containing a combustible dust, shall be maintained below the lower of either 80 percent of the ignition temperature (in °C) or 165°C (329°F).

Exception: It shall be permitted to maintain temperatures within 80 percent of the minimum ignition temperature (in °C) of the dust layer as determined by recognized test methods acceptable to the autho~ty having jurisdiction.

128

N F P A 6 5 4 ~ M A Y 2 0 0 0 R O P

5-8 Industrial Trucks. In areas containing a combustible dust hazard, only industrial trucks listed or approved for the electrical classification of the area, as determined by Section 2-7, shall be used in accordance with NFPA 505, Fire Safe~ Standard for Powered Industrial Trucks Including Type Designations, Areas of Use, Conversions. Maintenance, and Operation.

Chapter 6 Fire Protection

6-1 General. Fire protection systems, where installed, shall be specifically designed to address building protection, process equipment, mad the chemical and physical properties of the materials being processed.

6-1.1" Fire extinguishing agents shall be compatible with the conveyed materials.

6-1.2 Where fire detection systems are incorporated in pneumatic conveying systems, an analysis shall be conducted to identify safe interlocking requirements for air-moving devices and process operations.

6-3.2 Portable spray hose nozzles that are listed or approved for use on Class C fires shall be provided in areas that contain dust in order to limit the potential for generating unnecessary airborne dust during fire-fighting operations. Straight stream nozzles shall not be used on fires in areas where dust clouds can be generated.

6-$.$ Private outside protection, including outside hydrants and hoses, where provided, shall comply with NFPA 13, Standard for the Installation of Sprinkler Systems.

6-4* Automatic Sprinklers.

6-4.1" Where a process that handles combustible particulate solids uses flammable or combustible liquids, a documented risk evaluation that is acceptable to the authority having jurisdiction shall be used to determine the need for automatic sprinkler protection in the enclosure in which the process is located.

6-4.2 Automatic sprinklers, where provided, shall be installed in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems.

6-1.3 Where fire detection systems are incorporated in the pneumatic conveying system, the fire detection systems shall be interlocked to shut down any active device feeding materials to the pneumatic conveying system upon actuation of the detection system.

Exception No. 1: Where spark detection and extinguishing systems are provided, the process shall be permitted to continue operating.

6-4.3 Where automatic sprinklers are installed, dust accumulation on overhead surfaces shall be minimized to prevent an excessive number of sprinkler heads from opening in the event of a fire.

6-5 Spark/Ember Detection and Extinguishing Systems. Spark/ember detection systems shall b e designed, installed, and maintained in accordance with NFPA 69, Standard on Explosion Prevention Systems; NFPA 72, National Fire Alarm Code; and NFPA 15, Standard for ~...ter Spray Fixed Systems for Fire Protection.

Exception No. 2: Where a sl~ark detection s~stem actuates a diverter ..:.-.'i:;::'::":'::::ii.,.~.. valve that sends potentially burning materidl to a safe location. 6-6 S p e c l a l . ~ . Prot~'ction S~ystems. Automatic extinguishing

systems o..r.:!i~., .hazard extinguishing systems, where provided, 6-1.4 Where the actuation of fire extinguishing systems is achieved shall be ~ i g n ~ s t a l l e d , and maintained in accordance with by means of electronic fire detection, the fire detection system, the fo..~..~"~g s t a r i ~ as.applicable. The extinguishing systems including control I~anels, detectors, and notification appliances, sha]..ff~i'~":'~f'~med ax~e$:'i~ m a manner that minimizes the shall be designed, installed, and maintained in accordance with g.c..~fi~ra~.o.n of dust c l o ~ during their discharge. NFPA 72, National Fire Alarm Code• .::##.::ii!::, ":ii!i.-":!:: :'-"~

~::" ":~:"1.~i.::.:~'::.11, Standard for Low-Expansion Foam 6-1.5 All fire detection initiating devices shall be connected to the (2y~-i~A" I lA , Standard for Medium- and High-Expansion Foam fire detection control panel via Style D or E circuits as described in Syster~ii~i~i~i~: ....... NFPA 72, National Fire Alarm Code• ~..'-:-~::.:,. ($) ~ i i i ] : ~ , Standard on Carbon Dioxide Extinguishing Systems

'~iii.:'::.':~i!:!:.~..4.) N~.-'A 12A, Standard on Halon 1301 Fire Extinguishing Systems 6-1.6 All fire detection notification appliances shall be connected ".-:i}: "i:ii~i'~i~i.-.:.'~A 15, Standard for Water Spray Fixed Systems for Fire to the fire detection control panel via Style Y or Z circuits as.. "'!!.:., ...~i::":':':"Pro"i~?~'*"'n described in NFPA 72, National Fire Alarm Code. ~::igi~ii'i~-. %i::" (6~;"" NFPA 16, Standard for the Installation of Foam-Water Sprinkler

...:.'-:Y" ""~! : ~::...,~nd Foam-Water Spray Systems 6-1.7 All fire extinguishing system releasing device.s..,:i~!enoi~or ~..:.. ~ii.:-':; (7) NFPA 17, Standard for D o Chemical Extinguishing Systems actuators shall be connected to the fire detection tf~;fi~.0.kp~-:..::..~i: '':~ (8) NFPA 2001, Standard on Clean Agent Fire Extinguishing Style Z circuits as described in NFPA 72, National Fire j ; : ~ C O d " ~ Y Systems The supervision shall include the continuity . ~ i ~ t i n g " t ~ i ~ n g system releasing device, whether solenoid ....~11" c I ~ g r " " ~ : " 6-7 Alarm Service. Alarm service, if provided, shall comply with (explosive device) filament, or other su~i~evice. ":%!i?:i:: :iiiiY" NFPA 72, National Fire Alarm Code.

• . *:':~:%~i~. "~ii~'.. "::: . . 6-1.8 All supervtsory dewces that m o m t o r ~ a i elem.~.'ts or Chapter 7 Trmnmg and Procedures functions in the fire detection and extinguisl~i~:..system.iiShaU be connected to the fire detection control panel ~'.:.-~y!.g~$) or E 7-1 Employee Training. The requirements of %1.1 through 7-1.3 circuits as described in NFPA 72, National Fire/~'~::"Code. shall be applied retroactively.

,y 6-1.9 All fire protection abort gates or abort dampers shall be connected to the fire detection control panel via Style Z circuits as described in NFPA 72, National Fire Alarm Code. The supervision shall include the continuity of the abort gate or abort damper releasing device, whether solenoid coil, detonator (explosive device) filament, or other such device.

6-2 Fire Extinguishers.

6-2.1 Portable fire extinguishers shall be provided throughout all buildings in accordance with the requirements of NFPA 10, Standard for Portable Fire Extinguishers.

6-2.2* Personnel shall be trained to use portable fire extinguishers in a manner that will minimize the generation of dust clouds during discharge.

6-3 Hose, Standpipes, and Hydrants.

6-$.1 Standpipes and hose, where provided, shall comply with NFPA 14, Standard for the Installation of Standpipe and Hose Systems.

7-1.1 Operating and maintenance procedures and emergency plans shall be developed. The plans and procedures shall be reviewed annually and as required by process changes.

7-1.2 Initial and refresher training shall be provided to employees who are involved in operating, maintaining, and supervising facilities that handle combustible particulate solids.

7-1.$ Initial and refresher training shall ensure that all employees are knowledgeable about the following:

(1) Hazards of their workplace (2) General orientation including plant safety rules (3) Process description (4) Equipment operation, safe start-up and shutdown, and

response to upset conditions (5) The necessity for proper functioning of related fire and

explosion protection systems (6) Equipment maintenance requirements and practices (7)* Emergency response plans

129

N F P A 6 5 4 - - M A Y 2 0 0 0 R O P

Chapter 8 Inspection and Maintenance

8-1 General Requirements. The requirements of 8-1.1 through 8-1.3 shall be applied retroactively.

8-1.1 An inspection, testing, and maintenance program shall be developed and implemented to ensure that the fire and explosion protection systems and related process controls and equipment perform as designed.

8-1.2 The inspection, testing, and maintenance program shall include the following:

(I) Fire and explosion protection and prevention equipment in accordance with the applicable NFPA standards

(2) Dust control equipment (3) Housekeeping (4) Potential ignition sources (5)* Electrical, process, and mechanical equipment, including

process interlocks (6) Process changes (7) Lubrication of bearings

8-1.3 Records shall be kept of maintenance and repairs performed.

8-2 Specific Requirements.

8-2.1 Maintenance of Material-Feeding Devices.

8-2.5.2 All fire extinguishing systems shall be maintained pursuant to the requirements established in the standard that governs the design and installation of the system.

8-2.5.3* All vents for the relief of pressure caused by deflagrations shall be maintained.

8-2.5.4 All explosion prevention systems and inerting systems shall be maintained pursuant to the requirements of NFPA 69, Standard on Explosion Prevention Systems.

Chapter 9 Referenced Publications

9-1 The following documents or portions thereof are referenced within this standard as mandatory requirements and shall be considered part of the requirements of this standard. The edition indicated for each referenced mandatory document is the current edition as of the date of the NFPA issuance of this standard. Some of these mandatory documents might be referenced in this standard for specific informational purposes and, therefore, are also listed in Appendix D.

9-1.1 NFPA Publications. National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101. -

NFPA 10, Standard for Portable Fire Extinguishers, 1998 edition. NFPA 11, Standard for Low-Expansion Foam, 1998 edition. NFPA 11A, Standard for Medium- and High-Expansion Foam Systems,

1999 edition. NFPA 12, Standard on Carbon Dioxide Extinguishing Systems, 1998

8-2.1.1 Bearings shall be lubricated and checked for excessive edition. Ai.:::.. wear on a periodic basis. NFPA 12A, ~ . d . . : o n Halon 1301 Fire Extinguishing Systems,

1997 editioru~i~i-~ " 8-2.1.2 ff the material has a tendency to adhere to the feeder or NFPA l$~'ff':..--~rdfor the Installation of sprinkler Systems, 1999 housin~ these components shall be cleaned periodically to edition. @~ "~::.!i~i~::~ maintain good balance and minimize the prdbability of'ignition. NFp..~...1..~:. , ~ t a n ~ : . : ~ r the Installation of Standpipe and Hose

Syst.~,':'~'~J" e di t i o ri~:-:!~,::.-'.':" 8-2.2 Maintenance of Air-Moving Devices. ..f.~~A..:l...5, Standard ~"?'¢¢Vater Spray Fixed Systems for Fire Protection,

. ::~" . - '~ e d e n . ::: 8-2.2.1 Fans and blowers shall be checked periodically for ~::~" ~..~...~..i:$!t~?;":';.~tandard for the Installation of Foam-Water Sprinkler and excessive heat and vibration. Foa~a..ter Spray Systems, 1999 edition.

.. N F l c ; ~ : , Standard for Dry Chemical Extinguishing Systems, 1998 8-2.2.2 Maintenance shall not be performed on fans or blowers ~:::!i~::~iii::: .... edition:':':-:!i~'.-".:.-':'~i i::" while the unit is operating. ::i~':'~:::~iii:'."~i!i!~:~::::.:..L~'PA~::::. -,:.:::::::-:::~:.-z._" 3~:.2:, Code fior the Manufacture and Storage o,f Aerosol Products,

::i~:. " : . ~ i ~ o n . 8-2.2.3 Bearings shall be lubricated and checked periodica.l.l.y, for ::-'.'~!:...:::'~.:'-'?" N~...-'J~'51B, Standard for Fire Prevention During Welding, Cutting, excessive wear. ~::.~i~i:'.."iiiii~'~i: ":.'~!::" and::.~)ther Hot Work, 1999 edition.

.,..-:~.'-g::~ ":%'::~i %...:.:.NFPA 61, Standard for the Prevention of Fires and Dust Explosions in 8-2.2.4* If the material has a tendency to adhere to.d~;~.rotor.~ ~. "::ii#~gricuttural and Food Products Facilities, 1999 edition. housing, these components shall be cleaned periotl~.go~!.':-":~!$1~::~i!i:.-::.~."iii~ :~:";:" NFPA 69, Standard on Explosion Prevention S~stems, 1997 edition. maintain good balance and minimize the probability o~i~ion.":::::'.~iiii?:iV NFPA 70, National Electrical Code*, 1999 edition.

..:.::::!:.:~!i!~.::':~::':¢.:... ""-'~%:. NFPA 72, National Fire Alarm Code*, 1999 edition. 8-2.2.5* The surface's of fan housings and .~.'ieer:'i~"".:~.~r " : : i ~ : . NFPA 80, Standard for Fire Doors and Fire ~ndows, 1999 edition. components shall be maintained free o[..~st. Aiurnf"i~'~ pai~i::" NFPA 86, Standard for Ovens .and Furnaces, 1999 edition. shall not be used on interior steel s u ~ - ~ : : . ":ii~i~ "~ .... NFPA 91, Standard for Exhaust Systems for Air Conveying of Vapors,

. . . . . . ~i!i!i!i!::!~ .... :!i!!!i! Gases, Mists, and Noncombustible Particulate Solids, 1999 edition. 8-2.3 Maintenance of Air-Materlal Separat~i::ii::.. ..if" NFPA 101 ®, Life Safe~y Code*, 1997 edition.

.... ~i~i~i~i~.-......#" 8-2.$.1 Air-separation devices that are e q u i p p e d " ~ : " a means to dislodge particulate from the surface of filter me~5, shall be inspected periodically as recommended in the manufacturers' instructions for signs of wear, friction, or clogging. These devices shall be adjusted and lubricated accordingly as recommended in the manufacturers ' instructions.

8-2.$.2 Air-material separators that recycle air (i.e., cyclones and filter media dust collectors) shall be maintained to comply with 2- 1.3.

8-2.3.3 Filter media shall not be replaced with an alternate type unless a thorough evaluation of the fire hazards has been performed, documented, and reviewed by management.

8-2.4 Maintenance of Abort Gates and Abort Dampers. Abort gates and abort dampers shall be adjusted and lubricated as recommended in the manufacturers' instructions.

8-2.5 Maintenance of Fire and Explosion Protection Systems.

8-2.5.1 All fire detection equipment monitoring systems shall be maintained in accordance with the requirements of NFPA 72, National Fire Alarm Code.

NFPA 120, Standard for Coal Preparation Plants, 1999 edition. NFPA 220, Standard on Types of Building Construction, 1999

edition. NFPA 221, Standard for Fire Walls and Fire Barrier Walls, 1997

edition. N-FPA 432, Code for the Storage of Organic Peroxide Formulations,

1997 edition. NFPA 480, Standard for the Storage, Handling, and Processing of

Magnesium Solids and Powders, 1998 edition. NFPA 481, Standard for the Production, Processing, Handling, and

Storable of Titanium, 1995 edition. NFPA 482, Standard for the Production, Processing, Handling, and

Storage of Zirconium, 1996 edition. NFPA 485, Standard for the Storage, Handling, Processing, and Use

of Lithium Meta~ 1999 edition. NFPA 495, Explosive Materials Code, 1996 edition. NFPA 496, Standard for Purged and Pressurized Enclosures for

Electrical Equipment, 1998 edition. NFPA 505, Fire Safety Standard for Powered Industrial Trucks

Including Type Designations, Areas of Use, Conversions, Maintenance, and Operation, 1999 edition.

NFPA 651 , Standard for the Machining and Finishing of Aluminum and the Production and Handling of Aluminum Powders, 1998 edition.

NFPA 655, Standard for Prevention of Sulfur Fires and Explosions, 1993 edition.

130

N F P A 654 - - MAY 2 0 0 0 R O P

NFPA 664, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities, 1998 edition.

NFPA 780, Standard for the Installation of Lightning Protection Systems, 1997 edition.

NFPA 1124, Code for the Manufacture, Transportation, and Storage of Fireworks and Pyrotechnic Articles, 1998 edition.

NFPA 1125, Code for the Manufacture of Model Rocket and High Power Rocket Motors, 1995 edition.

NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems, 1996 edition.

NFPA 8503, Standard for Pulverized Fuel Systems, 1997 edition.

9-1.2 Other Publications.

9-1.2.1 ASME Publications. American Society of Mechanical Engineers, 345 East 47th Street, NewYork, NY 10017.

ASME B 31.3, Process Piping, 1996. ASME Boiler and Pressure Vessel Code, Section VIII, 1995.

9-1.2.2 ASTM Publications. American Society for Testing and Materials, 100 Barr Harbor Drive, West Comhohocken , PA 19428- 2959.

ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C, 1996. ASTM E 1226, Test Method for Pressure and Rate of Pressure Rise for

Combustible Dusts, 1994. ASTM E 1515, Standard Test Method for Minimum Explosible

Concentration of Combustible Dusts, 1993.

9-1.2.3 ISA Publication. International Society for Measurement and Control, P.O. Box 12277, Research Triangle Park, NC 27709.

ISA $84.01, Application of Safety Instrumented Systems for the Process Industries, 1996.

Appendix A Explanatory Material

Appendix A is not a part of the requirements of this NFPA document

assumes the role of the authority having jurisdiction; at g o v e m m e n t installations, the commanding officer or departmental official may be the authority having jurisdiction.

A-I-5 Combustible Dust. Any time a combustible dust is processed or handled, a potential for def lagradon exists. The degree of deflagration hazard varies, depend ing on the type of combustible dust and processing methods used.

A dust explosion has the following four requirements:

(1) A combustible dust (2) A dust dispersion in air or o ther oxidant at or exceeding the

min imum explosible concentra t ion (MEC) (3) An ignition source such as an electrostatic discharge, an

electric current arc, a glowing ember , a hot surface, welding slag, frictional heat, or a flame

(4) Conf inement

Evaluation of the hazard of a combustible dust should be de te rmined by the means of actual test data. Each situation should be evaluated and applicable tests selected. The following list represents the factors that are sometimes used in de termining the deflagration hazard of a dust:

(1) Minimum explosible concentrat ion (2) Minimum ignition energy (MIE) (3) Particle size distribution (4) Moisture content as received and as tested (5) Maximum explosion pressure at op t imum concentrat ion (6) Maximum rate of pressure rise at opt imum concentrat ion (7) Kst (norm.~.~.ed rate of pressure rise) as def ined in ASTM E

1226, Test Met.#::~:-.~. ressure and Rate of Pressure Rise for Combust~le ~ "

(8) L a y . ~ ] ~ n temperature (9) Dt~:{~.~lou~ii.:~jtion temperature (lO):==i-~.~ng O ~ t concentrat ion (LOC) to prevent ignition ( 1 : ~ : ' : " ~ | ~ cal voli$~::~$sistivity

:~"~) ...G.harge re laxad~" time ...... ¢ i::::i ~ i!....i..: ~ .! ~...~rgeability / .....

'::i:i:i:i-::....::i::''"::i::. but is included for informational purposes only. This appendix contains A-l-~.i?:i::~ml~ustible Particulate Solid. The term combustible

~,. partic~.::~ol.~ d addresses the attrition of material as it moves explanatory material, numbered to correspond with the applicable text ::i~'.-::::.-::,,. within t | ~ : : i ~ c e s s equipment. Particle abrasion breaks the

paragraphs. '%:':~ii~i?:ii..:.-:~i~..~.t.erial ~i~Wn and produces a mixture of large and small A-I-I.I Examples of industries that handle combustible particulate "iiii: " ~ i . ~ . M t e s , some of which might be small enough to be classified solids, either as a process material or as a fugitive or nuis .an.....c.e ::i~i...::~;ili~::as d ~ . Consequently, the presence of dusts should be dust, include but are not limited to agricultural, chemi .c~ . : . :~ "~i!i!: ant?~pated in the process stream, regardless of the starting particle food commodities, fibers, and textile materials; forest..~'~d "::'!iiiiiii %, ~ize of the material. furni ture products industries; metals processing; p.a.~.'~:.prod~.~i~; .::.-, ":iiiiif;" pharmaceuticals; resource recovery operat ions (ti(~'s'i::!~ni.#~|~.-%:i::,.. '!~#:'-'~" A-l-5 Hybrid Mixture. The presence of f lammable gases and solid waste, metal, paper, or plastic recycling opera t io t~ .~ !~d "":~'~iiiiiiii!!Y vapors, even at concentrat ions less than the lower flammable limit wood, metal, or plastic fabricators. .::i~i~i:::.:. "::!~ii::iii:. (LFL) of the flammable gases and vapors, will add to the violence

,::~?: ......... ::~:'~:'.."~i~i~i:':'::, "::ii::~i~::!::ii:::i.'.:Y" of a dust-air combustion. A-l-5 Air-Moving Device ( A I D ) . An a~.~ti;~oving d ~ . ~ (A~.'.'.~:" is The resulting dust-vapor mixture is called a hybrid mixture and is a fan, centrifugal fan, or mixed flow ~ : . . e s e devic~!~.~.ave':'::" discussed in NFPA 68, C, uidefor Venting of Deflagrations. In certain previously been called blowers or exhaus t"~ i : :. ~iiii~; circumstances, hybrid mixtures can be deflagrable, even if the dust

": :':~: :':::-.......,.:... ....:::~" is below the MEC and the vapor is below the LFL. Furthermore, A-I-5 Approved. The National Fire P r o t e c t i o : ~ i ~ o ~ t i o n does dusts de te rmined to be nonignit ible by weak ignition sources can not approve, inspect, or certify any in s t a l l a t ions , " :~edures , equipment , or materials; nor does it approve or ~.~luate testing laboratories. In de te rmin ing the acceptability o f installations, procedures, equipment , or materials, the authority having jurisdict ion may base acceptance on compliance with NFPA or o ther appropria te standards. In the absence of such standards, said authority may require evidence of proper installation, procedure, or use. The authority having jurisdiction may also refer to the listings or labeling practices of an organization that is concerned with product evaluations and is thus in a position to de te rmine compliance with appropriate standards for the current product ion of listed items.

A-l-5 Authority Having Jurisdiction. The phrase "authority having jurisdiction" is used in NFPA documents in a broad manner , since jurisdictions and approval agencies vary, as do their responsibilities. Where public safety is primary, the authority having jurisdiction may be a federal, state, local, or other regional dej)artment or individual such as a fire chief; fire marshal; chief of a t~re prevention bureau, labor depar tment , or health depar tment ; building official; electrical inspector; or others having statutory authority. For insurance purposes, an insurance inspection depar tment , rating bureau, or other insurance company representative may be the authority having jurisdiction. In many circumstances, the property owner or his or her designated agent

sometimes be ignited when part of a hybrid mixture. Examples for hybrid mixtures are mixtures of methane, coal dust,

and air or mixtures of gasoline vapor and gasoline droplets in air.

A-l-5 Listed. The means for identifying listed equipment may vary for each organization concerned with product evaluation; some organizations do not recognize equipment as listed unless it is also labeled. The authority having jurisdiction should utilize the system employed by the listing organization to identify a listed product.

A-l-5 Minimum Explosible Concentration (MEC). MEC is equivalent to the term lower flammable limit for f lammable gases. Because it has been customary to limit the use of the term lower .flammable limit to f lammable vapors and gases, an alternative term is necessary for combustible dusts.

The MEC is d e p e n d e n t upon many factors, including particulate size distribution, chemistry, moisture content , and shape. Consequently, designers and operators of processes that handle combustible particulate solids should consider these factors when applying existing MEC data. Often, the necessary MEC data can be obtamea only by testing.

A-l-5 Water-Compatible. These materials include many of the cellulosics such as wood waste, paper dust, textile fibers, bulk agricultural products, municipal solid waste (MSW), refuse-

131

N F P A 654 ~ MAY 2000 R O P

derived fuel (RDF), and other organic materials including coal and some plastic resins. Water spray ext inguishment can be used for these materials when they are hand led in systems in which the process equ ipmen t is also water-compatible.

A-I-5 Water-Incompatible . Water-incompatible materials are typified by those that dissolve in water or form mixtures with water that are no longer processable, for example, sugar. Although water is an effective extinguishing agent for sugar fires, the sugar dissolves into the water, resulting in a syrup that can no longer be processed pneumatically. A similar situation exists with flour; when mixed with water, it becomes dough. These materials are candidates for extinguishing systems that use media o ther than water until the damage potential of the fire approaches the rep lacement cost of the process equipment• Then water is used to protect the structure.

A-I-5 Water-Reactive. Water-reactive materials represent a very special fire protect ion problem. The application of water f rom fixed water-based extinguishing systems or by the fire service without awareness of the presence of these materials might seriously exacerbate the threat to human life or property. For example, many chemicals form strong acids or bases when mixed with water, thus in t roducing a chemical burn hazard. Additionally, most metals in the powdered state can burn with sufficient heat to chemically reduce water-yielding hydrogen, which can then suppor t a deflagration.

These types of materials should be handled very carefully. Small quantit ies of water usually make matters worse.

A-2-1.1 The design of the pneumatic conveying system should be coordinated with the architectural and structural designs. The plans and specifications should include a list of all equipment , specifying the manufacturer and type number , and information as shown in (1) th rough (8). Plans should be drawn to an indicated scale and show all essential details as to location, construction, ventilation ductwork, volume of outside air at s tandard tempera ture and pressure that is in t roduced for safety ventilation, and control wiring diagrams.

(1) Name of owner and occupant (2) Location, including street address (3) Point of compass % (4) Ceiling construct ion "~ (5) Full he igh t cross section (6) Location of fire walls (7) Location of partit ions ~ : : . : :':"~i~i~i~.::::':':':'":" (8) Materials of construction ~iy-"

A-2-1.6 The design basis generally includes, but i s ~ ! ~ i ~ . ~ the general scope of work, design criteria, process ~,-,des, ~b.'n, ':-'*'-'.-"..i material flow dmgrams, basis for deflagratioo,:.:~0g.~.~g.tion, ~ i s for fire protect ion systems, and the physical a i ~ : : " o f the process materials. ,:: . . . . . . . . . ~!'::"

The design generally includes, but i ~ i t e d t o , ' ~ , p m e n t layouts, detai led mechanical drawings," s p ~ . a t i o n s , sij.'~porting engineer ing calculations, and process and , u , ~ e n t ~ ; b n diagrams. '::i::::..:::.:..~ ~y

Except for iner ted systems, it is preferable to d~": '~ ,Tstems that handle combustible particulate solids to operate . :~lder negative pressure.

A-2-2.3.1 A relatively small initial dust deflagration can disturb and suspend in air dust that has been allowed to accumulate on the fiat surfaces of a building or equipment• This dust cloud provides fuel for the secondary deflagration, which can cause damage. Reducing significant additional dust accumulations is therefore a major factor in reducing the hazard in areas where a dust hazard can exist.

3 3 Using a bulk density of 75 Ib/f t (1200 k g / m ) and an assumed concentrat ion of 0.$5 oz / f t s ($50 g /mS) , it has been calculated that a dust layer averaging ' / s~ in. (0.8 mm) thick and covering the floor of a building is sufficient to produce a uniform dust cloud of opt imum concentrat ion, 10 ft (3 m) high, th roughout the building. This situation is idealized; several factors should be considered.

First, the layer will rarely be uniform or cover all surfaces, and second, the layer of dust will probably no t be dispersed completely by the turbulence of the pressure wave from the initial explosion. However, if only 50 percent of the l/s~-in. (0.8-mm) thick layer is suspended, this material is still sufficient to create an a tmosphere within the explosible range of most dusts.

Consideration should be given to the propor t ion of building volume that could be filled with a combustible dust concentrat ion. The percentage of floor area covered can be used as a measure of

the hazard. For example, a 10 ft )< 10 ft (3 m X 3 m) room with a 1/ ,¢in. (0.8-mm) layer of dust on the floor is obviously hazardous

~ " • • 2 2 and should be cleaned. Now consider this same 100-ft (9 .3-m) area in a 2025-ft ~ (188-m ~) building; this also is a moderate hazard. This area represents about 5 percent of a floor area and is about as much coverage as should be allowed in any plant. To gain proper perspective, the overhead beams and ledges should also be considered. Rough calculations show that the available surface area of the bar joist is about 5 percen t of the floor area. For steel beams, the equivalent surface area can be as high as 10 percent .

From the preceding information, the following guidelines have been established:

(a) Dust layers I/s~ in, (0.8 mm) thick can be sufficient to warrant immediate cleaning of the area [l/s~ in. (0.8 mm) is about the d iameter of a paper clip wire or the thickness of the lead in a mechanical pencil] .

(b) The dust layer is capable of creating a hazardous condit ion if it exceeds 5 percen t of the building floor area.

(c) Dust accumulat ion on overhead beams and joists contributes significantly to the secondary dust cloud and is approximately equivalent to 5 percen t of the floor area. Other surfaces, such as the tops of ducts and large equipment , can also contr ibute significantly to the dust cloud potential.

(d) The 5 p e r c e n t factor should no t be used if the floor area exceeds 20,000 ft ~ (1860 mS). In such cases, a 1000-ft ~ (9~-m ~) layer of dust is 9er limit.

(e) Due co given to dust that adheres to walls, since

(f) should also be given to other projec~ which can provide surfaces for dust

(I ~)ment should be moni tored to ensure it [~i~.~ dust collectors using bags

::#~ ........ y pressure drops o f 3 in. to 5"~ii (0.74 kPa to 1.24 kPa). An excessive decrease or low dr( indicates insufficient coating to trap dust.

• through (g) will serve to establish a cleaning

"A-2z~; Window ledges, girders, beams, and o ther horizontal protections or surfaces can have the tops sharply sloped, or other

• " can be made to minimize the deposi t of dust thereon. : : ~ J ' O V t s I O n S

"~)verhead steel I-beams or similar structural shapes can be boxed with concrete or o ther noncombust ib le material to eliminate surfaces for dust accumulation. Surfaces should be as smooth as possible to minimize dust accumulations and to facilitate deaning.

A-2-3.9 The use of load-bearing walls should be avoided to prevent structural collapse should an explosion occur.

A-2-4 The design of deflagration venting should be based on information conta ined in NFPA 68, Guide for Venting of Deflagrations.

A-2-4.1 The need for building deflagration venting is a function of equ ipment design, particle size, deflagration characteristics of the dust, and housekeeping requirements . As a rule, deflagration venting is r e c o m m e n d e d unless it can be reasonably assured that hazardous quantities o f combustible and dispersible dusts will no t be permi t ted to accumulate outside of equipment .

Where building explosion venting is needed, detaching the operat ion to an open structure or to a building of damage-limiting construction is the prefer red me thod of protect ion. Damage- limiting construct ion involves a room or building that is designed such that certain interior walls are pressure resistant (can withstand the pressure of the deflagration) to protect the occupancy on the o ther side and some exterior wall areas are pressure relieving to provide deflagration venting. It is preferable to make maximum use of exterior walls as pressure-relieving walls (as well as the roof wherever practical), ra ther than provide the min imum recommended . Further information on this subject can be found in N-FPA 68, Guide for Venting of Deflagrations.

Deflagrafion vent closures should be des igned such that, once opened, they will remain open to prevent failure from the vacuum following the pressure wave.

132

N F P A 6 5 4 - - M A Y 2 0 0 0 R O P

A-2-4.2 For fur ther information on restraining vent closures and fireball impingement areas, see NFPA 68, Guide for Venting of Deflagrations.

A-2-5 High-momentum discharges f rom relief valves within buildings can disturb dust layers, creating combustible clouds of dust.

A-9-7.9 Refer to NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.

A-3-1 Exception. A means to de termine protect ion requirements should be based on a risk evaluation, with consideration given to the size of the equipment , consequences of fire or explosion, combustible propert ies and ignition sensitivity of the material, combustible concentrat ion, and recognized potential ignition sources. See the American Institute of Chemical Engineers - - Center for Chemical Process Safety, Guidelines for Hazard Evaluation Procedures.

The following items are areas of concern during the design and installation of process equipmerit:

(1) The elimination of friction by use of detectors for slipping belts, t empera ture supervision of moving or impacted surfaces, and so forth

(2) Pressure resistance or maximum pressure conta inment capability and pressure-relieving capabilities of the machinery or process equ ipment and of the building or room

Cyclone g " - - - - - ::i:i~

Dust collector

,ff

Vent

gnition )oint

Figure A-3-1.3 An example of deflagration propagation without isolation.

The dynamics of a dust explosion are such that unburned dust is pushed ahead of the flame front by the expanding products of combustion. This dust is expelled f rom the conta inment vessel via every available exit path, in all possible directions of flow,

(3) The proper classification of electrical equ ipment for the area including flow via all connect ing ducts and out th rough any and condit ion provided e x p l o s ! ~ venting. The driving force pushing the dust

(4) Proper a l ignment and mount ing to minimize or eliminate away f rom the.~i~:-::9.f initiation (which unde r vented conditions vibration and overheated bearings might be in ~ rang"~:'of a few psi) can easily overcome the force

(5) The use of electrically conductive belting, low-speed belts, of norn?a!~,~t~ii:flow (which typically might be of t.h.e order of a and short center drives as a means of reducing static electricity tew mcn~._.ii...wate~!umn ). Furthermore, the velocmes produced accumulation (see Section 5-3~ by the.:~.e.t"l'~k, r a t i o ~ a l l y greatly exceed those of the pneumat ic

(6) For power transmit ted to apparatus within the processing c o ~ j . ~ t e m u ~ " ~ r r n a l design conditions. Consequently, room by belt or chain, a nearly dustt ight enclosure of the belt or u ~ m . . e a / l u s t and th'~i~l'i-'tlagration t lame t ront can Ioe expectecl to chain that is constructed of substantial noncombust ib le material . ~ . . u p s t r e a m ~ o u g h ductwork from the locus of the initial that should be maintained unde r positive air pressure; for power " : ~ ' c t ~ ~ . transmitted by means of shafts, the shafts passing through close- T ~ n v e ~ a n c e of the flame front via both the in-feed and fittint~ shaft holes in walls or partitions outfl6%~.ucts..should be evaluated. In most cases, this movement

- ' - ' ~ ...... of dust '~! : : t .~bpagat ing flame front will commute the deflagration A-3-1.1(1)b The maximum allowable concentrat ion of oxygen is ~ : . ~ . . . t h e co~ '~c ted equipment ~a ductwork..Wh, ere equipment and very d e p e n d e n t on the material , its chemical composition, and, in ":~i': ':~-'..:.~:~.¢-aoequateiy protectea pursuant to m~s stantaarta ant1 the case of particulate solids, the particle sizes. In addition, with ~!~. :.....'.-'..:i-'~Fl~f~i~, Guide for Venting of Deflagrations (when explosion many combustible metals, it is not advisable to complet.~'#~i~!i~i!~ii:: ":~#'iY" v e n ~ g is used), the consequences of explosion propagat ion might eliminate oxygen from the t ransport gas. Durin~ tran~.~rt"::':iiiiiiiii " %. n..ot increase the life safety hazard or significantly increase the particles can" be abraded and br~)ken,exposing ~ a n o ~ e d m~a l ~:., '"~;~roperty damage. However, in other cases, the transit of a ( virgin metal) to the t ransport ga.s When this met~]'%i:":~.t.~....-...::::~:-$i:-:-.:..::~ .':::~:::::'":":" "':: ::?::~ deflagration. ~ f a m e front does resu t in substantial increases in the exposed to oxygen containing air, the rapid oxidation 6¢f..i~ virg~!~i~i~i~:: seventy or an event. metal could produce sufficient heat to ignite ..~.'!:materiai'.'::!!::!][~.:is, "'" . In the case of several pieces of equipment connected together via therefore, preferable to provide for a low c . ~ : ~ of ~ : ~ : ouc .tworK, wnere eac.a piece ot equipment and tlae cluctworK are in the t ransport gas stream to ensure the....~idation " ~ g i n ~.'..~i prowded ' w~th explosmn.venung, the dust explosion can as it is exposed durin~ the course of tr " ~ r t . ":~ii~i~i~ .:U nevermeiess propagate ttarouglaout tlae system. Explosion venting

. . . . . . . ":::':.:.]ii!~::.. ":.i~ii!! on the equipment of deflagration origin will prevent overpressure A- - .3 1 1 ()2 Where defagra t ion venting is u~ii~,~..~, d e s i ~ s h o u l d be damage to. that vessel. If the concentration, within, the connect ing based on information contained in NFPA 68, " ~ J r V e n t i n e of ductwork ~s below the MEC prior to the deflagratmn, the Defla~rations For deflagration relief venting Ha ~ : d u c t s ° deflagration can still spread to the next vessel, but the explosion con" si~ieratiot'a should b~'given to the reduc(lon ~"~eflagrat ion venting there should protect that second vessel from overpressure venting efficiency caused by the ducts. The relief duct should be damage. In such a case, the provision of explosion isolation restricted to no more than 20 ft (6 m). would not provide any significant reduct ion in either the property

A-3-1.1(5) This method is limited in effectiveness due to the high concentrat ions of inert material required and the potential for separation during handling. Other methods are preferred.

A-3-1.3 Methods of explosion protect ion using containment , venting, and suppression protec t the specific process equipment on which they are installed. Flame fronts from a deflagration can propagate through connect ing ductwork to other unprotec ted process equ ipmen t and to the building from outside process equipment . Figure A-3-1.3 shows an example of how this

p ropagation might occur. Isolation techniques as shown in igures A-3-1.3.1(3) th rough (5) can be used to prevent the

propagation of the deflagration by arresting the flame front.

Both the direction and extent of potential deflagration propagation must be considered. Usually, a dust deflagration occurs in a fuel-rich regime (i.e., above the stoichiometric fuel-air ratio), making it likely that the initial defagra t ion will expand into volumes that are many times greater than the initial deflagration volume.

damage or life safety hazard. If the concentrat ion within a connect ing duct is above the MEC

prior to the deflagration, then the propagation through that duct will result in an accelerating f a m e front. Without explosion venting on the ductwork, this accelerating flame front will result in a significant prepressurization of the equ ipment at the other end of the duct and in a very powerful j e t flame ignition of a dust deflagration within that second vessel. Such a deflagration can overwhelm the explosion venting on that vessel, even if designed to NFPA 68, Guide for Venting of Defl.agrations, resulting in the catastrophic rupture of the vessel. In this case, the explosion propagat ion results in a significant increase in the property damage and, quite possibly, in an increase in life safety hazard due to the vessel rupture. Consequently, explosion isolation is a critical componen t to the managemen t of the fire and explosion risk.

In the case of a dust collector serving a large number of storage silos, an explosion originating in the dust collector can produce an acceptable level of damage to the collector if it is provided with adequate explosion venting per NFPA 68, Guide for Venting of Deflagrations. However, the propagat ion of that explosion

133

N F P A 6 5 4 ~ M A Y 2 0 0 0 R O P

upstream to all of the connected silos could cause ignition of the material stored in all of those silos. The initiation of such storage fires can significantly escalate the magnitude of the incident, in terms of property damage, interruption to operations, and life safety hazard. As with the previous example, explosion isolation would be warranted in this case.

A-3-1.3.1 (1) Figure A-3-1.3.1 (1) illustrates two different designs of chokes.

,"1.:~ l : Baffle plate . . . . . . . . ] . . . . . . = i ° . - - ° j

. . . . i - t

! - i

• Choke , ,

Example 1

A-3-1.3.1 (3) Figure A-3-1.3.1 (3) illustrates one example of deflagration propagation using mechanical isolation.

Cyclo e I I ~..=~lsolation

II

Vent Dust colleck

~'.:!i~.+.'i!--" ~lgnition ~" ~point

Figure A-3-1.3.1 (3) An example of deflagration propagation using mechanical isolation.

A-3-1.3.1(4) Figure A-3-1.3.1 (4) illustrates one example of deflagration propagation using flame front diversion.

"~ ~i

Example 2 .-'.:~!~!'~:'" N :iiii!!~!:i:#':" F'gure A-3-1.3.1(1) Two examples of screw conve)~i!/bl~J~e~i~ii~i~! " ]~

Flame front rsion

Vent Dust collectc

••lgnition ~( U point A-3-1.3.1(2) When rotary valves are install outlet of equipment, care should valve on the inlet is stopped before the See Figure A-3-1.3.1 (2).

E ectrica

,n,e,,0ck V-- "7 ROttaa;; valve A enejgiiz;i~[ B A d d ~ e _ - e e ~

. . . . . . / X , W , v e

Product ~ B outlet [ ~t [

"q::::::::;;..

be take.~.~8 ensur'~..".~ t h e ' ~ y e.:~.~ becomes""~rfill~[ flame front diversion.

~a/v A-3-1.3.1(5) Figure A-3-1.3.1(5) illustrates one example of i J deflagradon propagation using chemical isolation.

Hgure A-3-1.3.1 (4) An example of deflagration propagation using

I Dust collector

Figure A-3-1.3.1(2) An example of rotary valves.

Cyclo CZEEE

Vent

~" Chemical

~ - ~ Ignition "~" U p°int

Hgure A-3-1.3.1(5) An example of deflagration propagation using chemical isolation.

134

N F P A 654 ~ MAY 2 0 0 0 R O P

A-3-1.$.1 Exception No. 2. See A-3-1 Exception text for an explanation of the considerations in a documented risk evaluation.

A-3-1.3.2 Exposures of concern include, but are not limited to, bagging operations and hand dumping operations where the discharge of a fireball from the pickup point would endanger personnel.

A-3-2.1 Exception. Shipping containers can pose a deflagration hazard; however, deflagration protection measures for these units are not always practical. Consideration should be given to deflagration hazards when electing to omit deflagration protection.

A-3-2.4 Horizontal projections can have the tops sharply sloped to minimize the deposit of dust thereon. Efforts should be made to minimize the amount of surfaces where dust can accumulate.

A-3-2.5 For information on designing deflagration venting, see NFPA 68, Guide for Venting of Deflagrations.

A-3-2.3.2 Exception No. 2. Where explosion venting is used, its design should be based on information contained in NFPA 68, Guide for Venting of Deflagrations. For explosion relief venting through ducts, consideration should b e given to the reduction in explosion venting efficiency caused by the ducts. The ducts should be designed with a cross.sectional area at least as large as the vent. They should be structurally as strong as the air-materiai separator and should be limited in length to 20 ft (6 m). Since any bends will cause increases in the pressure developed during venting, vent ducts should be as straight as possible. If bends are unavoidable, they should be as shallow angled (i.e., have as long a radius) as is practicable.

A-3-2.3.2 Exception No. 3. Small containers can pose an explosion hazard; however, explosion protection measures for these units are not always practicable. Consideration should be given to explosion hazards when electing to omit protection.

A-3-2.3.3 Exception No. 2. See A-3-2.3.2 Exception No. 3.

A-3-$.$.2 Some chemical andplas t ic dusts release residual flammable vapors such as residual solvents, monomers, or resin additives. These vapors can be released from the material during handling or storage. Design of the system should be based on a ~ minimum airflow suflicient to keep the concentration of the particular flammable vapor in the airstream below 25 per o L o f the LFL of the vapor. . d ~ . , -

A-M.I . I Whether a metallic particulate reacts wi _tl~.,~. i on particle size, chemical purity of the particulate;~ox)~! concentration, and combustion temperature. Conse c tut~ engineering analysis should be performed p ~ ~ _ extinguishment strategy. In some cases, a~ volume water spray system has been s h ~ , : ~ : . the rapid absorption of heat.

Metals commonly encountered in a corr clude cadmium, chromium, cobalt, copper, h a f n i ~ , ' ~ o n , ; ~ d , manganese, molybdenum, nickel, niobium, p ~ i silver, tantalum, vanadium, and zinc. a r ~ / ~ '" Although thes, generally considered less combustible than the alkali rrLeta~ (aluminum, magnesium, titanium, and zirconium), thoystill should be handled with care when in finely divided form.

In many cases, water will be an acceptable extinguishing agent if used properly. Many infrared spark/ember detectors are capable of detecting burning particles o f these metals. Consequently, these metal particulates can often be treated as combustible particulate solids without the extremely hazardous nature of the alkali metals.

A-3-6.3 Whenever a duct size changes, the cross-sectional area changes as well. This change in area causes a change in air velooty in the region of the change, introducing turbulence effects. The net result is that a transition with an included angle of more than $0 degrees represents a choke when the direction of flow is from large to small and results in localized heating and static electric charge accumulation. When the transition is from small to large, the air velocitydrop at the transition is usually enough to cause product accumulauon at the transition and the existence of a volume where the concentration of combustible is above the MEC. It is strongly desirable to avoid both of these situations.

A-3-6.4 Isolation devices in accordance with 3-1.$ are provided to prevent deflagration propagation between connected equipment.

According to 3-1.3, additional protection is indicated when the integrity of a physical barrier could be breached through ductwork failure caused by a deflagradon outside the equipment. In some cases, a single equipment isolation device can provide protection in bo th scenarios if that isolation device is instailed at the physical barrier. In other cases, this concern can be addressed by strengthening the duct and supports to preclude failure.

A-3-10 It is recommended that bucket elevators be located outside of buildings wherever practicable. Although explosion protection for bucket elevators is required in 3-10.1, an additional degree of protection to building occupants and contents is provided by locating the bucket elevator outside of the building.

A-3-10.1 Deflagration vents on b u r e t elevators should .be distributed along the casing side in pairs, opposite each other, next to the ends of the buckets. Each deflagration vent should be a minimum of two-thirds of the cross-sectional area of the leg casing and should be located approximately 20 ft (6 m) apart. Vent closures should be designed to open at an internal gauge pressure of 0.5 psi to 1.0 psi (3.4 kPa to 6.9 l&a). Vent closure devices should be secured to eliminate the possibility of the closures becoming missiles. Vent materials should be of lightweight construction and meet the guidelines given in NFPA 68, Gui&for Venting of D~agratiens.

Bucket elevator head sections are recommended to have 5 ft * (0.5 m ~) of vent area for each 100 ft s (2.8 m s) of head section volume.

Vents should not be directed at work platforms, building ol~ening s , or other potentially occupied areas.

For bucket elevators inside of buildings, vent ducts should be designed with a~lgss-sectional area at least as large as the vent, should be s ~ a s strong as the bucket elevator casing, and should be ! ~ in l~ngth t o 1 0 ft (3 m). Since any bends will

k, t h e [ developed during venting, vent cause m c r ~ e ~ M wessure ducts s h ~ c l b e ' ~ t r a i g h t as possible. If bends are unavoidable, they s J ~ b e as have as long radius) as ; l o w . - ~ a g l e d (i.e., a

o r

ere it is d~sired to prevent propagation of an m the elevator leg to another part of the facility, an

isolation system should be provided at the head, hoot,

motor selected should not be larger than the ard motor capable of meeting this requirement.

Explosion protection should be provided when the risk is rot. (See ~1.1.)

A-3-12.2 Exception No. 1. Some systems are designed to operate at solids concentrations that pose no fire or deflagration risk. Such systems include nuisance dust exhaust systems and the downstream side of the last air-material separator in t h e pneumatic conveying system.

A threshold concentration limit of I percent of the MEC has been conservatively set to discriminate between such systems and other systems desi~paed to operate at a significant combustible solid loading. This limit ensures that normal variations in processing conditions will not result in the combustible particulate or hybrid mixture concentration approaching the MEC.

Where significant departures from normal conditions, such as equipment failure, could result in a combustible concentration approaching or exceeding the MEC, additional protection should be considered where the risk is significant. Such protection might include one of the following:

(1) Secondary filtration (e.g., high-efficiency cartridge filter) between the last air-material separator and the AMD

(2) Bag filter failure detection interlocked to shut down the AMD

A-3-12.2 Exception No. 2. These systems include pneumatic conveying systems that require relay (booster) fans and product dryers where the fan is an integral part of the dryer.

A-3-15.1.1 Exception No. 2. Where deflagration venting is used, its design shou ldbe based on information contained in NFPA 68, Guide for Venting of Deflagrations. For deflagration relief venting through ducts, consideration should be given to the reduction in deflagration venting efficiency mused by the ducts. The ducts should be designed with a cross-sectional area at least as large as the vent, should be structurally as strong as the dust collector, and should be limited in length to 20 ft (6 m). Because any bends will

135

N F P A 6 5 4 ~ M A Y 2 0 0 0 R O P

cause increases in the pressure that develops dur ing venting, vent ducts should be as straight as possible. If bends are unavoidable, they should be as shallow-angled (i.e., have as long a radius) as practicable.

A-3-13.1.5 For design requ i rements for fast-acting dampers and valves, flame f ront diverters, and flame front ext inguishing systems, see NFPA 69, Standard on Explosion Prevention Systems.

A-3-13.2.3.5 See NFPA 68, Guide for Venting of Deflagrations.

Ao3-15 Size reduct ion machinery includes equ ipmen t such as mills, grinders, and pulverizers•

A-3-16 Particle separat ion devices include screens, sieves, aspirators, pneumat ic separators, sifters, and similar devices.

A-3-16.3 For informat ion on designing deflagrat ion venting, see NFPA 68, Guide for Venting of Deflagrations.

A-3-16.3 Exception. As a practical matter , screens are difficult to protect against explosion by deflagration vent ing or inerting. Therefore, it is impor t an t tha t screens be isolated f rom the fire and explosion hazards of the r ema inde r of the process and be adequately protec ted against electrostatic ignit ion sources• Protect ion should be accompl ished by bond ing and g round ing of all conduct ive components .

A-3-18 Dryers include tray, d rum, rotary, fluidized bed, pneumat ic , spray, ring, and vacuum types. Dryers and thei r opera t ing controls should be designed, constructed, installed, and mon i to red so tha t requi red condi t ions of safety for operat ion of the air heater, the dryer, and the venti lat ion equ ipmen t are main ta ined .

FeE hol:

or of

; tock

A-3-18.8 The max imum safe opera t ing t empera tu re of a dryer is a funct ion of the t ime- t empera tu re ignit ion characteristics of the . part iculate solid be ing dried as well as of the dryer type. For short- ~::i.:iii:: t ime exposures of the material to the heat ing zone, the opera t ing ..~iiiiiii!,.'~ . . . . . . . . . . . I t empera tures of the dryer can approach the dust cloud ignit ion "-'..'." ".:~:.'...!~..:...;..-~::~::.~,,.:. I t roll temperature . "%::iiiiiii::, "

However, if part iculate solids accumulate on the dryer surfaces, .. F ~ A.-.~l.l.4(a) An example of a pneumat ic s e p a r a t o r . the opera t ing t empera tu re should be main ta ined below the dust ~.:'.':ii~!!:i~ ~. ":~!~.-':~? i:~ layer ignit ion temperature . The dust layer ignit ion t empera tu re is : : ~ : : . . . . . . . iiii i:'v a funct ion of time, temperature , and thickness of the layer. It can % ~:::~'.-"~:-.-'-.'::..-.-:---;-;~:: ~ '-~"~-Ad"eh.te temperature.be several h u n d r e d degrees below tile dust cloud lgmuon~!~....:: ~.~:::..iiii! ;'::i:;:: :...:;v.-:~:"' ~ ~ ¢ ¢ A

The operat ing t empera tu re limit of the dryer should..::~" bandy-:on '!~ii::....:,- / ~ . . . . an en~zineerin~ evaluation takin~ into consideration:.~'ate n r e c ~ n ~ .. :~i:' / • / / Operatlona position . . . . . s ~ ' ~ "::Y""~:::':'~""3:':~ :-"::::"~:i:'::':'~'" ":::":" ~i~;~:, / / ~ Of magnets The dust c loud ignit ion t empera tu re can be d e t e r m i n ~ . ~ the ~ ! - " • / ~ / ~ ' ~ ( ~ 1 ~ - ~ \ ~ ' ' ' ~

m e t h o d re fe renced in the U.a. Bureau of M i l k w o r t d$.!liii~ii! .... / / / ~ ' \ \ ~ l I l l i l I D Investigations, RI 8798, "Thermal and E t e ~ ~ ! l i t y ' ~ i i ~ ! : : : ¢ : " / / , ~ . ~ ' ~ x . ~ d ~ Open p o s i t i o n o f Dusts," Conti, IL S. et al (modif ied G o ~ ' r t - G r e ~ n ' ~ f u r t a ~ I / . - " '."t'"'"'~. i / m a g n e t s for r e m o v a the BAM Furnace, or other , methods) ~.:.-'~dust-.-...~::.~:~ . lay e r ~ ~taor~ " .... =~:, ......... P: .... ~ ' " ~ o f , tram p m e t a l t empera tu re can be de t e rmined by BureatF.::.~i~ ~llnes tes~ii~rocedure I / ~ ~ Z . ~ . ' ~ ' ' ~ oi ~ in Lazzara and Miron, "Hot Surface I g n i t i o r ~ : ~ p e r a . . ~ : e s of Dust I I J ....... Layers." ":%iiii~::.:::..'~#" ~ - . ..-,n:.: ............... "..

A-4-2.1 See A-2-2.3.1. jy.. C ~ i , %" : : : : : : : : : : : : : : : : : : : : : : . . . . . . . . t".', "'" " "

/:---, ..... f.:.', i . . - A-4-2.2 Vacuum cleaning systems are the preferred me thod for : ":. "~..~ Grinding i ~ l,~: ~:. ................ i c leaning surfaces• [ ! i l roach no i ~ [..A'.i "

: : : • ! n =;,.:.'... , . . . . . . . . . . ......... ~ , ." l g ° - . " . . . . . . . . . . . . . . .

A-5-1.1.3 If the part iculate particle size range includes dusts that .~ . . . . . : ~ .~ .a .......... can attain concentra t ions capable of propagat ing a f lame f ront ,"'"~,.~'::: i .... £~.'::::'.:::':: .........

! o ".... -..;'::..¢~ .......... -:.-:.;:':; ........ t h rough a fuel-a l r mixture, the risk m a n a g e m e n t opt ions in 3-1.1 are appropriate• Conversely, if the analysis indicates that the i ~ i J particle size and concent ra t ion do not predic t a propagat ing flame

Figure A-5-1.1.4(b) An example of a magnet ic s e p a r a t o r .

A-5-1.2 Transmission of power by direct drive should be used, where possible, in preference to belt or chain drives•

f ront th rough the fuel-a i r mixture, the fire protect ion methods in Chapter 6 should be considered.

A-5-1.1.4 Part icular a t ten t ion should be paid to combust ible particulate solids where they are in t roduced into the process stream. Some sources of part iculate might include stone, t ramp iron, o ther metallic contaminants , and already b u r n i n g material. Before a risk m a n a g e m e n t strategy is adopted, bo th the part iculate an d the process equ ipmen t must be carefully evaluated.

See Figures A-5-1.1.4(a) and (b) for examples of foreign material removal.

A-5-1.3 Considerat ion should be given to the potent ia l for overheat ing caused by dust entry into bearings. Bearings should be located outside the combust ible dust stream, where they are less exposed to dust and more accessible for inspect ion and service. Where bearings are in contact with the part iculate solids stream, sealed or purged bearings are preferred.

136

N F P A 654 ~ MAY 2 0 0 0 R O P

A-5-3 See NFPA 77, Recommended Practice on Static Electricity, for information on this subject•

A-5-3.1 Bonding minimizes the potential difference between conductive objects. Grounding minimizes the potential difference between objects and ground.

A-5-3.3 Exception. Certain fabrics that pose significantly less risk of ignition in f lammable a tmospheres have been developed for use in FIBCs. One such fabric that has been tested for use in a tmospheres having a min imum ignition energy of 0.25 mJ or greater and has been used in FIBCs is documen ted in Ebadat and Mulligan, "Testing the Suitability of FIBCs for Use in Flammable Atmospheres ."

A-5-6.1 Heat ing by indirect means is less hazardous than by direct means and is therefore preferred. Improved protect ion can be provided for direct-fired dryers by providing an approved automatic spark detect ion and extinguishing system.

A-5-7 The ignition tempera ture of a layer of dust on hot surfaces might decrease over time if the dust dehydrates or carbonizes. For this reason, the hot surfaces should not exceed the lower of either the ignition temperature or 329°F (165°C). The ignition temperatures for many materials are shown in NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.

(1) Cotton fibers (due to the resultant equipment damage from water discharge)

(2) Many foodstu t~ such as sugar, flour, spices, cornstarch, yeasts

(3) Grains and cereals (4) Tobacco (5) Many pharmaceuticals (6) Many chemicals

Because the conveyed material or the process equipment is irreparably degraded when water is added to these materials, the first line of defense is an extinguishing system that utilizes some other agent. Examples of agents used in these systems include carbon dioxide, sodium bicarbonate, m o n o a m m o n i u m phosphate , nitrogen, and clean agents. However, a water-based extinguishing system can be employed as a backup to the special agent extinguishing systems.

Examples of water-incompatible systems include water-soluble materials and flour. A spray of water into a pneumatic conveying duct that transports f lour will extinguish a spark, but the water will combine with the flour to form a paste that will clog the system and promote fermentat ion. Consequently, there is an operations- based incentive to consider alternatives to water-based extinguishing systems.

Water-reactive materials chemically react with water to produce some other material that might represent a different set of fire protect ion problems. The most notable water-reactive materials are the powdered metals. Many powdered metals, including aluminum, magnesium, titanium, zirconium, and lithium, react

A-6-1.1 Pneumatic conveying systems that move combustible violently with water to form an oxide, l iberating hydrogen gas as a particulate solids can be classified as water-compatible, water- by-product. Th...es..~::..materials can start a fire when exposed to water incompatible, or water-reactive• Inasmuch as water is universally if they are of ~ n t l y small particle size• Consequently water the most effective, most available, and most economical is not usual[~!~, opti~a as an extinguishing agent for an ' extinguishing medium, it is helpful to categorize combustible establishe.~!~.'.~..(,.olving these materials. particulate solids in relation to the applicability of water as the Other ~ s ~=:~..less violently with water and only under agent of chozce, cer t~ ' .~i~.~. . . r '~s tan '~ The use of water on these materials once

Water-compatible particulate solids are those combustibles that the~i.$;/~!".~tiieved i ~ temperature can also produce can be extinguished with water and nei ther react with nor form h.~l-rog~o. However, ~ s e d in copious quantities, water can be an mixtures with it. These solids include the following materials: ~.i~tiv~i!i.i~.x.finguishin~"strategy. Nevertheless, all metals should be

" : " h ' ~ e ~ care, given that their reactivity is highly d e p e n d e n t on (1) Wood dusts, fibers, chips, shavings, and flakes t h e ' ~ c u l a r metal particle size, and temperature. (2) Some paper dusts, dependi.n~ on ultimate use . The~.'~.i~.o.f .w~ter-reactive combustibles is no t limited to (3) Municipal solid wastes (MSw), including refuse-derived '-:iiiii~':~i~:.-::.:,. c o m b u s ~ ! ! ~ e t a i s but also includes some pharmaceuticals and ~::.-::.'::::: ~.:':~(~ . - : . : : : : . . . . .

fuels (RDF) ::~:'- ~ . '~ .¢ . .mical~: These chermcals produce ei ther a fire or a toxic or (4) Coal chunks, pellets, and dusts % " ~ . . " ..~"~"by-product when mixed with water. (5) Shredded plastic and papers at recycling facilities .,- ":'ii~.~;:: ~ i ~ r t e d system is often used because of the difficulties (6) Many plastic powders and pellets ~ ' ! . , . "%~:' encOUntered in extinguishing these materials. However, it should (7) Pulverized cork that is used in a f looring p r o d u ~ : " ":::¥.:':'!i: % .~. no ted that some commonly considered inerting agents, such as

manufactur ing process ~i~:~ .~#" ~, "~i~O~ or ni t rogen might be incompatible with certain metals at (8) Conveyed agncuhurai commodlUes such a s - ~ l ] [ ~ , ~ - . . ~ ? : , '.'..~.~".. high temperatures.

shells, and cocoa beans in a de-shelling operation "~...:-".~.:." ::~-'-".~!:: In summary, a combustible particulate solid should be classified ::::::: ..... " ...... only after a thorough review of the chemistry and physical form of (9) Chopped feathers in a dryer .~..--'.:'.-~:.:::.--:•.. "::i.'-'..':~:..

The cbemical and physical properties, : ~ g e of p a ~ . s ize~ii~d types of process equ ipment used with ~ . : . ? : c o m b u s t i ~ usff~ly allow these applications to be c o n s i d d i ' e & ~ r - c o m p a i ~ l e . A principal concern is the ignition of a dust c ~ : ~ i n . . . . . . the..:'~r-material~.::. . separator or the storage vessel. When the sou~.~j~f ~ql taon is genera ted upstream, this risk can often be r e d u d ~ t h e spark or ember is detected and extinguished prior to its e ~ into the a i r - material separator or the storage vessel. In some applications, spark detect ion and intermit tent water-spray extinguishing systems can be effectively used because the ultimate usefulness of the particulate material is no t affected if it is wet.

In numerous drying, chopping, crushing, and gr inding operations, the introduct ion of water does not represent a serious threat to the t ranspor ted material or to the process equipment. For example, in woodworking plants the wood waste is usually sold as raw material for particleboard or is used as fuel to hea t the facility. The moisture from the operat ion of an extinguishing system is of no consequence. This allows the use of spark detect ion and intermit tent water spray as the fire protection strategy. For other applications, a water deluge system is a more appropriate fire protection strategy, even though it might disrupt the normal flow of material or interrupt the process operation.

In contrast, in water-incompatible systems, the introduction of water will cause unacceptable damage to the equ ipment or to the material being processed. In these systems, the particulate solids are combustibles that can be extinguished with water but dissolve in or form a mixture with water that renders them no longer processable, or the process equ ipment cannot tolerate the introduct ion of water. Water-incompatible solids include the following materials:

the particulate, the type of process equipment , the subsequent use or processes, the relevant literature regarding loss history in similar processes and products, o ther hazards associated with the process material, and the response capabilities of the fire service.

A-6-2.2 Extreme care must be employed when using hand-portable fire extinguishers in facilities where combustible dusts are present. The rapid flow of the extinguishing agent across or against accumulations of dust can produce a dust cloud• When a dust cloud is produced, there is always a deflagration hazard. In the case of a dust cloud produced as a result of fire fighting, the ignition of the dust cloud, and a resulting deflagration, is virtually certain.

Consequently, when hand-portable fire extinguishers are used in areas that contain accumulated combustible dusts (refer to A-2- 2.3.1), the extinguishing agent should be applied in a manne r that does not disturb or disperse accumulated dust. Generally, fire extinguishers are designed to maximize the delivery rate of extinguishing agent to the fire. Special techniques of fire extinguisher use must be employed to prevent this inheren t design characteristic of the fire extinguisher from producing an un in tended deflagration hazard.

A-6-4 Automatic sprinkler protect ion within dust collectors, silos, and bucket elevators should be considered. Considerations should include the combustibility of the equipment , the combustibility of the material, and the amount of material present.

A-6-4.1 A risk evaluation should consider the presence of combustibles both in the equipment and in the area a round the process. Considerations should include the combustibility of the

137

N F P A 6 5 4 - - M A Y 2 0 0 0 R O P

building construction, the equipment , the quantity and combustibility of process materials, the combustibility of packaging materials, open containers of f lammable liquids, and the presence of dusts. Automatic sprinkler protection within dust collectors, silos, and bucket elevators should be considered.

A-7-1.3(7) All plant personnel , including management , supervisors, and maintenance and operat ing personnel , should be t rained to participate in plans for controll ing plant emergencies. Trained plant fire squads or fire brigades should be maintained.

The emergency plan should contain the following elements:

(1) A signal or alarm system (2) Identification of means of egress (3) Minimization of effect on operating personnel and the

community (4) Minimization of property and equipment losses (5) Interdepar tmental and interplant cooperat ion (6) Cooperat ion of outside agencies (7) The release of accurate information to the public

Simulated emergency drills should be per formed annually by plant personnel . Malfunctions of t h e p r o c e s s should be simulated and emergency actions undertaken. "Disaster" drills that simulate a major catastrophic situation should be under taken periodically with the cooperat ion and participation of public fire, police, and other local community emergency units and nearby cooperat ing plants.

A-8-1.2(5) Process interlocks should be calibrated and tested in the manne r in which they are in tended to operate, with written test

The following is the major advantage of containment: Low maintenance - - passive.

The following are disadvantages of containment: (1) High initial cost (2) Weight loading on plant structure

B-3 Inerting. Inerting protect ion is provided by lowering the oxygen concentrat ion, in an enclosed volume, to below the level required for combustion. This is achieved by introducing an inert gas such as ni t rogen or carbon dioxide. Flue gases can also be used, but they could first require cleaning and cooling. (See NFPA 69, Standard on Explosion Prevention Systems.)

The purge gas flow and oxygen concentrat ion within the process should be designed reliably with appropriate safety factors in accordance with NFPA 69, Standard on Explosion Prevention Systems. Consideration should be given to the potential for asphyxiation to personnel due to purge gas/leakage.

The following is the major advantage of inerting: Prevention of combustion, thereby avoiding product loss.

The following are disadvantages of inerting: (1) Ongoing (lost of inert gas (2) Possible asphyxiation hazard to personnel (3) High maintenance

B.4 Deflagration Venting. Deflagration venting provides a panel or door (vent closure) to relieve the expanding ho t gases of a deflagration from within a process c o m p o n e n t or room.

B-4.1 How Deflagration Venting Works. Except for an open vent, which allows flammable gases to discharge direcdy to the atmosphere, d e f l ~ a t i o n vents open at a p rede te rmined pressure

records mainta ined for review by management . Testing frequency referred to as ~ " : i ~ e vent is either a vent panel or a vent door. should be de te rmined in accordance wtth the AIChE, "Guidelines The pressur~ .gase ' s ' : ' a re discharged to the a tmosphere either for Safe Automation of Chemical Processes." directly or.::.~a:~"":"~i~nt duct, resulting in a reduced deflagration

p r e s s u r e ; : ' ~ . ~ ? d e f l a g r a t i o n vent a r rangement is designed to A-8-2.2.4 Periodic cleaning of components is especially impor tant ensur~'-~i~.ressu'i~i:xP,~, is below the rupture pressure of the if the blower or fan is exposed to heated air. p r q ~ ' : ~ ' i ~ l or ro~i!i:::-~fiis process is illustrated in Figure B-4.1.

iir y .,..: ..~.

A-8-2.2.5 If rust is allowed to form on the interior steel surfaces, it ..:~iiii~:. '~iii~ii:. :: is only a matter of time before an iron oxide (rust) becomes "::"~%::i!::!!i::....:i::::ii;:~:i:iiii::. ~ p dislodged and is taken downstream, striking against the duct walls, l P'~:.[e " ~ max In some cases, this condit ion could cause an ignition of -:-':-:,~. ] "::i:i::i:i::...:::::::..:::- combustibles within the duct. The situation worsens if aluminum~,~.-......, l .... !i~!~i!i~::" / " ~ . paint is used. If the a luminum flakes off or is struck by a foreign :~-'-.:::'~:%-'.~.:-.:~ii$ ..I . . . . . . :i::i~::: / 1 % % t object, the heat of impact could be sufficient to cause the -~ii: ' % ~iiii~ii!i.."..!~!$:::.::!i ..... / a luminum particle to ignite, thereby initiating a fire dow~_a: . .m. ::~$i.'-" "iiiiiii!i:; .... /

A-8-2.5.3 For information on maintenance of deflag . r ~ ' n v ~ n g , "+:':'.i~i::... / Unrented see NFPA 68, Guide for Venting of Deflagrations. .-#i'~i: . . . . . W. . . . . . . :~'~ / . . . . . . . .

/ Appendix B Additional Informat ion on Ex+.p.l:o..s.!on l~ition+'++:+:+.:.++++++i++!i "::. / ^.

This appendix is not a part of the requireme~... "+:':of " t :+#!~A c i ~ ' t / / Strength of vessel but is included for informational purposes o..~ "':~.~ii-:. .i~ i~ .... - - - - - - - - -- / . . . . . . ~ . . . .

+!:+::'::i~::iiiii::ii--. :: '%ii: ..... / ~ Vented deflagrafion pressure B-1 General. This section covers the f o l l g ~ g comm~-~ methods / at/ '°~ - of explos on protect ion '::i:-::i"~:. ..::~::" r~ , ,~

" ":'"~::::::!~ . . . . ":':':" ~ / Pstat -- Vent opening pressure (1) Conta inment .... ~::iiiii+ !~::" ~ . - - ~ __il~__ - - - - (2) Inert ing .::# . . . . . " 7 - " -- -- "~-- -- -- (3) Deflagration venting / Vented (4) Deflagratlon suppression / ~ . (5) Deflagration isolation ~ T~me )t

B-2 Containment. The basis for the con ta inment me thod of protect ion is a process des igned to withstand the maximum deflagration pressure of the material being handled. The equ ipment is des igned in accordance with ASME Boiler and Pressure Vessel Code, Section VIII, Division 1. The final deformat ion pressure depends on the maximum initial pressure within the vessel prior to the deflagration. NFPA 69, Standard on Explosion Prevention Systems, limits this maximum initial gauge pressure to 30 psi (207 kPa) for conta inment vessels.

The equ ipment is designed either to prevent pe rmanen t deformation (working below its yield strength) or not to rupture, with some pe rmanen t deformat ion allowable (working above its yield s trength but below its ultimate strength). The shape of the vessel should be considered. To maximize the s trength of the vessel, its design should avoid flat surfaces and rectangular shapes. The strength of welds and other fastenings should also be considered.

Figure B-4.1 Pressure-time graph of a vented deflagration.

B-4.2 Deflagration Vent Panel. The deflagration vent panel is a flat or slightly domed panel that is bolted or otherwise at tached to an open ing on the process c o m p o n e n t to be protected. The panel can be made of any material and construction that will allow the panel to ei ther rupture, detach, or swing open f rom the protected volume; materials that could f ragment and act as shrapnel should no t be used. Flat vents could require a vacuum support a r rangement or a support against high winds. Domed vents are des igned to have a greater resistance against wind pressure, process cycles, and process vacuums. A typical commercially available vent panel is detailed in Figure B-4.2... These vents are either rectangular or circular.

138

N F P A 654 ~ MAY 2 0 0 0 R O P

t r io

tne

F'~rure B-4.2 Deflagration vent panel and suppor t grid.

/ \

n M

m

m

IL" . . L I

o/

\ Z

f Dv~Oflt paga~ot~l n

Isolation system detlagration pres.suro detectors

Chemical isola~on extinguisher

Inlet duct

B-4.3 Deflagration Vent Door. A deflagration vent door is a . ~ h ~ " sa

hinged door m oun ted on the process componen t to be protected. It is des igned to open, at a p rede te rmined pressure that is governed ~ " ~ by a special latch arrangement . Generally, a vent door has a ~ ~ ~ . ':~, '~ greater inertia than a vent panel, reducing its efficiency. ~'* " ~ ~ --

. . . . . . . . . . . . . . . . . . ~,¢.~Krure B-4.4 An example of a vented dust collector. ~,-a.4 Appncauons. Detlagrauon vents are usea tor appncauons . -~,x~ .. that h a n ~ e gases, dusts, or hybrid mixtures. Typical a p p l i c a t i o n s ~ . " ~ include dust collectors, silos, spray dryers, bucket elevators, and ~ H ~ D e ~ d o n Su ion W e - - An ex losi is no t mixers. Figure B-4.4 shows a typical vent panel installation on a ~ , " ~ . u ~ . m ~ , , ~ . . w h p p r ~ l g~.krDl~ h ~ ~ g.,,Pt'~.l°nht,. dust collector. , ~ ~ ~ , crTate"i~ ae;~ucti'vTpr"e~s~t~r"eSs.~'T}~pi~c,~lTthe"~fireba'~ "

. . . . . es . . . . . o v " ~ , ,~s~ "~ expands at speeds of ~0 f t / sec (9 m/ sec ) , whereas the pressure l n e t o a o w m g a r e a n v a n t a g o t a e n a g r a n n enung-,~ ~ x ~ ~" ~ " ' ' " ' " v . . . . . . . . " . . . . . . . t~x ] . . . . . t : c , t . . . . . . . s s c . . . . . . . t i s l o ~*--~2~o:-~. ~ * ~ . w a v e a n e a o o t l t w a e m a t l l u u t t / s e c ( ~ 3 ~ m / s e c ) . l n e t , x } I . J U W 4 L . U a I Jk L l l ¢ D / U I ~ U U I I I ~ J U I I U I i I . .~k i lK • • • . . . . . . . . . ~ ~ . ~ ~ d e f l a g r a t i o n is detec ted ei ther by a pressure detector or a flame tz) Low mmntenance - - passive aewce ~ • • . . . . . . . . . . . . . . ~" ~ " ~ ] ~ detector, whereby a signal passes to a control unit, which actuates J ne renewing are oasaavanmges o[ aeriagrauon v e n u n ~ , w v . . . . ra . . . . . . . . . . . i s - "l" T " tential fo ostve ti ~ e wi . . . . . m coKa~i~h,~nt. .... one or se eral mgn- te oascnarge exUnt, uLsners. J n e exungu hers ( ) ne po r a p n ng n r c t, to ~)epr

. . . . : h ~ r ~ t ~ ~ m ~ sarg~r " p r o c e s s prar2ecu0arly if combustthte materials, su ~snntg°d~d~refir~aa~. ~r~leP~0~oe~ee ~:eCtse~i~PelcdloYnds.

P tg , Th . . . . . . . . . a o * ~ . ,h .* , h . . V ~ . . . . . 7 , ' , ~ ,,.'s~'~,~ The sequence for deflagration suppression is shown in Figure B-

outside wall or located outside " " ~ h ~ ~ o. . ~ , . ($) Fireball exiting a vented component , 0 1 ~ is a . ~ e r e fire

hazard to the plant and personnel located in t l ~ " " of the aw D ~ defiagration vent open ing ~ .~¢y t r ~ n o u \ I

(4) Contraindicat ion of the process for toxic c ~corrosive ~ material 1

17,-4.5 Design Considerations. The following points should be considered =when designing and evaluating the suitability of deflagration venting:

(1) Reaction forces (2) Postexplosion fires (3) Material toxicity or corrosiveness (4) Good manufactur ing practices (GMP) (food and

pharmaceutical applications) (5) Vent efficiency (6) Connect ions to o ther process equ ipment (7) Vent duct back pressure (8) Thermal insulauon (9) Safe venting area (10) Vacuum protect ion (11) Location

B-5 Deflagratioa Suppression. Deflagration suppression involves a high-speed flame extinguishing system that detects and extinguishes a deflagration before destructive pressures are created.

"rime: 0 r,y,e¢ 2011.4m¢ 30 mse¢ 40 rMe¢ I ~

Figure B-5.1(a) Deflagration suppress ion sequence - - s t a r c h in $5-ft s ( l -m ~) vessel.

In suppressing the fireball at its early stage, rupture of the vessel is prevented. Figure B-5.1(b) shows the pressure- t ime gvaph of the suppression of a starch defiagration in a 65-ft s (1.9-m s) vessel., Note that the reduced deflagrafion gauge pressure is approximately 3.5 psi (24 kPa) in this test.

139

4-

~ 3-

2- 13-

1-

Deflagration suppression: pressure vs time

Vessel: 1 9 m 3 (67 ft 3) Dust: dry starch Dust concentration: 1000 g/m 3 (35 oz/ft 3) Ignition energy: 5 kJ Agent: sodium bicarbonate ~ 1 1 [ = 1 " Detection pressure:05 psig ~' (gauge I

HRD discharg~

Igniti9n

• 1|~1

tge pressure o~ 34 kPa)

Pneumatic dust injection

0

Figure B-5.1 (b)

NFPA 654 m M A Y 2 0 0 0 ROP

The following are disadvantages of a deflagration suppression system:

(1) Generally higher cost than for deflagration venting (2) Requirement for regular maintenance (3) Ineffectiveness for certain metal dusts, acetylene, and

hydrogen

B-5.3 Design Criteria. Deflagration suppression systems are designed in accordance with NFPA 69, Standard on Explosion Prevention System~ and ISO 6184-4, Explosion Protection Systems - - Part 4: Determination of E, O%iency of Explosion Suppression Systems. The following information is required, to design a suppression system:

(1) Process material (2) Kst or K a value in psi-ft/sec (bar-m/sec) (5) Vessel strength (4) Vessel dimensions and volume (5) Maximum and minimum operating pressures and

temperatures (6) Connections to other process equipment

o'.4 B-6 Deflagration Isolation. A process component such as a dust collector or silo might be protected from an explosion by venting, suppression, or containment. However, its connections to other process components by pipes and ducts pose the threat of deflagration propagation. A deflagration vent on a dust collector might save it from destruction. However, the inlet duct might still propagate flame to other parts of the plant. Such propagation can and has resulted in devastating secondary explosions. The importance of d ~ isis stated in NFPA 68, Guide for Venting of Deflagrations, .~J~-"~.'fion, Section 5-6.7, which says:

" I n t e r c o n ~ . ~ b e t w e e n separate pieces of equipment present a special . ~ d . ~. , .Where such interconnections are necessary, d e f l a ~ . . ~ i s o l a ~ . . d e v i c e s should be considered, or the mt~" ~ ' ~ t o n s s h ~ . ' ~ . ~ vented."

.~..::~..daoff~.~ NFPA 68, :~Gulde for Venting of Deflagrations indicates v ~ ~ opuon for mterconnecUons, venUng ts vahd only w h e ' ~ e r c o n n e c t e d equipment is protected from explosions.

. . . . T h e ~ f.9..~ isolation is further supported by research that ~.iiii~&':-'.:, shows ~ .~ .~e rconnec t ing vessels "can result in precompression of

g::: ' :e~:"~es w ] ~ connected vessels caused by a deflagrauon. The result ,::::. - . - : : : ~ : ; .~, .., . . . . .~::: . ~ i ] ~ . : ~ e f l a g r a t m n ,n one vessel can produce cons,derably i~iL~'.-"]-*~aig~;:~ressures in the connected vessel. Mechanical or chemical '%~:" i so l~on methods should therefore be considered where

~:-¢":" "'~]~]~] ~:~. j~terconrtections between one vessel and another are present. ~..-'..~.. :.~:'. ~ ":~:, 41: -'~

~""":~,.:-";~.~ .-::~:~:-'::~-~!.'::.~.~ ~ i~sB-6.1 Mechanical Isolation. Mechanical deflagration isolation can -..-$!~l~mtt.~:.,,i$:~!:: .- ~ # i o n ":" be provided by rotary airlock valves of suitable construction. An

"~'~'-,'~.,'~ ~t ~.::. ,.,'- example of their use is at the discharge of dust collector hoppers. ::.:,..,~*.'~" To be effective and to prevent the trammission of flame and

' : ' ~ " ~ ~ ~ -~$~!~::" burning materials, rotary airlock valves should be stopped at the '" moment a deflagration is detected. To be truly effective, rotary

alrlock valves should be integrated into an explosion detection/protection system for the piece of equipment being protected.

~ ']][~::~J~--b Re tary air lock valves for deft ag ration isolation should be of rugged construction and suitable design. Such design is. particularly important for pieces of equipment protected by deflagrafion venting and containment. This requirement puts more demand on the integrity of rotary airlock valves than for

Inlet duet components protected by suppression. The reason is that suppression extinguishes the flame in addition to mitigating the pressure.

Another example of mechanical isolation is the high-speed knife gate valve. High-speed gate valves should be capable of withstanding the maximum deflagration pressure. Typically, valves are rated for gauge pressures up to 150 psi (1035 kPa) and should be capable of closing in milliseconds. The pipework also needs to withstand the maximum deflagration pressure, p ,~ . Figure B-6.1 shows a typical arrangement for a high-speed gate valve. A detector, which might be a pressure switch or an optical detector, detects the deflagration pressure or flame front. This trigger then initiates the rapid valve closure to prevent the propagation of flame and pressure. If the connected piece of equipment is protected by deflagration venting or deflagrat]on suppression, then [itde pressure can be expected. In such cases, the valve that isolates a connected pipe can be replaced by a chemical isolation barrier.

' 012 ' Time (soc)

Suppressed deflagration: pressure vs time.

B-5.2 Applications. Deflagration suppression systems are used for applications that handle gases, dusts, or hybrid mixtures. Typical applications include dust collectors, silos, spray dryers, bucket elevators, and mixers. Figure B-5.2 shows a typical suppression system installation on a dust collector.

Deflagtation suppression bottle

Deflagration / pressure

detectors

..:::.'::::.:~ ~ .':::::.~.,'

j C / ":'::'~ , : :~ : : := : : : :~

,, /

F'tgure B-5.2 An example of a dust collector suppression system.

The following are advantages of a deflagration suppression system:

(1) Elimination of flame and reduced chance of subsequent fire (2) Reduced risk of ejecting toxic or corrosive material (3) Flexibility in process component locations

140

N F P A 6 5 4 - - M A Y 2 0 0 0 R O P

:iiiiill i '

~ - Y " " ' ~ l l l l l l l l l l , , , , , " ~ , , , " " l I l k I /

Ignition Flame Mechanical front barrier

Figure B-6.1 An example of mechanical isolation.

Appendix C Informational Primers on Prevention and Extinguishing Systems

This appendix is not a part of the requirements of this NFPA document but is included for informational purposes only.

C-I Primer Design Concepts for Spark Detection and Extinguishing Systems.

C-I.I Spark/Ember Detectors. Spark/ember detectors are radiant energy-sensing fire detectors. The design, installation, and maintenance of radiant energy-sensing fire detectors are covered in Chapter 5 of NFPA 72, National Fire Alarm Cod~ Where required by this standard, spark detectors are used to actuate an abort gate to divert fuel, flames, and combustion gases to a safe location.

However, spark detectors are more commonly integrated into a spark detection and extinguishing s~stem. In this second case, the extinguishment is usually an intermRtent water spray designed and installed pursuant to NFPA 15, Standard for Water Spray Fixed Systems for Fire Protection, and maintained pursuant to NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. Since the overwhelming majority of the applications that employ spark/ember detectors are pneumatic conveying systems, it is appropriate to provide a primer on these devices as part of this standard.

B-6.2 Chemical Isolation. Chemical isolation is achieved by the rapid discharge of a chemical extinguishing agent in the interconnecting pipe or duct. Figure B-6.2 shows a typical arrangement for chemical isolation. A deflagration detector, which might be a pressure switch or an optical detector, detects the deflagration pressure or flame front. This trigger then initiates the rapid discharge of extinguishing agent from a high-speed extinguisher bottle, thus preventing the propagation of flame and burning materials.

Chemical deflagration isolation should not be confused with ignition source (spark) suppression systems. Such systems are intended to detect burning particles traveling down a duct and extinguish them with a downstream spray of water. They are not designed to stop tleflagrations once they have started and are ............. I I ineffective for preventing deflagration propagation through a r I I interconnected equipment. :~-&-*-..:., :'~i.'i!i~::~>':"

~ _ . . Chemical ~..:i#~::::':"%ii~.':"-'::': ~iii~., ~. ~ , ~ suppressor ....:..'.'il:.~ ii!i': . ""~'.":"

d

Detector ~ .:..:i~!~i~::.. "::!!~ii~iii:: " ..... ~ . _ _ . ""~" "'*-:::-:~::::~. "::'::~$~:~::..,4:.

9 ~ ' : ~ ~ ; : ; ; ; ; ~' :,l' n; ;[i..:#i!t~[lit:[lllll t,,ai'~!!~ ~ Duct t ~ : ~ i : : ~ : ~ , ~ : ~ , , , , , , ~ " , , , , , t / l f f ~ i ~ B ' ' ' ' ~it ""~11 - - - -

,/ .... / .%:iii:.~...~..:~i~:: 1 - - ~,n,ow

Chemica-I Flame "%i~::" / barrier front ..4:: Ignition

C-I.I.1 Actuation of Abort Gate. When spark detectors are used to actuate an abort gate, the design concepts are fairly straightforward. The detectors are mounted on the duct upstream from the abort ~ate and are wired to a control panel listed and approved for th!:~,...~..urpose. When a detector senses a spark, the signal causes ~ o l panel to alarm and the solenoid or other releasing d e . ~ o n t~:~ abort gate is energized. This type of system is shown ~! i~ . . c~1 .1 .1 .

" ":-:~::.:!i.:.:~..-::....:ii~*:"% I I 1

Figure B-6.2 An example of chemical isolation.

B-7 Limitations of Flame Front Diverterg Flame front diverters can divert deflagration flames by directing them to the atmosphere. However, these devices do have limitations. If the air-moving device is located downstream of the flame front diverter, an explosion originating upstream of the diverter can propagate past it because of the deflagration flames being sucked into the downstream side, despite the open diverter cover. Also, tests suggest that some diverters might be ineffective in completely diverting a deflagration involving a hybrid mixture whose vapors exceed file LFL, regardless of the location of the air-moving device. In both of these situations where a flame front diverter will allow propagation, the deflagration severity in the system is nevertheless expected to be reduced.

Figure C-I.I.1 Spark detectors and abort gate.

C-1.1.2 Spark Detection and Extinguishing Systems. Spark detection and extinguishing systems usually consist of a group of detectors that are located on the conveying duct, a confi'ol panel in a safe accessible location, and an extinguishment solenoid valve and nozzle set located on the duct downstream from the detectors. Such a system is shown in Figure C-1.1.2.

141

N F P A 6 5 4 ~ M A Y 2 0 0 0 R O P

Dust collector

Detector Extinguishment

Duct

- - Airflow

Figure C-1.1.2 The typical spark detection and extinguishing system.

o >

or"

Emission spectra

UV ='Visible~ Infrared Gasoline flame

Typical I l l i ~ / O a k ember spark/ember fl~'Hlll. - Y

detector I IIIgllll. / t response I IIRIlIIII ~ !

X

0.'1 o.s 1.'0 2:0 3:0 4:0 5:0 6:0 7:0 Wavelength (microns)

Figure C-I.2.1 The emissions of an oak ember and gasoline flame compared to the spectral sensitivity of a spark/ember detector.

Caution: The sensitivity of spa rk / ember detectors is quite speed sensitive. If the fire is moving too slowly, the typical spa rk / ember

When a spark or ember enters the detector(s) , the detector detector might not detect it. In general, spa rk /ember detectors responds with an alarm signal that actuates the extinguishing will not detect a . ~ t i o n a r y ember or flame. system valve, establishing an extinguishing concentrat ion of water, Another c o ~ . . . o . n is the absolute necessity for a predictable before the spark arrives. The water spray is maintained for a time time betwee..~i~e det~'~tion of the spark and the actuation of the period long enough to ensure ext inguishment and is then turned abort ga te :~ ' :~2~s tab l i shmen t of the water-spray extinguishing off. This feature minimizes the quantity of water injected into the c o n c e n ~ o n . ~ . r e s p o n s e times of the detector, control panel, duct. The pneumat ic conveying system is not shut down; it and s ~ . n . . ~ valv#(~$, known, verified, and extremely reliable. continues to run. Each time a spark comes down the duct, it is H 0 ~ i ~ i ~ l e s s the'~..v.,qff time of the spark at the abort gate or quenched . . e . .~lgu~hin.g water s ~ ; is equally predictable, these systems are

~ :~ap l t~ . .~na t e . :~:-" C-1.2 Critical Design Concepts. For both system design concepts, :~:"" " ~ : : . ~ l : . . . t i m e of the spark is a function of the conveying system several critical factors should be addressed if they are to work. air ~ and the distance between the detector and the First the detector should be able to reliably detect a spark an e x t i n ~ n g : , s y s t e m . Actually, most spark detection and ember , or a flame. Second, the alarm stgnal should be processed:~i:..::,,, e x t a n g m ~ s y s t e m s provide designers with a formula to compute quickly. The t iming should also be predictable enough to a l l o w ~-':'!~!~....~...e. requi#~] distance between the detectors and the abort gate or the abort gate to operate or allow the extinguishing system ":-'iii:. '~i i~. .~. '$1: iment . Generally, it is in the following form: sufficient time to establish the water spray. Finally, in the case of ::~.-...::#::" ~!i:~ii;~:' the extinguishing system, there should be a provision t o , : ~ . J . y :"~:"{~:: (AJ#~peed)(system factor) = the water-spray ext inguishment repetitively. The o c c ~ n c e ~ a ....... .. distance between detectors and ext inguishment s ark is rarel an isolated incident; usuaU s arks ar~i!:~roduc..~, m . ":.::'.::'i~i;:':" P Y Y P ..... :i~..~ . . . . . . . . . . . . . . ,:.,.. ::.:::,: . a burst or stream. The extinguishing system shout~I~ii~le.-:~6::::~::~::~;~:i::.:, "::~?."~:: The air speed and hence the ember speed should be both reactivate as each successive spark is detected• Unless ~!~ithes~::ii!iiiii~.."i~ ~ constant and controlled. It is this necessity that established the concerns are addressed, s p a r k / e m b e r d e t e c t i . ~ ! ~ "~ili~i~iii::.. r equ i rement that the combustible concentrat ion be less than one- ext inguishment cannot be used as usually..~t~ph~!~.:~::. ':%iiiii::.::-:~:':': half the LFL or MEG. If the combustible concentrat ion exceeds

....:'i?-" . . . . . ":"~iiik "::!ii::ii ~ .... the LFL or MEC, a deflagration can result f rom the introduction of C-1.2.1 Spark Detector Reliability. T ~ i ~ l ~ c o n c e r r ~ d f ~ g a a spark. The speed of the flame front equals the sum of the flame spa rk / ember detector is the ability to ~et~i.~.:.zpark, e ~ e r , or, f ront velocity for that combustible at that concentrat ion plus the fire. NFPA 72, Nat ional Fire A larm Code, defi:~!:xa spark.i~ "a nominal air velocity of the conveying system. The deflagration moving ember" and defines an ember as "a p a ~ : ~ e ....~.'."~olid flame f ront would pass the abort gate before it opened or pass the material that emits radiant energy due to either ] : ~ ! ~ p e r a t u r e or ext inguishment before the valve had opened and established a the process of combustion on its surface." Figur4~'-~::~-l.2.1 shows spray pattern. This is why the criteria regarding combustible the radiation intensity as a function of wavelength for an oak concentrat ion are so important . A spark detect ion system on a ember and a gasoline flame.

The spectral sensitivity of the typical spa rk / ember detector is super imposed on the graph in Figure C-1.9.1. One can see that the spa rk / ember detector will sense the radiation from both an ember (spark) and a flame.

C-1.2.2 Detector Sensitivity and Speed. The second concern regarding the detectability of a spark or flame in the duct is the sensitivity and speed of the detector. Because the detector is designed to be moun ted on a duct that is dark, silicon photodiode sensors can be used and there will be few, if any, sources of spurious alarm within the duct. The sensors allow the detectors to be made both extremely sensitive and extremely fast. Sensitivities of 1.0 microwatt and speeds of 100 microseconds are common. The result is a detector that can detect a spark the size of a p inhead moving faster than the speed of sound. The outcome is that both sparks and flames are easily de tec ted in pneumatic conveying systems with modern s p a r k / e m b e r detectors.

conveying line where the concentrat ions are above the LFL or MEC cannot be expected to make a meaningful contribution to the survival of the site or its occupants should a deflagration occur.

C-1.2.3 Control Panel Design. The third concern regarding these systems involves the extinguishing system. Because the cause of the first spark usually causes additional sparks, the control panel should be des igned for the successive and repetitive reapplication of the extinguishing agent. This type of function is not found in the average fire alarm control panel. Specially des igned control panels for spark detect ion and ext inguishment are the norm.

C-2 System Basics.

C-2ol General. This standard requires the use of spark detection systems in those installations in which conveying air is being re turned to the building. It requires that the spark detect ion be used to activate an abort gate, diverting the airstream to outside ambient air. This requi rement is a critical life-safety and property- conservation measure. Sparks enter ing a dust collector are apt to initiate a deflagrafion. If the abort gate is not activated, the flames and combustion gases would be conveyed back into the facility,

142

N F P A 654 - - MAY 2 0 0 0 R O P

igniting secondary fires and posing a serious threat to the occupants. Figure (3-2.1 is a diagram of this type of system.

Abor t gate

Detector

Retu rn a i r

Dus t collector

Dt~t-lad~n ah"

Duc t

Figure C-2.4 The basic spark detection and extinguishing system for a single air-material separator.

Ai r f low ~__ [ I C-2.5 Additional System Features. The spark detection and extinguishing system involves more than jus t detectors and a water spray. To provide the degree of performance necessitated by the application, the system should require a number of additional system attributes.

First, the detect.~rs should be listed and approved to operate in conjunction w i ~ . . . ~ control panel and the water-spray extinguishin~.::~:'fiit. ~ 1 three components should be listed as a

Fioa,ro 6_9 ! The ,-;-; ,- ,~m Cnmnllanee Snark rlotoet~nn ~',~tom System. T ~ : ' ~ l e s that are used are specifically designed for this t, . . . . . . . . . . . . . . . . . . r . . . . r . . . . . . . . . . . . . . : . . . . . . . type of s ~ c e i " ~ . , are not "off the shelf" sprinkler heads. The

solenq.~. ~ y e is ~ ' ~ c a l [ y matched to the control panel to ensu ~ orm, c le response nine C-2.2 Dual Detectors. Because snark detectors have limited fields _ . . . : ~ " ' i ~ ~ . , . . , ~ b . . " . .

• • - Jk~'e o et'atin re Ull..~.'..'j[$'t~ents o t a s ark detection and of wew, most systems reqmre two detectors to cover a round duct. .,::..::~ .P,. g q .::::. . . P The detectors are usuall)~ situated on the inlet to the collector, as . : ~ n g u ~ n g system :~1 for addiuonal features• The windows.or ~ h n w n i n 17io~tre ( ~ 9 1 T h i ~ ~ w t e m i~ t h e n n l v t v n p mf ~ n m r k ":.:~'::l'~0i~e_.~ ~ $ t e c t o r s can become scratched broken or coated ruth detection s~ tem that is required by the stan~larcl, r However as a m~'t~:;.r6~fluc, ng thew sens,tlvaty... Consequently, a means should

. . . . . . ' be pe . . . . ed to measure me sensiUvaty of the detectors to ensure min imum comphance standard, it does allow addtuonal measures. . ~ : . . . . . . . . . . . :ii~::i:..~.,. mat the~..~e...iz'apable of detecung sparks after the mlual mstallaUon

C 9 3 t ; ~ h o t i o n s of ~ ; - ; ~ u m ~ o ~ n ~ n c e A . . . . . . h wh~ :(!!~!!!iii!!~':i.,....,,tests. Th'~::~nsitivity measurement capability is required by NFPA n r ~ h l o r n ~ A t h t h ] ~ m | n ; m , , m c ~ m n l i ~ n e ~ ~ n n r ~ r h ;~ ~ h ~ t i t c ~ n ~'~::. ":'::!::.:.~.~?:..~.~tto.~'at Pire Alarm Code. I t t h e m a t e r i a l t s O a s c o v e r e d t o cling often reduce the productivity of the site. When a snark is detected :i:i .:j~.~o ~ i ~ t e r l o r surfaces of the duct, a means to keep the detector the abor t wate transfers Now the air-handlinw system s h ~ - ' - : h e ' %ii!~::" w i n ~ W / l e n s clean is required by NFPA 72. This usually involves shut do~vta°in order to restore the abort - - t e to tt~e - ~ 1 ~'~i~!:~ ~i~, an air-purging option that bathes the detector window/lens with I6a t m...~,~t ":i~i~i: ".~?::. . . . . . .~dean mr position. This shutdown could require an hour o f ~ . d u c d n l ~ : .~ :~.:':':'i:'-:: " . . . . . . . . . ~. : . . . . . . . . . . . . . . . . ,.:. : . . . . . ~ - ~ __~.~.-~ ":.'.-':: ~*:" To work rehablv the extinguishing system should have a strainer However in many swtem% snarks a r o a common n c r t t ' ~ : g 17~':':".":': t requtrea oy INeV.ak 1 D, aranaara jor water ~pray rzxea oyswms jot e x a m ~ l e ' i n a"woodworki"n~ i~acili"'-one coulcl'" "]" ~ t s e v 6 " ~ a ' r k ~ ' s ........ ~ire Protection) to prevent pipe scale from clogging the nozzle. The p , ~ t y . . ~ r~g.': ~ . . . ~er da" Obviousl" a s" stem that shuts d o " d ~ ' : ~ f f ' ! ~ fo~:~i "":" water sunply should be rehable and superwsed wath a pressure ~our sYeveral timesYa da y is not a viable s ' ~ n ~..-Y, ~ i ! i ~':::" switch. ~ecanse the extinguishing system components are

~J.-'.'~, ' ":~".:i:. ..,:;~i !i .... mounted on a duct that could be outdoors, freeze-prevention C-2 4 A - - r o a c h to Minimize S h u t d o ~ J i i i ~ , ~ use of~i~-ark measures should be implemented. Antifreeze solutions are not a pp .::.x.:~ v

-" .. ~ .. - ~ . . . . " : : ~ . . . . ,~.::: - viable option on extinguishing, systems that are exnected to onerate oetecuon ann exungulsnlng system on me Irrt~.~.:t.o me .t~st , ~ o 1- . , , , .r - ~ r . . . . f preve~:'x"" p...r;~du cuon'~"~ • regularly, t~onsequenfly, heat-tracing ShOUld De ttiougtlt ot as a

a s econd : :$~e" of spark collector is an extremely effective way of prey stoppages. This type of system mounts detectors on the pneumatic conveying duct far e] Igh upstream to allow the installation of an intermittent water-spray extinguishing system on the inlet duct prior to entry into the primary dust collector (air-material separator). This spark detection and extinguishing system quenches each spark as it comes down the duct, before it reaches the air-material separator. A properly designed and installed spark detection and extinguishing system is very effective in preventing ignitions in the AMS. The spark detector that activates the abort gate is moved to the oudet of the AMS, providing a secondary detection. This type of system is shown in Figure C-2.4.

mandatory constituent of the system along with thermostats to turn the beat-trace on and to warn of impending freeze-up.

Finally, there are desirable system components such as system testing, event recording, and flow indicators that should be considered as part of any system.

Appendix D Referenced Publications

D-I The following documents or portions thereof are referenced within this standard for informational purposes only and are thus not considered part of the requirements of this standard unless also listed in Chapter 9. The edition indicated here for each reference is the current edition as of the date of the NFPA issuance of this standard.

D-I.I NFPA Publications. National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101.

NFPA 15, Standard for Water Spray Fixed Systems for Fire Protection, 1996 edition.

NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, 1998 edition•

NFPA 68, Guide for Venting of Deflagrations, 1998 edition• NFPA 69, Standard on Explosion Prevention Systems, 1997 edition• NFPA 72, ® National Fire Alarm Code , 1999 edition.

143

N F P A 6 5 4 ~ M A Y 2 0 0 0 R O P

NFPA 77, Recommended Practice on Static Electricity, 1993 edition. NFPA 499, Recommended Practice for the Classification of Combustible

Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 1997 edition.

D-1.2 Other Publications.

D-1;2.3 ASTM Publication. American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428- 2959.

ASTM E 1226, Test Method for Pressure and Rate of Pressure Rise for Combustible Dusts, 1994.

D-1.2.1 AIChE Publications. American Institute of Chemical Engineers, 345 East 47th Street, New York, NY 10017.

D-1.2.4 ISO Publication. International Standards Organization, 1, rue de Varemb~, Case Postale 56, CH-1211 Geneve 20, Switzerland.

AIChE's Center for Chemical Process Safety, Guidelines for Hazard Evaluation Procedures, 2nd edition with Worked Examples, 1992.

AIChE's Center for Chemical Process Safety, Guidelines for Safe Automation of Chemical Processes, 1993.

Ebadat, V., andJ . C. Mulligan. "Testing the Suitability of FIBCs for Use in Flammable Atmospheres." Paper 10a, 30th Annual Loss Prevention Symposium, AIChE, 1996 Spring National Meeting, New Orleans, LA, February 26-28, 1996.

D-1.2.2 ASME Publication. American Society of Mechanical Engineers, 345 East 47th Street, NewYork, NY 10017.

ISO 6184-4, Explosion Protection Systems - - Part 4: Determination of Efficiency of Explosion Suppression Systems, 1985.

D-1.2.5 U.S. Bureau of Mines Publication. U.S. Bureau of Mines, Pittsburgh Research Center, Cochrans Mill Road, Pittsburgh, PA 15236-007O.

Conti, R. S., g- L. Cashdollar, M. Hertzberg, and I. Liebman. 1983. "Thermal and Electrical Ignitability ofDusts." U.S. Bureau of Mines, Report of Investigations, RI 8798.

D-1.2.6 Other Publication.

ASME Boiler and Pressure Vessel Code, Section VIII, 1995. Lazzara, C., and Y. Miron. 1988. "Hot Surface Ignition Temperatures of Dust Layers." Fire and MaterlalsJournal 12:115- 126.

..~.-:'%

.-::.:-':':~i:i:i:!--. .....

144