I-A. !

~USAFOEHW REPORT_______ -

- - 88-064EHOO97DNA

" 2-

0 Impulse Noise Level Measurements inLn Defensive Fighting Position Shelters, AFM Weapons Laboratory, Kirtland AFB NM

0 ~LE

4JOHN C. ELUS I, Maj, USAF, SC MAY 1 6 ,

April 1988

Final Report

Distribution Is unlimited; approved for public release

USAF Occupational and Environm ental Hga!th LaboaratoryHuman Systems Division (AFSC-•

Brooks Air Force Base, Te^as 73a5G5-.1

' •

UNCIASSIF.UDS-ECU?,TY CLASS IF ICATION PrCT-

REPORT DOCUIMENTATION PACE -M OrNAo 074-18

I a. REPORT SECURiTY CLASSFCATION lb RESTRICTIVE MARKINGSUNCLAS~SIFIE.D NA

2a. SECURITY CLrASSIFiCATION AUTHO'RITY 3 DiSTR8_UTIIOINI IAlTY OF REPORTNA Approved for public release;

2b. DECLASSIFICATION;/ DOWNGRADING SCHEDULE ds-bionis un,4rited.

4. PERFORMING ORGAINIZATNON REPORT NUMBER(S) 5 MO-Ni .-5 ORGAN'ZAI¶.C REPnRT NUM8ERfS)

USAFOEHL Report 88-064EHOQ97DNA

I6^ NAME 0Q PERFORMING ORGANIZATION ~b OFFICE SYMBOL 7a. NAME OF NMONiJORINQ OFICANIZAIO0N

~m n a e l h L b~ a~vUSAF Occupational and En~viro - (if applicable)

~6r- ADDRESS (City, State, and ZIP Code) 7b. -ADDRESS (City. State, inri ZjP Code)

Brooks AFB TX 73235-550!1

8. AMEOF UND~JGSPOSORNG8-bOFFICE SYMBSO.. 9 PROCUREMENT !NSTRUMEiT iDENT,FICA' ON NU'VBERORGANIZATION I'!' applicable)

A ~~Same as 6a ______ _________________

J8c. A-DaDRESS (City, State, and 4PCd)10 SOUjRCE OF FUNDING NUMBERSPROGRAM IPROJEC' ASK WORK UNITELFAAENT NO NO NO ACCESSION NO

11. TITLE (include Securrty Classoficatior.)

Impulse Noise Level Measurements in Defensive ?-ighting Position Shelters t 'uI

12 ~RONAAUHC~S)Major John C. Ellis 1I13a.TY EOFPIEPORT 1?b. TIME COVERED 14 AEO EOtierMnth.D-3y. 15 PAGE COUNT

Pinat FROM s-nJ.. 19%8 1 7 __ __

16 SUPPLEMENTARY NOTATION

1'7. COSATI CODES 18 SUBJECT TERMS (Continue on reverse f necessary and ýdentify' by block -wu',berijQ FIELD GROUP 1, SUB-GROUP NJoi se --Hearing protectionImpulse Weapon noise.Defensive DO~r Fighting Poiios

19.,ABSTRACT (Continue on reverse df neces:sary anya tdentdy by block number)

J~oa h .. A? ocsi uoedsg; h teteArFreWaosLbrtrThe rmeasurement of impullse noise levels produced by the firing of weapcns in two designsof tne Defensive Fighting Position Shelte'r was performed. One of the designs is referreddesign. Tefrnoftefollowing weaoons in each shelter was measured: M-106, M-60,MK19an -2.Te upoeof the test was to evaluate whether exposures to weapons fireunder these conditions are hazardous and, if so, what hearing protection, limitation innumber oi:rud frd r both would be required to protect the hearing of those nexposed. Double or single hiearing protection is recornmieoded under all firing conditions,and is dependent on the type of weapon used and number of rounds fired per day.

20ODS7RiBLTiONIAVA'LA8ILIT' OF AýBSTACT 21 t BSTRACT SECURiTy CLASSIFICATIONC3UCLASSF1D!NLN1ITE C2SAAEASRPT D7,C US ERl _Un ] gs if ied

22a NAME OF RESPONS8BLE' INDIVIDUAL 22b TELEPHONE (include Area Cocfe) I 2c OFFIC, S'yVBQLO1*P C. ELLIS I, MaioUA.BC(1' -i I c

DO Form 1473, JUN 86 Previous ed'rvons are )bsolete S.ECURITY CLASSIFICATION OF THIS PAGE

!;NIINLASS IF I ED

S,- • , . . - -:•. .. •I • • - • • i_ . , a= . i . . . . L • .. .

ACKNOWLEDGMENTS

The dedicated effort of Capt Terry M. Fairman, USAFOEHL/ECH, in assisting inperforming this survey is sincerely appreciated. The on site assistance ofCapt Susan Cheney and MSgt John E. Schwartz, AFWL/WTEO, was instrumental inassuring a successful survey. The weapon firing was performed by the 1608thSecurity Police Squadron and their cooperation is gratefully acknowledged.The measurement of the M-16 impulse noise by the USAF Hospital Kirtland/SGPBis also very much appreciated.

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PdI ' I

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iii

"CONTENTS

Page

DD Form 1473 i

Acknowledgments ii

I. INTRODUCTION

A. Purpose 1B. Problem 1C. Scope 1

II. DISCUSSION

A. Methodology 1B. Standards 1C. Results 2D. Observations 2

III. CONCLUSIONS '2

IV. RECOMMENDATIONS 2

Appendix

A Measurement Equipment List 7B Draft AFOSH Standard 161-YY, Hazardous 11

Noise Program Impulse Noise StandardsC Pressure Versus Time Waveforms 17

Distribution List 25

.i 1• iv

I. INTRODUCTION

A.- Purpose: This report provides the results of the analysis of impulsenoise data collected during the firing of weapons inside two different designsof the Two Man Defensive Fighting Position Shelter (DFP). The tests wereconducted.at-*K-rtland AFB NM on 5 Aug 1987. -The survey was requested-by-theA4i---orce ,Weapons-Laboratcry-Civil Engineering Research Operations BranchAF•W/TE)'1to determine the health effects of noise on personnel firing

weapons frowi inside the shelters.

B. Problem: Two shelter designs were being evaluated by the AFWL. Onedesign is referred to as the USAFE design (DFP-USAFE), the other on the AFWLdesign (DFP-AFWL). Training will be performed in the shelters using liveammunition, creating the potential for hearing loss if the proper protectivemeasures are not taken (i.e., wearing personal hearing protection, limitingthe number of rounds fired, etc.).

C. Scope: The results of measurements of the peak pressure and durationtaken inside each of the shelter designs using a microphone at the position ofthe ear of the person firing each of four different weapons are reported.Recommendations are made on the proper hearing protection to use duringtraining with the weapons tested.

II. DISCUSSION

A. Methodology. Each of the weapons, except the M-16,, was fired from theprototype shelters on 5 Aug 1987. Two microphones were placed inside theshelter during firing. One was positioned within one foot of the Jperator'sear, oriented so tft sound from the weapon struck the microphone with grazingincidence. The seccnd microphone was positioned in the center of the shelterto serve as a backup measurement and to determine if exposure to a secondperson in the shelter was higher than the operator's exposure. The signalswere fed to a Nicolet Model 4094B Digital Oscilloscope for recording %ndstorage on floppy disks. The signals were also recorded on a tape recorder asa backup to the digital signals. A 114 decibel (dB), 1,000 Hertz (Hz)acoustical calibration signal was applied to both microphones before and afterthe survey. A complete list of equipment is given at Appendix A. The datarecorded on the floppy disks on 5 Aug 87 was then analyzed after return to theUSAFGEHL. The M-16 was not available on 5 Aug 1987 for testing. Personnelfrom the local bioenvironmental engineering office performed testing on theM-16 at a later date and provided us the results. No pulse durations weremeasured fir the M-16, but since the peak levels are low this is notparticularly significant.

B. Standards. Air Force policy on exposures to impulse z-oise is outlinedin AFR 161-35, Hazardous Noise Exposure. No unprotected exposu-e to levels ofmore than 140 dB peak sound pressure level is permitted. Exposure to levelsin excess of 160 dB requires the use of double hearing protection (plugs andmuffs). A new draft noise standard, AFOeH Standard 161-YY, Hazardous NoiseProgram, is under consideration by HQ USAF/SGPA and provides criteriaconsistent with the present standard. However, this draft standard is moredefinitive, since peak levels as well as pulse durations are used in the

------------

selection of hearing protection. The applicable portion of this draftstandard is outlined in Appendix B. Comparison will also be made to thisstancatJ

C. Results. A summary of the values measured is shown in Table 1. Theaverage values for the peak pressures in kilopascals (kPa) and the equivalentpeak pressure levels in decibels, recorded for each of the weapons in bothshelters, are shown. The maximum values actually measured are listed also.The average value plus two standard deviations were calculated and are thevalues used for comparison to the standard and to provide recormvendations.Representative pressure versus time curves are shown in Appendix C, Figures 1through 6, for each of the three weapons in each of the two s~hEter designsmeasured by the USAFOEHL. These pressure-time curves are, of course, notavailable for the M-16.

D. Observations. The hearing protection required by AFR 161-35 •s afunction of both the level of the impulse and its B-duration, as w~ll as thenumber of rounds fired in a siyngle day. Above 140 dB peak sound pressuirelevel AFR 161-35, Hazardous Noise Exposure, requires the ute cf single hearingprotection (plugs or muffs) regardless of the duration of' exposure. Above 160dB the use of doubTl hearing protection (plugs and muffs) is required.Applying the criteria from paragraph 21.c. and T..achment 22 of AFR 161-35w-esults in the protection criteria for the DFPs outlined in Table 2. Thehearing protection which would be requirid by the draft AFOSH Standard 161-YYis shown in Table 3. Again, exposures above 140 d8 require Mt, least singleprotection. However, the pulse duration plays a greater roi: in determiningthe required protection.

III. CONCLUSIONS

A. The noise produced by the weapons tested in the two shielters is

hazardous to hearing and hearing protection is required .u 3rotect exposedpersonnel from hearbig loss.

B. The proteucion and firing limitations outlined in Table 2 will protectthe hearing of persons firing the weapons listed from the two 0FP sheliters.The protection outlined in Table 3 would be required if the draft AFOSHStandard is adopted.

IV. RECOMENDATION

The hearing protection outlined in Table 2 should be worn when the numberof rounds to be fired in a day is as indicated for the appropriate weapons.Should the draft AFOSH Standard 161-YY, Hazardous Noise Program, be adopted,the protection outlined in Table 3 may be used.

2

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Table 2. Personal Hearing Protection Criteria for Weapons Fire in Defensive

Fighting Position Shelters Required by AFR 161-35.

Shelter Protection Requi redN - None

-Weapcn S - Sipgle (Plugs or muffs)D - Double (Plugs in-d muffs)

Rounds Fired per Pay 5 100 1,000

DFP-USAFE

M-16 N S S

M-60 S C D

MK-19 D P D

M-2 S S S

DFP-AFWL

M-16 N* S S

M-CO S S D

MK-19 S D D

M,-2 S S S

• - Technically no protection is required under these conditions, however, itis always best to wear at least single protection for these types of exposure.

i

Table 3. Personal Hearing Protection Criteria for Weapons Fire in DefensiveFighting Position Shelters Proposed by Draft AFOSH Standard 161-YY.

Shelter Protection Requi redWeapon N - None

SS - Single (Plugs or muffs)DO - Double (Plugs 7nd muffs)

Rounds Fired per Day 5 100 1,000S~DFP-USAFE

M-16 S S S

M-60 S S S

MK-19 S S D

M-2 S S S

DFP-AFWL

M-16 N* S

M-60 S S S

t4K-19 S S D

M-2 S S S

* - Technically no protection is required under these conditions, however, itis always best to wear at least single protection for these types of exposure.

5

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6

APPENDIX A

Measurement Equipment List

7

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8

N, I• f- • r( '• •• ." "X1 'JwJ Nj.J is -w• 4 r F •J p ,'• Wx••_S, I-v 'N. 'N 'Cia -• Ct w b4-t W -. w"•, I - 17W, ,,F h. , -.- Cw" , .", 5.'.,•. , - , I.

MEASUREMENT EQUIPMENT LIST

Equipment Manufacturer Model/Type Serial Number

Digital Oscilloscope Nicolet 4094B 88B02987Tape Recorder B & K Instruments 7006 1307051Microphone B & K Instruments 4136 392527Microphone Preamplifier B & K Instruments 2619 594034Microphone B & K Instruments 4136 392542Microphone Preamplifier B & K Instruments 2619 418488Microphone Power Supply B & K Instruments 2804 1338144

9

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10

APPENDIX B

Draft AFOSH Standard 161-YY,

Hazardous Noise Program Impulse Noise Standards

1 11

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12

A -4 -. 1..~-

Y ,. -

AFOSH STANDARD 161-YY Attachment 1 16

IMPULSE NOXSE

1. xmpulse or Impact Exposure Limits. Unprotected exposures shallnot exceed 140 dB peak sound pressuwr level. Above 140 dB peaksound pressure level the applicable impulse noise limits aredetermined based on the expected aumber of exposures per day and thetype of hearing protection used. Table AI-I identifies the requiredhearing protection curve, show- in Figure A--1, based on the type ofprotection and numb*r of daily exposures. The limit for a givenprotection requirement becomes more restrictive (a lower curvelimits exposures) as the number of impulses per day increases.rigure Al-I shows the peak level versus B-duration curves whichlimit the allowable exposure based on the type of protection worn.Table AI-S lists the peak impulse levels produced at the ear byvarious weapons under non-reverberant conditions (outdoors) for asingle shot. These levels should not be used for reverberantconditions (such as indoor firing ranges) and do not include thenoise produced by other weapons firing near the shooter.

2. Impulse Noise Evaluations. There are two types of measurementsto be used in ev&luating impulse or impact noise exposures:screening measureiients and detailed evaluations.

a. Screening Measuraments. To determine if levels exceed 140 dBpeak sound pressure level, a sound level meter having the capabilityto measure impulse or impact noise may be used to determine the peakof the impulse. This measurement shall be documented on the DD Form2214. If measurement shows the levels to exceed 140 dB, thedetailed evaluation shall be performed. Levels less than or equalto 140 dB may be evaluated as in para. 3a, with no unprotectedexposure allowed above 115 dB(A).

b. Detailed Evaluations. Field measurements of impulse andimpact noise are sometimes difficult and require special equipmentto measure the B-Duration. When peak impulse levels are determinedto be above 160 dB consultation with the USAFOEHL should be obtainedas described in AFR 161-17, USAF Occupational and EnvironmentalHealth Laboratory (OEHL) Services.

13

AMOSH STANDARD 161-YY Attachment 1 17

Table Al-I. Impulse Noise Personal Protection Selection Criteria.

Impulse Noise Limit CurveMaximum ExpectedNumber of Exposures No Either Plugs Both Plugsin a Single Day * Protection Or rluffs and Muffs

1000 W X Y100 W Y z

5 W Z Z

* A single exposure consists of either (a) a single pulse fornon-repetitive systems (systems producing not more than one impulseper second, such as semi-automatic weapons), or (b) a burst forrepetitive systems (systems normally producing more than one impulseper second, such as automatic weapons).** Higher levels than curve Z are not permitted since other,non-auditory physiological injury may occur.

Table A1-2. Impulse Levels for Weapons.

Single Fire, Peak Impulse

Weapon Peak Level (dB)

X-1, Rifle, .30 caliber 161Submachine gun, .45 caliber 160M-58, .50 caliber 161K-14, (EZ) Rifle 140M-16. Rifle, 7.62 mm 16090 mm Recoilless Rifle 188M-60, Machine Gun, 7.62 mm 161

Note: Levels measured outdoors at shooter's ear with no otherweapons firing.

14

AFosa STANDARD 161-YY. Attachment 1 t

Figure Al-i. Peak Pressure Level and B-Duration Limits for Impulse

(See Table Al-i to selec-t curve for safe use. Note: Exposure tolevels in excess of limit W requires mandatory heariaig protection.)

CO*190

I..NO41 omls o ltigth uvsae

1705

AFOSH STANDARD 161-YY Attachment 1 107

P

U,

- (a)-.

0LU

WLU

LU 20 db

Z~ 1-

z

TIMEP is the peak pressure level measureJat the position of the ear

when the individual is not present (if it is possible for the deviceto be operated without the individual present).

A-duration, the pressure-wave duration, is the time required-forthe initial or principal wave to reach the peak pressure level andreturn momentarily to zero. In part (a) of this figure thisduration is from point V to point W.

B-duration, the pressure-envelope duration, is the total tinie theenvelope of the pressure fluctuations (both positive and negative)is within 20 dB of the peak pressure level, including reflectedwaves. In part (b) of this figure the B-duration would be from V to-X plus Y to Z.

Figure AI-2. Dete~rmination of A-Duration and B-Duration.

16

APPENDX C

Pre3sure versus Time Waveforms

17

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Figure 1. M-60. DFP-USAFE, Pressure Versus Time Waveform,.163 dB Peak, 62.0 mns B-duration

16

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155 dBPeak, 6.6 ms B-uratioa

19

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Figure . MK-19, DFP-USAFE, Pressure Versus Time Waveform,164 dB Peak, 8G.8 ms B-duration

20

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Figure 4. MK-19. DFP-AFWL, Pressure Versus Time Waveform,163 dB Peak, 74 2 ms B-duration

21

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Figure 5. M-2, DFP-USAFE, Pressure Versus Time Waveform,

148 dB Peak, 101 mis B-duration

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Figure 6. M-2, DFP-AFWL, Pressure Versus Time Waveform,148 dB Peak, 76.6 ms B-duration

23

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Distribution List

No. of Copies

AFWL/NTE 10Kirtland AFB NM 87117-6008

HQ AFSC/SGPB 1Andrews AFB DC 20334-5000

HQ USAF/SGPA 1Bolling AFB DC 20332-6188

USAF Regional Medical Center Weisbaden/SGB 1APO New York 09220-5300

OL AD, USAFOEHL 1APO San Francisco 96274-5000

USAFSA•I/TSK 1Brooks AFB TX 78235-5301

Defense Technical Information Center (DTIC) 2Cameron StationAlexander VA 22319

HQ HSD/EV 1Brooks AFB TX 78235-5000

USAFSAM/EDHBrooks AFB TX 78235-5301 1

USAF Hospital Kirtland/SGPBKirtland AFB NM 87117-5300 1

25