i · shock waves are side-on blast overpressure (p.) and the duration of the positive overpressure...

AD-A286 212

TECHNICAL REPORT ______

NATICKIrM-95/003

BLAST OVERPRESSURE ANDSURVIVABILITY CALCULATIONS FOR

VARIOUS SIZES OF EXPLOSIVE CHIARGES

ByPhilip W. Gibson

NOVEMBER 1994

941-35069 FINAL REPORT wV15I

\\I\\1\1\1~\\\\\\1\1II~\\I \ \~(JUNE 1994 A

Approved for Public Release; Distribution Unlimited

UNITED STATES ARMY NATICKRESEARCH, DEVELOPMENT AND ENGINEERING CENTER

NATICK, MASSACHUSETTS 01760-5018

SURVIVABILITY DIRECTORATE

jyjjý, Wj _ý A4I J L iO

94 11I 013

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Puol~ report,,9 burden 4or this oliection of information is etmated to avreag u sp nr tonse n cc Lalg theripme tor reviewing Instrucriorn. searching existling data soulice%.gattiplrirg and maintaining the dlata needed. and compteting ano re-"- tmigI tc Ie tion of-ifornatide Send comnments regarding thiS urden -Itlimate Of any OIher aspect of thiscollert~n 0f informatio,. inn edmrg stigge ti nti or redncirg ths ourcder t- Washington Headquarte' Se rvics. Directorate foi information Operations and Report%. 1215 jeffersonDavis .t-ii a~y . S.-t- '204 Arlington. VA 1221.12-4301i and to tie ofice of i.canagemfisl and Budget. Ocinerwo R-ductrifl hioiCCI (0704.01SB). Wavishington. OC 2DS03

1. AGENCY USE ONLY (Leave blank) I2. REPORT DATE I3. REPORT TYPE AND DATES COVEREDNovember 1994 Final June 1994

4. TITLE AND SUBTITLF S. FUNDING NUMBERS

Blast Overpressure and Survivability Calculations for VariousSizes of Explosive Charges Cost Code:

6. AUTHOR(S) 4304106CCOAOO

Phillip Gibson

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) B. PERFORMING ORGANIZATIONREPORT NUMBIER

U.S. Army Natick RD&E CenterKansas Street, ATTN: SATNC-1TFR NATICK[TR-95/003Natick, MA 01760-5019

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Approved for public release; distribution is unlimited.

13. ABSTRACT (Maximum 200 words)

Blast overpressures and durations were calculated for several different explosive charge sizes. Thecharge sizes range froin 1 ounce of TNT to 32 ounces of TNT. The distance from the charge rangedfrom I to 3 feet. When the blast calculations were compared to human blast tolerance limits, it wasfound that the blast exposures mostly fell in between the 1 % survival limit and the threshold of lungdamage. This probably means that a heavily-protected explosive ordnance disposal technician,supplied with a rigid enclosed thoraco-abdominal protector, may be able to survive the air blasteffects at these distances. Note that these calculations only pertain to direct air blast effects andignore fragments and thermal effects entirely.

14. SUBJECT TERMS BL AST EXPLOSIVE CHARGES 15. NUMBER OF PAGES

BLAST WAVES SHOCK WAVES WOUNDS AND INJURIES 20SURVIVABILITY PROTECTIVE CLOTHING TOLERANCES (PHYSIOLOGY) 16. PRICE CODEOVERPRESSURE EXPLOSIVE ORDNANCE DISPOSAL_________

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACTOF REPORT I OF THIS PAGE I OF ABSTRACTUNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

NSN 7540.01-280-5500 Standard Form 298 (Rev 2-89)Piftittibed by ANSI Std 139-18298-102

TABLE OF CONTENTS

page

LIST O F FIG URES ............................................................................... v

P R E FA C E ................................................................................................. vii

1. INTRO DUCTIO N .................................................................................... 1

2. A PPRO AC H .......................................................................................... 1

3. R ES U LTS ............................................................................................... 5

4. CO N CLUS IO NS ................................................................................... 8

5. R EFERENC ES ...................................................................................... 9

AaoU~OUTor

FITIS GRA&tDT17C TAB~ 00

iiai.. __ e ] ---

n(A" 5trI', dt 0 •

Uua !,ý,a.z ,ao

S"L i and/oiii .. . ...e.ial

LIST OF FIGURES

Figure page

1. Predicted survival curves for man exposed in the free stream to surfacebursts of TNT where the long axis of the body is perpendicular tothe blast winds (from Reference i) .......................................................... 2

2. Predicted survival curves for man exposed in the free stream to surfacebursts of TNT where the thorax is near a flat rigid surface reflectingthe blast wave at normal incidence (from Reference 1) .......................... 3

3. Peak side-on overpressure versus distance from the charge forseveral different charge weights of TNT. Surface burst assumedwith a ground reflection factor of 2.0 ............................... 5

4. Survival curves predicted for a 70 kg man, applicable to free-streamsituations where the long axis of the body is perpendicular to the directionof propagation of the blast wave (from Reference 4) ................................ 6

5. Sur'vival curves predicted for a 70 kg man, applicable tc situationswhere the thorax is near a surface against which a blast wavereflects at normal incidence (from Reference 4) ....................................... 6

6. Calrulated TNT blast curves superimposed on human blast tolerancelimit plot for the free-stream situation ........................................................ 7

7. Calculated TNT blast curves superimposed on human blast tolerancelimit plot for the reflected shock situation .................................................. 8

v

PREFACE

This report was written for the purpose of calculating the potential for air blast lung injuries due to varioussizes of explosive charges that soldiers engaged in clearing mines or explosive ordnance might beexposed to.

Several reviewers provided comments and suggestions which we-e incorporated into the report. Theyinclude Andreas Blanas, Janet Ward, and Thomas Tassinari of the Textile Research and EngineeringDivision, Survivability Directorate; Denise Tolliver and Stanley Waclawik of the Soldier IntegratedSystems Division, Survivability Directorate; and Heidi Schreuder-Gibson of the Fiber and PolymerScience Division, Science and Technology Directorate.

vii

Blast Overpressure and Survivability Calculationsfor Various Sizes of Explosive Charges

1. Introduction

The purpose of L-his report is to present blast overpressures and durations for several small explosivecharge sizes and compare them to human blast tolerance limits. The calulations look only at theproperties of the air shock wave, and their potential for causing lung damage. Other sources of injuryare not considered, such as fragments, burns due to the fireball, or injuries due to being thrown downor away from the blast. It should be noted that these other sources of injury are usually more importantfor small charge sizes than lung injuries due to the air shock wave.

The motivation was to determine the possible v ulner, bility to lung damage of soldiers who must performtasks such as clearing mines and disposing of explosive ordnance. For smaller anipersonnei mines, thesesoldiers are quite well protected from fragments, by virtue of their ballistic armor. However, the soldierswho are wearing soft body armor without a rigid chest protector may still be vulnerable to the effectsof the blast wave even if they are protected from fragments.

2. Approach

For the purpose of these estimates, explosive properties were calculated in terms of the peak overpressureand positive phase durations of the air shock wave resulting from the detonation of a given bare explosivecharge. Therefore, these are very rough estimates of what might occur for soidiers exposed to a blaston the battlefield, since the confinement of the charge by a metal case, which is important for mines andmortar shells, will change both the peak overpressure and the duration of the resulting air shock wave.

The explosive charge was assumed to be composed of TNT. Charge weights of I ounce up to 32 ounceswere used for the calculations. The calculations could also easily be performed for Composition C-4(90% RDX), which has a TNT equivalency of about 1.3. Other assumption were: 1) a standardatmosphere (14.7 psi), 2) the explosive charge was located on the ground surface, 3) the groundreflection factor was equal to 2.0 (a hard surface). These are worst case conditions.

Handbook values are available for estimating human blast tolerances. Most of these were derived fromextensive animal testing.' Examples of these plots are shown in Figures 1 and 2. Unfortunately, theseplots do rot extend down to the lower charge weights and distances from the charge that are of interestin this report. However, these plots suggest that a person can get very close to charge weights of wound1 lb and still survive.

10 7 1 10 KT

Surface Burst, Standard Sea-Level CondiltonsAssumed Ground "eflection Factor: 1.8

101

()4'

100

15 10 10

1 1

_ _ _ __I itI101 -__

"- "Long Axis of Body Porpondicular to BlastWinds, Subject Fachig Any D;iection

1 10 100 1000 10000

Range (feet)

Figure 1. Predicted survival curves for man exposed in the free stream to surface bursts of TNTwhere the long axis or the body is perpendicular to the blast winds (from Reference 1).

2

10 10K'T

Surfamc Burst, Slandard Sea- Level ConditionsAssu.nod Ground Reflection Factor: 1.8

10' IKT

100-

10" - 10

S10-

101 - Thorax Nea i Reiiclin9 bSulaoe Whnich isPerpendicular to Blast Winds, SubjectFacing Any Direcion

10 100 1low 10000

Range (feel)

Figure 2. Predicted survival curves for man exposed in the free stream to surface bursts of TNTwhere the thorax is near a fiat rigid surface reflecting the blast wave at normal incidence (fromReference 1).

There are critical factors that contribute to the potential of lung damage from small explosive charges:1) the large dimeaisions of the human body relative to the radius of curvature of the shock wave, and

2) the rapid change in shock properties as a shock wave travels away from the explosion source. Bothwould have an influence on the possible lung damage to a human. Figures 1 and 2 assume that the shockwave is essentially planar in nature, since those plots were developed to assess possible injuries from airshock waves due to nuclear weapons. For ,he purposes of this report, the blast wave will be assumedto be planar in nature, and the influence of the human body size will be ignored.

To get a betterestimnate of blast effects down in this lower range, the blast wave properties were calculatedbased on Hopkinson-Sachs blast wave scaling laws which have been established for chemicale.plosives.' The blast parameters of most use in establishing the po:ential of human casualties from airshock waves are side-on blast overpressure (p.) and the duration of the positive overpressure phase (t1).

The charge weights were 1 oz, 2 oz, 4 oz, 8 oz, 16 oz, 24 oz, and 32 oz. Calculations of po and t, weredone foreach charge size at ranges of one to three feet, and at intervals of 0.1 foot. Rather than use scaledblast tables and look up each value, empirical equations developed at the Naval Weapons Center wereused.'

3

Overpressurep, (psi) was calculated using the equations shown below where W= TNTcquivalcncy (kg),and Z (scaled distance)= actual distance((meters)/W' ',. The appropriate constants for converting frommetric to English units are included in these two equations.

p0pi)= (797)(14.7 psi) I+(B1I2po (psi) (4.

+C0.048J 4+(32)1 F 1-•5

Positive phase duration t, (msec) was calculated from:

td(MSe98(W3)[1[+( " 0.54]

( 3]1(Z )6]r

The tables of calculated values using these equations are given in the Appendi,, along with a simplecomputer program to generate the values.

4

3. Results

The peak overpressure (psi) is plotted versus distance (feet) f;om the explosive charge in Figure 3.

1500

TNT Charge Size

1200 ---- 32 ounces------. 24 ounces

tx -. 16 ounces-"-. ounces

S900 .. \... 4ounces(0

a, ---,-\2 ounces----- 1 ounce

0 600 • N

13_"., "•--. -

300 "" -

- - -............ --- --- -.

01 ,_ _, - '-- '7 - -- - -r-

1.0 1.5 2.0 2.5 3.0

Distance from Explosive Charge (feet)

Figure 3. Peak side-on overpressure versus distance from the charge for several different chargeweights of TNT. Surface burst assunmed with a ground reflection factor of 2.0.

5

The two situlations of most interest are: 1) when a soldier is standing out in the open (free-streamsituation), and 2) when the soldier is standing next to a rigid surface which reflects the shock Wave andessentially doubles its strength. flunln tolerance curves" for the two situations are shown in Figures 4and 5.

160C0

1000 7-

400

Long xAI[ of Body Perpand~icuar to 04 1at

0.2 0.4 0.7 1 2 4 7 10 20 40 70 100 200 400 7001000 2000 5000

Duration of Positive Incident Overpressure (msec)

Figure 4. Survival curves predicted for a 70 kg man, appnlicable to free-streamn situation-swherc the long axis of the body is perpendicular to the direction of propagation of the blastwave (from Reference 4).

600- .1-400

C~200-L JU-Thoraix.a Hfeing rc Which is'

Perpendicular to Blast Winds. Subjecto 100 %~•~,Facing Any Direction

70 - All

F1Q

50.2 0.4 0.7 1 2 4 7 10 20 40 70 100 200 400 700 1000 2000 5000


Figure 5. Survival curves predicted for a 70 kg man, applicable to situations where the thoraxis near a surface against which a blast wave reflects at normal incidence (from Reference 4).

6

We can take the calculated overpressur-di.tanlce data for the various charge weights and combine them

with the survival curves shown in Figures 4 and 5. This is complicated by the fact that both the peakblast overpressure and the positive phase duration are required to determine the injury potential of a givenair shock wave.

This is done in Figures6 and 7. Figure 6 covers the free-stream situation and Figure 7 covers the reflectedshock situation. Each individual curve is for a different charge weight. Each curve is a composite ofdifferent distances from the explosive charge. The points corresponding to a 1 foot, 2 feet, and 3 feetdistance away from the charge are indicated on each curve. The actual values are also shown in the tablesin the Appendix. The doubling back of the curves for the higher charge weights is due to the proximityto the blast origin. The minimum in positive phase duration is due to inertial effects and the initialresistance of the air to expansion. This minimum in td is physically real, and is seen in all explosionsclose to the fireball.

104 -

Distancefrom Charge0 1 foot* 2 feet

-- 10a . 3 feet

(n

U _•'W• 1% Survival10 TNT Charge Size ,k 7

0> )0 32 ounces Threshold of-• -- 24 ounces \ '• Lung Damage

) 16 ouncesC 101 8 ounces

4 ounces2 ounces1 ounce

100 ,.01 .1 1 10


Figure 6. Calculated TNT blast curves superimposed on human blast tolerance limit plot for thefree-stream situation.

7

-0 . . .. . . . -" , .... *'

Distancefrom Chargee 1 foot* 2 feet

1- 10 3 - 3 feeti)CL

V)

10 TNT Charge Size ",1%

0 -------- 32 ounces k

14 ounces \Threshold of-0 16 ounces Lung Damage

l ... 84 ounces2 ounces

1 ounce

100.01 .1 1 10

Durafon of Positive Incident Overpressure (msec)

Figure 7. Calculated TNT blast curves superimposed on human blast tolerance limit plot for thereflected shock situation.

Above the i % survival curves shown on the plots, death would be likely within 24 hours. Forthosepointsbelow the threshold of lung damage, significant injury from the air shock wave is unlikely, butunprotected eardrums would likely be damaged. In addition, the person may be knocked down or thrown,and various injuries may occur due to fragments or burns.

4. Conclusions

When the blast calculations for explosive charge sizes from I to 32 ounces, at ranges of one to three feet,were compared to human blast tolerance limits, it was found that the blast exposures mostly fell inbetween the 1% survival limit and the threshold of lung damage. This probably means that a heavily-protected explosive ordnance disposal technician, supplied with a rigid enclosed thoraco-abdominalprotector, might survive a blast of this magnitude. Those individuals who only have soft body armor,although they may be adequately protected against fragments, may be vulnerable to lung damage fromthe air shock wave. Again, note that these calculations only pertain to direct air blast effects and ignorefragments entirely.

This document reports research undertakenat the U.S. Army Natick Research, Developmentand Engineering Center and has been

8 assigned No. NATICK/TR-5/'3 in the seriesof reports approved for publication.

5. References

1. Bowen, I., Fletcher, E., Richmond, D., "Estimate of Man's Tolerance to the Direct Effects of Air

Blast," Technical Progress Report, DASA-2113, Defense Atomic Support Agency, Oc~ober 1968.

2. Kinney, G.F., and Graham, K.J., Explosive Shocks in Air, 2nd Edition, Springer-Verlag, NewYork, 1985.

3. Sewell, R.G.S., Zulkosi, T.R., and Kinney, G.F., "Blast Parameter Characterization", NavalWeapons Center Technical Report TP 5920, Part 1, Volume 2, China Lake, CA, 1979.

4. White, C.S., et. al., "The Biodynamics of Airblast", Defense Nuclear Agency Report DNA2738T, July 1971.

9

- ~ ~ ~ ~ ~ ,- r.r r.47 .. ~

10

APPENDIX

Tables of Blast Overpressure and Positive Phase Durationas Function of Distance for Small Explosive Charges

and Computer Program to Generate the Values

11 -

1 ounce charge 2 ounce charge

Distance Overpressure Duration Distance Overpressure Durationfeet p. (psi) td(msec) feet P0 (psi) t%(msec)

1.000 144.520 .158 1.000 235.302 .1141.100 117.342 .185 1.100 193.044 .1491.200 96.700 .209 1.200 160.502 .1821.300 80.733 .230 1.300 135.011 .2111.400 68.182 .250 1.400 114.745 .2371.500 58.179 .269 1.500 98.422 .2601.600 50.107 .287 1.600 85.123 .2821.700 43.521 .305 1.700 74.177 .3021.800 38.092 .323 1.800 65.082 .3221.900 33.577 .340 1.900 57.463 .3412.000 29.790 .357 2.000 51.032 .3592.100 26.590 .373 2.100 45.564 .3772.200 23.866 .390 2.200 40.886 .3952.300 21.532 .406 2.300 36.860 .4122.400 19.520 .422 2.400 33.375 .4292.500 17.776 .437 2.500 30.343 .4462.600 16.256 .453 2.600 27.692 .4632.700 14.924 .468 2.700 25.364 .4792.800 13.752 .483 2.800 23.311 .4952.900 12.717 .497 2.900 21.493 .5113.000 11.797 .512 3.000 19.877 .527


Distance Overpressure Duration Distance Overpressure Durationfeet P. (psi) tV(msec) feet P0 (psi) td(msec)

1.000 372.799 .062 1.000 573.383 .0511.100 309.409 .089 1.100 481.870 .0541.200 259.885 .122 1.200 409.255 .0661.300 220.586 .158 1.300 350,832 .0881.400 188.972 .193 1.400 303.248 .1161.500 163.233 .225 1.500 264.067 .1501.600 142.051 .255 1.600 231.488 .1851.700 124.452 .282 1.700 204.159 .2211.800 109.704 .307 1.800 181.051 .2551.900 97.248 .330 1.900 161.370 .2872.000 86.653 .352 2.000 144.498 .3172.100 77.583 .372 2.100 129.945 .3452.200 69.772 .392 2.200 117.324 .3702.300 63.008 .412 2.300 106.322 .3942.400 57.121 .430 2.400 96.685 .4172.500 51.973 .449 2.500 88.208 .4392.600 47.451 .467 2.600 80.720 .4602.700 43.463 .485 2.700 74.080 .4802.800 39.931 .502 2.800 68.171 .5002.900 36.793 .519 2.900 62.896 .5193.000 33.994 ,537 3.000 58.170 .538

12


Distance Overpressure Duration Distance Overpressure Durationfeet P. (psi) td(msec) feet P0 (psi) td(msec)

1.000 854.393 .098 1.000 1062.529 .1661.100 727.636 .078 1.100 912.178 .126

1.200 625.363 .067 1.200 789.657 .1001.300 541.840 .064 1.300 688.684 .0831.400 472.894 .069 1.400 604.639 .0751.500 415.429 .082 1.500 534.060 .0741.600 367.117 .101 1.600 474.310 .0791.700 326.177 .127 1.700 423.358 .0911.800 291.235 .158 1.800 379.617 .1091.900 261.215 .192 1.900 341.834 .1332.000 235.268 .228 2.000 309.015 .1622.100 212.717 .264 2.100 280.356 .194"2.200 193.016 .299 2.200 255.210 .2292.300 175.723 .332 2.300 233.046 .2642.400 160.478 .364 2.400 213.430 .3002.500 146.983 .394 2.500 195 999 .3352.600 134.990 .422 2.600 180.456 .3692.700 124.296 .448 2.700 166.547 .4022.800 114.727 .473 2.800 154.061 .4322.900 106.139 .497 2.900 142.819 .4623.000 98.407 .520 3.000 132.668 .489

32 ounce charge

Distance Overpressure Durationfeet P0 (psi) td(msec)

1.000 1231.714 .2431.100 1063.488 .1831.200 925.449 .1421.300 810.952 .1141.400 715.079 .0961.500 634.123 .0851.600 565.241 .0811.700 506.226 .0831.800 455.345 .0911.900 411.220 .1042.000 372.749 .1242.100 339.040 .1492.200 309.366 .1772.300 283.133 .2102.400 259.848 .2442.500 239.103 .2802.600 220.554 .3162.700 203.915 .3512.800 188.945 .3862.900 175.434 .4193.000 163.209 .451

13

c***program tntblast in fortranctt*** uses hopkinson scaling laws to calculate yields

c*** phil gibsonwrite(*,*)'input charge weight in ounces'

c*** wl =-charge weight, ouncesc*** wr=charge weight, tnt equivalent (kg)e** d~distan-.e from charge in metersce*** z=scaled distance

c***po=peak overpressurec***** td~=posive phase duration, milliseconds

read(*,*)wlw~wl *.02835feet=1 .0d=feet*.3048open (2 1,file='tntblast. dat')write(21,*) feet po td(msec)do 1 000 k=1,21z=d/w**.3333po=((1 4.7)*(797)*(1 .0+(z/4.5)**2))/((sqrt(1 .+(zI0.048)**2))*

&(sqrt(1 .+(z/O.32)**2))*(sqrt(1 +(zJ./135)**2)))

&o.74)**6)*(sqrt(1 .(z69*2)

write(*,*)feet, po,tdwrite (421 ,900)feet, po,tdfeet 4eet+. 1d=feet*. 3048

1000 continue900 format (3f 15.3)

close(2 1)stopend

14