blast humans

8/6/2019 Blast Humans

http://slidepdf.com/reader/full/blast-humans 1/22

Excerpted from "A Manual for the Prediction of Blast and Fragment Loadings onStructures," US Department of Energy, August 1981.

http://www.osti.gov/bridge/servlets/purl/5892901-5PuqGG/ (775pp, 34MB)

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4.6 HAZARDS TO PERSONNEL FROM A IR BLAST

L i t e r a t u r e c o nc e rn i n g t h e h a rm f ul e f f e c t s o f b l a s t on humans h a s b ee n

publ ished as e a r l y as 1768 . However, knowledge of t h e mechanisms of b l a s t dam-age to humans was extremely incomple te un t i l World War I , when th e phy s ic s o f

e x p l o s i o n s were b e t t e r u n de rs to od . S i nc e t h a t t i m e , numerous au th or s have

c o n t r i b u t e d c o n s i d e r ab l e t i m e and e f f o r t i n th e s tud y of b l a s t damage mechan-

Each a c c i d e n t s i t u a t i o n h a s i t s own unique environ-

ment with t rees , b u i l d i n g s , h i l l s , and v a r i o u s o t h e r to p o gr ap h ic a l c o n d i t i o n s

which may d i s s ip a t e th e ener gy o f the b l a s t wave o r r e f l e c t i t and amplify i t s

e f f e c t on a n i n d i v i d u a l . B ecau se of t h e s e d i f f e r e n t v a r i a t i o n a l f a c t o r s i n -

volved i n an explosion-human body receiver s i t u a t i o n , on ly a s i m p l i f i e d a n d

l i m i t e d s e t of b l a s t damage c r i t e r i a w i l l b e i n c l u d e d h e r e . The human body

ground when contacted by t h e b l a s t wave. E xc lu di ng c e r t a i n r e f l e c t e d wave

s i t u a t i o n s , t h i s i s th e most hazardous body exposure cond i t i on . A i r b l a s t

e f f e c t s c a n be d i v id e d i n t o f o u r c a t e go r i e s :

b l a s t e f f e c t s , ear damage, and b l a s t generate d fragmen ts (Ref . 4.61) . Second-

a r y e f f e c t s i n v o l v i n g f ra gm en t i mp ac t by miss i le s f rom th e exploding device

i t s e l f o r f ro m o b j e c t s l o c a t e d i n t h e n ea rb y e nv ir on me nt w hi ch are a c c e l e r a t e d

a f t e r i n t e r a c t i o n w i t h t h e b l a s t wave ( ap pu rt en an ce s) s h a l l b e di s cu s se d i n

Chapter 6.

. i s m s a nd b l a s t p at ho lo g y.

receiver" w i l l b e assumed t o be s t a n d i n g i n t h e f r e e - f i e l d on f l a t and l e v e l1f

p ri mar y b l a s t e f f e c t s , t e r t i a r y

4.6.1 Pr imary Blas t Damage

P ri ma ry b l a s t e f f e c t s are a ss oc i a t e d wi th c hanges i n e nvi ronme nt p r e s -

s u r e du e t o t h e o c c u r r en c e of t h e a i r b l a s t . Mammals are s e n s i t i v e t o t h e in -

c i d e n t , r e f l e c t e d a nd d ynamic o v e r p r e s s u r e s , t h e r a t e of r i s e t o peak over -

p r es s u re a f t e r a r r i v a l of t h e b l a s t wave, an d t h e d u r a t i o n o f t h e b l a s t wave( R ef . 4 .61 ). S pe c i f i c im pul se o f th e b l a s t wave a l s o p l ay s a m a jor r o le ( R e f s .

4 .62 a nd 4 .63) . O the r pa r a m ete r s which de te rm ine the e x te n t o f b l a s t i n ju r y

' a re t he a m bie n t a tm osphe r i c p r e s su r e , the s i z e a nd type o f a n im a l , a nd pos s ib ly

age . P a r t s of th e body where t he re a r e t h e g r ea t e s t d i f f e r e n c e s i n d e n s i t y of

a d j a c e n t t i s s u e s a re t h e most s us c e p t ib l e to p r im a ry b l a s t damage ( R e f s . 4 .61 ,

4 . 6 4 , a nd 4 .65) . Thus, t he a i r - c o n ta i n ing t i s s ue s o f the lungs are more sus-

c e p t i b l e t o p ri ma ry b l a s t t ha n an y o t h e r v i t a l organ (Ref . 4 .66) .I

P ulm on ary i n j u r i e s d i r e c t l y o r i n d i r e c t l y c a u s e many o f t h e p at h op h ys i-

o l o g i c a l e f f e c t s of b l a s t i n j u r y ( Re f. 4 .6 7). I n j u r i e s i n c l u d e pulm onary

hemorrhage and edema (Refs. 4 .61 and 4 .67) , ru pt ur e of th e lungs (Ref . 4 .61) ,

a i r- e mb o li c i n s u l t t o t h e h e a r t a nd c e n t r a l n er vo u s s y st em ( Re f . 4 . 6 1 ), loss

o f r e s p i r a t o r y r e s e r v e ( Re f. 4 .6 1) and m u l t i p l e f i b r o t i c f o c i , o r f i n e scars,of th e lung s ( Re f. 4 .64) . O the r ha rm f u l e f f e c t s a r e r u p t u r e of th e e ar dr um s

( t o be d i s c u s s e d l a t e r ) and damage to th e middle ear , damage to the la rynx,

t r a c h e a , a bd om in al c a v i t y , s p i n a l m en in ge s, a nd r a d i c l e s o f t h e s p i n a l n e r v es

a nd v a r i o u s o t h e r p o r t i o n s of th e body (Ref . 4.61) .

4 -1 6 1



c

Bowen, e t a l . (Re f. 4.65) and White, e t a l . (Ref. 4.6 2), have developed

p r e s s u r e v e r s u s d u r a t i o n l e t h a l i t y c u r v e s f o r humans w hic h are e s p e c i a l l y

amenable to t h i s document . Some of t h e major fa c to r s which determine th e ex-

t e n t of damage from th e b l a s t wave are t h e c h a r a c t e r i s t i c s of t h e b l a s t wave,ambient a t m o s p h e r i c p re s s u re , and t h e t y p e o f an i ma l t a rg e t , i n c l u d i n g i t s

mass a nd g e o m et r ic o r i e n t a t i o n r e l a t i v e t o t h e b l a s t w ave a nd n e ar by o b j e c t s

( R e f . 4.62 ). Althou gh Richmond, e t a l . (Ref. 4.63) and l a t e r White, e t a l .(Ref. 4 . 6 2 ) , bo th f rom th e Lovelace Foundat ion, d i s cu ss th e tendency o f th e

l e t h a l i t y c ur v es t o a pp ro ac h i s o p r e s s u r e l i n e s f o r " long" d u r a t i o n b l a s t

waves, t h e i r l e t h a l i t y cu rv es dem o n st r a te d epend en ce o n p re s s u re and d u ra t i o n

a l o ne . S i n ce s p e c i f i c i mp ul se i s dependen t on p r es su r e as w e l l as d u r a t i o n ,

p r es su r e- i mp u ls e l e t h a l i t y o r s u r v i v a b i l i t y c u r v e s ap p ea r t o b e more a pp ro -

p r i a t e .

t o t i c l i m i t s i s a l s o v e ry a e s t h e t i c a l l y a p p e a li n g fr om a mathemat ica l po in t

o f view.

t a n c e f ro m m os t e x p l o s i o n s c a n b e c a l c u l a t e d d i r e c t l y u s i n g m ethod s d e s c r i b e d

i n t h i s doc um ent, i t i s e s p e c i a l l y a p p r o p r i a t e t h a t p r es su re -i mp ul se l e t h a l i t y( o r s u r v i v a b i l i t y ) c u r ve s b e d e ve lo pe d.

i n R e fe r en c e 4.59.4.68.

The tendency fo r p ressu re- impulse l e t h a l i t y cu rves to approach asymp-

A l so , s i n c e b o th p r e s s u r e an d s p e c i f i c i m p ul s e a t a s p e c i f i e d d i s -

This h a s been done and i s descr ibed

T hese cu rv es and t h e i r u s e are rep roduced here as F i g u r e

S i m p l i f y i n g L o v el a c e' s s c a l i n g l a w s i n su ch a manner that only t h e

human s p ec i e s o r l a rg e animals are cons idered , one i s a b l e t o a r r i ve a t t h e

f o ll o wi n g r e l a t i o n s h i p s - o r s c a l i n g l a w s :

1. The a f f e c t of i n c i d e n t o v e r p r es s u r e i s dependent on the ambient

a tmospher ic p re ssu re . That i s ,

S

0

P-Ps = p (4.70)

-

where Ps i s s c a l e d i n c i d e n t p ea k o v e r p r e s s u r e , Ps i s p eak i n c i -d en t o v e rp re s s u r e , and po i s ambien t a tmospher ic p ressu re .

2 , The e f f e c t of b l a s t wave p o s i t i v e d u r a t i on i s dependent on ambi-en t a t m o sp h e r ic p re s s u r e an d t h e mass of th e human ta r ge t . That

i s ,

(4.71)

where r is s c a l e d p o s i t i v e d u r a t i o n , T i s p o s i t i v e d u r a t i o n, a nd

m i s weigh t of human body.

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0

(II

a

PI

\

I1

TJ

a,l-l

l o 2

5

2

lo 1

5

2

l o o

5rdVr n

2

-110

2 5 2 5 10-1 2 5 l o o 2 5 lo1

f

Figure 4 . 6 8 Survival Curves f o r Lung Damage to Man

4 - 163



3. Impulse is can be approximated by

P Ti = -

s 2

S(4.72)

Equat ion (4 .72) assumes a t r i a n g u l a r wave shape and i s co n s e rv a t i v e ,

f ro m a n i n j u r y s t a n d po i n t , f o r " lo ng " d u r a t i o n b l a s t waves which approach

s q u a re wave s h ap es b ecau s e i t u n d er e s ti m a te s t h e s p e c i f i c im p ul se r e q u i r e d f o r

a c e r t a i n pe rc en t l e t h a l i t y . I t i s a l s o a c l o s e ap p rox i m a ti o n fo r " s h o r t" d u r-

a t i o n b l a s t waves w hic h c h a r a c t e r i s t i c a l l y ha ve a s h o r t r i s e time t o p eak o v e r -

p r e s s u r e a nd a n e x p o n e n ti a l de ca y t o a m bi en t p r e s s u r e , t h e t o t a l wave shape

b e i ng n e a r l y t r i a n g u l a r .

F o un d at i on f o r p ea k o v e r p r e s s u r e an d p o s i t i v e d u r a t i o n t o t h e c o n s e r v a t i veest imate f o r s p e c i f i c impulse de te rmined by Equat ion (4.72) above , one can

a r r i v e a t a s c a l i n g l a w f o r s p e c i f i c ' i m pu ls e:

A pp ly in g t h e b l a s t s c a l i n g d ev el op ed a t the Lovelace

- 1--i - -s - 2 PsT

(4.73)

-where is i s s c a l e d s p e c i f i c i mp ul se . From Equa tion s (4.71), (4. 72) , and ( 4 . 7 3 )

P T

112 113m

(4.74)S

is = 5

PO

o r f rom Equat ion (4 .72)8

iS

1 1 2 1 / 3m

i =s

PO

(4.75)

Thus, as i n d i ca t ed by Eq u a t io n (4 .7 5 ), s ca l e d s p e c i f i c i m p u ls e i s dependent

on ambient a tmospher ic p ressu re and th e mass of th e human t a r g e t .

Recons t ruc ted cu rves f rom Reference 4 .59 a re shown i n Fi g u re 4 . 6 8 . I t

s h ou l d b e n o te d t h a t t h e s e c u r v es r e p r e s e n t p e r c e n t s u r v i v a b i l i t y , and h ig h e r

s ca l e d p re s s u re an d s ca l ed i m p u ls e co m b in a t io n s a l l o w fewer s u rv i v o r s . P re -

s e n t in g t h e c u r ve s i n t h i s f a sh i on i s ad van tag eo u s s i n ce t h ey ap p l y t o a l l

4-164



a l t i t u d e s w it h d i f f e r e n t a tm o sp h er ic p r e s s u r e s and a l l masses ( o r s i z e s ) of

human bodi es . Once one de te rmines the inc ide nt over press ure and sp ec i f i c h-

pu l se f o r a n e xp los ion , t he y c an be sc a le d us ing Equa t ions ( 4.70 ) a nd ( 4 .75) .

0 The proper ambient a tmospher ic pressure t o u s e f o r t h e s c a l i n g c an b e a cq u ir e d

from Figure 4 .69 , which shows how a tmospher ic pre ssu re d ecre ase s wi th inc re as-

i n g a l t i t u d e a bove sea l e ve l ( R e f . 4 .19 ) . The va lue f o r body we igh t u sed i n

t h e s c a l i n g i s de te rmined by th e demographic composi t ion of th e pa r t ic u l a r

area u n d e r i n v e s t i g a t i o n . I t i s recommended t h a t 11 l b b e us ed f o r b a bi e s ,

55 l b f o r small c h i ld r e n , 121 l b f o r a d u l t women, a nd 154 lb f o r a du l t males.I t s h ou l d b e n o t i c ed t h a t t h e smal les t b od ie s i n t h i s case are th e most sus-

c e p t i b l e t o i n j ur y .

I

4-165



15

1 4

13

-4rna

0

a

a,&!

rnal

&!

PI

L1

12

211

10

9

8

7

6

F i g u r e 4.69 Atmospher ic Pre ssu re as a F unc t ion of

Al t i tude Above Sea Leve l

4-166



EXAMPLE PROBLEM 4.14

PROBLEM - Assess lu ng damage t o humans a t a n a p p r o p r i a t e d i s t a n c e from a g iven

e x p l o s i v e s o u r c e .

GIVEN: W = exp los ive cha rge we ight

R = d i s t a n c e f r o m c e n t e r of exp los ive cha rge

A l t i t u d e (no symbol)

m = weight of body of human subject

FIND: Probabi l i ty of s u r v i v a l

SOLUTION: 1. Determine peak inc ide nt overpr ess ure

Ps a nd s p e c i f i c i m p ul s e is f o r g iv e n

charge we igh t W and d i s t ance R2 . Determine ambient atmo sphe ric pres-

s u r e f rom a l t i t u d e

3. C a l c u l a t e s c a l e d i n c i d e n t o v e rp r e s-

s u r e Fs

4. Choose weight of t he l i g h t e s t human

exposed a t d i s t a n c e R

5 . C a l c u l a t e s c a l e d s p e c i f i c im pu ls e is

6 . P l o t Fs and is nd determine proba-

b i l i t y of s u r v i v al

CALCULATION

REFERENCE

Fig . 4 .5

Fig. 4.69

Eq. (4.70)

GIVEN: W = 100 l b

R = 100 f t

A l t i t u d e = 4000 f t

m = 130 l b

FIND: P e r c e n t s u r v i v a l

SOLUTION: 1. R/W1l3 = 100/1001/3 = 2 1 . 5 f t / l b1/

= 1.8 p s in ter F igu re 4 .5 and rea d P

and i /W1/3 = 2.55 X 10

S

-3 1/3p s i - s e c / l b

S

'Vnscale" t o d e t er m i ne iS

i - W1/3 = 2.55 X X 101'3 = 5.49 X ps i -sec2%W

2 . From Fig ure 4 .69 f o r 4000 f t a l t i t u d e ,

po = 12.6 p s i

4-167



3 . -rom Equation ( 4 * 7 0 ) ,P = 1 . 8 1 1 2 . 5 = 0 .144

4 . Given m = 130 l b

5 . From Equation ( 4 . 7 5 ) ,

i

S

1 1 2-3 p s i sec

= 1 . 0 8 X 10.4 9 x-

S 1 1 2m 1 3 12.6 ' I 2 X 130113 d I 3Si =

Po6 . From Figure 4 . 6 8 , e n t e r w i t h Fs = 0 . 1 4 4 and

i = 1 . 0 8 X The p o i n t l i e s w e l l below

the t h r e sh o ld f o r lung damage. So , t h e r e i s

no in ju r y a nd su r v i va l i s 100%

-

S

4-168



..?

4 .6 .2 Ter t i a ry Blas t I n j u r y

During whole-body d i sp lacement , b la s t ove rpre ssur es and impulses in t er -

a c t w i t h t h e body i n s uc h a manner thatit

i s es se n t i a l l y p i cked up and t r an s -la te d . Te r t ia ry b l a s t damage involves t h i s whole-body d i sp lacement and subse-

quent de ce le ra t i ve impact (Ref . 4 .61) . Bodi ly damage can occur dur ing the

acc e l e ra t i n g phase o r du r ing de ce l e r a t i ve impac t (R ef. 4 .68 ) . The ex t en t o f

i n j u r y d u e t o d e c e l e r a t i v e i mp ac t i s th e more s i gn i f ic an t (Ref . 4 .69) , however ,

and i s determined by the ve lo ci ty change a t impact , the t i m e and d i s ta nc e over

which de ce l e r a t i on occu r s , t he t ype o f su r fac e impac ted, and t h e area of t he

body involved (Ref. 4.61).

Although th e head i s th e most vu ln era b le po r t i on of th e body to mechani -

c a l i n j u r y d u r in g d e c e l e r a t i v e i m pa ct , i t i s a l s o t h e b e s t p r o t ec t e d (R ef .

4 . 67 ) . Be ca us e o f t h e d e l i c a t e n a t u r e of th e head , many may f e e l t h a t t ran s-

l a t i o n damage c r i t e r i a should be based on sk ul l f r ac tu re or concuss ion . How-

ever, s in ce body impac t pos i t i o n i s l i k e l y t o b e ra ndom ly o r i e n t e d a f t e rt r a n s l a t i o n , o t h e r s may f e e l t h a t t h i s f a c t o r s ho ul d b e t a k en i n t o ac co un t i n

determining expected amounts of impact damage. I n an e f f o r t t o sa t i s f y pro-

ponents of each poin t o f view, bo th t ypes of impac t, e s se n t i a l l y head fo remos t

and random body impact orientat ion, w i l l be cons ide red .

a

Because of th e many parameters involved i n de ce le ra t i ve impact, a few.

assumptions w i l l be made. F i r s t o f a l l , t r ans l a t i on damage w i l l be assumed t o

occur d u r i n g d e c e l e r a t i v e i mp ac t w i t h a h a rd s u r f a c e , t h e most damaging case

(Ref. 4 .69). Another assumption i s t h a t , s i n c e i mp ac t o n t o o n ly h a r d s u r f a c e s

i s be ing cons ide red , t r an s l a t i o n damage w i l l depend only on impact ve lo ci ty .

This i s , impac t ing on ly one t ype o f su r f ace p rec lude s t he need f o r cons ider ing

change i n ve lo ci ty of t h e body dur ing impact. This assumpt ion , however, i s

n o t e n t i r e l y v a l i d when on e c o n s i d e r s t h a t t h e c o m p r e s s i b i l i t y of v a r i o u s por-

t i on s of t h e body can va ry cons ide ra b ly .

White (Re fs. 4. 61 and 4.62) and Clemedson, e t a l . (Ref . 4 .69) , agr eet h a t t h e t e n t a t i v e c r i t e r i a f o r t e r t i a r y damage ( d e c e l e r a t i v e i m p a c t ) t o th e

head should be those presented i n Table 4.11. Whi te ' s (Ref . 4 .62) re ce nt ly

r e v i s e d c r i t e r i a f o r t e r t i a r y damage d ue t o t o t a l body i m pa ct a r e summarized

i n Table 4.12.

c r i t e r i a fo r each t ype of impac t cond i t i on a r e i d e n t i c a l .

I t i s b e n e f i c i a l t o n o t e t h a t t h e m os tl y "s af e" v e l o c i t y

Baker, e t a l . (Ref. 4.59) h ave developed a method fo r p re d i c t i n g t he

b l a s t i n c i de n t ove rp res s u re and s pe c i f i c impu lse combina ti ons wh ich w i l l trans-l a t e human bodies and propel them a t t h e c r i t i c a l v e l o c i t i e s p r es e nt e d i n

Tables 4.11 and 4 .12. This method and as soc ia t ed pr ed ic t i on curves are repro-

duced here .

F igu re 4 .70 con ta in s the pressure-scaled impulse combinat ions req ui re d

t o p ro du ce t h e v e l o c i t i e s f o r v a r i o u s e x pe c te d p e rc e n ta g e s of s k u l l f r a c t u r e

(See Table 4.11) a t s ea l e v e l , w h i l e F i g u r e 4 . 7 1 con t a in s t he p res su re - sca l ed

4-169



Table 4 .11 C r i t e r i a For T er ti ar y Damage

(De cel era t ive Impact ) To The Head

(Ref eren ces 4.61, 4.62, and 4.69)

S k u l l F r a c t u r e T o l er a n ce

~ 0 sl y "safe"

Threshold

50 percent

Near 100 percent

Rela ted Impact Veloci ty

f tl e c

Table 4.12 C r i t e r i a For Te rt ia ry Damage

Inv olv ing To ta l Body Impact

(Reference 4.62)

1 0

1 3

18

23

To ta l Body Impact Toler ance

Most ly "safe"

L e t h a l i t y t h re s ho l d

L e t h a l i t y 50 p e r c e n t

L e t h a l i t y near 100 percent

4-170

R ela t ed Impac t Ve loc i t y

f tl sec

10

21

54

138



,

N .-

-

4

4

r

NO v

NI r

NI

0

0

0

0

4

d

4

r

vN d 0 lV

l

h0 0 rlr

N

4I rlr

N

N I d

I

4 ..

vp.In1

0 fV

4



N

O

u

NI

NI 04

0

0 r

rl

u

-44 0 I4

4-172



i m pu l se c om b in a ti o ns r e q u i r e d t o p ro du ce t h e v e l o c i t i e s f o r v a r i o u s e x p e c t ed

percen tages of l e t h a l i t y f rom whole body impac t (See Table 4 . 1 2 ) a t sea l e v e l .

Curves f o r o t h e r a l t i t u d e s d i f f e r o nl y s l i g h t l y from t h e sea l e v e l c u r v e s .

4-1.7 3




PROBLEM - P r e d i c t p o s s i b l e t e r t i a r y b l a s t damage t o humans a t a s p e c i f i e d d i s -' t ance f rom a g iven exp los ive sou rce .

GIVEN: W = exp los ive we ight

R = d i s t a n c e fr om c e n t e r of e x p l o s i v e c h a r ge

m = weig ht of body of human s u bj e c t

FIND: Probabi l i ty of i n j u r y

SOLUTION: 1. Dete rmine peak i n c id en t ove rp r es su re

Ps and spe c i f ic impulse i s f o r g i v e n

charge weight W a n d d i s t a n c e R

weight of an exposed human, and calcu-

l a t e i s / m

2. D ete rm in e t h e l i g h t e s t r e p r e s e n t a t i v e

1 / 3

3 . Locate PS and i s /m1 / 3 on g raphs fo r

REFERENCE

Fig. 4 .5

s k u l l fracture and l e t h a l i t y f o r w h o l e

b o d y t r a n s l a t i o n , and read impact velo-c i t i e s Fig. 4 .71

p r i a t e i mpa ct v e l o c i t i e s Table 4.11

F ig . 4 .70 &

4 . Determine degree of in ju ry f o r appro-

CALCULATION

GIVEN: W = 1 00 l b

R = 100 f tm = 130 l b

FIND: T e r t i a r y b l a s t i n j u r y , b as ed o n s k u l l f r a c t u r e

and who le body t r a ns l a t i on

1/

SOLUTION: 1. R / d / 3 = 100/1001/3 = 21.5 f t / l bEnter F ig ure 4 .9 and read PS = 1.8 p s i and

- 3 1/p s i - s e c / l b/w1l3 = 2.55 x 10

"Unscale" t o determine i

S

Si

-+ 1l3 = 2.55 x x 1001/3 = 1.18 10-2 paitsec

2 . Given m = 1 3 0 l b . Calculate

i /m1l3 = 1.18 X 10-2/1301/3 = 2.33 X p s i - s e c / l b 1 / 3S

Change 1 - 15 August 1981

' C

4-174



3.

4.

En te r F igu r e 4.70 wi th P

i s /m1l3 = 2.33 X This i s o f f t he l e f t s i d e

o f t h e F i g u re , b u t w e l l below t he lowest c urves

f o r s k u l l f r a c t u r e . So, V << 1 0 f p s . E n t e r F ig -

4 . 7 1 w i t h t h e same numbers. Again, V << 1 0 f p s

R e f e rr i n g t o Table 4 .11 f o r c o r r e l a t i o n of v e l o-

c i t i e s w i t h i n j u r y , we f i nd t h a t f o r e i t h e r t h e

s k u l l f r a c t u r e o r w ho le bo dy i m p ac t c r i t e r i a , t h e

i m p a c t v e l o c i t i e s are w e l l below th e most ly "sa fe"

v e l o c i t i e s . So, no in j u r y would occur .

NOTE: Had t h e v z e s f o r o r d i n a t e and a b s c i s s a i n

= 1.8 andS

1 / 3 -Fi gu re s 4.70 and 4.71 been P = 1 p s i , i s / mS

1 p ~ i - s e c / l b " ~ , t h e v e l o c i t i e s f o r s k u l l f r a c t u r e

ve lo c i ty would have been V = 1 5 f p s , a nd f o r whole

b o d y t r a n s l a t i o n V = 13 f p s . S k u l l f r a c t u r e i n j u r y

p r o b a b i l i t y would l i e be tween threshold and 50%,

w h i l e l e t h a l i t y d ue t o w ho le body t r a n s l a t i o n w ould

l i e betwe en m os t ly " saf e " a nd th e th r e s ho ld f o r

l e t h a l i t y . So , t h e human would hav e a r e l a t i v e l y

h i g h p r o b a b i l i t y of s k u l l f r a c t u r e , b u t a low pro-

b a b i l i t y o f d e a t h. W hether t h i s l e v e l o f i n j u r y

wou ld o r would no t b e a c c e p t a b l e c ou ld on ly be a d-

d r e ss e d i n s e p a r a t e s a f e t y c r i t e r i a .

. .

4-175 Change 1 - 1 5 August 1981



4.6.3 E a r Damage Due To A i r Blas t Exposure

The ear , a s e n s i t i v e o rg an s y s tem whi ch co n v e r t s s ou nd waves i n t o n e rv e

impulses , responds to a band of f re que nci es rang ing f rom 20 Hz to 20,000 Hz.This remarkab le o rgan can respond t o energy l e ve l s which cause t he eard rum t o

d e f l e c t l e s s t h an t h e d i am e t e r o f a s i ng le hydrogen molecule (Ref. 4 .70). Not

b e i n g a b l e t o r e s po nd f a i t h f u l l y t o p u l s es ha v in g p e r i od s l e s s t h an 0 . 3 m i l l i -

second, i t a t t e m p t s t o do s o by making a s i n g l e l a r g e e x c u r s i o n ( Re f. 4 . 70 ) .

I t i s t h i s mo t io n w hic h c a n ca u s e i n j u r y t o t h e ear .

The human ear i s d i v i d e d i n t o t h e e x t e r n a l , m i dd le , a nd i n n e r ear .The external ear a m p l i f i e s t h e o v e r p r e s s u r e of t h e so un d wave by approximately

20 p e rc en t and d e t ec t s t h e l o ca t i o n of t h e s o u rce o f s o un d (R ef . 4 . 7 0) .

t u re o f t h e ea rd ru m i s a good measure of serious ear damage. Unfortunately,

t h e s t a t e - o f - t h e - a r t f o r p r e d i c t i n g e ar dr um r u p t u r e i s n o t as w e l l developed

as t h a t f o r p r e d i c t i n g l u n g d amage f ro m b l a s t waves. A d i r e c t r e l a t i o n s h ip ,

however, h a s b een e s t ab l i s h ed be t ween t h e p e rcen t age of ru p t u re d eardrum s an dmaximum overpressure. H i r s c h (R e f. 4. 67 ) co n s t ru c t e d a g ra ph s i m i l a r t o t h a t

shown i n Figure 4 .72 and concluded th a t 50 pe rc en t of exposed eard rums ru p t u r e

a t an o v e r p r e s s u r e of 15 p s i . White ( R e f . 4 . 6 1 ) suppor t s t h i s c o n c l u s i o n for

" f a s t " r i s i n g o v e r p r es s u r e s w i t h d u r a t i o n s of 0.003 second t o 0 .4 second .o c c u r r i n g a t am bi ent a t m o s p h e r i c p re s s u re o f 1 4 .7 ps i . Hi rsch (Ref. 4 .67) ,

a l s o c on cl ud ed t h a t t h r e s h o l d e ar dr um r u p t u r e f o r " f a s t " r i s i n g o v e r p r e s s u r e s

o c c u r s a t 5 p s i , wh i ch i s a l s o s u p po r t ed b y White (Ref. 4.61) f o r t h e r a n ge

o f d u r a t i o n and a t th e a tmospher ic p re ss u re men t ioned above .

Rup-

A t l o we r o v e r p r e s s u r e s t h a n t h o s e r e q u i r e d t o r u p t u r e e ar dr um s, a t em -

p o r a r y l o s s o f h e a r i n g c a n oc c u r. Ross, e t a l . ( R e f . 4.701, have produced ag ra ph o f p ea k o v e r p r e s s u r e v e r s u s d u r a t i o n t o r t e mp or ar y t h r e s h o l d s h i f t (TTS) .

Below the l imits of t h e g r a p h s , a m a j o r i t y (75 p e r c e n t a t l eas t ) o f t h o s e ex-posed a r e n o t l i k e l y t o s u f f e r excessive h e a r i n g l o s s .

e t a l . (R e f . 4 . 7 0 ) , t h e i r cu rv es s h o u l d b e l o wered 1 0 dB t o p r o t ec t 9 0 p e r -

c e n t of th ose exposed, lowered 5 dB t o a l l ow f o r a n orm al an g l e of i n c i d en c e

of t h e b l a s t wave, a nd i n c r e a s e d 1 0 dB t o a l l o w f o r o c c a s i o n a l i m p ul s es . I n

sum, t o a s s u r e p r o t e c t i o n t o 90 p e r c e n t o f t h o s e e xp os ed and t o a l l o w f o r n or -

m a l i n c i d en c e t o t h e ear ( t h e wo rs t ex p o s ure case) o f a n o c c a s i o n a l a i r b l a s t ,

t h e i r c u r v e s s h o u l d b e l o w e r e d 5 dB.

According t o ROSS,

L i m i t s f o r e a rd ru m r u p t u r e an d t e mp or ar y t h r e s h o l d s h i f t , as p r e s e n t e d

above, are d epen den t on p eak i n c i d e n t o v e r p re s s u re an d d u r a t i o n .

f i c i mp ul se i s d epen den t u po n t h e d u r a t i o n of t h e b l a s t wave an d s i n c e b o t h

p ea k i n c i d e n t o v e r p r e s s u r e an d s p e c i f i c i m p ul s e a t a s p e c i f i e d d i s t a n c e from

a n e x p l o s i o n c a n b e c a l c u l a t e d u s i n g m eth od s i n t h i s doc um en t, i t i s e s p e c i a l l y

a p p r o p r i a t e t h a t p r e s s u r e - i m p u l s e ear damage curv es b e developed from th e pres-

su r e-d ura t io n cu r ves . Assuming a t r i a n g u l a r s h a pe f o r t h e b l a s t w ave a l lo w s

f o r s i m p l e c a l c u l a t i o n s w hic h a re c o n s e r v a t i v e fr om a n i n j u r y s t a n d p o i n t .

S i n ce s p ec i -

Change 1 - 15 August 1981 4-176



98

9 5

9 0

. .a 6 0

+I 50

01

M

a7pr: 40w0

30LIEu 20M01

P.l

10

5

2

1

i 1 ' 1 I I I I 1 1 I I 1

-

-

I I I 1 1 1 1 I I 1 I 1 '3 4 6 l o 1 2 4 6 8

Peak Overpressure P , psiS

Figure 4 . 7 2 Percent Eardrum Rupture as a

Function of Overpressure

4-17 7



The ear damage c r i t e r i a p r es e n te d i n Figure 4 . 7 3 w e r e developed from

t h e c r i t e r i a f o r eard rum rup tu re developed by Hirsch (Ref . 4 . 6 8 ) and White

(Ref . 4.61) and from the c r i t e r i a f o r t em po ra ry t h re s h o l d s h i f t d eve l op ed by

Ross, e t a l . (Ref. 4 . 7 0 ) . Equat ion ( 4 . 7 2 ) w a s u se d t o c a l c u l a t e s p e c i f i c i m -

p u l s e , and t emp ora ry t h re s h o l d s h i f t r ep re s en t s t h e case where 90 precen t o fthose exposed to a b l a s t wave advancing a t n orma l an g l e of i n c i d en ce t o t h e

e a r a r e n o t l i k e l y t o s u f f e r a n e x c e s si v e d eg r ee of h e a r in g l o s s .

h o l d fo r ea rd rum ru p t u re cu rv e i s t h e loc a t i on be low which no r up tu re d earsa re expec ted t o occur and th e 50 perce n t o f eard rum rup tu r e cu rve i s t h e

l o c a t i o n a t which 50 p e rcen t o f ears exposed a re ex p ec t ed t o ru p t u r e .

The thres-

1.

4-178



4VIa

F4

ak310v)

akak

L

co

d4

caJQ.ti

0

cH

l o 2

5

3

2

lo 1

5

3

2

l o o

5.

3

2

10-1

2 3 5 2 3 5 2 3 5 10-1 2 3 5 l o o

S p e c i f i c I m p ul se is, ps i - sec

Figure 4 . 7 3 Human Ear Damage fo r B l a s t Waves A r r i v i n g a t Normal

Angle of Incidence




PROBLEM - F in d t h e p r o b a b i l i t y of ear i n j u r y a t a g i v e n d i s t a n c e f ro m a spec i -

f i e d e x p l o s i v e s o ur c e.

W = e xp los i ve c ha rge we igh t

R = d i s t a n c e f ro m c e n t e r o f e x p l o s i v e c ha r ge

GIVEN:

FIND: Probabil i ty of ear i n j u r y

SOLUTION: 1. Deter mine pe ak inc ide n t ove r p r e s su r e

Ps and s p e c i f i c impulse is f o r g i v e n

charge w e i g h t W a nd d i s t a nc e R

Determine degree of i n j u r y b y p l o t t i n g

Ps and is on human ear damage curve

2.

CALCULATION

GIVEN: W = 100 lb (free air)

R = 100 ft

FIND: Level

SOLUTION: 1.

2 .

of e ar i n j u r y

1 / 3R/dl3 = 100/1001/3 = 2 1 . 5 f t / l b

Ent e r F ig ure 4.5 and read Y = 1 .8 p s iS

1/and i W1j3 = 2.55 X p s i - s e c / l b

REFERENCE

Fig. 4.5

Fig. 4.73

"Unscale" t o ob ta in iS

-2-. d'3 = 2.55 X X = 1.18 X 10 psi - sec

P l o t t i n g P a nd i on Figure 4 .73 , one

f i n d s t h a t t h e p oi n t l i e s w e l l above the

c ur ve f o r TTS, b u t be low t he c u r ve f o r

th r e sho ld o f e a rd rum r up t u r e . So, humans

w ould s u f f e r t em po ra ry h e a r i n g l o s s , b u t

n o s e r i o u s ear i n j u r y .

NOTE: When comparing ear i n j u r y , p r i m a r y

b l a s t damage, a nd t e r t i a r y b l a s t d amage

f o r t h e same s o u r c e , as ha s be e n done i nExample Problems 4.14 , 4.15, and 4.16, one

i n v a r i a b l y f i n d s t h a t ear i n j u r y occurs a t

a g r e a t e r d i s t a n c e t h a n t h e o t h e r , more

s e r i o u s , t y p e s of b l a s t i n j ur y . So , i f

S S

Change 1 - 15 August 1981 4-180



s a f e t y c r i t e r i a i nc lude an ear damage l i m i t ,

one can be assu red t ha t no more se r i ou s

b l a s t i n j u ry w i l l occur a t t h e d i s t a n c e s

co r respond ing t o t he ear damage l i m i t .

4-181

blast humans

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