This work, a n a s p e c t of investigations dealing with the Biological Effects of B l a s t f r o m Bombs by the Defense Atomic Support Agency of the Department of Defense.

This work, a n a s p e c t of investigations dealing with the Biological Effects of Blast from Bombs, was supported by the Defense Atomic Support Agency of the Department of Defense. (Reproduction in whole o r in p a r t is p e r m i t t e d f o r any purpose of the United States Government.) "The Ov,erpressure-Duration Relationship and L e t h a l i t y i n Small Animals" was conducted according t o t h e P r i n c i p l e s of Laboratory Animal Care as promulgated by t h e National S o c i e t y for Medical Research.

FOREWORDThis report, in the field of Blast and Shock Biology, is the second in a series describing experiments to determine the tolerance of animals to air blast in relation to their geometry of exposure. Guinea pigs were exposed to air blast while in shallow, deep, and deep-with-offset chambers on a shock tube, and the lethality was correlated with the pressure "dose" measured inside and outside the chambers.The results apply only to the primary blast effect, to guinea pigs, and to conditions of these experiments, and might not apply to the full-scaleThis work is part of a broad research program aimed at a better understanding of human response to air blast and methods of protecting against it. ABSTRACTOne hundred and eighteen guinea pigs were exposed to air blast in shallow, deep, and deep-with-offset chambers mounted on a shock tube.The LD50-24 hours, in terms of the incident shock pressures measured adjacent to the chambers, was calculated by probit analysis to be 34. 9 psi, 19. 5 psi, and 26.8 psi for animals in the shallow, deep, and deep-withoffset chambers, respectively. According to the LD 5 0 incident pressures, the shallow chambers offered the most protection against air blast; the deep chambers, the least.Comparing the LD 5 0 -pressure "dose" at the animals' location revealed little difference in their tolerance to overpressure, per se; i. e., LDS 0 reflected pressures measured by gauges within the deep and deepwith-offset chambers were 34. 6 psi and 35. 9 psi, respectively. The LD50 incident shock pressure of 34. 9 psi in the shallow chambers was considered to be the "dose" at the animal's location in that instance.The protection against blast provided by the three chambers and the response of animals to the particular pressure-time patterns encountered are discussed.ii ACKNOWLEDGMENTS

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