A total of 308 guinea pigs were exposed to air blast in 4 close-fitting, shallow, rectangular chambers mounted on the top, bottom and sides of an air-driven shock tube. With a reflecting plate at the downstream edge of the chambers, the animals were exposed to long-duration shock overpressures that initially rose in a single step. The LD50-24-hr reflected pressure calculated from grouping all positions was 36.2! 0.8 psi. By moving the reflecting plate to various distances downstream of the chambers, shock overpressures that initially rose in two steps were applied. The results were that the animals' tolerances to overpressure rose as the time between pressure steps was increased. Comparison of the LD50's obtained with animals in each chamber revealed that there was not a significant statistical difference in their tolerances, whether they were loaded initially with the single-step pulse from their right, left, dorsal or ventral surfaces. (Author).

One hundred and eighteen guinea pigs were exposed to air blast in shallow, deep, and deep-with-offset chambers mounted on a shock tube. The LD(50)- 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-with-offset chambers, respectively. According to the LD(50) incident pressures, the shallow chambers offered the most protection against air blast; the deep chambers, the least. Comparing the LD(50)pressure dose at the animals' location revealed little difference in their tolerance to overpressure, per se; i.e., LD(50) reflected pressures measured by gauges within the deep and deep-with-offset chambers were 34.6 psi and 35.9 psi, respectively. The LD(50) 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.

Tentative estimates of the sharp-rising overpressures as a function of duration which represent a lethal hazard to the 70-kg animal 1, 50 and 99 per cent of the time were presented. The predictions were based on interspecies correlations and extrapolations encompassing blast-tolerance data for six mammalian species. The tentative application of the data to indicate human blast tolerance was discussed and relevant uncertainties in the estimates were emphasized. It was also pointed out that biologic tolerance would be different for air-blast pulses having non-ideal wave forms frequently associated with various geometries of exposure. Selected pathophysiological information pertinent to the biological response following blast exposure was given; namely survival time and selected postshot observations of dogs and goats.

Experience with animals exposed in a variety of above and below ground structures during full-scale field operations at the Nevada Test Site in 1953, 1955 and 1957 were reviewed. The data were assembled and summarized to illustrate the nature of the blast-induced problems of significance in protective shelters, "open" as well as "closed". Potential hazards were related to the following: various patterns of variation in environmental pressure; translational events associated with transient, high-velocity winds, ground shock and gravity involving the impact of energized inanimate objects on the one hand the the consequences of whole-body displacement on the other; non-line-of-site thermal phenomena including hot objects and rapidly moving hot, dust- laden air and debris; and dust, in the respirable size range, sufficiently high in concentration even in "closed" shelters as to warrant design measures to minimize or eliminate the occurrence of small particulates whether arising from wall spalling or otherwise. Tentative biological criteria, conceived to help assess human hazards from blast-related phenomena, were presented. Relevant data from the literature and on- going research in environmental medicine were set forth to aid the reader in appreciating how the criteria were formulated, what information was extrapolated from animal data, and wherein "best estimates" were employed. "State-of-the-art" concepts were noted to emphasize areas in which more thinking and research must continue if more refined, complete and adequate criteria are to be forthcoming for assessing man's response to blast-induced variation in his immediate environment.