loading, an understanding of which is essential to evaluating the decelerative hazard of blast-produced displacement in man.

GENERAL

A critical review of the blast literature was prepared and published in 1954. Likewise, a similar, though more comprehensive and up-todate critical assessment of the field of blast biology was prepared in 1956 and included in the report of the primary blast work carried out during the 1955 field test series. This is TR-1179, project 33.1 test report.

THE PERIOD 1957 TO THE PRESENT

FIELD RESEARCH

During 1957 Plumbbob test series the field phase of six projects were completed by program 33 civil effects test group personnel. Four of these projects were planned ahead of time and two were conceived and activated in the field. Preliminary evaluation of the results of all six projects has been accomplished and interim test reports are now available. Further analytical assessment of data has been progressing but is far from complete.

PRIMARY AND TERTIARY BLAST EFFECTS

The experiments that dealt with primary and tertiary blast effects will now be described. A total of 562 animals on this occasion ranging in size from the mouse to the dog were exposed in 2 open instrumented shelters each 1,050 feet from 2 separate nuclear detonations. These structures were the same ones used in the 1955 field test operation. Peak internal pressures ranged from 3.8 to 24.5 pounds per square inch. Dynamic pressures near the doorway were close to 11 and 3 pounds per square inch. Mortality due to primary blast effects was limited to 18 and 38 on mice, 2 of 100 guinea pigs, and 1 of 8 pigs. Except for rupture of the eardrum, significant primary blast damage was not observed in dogs though 2 pigs and numerous of the small animals exhibited lung hemorrhages.

One tethered dog was severely injured by decelerative impact following violent displacement from his station near the main entryway. As on previous occasions, skin burns and singeing of the fur of animals were noted. Also delayed mortality attributable to ionizing radiation was observed from 4 to 17 days following the shot.

Simple protective pieces of solid metal plate and metal screens were effective in preventing singeing of the fur and wind displacement of the animal.

Displacement of anthropometric dummies in another experiment by blast-produced winds was studied on two occasions in the open, once successfully with a photographic technique.

In one instance involving maximal static and dynamic pressures of 5.2 and 0.25 pounds per square inch, respectively, a standing dummy was translated 21.9 feet and reached a peak velocity of about 23 feet per second in 0.5 of a second. A prone dummy was not disturbed by the blast.

On another occasion wherein the static and dynamic pressures were 6.6 and 15.8 pounds per square inch, respectively, a standing dummy was translated 256 feet downwind and 43.7 feet to the right (looking away from ground zero), and a prone dummy was blown 124 feet downwind and 19.5 feet to the right (facing away from ground zero).

SECONDARY BLAST EFFECTS

A major missile study was successfully carried out on three separate shots. Missiles captured and analyzed consisted of glass in the open and in houses, "planted" natural and artificial missiles including "military debris," spheres of different masses and diameters, natural missiles (those native to the area), and debris from a concrete block wall. Some work was done in "open" and "closed" underground structures, in the former case to determine the velocities imparted to spheres by internal winds and in the latter case to assess the velocities of particles which might spall or come from the inner concrete surfaces. Missile experiments and experience in Plumbbob extended previous studies over wider ranges from ground zero and through different explosive yields. In fact, about 200 missile traps were involved in the Plumbbob program which is between six and sevenfold the number employed in the 1955 test series. Postfield evaluation procedures are well underway, though it is too early as yet to appreciate the general applicability of the theory developed from the 1955 data.

Field missile studies from 3.7 to 8.2 pounds per square inch using a biological target were successfully consummated in Plumbbob and pathological work completed. Correlation of biological and physical data must await evaluation of the missile traps exposed near the animal stations. However, 243 wounds from blast fragments were observed in 14 dogs. Lacerations deeper than the subcutaneous tissues were noted in 21 instances and 17 of these involved missiles which could well have entered the abdominal cavity had the impact area been appropriate. These full-scale observations tentatively seemed consistent with missile penetration studies completed previously in the laboratory.

Lung damage in one animal from impact of a nonpenetrating missile was discovered during the routine postshot examinations. Also seen in the other animals were lung hemorrhages attributable to primary blast. These instances involved exposure to a side on P-max of between 8 and 8.5 pounds per square inch.

Dust

MISCELLANEOUS

In the miscellaneous category some dust experiments were performed. Because dust intoxication was known to have been the cause of death in structures subjected to conventional bombing in Germany, a project to study the occurrence of dust inside protective shelters as a consequence of nuclear explosion was conceived and activated in the field through the mutual cooperation of AEC, DOD, and FCDA personnel.

Eighteen underground structures subject to atomic blast during operation Plumbbob were made available. There locations ranged from 4,320 to 840 feet from ground zero. The existence of consider

able postshot dust inside the structures was established using "stickytray" fallout collectors. Captured particulates arose from the dust on the floor existing preshot in some shelters and from the internal surfaces of the structure. The latter was established by treating the walls and ceilings of four selected shelters with a solution containing a fluorescent dye and subsequently demonstrating that fluorescent particles had been captured by the collectors. The feasibility of dustcollector technique was established as a useful procedure in future evaluation of the internal environment of shelters. Too, the occurrence of fine spalling appeared to be a more sensitive indicator of structural response than gross spalling, an observation, if evaluated further, might result in use of the fluorescent method to indicate structural response at greater ranges than is now possible without using costly instrumentation.

Preliminary studies have indicated that dust as it occurred in the shelters studied would not have been an immediate hazard to occupants. However, the annoying and irritating effects of airborne particulates make it desirable for designers to minimize or completely eliminate blast-produced dust from the interior of protective shelters. Such things as plaster, for instance, must not be used on the inner walls. A thin metal or plastic liner could certainly be useful in stopping the spalling, or in containing the spall particles.

BIOLOGIC ASSESSMENT OF SHELTER ENVIRONMENT

A second project had its inception and activation during the Plumbbob test series. At the request of the Federal Civil Defense agency, 20 mice were placed preshot inside each of 12 closed underground structures. All were recovered successfully after the detonation. Immediate mortality as observed on recovery, included 19 of 20 mice shielded from radiation only by a sliding metal hatch guarding the entryway to one shelter and 20 of 20 mice from carbon monoxide present in fumes from a gasoline engine driving a power generator, even though the exhaust fumes from the regular exhaust stack were vented to the exterior. No blast lesions were observed in any of the expired animals.

Delayed death of animals which occurred in a 20-day period is noted in the reports and these were presumably of radiation sickness. However, final evaluation must await the not yet complete pathological assessment of tissues from both experimental and controlled animals.

LABORATORY RESEARCH

In 1957 exploratory work was undertaken in the laboratory using the blast-facility shock tube to determine the biological effects of long duration by this I mean 5- to 20-second duration overpressures of different magnitudes, and which rose to peak values in various times. Maximal pressures ranging from 74 to 170 pounds per square inch rising to a maximum in from about 30 to 155 milliseconds were not fatal to dogs restrained to avoid translational impact. Now the peak pressure inside of the Teapot open structures at 1050 feet were in the order of 66 pounds per square inch rising to a maximum in 90 to 100 milliseconds. The laboratory studies thus bracket the actual field experience in shelters.

Damage in the shock tube studies was limited to eardrum rupture and sinus hemorrhage for all animals and in some instances to wedgeshaped hemorrhagic lesions of the lung. The latter were not observed for overpressures as high as 167 pounds per square inch when the pressure rise was comparatively slow-about 150 milliseconds to maximum pounds per square inch. However, for faster rising pressure pulses going to peak in 30, 60, and 90 milliseconds the wedge-shaped multilesions were a constant finding except for the lower overpressures, that is, below 118 pounds per square inch for the the 90-milliseconds-to-peak rise times and below 86 pounds per square inch for the 30 milliseconds-to-peak rise time.

These laboratory observations confirmed and extended the 1953 and 1955 field test observations, suggesting that the rate of pressure rise was a blast parameter of biological significance and that animals could indeed survive quite high pressures if the "load" was applied slowly enough.

Fatalities from translational impact were noted in some experiments from winds accompanying the blast tube overpressures which ranged from 57 to 103 pounds per square inch maximum with rise times of 44 to 90 milliseconds. In one case an impact fatality occurred following only a 9-inch movement of the test animal.

Recent additional studies with the shock tube are of considerable basic significance. Five- to twenty-second duration pressure pulses rising in a matter of a few hundreds of microseconds have been employed to establish mortality curves for guinea pigs, mice, and rats. In one series of experiments-to use the guinea pig results as an example-metal-mesh cages (the same as those used in the field) were bolted to the end of the shock tube and animals were exposed to the almost instantaneously rising pressures developing from the primary shock and its reflection from the end of the tube. Reflection causes a pressure again of twofold to threefold that in the primary shock and the amount of increase depends upon the magnitude of the primary shock pressure. Using 140 animals, a mortality curve was determined. The pressure required to injure fatally 50 percent of the animals, or the P-50 figure, was about 36 pounds per square inch. The standard deviation was 5.37 percent. Pressures associated were 5 and 95 percent mortality and were nearer 29 and 44 pounds per square inch, respectively.

Á second series of 111 guinea pigs was likewise exposed except that the cages were not located right on the end but 1 foot from the end plate of the shock tube. These animals were exposed to a stepwise increase in pressure which involved 2 fast-rising pressure pulses. The first step involved the overpressure accomplishing the primary shock which came down and passed over the cage while the second involved the increase in pressure as a consequence of the reflection from the end of the tube, which reflected back and traveled back over the cage. This second pressure rise was superimposed upon the shock pressure slightly less than 2 milliseconds following the arrival of the primary pulse. Using the maximum pressure associated with the reflected shock (Pr) as the significant parameter, mortality curves were plotted and the P-50 surprisingly enough, proved to be approximately 57 pounds per square inch, instead of 36 as I noted a moment ago, with a standard deviation of 10.3 percent. Mortalities of 5 and 95 percent

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were associated with reflected pressures near 46 and 70 pounds per square inch, respectively.

It is important to realize that for the animals located against the end plate of the shock tube, the primary shock pressure associated with the P-50 value of 36 pounds per square inch for the reflected pressures was close to 14 pounds per square inch. For the P-50 reflected pressure of 57 pounds per square inch for animals located 1 foot from the end of the closed tube, the incident or side-on pressure associated with the primary shock was close to 20 pounds per square inch.

These observations are most significant because: (1) The pressure conventionally spoken of in the pressure-distance-yield relations for nuclear explosions are static pressures and are not comparable to the reflected pressures quoted for the shock tube data. Rather they are comparable to the primary shock pressures. (2) The importance of the geometry of exposure of a biological target is clearly emphasized as are the dangerous natures of positions close to reflecting surfaces and the necessity to design shelters to avoid the development of sharp pressure reflections inside. (3) A laboratory tool is now at hand to explore further the biological significance of various rates of pressure loading, from long duration pulses incorporating multiple, sharp, stepwise components during the rising phases of the overpressure.

DISCUSSION

By way of discussing the data briefly summarized above and noting their relation to protective construction, a few points deserve emphasis. First, it can be said that blast biology studies are progressing and the relation of these investigations to protective construction is fairly well advanced. Secondly, the problem of protection for survival requires adequate measures to survive the first seconds, then minutes, hours, days, and months. Thirdly, appreciation of the gamut of environmental alterations produced by a nuclear detonation as a function of distance, weapon type, topography, and height of burst sets the problem for the protective designer who, for a given location, must ask what are the likely overpressures, winds on the surface, and ground shock beneath the surface? What is the thermal flux? What are the anticipated levels of prompt ionizing radiation and those due to induced and fallout phenomena?

One logical approach to protective design can well be visualized as including those measures to combat:

1. NUCLEAR DETONATIONS

(a) Immediate or early effects, such as (1) thermal radiation, (2) prompt, induced, and fallout ionizing radiations, (3) blast overpressures and ground shock, (4) winds responsible for pressures, missiles, dust, and displacement damage to human targets, (5) blast associated fires, (6) interruption of utilities potentially hazardous because of flooding from ruptured water mains, explosions, and toxicity from gas escaping broken lines and power failures and interruption of ventilation, and (7) danger from industrial materials peculiar to certain areas-toxic chemicals, reactors, powder and fuel plants and the like.