Declassified data on structures exposed to nuclear weapons tests in the Pacific

Castle Yankee 13.5 megatons.

Castle-Bravo 12 vacuum tube array from bomb.

The pipes along the causeway from the Bravo bomb to Namu (Charlie) island were Dr Sterling Colgate’s experiment to measure Bravo’s thermonuclear burn rate: piping collimated neutron radiation inside 12 vacuum pipes each of 15 cm diameter, extending 1.4 miles from the bomb to Station 1200 (the shelter located at the far end of Namu Island, still there today). These vacuum pipes, to minimise absorption of the collimated neutrons, replaced the Krause-Ogle helium-filled box used at the so-called "Ganex" GAmma-Neutron EXperiment in the 1952 Mike test, where secondary gamma rays from neutrons striking Mike’s steel case travelled through helium, arriving with little attenuation before the neutrons. The 14 MeV neutrons arrived at the detector before the tube was destroyed by blast near the bomb, and travelled faster than the lower energy neutrons, allowing the spectrum of the neutrons to be determined simply by using the time-of-arrival discrimination method.

Above: above ground shelter survived 130 psi peak overpressure and fireball engulfment from 15 megaton Bravo nuclear test.  Station 1200 on Namu ("Charlie") island, Bikini Atoll, survived just 1.4 miles from 15 megaton Castle-Bravo nuclear bomb test, despite being designed to withstand only 50 psi from the predicted 6 megaton yield.  This shelter was connected directly to the nuclear bomb by Colgate's 12 neutron-carrying vacuum pipes (seen extending to the bomb in the photo above).  Bravo’s predicted yield was 6 Mt, but was unexpectedly boosted by a factor of 2.5 when Li-7 (60% of Bravo’s lithium) was fissioned into tritium by 14 MeV neutrons.  Bravo's crater (before and after photos) is shown below and comes up to the edge of Namu Island, but Station 1200 was intact despite ground shock; please remember that coral is easily crushed by the blast, unlike ordinary silicate soil, so craters on a city will be much smaller, even if you forget the error due to ignoring gravitational potential energy for excavating in the Glasstone and Dolan crater scaling laws.

"This structure [Station 1200] proved remarkably resistant to very high blast pressures. ... The structure performed its mission despite an overpressure [130 psi incident peak overpressure, before more than doubling due to blast reflection], almost three times that for which the structure was originally designed." - Wayne J. Christensen, Blast Effects on Miscellaneous Structures, Operation Castle, Project 3.5, July 1955, Secret - RD, WT-901, page 27.

Wayne J. Christensen explains in weapon test report WT-901 (Blast effects on miscellaneous structures, Operation Castle, Project 3.5, July 1955, Secret - Restricted Data) that Station 1200 on Namu Island (codenamed Charlie Island for security) at 7564 ft from Bravo, and Station 1341, a 3-storey above ground reinforced concrete building on Bokobyaadaa Island (Able Island) at 7500 ft from Bravo, survived about 130 psi peak overpressure.  Castle weapon test report WT-934, Operation Castle, Summary Report of the Commander, Task Unit 13, Military Effects, Programs 1-9 (1959) explains on page 61: "These shelters maintained their structural integrity, but failed functionally because of detail failure."

The detail failures were things like a blast doors (facing the blast) being forced into Station 1341.  This blast door was however not shut but actually open at the moment of explosion to allow instruments to observe the fireball growth, and then a gadget tried to slam the door shut automatically just before the supersonic blast wave arrived (a feature that depended on the exact yield, because the arrival time is much faster than sound within the fireball radius).  The easy swing-close door, designed for only 50 psi incident overpressure, was forced in by 130 psi from the unexpected 15 megatons yield of Bravo.

When the second shot of Castle, 11 megaton Romeo, was fired on a barge moored over the Bravo crater, it subjected Station 1341 to 95 psi peak overpressure which blew off the already cracked 3rd floor (see WT-1631 / AD 355505, page 21, linked here).  But what do you expect after 130 psi from 15 megatons and then 95 psi from 11 megatons?  The point is, the two lower floors of Station 1341 survived both multimegaton onslaughts.  But Castle was only a start.  In 1958, 9.3 megaton shot Hardtack-Poplar subjected Station 1341 to 350 psi peak overpressure and a ground shock which caused a peak floor slab acceleration of 210 g's (210 times normal gravity), which sheered off the cracked 2nd floor (see page 33 of WT-1631).  But even then, the first floor survived!  See photo at top; the thing is still at Bikini Atoll today!

At Eniwetok Atoll, structures were torn down in 1979 during the decontamination process (most of the danger was from unexploded WWII shells remaining from the Japanese occupation of Eniwetok, not fallout).  Photo below shows a typical shelter surviving intact after several H-bomb tests over on Eniwetok Atoll in 1977, before the clean up operation of 1977-9 (see the 1957 edition of Glasstone's Effects of Nuclear Weapons - not later editions - for the internal blueprint of a standard 100 psi peak overpressure nuclear tested shelter):

Above: the 100 psi peak overpressure surviving nuclear test-proved shelter in the 1957 edition of Glasstone's Effects of Nuclear Weapons. 

A SUMMARY OF UNDERGROUND AND EARTH-COVERED LOADING AND RESPONSE SYSTEMS SUBJECTED TO THE EFFECTS OF NUCLEAR WEAPONS DURING FULL-SCALE TEST OPERATIONS CONDUCTED 1951 - 1958, 31 August 1963, report DASA-1390, AD340311, previously Secret-FRD. This report lists all the nuclear weapons tests, the blueprints for the structures exposed at each, the distance and peak overpressure, etc., and the effects which resulted.

Since Bikini and Eniwetok atolls are relatively small, the higher yield tests repeatedly exposed instrument station structures left over from previous testing to further detonations, so that the effects of repeated blasts were ascertained. This is contrary to so much of the ignorance-based anti-civil defense propaganda which insists that nobody knows what repeated nuclear explosions will do to targets.

DAMAGE TO EXISTING EPG STRUCTURES, 17 October 1960, report WT-1631, AD355505, previously Secret-FRD, contains useful tables of the effects of repeated nuclear detonations on the testing structures at Bikini and Eniwetok atolls during the nuclear tests at those atolls, including the final tests there in 1958.

Wayne J. Christensen, Blast Effects on Miscellaneous Structures, Operation Castle, Project 3.5, July 1955, Secret - RD, WT-901.


What needs to be produced is a new summary of atmospheric nuclear tests, incorporating these detailed data on the effects of specific tests upon specific target structures.

Above: in the 10.4 megaton Mike nuclear test on Elugelab Island, Eniwetok Atoll, 1952, the rats (species Rattus exulans) of Engebi survived the heat, blast, and fallout as explained by Neal O. Hines in his book Proving ground: An account of the radiobiological studies in the Pacific, 1946-1961, dramatically on pages 143, 151, 209-212, and 297:

Page 143: "On ... November 8 [7 days after Mike] ... At Engebi the group went ashore on an island ... that had been swept by the blast and by the succeeding surge of water. ... survey meters indicated radiation was at 2 to 2.5 R/hr [about 1,000 R/hr at 1 hour after detonation, allowing for t^-1.2 fallout decay] ...

Page 151: "The exposure of Engebi to the effects of the Mike shot made it seem impossible that rats had survived.  The view was expressed in a subsequent summary by [Frank] Lowman, who said that there was 'little probability that rats had lived through the heat, the shock wave, the rush of water, and the nuclear radiations that Mike had inflicted on the island.  Members of the rat colonies apparently did live through the holocaust, however, and the questions presented by this circumstance would intrigue the investigators for years."

Page 209: "Their nests, composed of loosely matted grass stems, usually are built in burrows 6-12 inches below the surface of the ground, but occasionally the tunnels extend to 18-24 inches below the surface, or nests are found immediately beneath boards, slabs of concrete, or protective rubble. ... In 1955 the rats of Engebi were living on a treeless plain ... they fed on the seeds of Lepturus, Thuarea, and Fimbristylis, and on the leaves of Triumfetta and Sida, all common grass plants."

In 1954, the rats that of Engebi surviving Mike were exposed to the 1.69 megaton Castle-Nectar test, which is discussed on page 212:

"After the Nectar detonation concentrations [of I-131] in the thyroid were at levels considered excessive ... within 9 weeks activity in the thyroid was so low that measurement was difficult. ... most of the radioactivity in muscle was due to the presence of cesium-137, and no strontium-89/90 was found in that tissue. ... In January, 1955, the bones of rats contained strontium 89/90 in amounts approximating the maximum permissible dose, but no bone tumors have been discovered and none was found in specimens collected later."

Page 297: "The survival of the rats in the face of repeated atomic bombardment had seemed in 1955 a circumstance approaching the phenomenal.  Even more so was the continued health of the colonies ... The case was important because it seemed to bear so directly on one of the broadest of the unanswered questions of the nuclear age, the effect on warm-blooded, vertebrate animals of continued exposure to low-level irradiation."

Noddy tern at Engebi Island, Eniwetok Atoll, 1965.

Above: the rapid fall in cesium-137 uptake by plants and animals with distance from the lip of the 1956 Redwing-Cactus nuclear surface burst crater in 1967 (twelve years later, in 1979 this particular crater was used as a convenient dump for contaminated soil and WWII munitions found during the Eniwetok Atoll cleap up campaign, and then it was simply sealed up with a concrete dome).

Vaporization myths

Nobody has ever been "vaporised" by thermal radiation from a nuclear explosion, e.g. in Hiroshima even at ground zero you're talking about 100 calories per square centimetre in the open.  Useful information: heat of vaporization of water = 2257 J/g = 540 calories/gram.  Density of water or skin (70% water) = 1 gram/cubic centimetre.

Therefore, 100 calories per square centimetre (ground zero Hiroshima) is only enough energy to vaporize a layer of water or skin 100/540 = 0.185 cm thick, or 1.85 mm thick.

In fact, even less will be vaporized because some heat is reflected by the skin, and some is absorbed by clothing.  If clothing ignites, it can be extinguished easily by rolling it out.  Remember, contrary to propaganda, thermally ignited clothing is easier to extinguish than petrol soaked clothing in peacetime car accident victims.  The 1946 U.S. Strategic Bombing Survey report documents the fact that clothing ignition could be beaten out.

The main danger in cities is not from thermal radiation or fires, because modern city buildings absorb almost all of the thermal and much of the nuclear radiation.  So the really widespread danger is flying glass and blast winds, which are dealt with by duck and cover on seeing the bright flash, which arrives prior to the blast wave.