Accidents during the Manhattan Project

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The Philadelphia Incident

On September 2nd, 1944, three men entered the transfer room of the Liquid thermal diffusion semi-works at the Philadelphia Navy Yard to repair a clogged tube. The tube they were working on consisted of two concentric pipes with liquid uranium hexafluoride circulating in the space between them and the innermost pipe contained high-pressure steam.

These men, all from different backgrounds and each representing a different facet of the complex Manhattan Engineer District, had one thing in common: they had all volunteered to work in a dangerous environment on a process that had only recently moved from the laboratory experimental stage to a pilot plant operation. Peter N. Bragg Jr., a chemical engineer from Arkansas, was hired in June by the Navy Research Lab; Douglas P. Meigs was an employee of the H. K. Ferguson Company of Cleveland, OH, the prime contractor for the thermal diffusion project; and, Arnold Kramish, a physicist by education and a member of the Special Engineer Detachment (SED), was on loan from Oak Ridge, TN.

Kneeling on the floor with a Bunsen burner, Bragg and Meigs worked to free the clogged tube. Without warning, at 1:20 PM, there was a terrific explosion. As the tube shattered, the liquid uranium hexafluoride combined with the escaping steam and showered the two engineers with hydrofluoric acid, one of the most corrosive agents known. Within minutes, both Peter Bragg and Douglas Meigs, with third degree burns all over their bodies, were dead and Arnold Kramish, also burned, was near death. Thus began one of the most extraordinary events in the history of the Manhattan Project.

As the explosion ripped through the transfer room of the Naval Research Laboratory's thermal diffusion experimental pilot-plant, the battleship U.S.S. Wisconsin sat berthed not more than two hundred yards away. Just back from its "shakedown" cruise, the sailors on board were never made aware that they had been exposed to a cloud of uranium hexafluoride. Although not highly-radioactive, the uranium-hexafluoride is nevertheless, toxic.

Due to the extreme secrecy surrounding the Manhattan Project and specifically this experimental facility at the Philadelphia Navy Yard, General Leslie Groves immediately drew a veil over the incident, as exemplified by this vague press release: Explosion at Navy Yard. Even the Philadelphia coroner was not made aware of the actual causes of death. It was not until many years later that the true facts began to emerge, and by then it was too late for the parents of Peter Bragg, who both passed away never knowing how their son had died.

Later printed reflections on the incident include:

The Dragon Bites Twice: Daghlian and Slotin

Slotin Accident Mockup

First in August of 1945 and again in May of 1946, two Los Alamos, NM scientists, Harry Daghlian and Louis Slotin, were exposed to lethal doses of radiation while performing experiments to determine critical mass. These experiments, performed at the Omega Site, were commonly referred to as "Tickling the Tail of the Dragon". Although several months apart, both accidents occurred on a Tuesday and both on the 21st of the month, and ultimately both men died in the same hospital room at the U.S. Engineers Hospital at Los Alamos, NM.

See here for a short biography of Harry Daghlian: Harry Daghlian

See here for an article announcing the death of Harry Daghlian: "Bomb Worker Dies of Burns"

On Tuesday, May 21st, 1946, Louis Slotin was demonstrating a criticality experiment that involved gradually bringing together two beryllium-coated halves of a sphere that held plutonium at its core- without allowing the halves to touch- and recording the increasing rate of fissioning. Then, in one fateful moment, the screwdriver slipped. A blue glow flashed from the sphere and the Geiger counter clicked furiously. Slotin, exposed to nearly 1,000 rads of radiation (well above a lethal dose), reacted instinctively and knocked the spheres apart. His action stopped the chain reaction and prevented the seven other individuals in the room from being exposed to the same high levels of radiation as he experienced. Slotin's health rapidly deteriorated and he spent his last nine days receiving around-the-clock care as he went through the ravages of radiation sickness, passing away on May 30th, 1946.

It was not until the second accident and Louis Slotin's death that more rigorous safety procedures were applied. After the incident, criticality experiments at Los Alamos were conducted remotely, with roughly a quarter of a mile separating scientists from radioactive material. Louis Slotin's death helped incite a new era of health and safety measures.

See this article detailing Louis Slotin's background, Manhattan Project experience, and the accident: "Louis Slotin and 'The Invisible Killer'"

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