u/Positive_Purpose_950

From Stephen Schwartz (@atomicanalyst)

"Late in the morning today in 1969, plutonium flecks in oil-saturated rags on the floor of a plutonium briquette press glovebox on the north foundry line inside Building 776-777 (the largest building below) at the Rocky Flats Plant near Denver, Colorado, spontaneously ignited. The rags began to burn.

The glovebox ventilation fans continually pulled air into filters on the second floor, sucking heat from the oily rag fire into a nearby storage glovebox, eventually igniting a plutonium briquette inside an open steel can. It began burning like a charcoal briquette. Because it was Mother’s Day, no regular operations were scheduled until midnight. Building 776-777 was a large plutonium foundry and assembly facility, manufacturing plutonium pits or triggers for thermonuclear weapons. When the previous day’s shift ended, 7,461 pounds of plutonium in various forms were inside.

Although the 14-by-2-foot Benelex plastic “jewel box” where the plutonium briquette was stored did not catch fire, it did release hot, combustible gases which in turn ignited other briquettes inside the long stainless steel glovebox assembly line.

The plutonium fire should have immediately triggered heat detectors to warn personnel at the plant, but these had been removed from the storage gloveboxes some two years earlier to make room for the anti-radiation “jewel boxes.” Instead, the detectors sat uselessly on the floor.

Gradually, the smoke clogged the air filters on the second floor. More plutonium in the glove boxes caught fire. And as the heat intensified, so did combustible rubber gloves and plastic windows. But confined to the gloveboxes, the fire still remained undetected.

As the multiple Plexiglass windows and glove portholes were breached, flames erupted and spread quickly. Because the sealed gloveboxes were routinely kept at low air pressure (to prevent plutonium particles from escaping), the sudden influx of air fanned the flames.

At 2:27 PM, operational heat detectors finally triggered an alarm at the site fire station. Within minutes, four firefighters arrived to find heavy smoke and 18-inch flames erupting from the tops of some gloveboxes. They discharged two large carbon dioxide extinguishers into the fire with no effect.

Why only CO2? The firefighters had been repeatedly ordered never to use water on a plutonium fire because it could trigger a criticality accident, a hydrogen explosion, or both. But the risk the fire would engulf the building, causing its collapse and releasing airborne plutonium was also high.

At this point, thick plastic radiation safety walls were burning. Lead shielding melted and fell like glowing rain from overhead conveyors. So at 2:34 PM, Capt. Wayne Jesser ordered his men to deploy fire hoses. They used fine spray nozzles and tried not to spray water directly onto the plutonium.

Meanwhile, the ventilation fans continued to operate, sucking flames into the paper filters designed to trap plutonium and keep it inside the building. Two of the three banks of filters were already destroyed and the third was beginning to burn.

Luckily, a firefighter accidentally back his truck into a power pole outside the building, cutting off the electricity and shutting down the fans. But the fire continued to burn intensely. One firefighter later told investigators he tried to use his hose to push all the plutonium into a corner “so he could really squirt it.” That probably would have triggered a brief and dangerous chain reaction (a criticality accident). Fortunately (again), the plutonium oxide from the burning plutonium metal became sticky like dough when soaked with water, and the plutonium did not move.

The firefighters contained the fire by 6:40 PM and had essentially extinguished it by 8:00 PM. Fifteen had received significant exposures. But as with an earlier serious plutonium fire in 1957 in another building (771), the plutonium continued to smolder and reignite.

The Atomic Energy Commission (AEC) insisted that although the building was “radioactively hot,” no radioactivity had escaped into the atmosphere. That claim was refuted several months later when independent scientists tested soil near Rocky Flats and found plutonium from the fire.

Much of the plutonium oxide was able to be reprocessed back into plutonium metal. But the AEC estimated $22.3 million worth of plutonium went up in smoke. Combined with $48.4 million in damage to the building, the $70.7 million loss made it the most expensive US industrial accident up to that time.

Managers with Dow Chemical Company, which operated Rocky Flats for the AEC, dismissed the near disaster, telling AEC investigators “that there was no need to have plans for possible off-site damage or personal injuries, since it was not possible for serious off-site contamination to occur, and expressed the view that if such contamination were possible the plant should not be located where it is.”

The 1969 fire released about 1⁄1000 as much plutonium as was released in the 1957 fire. But the 1969 fire led local health officials to perform independent tests of the area surrounding Rocky Flats to determine the extent of the contamination. This resulted in the first releases of information to the public that populated areas southeast of Rocky Flats had been contaminated