A 6.1 x 9.1 m (20 x 30 ft) room with concrete block walls was used for distribution of process gases to clean room areas. Silane cylinders were located in 12-gauge metal gas cabinets. The ventilation system for the cabinets was in the process of being upgraded and the cabinets were protected by automatic sprinklers.
The silane cylinder involved was installed about 30 minutes prior to the incident. Employees in the area heard a loud "pop" from the process gas distribution room. Upon investigation, they found the windows of the cabinet broken, the doors open, and fire coming from the cylinder valve. The sprinkler activated properly and confined the fire to the cylinder head.
The escaping silane was caused by an improper connection of the cylinder to the distribution piping. There was evidence that the connection was cross-threaded, allowing the leakage. The flow of silane could not be shut off because of damage to the cylinder manifold connections. The fire continued to burn for about 8-1/2 hours until all silane in the cylinder had been consumed.
In 1992, a DOE site experienced a coal fire initiated by spontaneous combustion. Because of the nature of the fire and initial ineffectiveness of the means used to fight it, the fire required more than 28 hours to completely extinguish from the time a hot spot was first detected in a coal bunker. The initial strategy involved trying to remove coal from the bunker by feeding it more rapidly to the boiler and by using a drag chain to move more of it to the field. The drag chain failed in 30 minutes, however. Subsequent efforts to control the fire with carbon dioxide applied through inspection ports at the bottom of the bunker and from the tripper (switchgear) room high above the bunker were ineffective, and may have worsened the situation. The drag chain emptying coal from the bunker worked intermittently after being repaired, and finally stopped. Boiler plant personnel then began to remove burning coal by hand shovel.
Twenty-one hours after the fire was discovered, it had involved a large amount of the bunker. At one point, flames appeared at the tripper room windows, which were approximately 75 feet above the seat of the hot spots. A strong concern for a steam explosion delayed the application of water, but the decision was finally made to use water, which was applied without incident and eventually ended the fire.
Up to May 1955, no serious fires had been encountered during storage of scrap Zr turnings, chips, plates, rods, etc. Such scrap had been stored (pending contemplated future recovery) in segregated open-top bins. Several days after a heavy rain, a fire of unknown origin took place in one of the bins with flames extending 100 feet into the air. Shortly afterwards, contents of other (but not necessarily adjoining) bins suddenly and intermittently flared up. Material in all bins soon became involved and 159,000 pounds of Zr were consumed. The heat was sufficiently intense to crack windows and ignite wood located over 150 feet away. Particles of burning Zr were carried over one-quarter mile through the air.
In 1951, some water-wet scrap Zr powder in wooden barrels was placed in outside storage pending development of scrap-recovery processes. During the next several years, a few minor spontaneous fires broke out in this material. In January 1956, the material in several deteriorated wooden barrels was wet with water and repackaged in steel drums. In May 1956, employees working in the area noted that one of the steel drums lying on its side contained a black material "similar to carbon dust." What happened is uncertain, but a spontaneous explosion occurred accompanied by streaks of red fire with black smoke extending 100 feet into the air. A pronounced concussion wave was noted and the sound of the blast was heard several miles away. Two employees were killed, one having been blown 80 feet through the air, and a the third lost an arm. The drum contained Zr, probably in the form of a fine powder. Using extensive precautions, the remaining drums of scrap Zr were subsequently burned. During this operation, one of the drums exploded.
Two men died and two others were seriously injured in 1954 in a spontaneous explosion initiated during removal of the friction-top lid from a polythene-bag-lined, 1-gallon metal can containing Zr powder 16 percent wet with water. A ball of flame enveloped the entire area, accompanied by a concussion wave.
A 2-pound sample of carbon-tetrachloride-moistened powdered Zr was placed in a glass flask, vacuum applied, and the flask very gently heated with a Bunsen burner. The Zr suddenly began to heat up and detonated with a blinding flash. The explosion was attributed to a small amount of water.
In January 1955, an attempt was made to roll two 1,000-lb U slabs into 0.01-inch thick strips. After initial heating to 1,150 degrees F in a lithium-carbonate-potassium/carbonate bath, several 30 percent reductions were made by rolling. It was observed that heavy work passes had caused overheating. The strip, then 3/4 inch thick, was cooled to 1,200 degrees F. The strip again excessively heated during the next three reductions and became so ductile on entering the fourth that it pulled into two parts. The strip at this stage was cherry red, but by the time it had been removed to the mill floor it was observed to increase in temperature to a white heat followed by melting and burning.
In February 1956, a technician was attempting to roll a plate consisting of Zr-clad U, which, in turn, was clad in a low-carbon-steel jacket. During preheating, the furnace temperature control (which had been set to 1,450 degrees F) failed, allowing the temperature to rise to 1,800 degrees F. During subsequent rolling, molten Fe-Zr eutectic alloy within the steel jacket was forced to one end of the strip where it burst into flames as it sprayed out over an area approximately 10 feet wide, 10 feet high, and 25 feet long. One employee was seriously injured.
In the early program for the large-scale manufacture of metallic U, fine powder was allowed to collect under roughly 25 feet of water. At approximately 1-month intervals, and without prior warning, a geyser about 30 feet high would suddenly develop over the powder and then immediately subside.
A series of cases is known in which massive pieces of metallic U, Pu, and Th have displayed unusual pyrophoricity, e.g., spontaneously igniting at room temperature. Spontaneous fires in U chips are, however, much more common and in one case ignition occurred 6 months after the chips had been placed in storage. One investigator of spontaneous fires in briquette U chips opened a drum filled with briquettes that had been in outside storage for several weeks. After noting that the drum contents were normal and at approximately room temperature, he was warned by an operator to stand back. A few seconds later, a flame shot to a height of about 25 feet and then immediately subsided. Upon reinspecting the drum interior, he noted that all of the briquettes were at an incandescent temperature.
A series of incidents have been experienced in which U and Ti alloys have displayed explosive surface films following acid treatment. Studies at Argonne National Laboratory showed that such explosions could be averted through use of adequate fluoride ion concentrations in nitric acid etching baths. Witnesses have described metal-surface explosions of this type as involving a brilliant flash of white light, accompanied by a sound similar to that of a 22-caliber rifle shot.
For several years scrap thorium (Th) powder had been disposed of by burning in successive small amounts. In July 1956, employees were engaged in burning scrap Th powder that had previously been washed with several aqueous solutions and vacuum-dried 3 days earlier. Some of the Th was placed in a special hood and ignited without incident. An employee took a "golf-ball-size" piece of Th from a metal pail containing 30/40 pounds, replaced the pail lid, and placed the piece on a small Th fire. An immediate sharp explosion blew the employee 20 feet across the room. Almost immediately, a second blast involving the Th in the pail was accompanied by a jet of orange fire and big cloud of dust. A third explosion occurred in a nearby vacuum dryer containing about 7 pounds of moist Th powder. One employee suffered fatal burns, while three others suffered serious injuries.
In preparing an experimental charge for making metallic Th in a reduction bomb, a mixer was being used to blend metallic calcium, dry zinc chloride, and dry thorium fluoride. After several revolutions of the mixer, the operator opened the mixer vent and, noting the dust and gas were escaping, decided to call his foreman. A second operator closed the vent, started the mixer, and soon heard a rumbling noise, followed by a sudden burst of flame covering a 45 degrees angle and extending parallel to the floor for 40 feet. Of the eight persons injured by the blaze, two subsequently died. Reason for initiation of the reduction reaction in the blender is uncertain and unprecedented. It was subsequently found that the calcium used was particularly reactive.
On June 16, 1954, employees of a high-energy-fuel laboratory were sampling 15 drums of "bag fines" Mg powder, which were opened in a special room that had been purged with nitrogen until the oxygen content had dropped below 1 percent. During sampling of the fifth drum, the powder ignited suddenly. The flame shot out from the drum, immediately subsided, and the operators left the room after replacing the drum cover. From an external observation window, the employees noticed a gradual darkening of the drum's exterior, moving down to within 2 to 4 inches of the drum bottom. The following day the drum was opened and contained a definite yellow coloration, which was presumed due to formation of magnesium nitride.
A massive block of metallic barium was cut into 3/4-inch square pieces while submerged in kerosene. During attempts to remove residual kerosene with carbon tetrachloride (an operation that had been performed many times before without incident), a violent reaction dispersed glass fragments and burning barium over the immediate area. Similar explosions have also occurred when Na, U, and Zr were treated with carbon tetrachloride.
Trouble had been experienced in getting a Kroll process reduction of ZrCl, with Mg to go to completion. When the furnace was opened up, a slate grey material was noted on the surface, which was thought to consist of Zr, Mg, and MgCl. A sample of this material, roughly 1/4 inch thick and 8 inches square, was removed for test and was totally inert when scratched with a file or hit with a hammer. A piece of the sample melted under an oxyacetylene flame but showed no pyrophoric properties. Samples were then placed in water and a slight evolution of gas was noted. The following day an attempt was made to further wash the samples in several changes of water. While under 5 inches of water and without any prior evidence of reaction, an explosion occurred that shattered the laboratory bench, threw the technician against the wall, and blew out a window 25 feet away. Portions of the water-washed sample blown to the floor ignited and "spit" when stepped upon. Small samples were subsequently tested and found to contain Mg, Zr, and 1 percent C.
On May 11, 1969, Rocky Flats Plant experienced the worst accident in plant history, a major fire in the 776-777 building, initially caused by pyrophoric plutonium scrap. One of the costliest industrial fires of all time damages were estimated at between $26 to $50 million dollars this accident was intensified and confounded by a number of operational errors.
The fire at 2:27 p.m. Sunday was reportedly caused by spontaneous ignition of a 1.5-kg briquette of plutonium alloy scrap contained in a metal can. This scrap was believed to have been oily and coated with residual CCl{sub 4} (carbon tetrachloride). Once ignited, the fire spread through several hundred interconnected gloveboxes in the two connected buildings.
The fire started in the west end of the north line, progressed eastward, crossed over to the south line through the interconnecting boxes, and spread through the south line. The fire spread through the machining boxes at the east end of 776 and into the inspection boxes in 777. Damage was extensive. Both Benelex, a combustible neutron shielding material added to the gloveboxes, and the combustible Plexiglas glove box windows contributed to rapid spread of the fire.
The main fire lasted about 4 hours, with minor flareups occurring through the next night. After futile attempts to control the fire with conventional procedures, the firemen finally resorted to the unorthodox procedure of applying water to bring the fire under control. This was the first time in history that water had been used to fight a plutonium fire. Despite attendant criticality dangers, the use of water was successful in controlling the fire.
The interiors of the two extremely large, high-bay buildings were grossly contaminated. An extensive, long-term cleanup effort was necessary for decontamination. Limited production was restarted about 6 months later in a temporary production line constructed in an adjacent building.
As damaging as the fire was, the water use prevented breaching of the outer walls and ceiling of 776 and 777, thus preventing a major release of plutonium to the environment. The small amount of plutonium released almost entirely contained on plantsite was about 0.0002 curies. Slightly contaminated external areas were subsequently cleaned up.
Fortunately, the fire caused no direct deaths. However, one fireman received significant plutonium lung burdens, and other firemen and personnel incurred smaller radiation inhalations and exposures while fighting the fire and later cleaning up heavily contaminated areas.
Immediately prior to the fire, personnel levels were significantly cut with no real decrease in work load or production demands. Strict attention to plutonium chip handling no longer seemed to have been a top priority.
The many lessons learned from this 1969 fire include the following:
These lessons learned from the 1969 fire have led to a number of current-day, continuing safety improvements including the following equipment modifications and procedural revisions:
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Appendix A