The conversion of UF to metal was accomplished by the thermite reduction of green salt with magnesium in a refractory lined steel reaction vessel. 450 pounds of green salt were blended with approximately 72 pounds of magnesium. The resulting mixture was uniformly packed into the reduction "bomb", which has previously been lined with refractory slag in a jolting apparatus. Following these steps, the bomb was capped with refractory, sealed, and placed in one of 49 electric muffle furnaces. The furnace temperature was raised to approximately 1,225 °F and after about four hours the thermite type reduction reaction occurs: UF4 + 2Mg → 2MgF2 + U (metal). The charge was then allowed to separate and cool in the furnace for 10 minutes, after which it was removed and cooled to room temperature. Finally, the solidified uranium metal (derby) was separated from the slag and liner materials in a sequence of manual and mechanical operations that take place at the breakout station. The yields expected from this operation were about 95%. There are many documented explosions of these furnaces due to improperly packed refractory lining or a magnesium flare. Whatever the cause, the building would fill with radioactive smoke along with a real probability that molten uranium metal would come pouring out of the bottom of the furnace.