Abstract: An ammoniation granulation (AG) process was in operation until a screw auger for the dry chemical feed choked, placing pressure on the anhydrous ammonia flowmeter, valves, and piping (locked and tagged out). The AG sparger pipe was down (locked and tagged out) at the globe valve. The rotary drum was off; the dry feed was off; the dust collection system was on; the fines return screw auger was on; and the anhydrous ammonia pump was off. The anhydrous ammonia and water process lines were open to purge. The valve ahead of the meter cage was not completely shut, and anhydrous ammonia, from the tank, was trapped in the cage and the pressure increased from 60 psig to 75 psig. Fines return continued to the rotary drum while the ammoniation granulation process was down. Wetted dry chemical base formed a crust over fugitive anhydrous ammonia from the cage valve (purged anhydrous ammonia). When the rotary drum was restarted, the crust at the fines return broke, allowing approximately 5 lb of liquid anhydrous ammonia to vaporize. Employees #1 and #2 were working on the AG process at that time without respiratory protection or escape respirators. The valve at the meter cage was not completely shut; the flowmeter was not checked; and the dry feed elevator and screens were not locked out.