Abstract: Employees #1 and #2 were adding ammonium perchlorate into a mixer that was mixing a batch of solid propellant. A flash fire occurred, causing multiple burns to Employee #2 and arm burns to Employee #1. They were both hospitalized. Both employees were in on-the-job training and were supposed to be supervised at all times during any mixing operation. The supervisor had left prior to the mixing operation and did not return. The lack of a supervisor and inadequate hazard communication resulted in the following violations: non-conductive shoes were worn in a conductive shoe area; the sieve that was used was not provided with a bonding strap, which would have allowed a bond to form between the mixing unit and the sieve; nor was there a proper sieve available for use within the room. Also, the standard operating procedure is to have a mixing employee and supervisor in the mixing room and another employee in the remote operating station or bunker watching a TV monitor to react to any emergency situation, but the remote station was not staffed. Further contributing factors which may have influenced this accident include the fact that the employees were adding 2 1/2 micron sized ammonium perchlorine to the mix, causing the humidifier to malfunction. The humidity therefore dropped down to approximately 5 percent (normal humidity at 75 degrees is between 30 percent and 70 percent) and on-site weather station recorded an abrupt weather change at approximately the same time as the accident. In addition to the humidity changes, the wind picked up and a sudden temperature change took place. Employees #1 and #2 stated in a interview that they saw the ammonium perchlorate cling to the sides of the mixer when they were attempting to add it to the batch. This should have been a red flag to the employees that a static charge was present, but they were unable to recognize the hazard due to their lack of training.