Investigation of an Explosive Accident Using Simulation as a Tool

Abstract : A new energetic polymer (EXP) under development at the pilot plant was produced in 5-kg batches. Solvent extraction to purify the EXP was required and a piece of equipment called the Rotary Film Evaporator (RFE) was available and selected for use. The RFE was last operated some 15 years ago with inert polymer. Prior to further use and in consultation with the previous users, the RFE was cleaned and operated with inert polymer so that the new users could develop their expertise in operating it. On 12 Oct 89 after 24 hours of preheating the RFE, the EXP polymer was introduced in the piping. Approximately 30 to 60 seconds later an explosion occurred in the piping followed by a small fire. One employee was slightly injured and the fire was quickly put out by the other employee present. A board of inquiry was immediately formed. The board interviewed the employees as the first step in the investigation. After examination of the evidence -- the temperature recordings and the depositions of the witnesses -- a few hypotheses were set forth to explain the EXP explosion. An extensive laboratory study was conducted on samples of EXP left over from the same batch that exploded, but it did not reveal any clear explanation for what happened. Overheating of the equipment or of the piping was still the favored hypothesis despite the fact that the temperatures recorded at the time of the explosion (between 90 and 135 degrees C) were appreciably lower than the auto-ignition temperature of EXP (215 degrees C). It was only after a detailed and exact simulation of the conditions that prevailed at the moment of the explosion that proof of a much higher temperature (350 degrees C) in one section of the piping was discovered. The simulation allowed the investigation team to understand what caused the ignition of EXP and make proper recommendations to correct the situation.