An explosion occurred within a grinder on a plastics manufacturing plant which blew off the grinder door. As it was not practicable to protect the system from the effects of a dust explosion with explosion vents, a chlorofluorocarbon explosion suppression system had been fitted. The system operated off a pressure sensor, which was designed to detect the onset of a dust explosion and rapidly release the CFC to quench the explosion before sufficient pressure was generated to damage the equipment or associated piping.
The grinder had operated without incident for many years, and the suppression system had never been put to the test. At the time of the incident in question, water had inadvertently got into the plastic grinding system and accumulated in the pipework below the grinder. Eventually the water pressure became sufficient to activate the suppression system. As the plastic powder was wet, it did not flow freely, and hence the suppressing agent was not able to flow freely through the system. The pressure of the CFC released into the grinder caused the over-pressurisation of the grinder, which failed at the grinder door.
A.M. Dowell, D.C. Hendershot and G.L. Keeports, ‘Explosion Caused By Explosion Suppression System’, Loss Prevention Bulletin, Issue No. 146, April 1999, pp 3-4, Institution of Chemical Engineers, ISSN 0260-9576.