Detonation Flame Arrester Qualifying Application Parameters For Explosion Prevention In Vapour Handling Systems

Abstract

Abstract Compliance with air quality initiatives often involves the installation of a vapour collection system (VCS). The purpose of a VCS is to collect and direct vapours to a flare, incinerator or recovery unit. This practice creates a hazardous situation wherein an explosive vapour is exposed to an ignition source. This paper addresses the parameters of flame propagation within pipes and for operation of a Detonation Flame Arrester. The paper examines the division of responsibility between the end user and the manufacturer for the proper selection or proof of capability in each parameter. There are ten factors in creating the most severe flame front possible in a practical, full-sized piping system. They are: gas type, gas/air mixture, preignition pressure, temperature of the ignition source, temperature of the mixture, ignition location, pipe configuration, pipe size (larger line sizes than arrester size), protected-side restrictions and endurance to stabilized flame. Many certification standards define the acceptance testing of detonation flame arresters. They have been evolving and improving over the past two decades. A summary is made of which flame propagation parameters are addressed by various standards. Application reviews and installation in operating conditions using these parameters would have a significant impact on operational safety. The critical variables within the control of industry are outlined and qualified. When these parameters are applied, new levels of confidence would be created and the current high frequency of vapour transportation explosions reduced. Introduction Interest in the nature of vapour line explosions in Alberta, Canada began in earnest in the 1960s when, for environmental reasons, operators of oil and sour gas wells were required to collect vapours and burn them in flare stacks. Although these actions resulted in increased protection of the environment, they also subjected the workers and equipment owners in the oil industry to increased hazards from storage tank explosions. Prior to 1990 approximately 30 explosions per year occurred in Alberta alone, with each costing approximately $100,000 US or more in lost production and equipment replacement. Ironically, the cause of these explosions was directly attributable to the misapplication of equipment that is designed to stop an explosion from occurring-the "Flame Arrester." This passive device is the first line of defence against flame propagation from a flare to a storage tank. Conventional flame arresters designed for "end-of-line" applications and incorrectly located in pipes, produced a dismal operation performance record. Some explosions which occurred outside of Canada were the U.S. Green Lake barges (1983), a tanker in Malaysia (1992), Australian Coode Island storage tanks (1991), a tanker (1989), and a barge (1992) in the Houston ship channel. Practical and theoretical knowledge of flame propagation in piping systems, along with the technology to arrest such a flame has increased considerably in the last 15 years. A research program was started which dealt with flame propagation prevention technology and the development of reliable Detonation Flame Arrester (DFA) devices. Since 1985 activities included comprehensive explosion investigations(3), an analysis of ten Alberta oil field explosions(2), and the outlining of industry demands for flame arrester design parameters.