Protecting against Vapor Explosions with Water Mist

This paper examines a number of practical questions about the possibility of using water mist to mitigate explosion hazards in some industrial applications. Water mist systems have been installed to replace Halon 1301 in gas compressor modules on Alaska’s North Slope oil fields. The hazard in the compressor modules includes fire in lubrication oil lines for the gas turbines that drive the compressors. The hazard also involves the potential for a methane gas leak, ignition, and explosion, although the probabilities of occurrence for the explosion hazard are not the same as the lube oil fire. The performance objective for the original halon systems was to inert the compartment, thus addressing both fire and explosion concerns. The design concentrations for the compressor modules were closer to 1.5% than to S%, indicating they were intended to provide an inerting effect. As part of the global move to eliminate ozone-depleting fire suppression agents, companies are replacing Halon 1301 systems with water mist systems. The water mist systems were developed and tested for control of liquid fuel or lubricating oil spray or pool fires associated with the turbines that drive the gas compressors. The water mist systems address the most likely hazard, the lube oil fire, hut the inerting benefit provided by Halon I301 has been lost. This has left the question of what to do if there is a methane gas leak unanswered. The question has been asked by the operators of these modules as to whether water mist can provide any benefit for mitigating the gas-air explosion hazard.