Ignition and explosion from accidental leaks of large amount of flammables into a long, underground trench may result in extensive damage and fatalities. Mitigation of such leak and explosion is difficult although not impossible. Typical explosion suppression measures such as water spray and inert powder cannot be readily applied owing to underground location. In this work, we proposed a concept of suppression the flame propagation rather than the explosion overpressure by injecting inert gas into the underground duct. Experimental studies were carried for the suppression by an inert gas of flame propagation in one section of a tube to another section with flammable mixtures. The critical length of the inert gas section required for successful suppression is determined to be less than 0.3 m for a 3-m ignition section containing propylene/air mixture near stoichiometric concentration. Application of the results in responding to large-scale leak into duct is discussed.
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