TY - JOUR PY - 2001// TI - Deflagrations involving stratified heavier-than-air vapor/air mixtures JO - Fire safety journal A1 - DeHaan, John D. A1 - Crowhurst, D A1 - Hoare, D A1 - Bensilum, M A1 - Shipp, MP SP - 693 EP - 710 VL - 36 IS - 7 N2 - The distribution of explosion damage in a structure is a major indicator of the type of explosive material involved and its location. A solid-phase explosive material typically produces localized or "seated" damage, where a vapor/air explosive mixture typically produces generalized, omnidirectional damage. Investigators have been taught that the finding of more intense blast damage to lower portions of an enclosure indicates that the vapors were heavier than air, while explosion damage to upper portions indicates a lighter-than-air gaseous fuel. Most of the explosion pressure data in the literature deal with well-mixed mixtures that are uniform in concentration prior to ignition. This study explores the pressure distributions produced by the ignition of shallow (0.05-0.2 m deep) layers of hexane vapor created by the evaporation of liquid in a still, isothermal compartment. The floor-level vapor layers thus produced were ignited by an electric arc and the pressures at five different locations in the room were monitored. It was found that pressures increased in an exponential fashion over a period of 300-400 ms after ignition until the relief panel failed (at ~5-6 kPa). The peak pressures observed at all five locations in the compartment coincided in time (to within +/-5 ms) and intensity suggesting that the pressures produced within the 3.6 m x 2.4 m x 2.4 m chamber equilibrated very quickly. Any failure of the compartment, then, would be the result of failure of the weakest part of the confining structure, rather than the result of pre-ignition distribution of the fuel/air mixture. A small (~-2 kPa), but reproducible negative pressure peak was observed some 60-70 ms after the maximum positive pressure. This finding shows that negative pressure peaks can be produced by deflagrating vapor/air mixtures that could exert physical effects on lightweight debris dislodged by the initial positive pulse.

LA - SN - 0379-7112 UR - http://dx.doi.org/ ID - ref1 ER -