The paper addresses one aspect of the definition of the explosion hazard from flammable liquid spills or slow heavy vapor releases in enclosures. In this type of accidents, the explosive mixture is typically confined to a layer near the floor. No methods are currently available for the sizing of explosion vents in these partial-volume deflagrations. Resolution of the issue was sought through tests carried out in a 63.7 m3 (2250 ft3) chamber with stratified mixtures of propane in air. The layers were formed by slowly injecting propane at the chamber floor through diffusers, at a rate of the order of the estimated rate of vaporization of a typical solvent such as acetone. The layer composition was carefully characterized through gas concentration measurements at twelve locations, using a single continuous analyzer connected to a multiplexed sampling system. Following ignition of the layers, data were obtained on the propagation velocity of the flame and on the pressure developed by the explosion in the room both with and without venting.

The results of the experiments have been correlated using an existing model, modified to account for the cylindrical geometry of the system and for the dual-mode character of the combustion process (a premixed flame is typically followed by diffusive/ convective burning of the rich portion of the fuel/air layer). While confirming the conservatism of current design recommendations, which are based on the assumption of a full-volume explosion, the work has brought out the fact that the contributions to pressure development from the different portions of the layer must be properly taken into account.

Work is currently in progress to predict the fuel distribution in the explosive layer as a function of the parameters that define the spill (or fuel release) scenario. This step is being done through modeling of the rate of vaporization of a liquid pool and the subsequent dispersion of the vapors in the surrounding area. The model, when combined with the already-developed treatment of the explosion problem, will provide an integrated tool for predicting the protection requirements of flammable liquid process/dispensing areas.