On flammability hazards from pressurised high-flashpoint liquid releases

Hazardous area classification is well established for dust and vapours, however this is not the case for high flashpoint liquid fuels. This study highlights the limitations of current guidance in relation to flammable mists, through demonstration of flammability of a representative high flashp'dint fuel for releases in the range of representative industrial dperating pressure, complemented by a phenomenological analysis and semi-quantification of the results observed. Flammability results are presented from low-pressure practical releases (<20barg) of a representative fuel (gas-oil with flashpoint > 61 degrees C), through a plain orifice, at temperatures well below its flashpoint. Based on a proposed two-phase flow-regime diagram, a semi-quantitate analysis of the results observed is offered via a simple 1-D phenomenological model, accommodating jet breakup length, spray quality, air entrainment and droplet dynamics. The complex scenario of liquid releases impinging onto an unheated flat surface is also considered. An impingement model is utilised to show the relative increase in volume of fine secondary spray induced post-impingement relative to the unobstructed case, resulting in a significant volume of flammable mist. This is demonstrated experimentally by showing flammability of a 5 barg release post impingement whereas the unobstructed 10 barg case would not ignite. (C) 2017 Elsevier Ltd. All rights reserved.