COMBUSTION HAZARDS POSED BY THE PRESSURIZED ATOMIZATION OF HIGH-FLASHPOINT LIQUIDS

Study of the revised Institute of Petroleum Model Code of Safe Practic e for area classification of petroleum installations has raised the qu estion of whether pressurized systems of high-flashpoint liquids (e.g. diesel, kerosene) should be considered hazardous in respect of their potential to atomize to produce flammable aerosol systems. This work c ollates relevant scientific studies to assist in investigation of the possibility of combustion hazards posed by these systems. It is envisa ged that it will serve as an initial assessment in an area where indus try acknowledges that insufficient information exists. A simple method is presented for characterizing liquid leaks in terms of their potent ial to atomize, which is considered a necessary condition to give rise to a flammable atmosphere. A cloud of very finely atomized liquid nea r stoichiometric concentration is shown to be hazardous with regard to a 'low-energy' spark. Empirical formulae for estimating the initial ' average' droplet size and the functional form of the volume of fuel co ntained in droplets that are less than a particular droplet size for t his type of leak give an indication of the nature and potential severi ty of the hazard. These correlations need to be validated for use outs ide their ranges of applicability or to be updated. Information collat ed here facilitates what is likely to be a very conservative assessmen t of the hazard potential. Identification of areas where there is a de arth of information is just as important, and it is hoped that this pa per will provoke further interest leading to improved methodologies fo r hazard quantification. However, at this stage, it has to be conclude d that, even under low pressures, the possibility of creating aerosols that result in flammable systems cannot be eliminated for commonly-ha ndled high-flashpoint liquids. Two practical illustrations, a large-sc ale study and a real incident, are given to support this conclusion. F inally, in the specific context of area classification, a simple solut ion to some potentially hazardous aerosol leaks is suggested.