Current European Health and Safety Legislation was implemented to limit the chance of a serious explosion occurring in the workplace by highlighting potentially explosive atmospheres and ensuring that ignition sources are not present in these areas. Though hazardous area classification for gaseous and dust explosion hazards are well established, the same cannot be said for mists especially for high flash point liquids. However, a recent literature review of a range of (some fatal) incidents has shown that mist explosions are more common and the consequences more severe than previously anticipated. This work is, for example, applicable to the safe use of fuels and lubricants utilised in the gas turbine power generation and propulsion industries.
Previous studies of jet breakup regimes and idealised flammability studies have indicated that low pressure releases (<10 bar) of low volatility fuels may still give rise to combustion hazards. Impingement of accidental releases onto surfaces has been shown to exacerbate the potential hazard, or broaden the range of hazardous release conditions. However, although a theoretical case can be made for generating flammable environments under moderate release conditions, very little evidence has been provided to bridge the gap between ‘idealised’ studies and full-scale incidents. The aim of this first programme of work is to start the process of bridging this gap, leading to well founded safety guidance.
The test programme was conducted in a custom built spray chamber located in the Gas Turbine Research Centre (GTRC) of Cardiff University. The fuel was released at a predefined range of pressures of industrial relevance at atmospheric temperature. Igniters were positioned at three downstream locations and the continuous electrical discharge had an energy no greater than 4 mJ. Tests were conducted for ‘free sprays’ where the spray was directed along the length of the chamber, and for impinging sprays where the spray was aligned to impinge normal to a flat un-heated surface.
Gas oil (flash point > 61 °C) ignited as a free jet at a working pressure consistent with previous hypotheses. However, when the jet impinged on a solid surface then the resulting spray could be ignited at considerably lower delivery pressures. Although the impingement process is complex, the data will be discussed in light of contemporary models that predict initial jet/spray characteristics along with post-impingement characteristics. This paper presents a first step towards consolidating previous studies and improving future safety guidelines concerned with the risk posed by the flammability of accidental releases of pressurised high flashpoint fuels.