Shared Research Project – Flammable Mists (

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Generation of Flammable Mists from High Flashpoint Fluids

“There is a pressing need for clear guidance on mist hazards to allow operators to determine the extent of areas where flammable mists may be present and to select appropriate equipment for use in those areas”.

It is well-known that mists of high-flashpoint fluids such as hydraulic oils, lubricating oils, diesel and heavier fuels can ignite a produce explosions at temperatures below their flashpoints. A review in 2009 identified 37 historical ignition incidents involving flammable mists, including 20 explosions of which nine were collectively responsible for a total of 29 fatalities.

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At present, Hazardous Area Classification (HAC) for explosive gas atmospheres is well established. However, although there is a legal requirement to consider flammable mists, the current guidance on mist hazards is limited, brief and largely qualitative.

To address this issue, a project on the formation and mitigation of flammable mists was intiated by HSE in December 2011 and jountly sponsored by 16 industry and regulatory partners. The objective was to develop practical criteria to define the likelihood of flammable mist formation that could be used as part of an area classification exercise.


Although the work undertaken represented a major step forward in understanding this phenomenon, knowledge of flammable mists is still relatively limited in comparison to flammable gases.

HSE would like to invite stakeholders to a workshop to discuss a potential HSE Shared Research Project to address some of the outstanding issues.

These are likely to include:

  • The development of an alternative approach to determining the Lower Explosive Limit (LEL) for mists in realistic leak scenarios
  • A study of the break-up into mists of realistic leaks, to improve the modelling approach
  • A study of the practical ignitability of mists from realistic leaks
  • A study of detection characteristics of Oil Mist Detectors
  • A study of mist explosion over pressures/pressure profiles, in particular for mist ignition inside turbine enclosures


The objective of the workshop will be to identify current knowledge gaps and to formulate the key outstanding research questions.

For more information, or to express your interest in attending the workshop,
please contact Dr Paul Grant on +44 (0)1298 218197 or email

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