Understanding Flammable Mist Explosion Hazards

While there is extensive testing and validation of hazards from flammable vapors, less information is available regarding flammable liquid mists. A method is suggested for reasonably estimating the nature and severity of flammable liquid mist hazards by applying published mist property correlations to model inputs and outputs in dispersion modeling software. Better estimating these hazards is important to properly evaluate what mitigations will be needed.

One common high flash point liquid that can pose a flammable mist hazard is heating oil. Published literature has documented that the lower explosion point (LEP) temperature of a flammable mist can be much lower than the flash point of the vapor-phase material, and the lower flammability limit (LFL) concentration of a flammable mist can be as low as 10% of the material’s vapor-phase LFL. The actual LFL of a flammable mist has been experimentally observed to be a function of the droplet size.

Since many oils consist of a blend of hydrocarbons with various carbon chain lengths, only a few compounds may be chosen to represent the material in commercially available consequence modeling software. This paper will propose: 1) further guidance on an approach that will reasonably approximate the mist properties in the model; and 2) a practical example of modeling the consequences of a mist release.

Finally, a case study will be provided where a range of known real world preventative and mitigative measures were tabulated, the existing measures were evaluated against these measures, and then upgrades were proposed based on the model observations.



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