We have a number of storage vessels that are used for various solvents contained in a bund of approx 4" depth. All electrical items located in the bund are EEx rated for a zone 2 area. My question is whether the zoned area should continue beyond the confines of the bund and if so how to I establish how far both vetically and horizontally?
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Hazardous area classification 1
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Spill containment with dikes is an excellent release mitigation approach. Whether vapours will or will not reach dangerous levels at a distance depends on the ventilation provided by winds and whether it is day or night, factors that affect atmospheric stability, and the dilution effects thereof.
There are tables and graphs that enable estimating the concentrations of the vapour at a vertical and horizontal distance to verify whether these are lower than the LFL or the TLV of the particular solvent, using dispersion coefficients such as those given by the Pasquill-Gifford model.
I can recommend one book that has worked out examples: Chemical Process Safety: Fundamentals and Applications by Crowl and Louvar (Prentice Hall).
There are tables and graphs that enable estimating the concentrations of the vapour at a vertical and horizontal distance to verify whether these are lower than the LFL or the TLV of the particular solvent, using dispersion coefficients such as those given by the Pasquill-Gifford model.
I can recommend one book that has worked out examples: Chemical Process Safety: Fundamentals and Applications by Crowl and Louvar (Prentice Hall).
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