The Energy Institute’s guidance on hazardous area classification “Area classification code for installations handling flammable fluids”, commonly known as EI15 (and previously IP15), is used extensively in the UK and elsewhere by the petroleum industry and others, and is currently under revision. Ventilation is a key factor in area classification and it was recognised that the current Edition 3 of EI15 required improvement in this area in particular. The current approach, based on air changes per hour, is shown to be inappropriate since it is not related to the size of the release it is trying to dilute. The main aim of the work reported here is to provide an improved methodology for assessing the adequacy of the ventilation such that an enclosure containing secondary grade release sources can be properly classified as Zone 2 as defined by BS EN 60079-10-1:2009.
It is shown that limiting the average concentration to 25% LFL in the enclosure generally achieves the ventilation objective for a Zone 2 area but the degree of confinement and congestion at the point of release must be assessed. Guidance on this assessment is provided including the use of a factor to quantify the efficiency of mixing.
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Article source: http://www.hse.gov.uk/research/rrhtm/rr993.htm