Your hazardous area classification study should be conducted in the early stages of plant design, and be adapted and updated as the plant is being constructed, to reflect the “as built” plant. But your compliance requirements shouldn’t end there: if the plant has been established for some time, then reviewing the classification is just as important to ensure the details are still correct.
Area classification is mandatory as noted in the wiring rules (AS/NZS 3000) under section 7.7, which refers to two main classification standards used in Australia.
Part 10:1 Classification of areas
Explosive gas atmospheres
(IEC 60079-10-1, Ed.1.0(2008) MOD)
Part 10:2 Classification of areas
Explosive dust atmospheres
Different methods can be used to classify plant and equipment which are referred to in the standards.
Method by Example
Source of Release
Modelling
When using Method by Examples, there are several examples in Annex Za. This method is conservative and sometimes overly large but is accepted within the industry and identifies Zone 1 and Zone 2 areas distinctly.
Where a lack of detailed data or operating experience makes it impossible to identify and assess individual sources of release in a plant, a generalised method may be used.
Generalised methods require judgements to be made (usually for quite large sections of the plant) on whether the overall hazard is high (Zone 0 or Zone 1) or low (Zone 2).
This Annex provides examples of hazard area classification for areas associated with the production, processing, handling and storage of flammable liquids and gases in refineries and major processing plants.
Although the Method by Calculation is more precise, and potentially reduces the zones, it finds a hypothetical volume Vz which represents the volume over which the mean concentration of flammable gas or vapour will typically be either 0.25 or 0.5 times the LEL. This calculation of Vz is only intended to assist in assessing the degree of the ventilation; it is not directly related to the size of the hazardous area.
Modelling is more precise, and the result is potentially smaller. This can replicate on-site conditions more accurately, as well as providing detail on how a leak might behave.
Where it can be clearly demonstrated, classification in accordance with the following codes are also acceptable
EI 15: Model Code of Safe Practice for the Petroleum Industry
API RP 505: Recommended Practice for 'Classification of Locations for Electrical Installations at Petroleum Facilities classified as Class I, Zone 0, Zone 1 and Zone 2'
BS 5908: Code of practice for fire precautions in the chemical and allied industries
Once a standard is selected for Hazardous Areas Classification, it is strongly recommended to stick with this standard, rather than mixing and matching standards or definitions.
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The HAZ team of expert engineers takes a practical approach to finding simple, productive and cost-effective compliance solutions for
equipment installed and operated in hazardous areas. With our head office in Brisbane we have delivered practical solutions to clients
throughout Australia, SE Asia and the USA.