Hazardous area classification (fire and explosion prevention)

The purpose of a hazardous area classification (HAC) is to reduce the chance of an explosive/flammable atmosphere contacting an ignition source.

This is achieved by:

• assessing the risk of fire and explosion hazards in and around installations and plant involving flammable liquids, vapours, gases and combustible dusts
• establishing zones where explosive atmospheres are expected to exist and determining the size and ignition characteristics of the atmospheres
• categorising the minimum level of ignition source protection required for equipment to be installed or taken within a hazardous area to control the risk of a fire or explosion.

Hazardous area classification

A hazardous area is an area (three-dimensional space) in which a flammable/explosive atmosphere is or may be expected to be present in a quantity that requires ignition source controls to manage safety risks (i.e. fires and explosions).

Fire and explosion can result in catastrophic consequences for people and property causing loss of life or serious injury and possible loss of business.

For this reason, electrical safety and work health and safety legislation imposes a duty of care on a person conducting a business or undertaking (PCBU).

HACs may be carried out by direct comparison with typical installations described in established codes, or by more quantitative methods that require a detailed knowledge of the plant. HACs for new or complex installations may need additional support from other hazard identification processes such as a Preliminary Hazard Analysis (PHA) and Hazard and Operability Study (HAZOP) and calculations using specialised modelling software.

HACs must always be supported by representative data on the explosive properties of the flammable materials involved, e.g. manufacturer’s safety data sheets (SDS). HACs involving combustible dusts may require additional support from testing to determine the dust’s explosive properties, e.g. particle size and chemical composition.

The first step to control the risks is to conduct a hazardous area classification, to identify where flammable atmospheres may exist and either eliminate or control potential ignition sources.

Sources of release of flammable gases and vapours or combustible dusts may arise:

• from constant activities
• occasionally, as part of normal operation
• as the result of an unplanned event.

In addition, inside process equipment may be a hazardous area if both gas/vapour/dust and air are present, though there is no actual release.

Hazardous area classifications must be done by a suitably qualified person.

The Managing risks of hazardous chemicals in the workplace Code of Practice 2021 (PDF, 1.21 MB) references the following Australian Standards for classifying hazardous areas:

• AS/NZS 60079.10.1 Explosive atmospheres-Classification of areas_Explosive gas atmospheres
• AS/NZS 60079.10.2 Explosive atmospheres-Classification of areas_Explosive dust atmospheres

HACs are a living document. They should be referred to during new installations, site inductions, change assessments and inspection, maintenance and repair activities. They also require periodic review assessments.

View more information on controlling fire and explosion risks.