Hazardous Area Classification (HAC) is a structured risk assessment used to identify and classify areas where flammable liquids, gases, or combustible dusts may be present. The aim of Hazardous Area Classification is to determine the likelihood and duration of an explosive atmosphere so the correct equipment, such as ATEX-rated devices, can be selected. Properly rated equipment prevents ignition sources and supports a safe, compliant site.
HAC is a fundamental requirement for any process or facility that handles, stores, or transfers flammable substances.
When Do You Need a Hazardous Area Classification?
You should carry out a HAC study if your plant stores or processes any flammable gases, liquids, vapours, or combustible dusts.
It ensures that ignition sources are eliminated, risks are understood, and equipment selection meets legal and industry standards.
What Influences the Size of a Hazardous Zone?
Several factors affect hazardous-zone type and extent, including:
- Material properties – such as flash point, vapour density, and lower explosive limit
- Release characteristics – velocity, concentration, and quantity of the release
- Dispersion behaviour – how quickly vapours or dusts disperse into the surrounding area
These factors combine to determine the zone type (Zone 0, 1, or 2 for gases; Zone 20, 21, or 22 for dusts) and its distance from the source.
How Ventilation Reduces Hazardous Zone Size
Ventilation has a significant effect on zone classification. Both the availability and quality of ventilation can reduce the extent of a zone or even change its type.
Improved ventilation can:
- Increase dilution of flammable atmospheres
- Reduce persistence of vapours and dust
- Potentially downgrade a zone type (e.g., from Zone 1 to Zone 2)
- Reduce the hazardous distance from the source of release
OTECSA frequently supports clients in improving zoning outcomes through targeted ventilation upgrades.
Why a Zone May Extend Beyond a Bund
Hazardous zones originate from the source of release, not the bund wall.
Because a bund is designed to contain leaks anywhere within it, the zone is calculated from the edge of the flammable pool, which is conservatively assumed to be anywhere inside the bund. This means the zone can extend beyond the bund, depending on:
- Liquid properties
- Pool size assumption
- Release scenarios
- Ventilation conditions
It is important to note that catastrophic releases are not considered in HAC studies.
Expert Support for Hazardous Area Classification
Hazardous Area Classification is a specialised area of process safety, requiring a detailed understanding of materials, release scenarios, and relevant standards such as BS EN 60079-10-1:2021.
OTECSA’s Senior Process Safety Consultant, Ryan Roche, supports clients across the UK with:
- HAC studies
- DSEAR risk assessments
- Hazard studies
- Ventilation improvement strategies
If you need clarity on zoning, compliance, or risk reduction, our team is here to help.