HSE COMAH Technical Measures – Hazardous Area Classification and Control of Ignition Sources

A Comprehensive Guide to Hazardous Area Classification, DSEAR and Explosion Protection

LEVCentral Expert Commentary

Whenever flammable gases, vapours, mists or combustible dusts are present, there is the potential for an explosive atmosphere to form. In these situations, it is essential that plant, equipment and ignition sources are carefully managed to prevent fires and explosions.

This HSE technical guidance forms part of the COMAH Safety Report Assessment Guidance (SRAG) and provides one of the most comprehensive freely available overviews of hazardous area classification, the control of ignition sources and the selection of equipment for use in potentially explosive atmospheres. Although written primarily for COMAH inspectors and operators of major hazard installations, its principles are directly applicable to many workplaces subject to the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR).

For LEV professionals, the guidance is particularly valuable because dust extraction systems frequently handle flammable dusts, vapours and gases. Correct hazardous area classification influences the selection of fans, motors, electrical equipment, instrumentation, explosion protection measures and maintenance arrangements. Understanding how zones are established is therefore fundamental to the safe design of many LEV installations.

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Key Learning Points

The guidance explains:

The purpose of hazardous area classification.
How explosive atmospheres are formed.
Identification of potential release sources.
The influence of ventilation on hazardous area extent.
The physical properties of flammable gases and vapours.
Assessing the probability and duration of explosive atmospheres.
Classification of hazardous zones.
Selection of suitable ATEX/Ex-rated equipment.
Temperature classes and ignition temperatures.
Equipment categories appropriate for different zones.
Documentation of hazardous area studies.
Ongoing inspection and maintenance of explosion-protected equipment.

Understanding Hazardous Area Classification

One of the most useful aspects of this guidance is its explanation of hazardous zones.

Zone	Description
Zone 0	An explosive gas atmosphere is present continuously, for long periods or frequently.
Zone 1	An explosive gas atmosphere is likely to occur during normal operation.
Zone 2	An explosive gas atmosphere is not likely to occur during normal operation and, if it does occur, will exist only for a short period.

The guidance also explains how these zones influence the selection of electrical and mechanical equipment, ensuring that ignition sources are adequately controlled within hazardous areas.

Source Document Information

Organisation: Health and Safety Executive (HSE)

Document: Hazardous Area Classification and Control of Ignition Sources

Series: COMAH Safety Report Assessment Guidance (Technical Measures)

Document Type: HSE Technical Guidance

Primary Topics: Hazardous Area Classification, DSEAR, ATEX, Explosion Protection, Ignition Sources, Flammable Atmospheres

Audience: LEV Designers, DSEAR Assessors, Process Engineers, Occupational Hygienists, Electrical Engineers, Health & Safety Professionals and Duty Holders.

LEVCentral Perspective

Although this guidance was developed for major hazard industries, its principles are equally relevant to many LEV systems handling combustible dusts, solvent vapours or flammable gases.

Too often, hazardous area classification is viewed as a specialist electrical engineering exercise. In reality, it begins much earlier by understanding:

what hazardous substances are present;
where they may be released;
how often releases may occur;
how ventilation influences dispersion; and
whether an explosive atmosphere could reasonably develop.

Only once these questions have been answered can suitable equipment be selected.

For LEV designers, this has direct implications. Fans, motors, dampers, instrumentation and control systems serving combustible dust or flammable solvent extraction systems may all require consideration under DSEAR. The hazardous area study therefore becomes an integral part of the overall ventilation design rather than a separate compliance exercise.

Further Resources

Recommended Learning

Thought Leadership

Hazardous area classification is sometimes perceived as a specialist discipline confined to the chemical or petrochemical industries. In reality, its principles apply wherever flammable atmospheres may be created—including many industrial LEV systems.

The most important message within this guidance is that hazardous zones are not determined by the equipment installed—they are determined by the likelihood of an explosive atmosphere being present. Once the hazardous area has been correctly assessed, the appropriate engineering controls, ventilation strategy and explosion-protected equipment naturally follow.

For LEV professionals, this reinforces a fundamental engineering principle: ventilation is not simply about controlling exposure. In many applications it also plays a critical role in preventing the formation of explosive atmospheres by limiting the accumulation and dispersion of flammable gases, vapours or dusts.

Understanding this relationship is essential for designing extraction systems that are not only effective but inherently safe.