DSEAR 2002 — Dangerous Substances and Explosive Atmospheres: Full Guide

The Dangerous Substances and Explosive Atmospheres Regulations 2002 (SI 2002/2776), known as DSEAR, implement two European Directives into UK law: Directive 1999/92/EC (the ATEX Users Directive, minimum requirements for improving safety and health protection of workers potentially at risk from explosive atmospheres) and elements of Directive 98/24/EC (the Chemical Agents Directive). DSEAR applies to virtually all workplaces where dangerous substances — defined as any substance or preparation that, by virtue of its flammable, explosive, oxidising, or similar properties, creates a risk — are present. This guide provides a complete technical reference for employers, safety managers, and compliance officers.

Scope and Definitions

A dangerous substance under Regulation 2 includes: any substance or preparation classified as explosive, oxidising, extremely flammable, highly flammable, or flammable under the Chemicals (Hazard Information and Packaging for Supply) Regulations (CHIP); any substance that creates a comparable hazard through its physical or chemical properties; and dust of any kind where it may form an explosive atmosphere. DSEAR does not apply to substances that are dangerous solely by reason of their toxic, harmful, corrosive, or irritant properties — those are governed by COSHH.

An explosive atmosphere means a mixture, under atmospheric conditions, of air and one or more dangerous substances in the form of gases, vapours, mists, or dusts in which, after ignition has occurred, combustion spreads to the entire unburned mixture.

Regulation 5 — Risk Assessment

Regulation 5 is the cornerstone duty. Before work begins with any dangerous substance, the employer must carry out a suitable and sufficient assessment of the risk to employees from fire, explosion, or other energetic events. The assessment must consider:

• The hazardous properties of the dangerous substances present (flash point, auto-ignition temperature, explosive limits, vapour density)
• The quantities of dangerous substances present and their physical state
• The work activities involving dangerous substances
• The processes and operational conditions including temperatures and pressures
• The likelihood that explosive atmospheres will form and their persistence
• The likelihood that ignition sources — including electrostatic discharges, hot surfaces, open flames, and mechanical sparks — will be present
• The scale of anticipated effects of a fire or explosion
• Any places connected by openings to areas with explosive atmospheres

Where five or more employees are employed, the significant findings of the assessment must be recorded. The assessment must be reviewed whenever there is reason to believe it is no longer valid, or following a fire, explosion, or near miss.

ATEX Zone Classification

A critical output of the DSEAR risk assessment is the classification of locations where explosive atmospheres may form into hazardous zones. Zone classification drives equipment selection and forms the basis for the safety case. The classification system distinguishes between gas/vapour/mist atmospheres and dust atmospheres:

Zone	Type	Definition	Typical Examples	Required Equipment Category
Zone 0	Gas/Vapour/Mist	Explosive atmosphere present continuously, for long periods, or frequently	Interior of fuel storage tanks, inside solvent vessels, spray booths in continuous use	Category 1 (Group II) only
Zone 1	Gas/Vapour/Mist	Explosive atmosphere likely to occur in normal operation occasionally	Immediate vicinity of fuel filling points, areas around pump seals, loading/unloading bays for flammable liquids	Category 1 or 2 (Group II)
Zone 2	Gas/Vapour/Mist	Explosive atmosphere not likely to occur in normal operation, but may in abnormal conditions for short periods	Perimeter of Zone 1 areas, storage rooms for flammable liquids with adequate ventilation	Category 1, 2, or 3 (Group II)
Zone 20	Dust	Explosive dust cloud present continuously, for long periods, or frequently	Inside hoppers, silos, cyclones, filter units handling combustible dusts	Category 1 (Group III) only
Zone 21	Dust	Explosive dust cloud likely to occur in normal operation occasionally	Immediate vicinity of powder filling points, bag emptying stations, dust extraction systems	Category 1 or 2 (Group III)
Zone 22	Dust	Explosive dust cloud not likely to occur in normal operation, but may in abnormal conditions for short periods	Areas near dust handling plant where leaks may create dust clouds; bag storage areas	Category 1, 2, or 3 (Group III)

Regulation 7 — Measures to Eliminate or Reduce Risk

Regulation 7 requires that where a DSEAR risk assessment identifies risks from dangerous substances, the employer must apply the following hierarchy of measures:

1. Eliminate the dangerous substance or substitute with a substance that does not create a risk (or creates a lesser risk)
2. Reduce quantities of dangerous substances to a minimum
3. Avoid or minimise release through process design, engineering controls (enclosures, extraction)
4. Control releases at source through venting, absorption, suppression
5. Prevent formation of explosive atmospheres — adequate ventilation to maintain concentrations below 25% of the lower explosive limit (LEL)
6. Collect, contain, and remove any releases — using appropriate flammable liquid spill kits and non-sparking absorbents
7. Avoid ignition sources — using intrinsically safe equipment, anti-static measures, hot work permit systems
8. Mitigate detrimental effects — explosion relief panels, suppression systems, blast barriers

Equipment Selection by ATEX Zone

The ATEX Equipment Directive (Directive 2014/34/EU, as retained in UK law through the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 2016, SI 2016/1107) requires that electrical and non-electrical equipment used in hazardous zones carries the appropriate ATEX marking:

• Category 1 equipment (Ex marking with suffix): suitable for use in Zones 0, 1, 2 (gases) or Zones 20, 21, 22 (dusts); provides very high level of protection; must remain safe even in rare malfunctions
• Category 2 equipment: suitable for Zones 1, 2 (gases) or Zones 21, 22 (dusts); high level of protection; safe under normal and frequently occurring disturbances
• Category 3 equipment: suitable for Zone 2 (gases) or Zone 22 (dusts) only; normal level of protection; safe under normal operating conditions

Interaction with COSHH Regulation 7

Where a substance presents both health risks (governed by COSHH) and fire/explosion risks (governed by DSEAR), the two regulatory regimes must be read together. Regulation 7 of COSHH requires that employers prevent or adequately control exposure; however, where DSEAR also applies to the same substance, the measures adopted must satisfy both regulatory regimes simultaneously. The HSE guidance makes clear that DSEAR takes precedence for fire and explosion risk management — the DSEAR hierarchy of controls applies to ignition source elimination and explosive atmosphere prevention, while COSHH controls govern inhalation, skin contact, and other health exposure routes. Employers conducting a combined COSHH/DSEAR assessment should document both risk pathways and ensure control measures address each independently.

Regulation 13 — Emergency Procedures

Where the DSEAR risk assessment reveals risk from dangerous substances, Regulation 13 requires that emergency procedures are drawn up, covering accidents, incidents, and emergencies. This includes: alarm and warning systems; emergency shutdown procedures; safe escape routes and assembly points; first aid arrangements; firefighting procedures and equipment; contact details for the fire service and other emergency responders. Emergency drills must be conducted at regular intervals. All employees must be briefed on emergency procedures before they commence work involving dangerous substances. Intrinsically safe spill response equipment and non-sparking containment systems are essential in DSEAR-designated workplaces.

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Last reviewed: April 2026