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Practical DSEAR assessments for workshops, fuel installations, warehouses and commercial environments handling dangerous substances.
A DSEAR risk assessment is required under the Dangerous Substances and Explosive Atmospheres Regulations 2002 wherever flammable gases, vapours, liquids or combustible dusts could create a fire or explosion risk. Oak Tree Rule provides DSEAR risk assessments and coordinates specialist hazardous area and compliance services through competent delivery partners where required, ensuring assessments are undertaken by appropriately qualified professionals.
Reports are written to be used — by your engineers, your insurers and your enforcing authority — not filed and forgotten.
Combining property, operational and compliance experience across large multi-site estates, Oak Tree Rule provides practical solutions focused on achieving compliance while maintaining operational efficiency.
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DSEAR Risk Assessments
Practical DSEAR assessments for workshops, fuel installations, warehouses and commercial environments handling dangerous substances.
Hazardous area classification divides a workplace into zones according to how likely an explosive atmosphere is to be present, and for how long. The zone dictates which equipment can be installed, what controls are needed and how the area must be marked. Gases, vapours and mists use Zones 0, 1 and 2; combustible dusts use Zones 20, 21 and 22.
An explosive atmosphere is present continuously, for long periods or frequently. Typically the vapour space inside a fuel or solvent tank. Only Category 1G equipment is permitted, and ignition sources must be eliminated rather than merely controlled.
An explosive atmosphere is likely to occur in normal operation occasionally. Typical examples include the area immediately around a tanker fill point, a solvent decanting station or a vent outlet. Category 2G equipment is required.
An explosive atmosphere is not likely in normal operation and, if it does occur, will persist only briefly. Often the buffer area around a Zone 1, or a well-ventilated space containing sound pipework. Category 3G equipment is acceptable.
A cloud of combustible dust is present continuously, for long periods or frequently — normally inside silos, hoppers, cyclones, filters and conveying equipment. Requires Category 1D equipment.
A dust cloud is likely occasionally in normal operation, such as around bag-tipping stations, discharge points and open transfer operations. Requires Category 2D equipment and careful housekeeping control.
A dust cloud is unlikely in normal operation and short-lived if it occurs, often where dust layers can be disturbed. Requires Category 3D equipment; layer depth and cleaning regimes are as important as the equipment rating.
Zone size is calculated from the substance's properties, the release rate and the ventilation available, using BS EN 60079-10-1 for gases and 60079-10-2 for dusts. We issue marked-up zoning drawings so the boundaries are unambiguous on site.
Once zoned, equipment suitability is checked against the ATEX category and temperature class, entry points are signed with the EX warning sign, and the classification is reviewed whenever substances, quantities, plant or ventilation change — and at least every two to three years.
Zoning is not an end in itself: the aim is to remove or reduce the zone wherever possible through substitution, containment and ventilation, then control what remains. Where a zone can be designed out, that is almost always cheaper than certifying equipment to live inside it.
Illustrative, anonymised scenarios showing how we typically approach this work. Details are representative rather than specific client records.
Fleet depot · Multi-site
Challenge: A fleet operator had inconsistent, out-of-date assessments across workshops with fuel dispensing, paint and battery charging.
Approach: One method across all sites, hazardous area classification drawings, equipment suitability checks and a shared action tracker.
Outcome: The operator gained a comparable view of risk across the estate and a prioritised plan for remedial spend.
Manufacturing · Combustible dust
Challenge: A production line generated fine combustible dust, with extraction ducting and electrical equipment not reviewed since installation.
Approach: Zone 21/22 classification, review of LEV and housekeeping, ignition-source and ATEX equipment assessment, and an Explosion Protection Document.
Outcome: Clear zone boundaries, a reduced zone footprint through better extraction, and a defined list of equipment upgrades.
Warehouse · Battery charging
Challenge: A warehouse expanded its lead-acid forklift fleet into a smaller charging bay with limited ventilation.
Approach: Hydrogen release and ventilation assessment, zoning review, signage and charging-procedure recommendations.
Outcome: The charging layout and ventilation were adjusted so the area could be managed without extending hazardous zones.
Full assessments to the 2002 Regulations and supporting ACOPs, written to be used — not filed and forgotten.
ATEX zoning review (Zone 0/1/2 and 20/21/22) where required, with clear drawings and equipment suitability guidance.
Prioritised action plans, compliance recommendations and ongoing portfolio support across multi-site estates.
Structured to the 2002 Regulations and supporting ACOPs, with a deliverable that supports both insurers and the enforcing authority.
Substance & process review
Inventories, SDS, quantities, storage and process conditions reviewed off-site first.
Site walkdown
On-site review of plant, ventilation, ignition sources and existing controls.
Hazardous area classification
Zoning review with drawings and ATEX equipment suitability assessment where required.
Risk assessment & documentation
Full DSEAR risk assessment and written explosion protection documentation.
Action plan & recommendations
Prioritised actions, control measures and compliance recommendations.
A structured deliverable that covers identification, assessment and clear next steps.
When is a DSEAR assessment legally required?
Whenever your work activity involves dangerous substances capable of causing harm from fire, explosion or similar energetic events — regardless of quantity. Even small amounts of solvents, LPG or combustible dust can trigger the duty.
How often should it be reviewed?
Reassess whenever processes, substances, quantities or the building change, and as a minimum every 2–3 years to keep zone classifications and control measures current.
Will you produce hazardous area classification drawings?
Yes — zoning drawings are issued as part of the assessment where relevant, covering Zone 0/1/2 for gases/vapours and Zone 20/21/22 for combustible dusts.
What is an Explosion Protection Document?
A written record required under DSEAR demonstrating that explosion risks have been identified, assessed and controlled. We produce this as part of the assessment deliverable.
Do you cover combustible dusts as well as flammable gases?
Yes — flour, sugar, wood, metal, plastic and chemical dusts are assessed against ATEX Zone 20/21/22 classifications alongside gases, vapours and mists.
Who needs DSEAR — only manufacturing sites?
No. Vehicle workshops, fuel storage and dispensing areas, fleet depots, warehouses, spray booths, battery charging facilities, plant rooms, manufacturing facilities and any site with flammable substances above screening thresholds all need a DSEAR assessment.
What's the penalty for non-compliance?
DSEAR is enforced by the HSE under HSWA 1974, with unlimited fines and potential custodial sentences for serious breaches. Insurers also typically require a current DSEAR assessment.
How does DSEAR interact with ATEX equipment regulations?
DSEAR (ATEX 153) covers the workplace duty; ATEX 114 / Equipment and Protective Systems Regs cover the equipment placed in hazardous areas. We review equipment suitability as part of the assessment.
Do you provide staff training?
Bespoke DSEAR awareness training for operators, maintenance teams and managers can be arranged through our delivery partners where required.
How long does a DSEAR assessment take?
Typical single-site assessments take 1–2 days on site with a draft report within 2–3 weeks. Multi-site or complex chemical processes are scoped individually.
Do EV and forklift battery charging areas need a DSEAR assessment?
Often, yes. Lead-acid batteries release hydrogen while charging, so charging rooms need ventilation assessment and may need zoning. Lithium-ion fleets bring different fire and off-gassing risks that should be reviewed in the fire and DSEAR risk assessments together.
Is a DSEAR assessment the same as a fire risk assessment?
No. A fire risk assessment under the Fire Safety Order covers general fire safety for people in the building. DSEAR specifically covers dangerous substances and explosive atmospheres from work activities. Most sites with flammable substances need both, and they should reference each other.
What information should we have ready before the visit?
Safety data sheets for substances used or stored, approximate quantities, site and plant layouts, ventilation details, existing risk assessments, and any previous zoning drawings or equipment certificates.
Can existing electrical equipment stay in a newly zoned area?
Only if it is suitable for that zone. We check equipment against the zone and gas or dust group, then recommend whether to relocate, replace with ATEX-rated equipment or reduce the zone through better ventilation or containment.
Do you assess multi-site portfolios consistently?
Yes. For fleets of depots, workshops or warehouses we use one method, one report format and one action tracker, so estates teams can compare sites and prioritise spend.
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