Dangerous substances
Properties relevant to safety: flammability, flash point, vapour characteristics, gas behaviour, dust explosibility information, storage conditions and quantities.
Dangerous substances • fire • explosion • zoning
DSEAR Risk Assessments
Assessment of dangerous substances, release scenarios, ignition sources, existing precautions, explosive-atmosphere risk and emergency arrangements under the Dangerous Substances and Explosive Atmospheres Regulations 2002.
DSEAR in plain English
Where can a dangerous atmosphere form, what could ignite it, and are the controls sufficient?
DSEAR applies to safety risks from dangerous substances at work. The assessment starts with the substances and the way they are actually stored, transferred, mixed, heated, sprayed, charged, extracted or generated. It then examines credible releases, ignition sources and the effectiveness of measures used to eliminate or reduce risk.
The level of detail should be proportionate. A small workplace handling limited quantities may need a straightforward documented assessment. A process involving multiple release sources, ventilation dependencies, flammable vapours or combustible dust can require a much more detailed technical evaluation.
Key distinction: DSEAR is the overall assessment of fire and explosion risks from dangerous substances. Hazardous area classification is one part of that process where explosive atmospheres may occur and zones are needed.
What is assessed
The DSEAR assessment structure
Release scenarios
Normal and foreseeable releases from containers, vents, connections, charging, transfer, leaks, cleaning, maintenance and process upset.
Ventilation
Natural or mechanical ventilation, enclosure, dilution, air movement, extraction and the effect of ventilation reliability on accumulation.
Ignition sources
Electrical equipment, hot surfaces, flames, hot work, static electricity, mechanical sparks, vehicles, smoking, heaters and other credible sources.
Controls & mitigation
Elimination/substitution, containment, ventilation, separation, ignition control, equipment suitability, housekeeping, procedures, inspection and maintenance.
Emergency arrangements
Detection, isolation, shutdown, spill response, fire precautions, evacuation, information, instruction and arrangements for foreseeable incidents.
Substances & processes
Examples of situations that can require DSEAR consideration
Flammable gases and vapours
- LPG and propane/butane systems
- Natural gas installations and process use
- Solvents, thinners, paints and coatings
- Fuel storage and transfer
- Spray booths and mixing areas
- Aerosols and flammable cleaners
Combustible dusts and energetic materials
- Woodworking and MDF dust
- Food and ingredient powders
- Metal dusts where relevant
- Dust extraction systems and collectors
- Powder transfer and handling
- Waste or residues capable of forming explosible dust clouds
Assessment process
From substance inventory to action plan
Define the process
Identify substances, activities, operating modes, plant, storage and maintenance tasks that could create fire or explosion risk.
Identify releases
Establish where dangerous substances could be released, the likely state of release and the conditions affecting dispersion or accumulation.
Assess ignition
Map credible ignition sources against locations and operating activities, including maintenance and abnormal but foreseeable conditions.
Classify if required
Where explosive atmospheres may occur, identify and classify hazardous places and document the basis for zones and extents.
Evaluate safeguards
Assess elimination, containment, ventilation, separation, equipment suitability, maintenance, procedures and emergency measures.
Prioritise actions
Produce a clear action register so higher-consequence or weak-control issues are addressed before lower-priority improvements.
Deliverable
What the report can include
- Scope and premises/process description
- Dangerous substance register or assessment table
- Credible release scenarios
- Ignition-source assessment
- Existing control measures
- Fire and explosion risk evaluation
- Hazardous area classification where required
- Zoning drawings or marked plans where within scope
- Equipment/ignition-control observations where relevant
- Emergency and management arrangements
- Prioritised action plan and review triggers
Typical DSEAR sectors
Vehicle workshopsSpray & coatingsJoineryManufacturingMarineAgricultureFuel storageWarehousingLaundriesBreweriesPlant roomsConstruction support
Technical references
Regulations and HSE guidance
Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) — including risk assessment, elimination/reduction of risk, hazardous places, emergency arrangements, information/training and co-operation duties.
HSE L138 — Approved Code of Practice and guidance on DSEAR. HSE guidance emphasises that all employers must assess relevant risks, while the amount of recorded detail should be proportionate to the hazards and risks present.
Authoritative sources: HSE DSEAR • HSE L138 • DSEAR 2002 legislation.
DSEAR FAQ
Common questions
What is DSEAR?
DSEAR is the Dangerous Substances and Explosive Atmospheres Regulations 2002. It requires employers and relevant dutyholders to assess and control safety risks from dangerous substances that could cause fire, explosion or similar energetic events.
Does every dangerous substance mean a complex DSEAR report is required?
No. The assessment should be proportionate to the risk. Some workplaces have limited quantities and simple controls; others require detailed release assessment, ventilation consideration, hazardous area classification and equipment review.
Does DSEAR only apply to gases and solvents?
No. It can apply to flammable gases, flammable liquids and vapours, combustible dusts, some aerosols and other substances capable of creating fire or explosion risk under workplace conditions.
Is hazardous area classification part of DSEAR?
It can be. Where explosive atmospheres may occur in quantities requiring special precautions, places must be identified and classified into zones according to the likelihood and persistence of the explosive atmosphere.
Can DSEAR and fire risk assessment findings overlap?
Yes. Dangerous substances can affect fire loading, ignition control, emergency arrangements, storage and means of escape. Where both assessments are required they should be consistent.
Page reviewed: 25 September 2026.
Need a DSEAR assessment?
Send the site location and a brief description of the substances, quantities and processes involved. Safety Data Sheets, photographs, plans and equipment information are helpful at quotation stage where available.