Guidance · Reviewed August 2026
What DSEAR stands for, what counts as a dangerous substance, how hazardous area zoning works, and where DSEAR sits alongside COSHH and fire safety law.
The short answer
DSEAR stands for the Dangerous Substances and Explosive Atmospheres Regulations 2002. They require employers to control risks to safety from fire, explosion and corrosion of metal — and, where an explosive atmosphere can form, to classify the area into zones and select equipment to match. Since 2015 the scope also covers gases under pressure.
What Does DSEAR Stand For?
The Dangerous Substances and Explosive Atmospheres Regulations 2002. They are made under the Health and Safety at Work Act 1974 and apply wherever a dangerous substance is used, stored, handled, manufactured, disposed of — or generated by a work process.
That last part catches people out. DSEAR does not only cover what you buy in. Wood dust from a saw, flour dust in a bakery, and hydrogen released while charging batteries in a warehouse are all dangerous substances generated by ordinary work.
The scope widened in 2015
From 1 June 2015, DSEAR also covers substances corrosive to metals and gases under pressure. Employers must assess the risks from substances classified for those properties and put suitable control and mitigation measures in place. Guidance written before that date describes a narrower scope than the Regulations now have. Separately, from April 2015 mines are no longer exempt from regulations 5(4)(c), 7 and 11.
Where DSEAR Sits
This is the most useful thing to get straight, because three regimes overlap and each covers something the others do not.
| Regime | Covers |
|---|---|
| DSEAR | Fire, explosion and energetic events from dangerous substances. The physical hazard. |
| COSHH | Harm to health from hazardous substances. COSHH explicitly excludes substances that are hazardous only because they are flammable or explosive — that gap is DSEAR. |
| Fire Safety Order | General fire precautions — detection, alarm, means of escape, evacuation. Enforced by the fire and rescue authority. |
A site handling solvents needs all three, and they are usually enforced by different bodies: general fire safety by the fire and rescue authority, DSEAR by HSE or the local authority. A fire risk assessment does not discharge the DSEAR duty, and a COSHH assessment does not either. That is the single most common misunderstanding on this subject.
What Counts as a Dangerous Substance?
Anything present at work that could cause harm through fire, explosion or a similar energetic event. In practice:
Flammable liquids and vapours
Solvents, paints, thinners, adhesives, fuels. The vapour is the hazard, not the liquid — flash point and evaporation rate decide how far it travels before finding an ignition source.
Flammable gases
LPG, acetylene, natural gas, hydrogen. Including hydrogen given off during battery charging, which is routinely missed in warehouses and workshops.
Combustible dusts
Wood, flour, sugar, grain, animal feed, metal powders, plastics, coal. Generated by milling, grinding, conveying, bagging and sanding — and by the settled layers those processes leave behind.
Oxidising substances and mists
Materials that intensify fire in others. Mists too — a flammable liquid sprayed as a fine mist can ignite well below its flash point.
Gases under pressure
Compressed, liquefied and dissolved gases. Brought into scope by the 2015 amendment, and easy to overlook where the gas itself is inert.
Substances corrosive to metals
Also added in 2015. The concern is structural — corrosion of pipework, vessels and containment leading to release or failure.
Hazardous Area Classification and Zones
Where an explosive atmosphere can form, DSEAR requires the area to be classified into zones based on how likely it is that the atmosphere is present and for how long. Six zones: three for gases, vapours and mists, and three for combustible dust on the same scale.
| Gas / vapour | Dust | Explosive atmosphere is… |
|---|---|---|
| Zone 0 | Zone 20 | Present continuously, or for long periods, or frequently. |
| Zone 1 | Zone 21 | Likely to occur occasionally in normal operation. |
| Zone 2 | Zone 22 | Not likely in normal operation, and if it does occur, only briefly. |
DSEAR was the first UK legislation to impose a specific legal requirement to carry out a hazardous area study and document the conclusions as zones. The starting point is identifying sources of release — from constant activities, from normal operation, or from unplanned events — then working out how far the resulting atmosphere would extend given ventilation, temperature and pressure.
Zoning for dust follows the same method as for gases, substituting dust-air mixtures for gas atmospheres. But the physics differ enough to matter: dust turns on particle size, dispersion and the depth of settled layers, where gas and vapour turn on flash point, evaporation rate and how far a release travels. A site doing both needs both assessed.
The zone decides the equipment
Once an area is zoned, any equipment used in it must be selected so it cannot become an ignition source — which in practice means ATEX-certified equipment rated for that zone. This is where classification stops being paperwork: get the zone wrong and you have specified the wrong kit for the space.
What Employers Must Do
STEP 1
Identify the dangerous substances
Everything present, used, produced or generated — including by-products of the process. Safety data sheets cover what you buy in; the dust from your own machinery will not appear on any of them.
STEP 2
Assess the risk
A DSEAR risk assessment covering release scenarios, ignition sources, the likelihood of an explosive atmosphere forming, and the consequences if it ignites. This sits alongside your general risk assessment, not inside it.
STEP 3
Eliminate or reduce
Substitute for something less hazardous, use less of it, contain the process, extract at source, control ignition sources, and keep dust from accumulating. Elimination first — every step below it is managing a hazard you decided to keep.
STEP 4
Classify and equip
Zone the areas where an explosive atmosphere may occur, mark them, and select equipment certified for the zone.
STEP 5
Plan for emergencies and train
Procedures, drills and equipment for dealing with an incident, plus information and training for anyone working with or near dangerous substances.
STEP 6
Record it
DSEAR requires the findings of the assessment to be recorded. In practice that record draws together the substance inventory, the hazardous area classification, the equipment register, the maintenance regime, emergency arrangements and training records. It is widely referred to as an Explosion Protection Document, a term that comes from the European Explosive Atmospheres Directive rather than from DSEAR itself — so do not be thrown if a consultant uses one name and an inspector the other.
Reviewing the Assessment
The assessment must be reviewed and revised if it is no longer valid, or where there has been a significant change — a new dangerous substance, a change to the process, new equipment, a change to the workplace, or following a fire, explosion or near miss.
There is no fixed interval, but a periodic review is worth having as a backstop. Processes drift, and the assessment written for the original layout stops describing the site fairly quickly.
Training
| If your process involves… | Usual route |
|---|---|
| Combustible dust | DSEAR Dust Explosion Risk Assessment — milling, grinding, conveying, bagging, or anything that disturbs settled dust. |
| Flammable gases or liquids | DSEAR Gas and Liquid Explosion Risk Assessment — solvent handling, drum filling, gas storage, breaking into lines. |
| Both | Both courses. A coatings plant with a powder line has two different physics problems, not one. |
| Wider fire safety duties | Fire safety training courses, which sit alongside DSEAR rather than replacing it. |
Frequently Asked Questions
What does DSEAR stand for?
The Dangerous Substances and Explosive Atmospheres Regulations 2002.
Does a fire risk assessment cover DSEAR?
No. A fire risk assessment under the Fire Safety Order deals with general fire precautions — ignition sources, means of escape, detection, alarm and firefighting equipment. DSEAR requires a separate assessment of explosion risk, together with hazardous area classification, zoning and equipment selected to match the zone. A site handling solvents or generating combustible dust needs both, and they are often enforced by different authorities.
Isn’t this covered by COSHH?
No, and the two are deliberately complementary. COSHH covers substances hazardous to health and explicitly excludes those that are dangerous only because they are flammable or explosive. DSEAR fills that gap. The same solvent can require a COSHH assessment for what the vapour does to lungs and a DSEAR assessment for what it does when it meets a spark.
What are the DSEAR zones?
Six, based on how often and how long an explosive atmosphere is likely to be present. Zones 0, 1 and 2 cover gases, vapours and mists — continuously or frequently, occasionally in normal operation, and rarely and briefly. Zones 20, 21 and 22 cover combustible dust on the same scale.
Does DSEAR apply to a small workshop?
It applies wherever a dangerous substance is present, whatever the size of the business. A joinery shop generating wood dust, a garage storing fuels and solvents, or a bakery handling flour all fall within it. What varies is the scale of what compliance looks like — a small workshop is not expected to produce the same documentation as a chemical plant.
What is an Explosion Protection Document?
The written record DSEAR requires. It pulls together the inventory of dangerous substances, the hazardous area classification and zone drawings, the equipment register, the maintenance regime, emergency arrangements and training records — the evidence that the assessment was done and acted on.
Related Guidance
COSHH →
Dust in the workplace →
Risk assessment →
Fire safety training →
All guidance topics →
General guidance only, reviewed against HSE guidance INDG370 and ACOP L138, and the Dangerous Substances and Explosive Atmospheres Regulations 2002 as amended, in August 2026. Hazardous area classification should be carried out by a competent person. Envico is an independent training intermediary and is not affiliated with the HSE.