What Is DSEAR? The Dangerous Substances and Explosive Atmospheres Regulations Explained
DSEAR is the Dangerous Substances and Explosive Atmospheres Regulations 2002, the law in Great Britain that requires employers and the self-employed to find, assess and control the safety risks from fire, explosion and similar events caused by dangerous substances at work. It is much wider than most people assume: it does not only cover chemical plants and refineries, but bakeries, joinery workshops, garages, paint sprayers, petrol forecourts and any business storing LPG or solvents — because ordinary dusts such as flour, sugar and wood dust can explode if they form a cloud in air and meet an ignition source.
On this page
- 1What is DSEAR and what does it require employers to do?
- 2How is DSEAR different from COSHH?
- 3What counts as a dangerous substance under DSEAR?
- 4Which workplaces does DSEAR apply to?
- 5What does a DSEAR risk assessment need to cover?
- 6What are DSEAR hazardous area zones?
- 7What control and mitigation measures does DSEAR require?
- 8What is ATEX equipment and when do you need it?
- 9What arrangements does DSEAR require for accidents, incidents and emergencies?
- 10What information and training does DSEAR require?
- 11What training helps employers and staff meet DSEAR?
- 12Frequently asked questions
- Safety, not health. DSEAR covers fire, explosion and similar physical risks from dangerous substances; COSHH covers the health risks.
- Ordinary dust counts. Flour, sugar and wood dust can explode as a cloud in air, so bakeries and joinery workshops are covered.
- Assess, then record. Employers must assess the risks before work starts; those with five or more employees must record the significant findings.
- Zones and equipment. Places where explosive atmospheres may occur are zoned, and only suitable category equipment may be used there.
This guide is for employers, managers, supervisors and safety leads in England, Scotland and Wales, checked on 7 November 2026 against the regulations on legislation.gov.uk and HSE guidance. It covers the fire and explosion side of dangerous substances; the health side is a different law, COSHH, covered in our guide to what COSHH is. All examples are invented. General information, not legal advice.
What is DSEAR and what does it require employers to do?
DSEAR is Statutory Instrument 2002 No. 2776, the Dangerous Substances and Explosive Atmospheres Regulations 2002. It puts duties on employers and the self-employed to protect people from the safety risks that dangerous substances create at work, and HSE is clear that this protection extends to members of the public who may be put at risk by the work activity, not only to employees. DSEAR is goal-setting law: it does not hand you a list of approved products, it requires you to understand your own substances and processes and control what could go wrong.
In HSE’s summary, employers must find out what dangerous substances they have and what the risks are, remove or control those risks, reduce the effects of any incident, plan for emergencies, inform and train employees, classify areas where explosive atmospheres may occur, and keep ignition sources out of those areas. Each duty sits in a specific regulation:
| Regulation | What it covers |
|---|---|
| Regulation 5 | Risk assessment before work starts, kept under review, with significant findings recorded by employers of five or more |
| Regulation 6 | Eliminate or reduce risk: substitution first, then control measures, then mitigation |
| Regulation 7 | Places where explosive atmospheres may occur: zoning, suitable equipment, warning signs, verification and anti-static clothing |
| Regulation 8 | Arrangements to deal with accidents, incidents and emergencies |
| Regulation 9 | Information, instruction and training for employees |
| Regulation 10 | Identifying the hazardous contents of containers and pipes |
| Regulation 11 | Co-ordination where two or more employers share a workplace |
How is DSEAR different from COSHH?
The simplest way to remember it: COSHH is about health, DSEAR is about safety. COSHH deals with substances that make people ill through breathing, skin contact or swallowing. DSEAR deals with substances whose physical or chemical properties can cause sudden physical harm: fire, explosion, a violent release of pressure, or corrosion that weakens metal.
HSE’s own guidance makes the overlap explicit: some dangerous substances also create health risks, because they are toxic or irritant, and “these kinds of risks are covered under separate health law”. So the same tin of solvent-based paint can need two assessments — COSHH because the vapour is harmful to breathe, DSEAR because the same vapour can ignite. One does not discharge the other. Our COSHH questions and answers make the same point, and our guide to a COSHH risk assessment covers the health half. This guide stays on fire, explosion and the physical hazards DSEAR adds.
COSHH work revolves around exposure: how much gets into the body. DSEAR work revolves around a fuel, oxygen and an ignition source coming together — the fire triangle — and almost every DSEAR control keeps one side of that triangle away from the other two.
What counts as a dangerous substance under DSEAR?
The legal definition in regulation 2 has three parts. A dangerous substance is:
- a substance or mixture that meets the criteria for classification as hazardous within any physical hazard class under the CLP classification rules, whether or not it has actually been classified — flammable liquids and gases, oxidisers, explosives, gases under pressure, substances corrosive to metals and so on;
- any other substance or mixture that, because of its physico-chemical or chemical properties and the way it is used or present in the workplace, creates a risk — for example, a liquid that is not classed as flammable but is heated above its flashpoint in a process; or
- any dust, whether solid particles or fibres, that can form an explosive mixture with air or an explosive atmosphere.
That third limb is the one that surprises people. A bag of flour on a shelf will not explode; the same flour thrown into a fine cloud inside a mixer, sieve, silo or extraction filter, meeting a spark, hot surface or static discharge, can. HSE’s food industry guidance lists flour, custard powder, instant coffee, sugar, dried milk, potato powder and soup powder among the explosible dusts found in food businesses, and its woodworking guidance is blunt: “Wood dust can cause fire and explosion.” HSE gives the minimum explosible concentration for fine “wood flour” as 60 grams per cubic metre — a cloud it likens to dense fog.
Changes in force from 1 June 2015 widened the scope further. Aligning DSEAR with the CLP Regulation raised the upper flashpoint for a flammable liquid to 60°C, so liquids such as diesel, gas oil and light heating oils now count as flammable, although HSE notes many may not normally present a significant fire risk as stored. DSEAR also now covers gases under pressure and substances corrosive to metals. The supplier’s safety data sheet is the place to start spotting all of these.
Which workplaces does DSEAR apply to?
Far more than chemical works. HSE says dangerous substances “can be found in nearly all workplaces” and gives solvents, paints, varnishes, flammable gases such as LPG, dusts from machining and sanding, dusts from foodstuffs, pressurised gases and substances corrosive to metal as examples. If any of those are used, stored, produced or delivered on your premises, DSEAR applies to you, even if the quantities are small — although, as later sections explain, small quantities and low risk mean the measures you need can be proportionately simple.
| Workplace | Typical DSEAR hazard |
|---|---|
| Petrol filling stations and sites storing petrol | Flammable vapour from tanks, dispensers and tanker deliveries |
| Vehicle body shops and paint spraying | Solvent vapour and paint mist in booths and mixing rooms |
| Bakeries, mills and food manufacturers | Flour, sugar and other food dust clouds in mixers, sieves, silos and filters |
| Joinery, furniture making and sawmills | Fine wood dust in extraction systems, filters and on surfaces |
| Engineering and maintenance workshops | Degreasing solvents, aerosols, welding gases such as acetylene, metal dusts |
| Kitchens, sites and warehouses using LPG | LPG cylinders for cooking, heaters and gas-powered forklift trucks |
| Landfill sites and wastewater works | Naturally occurring flammable gases such as methane |
HSE’s own examples also include storing petrol for boats or horticultural machinery and road-tanker deliveries of bulk powders. Petrol forecourts sit under an extra layer: the Petroleum (Consolidation) Regulations 2014 require premises that store and dispense petrol to hold a storage certificate from the local petroleum enforcement authority, alongside their DSEAR duties.
DSEAR is about work activities, not domestic use at home, and HSE notes that some of its explosive-atmosphere requirements do not apply in industries such as offshore oil and gas production. For almost every onshore business, assume DSEAR applies until a proper look at your substances shows otherwise. If you store flammable liquids, our guide to storing hazardous chemicals at work covers cabinets, bunds and workroom quantities in detail.
What does a DSEAR risk assessment need to cover?
Regulation 5 requires every employer to make a “suitable and sufficient” assessment of the risks to employees wherever a dangerous substance is, or may be, present at work. It must consider:
- each substance’s hazardous properties and the supplier’s safety information, including the safety data sheet;
- the circumstances of the work — processes, quantities, combinations of substances, and handling, storage, transport and waste;
- activities, such as maintenance, where the risk could be high;
- the likelihood that an explosive atmosphere will occur, and how long it will persist;
- the likelihood that ignition sources, including electrostatic discharges, will be present and become active;
- the likely scale of a fire or explosion, and places connected by openings to places where explosive atmospheres may occur.
Three further rules matter. No new work activity involving a dangerous substance may start until the assessment is done and its measures are in place. The assessment must be reviewed regularly and after any significant change, such as a new product, machine or layout. And an employer with five or more employees must record the significant findings, including — where an explosive atmosphere may occur — the zone classification, the equipment needed, the verification of explosion safety and any co-ordination with other employers.
HSE describes DSEAR as complementing the general risk assessment duty under the Management of Health and Safety at Work Regulations. What matters is that the explosion questions above are answered by someone who understands them. For a bakery with one mixer and bagged flour, a competent manager using HSE guidance may manage it; for flammable liquid processes, large dust-handling plant or bulk storage, a specialist assessor is usually the sensible route.
What are DSEAR hazardous area zones?
Where an explosive atmosphere may occur, regulation 7 requires the employer to classify those places as hazardous or non-hazardous, and then to divide the hazardous places into zones. Schedule 2 sets out the zones, which are graded by how often an explosive atmosphere is present and how long it lasts. There are three zones for gases, vapours and mists, and three matching zones for dust clouds:
| Gas, vapour or mist | Dust cloud | What it means in plain English |
|---|---|---|
| Zone 0 | Zone 20 | An explosive atmosphere is present continuously, for long periods or frequently |
| Zone 1 | Zone 21 | An explosive atmosphere is likely to occur occasionally in normal operation |
| Zone 2 | Zone 22 | An explosive atmosphere is not likely in normal operation and, if it does occur, will only persist for a short time |
Read it this way: the lower the number within each family, the more often the dangerous atmosphere is there, and the stricter the controls on anything that could ignite it. The inside of a closed vessel holding vapour or a dust cloud for long periods is the kind of place that tends to be Zone 0 or 20; the area around an opening where vapour or dust escapes now and then, Zone 1 or 21; a wider area that would only see an explosive atmosphere after a leak or a split bag, Zone 2 or 22. These are illustrations, not a classification: real boundaries depend on the substance, ventilation and process, and should be set by a competent person.
Two notes in Schedule 2 are easy to miss. “Normal operation” means installations used within their design parameters. And layers, deposits and heaps of combustible dust must be treated like any other source that can form an explosive atmosphere, because settled dust can be disturbed into a cloud. That is why HSE’s food dust guidance tells employers to “maintain scrupulous cleanliness” and to avoid sweeping brushes and compressed air in dusty areas.
Where necessary, entry points to hazardous places must carry the Schedule 4 warning sign — a yellow triangle with a black edge, which HSE calls the “EX” sign. Before a workplace with hazardous places is first used, its overall explosion safety must be verified by a person competent in explosion protection. Employers must also provide work clothing that does not cause electrostatic discharges for people working there.
What control and mitigation measures does DSEAR require?
Regulation 6 sets an order of priority, applied so far as is reasonably practicable. The first duty is to eliminate or reduce the risk, preferably by substitution: a water-based paint instead of a solvent-based one, a non-flammable degreaser, or a ready-mixed product instead of mixing powders on site.
Where elimination is not reasonably practicable, regulation 6(4) lists control measures in order of priority:
- reduce quantities to a minimum — only what the job or shift needs in the workroom;
- avoid or minimise releases — sealed containers, closed transfer, lids on mixers;
- control releases at source — extraction hoods, spray booths;
- prevent an explosive atmosphere forming, including by ventilation;
- collect, contain or remove any release to a safe place;
- avoid ignition sources, including electrostatic discharges; and
- segregate incompatible dangerous substances.
The employer must also apply mitigation measures under regulation 6(5) to limit harm if a fire or explosion happens: fewer employees exposed, measures to stop fires and explosions spreading, explosion relief and suppression, plant built to withstand explosion pressure, and suitable personal protective equipment. Regulation 6 further requires safe handling, storage and transport, and the general safety measures in Schedule 1. Those include appropriate systems of work: written instructions, and a permit to work system, with permits issued by a responsible person before the work starts, for work carried out in hazardous places or involving hazardous activities.
In a small bakery that might mean flour tipped gently into a lidded mixer under extraction, dust removed with a suitable vacuum rather than swept, and the dust filter maintained to a schedule. In a garage, it might mean a day’s supply of solvent in the workshop with the rest in a fire-resisting cabinet, spraying only in the booth, and hot work controlled by a permit and kept away from the booth. Nothing exotic — but it depends on staff understanding why the rules exist.
What is ATEX equipment and when do you need it?
ATEX is the shorthand, taken from the French “atmosphères explosibles”, for two European directives on explosive atmospheres. In Great Britain, HSE explains, the workplace directive is implemented by DSEAR and the equipment directive by the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 2016, under which certified equipment carries the conformity mark and the “Ex” symbol.
For employers, the practical rule is in Schedule 3 of DSEAR, which links each zone to the category of equipment that may be used in it, unless the risk assessment finds otherwise:
| Zone | Equipment that may be used |
|---|---|
| Zone 0 or Zone 20 | Category 1 equipment |
| Zone 1 or Zone 21 | Category 1 or 2 equipment |
| Zone 2 or Zone 22 | Category 1, 2 or 3 equipment |
The equipment must also be suitable for gases, vapours, mists or dusts, as appropriate: a light fitting certified for a gas atmosphere is not automatically suitable for a dust zone. That is why an ordinary extension lead, vacuum cleaner, battery tool or heater can be a serious problem in the wrong place: safe in an office, it becomes exactly the ignition source DSEAR is trying to keep out of a paint mixing room or the area around a flour sieve. Our guide to whether lithium-ion batteries are a fire risk at work covers the separate hazard of battery devices and charging.
The habits that follow need training to stick: know where the zone boundaries are, take only suitably rated equipment across them, report damaged equipment in a zone straight away, and never assume a tool is suitable because it “has always been used there”. Maintenance inside a zone is one of the higher-risk activities regulation 5 expects the assessment to address.
What arrangements does DSEAR require for accidents, incidents and emergencies?
Regulation 8 requires employers to plan in advance for something going wrong. The arrangements must include procedures, first-aid facilities and safety drills tested at regular intervals; information on the hazards likely in an emergency; warning and communication systems that allow an immediate response and rescue; where necessary, warnings so employees can be withdrawn before explosion conditions are reached; and, where the assessment shows they are needed, escape facilities so people can leave “promptly and safely”.
That information must be made available to the emergency services and displayed at the workplace unless the assessment shows that is unnecessary. If an event happens, the employer must act immediately to mitigate it, restore normal conditions and inform affected employees; only people essential to repairs may enter the affected area, with suitable protective equipment.
There is a proportionate exemption: these arrangements are not required where the assessment shows that, because of the quantity of each substance present, there is only a slight risk to employees and the regulation 6 measures are sufficient to control it. A small office with a few aerosol cans would usually fall here; a bakery with a flour silo would not. Join the DSEAR arrangements up with your fire risk assessment so that one evacuation plan works for every scenario.
Where two or more employers share a workplace in which an explosive atmosphere may occur, regulation 11 requires the employer responsible for the workplace to co-ordinate all the DSEAR measures — in practice, telling contractors where the zones are, what equipment they can bring in and what the emergency arrangements are before they start.
What information and training does DSEAR require?
Regulation 9 applies wherever a dangerous substance is present. Employers must give employees suitable and sufficient information, instruction and training on the precautions needed to safeguard themselves and others, including the names and risks of the substances, access to safety data sheets, and the significant findings of the risk assessment. It must be updated when the work or working methods change significantly, in a way proportionate to the risk.
Regulation 10 adds that where containers and pipes are not already labelled under the relevant marking legislation, their contents and hazards must still be clearly identifiable. Unlabelled decanted solvents and unmarked drums undermine training, because people cannot avoid a hazard they cannot identify.
Good DSEAR training covers why dust and vapour can explode, what your own zones mean, which equipment can go into them, the controls each person owns — housekeeping, lids on, reporting leaks — and what to do in an emergency. Awareness training is the foundation, not the whole answer. It is not a regulated qualification, it does not make anyone competent to classify zones or verify explosion safety, and it does not replace site-specific instruction on your own substances, procedures and plant.
What training helps employers and staff meet DSEAR?
Three Nexis CPD courses build the knowledge behind this guide:
Together they cost £18 rather than £27 under the pay-for-2-get-3 offer, and employers training 5 or more staff pay £6 a course place on the team plan. These are awareness-level CPD courses, not regulated qualifications, and they do not replace a competent DSEAR risk assessment, hazardous area classification by a specialist, or site-specific training on your own substances and procedures. If you take one, start with DSEAR Awareness: 20 questions, 80% to pass, and an instant certificate.
DSEAR Awareness: Dangerous Substances and Explosive Atmospheres
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Frequently asked questions
What does DSEAR stand for?
DSEAR stands for the Dangerous Substances and Explosive Atmospheres Regulations 2002 (SI 2002/2776). They require employers and the self-employed in Great Britain to assess and control the safety risks from fire, explosion and similar events caused by dangerous substances at work, and since 2015 also from gases under pressure and substances corrosive to metals.
What is the difference between DSEAR and COSHH?
COSHH covers the health risks of hazardous substances, such as toxic fumes or dusts that damage the lungs. DSEAR covers the safety risks, such as fire and explosion. The same substance, for example a solvent that is both harmful and flammable, can need both assessments, and one does not discharge the other.
Can flour or wood dust really explode?
Yes. DSEAR treats any dust that can form an explosive mixture with air as a dangerous substance. HSE lists flour, sugar, custard powder, instant coffee and dried milk among explosible food dusts, and says wood dust can cause fire and explosion. A dust cloud within its explosive limits needs only an ignition source of enough energy.
Do small businesses need a DSEAR risk assessment?
Yes, if a dangerous substance is or may be present at work, the employer must assess the risks under regulation 5. Employers with five or more employees must record the significant findings. For small quantities and low risk the assessment and controls can be simple, but they still need to be done.
What are DSEAR zones 0, 1 and 2?
They classify places where a gas, vapour or mist explosive atmosphere may occur. Zone 0 means it is present continuously, for long periods or frequently; Zone 1 means it is likely occasionally in normal operation; Zone 2 means it is unlikely in normal operation and short-lived if it occurs. Zones 20, 21 and 22 are the equivalents for dust clouds.
Is DSEAR awareness training a legal qualification?
No. Awareness CPD helps staff understand dangerous substances, zones and controls, but it is not a regulated qualification. It does not make someone competent to classify hazardous areas or verify explosion safety, and it does not replace site-specific instruction on the employer’s own substances, procedures and plant.
General information, not legal advice. This guide reflects the Dangerous Substances and Explosive Atmospheres Regulations 2002 (regulations 2 and 5 to 11, and Schedules 1 to 4), the Petroleum (Consolidation) Regulations 2014, and HSE guidance on DSEAR, ATEX and combustible dusts, as checked on 7 November 2026. It applies to England, Scotland and Wales; Northern Ireland has its own equivalent regulations. Nexis CPD courses are CPD-accredited awareness training, not regulated qualifications, and they do not replace a competent DSEAR risk assessment, specialist advice or an employer’s own procedures and site-specific training.