About dangerous substances

Fires and explosive atmospheres can be caused by work which involves storage, use or creation of flammable substances including gases, mists, or vapours or by combustible dusts.

If there is enough of a substance, mixed with air, then all it needs is a source of ignition to cause an explosion.

The effects of an explosion or a fire in the workplace can be devastating in terms of lives lost, injuries, significant damage to property and the environment, and to the business community.

Most fires are preventable, and dealing with workplace fire safety is important. Those responsible for workplaces and other non-domestic premises to which the public have access can avoid them by taking responsibility for, and adopting, fire safe behaviours and procedures.

Our website has more detailed information on explosives and similar substances. You can also find guidance on gas safety.

What you have to do

To help prevent accidental fires or explosions, you first need to identify:

  • what substances, materials, processes have the potential to cause such an event, that is, substances that burn or can explode and what might set them alight
  • the people who may be at risk/harmed

Once you have identified the risks, you should consider what measures are needed to reduce or remove the risk of people being harmed. This will include measures to prevent these incidents happening in the first place, as well as precautions that will protect people from harm if there is a fire or explosion.

  • Think about the risks of fire and explosions from the substances you use or create in your business and consider how you might remove or reduce the risks
  • Use supplier safety data sheets as a source of information about which substances might be flammable
  • Consider reducing the amount of flammable/explosive substances you store on site
  • Keep sources of ignition (for example naked flames, sparks) and substances that burn (for example vapour, dusts) apart
  • Get rid of flammable/explosive substances safely
  • Review your risk assessment regularly
  • Maintain good housekeeping, for example avoid build-up of rubbish, dust or grease that could start a fire or make one worse

You also need to consider the presence of dangerous substances that can result in fires or explosions as part of your fire safety risk assessment. This is required under the Regulatory Reform (Fire Safety) Order (in England and Wales) and under Part 3 of the Fire (Scotland) Act.

Enforcement responsibility for fire safety where dangerous substances are kept and used generally lies with HSE (or local authorities if they inspect the premises).

The Fire and Rescue Authorities deal with general fire safety matters in workplaces apart from on construction sites including shipbuilding, where these are dealt with by HSE or its agents.

The hazards

Many substances found in the workplace can cause fires or explosions. These range from:

  • the obvious, for example:
    • petrol
    • cellulose paint thinners
    • welding gases
    • other flammable chemicals
  • to the less obvious, for example:
    • engine oil
    • grease
    • dusts from wood
    • flour and sugar

It is important to be aware of the risks and to control or get rid of them to prevent accidents.


Liquids (such as petrol and other fuels) and solvents in industrial products (such as paint, ink, adhesives and cleaning fluids) give off flammable vapour which, when mixed with air, can ignite or explode.

The ease by which liquids give off flammable vapours is linked to a simple physical test called the ‘flashpoint’ (the minimum temperature at which a liquid, under specific test conditions, gives off sufficient flammable vapour to ignite momentarily on the application of an ignition source). This allows them to be classed according to the fire hazard they present in normal use.

Flammable liquids are classed as a liquid with a flashpoint of 60⁰C or below.


Dusts which can form explosive atmospheres are also classed as dangerous substances. They can be produced from many everyday materials such as coal, wood, flour, grain, sugar, certain metals and synthetic organic chemicals.

Dusts are found in many industries such as food/animal feed, chemicals, woodworking, rubber and plastic processing and metal powders. They may be raw materials, intermediates, finished or waste products. A cloud of combustible dust in the air can explode violently if there is a source of ignition (eg naked flame, sparks).

Find out more:


Gases, such as liquefied petroleum gas (LPG), hydrogen or other flammable industrial gases,  are usually stored under pressure in cylinders or  bulk containers. Uncontrolled releases can readily ignite or cause the cylinder to become a missile.

Methane (mains gas) is also a flammable gas which can cause explosions.

Find out more:


Solids include materials such as plastic foam, packaging and textiles can burn fiercely and give off dense black smoke, sometimes poisonous.

Welding gases

The flammable gases and oxygen used as a fuel for hot work and flame cutting can give rise to fire and explosion risks on their own without any involvement of any other dangerous or combustible substances.

A risk assessment carried out according to DSEAR will help to identify the correct controls and equipment before the work is carried out.

Find out more:

Other fire and explosion hazards

Many chemical substances can give rise to harmful heat and pressure effects because they are unstable or because they can react violently with other materials.

Chemicals need to be stored correctly and when reacted together sufficient information obtained to ensure that correct process controls can be used to prevent dangerous exothermic runaway reactions.

Find out more:


Cellulose thinners

A worker was using highly flammable cellulose thinners in an open-topped container to wash paint-spraying equipment. He knocked the container over, splashing the thinners over his trouser leg and shoe.

He went into a nearby room to clean himself up, but the room happened to contain drying ovens. These ignited the flammable vapours coming from the thinners, which set his trouser leg and shoe on fire, causing serious burns to his leg and foot.

How this incident could have been avoided

It could have been easily prevented if the employer had carried out a risk assessment to identify that cellulose thinners should not have been used in this way, and instructed the worker accordingly.


The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) require employers to assess the risk of fires and explosions arising from work activities involving dangerous substances, and to eliminate or reduce these risks.

HSE and local authorities are responsible for enforcing those workplaces covered by the legislation on working in potentially explosive atmospheres. These are covered in the following pages:

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Updated 2023-09-08