Avoiding Explosion Risks


People often think that explosions are only caused by obviously flammable substances such as oil or gas. But this is far from the case, as a new HSE guidance paper makes clear.

Other vapours or dust, when mixed with air, need only a spark to explode.

Accidental explosions of this kind account for many workplace injuries every year. Working with chemicals, liquids, vapours and dusts is inherently risky.

Most explosions start as fires; these can be prevented. Managers with Health and Safety responsibility can avoid them if they adopt safe behaviours and procedures. The Dangerous Substances and Explosive Atmospheres Regulations 2002, DSEAR and ATEX, require an assessment of the risk of fires and explosions arising from work that involves dangerous materials, and require action to eliminate or reduce these risks.

When carrying out such technical risk assessments it is always advisable to use professional Safety Consultants who have the correct training and technical know-how.

Risky Substances


Petroleum and other fuels, and solvents in industrial products (e.g. paint, ink, adhesives, cleaning fluids) give off flammable vapour which, when mixed with air, can ignite or explode. The ease with which liquids give off flammable vapours is linked to a simple physical test called Flashpoint (the minimum temperature at which a liquid ignites when an ignition source is applied). This gives rise to three categories of flammable liquids, broadly:

  1. Extremely flammable – flashpoint <0°C and a boiling point of 35°c or less.
  2. Highly flammable – flashpoint <21°c.
  3. Flammable – flashpoint 21° – 55°c, combust when tested at 55°c.


Dusts are also dangerous. They derive from seemingly inert materials like flour, grain, sugar, coal, wood and synthetic chemicals. A cloud of combustible dust can explode violently if there is a source of ignition (a naked flame or a spark).

Vessels containing such products must be fitted with safety ventilation that automatically operates when the dust concentration reaches dangerous levels. It can be hazardous to enter such areas, and precautions must be taken to wear the right footwear with no metal on the soles, and to avoid any activity that might cause a spark. Wherever practicable, the dangerous dust must be cleared before workers enter the area.


Gases, (e.g. liquefied petroleum gas and methane) are stored under pressure in cylinders and tankers, which if ruptured can ignite and even cause the container to become a missile.


Packaging, plastics and textiles can burn fiercely and give off dense black poisonous smoke.

Other Risks

Most organic substances will become dangerous when heated to a sufficiently high temperature as they can then release flammable vapours or fumes that can burn or explode.

Before carrying out cutting or hot work on equipment that may have contained a liquid or combustible solid you must do a risk assessment. If in any doubt, seek assistance from qualified Health and Safety consultants.

Flammable gases and oxygen used as 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.

Seek Professional Help

A risk assessment carried out according to DSEAR will help to identify the correct controls and equipment before hazardous work is carried out. Where this work forms part of a construction project, it is essential to seek the services of a CDM Co-ordinator to ensure that health and safety factors have been planned into the design and that all contractors are coordinated properly to avoid risks.

You may be sure that HSE and Local Authority inspectors will be focusing on these aspects of your business.
There are many aspects to consider and to make sense of it all, McCormack Benson Health & Safety have hands-on consultants who can draw up assessments, advise on necessary changes to plant, equipment and working practices, and can help you to see it all through successfully.

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