Last reviewed 16 September 2019

It’s always a good time to look at the risks of dangerous substances and explosive atmospheres, including the critical concentrations of airborne dust from many sources, since without systematic care and good practice these risks will be present at all times, writes Jon Herbert.

There are no half-measures with workplace fires and explosions. Ensuring safety requires a clear understanding of the obvious and less obvious risks, plus continuous vigilance.

The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) make it a duty for employers and the self-employed to control any work-related safety risks associated not only with combustion and blasts but also substances corrosive to metals that can endanger employees or members or the public.

What are dangerous substances?

DSEAR define dangerous substances as:

  • explosive, oxidising or flammable

  • having chemical or physical properties that create a risk in the workplace

  • any dust which can form an explosive atmosphere.

Dangerous substances can be found in nearly all workplaces. They include solvents, paints, varnishes and flammable gases such as liquid petroleum gas (LPG). They also cover dusts not only from machining and sanding operations but also foodstuffs. Other sources are pressurised gases and substances that are corrosive to metal.

DSEAR requirements for employers

The methodology for identifying and mitigating risks defined by DSEAR mirrors other health and safety risk assessment standard practice.

This is to:

  • identify dangerous substances in the workplace and calculate their risks

  • put controls in place to preferably remove risks, or manage them where that is not possible

  • put further controls in place to reduce the impacts of incidents involving dangerous substances

  • prepare plans and procedures to respond to accidents, incidents and emergencies

  • ensure employees are properly informed about, and trained to control or respond to, risks

  • identify and classify workplace areas where explosive atmospheres may occur

  • avoid ignition sources, including from unprotected equipment.

Risk assessment

Specifically, a risk assessment must be carried out before work begins to identify dangerous substances, work activities involved with them, all forms of impact and appropriate mitigations.

If there are no safety risks, or risks are trivial, no further action is needed. However, if risks are identified, employers must act to comply with DSEAR. Where an employer has five or more employees, significant risk assessment findings must be recorded.

Croner-i’s DSEAR risk assessment workflow can get you started.

Preventing or controlling risks

Reasonably practicable control measures are mandatory to eliminate or reduce risks from dangerous substances. Where complete elimination is not possible, mitigation to reduce the severity is needed.

The best solution to eliminate a risk completely is to replace a dangerous substance with a safe one or use a different work process. In the regulations, this is called substitution. That may be difficult to achieve in practice, such as at petrol filling stations. But it is an effective step where possible, an example being the replacement of a low flashpoint liquid with a high flashpoint alternative.

Control measures

Where risks cannot be eliminated, DSEAR require the following control measures to be taken in the following order.

  • Reducing quantities of dangerous substances to a minimum.

  • Avoiding or minimising releases of dangerous substances.

  • Controlling releases of dangerous substances at source.

  • Preventing the formation of a dangerous atmosphere.

  • Collecting, containing and removing releases to a safe place, eg by ventilation.

  • Avoiding ignition sources.

  • Avoiding adverse conditions, eg exceeding temperature limits or control settings.

  • Keeping incompatible substances apart.

Control measures should be linked to the risk assessment and the nature of the activity.


In addition to control measures, under DSEAR employers must put mitigation measures in place that are again consistent with the risk assessment and operational activities. These include:

  • reducing the number of employees exposed to risk

  • providing explosion resistant plant

  • providing corrosion resistant plant

  • providing explosion suppression or explosion relief equipment

  • taking measures to control or minimise the spread of fires or explosions

  • providing suitable personal protective equipment.

Emergency plans and procedures

Preparation is all important. Arrangements to deal with emergencies must be made. Plans and procedures should cover safety drills, plus suitable communication and warning systems, and should be proportionate to the risks. If an emergency occurs, workers with repair tasks or other vital work must be provided with appropriate equipment for safety.

Emergency plans and procedure information must also be available to the emergency services for them to develop their own plans if necessary.

Providing information, instruction and training for employees

Employee information, instructions and training must cover:

  • dangerous substances and risks in the workplace, including access to relevant safety data sheets plus information on any other legislation applying to dangerous substances

  • risk assessment findings and control measures

  • emergency procedures.

Information, instruction and training for non-employees is only needed where it is required to ensure their safety and should be in proportion to the level and type of risk.

A special case is the contents of pipes and containers. These must be identifiable to warn employees and others about the presence of dangerous substances. However, if the contents have already been identified under other law, this does not need to be repeated under DSEAR.

Controlling dust explosion risks

DSEAR also regulate flammable solids in the form of a fine dust which, if dispersed in air, can lead to a serious fire or an explosion. However, flammable dusts risks differ from those posed by flammable gases and liquids.

Combustible dust is fine material that can catch fire and explode when mixed with air; many dusts are not normally combustible but can burn or explode if the particles, their sizes and their concentration in air are within critical limits. To explode, a dust/air mix must also be confined.

Dust can gather on surfaces, rafters, roofs, suspended ceilings, ducts, crevices, dust collectors, and other equipment. When disturbed, and under certain circumstances, serious explosions can occur.

A primary explosion can dislodge further dust which, again as a dust/air mixture, can result in a secondary detonation. Even very small amounts can cause serious damage. Best practice includes keeping workplaces as dust free as possible.

Potentially explosive substances can range from egg whites to powdered milk, corn-starch, sugar, flour, grain, potatoes and rice. They can include aluminium, bronze, magnesium and zinc as well as coal, sulphur, pesticides, rubber, wood, textiles and plastics.

This is why businesses across the UK are being targeted through summer 2019 by Health and Safety Executive (HSE) dust control inspections. The focus is on construction, woodworking and food manufacturing where occupational lung diseases, including occupational cancers, are more common, with asbestos, silica, wood and flour dust in the spotlight. Again, awareness of risks, work planning and appropriate controls for protection are priorities.

The HSE’s chief inspector of construction, Sarah Jardine, stated, “We want to ensure employers and their workers are aware of the risks associated with any task that produces dust. Such work needs to be properly planned and use the right controls, such as water suppression, extraction and masks.”

Further information

For in-depth information and advice as well as a template policy, a training presentation and useful forms, see the Croner-i topic DSEAR. There is also a topic looking specifically at Dust in Construction