How Do I Know if My Dust is Combustible? - A UK Guide to Testing & DSEAR

In the UK, these risks are regulated under the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR), enforced by the Health and Safety Executive. Employers have a legal duty to assess and control the risks associated with dangerous substances, including combustible dust.

Understanding whether your dust presents a fire or explosion risk is not always straightforward, and assumptions can be dangerous.

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What is combustible dust?

Combustible dust is any fine particulate material that can ignite and explode when suspended in air under the right conditions. Small particles have a large surface area relative to their volume, making them highly reactive.

A dust explosion typically requires five elements (often referred to as the “dust explosion pentagon”):

• Combustible dust (fuel)
• Oxygen (air)
• An ignition source
• Dispersion of dust particles
• Confinement

If these conditions are present, even a material that seems harmless can become a serious hazard.

Which materials can create explosive dust?

Combustible dust hazards occur across industries including food processing, woodworking, pharmaceuticals, composite machining, material handling & recycling, and metalworking.

Common examples include:

Organic materials

• Flour, sugar, starch and grain
• Cocoa powder and milk powder
• Animal feed and biomass

Wood and construction materials

• Hardwood and softwood dust
• MDF and composite boards

Industrial and chemical materials

• Plastics, resins, and rubber
• Pharmaceuticals and fine chemicals
• Textiles and paper dust

Composite Machining

• Carbon fibre (graphite)
• Fiberglass (glass-reinforced plastic/GRP)
• Plastic/resin dusts

Metal dusts (important considerations)

Certain metals are particularly hazardous in dust form:

• Aluminium, magnesium, titanium (highly explosive)
• Iron and mild steel are not typically highly combustible in bulk form, but finely divided particles can present an explosion risk under certain conditions

Why assumptions about dust can be dangerous

One of the most common misconceptions is that the type of material alone determines the level of risk. In reality, the explosibility of dust depends on a range of factors, including:

• Particle size and shape
• Moisture content
• Concentration in air
• Presence of contaminants
• Process conditions (e.g. grinding, drying, conveying)

This means that two facilities handling the same material may face vastly different levels of risk.

Visual inspection or past experience is not enough to determine whether a dust is explosive — or how severe an explosion could be.

How is dust explosibility measured?

To accurately assess the risks, dust must be tested in a controlled laboratory environment. During testing, a dust sample is dispersed and ignited under controlled conditions to measure its explosion characteristics.

Two key parameters are determined:

• Kst  (German: K = Konstant, st =Staub for dust) value – Indicates the rate of pressure rise during an explosion and therefore the relative severity (violence) of the explosion
• Pmax (Peak pressure, usually in bar or psi) value – Indicates the maximum explosion pressure that could be generated

These values are essential for:

• Designing explosion protection systems
• Selecting appropriate equipment
• Supporting DSEAR risk assessments

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Dust explosion classes (St 0 – St 3)

Based on the Kst value, combustible dusts are classified into explosion classes:

• St 0 (Kst = 0)
  No explosion risk
• St 1 (Kst 1–200)
  Weak explosion
  (e.g. many organic dusts such as sugar or wood dust)
• St 2 (Kst 201–300)
  Strong explosion
  (e.g. some processed industrial dusts)
• St 3 (Kst >300)
  Very strong explosion
  (e.g. reactive metal dusts such as aluminium)

The higher the classification, the greater the potential severity and the more robust the required control measures.

DSEAR and ATEX Compliance

Under DSEAR, UK employers must:

• Identify dangerous substances in the workplace
• Assess fire and explosion risks
• Classify hazardous areas (Zones 20, 21, 22)
• Implement mitigation measures
• Use ATEX-compliant equipment where required

ATEX, though an EU directive, is widely recognised in the UK through DSEAR and ensures that equipment and protection systems meet internationally recognised explosion safety standards.

Laboratory testing of dust properties — including Kst and Pmax values — provides the evidence needed to:

• Classify your dust according to its explosibility
• Determine appropriate hazardous zone classification
• Select suitable ATEX-rated equipment
• Demonstrate compliance with DSEAR

Guidance from the Health and Safety Executive makes it clear that risks must be assessed based on evidence, not assumption.

If you already know your dust is combustible, it is important to act quickly. Speak to our experts about tailored dust safety and explosion prevention solutions.

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However, understanding how DSEAR and ATEX work together is key to selecting the right protection measures.

Understanding the Difference Between DSEAR and ATEX

While ATEX-certified equipment is widely referenced across industry, it is important to understand that compliance in the UK is governed by DSEAR.

DSEAR advises employers to:

• Assess the risk of fire and explosion
• Identify hazardous substances, including combustible dust
• Classify hazardous areas (Zones 20, 21 and 22)
• Implement appropriate control and mitigation measures

In contrast, ATEX relates to the certification of equipment and protective systems used in explosive atmospheres.

Put simply:

• DSEAR sets out the requirements for managing risk
• ATEX ensures the equipment you use is safe for that risk

ATEX-rated equipment is therefore only one part of the solution. It must be selected based on a suitable and sufficient DSEAR risk assessment, supported by accurate data about the properties of your dust.

Without this information, there is a risk of:

• Under-specifying equipment, leading to unsafe conditions
• Over-specifying solutions, leading to unnecessary cost

When should you test your dust?

Dust testing should be considered in any of the following situations:

• You are handling powders, granules or fine particulates
• A new material is introduced into your process
• Your process involves grinding, milling or drying
• Dust properties are unknown or undocumented
• A DSEAR risk assessment is required or being updated
• There has been an incident or near miss

Testing provides clarity, ensures compliance, and informs the design of protection systems.

The role of dust testing in risk reduction

Understanding the properties of your dust is the foundation of effective explosion prevention. Testing enables you to:

• Quantify explosion risk
• Select appropriate explosion protection measures
• Design or validate dust extraction systems
• Support compliance with UK regulations
• Protect people, equipment and facilities

Without this data, it is difficult to make informed safety decisions.

Take the next step

Combustible dust risks are often underestimated — particularly when materials appear harmless in everyday use. However, under the right conditions, these materials can pose a serious threat to safety and operations.

Laboratory testing provides the data needed to accurately assess your dust, support your DSEAR obligations, and implement appropriate control measures.

If you are unsure about the properties of dust generated in your process, seeking specialist advice and testing is a practical first step towards reducing risk and ensuring compliance.

Do not leave your dust safety to chance:

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