Dust explosion is a rapid combustion event that can occur when combustible dust is dispersed in air and exposed to an ignition source under suitable conditions. The potential for a dust explosion depends on several factors, including the properties of the dust, its concentration, dispersion, ignition source and the presence of confinement.
Dust Combustibility Testing is performed to determine whether a particular dust or powder is combustible and to understand its relevant combustion and explosion characteristics under defined test conditions.
For industries that handle, process, grind, mill, mix, convey or store powders and dusts, testing can provide important material-specific information for further hazard evaluation and process safety decisions.
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Dust Combustibility Testing is a laboratory evaluation used to determine whether a dust or powder can ignite and support combustion when dispersed under specified test conditions.
The test is particularly relevant for fine particulate materials because reducing particle size can increase the available surface area and may influence the ignition and combustion behaviour of the material.
Depending on the testing requirement, dust testing may include:
The appropriate combination of tests depends on the material, process and purpose of the testing programme.
A dust explosion requires a combination of conditions to occur. These conditions are commonly represented by the Dust Explosion Pentagon.
The five necessary conditions are:
The characteristics of the material and the conditions under which the dust cloud is formed can significantly influence the resulting combustion behaviour.
For a broader discussion of dust explosion causes, risks and prevention, see our Dust Explosion Risks & Prevention Guide.
Particle size is an important factor when evaluating the combustion behaviour of dust.
As a solid material is divided into smaller particles, its available surface area increases. Fine particles can therefore ignite and burn differently from larger particles under comparable conditions.
Very fine particles suspended in air may have a large surface area available for combustion. If ignition occurs within a suitable dust-air mixture, combustion can take place rapidly and may result in a rapid pressure increase when the dust cloud is confined.
However, particle size is only one of several factors affecting dust combustibility and explosibility. The actual behaviour of a material should be determined through appropriate testing rather than particle size alone.
The behaviour of a dust cloud can be influenced by a combination of material and process-related factors.
Important factors include:
The industrial process can influence how dust is dispersed, how concentrated the dust cloud becomes and how turbulence develops. Therefore, laboratory test results should be considered together with the actual process conditions when carrying out a broader hazard evaluation.
Dust combustibility group (A/B) is introductory test to determine the dust cloud or powder cloud (ie., below 63 microns) whether combustible or not. This is a screening test for dust explosibility studies.
The dust concentration range between 500-1000g/m3 was usually taken for the conducting the test and that dust concentration range can create the perfect cloud for accessing the dust combustibility, when it was contact with the ignition source.
Combustibility of dust cloud or powder cloud was grouping by,
1. Combustibility (Group A) – Flammable or Explosible as a dust cloud
2. Non-Combustible (Group B) – Non-Flammable or Explosible as a dust cloud.
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The standard atmospheric conditions used for determining the characteristics of combustible dust are:
The test equipment consists of a vertical tube closed at the bottom with a dispersion cup having an approximate volume of 1.2 L and an internal diameter of 70 ± 5 mm.
The ignition source consists of a continuous induction spark with an electrode gap of approximately 4 mm. The transformer is rated at approximately 15 kV and 0.2 kVA.
The vertical separation between the bottom of the dispersion cup and the ignition source is approximately 100 mm.
The exact test conditions and equipment configuration should be interpreted according to the applicable testing standard and procedure.
Different international standards are used for determining the combustible and explosible characteristics of dust, depending on the property being evaluated and the selected test method.
ISO/IEC 80079-20-2 describes test methods for determining the characteristics of combustible dust and combustible dust layers. The information obtained from these tests can be used for the classification of areas where combustible dust may be present and for the appropriate selection and installation of electrical and mechanical equipment intended for use in such environments.
The standard is particularly relevant when evaluating the characteristics of dust that may create a combustible-dust hazard.
ASTM E1226 provides a method for evaluating the explosibility of particulate solids when dispersed as a dust cloud and exposed to an ignition source.
The method can be used as an explosibility screening test to determine whether a dust sample is explosible and, where applicable, to evaluate the degree of explosibility.
For an explosible dust, important parameters may include:
Maximum explosion pressure (Pmax)
Maximum rate of pressure rise, (dP/dt)max
Dust explosibility index, KSt
Depending on the testing requirement, explosibility parameters may be determined using suitable explosion test equipment, such as a 20-Litre sphere or 1 m³ apparatus.
The applicable standard and test method should be selected according to the specific dust material, property being evaluated and intended purpose of the testing.
A typical dust combustibility testing programme involves several stages.
1. Sample Submission
A representative sample of the dust or powder is submitted for testing along with relevant material and process information.
2. Sample Preparation
The sample is prepared according to the requirements of the selected testing method.
Particle size, moisture and sample condition can influence test results and should therefore be considered when preparing the test sample.
3. Dust Dispersion
The prepared sample is dispersed under controlled laboratory conditions to produce a dust cloud or dust layer appropriate to the selected test.
4. Application of Ignition Source
A specified ignition source is applied according to the applicable test procedure.
5. Observation and Evaluation
The response of the dust sample is observed and recorded.
Depending on the selected test, the result may indicate whether the sample demonstrates combustible behaviour or provide quantitative explosion characteristics.
6. Additional Testing
If the material is found to be combustible or explosible, additional testing may be required to determine characteristics such as MIE, MIT, LIT, MEC, Pmax or Kst.
The required testing programme should be selected based on the material and the intended engineering or safety evaluation.
Once a dust has been identified as combustible, additional testing can provide more detailed information about its ignition and explosion characteristics.
♦ Minimum Ignition Energy (MIE)
MIE testing determines the minimum electrical spark energy capable of igniting a dispersed dust cloud under specified test conditions.
This information can be useful when evaluating the sensitivity of a dust cloud to potential ignition sources.
♦ Minimum Ignition Temperature (MIT)
MIT testing determines the minimum temperature at which a dispersed dust cloud can ignite under defined conditions.
It can provide information relevant to equipment and surfaces that may operate at elevated temperatures.
Layer Ignition Temperature (LIT)
LIT testing evaluates the ignition characteristics of a layer of dust exposed to a heated surface under specified conditions.
This can be relevant where dust deposits may accumulate on process equipment or other surfaces.
Minimum Explosible Concentration (MEC)
MEC testing determines the minimum concentration of dust dispersed in air that can support an explosion under specified conditions.
Maximum Explosion Pressure (Pmax)
Pmax represents the maximum pressure developed by an explosible dust-air mixture under the specified test conditions.
Explosion Severity (Kst)
Kst represents the explosion severity characteristic of a combustible dust under the applicable test conditions and is commonly considered together with Pmax when evaluating explosion characteristics.
Dust Combustibility Testing provides material-specific information that can support technical evaluation of combustible dust hazards.
1. Hazard Identification
Testing can help determine whether a particular dust demonstrates combustible or explosible characteristics.
2. Material Characterisation
Testing provides information about important characteristics of the dust, which may vary depending on particle size, moisture and material composition.
3. Engineering and Safety Evaluation
Test results can be used as technical input for engineering assessments and the selection of appropriate safety measures.
4. Dust Hazard Assessment
Material-specific test data can be used as an input to a broader Dust Hazard Assessment (DHA) where applicable.
5. Process Safety
Understanding the characteristics of a dust can support process safety teams when evaluating equipment, processes and potential ignition hazards.
6. Risk Management
Reliable testing data can help organisations make better-informed decisions regarding combustible dust hazards and associated controls.
For a plant-level evaluation of where dust hazards may exist, see our Dust Hazard Assessment service.
Testing may be considered when:
Testing requirements should be determined based on the specific material and process.
Dust testing can be relevant across industries that handle or process combustible powders and particulate materials, including:
The need for testing depends on the characteristics of the material and the process in which it is handled.
Sigma-HSE provides Dust Combustibility Testing Services for industrial powders and dust materials.
Depending on the material and testing requirement, testing may include:
Our technical team can help identify the appropriate testing requirements based on your material, process and intended application.
If you need to determine the combustibility or explosion characteristics of an industrial dust or powder, share your material and testing requirements with Sigma-HSE.
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1. What is Dust Combustibility Testing?
Dust Combustibility Testing is laboratory testing used to determine whether a dust or powder demonstrates combustible behaviour under specified test conditions and, where required, to evaluate its relevant explosion characteristics.
2. What is Group A/B Dust Combustibility Testing?
Group A/B is an introductory screening approach used to determine whether a dust or powder cloud demonstrates combustible behaviour under the applicable test conditions.
3. What parameters can be tested for combustible dust?
Depending on the material and testing objective, parameters may include MIE, MIT, LIT, MEC, Pmax, Kst and burning behaviour.
4. What is the difference between MIE and MIT?
MIE relates to the minimum energy required to ignite a dispersed dust cloud, while MIT relates to the minimum temperature required to ignite a dust cloud under specified test conditions.
5. What is Pmax and Kst testing?
Pmax indicates the maximum explosion pressure measured under specified conditions, while Kst represents the explosion severity characteristic of the dust.
How do I get my dust tested?
You can contact Sigma-HSE with details about your material, process and required testing parameters. Our technical team can help determine the appropriate testing requirements.
Request Dust Combustibility Testing
Do you need reliable data on the combustibility or explosion characteristics of your industrial dust or powder?
Contact Sigma-HSE to discuss your testing requirements and request a quotation.
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