What is Combustible Dust Testing

What is combustible dust testing?

Combustible dust testing analyzes dust and powder materials to determine their potential to ignite, deflagrate, or explode under specific conditions. Industries like manufacturing, food processing, pharmaceuticals, wood, and mining rely on this testing because they regularly generate or handle fine particulate matter.

The fire and explosion characteristics of dust depend heavily on the material type, how it’s processed, and factors such as particle size, shape, and moisture content. The finest and driest particles usually create the highest ignition and explosion hazards.

Because dust behavior changes with these variables, one test alone can’t fully evaluate explosion risk. Labs perform a series of standardized tests to define critical properties like flammability, ignition sensitivity, and explosion severity. These tests deliver the data companies need to assess hazards, design safer systems, and meet standards like NFPA 652 and OSHA’s combustible dust regulations.

In this blog, we’ll provide an introduction to combustible dust testing by walking you through the most common and important tests used to evaluate the fire and explosion risks associated with combustible dust.

Go/No-Go Explosibility Screening Test

The Go/No-Go explosibility test is a key screening method for evaluating whether a dust sample can explode when dispersed in air and exposed to an ignition source. It provides a simple binary result: “Go” if the dust is explosible, or “No-Go” if it is not. Many industries—like manufacturing, food processing, pharmaceuticals, wood, and mining—use this test as a first step in identifying combustible dust hazards.

Dust behavior can change based on how the material is processed, stored, or handled. Small changes in moisture content, particle size, or composition can affect whether a dust can ignite or explode. The Go/No-Go test offers a fast and practical way to screen materials. A “Go” result means the dust poses a risk and requires more detailed testing or safety measures, such as ignition control and dust mitigation.

This test is performed following the guidelines of ASTM E1226, a recognized standard for dust explosion testing. While a “No-Go” result suggests a lower risk of explosion, it doesn’t mean the material is entirely free of hazards. Testing provides essential data for compliance with safety standards like NFPA 652 and helps facilities implement informed, proactive safety strategies.

Burn Rate /Fire Train Test

The Burn Rate or Fire Train Test measures how quickly a material burns and whether it poses a combustion hazard. Some dusts or solids that fail explosibility tests (i.e., get a “No-Go” result) can still burn rapidly and create a fire risk. This test helps assess a material’s combustibility and determines if it should be classified as a flammable solid for transport and handling. It is especially useful for materials like metals, propellants, and pyrotechnics that may ignite from heat, friction, or sparks.

Understanding a material’s burn behavior is critical for preventing flash fires and other hazards in processing environments. The test shows whether a material ignites and sustains combustion over a set distance and time. If a material burns easily, it may need special handling, fire controls, or hazardous materials packaging. Burn rate testing supports safe system design, routine safety checks, and compliance with regulations—especially in processes involving energetic or flammable substances.

This test is conducted according to UN/DOT Section 33 and VDI 2263, which outline standardized procedures for assessing flammable solids (Division 4.1 materials).

Dangerous When Wet Test

The Dangerous When Wet (DWW) Test checks if a material releases flammable gases or reacts hazardously when it contacts water. It applies to both solids and liquids. This test helps decide if a material falls under Division 4.3 of hazardous materials regulations. Materials that seem stable when dry can become dangerous when exposed to moisture. That’s why this test is essential for safe handling and proper classification.

Some materials react with water to produce gases that ignite spontaneously or release flammable vapors. These vapors can cause fire and explosion hazards. The DWW test is vital for correct labeling, packaging, and transport. It is especially important for reactive metals and chemicals used in industry and manufacturing. Performing this test supports risk assessments, ensures accurate Safety Data Sheets (SDS), and helps create protocols to reduce moisture-related incidents during storage, shipping, and use.

The test follows UN/DOT Section 33 procedures for Class 4 materials and consists of both a screening and full test.

Dust Explosion Severity (Kst/Pmax/dP/dt)

The Dust Explosion Severity Test evaluates how violently a combustible dust cloud can explode under specific conditions. It focuses on three key parameters: the maximum explosion pressure (Pmax), the maximum rate of pressure rise ((dP/dt)max), and the deflagration index (Kst). Kst reflects how quickly pressure builds during an explosion, while Pmax indicates the highest pressure the explosion can generate. These values help determine the severity of a potential dust explosion and classify the dust into explosion classes: St-1, St-2, or St-3.

Understanding explosion severity is vital for industries handling combustible dust. A dust explosion can lead to catastrophic equipment damage, facility loss, or injury. By identifying how severe an explosion could be, facilities can design effective explosion protection systems—such as venting, suppression, and containment—according to standards like NFPA 68 and ISO 6184. The severity data also plays a key role in regulatory compliance, safety planning, and adapting to material or process changes.

The test is performed according to American Standard Testing Method (ASTM) E1226 and BS EN 14034 Parts 1 & 2.

Minimum Explosible Concentration (MEC)

The Minimum Explosible Concentration (MEC), also known as the Lower Explosible Limit (LEL), defines the lowest concentration of combustible dust suspended in air that can ignite and sustain an explosion in a closed system. This test determines the point at which a dust-air mixture becomes capable of combustion. Mixtures below this threshold are too lean to ignite or explode. The MEC sets the lower boundary for when a combustible dust cloud becomes explosible.

Understanding a material’s MEC is essential for evaluating potential dust explosion hazards. It plays a vital role in risk assessments, process design, safety protocols, and regulatory compliance. Knowing the MEC allows industries to identify safe operating limits, prevent dangerous dust accumulation, and guide the selection of equipment or ventilation systems. This data is also valuable for safety training, process optimization, and investigating dust-related incidents.

The MEC test is conducted in accordance with ASTM E1515 and BS EN 14034 Part 3.

Limiting Oxygen Concentration (LOC)

Limiting Oxygen Concentration (LOC) is the minimum oxygen level below which a combustible dust cloud cannot sustain an explosion or combustion, even if an ignition source is present. This value marks a critical threshold where the atmosphere becomes inert enough to stop deflagration. When oxygen drops below the LOC, the dust-air mixture can no longer support combustion. This makes LOC essential for designing safe processing environments.

Determining LOC is crucial in industries handling combustible dust, especially where inerting is used for safety. Knowing the LOC helps control oxygen levels to prevent ignition during normal operations or upset conditions. It supports risk assessments, fire and explosion prevention, and regulatory compliance. LOC also guides the design and operation of inert gas systems to keep oxygen below levels that allow combustion.

Technicians perform the LOC test following ASTM E1291, Standard Test Method for Limiting Oxygen (Oxidant) Concentration of Combustible Dust Clouds, and BS EN 14034-4, Determination of Explosion Characteristics of Dust Clouds – Part 4: Determination of the Limiting Oxygen Concentration (LOC) of Dust Clouds.

Minimum Ignition Energy (MIE)

The Minimum Ignition Energy (MIE) of a combustible dust identifies the lowest amount of electrical energy needed to ignite a dust-air mixture at its most easily ignitable concentration. Labs typically determine this value using a capacitive spark discharge, which simulates ignition sources like electrostatic discharges or mechanical sparks common in processing environments. Knowing the MIE helps assess how likely a material is to ignite from low-energy sources.

MIE is a critical parameter in assessing ignition hazards during powder handling and processing operations. It plays a key role in evaluating the risk posed by electrostatic discharges, frictional heating, and electrical equipment. Materials with lower MIE values are more sensitive to ignition and require stricter safety controls to prevent fire or explosion. This data is essential for risk assessments, equipment design, hazard mitigation, and determining safe operating procedures in industries that handle combustible dusts.

Minimum Ignition Energy testing is performed in accordance with ASTM E2019, Standard Test Method for Minimum Ignition Energy of a Dust Cloud in Air.

Minimum Autoignition Temperature-Cloud (MAIT – Cloud)

The Minimum Autoignition Temperature (MAIT) of a dust cloud marks the lowest temperature at which a dust-air mixture ignites on its own, without an external ignition source. Laboratories determine this value under controlled conditions to assess the fire hazard of airborne combustible dust.

MAIT is a key factor in evaluating the risk of ignition from hot surfaces, sparks, or high operating temperatures. It matters most when selecting electrical and non-electrical equipment for areas where dust clouds may occur. Knowing a material’s MAIT helps engineers set safe surface temperature limits for process equipment. This reduces the risk of spontaneous ignition and fire hazards during routine operations.

MAIT testing is conducted in accordance with ASTM E1491, Standard Test Method for Minimum Autoignition Temperature of Dust Clouds.

Layer Ignition Temperature of Dust (LIT)

The Layer Ignition Temperature (LIT) is the lowest temperature at which a settled dust layer ignites on a hot surface without an external ignition source. To find this value, technicians place a fixed thickness of dust on a heated surface and watch for ignition signs like flame, glowing particles, or a temperature rise.

LIT is a critical safety parameter used to assess fire hazards from dust layers on equipment or surfaces. Safety engineers use it to set safe operating temperatures for electrical and non-electrical equipment in areas where dust may settle. Knowing the LIT helps prevent ignition from hot surfaces and reduces the risk of fires and explosions caused by dust layers.

Labs test for LIT using ASTM E2021, Standard Test Method for Hot-Surface Ignition Temperature of Dust Layers.

Particle Sieve Analysis

Particle sieve analysis is a widely used technique for determining the distribution of particle sizes within a granular material. This method separates particles by passing the sample through a stack of sieves with progressively smaller openings, allowing for quantification of the size ranges present. Understanding particle size distribution is essential, especially for powders and dusts, as it directly influences material properties including combustibility.

Accurate particle size distribution data is critical in various industries to ensure material quality and safety. In combustible dust testing, particle size affects ignition sensitivity and explosibility, making sieve analysis a prerequisite for reliable hazard assessment. This information helps decide whether the sample needs further preparation, such as grinding or sieving, before additional testing and supports quality control and process optimization across many applications.

Particle sieve analysis is performed following the American Society for Testing and Materials (ASTM) standard ASTM E11, which defines the procedures for determining particle size distribution of granular materials.

Moisture Content Analysis

Loss on Drying (LOD) is a widely used method to determine the moisture or volatile content in a material by measuring the weight loss after controlled heating and drying. This technique is essential across multiple industries—including pharmaceuticals, food, chemicals, and materials testing—to quantify moisture levels or other volatile substances present in a sample. Accurate moisture content measurement is vital for ensuring product quality, consistency, and regulatory compliance.

Determining moisture content through LOD analysis is critical for quality control and manufacturing processes. Moisture levels can significantly affect product stability, shelf life, processing characteristics, and safety. For many industries, controlling moisture content helps prevent spoilage, degradation, or hazardous reactions during storage and handling. Moreover, LOD data assists in meeting specific industry standards and regulatory requirements to ensure the integrity and performance of materials.

The Loss on Drying test is conducted following the ASTM standard ASTM E1131-08.

Cryogenic Grinding

Cryogenic grinding is an advanced particle size reduction technique that uses ultra-low temperatures, typically below -80°C (-112°F), to embrittle materials before grinding. The process cools materials with cryogenic gases like liquid nitrogen. This enables finer, more uniform particle size reduction while preserving the integrity of heat- or temperature-sensitive substances. Cryogenic grinding is especially useful for materials that degrade or change under conventional grinding.

The main advantage of cryogenic grinding is maintaining the chemical and physical properties of sensitive materials while achieving precise size reduction. It minimizes heat generation during grinding, preventing thermal degradation, volatilization, or loss of potency. Industries such as pharmaceuticals, food, and polymers benefit from this method. It ensures product quality, improves material handling, and produces fine powders with controlled particle size.

No single ASTM standard covers cryogenic grinding exclusively. However, the process follows industry best practices and material-specific guidelines to ensure reproducibility and safety. Proper protocols for temperature control, sample handling, and equipment operation are essential for reliable, high-quality results.

Conclusion

Combustible dust testing plays a critical role in identifying materials that can ignite, deflagrate, or explode under specific conditions. This testing process helps facilities understand the flammability, ignition sensitivity, and explosion severity of dusts commonly generated in manufacturing, food processing, pharmaceuticals, wood, and other industries. Accurate test data enables informed decisions about hazard mitigation, equipment selection, and safe operating procedures.

At Prime Process Safety Center, we recognize that thorough testing is essential for preventing fires and explosions. Our combustible dust testing services cover a wide range of standardized methods to evaluate dust behavior in both cloud and layer forms. By pinpointing risks and defining key safety thresholds—such as MIE, MAIT, LIT, LOC, and MEC—we help clients comply with NFPA 652 and OSHA guidance while reducing the likelihood of combustion-related incidents.

Testing is a regulatory requirement—it’s a proactive step toward creating safer work environments. Prime Process Safety Center remains committed to delivering accurate, dependable testing that supports hazard analysis, risk reduction, and long-term operational safety.

To learn more about our combustible dust testing capabilities, visit our combustible dust testing page. For answers to common questions and additional guidance, see our Most Frequently Asked Questions about Combustible Dust Testing page.