Combustible Dust Hazard Analysis & Facility Inspections

Root Cause Analysis: Electrical Fires & Explosions [EECS]

Alerts

Significant Changes to NFPA 921 Guide Future Fire and Explosion Investigations

How can industries minimize the risk of explosions due to combustible dust particles?

Even very small amounts of combustible dust can cause serious damage, and any workplace that generates or handles combustible dust is potentially at risk. Testing dust combustibility and explosivity can help characterize the risk of hazards and support the development of mitigation strategies to prevent accidents.

However, devising and maintaining effective mitigation strategies requires a high level of expertise: risks can vary from day to day across processes, materials, and equipment. The hazards associated with combustible dust can change due to the launch of new processes, lapses in cleanliness, or changes in raw materials.

Understand your dust hazards and the challenges that may arise throughout a dust hazard analysis.

Exponent's multidisciplinary team of thermal scientists and engineers are experts in fire and explosion investigation and the interpretation of NFPA standards. Our consultants actively contribute to the development of fire and explosion safety standards, including combustible dust hazard standards.

We work with clients to develop and execute combustible dust testing programs that support high-quality, value-added DHAs. We often work with facilities after a DHA has been completed to implement focused, cost-effective dust hazard management programs by helping our clients understand and prioritize a DHA's recommendations. We can also conduct more detailed technical or risk-based analyses in circumstances where adherence to prescriptive requirements in standards is not logistically or financially feasible.

Is your facility equipped to conduct an in-house industrial dust hazard analysis?

Industrial facilities that handle combustible dust can reduce the risk of enforcement agency citation, mitigate potential fire or explosion hazards, and most importantly, protect workers and surrounding communities from the dangers of combustible dust through a proactive approach to DHA. While some standards and references provide useful resources for conducting a DHA, interpreting and implementing these resources often requires combustible dust expertise and data from material testing.

One of the first steps an industrial facility can take to prepare for a DHA is to evaluate in-house resources to determine whether you can adequately complete a systematic examination of potential hazards and available mitigation techniques.

Facilities often lack the dedicated resources that form the foundation for completing a DHA, including sampling and testing dust, gathering data, and writing procedures for equipment operations and maintenance. Others may lack records that document the rationale behind equipment design, installation, and protection. This is especially understandable if the equipment has been designed, installed, and modified over the course of decades of operation.

Exponent can help your facility identify what existing documents are relevant and what additional information should be collected from field surveys, original equipment manufacturer documentation, sampling, and testing.

How does Exponent help you meet the NFPA standards requirements for a dust hazard analysis?

NFPA standards allow for some flexibility in how facilities conduct DHAs, but each facility needs to understand the exacting standards and the degree of technical expertise required. For over 30 years, Exponent's thermal scientists and engineers have investigated industrial dust explosions, contributing to our unique perspective on risk evaluation and providing clients with the practical insights needed to manage combustible dust risks.

In addition to leveraging our extensive experience from dust explosion investigation, Exponent also performs advanced thermal testing and evaluations in our state-of-the-art Combustible Dust Testing Laboratory. Our knowledge and experience in both explosion investigation and testing extend across multiple industries, providing further insights into how combustible dust hazards can surface and be mitigated.

Capabilities

We help you identify dust hazards and mitigate future risks from combustible dusts.

Exponent helps facilities identify equipment and process gaps that pose dust hazards or compliance risks. Our multidisciplinary teams leverage diverse capabilities to develop risk management strategies, with the goal of managing the largest risks first while also helping facilities evaluate the benefits and limitations of mitigation proposals from other vendors.

We integrate a risk-based process safety management approach into each step of your evaluation.
Many of the management system requirements found in NFPA 652 strongly resemble process safety management (PSM) requirements that regulate many processes handling highly hazardous chemicals and flammable liquids and gases. Exponent's multidisciplinary teams have extensive experience helping clients identify and interpret management system requirements in a practical way that reflects the true intent of the standard: managing the combustible dust fire and explosion hazards by reducing the risks associated with their handling, storage, and processing.
Exponent inspects facilities that contain potentially combustible dust, identifying areas where combustible dust hazards may exist, and evaluates those areas relative to regulations, consensus standards, and best practices. One of the key first steps of the evaluation is collecting and testing representative material samples. The initial challenge is determining which tests and which samples are necessary for the DHA. Exponent can help develop sampling and testing plans that set up a DHA for success.
Critical parameters to manage combustible dusts hazards include:
- whether a dust is combustible
- whether it is capable of dispersing to form an explosible mixture
- the ease of ignition of the mixture
- the magnitude and rate of pressure generation of the potential explosion
These parameters can also change not only with variations in material composition but with physical properties including particle size, shape, morphology, and moisture content. Thus, when testing dust, the location or equipment from which a sample is taken is important.
Exponent works with clients to identify the most relevant and efficient sample collection strategy. Samples of material from different portions of facilities are typically collected, either by Exponent or the client, and the samples are tested at Exponent's Combustible Dust Testing Laboratory.
Standard ASTM International testing and custom methods developed by Exponent are used to evaluate the fire and explosion hazard of materials. Based on the measured hazard level, when appropriate, we assist clients in identifying mitigation techniques and applicable standards and regulations for the prevention of dust explosions, including standards developed by the National Fire Protection Association (NFPA).
Exponent can also aid clients in evaluating proposals from equipment vendors to find cost-effective options to mitigate hazards.
Exponent professionals track changes to federal and state regulations and enforcement practices. We regularly analyze databases of Occupational Safety and Health Administration citations to identify common areas of noncompliance in facilities.
Many consensus industry standards are revised on a regular basis, and these revisions can retroactively change the landscape of requirements that a facility may face in its efforts to manage its combustible dust hazards. Exponent engineers are well versed in National Fire Protection Association (NFPA) standards and recommended practices, and many serve as members of the technical committees (or the technical correlating committee) that oversee the development, coordination, and updating of standards related to combustible dust including:
NFPA 61: Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities
NFPA 68: Standard on Explosion Protection by Deflagration Venting
NFPA 69: Standard on Explosion Prevention Systems
NFPA 91: Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids
NFPA 484: Standard for Combustible Metals
NFPA 499: Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
NFPA 652: Standard on the Fundamentals of Combustible Dust
NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
NFPA 655: Standard for Prevention of Sulfur Fires and Explosions
NFPA 660: Standard for Combustible Dusts
NFPA 664: Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities
Exponent's Combustible Dust Testing Laboratory (CDTL) provides results that help evaluate and mitigate combustible dust hazards. We help clients select the right testing and offer a variety of testing options including standardized ASTM International methods, as well as customized testing solutions. Our CDTL provides testing capabilities to screen materials for combustibility and measure the ignitability, thermal stability, and combustibility of materials, as well as other relevant material properties.
Exponent also leverages the CDTL to perform groundbreaking research, such as the development of a flash fire screening test for assessing the potential for flash fires (unconfined combustible dust deflagrations) and the performance of personal protective equipment fabrics in dust flash fires and explosions. Our staff are not only experienced in performing these tests, but they also have deep expertise in interpreting the test results and how the sample and method can impact the test result.
In addition to testing and characterization, we provide expert guidance on design validation for equipment, processes, or protection systems; upgrading existing dust collection systems or investing in new ones; and identifying safe dust control processes and equipment. Our expertise in all areas of combustible dust safety is based on our depth of experience as members of both the ASTM E27 Hazard Potential of Chemicals committee, which is responsible for many of the ASTM standards for testing combustible dust, and the National Fire Protection Association (NFPA) committees related to the assessment and mitigation of combustible dust hazards.
Brief descriptions of our most common test methods are listed below. Testing can also be performed in accordance with international standards, including EN 13281, EN 14034, EN 50281 ISO 6184-1, and VDI 2263. Exponent can design testing programs using additional methods in our laboratories or at other testing facilities.
For more information about Exponent's combustible dust testing capabilities, or to inquire about testing your material, please contact us at dust@exponent.com.
- Combustibility Screening Test: A torch is held at one end of a triangular cross-section trough or train of powder to determine whether the sample ignites and the rate of propagation along the length of the sample. The test is described in NFPA 484 Standard for Combustible Metals and NFPA 652 Standard on the Fundamentals of Combustible Dust. Testing can be performed based on criteria in NFPA 484, NFPA 652, UN/DOT/GHS 4.1, or EPA 1030 test methods.
- Explosibility (Go/No-Go) Screening Test: Dust samples of at least two different concentrations are dispersed in a 20-L spherical combustion chamber and exposed to a 2.5- or 5-kJ ignition source to determine whether the material is explosible (Go) or not explosible (No-Go). If a threshold overpressure is exceeded at any single concentration, the dust is considered explosible. Full explosion severity (Pmax/KSt) testing is often performed on dust samples found to be explosible during the Go/No-Go testing. Testing is performed in accordance with ASTM E1226 Standard Test Method for Explosibility of Dust Clouds.
- Explosion Severity (Pmax/KSt) Testing: Dust samples are dispersed in a 20-L spherical combustion chamber and exposed to a 10-kJ ignition source. Multiple tests are performed at increasing concentrations to find the maximum pressure and rate of pressure rise. The Pmax and KSt are used in the design of explosion protection systems, such as explosion vents and in hazard analysis calculations. Testing is performed in accordance with ASTM E1226 Standard Test Method for Explosibility of Dust Clouds.
- Minimum Explosible Concentration (MEC) Testing: Dust samples are dispersed and exposed to a 2.5- or 5-kJ ignition source in a 20-L spherical combustion chamber, beginning with a very small dust concentration. The concentration of dust in the chamber is varied incrementally until a threshold explosion overpressure is measured. The MEC is used to evaluate whether dust concentrations in an enclosure are high enough to be ignitable. Testing is performed in accordance with ASTM E1515 Standard Test Method for Minimum Explosible Concentration of Combustible Dusts.
- Limiting Oxygen Concentration (LOC) Testing: Dust samples are dispersed and exposed to a 5-kJ ignition source in a 20-L spherical combustion chamber in mixtures of diluent and oxygen. The limiting oxygen concentration occurs at the lowest concentration of oxygen at which a threshold explosion overpressure is exceeded. The LOC is used to determine the required level of inerting in some explosion protection systems. Testing is performed in accordance with the working draft of ASTM 2931 Standard Test Method for Limiting Oxygen (Oxidant) Concentration of Combustible Dust Clouds.
- Flash Fire Screening Testing: Exponent engineers have developed novel test methods for assessing the potential for unconfined combustible dust deflagrations (flash fires). Current standards rely on confined explosibility testing to determine whether or not a flash fire is a potential hazard. The flash fire screening test is performed by dispersing dust with compressed air into localized dust clouds and subjecting it to various ignition sources including spark igniters, chemical igniters, or flames.
- Minimum Ignition Energy: A dust cloud is dispersed in a glass tube and the electric spark energy is varied in multiple tests to determine the minimum spark energy that will ignite a dust cloud. The data can be used to evaluate whether various ignition sources, such as electrostatic sparks, can ignite the material. Testing is performed in accordance with ASTM E2019 Standard Test Method for Minimum Ignition Energy of a Dust Cloud in Air.
- Hot-Surface Ignition Temperature of Dust Layers: A layer of dust of specific thickness is placed on a hot surface, and the surface temperature is varied in multiple tests to determine the minimum surface temperature at which the dust layer ignites or rises above a threshold temperature. Tests can be performed at multiple thicknesses as the ignition temperature generally decreases with increasing dust-layer thickness. The data can be used to determine maximum allowable surface temperatures of equipment where dust layers may be present. Testing is performed in accordance with ASTM E2021 Standard Test Method for Hot-Surface Ignition Temperature of Dust Layers.
- Dust-Cloud Minimum Autoignition Temperature (MAIT) Test: Dust clouds are dispersed in a cylindrical furnace to determine the minimum temperature at which the dust cloud will self-ignite without an ignition source present. The MAIT is used to determine safe operating temperatures where dust clouds may be present in heated equipment such as ovens and dryers. Testing is performed in accordance with ASTM E1491 Standard Test Method for Minimum Autoignition Temperature of Dust Clouds.
- Differential Scanning Calorimetry and Thermogravimetric Analysis (DSC/TGA): DSC/TGA is performed on small dust samples to determine the approximate onset ignition temperature and heat of reaction of materials. The weight loss or gain of material can also be used to determine the fraction of the sample that is reactive (or combustible).
- Accelerating Rate Calorimetry (ARC): ARC testing is used to determine the onset (ignition) temperature for self-heating of materials. The apparatus approximates an adiabatic condition that is more representative of self-heating at industrial scales than DSC/TGA testing. The onset temperatures can be used to determine temperatures at which self-heating and ignition may occur in storage or heated process equipment like ovens or dryers.
- Oven Tests: Exponent performs a variety of oven tests using different sized samples and controlled air-flow conditions to determine onset (ignition) temperatures of self-heating in various processes or equipment.
- Sieve Analysis: A series of sieve screens with different-size openings is used on a sieve shaker to analyze the particle size distribution of the material. The sieves can also be used to screen out specific size fractions of material for testing.
- Size Reduction: Ball mills, grinders, and other equipment are used to reduce the size of particles when testing of a smaller particle size fraction is desired.
- Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM/EDS): SEM/EDS can be used to examine individual particles to determine their size, shape, morphology, and elemental composition. Exponent has also used SEM/EDS as a tool to examine post-explosion residues to determine whether the material served as a fuel in the explosion.

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