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NFPA 652
Guidelines for Managing Combustible Dust
NFPA 652 serves as an essential framework for effectively managing the risks associated with combustible dust. By adhering to NFPA 652, organizations can ensure the implementation of necessary measures to safeguard personnel, equipment, and facilities against the potentially devastating consequences of combustible dust fire, flashfire, and explosion incidents.
Since 1920, the National Fire Protection Association (NFPA) has been making rules to keep people safe from combustible dust. However, it was only in 2015 that they made NFPA 652, a big set of rules for managing the risks of fires and explosions from combustible dust. This was a big step in keeping workplaces safe from these kinds of accidents.
In this technical blog post, we’ll explore various aspects of NFPA 652 standards. Here’s what you’ll find in this article:
What is NFPA 652?
NFPA 652, Standard on the Fundamentals of Combustible Dust, outlines the general requirements for managing combustible dust fire and explosion hazards. It also directs users to NFPA’s industry or commodity-specific standards as needed.
NFPA 652 outlines crucial rules for identifying and handling fire, flash fire, and explosion risks linked to combustible dusts and particulate solids. The standard outlines the essential requirements for managing fire, flash fire, and explosion hazards associated with combustible dust. It also provides users with guidance on additional NFPA standards that address industry and commodity-specific requirements, as detailed in the table below.
The NFPA 652 standard is relevant to all facilities and operations engaged in manufacturing, processing, blending, conveying, repackaging, generating, or handling combustible dusts or combustible particulate solids.
The following are exempt from the standard:
Storage or use of consumer quantities of these materials in residential or office buildings
Storing or using commercially packaged materials in retail locations
Materials intended for personal, household, or building use, displayed in their original packaging in mercantile settings
Storage of sealed containers of these materials in warehouses, provided they are not linked to operations that handle or produce combustible dust
Storage of sealed containers of these materials in warehouses not involved in handling or producing combustible dust
What is combustible dust?
As per NFPA 652,combustible dust is defined as finely divided combustible solid particles that pose flash-fire or explosion risks when airborne in air or certain process-specific oxidizing mediums across various concentrations. When used in this standard, combustible dust includes powders, fines, fibers, etc.
Dusts were traditionally defined as materials 420 µm or smaller which can pass through a U.S. No. 40 standard sieve. To ensure consistency with other standards, a size of 500 µm, capable of passing through a U.S. No. 35 standard sieve, is now considered appropriate.
Combustible dust is dangerous because it can lead to fires and explosions. When fine particles of certain materials become suspended in the air, they can ignite easily, causing rapid combustion. Additionally, if these particles accumulate in confined spaces, such as within machinery or ductwork, the risk of explosion increases significantly.
The manager of a facility containing potentially combustible dust is tasked with the following responsibilities:
- Assessing the combustibility and explosibility risks of materials
Recognizing and evaluating fire, flash fire, or explosion hazards
Controlling identified fire, flash fire, and explosion hazards
- Informing affected personnel about the hazards
Elements Required for Combustible Dust Flash Fires and Explosions
When dealing with combustible dust, the same elements—fuel, oxidant, and ignition source—are essential for triggering dust flash fires and explosions. Understanding this mechanism is essential. The fire triangle—consisting of fuel, oxidant, and ignition source—illustrates the conditions necessary for combustion. A flash fire occurs when combustible dust is released into the air without confinement. In contrast, an explosion happens when there’s sufficient energy within a confined space to overwhelm the material’s containment capabilities.
According to NFPA 652, the definitions are as follows:
Fire Hazard: Any circumstance, procedure, substance, or state that can ignite a fire or contribute to fuel availability to increase fire spread or intensity, endangering life or property.
Flash Fire: A fire that swiftly spreads through a dispersed fuel like dust, gas, or the vapors of an ignitable liquid via a flame front without generating harmful pressure.
Explosion: The bursting or breaking of a container or enclosure caused by internal pressure buildup resulting from a deflagration.
Hazard Identification
The initial step requires the manager to determine if the potentially combustible dust is indeed combustible or explosive. If it is, they must then characterize the material’s properties as needed to support the Dust Hazard Analysis (DHA).
Laboratory Testing – Laboratory testing is conducted to determine the combustibility and explosibility of dust particles. This testing helps in understanding the specific characteristics of the dust, such as particle size, moisture content, and ignition sensitivity. NFPA recommends performing tests on materials rather than relying solely on literature data. Literature data may not accurately reflect the conditions under which materials are used or stored, making testing essential for ensuring safety.
Determination of Combustibility
To determine combustibility, the material shall be considered combustible if the tested dust ignites, propagates combustion, or ejects sparks from the heated zone after the heat source is removed.
If any of these criteria are met, the material is considered combustible. If the combustibility is not known, it should be determined by one of the following tests:
- A screening test based on UN Recommendations on the Transport of Dangerous Goods: Model Regulations- Manual of Test and Criteria, Part 3 Subsection 33.2.1, Test N .1, “Test Method for Readily Combustible Solids”
- Other equivalent and fire exposure test methods
Determination of Explosibility
The Go/No Go explosibility test is used when the explosivity is not known. Determination of explosibility of dust shall be determined according to one of the following tests:
- The “Go/No-Go” screening test methodology described in ASTM E1216, Standard Test Method for Explosibility of Dust Clouds
- ASTM E1515, Standard Test Method for Minimum Explosible Concentration of Combustible Dusts
- An equivalent test methodology
Standard Test Methods to Determine Explosibility Properties
Many individuals often inquire about the need for a dust hazard assessment to determine if their dust is explosive. The answer is unequivocally yes. The reason lies in the potential explosibility of materials used in various processes. Without accurate testing, it’s impossible to ascertain whether a material is explosible.
To conduct a dust hazard assessment, samples of the material must be tested in accredited laboratories capable of determining their explosibility. Relying solely on historical data or the absence of previous incidents is insufficient, as conditions may have changed over time or may differ from those in historical records.
Several factors influence the explosibility of materials, including particle size, humidity, and initial temperature. Particle size plays a crucial role, as finer particles have a greater propensity to suspend in the air, increasing the risk of dust explosions. Additionally, environmental conditions such as humidity and temperature can affect the combustibility of materials. NFPA recommends performing tests on materials rather than relying solely on literature data. Literature data may not accurately reflect the conditions under which materials are used or stored, making testing essential for ensuring safety.
Dust Hazard Analysis (DHA)
NFPA 652 defines a Dust Hazard Analysis (DHA) as a thorough examination of fire and explosion risks to assess potential consequences and identify measures to prevent or reduce those risks. The DHA assesses the hazards of fire, deflagration, and explosion and offers recommendations to mitigate them. Results, along with any required action items for changes to process materials, physical processes, operations, or facilities, must be documented. The facility owner with combustible or explosible materials in an enclosure must ensure a DHA is completed. The absence of previous incidents is not a valid reason to avoid conducting a DHA. A qualified individual must conduct or oversee the DHA, which should undergo review and updates at least every five years, regardless of any changes to the facility or processes. Additionally, a DHA is necessary for new installations, expansions, or upgrades to existing installations.
The DHA shall include:
- Identification and assessment of the areas within a process or facility where fire, flash fire, and explosion hazards are present
- Where these hazards are present, identification and evaluation of specific fire and deflagration scenarios, including::
– Determine safe operating ranges
– Identify existing safeguards for managing fire, deflagration, and explosion events.
– Provide recommendations for additional safeguards, including an implementation plan.
Provide recommendations for additional safeguards, including an implementation plan. The qualified person or team leader or performing the Dust Hazard Analysis (DHA) should have experience in conducting DHAs and be knowledgeable about the hazards associated with combustible dust. The team members can include facility operators, engineers, or equipment manufacturers, as well as consultants. The diverse background and expertise of the team should encompass the following areas:
- Familiarity with the process
- Operations and maintenance
- Process equipment and safety systems
- History of operation
- Properties of materials
- Emergency procedures
Management Systems
Following the DHA findings, specific management system measures are put in place to reduce risks linked with combustible dust. The manager establishes written procedures and training, in a language that participants understand, for operating the facility and equipment to prevent or mitigate fires, deflagrations, and explosions caused by combustible particulates. A periodic walkthrough of operating areas will be conducted to verify compliance with operating procedures and safe work practices. Additionally, the manager shall establish safe work practices to address maintenance and servicing hazards, applicable to employees and contractors.
These measures span various areas including engineering controls like building and equipment design, housekeeping practices, ignition source control, and personal protective equipment. In addition, they encompass dust control, explosion prevention/isolation, and fire protection systems. Administrative controls such as training programs, standard operating procedures, and emergency response plans are also established to maintain safety standards and regulatory compliance.
Training and Hazard Awareness
General safety and hazard awareness training for combustible dust and solids shall be provided to all affected employees, including contractors, temporary workers, and visitors, according to their potential exposure to combustible dust hazards and associated risks. Job-specific training ensures that employees are knowledgeable about the fire and explosion hazards of combustible dust and particulate solids in their work environment, and all training shall be documented.
Sigma-HSE can support you in effectively understanding and implementing the requirements of NFPA 652 in your facilities and operations. Our process safety consultants offer services such as laboratory testing, Dust Hazard Analysis (DHA), and training. We also provide employee training to ensure comprehensive understanding and implementation.
The content of this blog was partially developed with assistance from the NFPA standard titled ‘Standard on the Fundamentals of Combustible Dust’ (NFPA 652, 2019) by the National Fire Protection Association.
