Dust Explosion Prevention: Reducing Combustible Dust Hazards in Dust Collection Systems

In any industrial production environment, dust explosion prevention strategies and measures are essential to stop flash fires, explosions, or regular fires from occurring related to combustible dust produced and accumulated within the facility. Combustible dust hazards present very real dangers for fires and explosions in industrial production and processing plants and facilities. Dust explosion prevention protects workers, visitors, equipment and machinery, buildings and adjacent buildings, and in some cases, even neighborhoods, from the dangers posed by combustible dusts.

Evaluating Dust Explosion Risk

Combustible dust is a combustible particulate matter suspended in the air or through other oxidizing mediums. These dusts consist of exceptionally fine material that hold combustible properties which have the ability to catch fire and explode when mixed with air. They derive from most solid organic materials, such as flour, grains, sugar, wood, and so on. But they can also form out of finely ground metals and nonmetallic inorganic materials. In the U.S. alone, between 2016 and 2019 there were 450 fires and 133 explosions caused by combustible dust. The incidents resulted in 156 injured and 12 deaths, along with extensive property damage.

Combustible dusts in workplaces result from dry material processes—cutting, abrasive blasting, crushing, sifting, mixing, sifting or screening, and become suspended in the air in a variety of ways—during transportation, handling, processing, grinding, shaping and polishing of materials. The dried residue from wet materials can also produce combustible dusts that pose a risk. The buildup of dried residue from the processing of wet materials can also generate dusts. Essentially, any workplace that generates dust is potentially at risk.

The risk for dust explosion then, is present in workplaces that produce or generate dust, that is, any industry whose production processes produce fine particulate matter as a byproduct. This includes such environments as food production facilities, chemical manufacturing plants, woodworking facilities, furniture factories, and mills, metal processing plants, coal-fired plants, grain elevators, recycling facilities, wastewater treatment plants and facilities that produce paper products, pharmaceuticals, textiles and so forth.

The key to preventing dust explosions from occurring is in implementing effective dust collection systems to mitigate those risks. This would include: following OSHA guidelines on combustible dust and NFPA standards for limiting explosion risks, identify the hazards in workplaces, dust testing and dust testing analysis, and ensuring that the dust collector complies with regulations and is properly maintained. To elaborate:

The OSHA National Emphasis Program for Combustible Dust

The Combustible Dust National Emphasis Program is an OSHA instructional directive. Its focus established policies and procedures to inspect workplaces that create, produce, or handle combustible dusts—those types of dusts that may cause a deflagration, explosion or other fires. OSHA’s National Emphasis Programs (NEPs) are temporary programs that allow the agency’s resources to focus on a particular hazard or on high-hazard industries on local, regional or national levels. The Combustible Dust NEP was first issued in 2007, and reissued and expanded upon in 2008 after the Imperial Sugar Refinery incident, with additional changes made to it in 2015.

The purpose of the Combustible Dust NEP is to inspect facilities that generate or handle combustible dusts that pose a deflagration or other fire hazard. However, the NEP is but a set of instructions that contain policies and procedures for inspecting workplaces that generate or handle combustible dusts. OSHA can inspect facilities in any industry where a hazard from combustible dust exists, but under the Combustible Dust NEP directive it cannot specifically cite a company for violations because emphasis programs are not standards or laws. What the NEP does allow OSHA to do is inspect premises with potential combustible dust hazards and to enforce combustible dust safety with OSHA other standards found in Title 29 CFR, Part 1910 and in the General Duty Clause which requires companies to provide a safe, healthy workplace for their employees.

NFPA Standards for Limiting Explosion Risks

NFPA is the National Fire Protection Association. Established in 1896, it is a global, nonprofit organization (NPO) that promotes and develops standards, codes, and training, among other programs, for fire and explosion safety. As an independent NPO, NFPA is not a regulatory body nor does it issue fines or conduct inspections. What it does do is provide the standards by which other bodies and organizations follow. NFPA standards are used as the legal basis for many building codes and insurance companies.

NFPA standards play an important role in OSHA’s Combustible Dust NEP inspections by encouraging inspectors to follow NFPA standards to determine if there are dust safety issues at a plant or facility. OSHA inspectors can use NFPA standard 625, the Standard on the Fundamentals of Combustible Dust, NFPA standard 654 for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing and Handling of Combustible Particulate Solids, and NFPA 68 Standard on Explosion Protection by Deflagration Venting and NFPA 69 Standard on Explosion Prevention Systems. NFPA also has a newer combustible dust standard to dust hazard analysis on record for presentation to “the authority having jurisdiction” for the enforcement of building codes and fire safety inspections.

Identifying Combustible Dust Hazards

There are a number of factors that must be considered in identifying potential combustible dust hazards. All dust explosion possibilities should be inspected. Chief among these are analyzing methods of dust dispersion, the size of the particulate matter, the characteristics of the facility’s ventilation system, air currents within the facility, possible ignition sources, where dust is accumulating, formation and confinement of dust clouds, and noting physical barriers to effective dust collection. Conducting risk assessments are industry specific, with inspectors well aware of the combustible properties of material they are analyzing in the workplace.

Dust Testing and Dust Testing Analysis

Any type of dust resulting from a production and processing activity in a plant or facility should be tested to determine the risk of it being combustible. Following NFPA standards, facilities that generate potentially-explosive dusts must provide dust testing and a dust hazard analysis. Dust testing entails a comprehensive evaluation of the particulate matter. Testing should be conducted by a qualified laboratory that can not only test the dust’s explosive potential, but also has the capability to analyze and explain the findings, and provide the required documentation supporting compliance.

An economical and practical way to find out if dust from a facility is explosive is to perform a
Go/No-Go Explosive Screening Test, based on ASTM E1226, “Standard Test Method for Explosibility of Dust Clouds.” Testing consists of a small sample of fine dust exposed to low energy igniters within a small sized testing explosion chamber to determine the explosion over pressure. If the dust is not found to be an explosive threat, the analysis can be aborted to avoid unnecessary fees.

If the dust sample tests positive during screening, further testing should be conducted to determine how rapidly and severe the explosion could be. This requires a KSt/PMax Test which will quantify the severity of a dust explosion. It should be followed up by a MEC Test which shows the concentration of dust and oxygen in the air and the likelihood or risk that it will explode. Lastly, an MIE Test can determine whether a single spark—the smallest amount of ignition energy required—could ignite a dust cloud.

If the Go/No-Go test is negative, further tests can determine what temperature would ignite the dust. This would require to find the Minimum Autoignition Temperature (MIT) of a dust cloud in the air and then a Layer Ignition Test (LIT) to determine the hot-surface ignition temperature of a dust layer. The last test to determine whether a dust will burn and how quickly is a VDI 2263 burning behavior test followed by a UN 4.1 Burn Rate test for additional confirmation.

Ensuring Dust Collectors Complies with Regulations

An industrial dust collector is a type of air pollution control equipment used in factories, plants, warehouses and other industrial or commercial settings to meet environmental and workplace safety requirements.

Selecting the appropriate dust collector for a processing plant or production facility should be guided by the dust collector that is best-suited for the specific work environment of that company. Industrial dust collection systems must clear, filter and clean air inside and outside of plants in operations that generate particulate matter. The correct size dust collector will make sure the system is efficient at capturing particulate matter as well as in compliance with regulations.

To ensure compliance with regulations and that standards are met, CPE Filters designs and tailors dust collection and explosion protection solutions for each plant’s specific application and process conditions. In design of appropriate dust extraction and collection systems, inlets, ideally, should be located as close to the dust producing process as possible. Follow NFPA, ATEX, and FM required standards and codes when installing systems. To protect the workplace, adhere to OSHA guidelines, and keep manufacturing operations running reliably, dust collectors should be located outdoors, where possible.

The right dust collector system offers protection from combustible dust, will keep plants safe, and companies in compliance with the latest standards and regulations.

Dust Explosion Prevention Housekeeping Program

Establishing a housekeeping program that regularly removes dust from facilities is an important first step toward mitigating dust explosion hazards. As part of a good housekeeping program, plants and facilities should have proper dust collection systems and filters in place and in operation at all times. Employees should also be trained and familiar with the hazards of combustible dust. Housekeeping programs should identify open areas and overhead structures where dusts may accumulate. There are also many areas “hidden” in plain sight where combustible dust can gather. Some of the prime hiding places are above false ceilings, inside ducts, ventilation systems, conveyor equipment, and even on support beams. Settled dust should not be stirred by traditional cleaning methods. Use vacuums approved for dust collection only.

Combustible dusts are particulate matter from the residue of finely ground organic or metal materials generated in production facilities and processing plants. The dusts have combustible properties with the potential of catching fire and exploding when mixed with air. Risks of dust explosions are associated with any industry that produces or handles dry particulate material. To prevent dust explosions from occurring, follow OSHA recommendations, while implementing hazardous dust inspections and regular testing and analysis that comply with NFPA standards and codes. Finally, having a good housekeeping program in place can identify potential hazards in advance that enable companies to take effective preventive measures.

To learn more about dust explosion prevention, please contact us at CPE Filters today.