June 18, 2008Client Alert

Combustible Dust: Complying with OSHA Regulations and Preventing the Hazards of Combustible Dust

Over the last few decades, American industries have been plagued by fires and explosions caused by the ignition of combustible dust. Since 1980, there have been approximately 350 fires and explosions resulting in over 100 fatalities. The latest incident occurred on February 7, 2008, where an explosion, caused by the ignition of sugar dust, killed thirteen people at a sugar refinery in Port Wentworth, GA. Soon after the Port Wentworth explosion, the U.S. Congress began to take notice of this explosive issue, quickly placing blame on the Occupational Safety and Health Administration (OSHA) for failing to adequately address the hazard of combustible dust explosions. Congress has since introduced a bill, H.R. 5522, which would require OSHA to implement a new mandatory standard, forcing employers to address combustible dust hazards. Moreover, 60 Minutes recently severely criticized OSHA for not doing more to prevent such explosions.

In defense to the attacks by Congress and the media, Assistant Secretary of Labor, Edwin Foulke, argued before Congress that "OSHA already has tough standards on the books that address combustible dust hazards." Specifically, Foulke claimed that OSHA's housekeeping standards, 29 C.F.R. 1910.22 and 1910.176(c), general duty clause, Section 5 (a)(1), and electrical equipment safety requirements under 29 C.F.R 1910.307, adequately address the risk of hazardous dust accumulations. In his testimony in front of Congress this past spring, Foulke declared that OSHA intends to inspect hundreds of companies within the next year and issue citations under the above cited standards. This article will address those standards, how they are applied by OSHA, and employer defenses. In March 2008, OSHA issued a notice to about 30,000 companies nationwide indicating to them that they may be "at risk" for combustible dust explosions. OSHA area offices will use this list to target employers for inspection. These companies need to be aware not only of the risk combustible dust presents to their employees and facilities, but also how OSHA will target them and issue citations, and the measures that should be taken in response to this exposure.

Combustible Dust: What Is It?

Combustible dust is finely ground organic or metal material that can cause an explosion or fire when suspended in air and exposed to a sufficient source of ignition. According to the National Fire Protection Association (NFPA), combustible dust is any "finely divided solid material that is 420 microns or smaller in diameter (material passing a U.S. No. 40 Standard Sieve) and presents a fire or explosions hazard when dispersed and ignited in air." A variety of industries can produce combustible dust, including the production of plastics, wood, rubber, furniture, textiles, pesticides, pharmaceuticals, dyes, coal, metals (such as aluminum, chromium, iron, magnesium, and zinc) as well as food products (including candy, starch, flour, and animal feed). A material need not generally be combustible in its original form to become combustible dust when broken down into fine enough particles. For example, generally, sugar will not ignite, but the finely ground sugar dust at the sugar refinery in Port Wentworth, GA apparently was combustible. The NFPA has noted that "any industrial process that reduces a combustible material and some noncombustible materials to finely divided state presents a potential for a serious fire or explosion." Thus, items such as sugar, when ground fine enough, create combustible dust that can produce catastrophic fires and explosions.

Combustible Dust Explosions: How Do They Happen?

Five elements are needed for a combustible dust explosion to occur: 1) combustible dust, 2) ignition, 3) oxygen, 4) dispersion and concentration of dust particles, and 5) confinement of the dust cloud. Two of these elements, oxygen and confinement of the dust cloud, are difficult to control as oxygen is found within the air and materials are generally processed within confined buildings. The other elements, however, can be controlled through regular cleaning and removal of dust, use of proper electric equipment and control of other ignition sources such as open flames and static electricity, as well as the isolation of hazards and installation of proper sprinkling or extinguishing systems.

Often there are two explosions or fires in a combustible dust explosion. The first, or primary, explosion creates not only another ignition source but also may disperse more combustible dust in a confined area. This dispersion of material, if ignited, will create a second, often more destructive, explosion. If one of the five elements of a combustible dust explosion "is missing, a catastrophic explosion will not occur." However, there is still a great risk of a combustible dust fire occurring if elements 1 through 3 (combustible dust, ignition, and oxygen) are present.

Combustible Dust Citations: When Will OSHA Cite for Combustible Dust Violations?

Despite the fact no specific OSHA standard exists regulating the presence of combustible dust , OSHA has directed its compliance officers to cite employers under several regulations it uses to address the issue. Below is a listing of just some of the citations a company could receive for having combustible dust present in its plant or factory. In many cases, the accumulation of combustible dust will result in more than one citation.

I. General Housekeeping Citations, 29 C.F.R. 1910.22

The general housekeeping standard requires that "all places of employment, passageways, storerooms, and service rooms shall be kept clean and orderly and in a sanitary condition." The standard further demands that every workroom floor be kept clean, dry, and free from nails, splinters, holes, and loose boards. While this standard does not appear to be intended to address the hazards of combustible dust, OSHA has announced it will issue a citation for the presence of combustible dust under this standard if dust accumulations 1) exceed 1/32-inch deep, 2) cover at least 5% of a room's total area or 1,000 square feet, and 3) are combustible. Dust that has accumulated to a depth of 1/32 inch is about the thickness of a standard paper clip. Dust accumulations inside dust collection systems, containers, or mixers are not subject to this standard, but may be subject to OSHA's general duty clause as discussed below.

To determine whether dust is combustible, an OSHA inspector will collect samples of the dust to be tested for combustibility under laboratory analysis. Often, OSHA inspectors take "bulk samples," sampling dust from many different areas of the plant and combining them into a 1-liter plastic bottle. OSHA inspectors are instructed to take samples from lower areas within their reach, unless beams, joists, and ducts that are located higher can be accessed safely. Nevertheless, dust accumulations on overhead beams, joists, ducts, tops of equipment, and other surfaces are included in determining the total dust coverage area, even if no dust is sampled from those locations.

This bulk sample collection methodology is subject to attack because it does not accurately quantify the combustibility of dust in all areas of the factory. For example, in one small area, dust could be ground to a very fine powder because of the process in that area. If the bulk sample contains a significant portion of dust from that small area, the entire bulk sample could test out as combustible. Yet, other dusts in the facility, including the dust on beams, joists, conduits, and other high areas, would be different and might not be combustible. OSHA's methodology of testing may not meet OSHA's burden to prove a hazard because it only establishes the presence of some combustible dust.

Furthermore, citing an employer under this standard may not provide that employer adequate due process. Nowhere in the language of the general housekeeping standard, which is found under the "Walking-Working Surfaces" sub-section of the OSHA standards, does it state that an employer must keep clean and orderly places where employees do not work or walk. As areas such as ceilings, ducts, and beams are not commonly considered areas where employees work or walk, it would not be reasonable for an employer to be expected to consult this standard regarding obligations related to such high places. Thus, the standard, as applied to non-working or walking areas, appears to be overly vague and ambiguous and does not provide the employer adequate forewarning or due process.

Another problem exists with OSHA's instruction to its compliance officers. The threshold level of dust used for citation purposes (i.e. 1/32-inch over 5% of the total area) is contained in NFPA Standard 654. But, there are different NFPA standards for specific substances, such as wood dust, that contain a different threshold. Arguably, the NFPA standard governing the specific type of dust should supersede the more general NFPA Standard 654. NFPA standards are developed by multiple parties who have an interest in the particular subject matter. They are not law, and often one NFPA standard may disagree with other NFPA standards. As OSHA attempts to apply its citation policy in a mathematical fashion to industry, there are going to be many cases where an employer can point to conflicting NFPA standards and other industry guidelines. Until OSHA establishes a regulation, the general housekeeping standard will be a poor mechanism for providing notice to employers as to legal obligations concerning combustible dust. Other accidents may happen, and when they do, there will be serious disputes regarding the standards of care applicable to the specific worksite.

II. General Duty Clause Citations, Section 5 (a)(1)

The use of collection systems in industry has become widespread. These systems substantially reduce the amount of dust accumulations in the zone of employee work areas. However, it is very difficult to eliminate nuisance dust escaping these systems and accumulating in higher areas of facilities. The systems themselves can be, and often are, the origin of combustion. This is likely one of the contributing factors in the increased number of explosions in recent years. There is no OSHA standard specifically written to address the design or use of dust collection systems. Therefore, OSHA applies its general duty clause to alleged hazards involving dust collection systems. The general duty clause is contained in Section 5 (a)(1) of the Occupational Safety and Health Act (OSH Act), 29 U.S.C. ยง654(a)(1).

Section 5 (a)(1) of the OSH Act states that "each employer shall furnish to each of his employees, employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees...." OSHA will cite an employer under 5 (a)(1) for explosion or fire hazards that are caused from combustible dust within a dust collection system, containers, or mixers. The focus of the general duty clause citation is the presence of the hazard, rather than use a particular abatement method. A citation will only be issued if all elements of 5 (a)(1) are met: 1) place of employment, 2) recognized hazard, and 3) causing or likely to cause death or serious physical harm.

Before an OSHA inspector arrives, an employer should ensure that someone in the company understands the integral parts of the company's dust collection system enough to explain to OSHA inspectors what precautions are in place. Because a general duty citation will not be issued for the use or lack of a particular abatement method, it is difficult for OSHA to identify what is enough for a hazard to be controlled and a citation avoided. However, because perception is a big part of whether OSHA determines that an employer has taken precautions aimed at eliminating a "recognized hazard" the ability to explain integral safety equipment may be as important as the equipment itself, when it comes to avoiding citations. It is helpful to have someone within the company know and understand all parts of the system. Some important features include spark arrestors, heat sensors, alarms, blast gates and sprinkler systems. Drawings of the system identifying these safety features are very helpful in identifying them to OSHA and demonstrating the kind of advance precautions OSHA is looking for. An employer should not allow the inspection without the person who understands or can explain the safety features. It is difficult to reverse a poor first impression.

While OSHA may issue a citation alleging that the system is not adequately protected, if the system has been designed with some safety features and maintained well, it will be difficult for OSHA to establish a 5 (a)(1) violation based on the lack of other features. Of course, if an explosion has occurred, this may bolster OSHA's proof that the missing design element was a hazard. But even in that case, OSHA must also establish a recognition on the part of the employer or those in its industry, that a particular safety component was necessary to avoid the hazard. Obviously, if OSHA were to develop a standard which identified the required safety features for dust handling systems, its burden would be much lower.
For employers that have been placed on OSHA's target list, an assessment of dust collection system safety should be performed under the direction of legal counsel. The analysis may be subject to protection as attorney work product. If not, it may provide the requisite evidence that the hazard was recognized.

III. Housekeeping Citations in Storage Areas, 29 C.F.R. 1910.176(c)

The housekeeping standard for storage areas provides, in relevant part, that "storage areas shall be kept free from accumulation of materials that constitute hazards from, explosion...." Like the requirements for 1910.22 violations, OSHA will issue a citation under this standard if dust accumulations in storerooms 1) exceed 1/32 inch deep, 2) cover at least 5% of a room's total area or 1000 square feet (whichever is less), and 3) are combustible. The OSHA inspectors are instructed to also "document whether a reasonable person would recognize a combustible dust hazard under the circumstances." This demonstrates that OSHA has acknowledged the very broad nature of its standard for storage areas, and is looking for more obvious cases of excessive dust accumulation.

It would be beneficial to an employer to inspect dust in storage areas themselves prior to OSHA inspections. If dust accumulation is over 1/32 inch, a company should consult a qualified industrial hygienist to test the combustibility of the dust. Again, the company should consider having the inspection of the storage room done at the direction of legal counsel. Employers who are on one of OSHA's numerous inspection targeting lists may protect the results as attorney work product prepared in anticipation of inspection by a government regulator. If results are not protected under attorney work product, OSHA could use the information from the inspection as evidence to issue a willful citation against the company.
Similar to citations under the general duty clause discussed above, OSHA will need to meet a greater burden of proving a hazard under 1910.176(c) because the standard provides no specific actions that must be taken. Some evidence of a cleaning program in these areas may refute OSHA's citation. Additionally, different NFPA or other industry guidelines may provide a higher threshold for dust accumulation. Prior to accepting a citation, these other guidelines should be consulted.

IV. Housekeeping Citations for Coal-Handling Plants, 29 C.F.R. 1910.269

The housekeeping standard for coal-handling plants, 29 C.F.R. 1910.269(v)(11)(xii), requires that an employer eliminate or safely control sources of ignition in coal-handling operations that may produce a combustible atmosphere from flammable gases or dust. OSHA will issue a citation under this standard, and not under the general housekeeping standard, 1910.22, or the general duty clause, 5(a)(1), if an employer has not eliminated or controlled ignition sources in coal-handling operations to prevent ignition of a combustible atmosphere.

It appears from OSHA's National Emphasis Program (NEP) on combustible dust that because coal plants are subject to 1910.269 (which focuses on controlling ignition sources, not dust levels) the 1/32-inch dust requirement that OSHA applies to other industries may not apply to coal plants. It is unclear how OSHA will actually apply 1910.269 to coal plants.

V. Electrical Safety Citations, 29 C.F.R. 1910.307

Section 1910.307 requires that electrical equipment, wiring methods, and installations of equipment in Class II hazardous locations shall be: 1) intrinsically safe, 2) approved for Class II hazardous locations, or 3) safe for Class II hazardous locations. Class II hazardous locations are locations "that are hazardous because of the presence of combustible dust." There are two divisions of Class II hazardous locations. Specifically, Class II Division 1 locations are areas where combustible dust is or may be suspended in air under normal operating conditions, or where mechanical failure or abnormal operation of machinery might cause ignition, or where combustible dusts are electrically conductive. Class II Division 2 locations are areas where combustible dust is not suspended in air under normal operating conditions, but may be suspended as a result of malfunctioning handling or processing equipment, and such dust accumulations may be ignited by abnormal operation of electrical equipment. OSHA will issue a citation under 1910.307 if dust accumulations are 1) determined to be combustible, 2) found within a Class II location and 3) electrical equipment in the same area is not intrinsically safe, approved for Class II locations, or safe for Class II locations.

An employer should inspect and collect dust around electrical equipment. Open panels, missing knockouts on electrical panels and open wiring in areas where there is dust accumulation, may lead to multiple citations for electrical safety. This is probably the strongest standard for OSHA to cite in these situations because it is more specific. Additionally, OSHA can "stack" multiple citations, alleging the housekeeping violation, the electrical safety violation based on the same conditions - excessive dust. Often this forces an employer to accept one or more citations in exchange for deletion of several others.

Employers who are cited for housekeeping and electrical safety violations during the same inspections may have a defense that such stacking of citations is inappropriate, since the housekeeping abatement would eliminate the electrical ignition safety hazard. In addition, OSHA must establish that dust in the area of the alleged electrical ignition source is combustible. The bulk sample testing method discussed above does not prove this. The company would be wise to also test dust near the alleged ignition source separately to identify the hazard or lack of a hazard. Again, this should be done at the direction of legal counsel to protect the results as attorney work product.

VI. Powered Industrial Truck Citations, 29 C.F.R. 1910.178

Section 1910.178 requires that an employer use only certain designated powered industrial trucks, or forklifts, in areas where combustible dust is present. There are eleven different designations for powered industrial trucks. Specifically, in areas where metal or coal dust is present, or where other combustible dust is produced and suspended in air, under normal operating conditions, only power industrial trucks designated as EX may be used. In areas where dust accumulations are not normally suspended in air but may be ignited by sparks originating from the truck itself, or in areas where easily ignited fibers are suspended in the air, but not in large enough quantities to ignite, only powered industrial trucks designated DY, EE, or EX may be used. Also, in locations that store, but do not process, easily ignitable fibers, only trucks designated DS, DY, ES, EE, EX, GS, or LPS may be used. OSHA will issue a citation under 1910.178 if an employer does not utilize the appropriate designated truck for each specified area.

An employer should consider collecting and testing dust in areas where powered industrial trucks are used, particularly because of OSHA's "bulk sampling" method of collecting dust. Specialized fork lifts could be leased or purchased and designated for areas of greater risk. While the dust in one area may not be combustible, OSHA's bulk sampling methodology could lead to the false conclusion that the dust is combustible in all areas. An employer would then be incorrectly cited under 1910.178 for not using specially designed fork lifts in all areas. The abatement could require replacing all forklifts.

Of course, if there is no dust available to become suspended in the air, for example, because of a comprehensive cleaning schedule, specialized forklifts might not be required at all. If OSHA has stacked a housekeeping and forklift citation, it may be possible to eliminate the forklift citation, and the need to replace forklifts might also be eliminated through a comprehensive housekeeping plan.

The Next Step: What Should a Company do to Protect Against Combustible Dust Hazards?

Companies who produce combustible dust should take several precautions to avoid both injury and damage to their employees and facilities, as well as OSHA citations. When explosions occur, the loss of life and property can be devastating, widespread, and may put a company out of business.

First, a company should inspect their plant for dust accumulations throughout the workplace. One simple step is to walk through the facility and look at ducts and piping near the ceiling, tops of electrical panels and equipment, ledges and other surfaces. If they are discolored such that the original paint or metal surface is not visible or barely visible, it is probably time to take precautions. If dust accumulation is over 1/32 inch (the width of a standard paperclip), a company should consult a qualified industrial hygienist to test the combustibility of the dust. If combustible, a cleaning program may be necessary. There are contractors available to perform this service in most areas.

Second, a company should consider implementing ways to control the elements of a combustible dust explosion. The NFPA recommends several practices and policies to prevent combustible dust explosions, including:

  • minimizing the escape of dust from processing equipment or ventilation systems;
  • use of dust collection systems and filters and surfaces that minimize dust collection;
  • inspect and clean dust accumulations in hidden and open areas regularly;
  • use cleaning methods that do not create dust clouds (such as wet processes or vacuuming);
  • use appropriate electric equipment and wiring methods;
  • controlling static electricity, smoking, open flames, sparks, and friction;
  • proper type and use of industrial trucks and cartridge activated tools;
  • separate and segregate hazards with distance or barriers;
  • install and use spark/ember detection, extinguishing, sprinkling, and explosion protection systems.

As noted earlier, OSHA has created a target list of companies for inspection based on these hazards. OSHA has several other targeting programs and lists. Most companies have been placed on one of OSHA's lists. Therefore, legal counsel may be able to direct company self audits and protect the results as attorney work product. Legal counsel should be contacted regarding the specifics of an individual situation.


Combustible dust poses a real threat to America's industries. In light of OSHA's recent promises to target companies that are "at risk" for combustible dust, companies need to be aware not only of the risk combustible dust presents to their employees and facilities, but also how OSHA will target them and the measures that should be taken in response to this exposure. For further information or counseling, please contact your Michael Best attorney, or members of our Explosive and Fire Investigation Team: Charles B. Palmer at 262.956.6518, and Reince R. Priebus at 414.225.2746.

Michelle Wagner, Summer Associate, also contributed to this article.

View a pdf of this article complete with footnotes and sources

back to top