Combustible dusts, according to OSHA, are any combustible solid material composed of distinct particles or pieces, regardless of shape, size or chemical composition that presents a fire or deflagration (explosion) hazard when suspended in air. The National Fire Protection Association (NFPA) states that any material that will burn in air as a solid can be explosive in a finely-divided form, and any industrial process that reduces materials into small particles presents a potential for a serious fire or explosion. No single, universally-accepted definition of combustible dust is available – but it is undisputed that a large number of solid materials will burn or deflagrate when dispersed as dust in the air.
Facilities that intentionally manufacture powders as well as those that incidentally generate them through handling and processing solid materials are potentially subject to combustible dust hazards. Common types of combustible dusts include various metals, wood, plastic, rubber, coal, flour, sugar, and paper. By no means is this a comprehensive list, but is a starting point for determining what sorts of dusts may present danger at industrial facilities. For a partial list of identified combustible dusts, please refer to OSHA’s Combustible Dust Information Poster
Keep in mind, however, that many dusts may not appear on this list, yet still present significant explosion hazards. Referring to a material’s Material Safety Data Sheet (MSDS) can be helpful, but may not definitively establish the combustible danger of a dust. Numerous variables such as particle size, shape, and moisture content will significantly contribute to its explosibility. To determine a dust’s explosive capacity, then, appropriate testing must be performed. For more information on testing dusts to classify them as “combustible” or “non-combustible”, please refer to the Risk Management page.
Where are Combustible Dusts found?
Since a large number of processes can generate combustible dusts, a wide variety of industries are affected, including:
- Agriculture
- Textiles
- Pharmaceuticals
- Metal processing
- Wood and paper products
- Rubber Manufacturing
- Plastic Manufacturing
- Furniture Manufacturing
While certain industries are more obviously affected by combustible dusts than others, the presence and danger of such dusts are not limited to these specialized types of industries. Essentially, ANY facility that processes or produces combustible materials or their byproducts in a finely-powdered form has a work environment that may present a serious combustible dust hazard.
The OSHA enforcement program which is currently in effect (the National Emphasis Program, or NEP) identifies industry categories that have the potential for more frequent or catastrophic combustible dust explosions and those that have the potential for such explosions based on past events (see tables 1 & 2 below). It is estimated that some 426,000 facilities fall into these industrial categories targeted by the NEP. BEWARE: If your industry is not on the list, it DOES NOT mean you may not have combustible dust. We recommend everyone make an independant determination of the dust hazards at your facility, whether or not your industry is listed below.
Table 1
Industries with More Frequent and/or High Consequence Combustible Dust Explosions/Fires
| SIC | Industry | NAICS |
| 2046 | Wet Corn Milling | 311221 |
| 4911 | Electric Services –Establishments engaged in the generation, transmission, and/or distribution of electric energy for sale | 221112 |
| 2041 | Flour and Other Grain Mill Products | 311211 |
| 2493 | Reconstituted Wood Products | 321219 |
| 2899 | Chemicals and Chemical Preparations, Not Elsewhere Classified | 325510, 325998 |
| 2099 | Prepared foods and miscellaneous food specialties, not elsewhere classified | 311212 |
| 3471 | Electroplating, Plating, Polishing, Anodizing, and Coloring | 332813 |
| 3341 | Secondary Smelting and Refining of Nonferrous Metals | 331314 |
| 2834 | Pharmaceutical Preparations | 325412 |
| 2499 | Wood Products, Not Elsewhere Classified | 321920, 321219 |
| 2421 | Sawmills and Planing Mills, General | 321113 |
| 2062 | Cane Sugar Refining | 311312 |
| 2063 | Beet Sugar (Establishments primarily engaged in manufacturing sugar from sugar beets. | 311313 |
| 3061 | Molded, Extruded, and Lathe-Cut Mechanical Rubber Goods | 326291 |
| 3714 | Motor Vehicle Parts and Accessories | 336322 |
| 3365 | Aluminum Foundries | 331524 |
Table 2
Industries that may have Potential for Combustible Dust Explosions/Fires
| SIC | Industry | NAICS |
| 0723 | Crop Preparation Services for Market, Except Cotton Ginning | 115114, 115111 |
| 2052 | Fresh cookies, crackers, pretzels, and similar “dry” bakery products | 311821 |
| 2087 | Flavoring extracts, syrups, powders, and related products, not elsewhere classified | 311930 |
| 2221 | Broadwoven Fabric Mills, Manmade Fiber and Silk | 313210 |
| 2262 | Finishers of Broadwoven Fabrics of Manmade Fiber and Silk | 313311 |
| 2299 | Textile Goods, Not Elsewhere Classified | 313111 |
| 2431 | Millwork | 321911 |
| 2434 | Wood Kitchen Cabinets | 33711 |
| 2439 | Structural Wood Members, Not Elsewhere Classified | 321213, 321214 |
| 2452 | Prefabricated Wood Buildings and Components | 321992 |
| 2511 | Wood Household Furniture, Except Upholstered | 337122 |
| 2591 | Drapery Hardware and Window Blinds and Shades | 337920 |
| 2819 | Industrial Inorganic Chemicals, Not Elsewhere Classified | 325188, 325998, 331311 |
| 2821 | Plastic Materials, Synthetic Resins, and Nonvulcanizable Elastomers | 325211 |
| 2823 | Cellulosic Manmade Fibers | 325221 |
| 2841 | Soap and Other Detergents, Except Specialty Cleaners | 325611 |
| 2851 | Paints, Varnishes, Lacquers, Enamels, and Allied Products | 32551 |
| 2861 | Gum and Wood Chemicals | 325191 |
| 3011 | Tires And Inner Tubes | 326211 |
| 3069 | Fabricated Rubber Products, Not Elsewhere Classified | 326299 |
| 3081 | Unsupported Plastics Film and Sheet | 326113 |
| 3082 | Unsupported Plastics Profile Shapes | 326121 |
| 3086 | Plastics Foam Products | 326140, 326150 |
| 3087 | Custom Compounding of Purchased Plastics Resins | 325991 |
| 3089 | Plastics Products, Not Elsewhere Classified | 326199 |
| 3291 | Abrasive Products | 327910 |
| 3313 | Alumina and Aluminum Production and Processing | 331312 |
| 3334 | Primary Production of Aluminum | 331312 |
| 3354 | Aluminum Extruded Products | 331316 |
| 3363 | Aluminum Die-Castings | 331521 |
| 3369 | Nonferrous Foundries, Except Aluminum and Copper | 331528 |
| 3398 | Metal Heat Treating | 332811 |
| 3441 | Metal Cans | 332431 |
| 3469 | Metal Stampings, Not Elsewhere Classified | 332116 |
| 3479 | Coating, Engraving, and Allied Services, Not Elsewhere Classified | 332812 |
| 3496 | Miscellaneous Fabricated Wire Products | 332618 |
| 3499 | Fabricated Metal Products, Not Elsewhere Classified | 332999 |
| 3548 | Electric and Gas Welding and Soldering Equipment | 335129 |
| 3644 | Noncurrent-Carrying Wiring Devices | 335932 |
| 3761 | Guided Missiles and Space Vehicles | 336414 |
| 3799 | Transportation Equipment, Not Elsewhere Classified | 333924 |
| 3995 | Burial Caskets | 339995 |
| 3999 | Manufacturing Industries, Not Elsewhere Classified | 321999, 325998, 326199 |
| 4221 | Farm product warehousing and storage | 493130 |
| 4952 | Sanitary treatment facilities. | 221320 |
| 4953 | Refuse Systems | 562920 |
| 5093 | Scrap and waste materials | 423930 |
| 5162 | Plastics materials and basic forms and shapes | 424610 |
OSHA is currently developing a specific combustible dust standard (see the “ANPR” section on the Regulatory Information page), and many stakeholders are calling for this standard to apply to any facility that generates, processes or handles combustible dust, instead a singling out specific industries. A number of industries not identified in the NEP also have combustible dust hazards, therefore, the new standard will not likely include any facility that processes, generates, or handles combustible dusts.
The most important step that all industrial facilities can take right now is to determine if the dusts they generate or handle are combustible. Independent testing by licensed laboratories may be necessary to make this determination. If a facility deems that the dusts generated are combustible, the next step is to perform a combustible dust hazard analysis to determine the facility’s compliance with OSHA’s NEP and the various NFPA standards that apply to each individual facility. Professional engineering consultants are available to assist facilities with this evaluation. For further information on evaluation and response actions, and the help that is available in performing such tasks, please refer to the Risk Management page.
Are Combustible Dust Fires Dangerous?
A great deal of the discussions about combustible dust focus on Combustible Dust Explosions. However, over 80% of combustible dust events are fires that do not result in headline-making explosions. Despite this, the one thing to consider is that all major combustible dust explosion events have had one thing in common … the facility where the event occurred had a history of combustible dust fires before the major explosion occurred. Because of this, any facility that has experienced dust fires before should conduct a full hazard analysis to determine how vulnerable its employees and processes are to combustible dust fires and explosions.
How does a dust explosion occur? What are the dangers of combustible dust?
The workings of a combustible dust explosion are usually explained in terms of the “Dust Explosion Pentagon,” which consists of five factors that are essential for a dust explosion to occur:
- Oxidant (usually oxygen in the air)
- Ignition source (heat, open flame, electric spark, mechanical spark from friction or impact, static electricity)
- Dust (fuel)
- Dispersion of the dust (suspended dust burns more rapidly)
- Confinement of the dust (creates pressure buildup, leading to explosion)
The domino effect can continue, as the blast wave from the secondary explosion can cause more dust to become suspended in the air, creating further dust explosions. It has been determined that a 1/32 inch buildup over a surface area equal to 5% of the floor area of a room, greatly increases the likelihood of a secondary explosion. All surfaces within the room, including equipment, piping, and rafters, are included in this determination. OSHA regulations require that dust accumulation cannot exceed 1/32 inch on any surfaces equaling 5% of the floor area in the room.
Since all five factors of the “Dust Explosion Pentagon” must be present for a dust explosion to occur, eliminating the factors that can be controlled, dust accumulation and ignition sources, is essential to protecting a facility and its workers. Professional consulting firms, such as Lewellyn Technology, have the experience to evaluate industrial facilities for combustible dust hazards and develop solutions to eliminate the hazards. For more detailed information on eliminating combustible dust hazards and implementing proper work practices, please refer to the Risk Management page.
Introduction to Combustible Dust
Combustible Dust has lurked as a hidden danger in industrial facilities for years. However, recent events have made it clear that the danger presented by these dusts must be addressed immediately.
Created during the normal course of production at factories, most of these dusts seem like nothing more than a simple housekeeping nuisance – waste that collects on factory floors and equipment. However, they pose a serious threat to worker safety. This threat has been made evident in recent years – a series of tragic explosions have prompted government regulatory agencies to respond sternly. Now, industrial facilities are being pushed to respond as well.
A resolute Occupational Safety and Health Administration (OSHA) is demanding action by industry. OSHA is already actively inspecting facilities, issuing citations and fines, and is in the process of creating a firm regulatory standard for the proper handling of combustible dusts.
This information is intended to provide plant managers, safety officers, and workers within affected facilities with basic tools to understand the dangers of combustible dust and assist companies in taking steps to evaluate hazards and ensure worker safety.