Combustible Dust

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)

Explosion Pentagon
A dust explosion will occur when all five of these factors are present. When combustible dust in a container, room or piece of equipment becomes suspended in the air, even a small spark can create a dust explosion. This is known as the primary explosion. The primary explosion is often relatively small and weak. The primary explosion is often followed by a secondary explosion. Dust that has accumulated on floors, in ductwork, on equipment, etc. at the facility becomes disturbed by the pressure wave generated by the initial explosion, and this newly-suspended dust ignites and a secondary explosion occurs.

 

Example of Baghouse Explosion and Deflagration Propogation
Example of Baghouse Explosion and Deflagration Propogation

 

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.

Example of Secondary Explosion
Example of Secondary Explosion

 

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.