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How to Control Combustible Dust

In February 2008, a sugar plant near Savannah, Georgia, suffered the ultimate tragedy. Fourteen employees were killed and forty were injured when finely ground motes of sugar dust ignited, setting off a violent blast. Adding to the company’s tarnished reputation due to this preventable loss of life, the Department of Labor’s Occupational Safety and Health Administration (OSHA) then fined the company more than $8 million in workplace violations related to combustible dust.

Although it took this tragedy in a sugar plant to make combustible dust a national headline, industrial facilities have been aware of the risk for years. While the U.S. Chemical and Safety Hazard board estimates there are on average 10 explosions, 5 fatalities, and 29 injuries per year as a result of combustible dust-related incidents1 the reality is that these numbers are most likely underestimates, especially since smaller incidents such as fires and blasts without injuries happen daily and often go unreported.

 

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So what can be done to help prevent these types of accidents in the future? In March 2008, OSHA reissued their National Emphasis Program (NEP) on combustible dust to call attention to the agency’s rigorous expectations for combustible dust-related explosion prevention, which includes random unannounced audits.3 The program also outlines recommendations for decreasing a plant’s risk of a dust explosion and includes incorporating an explosion-proof vacuum cleaner into maintenance plans as a means to eliminate potentially hazardous combustible dust that settles on overhead pipes, walls, floors and machinery in industrial facilities.

Certifiable Explosion-Proof Vacuums: Beware of Imposters
Purchasing an explosion-proof industrial vacuum to combat combustible dust sounds easy enough, but there is actually some complexity to the investment, especially if the vacuum cleaner will be used to collect classified hazardous materials such as coal, fuel, or even sugar. Naturally, most plant supervisors assume the machinery in their plants is explosion-proof, including the industrial vacuums; however, if you plan on collecting hazardous materials, a certified explosion-proof vacuum/dust ignition-proof vacuum is imperative. In fact, using simply a basic vacuum, made of metal parts and exposed motors, can possibly increase the risk of explosion.

In an explosion-proof/dust ignition-proof vacuum, everything from the outer shell to the internal mechanics, including the motor, switches, filters and inner chambers are grounded and constructed of non-sparking materials such as stainless steel. Be aware that some industrial vacuum companies offer basic models dressed up with a few anti-static accessories and describe them as suitable for explosive material. These imposters can still create arcs, sparks or heat that can cause overheating and ignition of the exterior atmosphere  that can ignite dust blanketing the vacuum.

Purchasing an explosion-proof vacuum approved by a nationally recognized testing agency such as the Canadian Standards Association (CSA) or Underwriters Laboratories (UL)will help protect buyers from purchasing an inferior model by providing certification that the explosion-proof vacuum can be used in a particular NFPA-classified environment. It ensures every component in the vacuum from the ground up meets strict standards for helping prevent shock and fire hazards.

Explosion-Proof vs. Air-Operated
In environments where electricity is unavailable or undesirable, pneumatic vacuums made especially for hazardous locations are excellent alternatives, but plant managers should understand that not all air-operated equipment is explosion-proof. Pneumatic vacuums for hazardous locations must still be properly outfitted and meet the requirements for use in NFPA-classified (National Fire Protection Association) environments.

Filtration
Superior filtration does not have to be sacrificed on an explosion-proof vacuum model, especially when collecting potentially hazardous materials. For peak safety and operating efficiency, an explosion-proof vacuum should have a multi-stage, graduated filtration system, which uses a series of progressively finer antistatic filters to trap and retain particles as they move through the vacuum. In order to help eliminate combustible dust from being exhausted back into the ambient air, a HEPA (High Efficiency Particulate Air) or ULPA (Ultra Low Particulate Air) filter can be positioned after the motor to filter the exhaust stream. Quality HEPA filters offer an efficient and effective way to trap and retain the smallest dust particles, down to and including 0.3 microns. An ULPA filter captures even smaller particles, down to and including 0.12 microns.

Spill Response
The ability to safely and easily collect liquid spills should also be taken into account when purchasing an explosion-proof vacuum cleaner. Although OSHA’s National Emphasis Program is specifically looking at companies that handle dry solids, manufacturers’ maintenance plans are also under the microscope of OSHA. If workers might need to collect flammable or explosive chemicals, an explosion-proof vacuum capable of collecting liquids should be considered. Wet-models capable of handling liquids are also available in both electric and air-operated versions.

Watch For Updated OSHA Standards
In 2009, OSHA issued an Advanced Notice of Proposed Rulemaking, along with related stakeholder meetings to evaluate possible regulatory methods, and to request data and comments on issues related to combustible dust such as hazard recognition, assessment, communication, defining combustible dust and other concerns.4 The use of industrial explosion proof vacuums as a preventative housekeeping method has been a large part of these discussions and will likely appear in the final OSHA standard.

Purchasing a high-quality certified explosion-proof/dust ignition-proof vacuum is a solid first step in helping to prevent a combustible dust-related explosion, and selecting the right vacuum often raises a lot of questions, especially when it comes to disaster prevention. Like all investments, pre-sale research is key. Plant managers shouldn’t hesitate to ask the vacuum manufacturer for an onsite analysis of their vacuum needs in order to recommend what type of vacuum, hose and accessories may be needed for the application. The right vacuum can be used to collect dust and debris from the floor, machinery, walls and even overhead pipes and vents.

If used consistently and in conjunction with a comprehensive maintenance plan, a facility’s investment in an explosion-proof vacuum will result in much more than just a clean plant. It will help save money, protect company reputation, increase productivity, and most importantly, protect the company’s most valuable asset - its employees.

Guidelines On the Control of Dust
An ignitable material, an ignition source and oxygen are all it takes for a potential explosion at your facility. Most manufacturing plants have all three. In 2006, fatalities involving explosions and fires increased by 26% in the manufacturing sector according to the Bureau of Labor Statistics Census of Fatal Occupational Injuries. In addition to potential employee injuries, explosions may cost companies millions of dollars. Between 1992 and 2002, Factory Mutual Global’s pharmaceutical and chemical clients experienced dust explosions resulting in $32 million in losses. OSHA has estimated that there are approximately 30,000 U.S. facilities at risk for combustible dust explosions. Simply put, there’s a lot at stake.

NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, contains comprehensive guidance on the control of dust to prevent explosions. The following are some of its recommendations:

  • Minimize the escape of dust from process equipment or ventilation systems
  • Use dust collection systems and filters
  • Utilize surfaces that minimize dust accumulation and facilitate cleaning
  • Provide access to all hidden areas to permit inspection
  • Inspect for dust residues in open and hidden areas, at regular intervals
  • Clean dust residues at regular intervals
  • Use cleaning methods that do not generate dust clouds, if ignition sources are present
  • Only use vacuum cleaners approved for dust collection
  • Locate relief valves away from dust hazard areas
  • Develop and implement a hazardous dust inspection, testing, housekeeping, and control program (preferably in writing with established frequency and methods).

Article courtesy of Nilfisk CFM.
Image courtesy of the U.S. Chemical Safety Board.

1.“Investigation Report: Combustible Dust Hazard Study”. U.S. Chemical Safety and Hazard Investigation Board. 02 Jan 2008. <http://www.csb.gov/completed_investigations/docs/Dust%20Final%20Report%20Website%2011-17-06.pdf>
2.“OSHA Combustible Dust Prerule Agenda.” Combustible Dust Policy Institute. 03 Jun 2009. http://www.combustibledust.com
3.“Combustible Dust National Emphasis Program”. Occupational Health and Safety Association. 02 Jan 2008. http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=3729
4.“U.S. Department of Labor's OSHA announces rulemaking on combustible dust hazards.” National News Release. Occupational Health and Safety Association. 03 Jun 2009. http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=NEWS_RELEASES&p_id=17828