Dust to Dust
A seemingly harmless particle raises explosive issues.
- By Paul R. Miller
- May 01, 2011
Combustible dust, as defined by the National Fire Protection Association, is any finely divided solid material that is 420 microns or smaller in diameter and presents a fire or explosion hazard when dispersed and ignited in air. Through milling, sanding, grinding, crushing, or cutting, general manufacturing often generates large amounts of dust that settles on equipment and facility structure surfaces. If fire ignites in a contained area where combustible dust particles have accumulated, such as a duct system or overhead beam, the formula for an explosion is complete, and while an initial blast can be devastating, it often stirs up additional dust that can ignite, leading to a secondary blast that can destroy an entire facility.
Combustible dust explosions have been happening since the dawn of manufacturing. In fact, the first recorded dust explosion occurred at an Italian flour mill in 1785, creating an awareness that would steadily increase for the next 225 years. In the late 1800s, the first studies on mill explosions began in the United States, and in 1922, NFPA formed the first explosive dust committee.
Despite the early action to learn more about dust explosions in industrial manufacturing, hundreds of U.S. workers have fallen victim to combustible dust explosions in recent years. In a 2006 report, the U.S. Chemical Safety and Hazard Investigation Board (CSB) estimated combustible dust fires and explosions claimed 119 lives and injured 718 people in a 25-year period. The same CSB report urged OSHA to develop a comprehensive standard to control the risk of dust explosions in general industry.
Unfortunately, just two years after the CSB report, the Imperial Sugar factory in Port Wentworth, Ga. experienced the worst combustible dust explosion in history when finely ground motes of sugar dust ignited. The blast killed 14 workers and seriously injured dozens. It made headlines and put added pressure on OSHA to formally acknowledge combustible dust is a real risk that needs to be regulated.
In March 2008, OSHA issued the Combustible Dust National Emphasis Program (NEP), which outlines recommendations and guidelines for decreasing the combustible dust risk in a multitude of industries. The program specifically lists close to 70 industries by SIC code that are considered "at risk" for a combustible dust incident; these include those that handle wood, metal, coal, plastic, paper, textiles, biosolids, and organic materials, such as sugar, flour, soap, and blood. The NEP also announced an aggressive inspection campaign at more than 30,000 facilities considered to be at high risk.
Manufacturers can minimize their risk of injury and related regulation costs as a result of combustible dust by implementing best engineering practices -- practices that include a comprehensive maintenance plan. A solid first step in preventing a combustible dust-related accident, proper housekeeping also can greatly reduce the tragic effects of a secondary blast. By letting dust accumulate on horizontal surfaces, facilities are literally adding fuel to the fire. Efforts should be taken to dramatically reduce dust buildup.
Unfortunately, combustible dust is a loaded term, and no single cleaning method will work for all facilities. While many types of dust have the potential to ignite under the right conditions and in the right environment, certain particulates weigh higher on the combustibility scale than others. Facilities should be aware of the ignition sensitivity and explosion severity of their product. This information can be found by having the dust particulate tested by a private lab and also referencing an MSDS sheet. Combined, the results will determine the best way to tackle combustible dust and ensure the proper safety procedures are used.
Traditional methods such as sweeping and compressed air hardly combat fine dust. Not only are these processes time consuming, but also they create dust clouds and are limited in what they can clean. Instead, many manufacturing facilities often opt for low-cost shop-style vacuums that are sold on the shelves of local hardware stores.
Although these vacuums might be useful for general cleaning of dust and debris in non-hazardous areas, using them to collect combustible dust can be deadly. The use of these shop-style vacuums also may violate the requirements set forth in OSHA's Combustible Dust NEP, which calls for electrical vacuums used in dusty areas to be approved for the hazard classified location, as required under OSHA standard 1910.307(b). Naturally, most plant supervisors assume the machinery in their plants is explosion-proof, including the industrial vacuums, but as seen in multiple tragedies, often this isn't the case. In fact, using a vacuum that is not certified explosion-proof to collect materials classified explosive by the National Fire Protection Association actually adds to the risk of explosion.
Choosing the Right Industrial Vacuum
An "explosion-proof" vacuum (EXP) is explosion-proof to the core. This means that everything from the outer shell to the internal mechanics -- including the motor, switches, filters, and inner chambers -- is grounded and constructed of non-sparking materials, such as stainless steel.
Approval by a nationally recognized testing laboratory, such as the Canadian Standards Association (CSA) or Underwriters Laboratories (UL), will protect buyers from purchasing a knockoff. NRTL approval provides legal certification that the vacuum can be used in a particular NFPA-classified environment and ensures every component in the vacuum from the ground up meets strict standards for preventing shock and fire hazards.
Choosing the right industrial vacuum cleaner often raises a lot of questions, especially when researching and analyzing disaster prevention. Like all investments, research before the sale is key. Plant managers should not hesitate to ask the vacuum manufacturer for an on-site analysis of their vacuum needs in order to recommend what type of explosion-proof vacuum, hose, and accessories will be needed for the application. Excellent post-sale support and training will prevent headaches or loss of downtime when it's time to purchase replacement parts or filters or to service the vacuum.
With the right equipment, the industrial vacuum can be used to meet OSHA and insurance company requirements, easily and quickly collecting dust from the floor, walls, and even overhead pipes and vents. In addition, vacuums can be incorporated into machinery in order to collect dust at the source of processing before it can escape and settle in other parts of the plant.
In late 2009, OSHA issued an advance notice of proposed rulemaking, setting the wheels in motion to develop a comprehensive combustible dust standard. The agency has been gathering public comments from all industry stakeholders, including small businesses, a daunting process that may take years. However, even though there is no date set for a final rule, OSHA certainly isn't taking a break from citing facilities for combustible dust violations. In a recent NEP status report, the agency noted it has conducted more than 1,000 inspections and found more than 4,900 violations pursuant to combustible dust, with 20 percent of those related to poor housekeeping.
We've Come a Long Way
Of course, proper maintenance is just one part of the equation. Safety managers also should inspect their facilities to ensure they have proper safety measures in place, including Explosion Prevention as outlined in NFPA 69 and Deflagration Venting devices as outlined in NFPA 68.
Although combustible dust has raised real concerns on both sides of the rulemaking panel, it is clear that something needs to be done to decrease the frequency of these incidents, which often kill multiple people at a time. While Imperial Sugar paid the ultimate price, its recently renovated factory is now an exemplary model for safety in the industry. The new facility incorporates state-of-the-art technologies, including a modern packaging facility equipped with dustless loading devices, antistatic floors and firewalls, and many other safety features. From the ultimate tragedy to the ultimate example, the company is a true testament that we've come a long way from the workplace tragedies of the past. With endless resources of education and means of prevention at their fingertips, there is no reason why today's manufacturers can't rise from the combustible dust ashes.
This article originally appeared in the May 2011 issue of Occupational Health & Safety.