Combustible Dust 101

Combustible Dust 101

There’s no avoiding dust: it accumulates in our workplaces, our homes and even our cars. Many of us find dust irritating, but we tend to think of it as harmless. In the workplace, this misconception about dust can actually lead to very dangerous situations. Under the right conditions, many types of dust can catch fire and even explode. OSHA estimates about 30,000 U.S. workplaces are at risk for this type of explosion, and these combustible dusts are common in many industries, even industries you might not expect.

Consider the case of the Imperial Sugar Company in Port Wentworth, Georgia. On February 7, 2008, a day like any other for the crew that worked there, accumulations of sugar dust that had built up over years finally reached a tipping point in the refinery’s packaging building and resulted in a huge explosion and fire.

The tragic and very preventable accident resulted in 14 deaths and 38 injuries and turned out to also be the unfortunate nudge that prompted OSHA to consider creating official combustible dust standards.

The Imperial Sugar Factory after a combustible dust explosion in 2008. Photo: U.S. Chemical Safety and Hazard Investigation Board

Sugar may not seem like a material that could cause a spontaneous explosion, but many organic materials including wood, grains and spices can be dangerous when in a fine, powdery form.  Additionally, many nonorganic materials like metal dusts, chemical dusts and plastic dusts can also catch fire or explode.

Before you start worrying that your facility could have a serious problem, it’s worth understanding exactly what conditions are necessary for a combustible dust explosion to occur in the first place. While we know that combustible dusts are dangerous and need to be dealt with in most facilities, only in certain situations will an explosion actually happen. In other words, the conditions that allow combustion to occur in the first place need to be present and “just right.”

How Combustible Dust Explosions Work

A dust fire requires three components: fuel (dust), oxygen and a heat source (usually a spark). A combustible dust explosion requires two additional components: a high concentration of dust dispersing in the air (referred to as “deflagration”) and a confined space. Together these five components are called the Dust Explosion Pentagon.

combustible dust, explosion
Photo: OSHA

These five elements are present in the majority of industrial facilities. For example, dust can accumulate on beams and other surfaces near the ceiling in a closed room.

If the room has any sort of flame or heat source and something shakes some of that dust loose, an explosion can occur because the situation has fuel (dust), oxygen (in the air), a heat source/spark and dispersing dust (from the surfaces near the ceiling), and it’s all occurring in a room with walls (confined space).

This is a situation that could easily happen during normal operations. Dust can be disturbed and dispersed into the air by simple tasks like sanding, cutting, or handling powdered products.

According to the Chemical Safety Board, an explosion can result from a fairly small amount of dust buildup. Dust accumulation about the width of a dime covering just five percent of a room’s surface area can lead to an explosion.

This first explosion, referred to as the primary explosion, often causes a chain of secondary explosions because the primary explosion disperses even more dust—more fuel—throughout the area. These secondary explosions often cause more damage to people and property than the first.

Factors Contributing to the Dust Problem

As mentioned, part of the problem with combustible dust is most people don’t realize it’s a problem. Dust doesn’t look dangerous, and combustible dust incidents are less common than many other workplace accidents. Explosions, however, are much more devastating accidents when they do occur, often taking lives, severely burning people and destroying buildings.

The Chemical Safety Board advocates increased education about combustible dust to help raise awareness about the hazard. The group cites inadequate information on Safety Data Sheets (SDSs) and lack of explosion warnings on labels as significant factors that lead to these accidents; workers don’t realize they need to take special precautions with dust. OSHA considers combustible dusts hazardous chemicals, and as such these dusts must have the corresponding GHS labels and information sheets.

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Preventative Measures

Dust needs to be dealt with in most facilities, and doing so requires a combination of proper design, housekeeping and training.

Before doing anything else, though, assess all potential locations that could generate dust. OSHA suggests considering the following:

  • What materials used at the site are combustible
  • Which processes use or produce combustible dust
  • Where dust may accumulate (both open and hidden areas)
  • Ways dust may be dispersed through the air
  • What possible ignition sources are

Once you know what hazards exist, you can take preventative steps. Some elements of the Dust Explosion Pentagon are out of your control (oxygen will always be present and rooms will always have walls), but you can control other factors like the presence of dust and ignition sources.

Dust Reduction

To reduce the presence of dust, first consider any engineering and structural factors that are within your control. Perhaps you could install dust collection systems with filters or improve the ventilation in your building. These things can prevent the buildup of dust in the first place.

Next, put a plan for housekeeping in place. NFPA 654 (the Standard for the Prevention of Fire and Dust Explosion from the Manufacturing, Processing and Handling of Combustible Particulate Solids) states facilities must have housekeeping plans in place—preferably in writing—to keep dust from accumulating.

These practices could include daily vacuuming in areas where a task creates dust, washing down dusty areas and setting a regular time to clean out-of-reach areas where dust can accumulate. Make sure, though, that if ignition sources are present in an area you take precautions not to use cleaning methods that create dust clouds.

Finally, train employees so they understand the risk factors associated with combustible dust and what steps they need to add to their daily work routine to alleviate these hazards. Investigations of combustible dust explosions often reveal that employees weren’t aware of the hazards, or if they were aware, they weren’t taught to properly deal with the dust. Dust may look harmless, but you need to make sure everyone in your facility knows that isn’t always the case.

Ignition Sources

Aside from dust, you can also control ignition sources in your facility. Sparks, flames and other heat sources may very well be a part of your daily operations, so eliminating them entirely may not be possible. You can make sure these ignition sources are contained, though. You can also try to prevent dust accumulation in these areas.

OSHA also recommends making sure you’re using appropriate electrical equipment and wiring methods, controlling static electricity and paying attention to areas of friction that could generate heat. Keep in mind that ignition sources aren’t always obvious; oftentimes an unexpected spark can initiate an explosion.

Present and Future Regulations

Although OSHA has been working on creating a comprehensive combustible dust standard since the explosion at the Imperial Sugar Factory in 2008, these guidelines are still in the works. Even though your facility does not need to comply with specific OSHA regulations regarding combustible dust, it does still need to comply the OSHA Act’s General Duty Clause, which states that employers are responsible for providing employees with a work environment free from recognized hazards that could cause death or serious injury. Facilities can also be cited for not complying with OSHA standards such as those related to housekeeping (1910.22).

Furthermore, facilities need to comply with NFPA guidelines, which are enforced by local fire marshals and building inspectors. Currently, these guidelines are fairly industry specific and deal with industries where these hazards are most common.

The following NFPA standards can be consulted for more specific information:

  • NFPA 61 – Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities
  • NFPA 484 – Standard for Combustible Metals
  • NFPA 654 – Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
  • NFPA 655 – Standard for the Prevention of Sulfur Fires and Explosions
  • NFPA 664 – Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities

These guidelines are helpful, but combustible dust can impact almost all industries, so OSHA plans to eventually create a standard that can be enforced on the national level. In the meantime, the organization’s Combustible Dust National Emphasis Program is focusing on educating businesses about these hazards.

For safety managers looking for general guidance, NFPA 654 provides standards applicable to the most industries, and following these guidelines for housekeeping and other dust prevention strategies should help keep your facility safe and compliant.

 

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