By Phil La Duke
The safety rumour mill is buzzing about the probability that governments are about to target a hazard that many of us really haven’t given much thought to: dust. I can’t tell you how many times I have been on audits where the merest mention of poor housekeeping send eyes rolling and smirks crackling like lightning strikes across the faces of both leadership and the rank-and-file alike. “You’re going to write up poor housekeeping? Talk about nit-picking.” Given that “slip, trip, and fall” consistently score among the top causes (or contributors) of workplace injuries I happen to think housekeeping is an important and easy way to keep workers safe, but increasingly housekeeping is becoming one of the most important ways to save worker’s lives.
According to the U.S. Chemical Safety and Hazard Investigation Board (CSB) there have been 281 combustible dust incidents between 1980 and 2005 and these have caused 119 worker deaths, 718 injuries, and extensively damaged numerous industrial facilities—and this is just in the U.S. When dust blows up it blows up big,
Of course, not all dust is combustible, and the number of incidents are still a relatively small issue in workplace safety, but the problem has received enough public attention that it is likely to become an increasing target for enforcement agencies word-wide.
Any thing that can burn can do so quickly especially when it is in fine particles and airborne. A lot has to go wrong for a major catastrophe: the dust has to be suspended in air, it has to be in the right concentration, it needs an ignition source, and there are often other conditions that must be present depending on the material. But even things that don’t typically burn (like metals) will do so if they are in the form of a fine dust.
It’s tough for laymen to wrap their minds around why something like metal dust or sugar would explode. It doesn’t seem to make much sense after all, our Pop Tarts don’t explode when we put them in the toaster. Understanding explosives might help. There are two basic kinds of explosives: high explosives and low explosives. Both high explosives and low explosives have the same ability to create powerful destructive blasts. Low explosives don’t detonate, however, in a sense they just burn so fast that they appear to detonate, but they don’t they are just burning all at once (explosives experts call this process deflagration. Of course, the burn does happen fast enough to create great pressure (not as great as high explosives, but great enough to really mess up your day), heat, and light and this pressure causes the blast, so unless you are planning to blow something up (and don’t, by the way, there are enough whackos blowing things up in the world) the difference is fairly academic. The point is when something flammable burns quick enough you get an explosion and at that point do you really care if it was caused by a high explosive or a low explosive?
The force from such an explosion is often substantial and often causes employee deaths, injuries, and destruction of entire facilities. Combustible dust is a problem in a lot of diverse industries from to food to pharmaceuticals manufacturing, to metal to mining or oil and gas. Not long ago an explosion of titanium in West Virginia left three workers dead, and of course for many of us the 2008 Georgia sugar explosion that killed 14 workers still looms large in our memories.
Even though the dangers of combustible dust are palpable and volatile, in the dust itself doesn’t pose a great deal of risk, like most hazards, combustible dust needs other hazards to create a disaster, and facilities need to do more than just focus on the dust itself (although, of course, they can’t ignore the dust). Dust (or vapors for that matter, but this post isn’t about the dangers of explosive vapors) can’t explode without an ignition source. This is where things can get a bit sticky—a lot of workers resist restrictions on items that might provide the necessary ignition source.
Anatomy of a Combustible Dust Explosion
All fires need three things: an ignition source, fuel, and oxygen, but a combustible dust explosion requires several additional elements, namely, sufficient concentration of the dust particles and confinement of the dust cloud. Despite the clear definition of the elements required for a dust explosion, many organizations do an inadequate (or downright poor) job of recognizing the hazard of combustible dust and an even worse job of mitigating the risks.
Controlling the Fuel
Eliminating the accumulation and concentration of combustible dust in the air is the single greatest protection against a combustible dust explosion, but even here companies often put themselves at heightened risk simply through the use of equipment that is poorly suited for the task. An air filtration system that is poorly maintained, for example, can actually take dust that has settled (and thus far less a danger) and circulate it through the air. Additionally, some vacuums used by organizations to remove the dust can provide an ignition source and actually exacerbate the dangers.
Obviously, the biggest source of fuel associated with a combustible dust explosion is the dust itself, but those identifying the risks associated with combustible dust explosions need to be mindful of other considerations like:
- The presence of accelerants. Many chemicals present in the facility may speed the spread of the fire and increase the damage to facilities, and more importantly increase the severity of injuries to workers. The careful placement and storage of these chemicals is an important factor in mitigating the risk associated with a combustible dust explosion and fire.
- Release of toxic fumes. Often the resultant fire caused by the initial explosion cause materials to burn or melt and release harmful and even life threatening fumes. Companies should do their utmost to identify these materials and store them appropriately.
- Emergency response and evacuation. Explosions of the magnitude typically caused by combustible dust leave scarce little time for evacuation and emergency response. It is imperative that emergency response and fire-fighting equipment be kept in good working condition and that all workers are trained in emergency response, evacuation, and the use of firefighting equipment where appropriate.
Controlling Ignition Sources
In some workplaces just getting workers to understand that smoking represents more than just a threat to their health is a challenge, and incredibly these workers are often so complacent about the dangers of having a lit cigarette in close proximity to flammables that it can be very difficult to get them to respect the danger of fire or explosion. I remember auditing a manufacturing facility and finding a worker smoking a cigarette while working with acetone (beneath a prominent “no smoking” sign). When I approached with the site safety manager the worker quickly flung the cigarette from his hand, narrowly missing a barrel of acetone soaked rags.
Even where workers understand the risks of smoking the risk from other ignition sources can be a difficult sell (and when workers discount the risk, the likelihood that they will comply with the controls put into place drop considerably.) Some of the less obvious ignition sources are:
- Static electricity. When most people think of static electricity they think of dragging their feet across carpet and giving some unsuspecting victim a mild electrical shock. A spark less than the size of the one generated by this childish prank is enough to cause a massive explosion, provided that the other conditions are present. And one need not scoot across the carpet to generate a static electric spark: a plastic bucket, PVC piping or even a cellphone can generate enough of a spark to ignite a dust cloud.
- Heat. Hot work permitting is common practice in most industries, but depending on the criteria used to require a hot work permit, an organization may not be adequately protecting itself from a combustible dust explosion. Ambient heat in some locations can be enough to ignite a combustible dust cloud in some rare conditions (but let’s face it, it’s the rare circumstances that kill us). Cellphones and other electronic devices—particularly those that have been damaged or that have faulty batteries—are capable (if unlikely) of providing sufficient heat to be an ignition source.
- Strikers. Many organizations that prohibit the use of lighters on the premises will turn a blind eye to welders who have a striker hanging from their belts. A spark is a spark when it comes to igniting a dust cloud and allowing workers to have a device whose sole purpose is to produce a spark dangling from their belts is a recipe for disaster.
- Running Automobiles. The combustion engine is a good source of ignition, and workers are sometimes reluctant to shut off a vehicle if they are only going to be out of it for a moment (like while opening or closing a gate, or other quick task). Too often the cause of explosions of dust or vapors is a spark from an idling vehicle.
OSHA Standard NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, provides some excellent advice on how organizations can control ignition sources to prevent explosions.
“The following are some of its recommendations:
- Use appropriate electrical equipment and wiring methods;
- Control static electricity, including bonding of equipment to ground;
- Control smoking, open flames, and sparks;
- Control mechanical sparks and friction;
- Use separator devices to remove foreign materials capable of igniting combustibles from process materials;
- Separate heated surfaces from dusts;
- Separate heating systems from dusts;
- Proper use and type of industrial trucks;
- Proper use of cartridge activated tools; and
- Adequately maintain all the above equipment.”
The dangers of combustible dust aren’t new, or newly discovered, but if the rumours are true controlling and preventing these types of incidents will be given heightened priority among government regulators worldwide. But apart from running afoul of regulators, isn’t it wise to be mindful of the dangers and to recognize that one need not work in a flour mill or sugar refinery to face the very real dangers of a combustible dust explosion?