Anyone who works in the oil and gas industry, electrical trade, or any other line of work dealing with flammable materials must always be cautious while on the job. One of the biggest hazards that these workers face is the threat of combustible dust. In this complete guide to combustible dust types, you will learn everything you need to know about these threatening materials.
What Is Combustible Dust?
The Occupational Safety and Health Administration (OSHA) states that any fine particle with explosive capabilities—when suspended in the air—is combustible dust. Combustible dust can come in almost any shape or size. Here are some examples of types of combustible dust:
- Rubber – Fabrication processes such as sanding and grinding can leave behind fine, but flammable, rubber powder. As it is a petroleum byproduct, high heat can ignite this dust.
- Textiles – Both natural and synthetic textile fibers are combustible. Cotton and nylon dust are particularly hazardous in this respect.
- Wood – Just as sanding and grinding rubber leaves behind flammable dust, so too does woodworking. Sawdust is not only a respiratory hazard, but also a fire hazard.
- Plastic – Another petroleum product, the plastic dust that machining and fabrication leave behind can catch fire in high enough concentrations.
- Other organic materials such as flour, sugar, and grain can combust. The soot that intentional combustion processes leave behind can also linger and catch fire.
Any workplace with a significant amount of these particles in the air poses a threat to worker safety because of potential explosions or fires. The tiniest amount of dust could lead to an enormous explosion; OSHA states that combustible dust as small as one-thirty-second of an inch could lead to an explosion. That’s about the same thickness as a paper clip, just to give you some perspective on how small that is!
How Does an Explosion Occur?
There are five characteristics that could lead to an explosion from combustible dust. Most industry experts refer to these conditions as the “dust explosion pentagon.” The five conditions relate to dust, dispersion, confinement, oxidant, and an ignition source.
Dust refers to any part of the work that generates dust, while dispersion means that the dust spreads over a given area because it’s suspended in the air, forming a dust cloud. Confinement means the air is confined to an area without any circulation, so the dust is trapped.
An oxidant is the oxygen present in the air; fires require oxygen in order to light. The ignition source is what sparks the explosion, and it could be something as insignificant as static electricity, or a small spark from two pieces of metal scraping against each other.
Now, let’s get into the chain of events that comprises the dust explosion pentagon. First, workers handle products and create dust. Second, the dust travels through the air and settles on various pieces of gear and structures in the vicinity.
If this is in a confined area, such as a warehouse or factory, the dust will stay in the air because there’s insufficient circulation. After the dust gets into the air, even the smallest open flame or heat source could ignite the dust. On top of this, the initial explosion could worsen as it ignites settled dust in surrounding areas.
The Difference Between Primary and Secondary Combustible Dust Explosions
As you know by now, combustible dust can create an even more significant explosion when it ignites other nearby dust. When the steps in the pentagon are complete, workers call this initial explosion the primary explosion.
If the primary explosion is great enough, it will loosen the other dust that settled on nearby objects, creating a second dust cloud that could ignite. The next explosion is the secondary dust explosion, and this can create a chain of explosions until everything is destroyed.
As you can imagine, these explosions are devastating and can lead to injuries, structural damage, and even death. In the United States, the Chemical Safety and Hazard Investigation Board (CSB) reported 337 injuries and 66 deaths due to combustible dust between 2006 and 2017.
The Dangers of Deflagration
You should also understand what deflagration is and how it relates to combustible dust. Deflagration is when a substance heats up so much that it burns rapidly. In a deflagration reaction, a burning material releases heat, serving as the ignition source that spreads flames.
Some common examples of safe deflagration include using a gas stove in your kitchen, or gasoline combustion in your car’s engine. The presence of combustible dust in the air can quickly lead to deflagration after the ignition source lights the fire. Deflagration will lead to explosions due to the air pressure in a confined space.
Locations That Are Susceptible to Explosions
A combustible dust explosion could happen anywhere if the area has all five of the dust explosion pentagon conditions. Facilities that grind, process, cut, crush, or polish certain products will create dust, which could lead to explosions.
According to the CSB, many different industries experience dust explosions, including chemical, lumber, food, metal, plastics, electrical, rubber, and manufacturing industries. OSHA states that there are around 130 potentially combustible dust sources.
Regulations for Compliance With Combustible Dust Safety Guidelines
The National Fire Protection Association (NFPA) and OSHA have set standards for facilities to comply with to ensure safety for instances where combustible dust is present. OSHA has mandatory federal standards for a facility to operate legally. In addition, some states have their own OSHA-approved safety guidelines.
Although the NFPA standards are not legally binding, OSHA uses their standards as an example for creating federal and state mandates. The NFPA standard for combustible dust is very recent, and requires organizations to complete a dust hazard analysis (DHA) for the area before they can proceed with operating.
There are also steps for mitigating and preventing hazards outlined in their standards. If your company doesn’t comply with OSHA standards, you could face heavy penalties for violating federal law. OSHA wrote over 300 citations in 2017 for groups that violated standards relating to combustible dust.
Overall, practicing safety measures to keep work areas clean should be enough to prevent a combustible dust event. If you manage a facility, be sure to minimize dust accumulation by instructing workers on necessary cleaning procedures.
Ensuring that workers wear insulated FR coveralls and other fire-resistant gear will prevent injuries and fatalities. After reading through this complete guide to combustible dust types, you should be familiar with the terms and concepts related to these workplace hazards.
