Prioritizing the safety of workers is a difficult task. While occupational hazards like falls and slips are likely considered in company safety plans, lesser known risks such as combustible dust may need to be addressed.
Per OSHA: Combustible dust is defined as a solid material composed of distinct particles or pieces, regardless of size, shape or chemical composition, which presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations.
Combustible dust explosions are a potential risk in a number of areas within industrial facilities. The most common of these locations is the dust collection system of the plant. Though there are a variety of factors that can lead to a safety risk with combustible dust explosion, there are some frequently addressed issues that have been identified through the National Fire Protection Association (NFPA) and U.S. Occupational Safety and Health Administration (OSHA). The NFPA is responsible for setting the standards while OSHA is responsible for enforcement.
A risk analysis is the first step in identifying elements that can lend themselves to a combustible danger. This is often referred to as the “Dust Explosion Pentagon.”
There are five essential components that can contribute to an explosion:
1. Combustible Dust: A workplace has combustible dust. The presence of combustible dust may result due to poor industrial hygiene. It includes wood, pesticides and metals, and is found in many industries.
Current standards measure the explosive nature of dust by a Kst Value (its explosive index) and a Pmax (its maximum pressure rise). Refer to ASTM E 1226-12a, Standard Test Method for Explosibility of Dust Clouds. This data is used in choosing a correctly-sized explosion venting/suppression system. Having the correct numbers for your facility will save you money. Manufacturers can provide a correctly-sized system as opposed to planning for a worst case scenario. Some manufacturers will not provide equipment without this data.
Fact: Any dust particulate with a Kst value above zero (0) is considered explosive. Most dust falls into this category.
2. Ignition Source: There is an ignition source for the dust. The second condition is a source that may ignite the dust, which can include any item that generates a hot surface or spark like heaters or exposed electrical components.
3. Oxygen Source: Oxygen is always in the air. Oxygen fosters an environment for combustion.
4. Dust Dispersion/Concentration: The dust is concentrated in a certain amount. Dust can explode if it is suspended in the air and meets a particular level.
5. Containment: The dust cloud is confined or semiconfined in an area. Dust that’s in a confined area may concentrate and lend itself to explosive conditions.
Note: Open-style dust collectors still present a safety danger by meeting four of the five risk factors.
Other factors that can contribute to danger
1. Attitude: We have never had a problem before: It is important to note that even if your facilities have never had a problem, there is no safety guarantee. Depending on the environmental factors within the facility, it could take months or even years to create a dust accumulation safety hazard.
2. Knowledge: Dust is not combustible. Informed and educated staff will be empowered to be a partner in company safety. Misconceptions can lead to safety danger.
3. Failure to anticipate: We do not have a confined area so there is no risk of explosion. Even though an explosion may not be possible, flash fires could occur if four of the five safety parameters noted above are met.
4. Expecting a single explosion. It is more common to witness a series of deflagrations (burning extremely quickly instead of exploding). The initial combustion event can loosen/dislodge and expose hidden dust accumulation and trigger secondary explosion events. It is often these events that lead to the most damage and injuries.
5. No explosion protection. Failure to have explosion protection in place could result in a citation from OSHA, damage, injury, or death. Make sure a proper, adequately-sized explosion containment system is installed and maintained.
6. Saving short-term dollars. Consider total cost of ownership instead. A quality dust collection system saves dollars in energy and maintenance, especially when considered over the life of the equipment.
A cheap, low quality item will likely require replacement if an explosion occurs. A higher quality piece of equipment with a heavier gauge metal will likely be able to stay in service, requiring replacement of only smaller, lower cost accessories such as filter cartridges and explosion vents. Furthermore, lower quality products may not have been tested and may not perform properly, potentially resulting in fines from OSHA as well as danger of personal injury or worse.
Note: There is no such thing as an NFPA-approved device. Look for CE or ATEX certifications or statements that the item is “manufactured in accordance with NFPA standards” (make sure this is supported with test data).
7. Poor Housekeeping. Don’t just clean the floors. Make sure overhead areas, tops of machinery and other potential accumulation areas are regularly addressed. In 2011, OSHA noted that one of the most common violations resulting in high accumulations of dust was the failure to maintain good housekeeping standards. Make sure filters are also changed out as needed and do not store dust in the dust hopper. Dust should be emptied from the hopper into a proper storage container.
NFPA 654 notes that a dust layer of 0.8 mm (1/32 inch) or greater constitutes a hazard.
Note: Avoid the use of compressed air canisters. These canisters can increase the potential for a safety hazard by creating an increased density of dust in the air (a combustible dust cloud).
8. Don’t Over-Spec. Over-speculation is often unnecessary and creates added expense that does not actually augment safety. Consider using real-world test data to make inform decisions on design and equipment components that best serve the needs of your facility.
The NFPA actually requires facilities to conduct hazard analyses for fire and explosion protection, and you can conduct the ad-hoc test above to determine if you should bring in an independent consultant to research risks even further.
Implementing high-quality dust collectors and frequently emptying storage containers can help prevent dust explosions, according to OHS Magazine. Coupled with this, explosion-proof equipment can prevent common equipment like boxes and lights from becoming ignition sources.
Work with the industrial experts at Border States to help you answer questions about explosion-proof equipment that would help your facility comply with combustible dust regulations.
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