Mitigating risk of combustible dust hazard at food processing facilities
Dried or milled powders offer food and beverage companies many benefits, such as new product lines and increased revenue. However, these powders can create dusts that are major fire and explosion hazards. These hazards can severely damage plant structure and equipment. Even worse, they could potentially result in worker casualties.
Dealing with these powders requires a better understanding of the hazard. The severity of the hazard is related to the type of dust present. Dusts with smaller particle sizes pose a higher severity, as do dusts with high chemical energy content. A variety of sources, including OSHA, provide information to identify the severity of a hazard. Common dusts that have caused major damage and injuries include cocoa, flour, malt, starch and sugar.
Depending on the situation, dusts could pose fire, deflagration and detonation hazards. Fire is self-explanatory; the dust ignites and burns. Deflagration, a more severe event, occurs when rapid combustion moves faster than 0.5 meters per second. This can cause high heat and a pressure wave. Both the heat and pressure can injure people and damage structures. Detonation occurs when the pressure wave travels faster than the speed of sound. These initial events may also trigger a secondary explosion causing further damage.
The hazard of a given dust can be partially characterized based on the Deflagration index (Kst). The higher the index number, the more severe the explosion hazard. The hazard can be further characterized by the Autoignition Temperature, the temperature at which combustion starts due only to the temperature.
Mitigation of risk begins with understanding the characteristics of the combustible dusts. Facility design and administrative controls can also mitigate the risk. The following are some strategies for each.
- Include blowout panels to control how the explosion occurs.
- Minimize ignition sources such as electrical sparks and heat or flame generated by mechanical equipment. Mechanical and electrical equipment classified for Class II locations per the National Electrical Code helps address this.
- Reduce horizontal surfaces that collect dust.
- Improve ventilation and dust collection systems.
- Address static electricity concerns by properly bonding equipment and controlling humidity levels.
- Clean periodically to reduce the accumulation of dust. As little as 1/32-inch accumulation can cause problems. Equipment used for cleaning should not cause dust to disperse. Cleaning crews need to be properly trained.
- Add a hot work permit system for welding and cutting operations.
- Wet dust to prevent dispersion.
This is just the tip of the iceberg relating to combustible dust hazards. Understanding and addressing combustible dust hazards is a complex issue that requires knowledgeable and experienced teams.
ABOUT THE AUTHOR
As an electrical engineer and project manager, Brian Dunn, P.E., has prepared and coordinated construction documents for industrial processing plant design, direct industrial power design and extensive lighting design. Brian has more than 20 years of experience in a traditional architectural-engineering office, a progressive design-build firm and an energy consulting firm. During that time, Brian has been trained in HACCP and FSMA requirements. In his spare time, he enjoys hiking, mountain biking and kayaking.
Other blog articles by Brian include: Cleaning crew impacts food safety at new processing facility
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