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Safely removing combustible dusts
Q: We know that eliminating combustible dust is one of the most important things we can do to keep our plant operating safely. What are some different approaches to cleaning up dust accumulations, and what safety considerations should we keep in mind during removal?
Gary Q. Johnson, Workplace Exposure Solutions, says: While removing accumulated dust is important for preventing dust deflagration conditions in your plant, failing to pay attention to safety details during dust cleanup will increase the dust explosion risk.
You can use various methods to safely clean up combustible dust accumulations in your plant, as long as you apply them appropriately. These methods include compressed-air blowdown, sweeping, water washdown, and vacuum cleaning. They can be used by your plant's cleaning crew or an outside cleaning contractor and are suitable for initial cleanup of major dust accumulations as well as for later routine cleanup.
Safe dust cleanup is based on the three elements required for a dust explosion. You must:
1. minimize the fuel required for a deflagration by removing the dust from the area;
2. avoid dispersing the dust into a dense cloud; and
3. neutralize any potential ignition sources.
Translating these details into a safe cleanup plan starts with using cleaning methods and tools in ways that won't disperse dust into a dense cloud. For instance, using a compressed-air hose to blow dust down off all the equipment in a room, vigorously sweeping dust off the entire floor and overhead surfaces, or bumping overhead structures and dislodging the dust accumulated on them during cleaning can quickly create hazardous dust clouds.
Safe cleanup also requires planning how to avoid ignition sources that could ignite the dust cloud as you clean. For instance, you'll need to identify and avoid or eliminate ignition sources such as static electricity, hot surfaces, or a piece of electrical equipment not rated for dust hazards.
For safe dust cleanup, it's critical to know what it takes to ignite your dust. Although knowing all of your dust's combustible properties is important, be sure to know your dust's minimum ignition temperature (MIT) for a dust cloud or layer and the dust's minimum ignition energy (MIE) in particular. For more information, visit www.astm.org.
Gary Q. Johnson is principal consultant at Workplace Exposure Solutions.
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