Page 24 - Occupational Health & Safety, May 2018

COMBUSTIBLE DUST
That’s why OSHA recommends not letting dust accumulate more than 1/32” over more than 5 percent of the facility floor.11
Another thing to consider is whether your processes have changed. Even if you’ve been in business for 30 years, you’ve probably introduced new equipment and processes during that time. If so, your risk profile may have changed. This was the root of the problem in the ink manufactur- ing incident described above. The company didn’t do the proper checks because they assumed that the new dust collection sys- tem was similar enough to the old one—a
false assumption that led to a tragic result. Finally, this idea can also get you into hot water with OSHA and other inspec- tors that follow National Fire Protection Association standards. NFPA 652 requires all facilities that process, handle, convey, or manufacture potentially combustible dust to have their dust tested, even if you’ve never had a problem before and even if your type of dust has not caused problems in the past.12 In other words, in the eyes of regulatory agencies, past per- formance is not an acceptable indicator of
future performance.
‘We Have Dust, But the Particles Are Too Big for It to Be Combustible.’ This last idea is a particularly dangerous one because it can be the result of inad- equate dust testing.
When determining whether or not dust is combustible, size matters. In gen- eral, any particles smaller than 500 mi- crons should automatically be considered combustible, though larger dusts may be combustible, as well.
As Fauske & Associate’s Dr. Ashok Ghose Dastidar explained in a recent in- terview with Nilfisk,13 the trick is that many dusts (for example, the dust in a wood pro- cessing plant) aren’t uniform: they contain coarser materials (i.e., sawdust) as well as finer materials (wood flour). When these materials segregate (such as the wood flour accumulating on elevated surfaces), the finer materials can create a combustible dust hazard.
Dr. Dastidar went on to differentiate between two types of dust testing: “as re- ceived” and after sizing and drying. Com- panies frequently want to have their dust samples tested “as received,” meaning as if segregation doesn’t occur. This is useful for determining certain dust characteristics, such as ignition sensitivity,14 but it underes- timates the true risk because it ignores the fact that segregation does often occur.
Testing your dust after sizing and dry- ing provides more conservative, and more realistic, results. This is especially impor- tant in facilities handling large quantities of dust. Dr. Dastidar noted in his interview: “[Companies] don’t realize that even if just 5% of that material is less than 500 microns, if they’re handling large quantities (e.g., 1 or 2 tons of material), then 5% can repre- sent hundreds of pounds of dust, which is big enough to pose a risk.”
Do you have combustible dust in your facility? The answer is probably yes—even if your industry and your company never had a problem before. The only way to know for sure is to have your dust tested in accordance with NFPA standards. If it does turn out your dust is combustible, there is some good news. Combustible dust is con- trollable and dust-related incidents are 100 percent preventable through engineering controls and proper housekeeping.
Stephen Watkins is an Application Engineer for Nilfisk Inc.
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