The collection and testing of dust samples is a long-established practice used by industrial safety and hygiene professionals to make informed dust collection decisions. While dust-testing protocols have not changed markedly in recent years, the importance of dust testing has changed. While knowing your dust has always been good practice, it is rapidly becoming a necessity in today’s regulatory climate.
This article will review two types of testing: (1) explosibility testing, which determines whether a dust is combustible; and (2) bench testing, which pinpoints physical properties of the dust. Both categories of tests are needed to determine the right dust collection system for your application.
Every week brings new headlines about plants being fined for violating OSHA’s National Emphasis Program on safe handling of combustible dusts. To determine whether a dust is combustible, it must undergo explosibility testing in accordance with ASTM test methods as stated in the “National Fire Protection Association (NFPA) 68 Standard on Explosion Protection by Deflagration Venting.”
NFPA 68 stipulates that if a dust sample is available, it must be tested. The standard further states that it is the responsibility of the end-user (i.e., the plant or safety engineer) to commission testing and report on results. This is a noteworthy change from past practice; what used to be a “guideline” is now a “standard” and is regarded as mandatory.
Explosibility testing is available through several companies that specialize in explosion protection services. You can go directly to such a company or commission the testing through your dust collection supplier.
Using your dust sample, the lab will start with a screening test to determine whether the dust is inert or explosive. If the dust is inert, testing will stop there. If it is combustible, the lab will conduct further testing on dust cloud parameters to pinpoint the Kst (defined as the deflagration index of a dust cloud, or rate of pressure rise) and Pmax (the maximum pressure in a contained explosion). Costs may range from around $600 for screening only, to about $1,500 for the standard battery of ASTM explosibility tests, if needed.
Even if you believe your dust is inert, it still must be tested under NFPA 68. For example, paper dust may be inherently inert but if a coating is mixed in during processing, it can render the dust combustible. If your dust is found to be even slightly combustible, you will be required to use explosion venting equipment on your dust collector.