The collection and testing of dust samples is a long‐established practice used by many powder and bulk processors to make informed dust collection decisions. Dust testing protocols have not changed markedly in recent years. The importance of dust testing, however, has changed, and the implications are significant. While knowing your dust has always been good practice, it is rapidly becoming a necessity in today’s regulatory climate.
by Lee Morgan and Tony Supine, Camfil APC
This article will review two separate types of testing: (1) explosibility testing, which is used to determine whether a dust is combustible; and (2) bench testing, which pinpoints numerous physical properties of the dust. Both categories of tests are needed to determine the best dust collection system for your application and whether explosion venting equipment must be part of that system.OSHA has identified and contacted 30,000 companies considered to be at risk of explosion from combustible dusts. OSHA is addressing the issue aggressively through its National Emphasis Program on safe handling of combustible dusts and through enforcement ofthe “National Fire Protection Association (NFPA) 68 Standard on Explosion Protection by Deflagration Venting”, a 2007 standard that provides mandatory explosion venting requirements for dust collection applications involving combustible dusts. The main purpose of explosion venting is to save lives by preventing a dust collector from exploding, so the importance of getting this equipment right cannot be understated.
What does all this have to do with dust testing? To determine whether your dust is combustible, it must undergo explosibility testing in accordance with ASTM test methods. 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 the required 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 opt to go directly to such a company, or you can commission the testing through your dust collection supplier.
Using your dust sample a 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 explosibility 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 will range from around $600 for screening only to about $1,400 for the standard battery of ASTM explosibility tests if needed.
Even if you believe your dust to be inert, it still must be tested under NFPA 68. For example, paper dust may be inherently inert, but if a coating or glue is mixed in during processing, it can drastically change the combustibility characteristics of the dust. Explosibility testing is the only way to know for sure, and is therefore the only way to guarantee compliance. You might be surprised by the results when you submit your dust for testing.
If your dust is found to be even slightly combustible, you will be required to use explosion venting equipment on your dust collector. The specific results of the explosibility testing will enable your dust collection supplier to determine whether you can use a standard explosion vent; or whether the vent size, ducting and related components will need to be specially calculated and modified to ensure compliance. Either way, ask for documentation that the equipment has been manufactured in accordance with the latest NFPA standards.
Whether you are planning a new dust collection system or updating existing equipment, dust collection is a complex process affected by dozens of variables. Dust sample bench testing is an excellent tool for knowing your dust better, forming the basis for sound and accurate equipment selection.
Bench testing is beneficial in many ways. By identifying the dust characteristics properly, you can determine the right type of collector and filtration media for your needs and determine the right equipment sizing and air‐to‐cloth ratio needed for optimal energy savings and operational efficiency. This can help to minimize maintenance problems and meet more stringent emission requirements while extending filter life.
A few independent test laboratories have dust collection experience, and can perform bench testing at costs ranging from $300 to $1,000. Some equipment manufacturers have in‐house test labs and offer free testing as a value‐added service to customers. Find out whether you are obligated to buy a dust collector if the manufacturer conducts tests for you.
The lab will ask you for a sample (see Note on Sampling Procedures) and should also ask for detailed application data. This data may include information on the process generating the dust, operating requirements, airflow and pressure‐drop conditions, temperature and humidity, space constraints, and more. Without application data, no context exists for your test program, and test results will be less meaningful.
For more information about this topic, including types of bench tests, read this and other industry articles on Camfil APC's website.
