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Tablets & Capsules April 2015 17 requires conducting a risk assessment. Because of the importance and complexity of the task, hire an indepen- dent professional engineer and have him or her work with your dust collector supplier. That's the best way to ensure compliance with the applicable standards and the requirements of your insurance carriers. You can also conduct real-world destructive testing to help make decisions. The NFPA uses relatively conservative calculations in developing its standards for explosion-protec- tion equipment, which is understandable. But the NFPA also allows you to use real-world destructive test data instead of its textbook calculations, as long as the equipment supplier's data proves that the design of the dust collection system meets a specific set of criteria for a given situation. But few people use real-world destructive test data, probably because it is not required and can prolong the project and add cost if your equipment supplier hasn't already conducted similar testing. Still, many equipment suppliers recommend gathering the real-world data because it can pay off very quickly by preventing you from paying for an overdesigned system. The dust collector's vessel strength is another factor that can only be verified by physical testing. A heavy-duty dust collector—made with a thicker metal and bearing a higher pressure rating—will better withstand a dust explosion and may allow you to specify a simpler and less costly explo- sion-protection system. Stronger vessels also increase the options for equipment placement because they allow longer explosion vent ducting, potentially saving space inside your facility if you can locate the dust collector in a more remote location. Find out if your dust collector supplier can provide real-world test data to assist with this strategy. Is air recirculation an option? If you operate in a region where it gets very hot or cold, consider air recirculation downstream of the dust collector. By recirculating heated or cooled air through the facility, you eliminate the cost of replacing that con- ditioned air, and the energy savings can be dramatic. Most dust collection equipment suppliers have software that can estimate the savings based on system airflow, cli- mate, utility rates, and other factors. When recirculating air downstream of the collector, adding a HEPA after-filter is recommended and, if you're filtering hazardous or toxic dusts, it's required. HEPA fil- ters provide backup protection and a final scrub of the air before it returns to the facility. Ductwork and transition sections are usually required to connect a secondary filter module to the dust collection system. But in some appli- cations, an integral HEPA after-filter module mounts on top of the collector to save floor space and eliminate the need for transitional ducting, saving money. For contained coating operations, safe-change contain- ment HEPA filter systems are available, and the design and selection of after-filter components should be based on a risk assessment and the specifics of the application. If the collector is handling an explosive dust, HEPA after- filters—as well as the collector and ductwork—must comply with NFPA standards for combustible dust handling. T&C David A. Steil is pharmaceutical market manager at Camfil Air Pollution Control, 3505 South Airport Road, Jonesboro, AR 72401. Tel. 870 933 8048. Website: www.camfilapc.com/ pharma. His responsibilities include sales and marketing to the pharmaceutical and nutraceutical industries in North America and Canada. Steil spent 12 years in the environment, health, and safety group at a major pharmaceutical company. He is a member of the International Society for Pharmaceutical Engi- neering and the American Industrial Hygiene Association.