I recently gave a speech titled, oddly, “How to Get Around NFPA Combustible Dust Standards.” The first few slides were tongue-in-cheek and showed the need for a huge team of lawyers to defend oneself in court when one's facility blows up. It even showed a head-shrink and clergy required to deal with a difficult conscience due to causing the death of friends.
However, my ironic point was not to be flippant or even joking but to illustrate the best way to beat the explosive dust issues that we face daily. The answer is to come up with the best science. Having been a government agent 30 years previously, I know that OSHA and NFPA agents are not negatively motivated. AHJs want us to succeed, just not to the detriment of safety. NFPA has given us prescriptive examples of safe practices that can be instantly recognized as within those confines by auditors who may not understand the complexities of the science. Our job can be to take equivalent means to achieve a safe scheme of combustible dust mitigation or to take the science in our own hands or consult experts to determine a custom performance-based alternative. The outcome is the same: to reduce the combustible dust risks to acceptable levels that are more practical and/or more effective to the specific needs of our processes and applications at manufacturing facilities.
For example, a small brewery wanted a dust collector to remove dust from a beer brewing kettle that made two batches of a wonderful malted beverage per day. Installing a dust collector system was tantamount to adding a small bomb to the system terminal because it will bring the fine dust into a container and create a dust cloud inside an airtight chamber. The brewer was better advised, during the Dust Hazard Analysis (DHA) to completely clean the area of dust after the raw grain was added to the kettle, twice per day, thus reducing the risk of any dust explosion.
One last example, a small metal polisher controlled his finely-divided highly-explosive aluminum dust to an existing dust collector that was unprotected. Retrofitting the system to NFPA 484 prescriptive standards would have been incredibly expensive. A DHA showed that injection of a fine limestone dust at a defined, laboratory-tested ratio would render the dust non-combustible. The AHJ agreed to the alternate, performance-based approach, as long as the manufacturer did annual testing of the inerted dust to show that the dust was no longer a hazard.
More simply said, if any side of the combustible dust pentagon can be removed, the probability of dust explosion incidence is greatly reduced. For example, if a complete enclosure of the dust generating source is NOT provided, then combustible dusts -- if ignited -- can only cause a flash fire at the point of generation. Typical sources of dust do not cause a minimum explosive concentration (MEC) at the initial point of generation. Therefore, a dust collector attached to the dust hood enclosure rarely needs explosion protection. In any case, a DHA will reveal the explosion risks and is required for proper protection of the site and employees. As of this past year, NFPA 652 provides the mechanism to accomplish a real DHA. If you have not gone through this process before, I would encourage you to utilize the services of a professional consultant to help you through the process. You will sleep better at night.
Jonathan Hale is president of Air Systems Corp. He worked as an EPA inspector and permits engineer for nine years, and was the director of environmental engineering and industrial hygiene for Douglas Battery Mfg, Winston-Salem, NC for three years. He has been the co-chairman of the North Carolina Industrial Ventilation Conference – Faculty since 1986, on the faculty, Michigan State University Industrial Ventilation Conference, since 2009, vice chairman, ACGIH Industrial Ventilation Committee, and author of sections of Industrial Ventilation: A Manual of Recommended Practices.
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