Risk or consequences?

摘要

New classifying methods may offer options in U.S. Say you are classifying your chemical plant as a hazardous location. According to the existing zone method of classification, once you classify your plant as Zone 0 (the most hazardous according to the zone concept), you must use intrinsically safe equipment (equipment ia)—no matter the potential consequences of an explosion. This would be true if you had the same chemical process in the city of Raleigh, N.C., and in the middle of the California desert. However, this wouldn't be the case under a newly proposed method the IEC TC31 standards committee is considering. With the proposed method, if you had the same process in Raleigh and California, and they were Zone 0 in both cases, you might have future options in classifying your plant—based not only on explosion likelihood and ignition source, but on the consequences of that explosion. The proposed approach is a decoupling of the prescribed type of protection for equipment from the area classification zone, said Paris Stavrianidis, vice president and general manager at FM Approvals in Norwood, Mass. "Existing standards look at classifying an area in terms of zones," he said. "The end user then installs the type of equipment prescribed for use in a specific zone. If you're an end user and you follow the standards, you come up with Zone 0, and the standard says you must use [intrinsically safe] ia equipment. That's a prescriptive approach," he said. Under the current system, you would consider two components. The first is the likelihood of an explosive atmosphere—the zone. The higher the likelihood, the lower the zone number. "Zone 0 is the most likely to have a release," Stavrianidis said. The second component to consider is the likelihood of an ignition—the ignition source—present from equipment. "In the existing standards—using the prescriptive approach, if you have Zone 0, you must use equipment that has the least likelihood of creating an ignition source," he said.