New Standards Aid in Airborne Fiber Sampling and Counting
Laboratories that measure fibers in workplace samples will be the most likely users of two new ASTM International standards: D 7200, Practice for Sampling and Counting Airborne Fibers, Including Asbestos Fibers, in Mines and Quarries, by Phase Contrast Microscopy and Transmission Electron Microscope; and D 7201, Practice for Sampling and Counting Airborne Fibers, Including Asbestos Fibers, in the Workplace, by Phase Contrast Microscopy (with an Option of Transmission Electron Microscopy). Both standards were developed by Subcommittee D22.04 on Workplace Atmospheres, which is under the jurisdiction of Committee D22 on Air Quality.
“Standards D 7200 and D 7201 were originally a single work item,” says Martin Harper, secretary of Subcommittee D22.04. “The work item was split into two standards because concerns specific to the mining industry could be addressed in a standard specific to that industry (D 7200), while leaving a similar, but not identical, standard to cover other workplaces (D 7201).”
Both new standards describe several different published methods of analyzing air samples for fibers under the optical phase-contrast microscope (PCM). In addition, a procedure is presented for identification and counting through the transmission electron microscope (TEM). The difference between these procedures is that PCM is quick and not costly, but cannot differentiate asbestos fibers from any others. TEM is more expensive and complicated, but it can differentiate asbestos from fibers of other common materials (e.g., glass fibers or organic fibers).
All particles that meet the geometric rules that define a fiber are included in a PCM count using Practice D 7201. Practice D 7200 proposes a method for discriminating amphibole cleavage fragments, common in many mines and quarries, from asbestiform amphibole fibers.
Harper says that all interested parties are invited to participate in future revisions of the standard. The subcommittee is hoping to launch a round-robin study for Practice D 7200 to provide the required database on interlaboratory comparison.ASTM International standards are available for purchase from Customer Service (phone: 610/832-9585; service@ astm.org) or at www.astm.org. //
ASTM Staff: George Luciw
October Committee Week