The Proficiency Analytical Testing (PAT) Program is managed by the American Industrial Hygiene Association (AIHA) in Fairfax, Virginia. The PAT Program provides quality control reference samples to approximately 1200 occupational health and environmental laboratories in 17 countries. Although one objective of the PAT Program is to evaluate the analytical ability of participating laboratories, the primary objective is to assist these laboratories in improving their laboratory performance. A total of 1196 laboratories were enrolled in the PAT Program with 1098 laboratories submitting results on round 135. Of the 1098 laboratories submitting results, 925 used the Internet data entry system. The percentage of labs rated proficient for PAT round 135 ranged from 90.6% for asbestos to 98.7% for Silica. Results from the PAT Diffusive Sampler program (rounds 128-134) and various protocols for diffusive sampler evaluation were studied to determine if laboratory performance could be improved. Recommendations were made that active sorbent tubes be used to establish the reference concentration of a generated atmosphere. The AIHA PAT subcommittee of the Laboratory Accreditation Committee has accepted the following recommendations for the PAT diffusive sampler round 138, in July 1999. The reference concentration of the test atmosphere will be determined from the active sorbent tube results. At least five measurements, distributed throughout the chamber, should be made for each generation run. The calculated concentration values would also serve as a quality control check. If the active and calculated concentrations differ by more than 10%, the run would be voided. The RSD for the active samplers should be less than 5%, and individual active sampler results should be plotted to ensure that no large variation exists in analyte concentration throughout the generation system.
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