A PC-based quality control (QC) program for an industrial hygiene laboratory

Our plain-English summary of A PC-based quality control (QC) program for an industrial hygiene laboratory, by D.K. Verma, K. Ferguson, S.A. McCollin, et al (Journal of Occupational and Environmental Hygiene, 2006).

The study

• Authors: D.K. Verma, K. Ferguson, S.A. McCollin, L. Shaw, K. des Tombe
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2006;3(7):D56-66
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This was a technical column, not a health study. It described the quality control computer program of a laboratory at McMaster University in Hamilton, Ontario, with fewer than 10 analysts. It reported no findings about asbestos exposure or disease. The program was first written in 1990 for DOS and was converted to a Windows-based add-on for Microsoft Excel by 2001. It used Visual Basic to build accuracy (Xbar) and precision (R) control charts from quality control samples. It covered eight kinds of analyses, including asbestos fiber counts and bulk asbestos. For fiber counts, analysts counted two slides per batch. These were drawn from randomly numbered slides made from a pool of 40 slides from past proficiency testing rounds. For bulk asbestos, one sample with a known value was analyzed per batch. The result had to be correct on whether asbestos was present and on its type, such as chrysotile, crocidolite or amosite. If those were correct, a result one percentage category from the true category was accepted. The authors described the program as flexible, user friendly and particularly suitable for small industrial hygiene laboratories.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Technical column describing a laboratory quality assurance plan and a PC-based quality control computer program (not a study of people or exposure)
• Who was studied: One industrial hygiene laboratory: the Occupational and Environmental Health Laboratory, McMaster University, Hamilton, Ontario, Canada, with fewer than 10 analysts
• Exposure: No exposure was studied. The program covered eight kinds of laboratory quality control analyses, among them asbestos fiber counts (phase contrast microscopy) and bulk asbestos (polarized light microscopy).
• Main results:
  • The first version of the program was written in 1990 as a DOS-based Lotus Symphony program. It was converted to a Windows-based program, written in Visual Basic, that uses Excel and Word. The conversion was complete by 2001.
  • The program sets limits for two charts. For the accuracy (Xbar) chart, the control limits are Xbar plus or minus 3 standard deviations and the warning limits are Xbar plus or minus 2 standard deviations. For the precision (R) chart, the upper control limit is 3.27 times Rbar and the upper warning limit is 2.51 times Rbar.
  • Until 30 quality control results are available, the program uses default settings: an Xbar of 100% with a standard deviation of 3.33. This corresponds to an upper control limit of 110% and a lower control limit of 90% on the accuracy chart.
  • In the example lead quality control data, after 30 analyses Xbar was 99.63 (percent recovery), the standard deviation was 3.60 and Rbar was 2.50. Values marked as outliers were not used to calculate the limits.
  • Fiber count quality control used a pool of permanent mounted slides from past proficiency testing rounds, of which 40 always remain in the pool. Two of the 20 randomly numbered quality control slides were counted with each batch of client samples.
  • Bulk asbestos quality control used 40 samples with known reference values from previous Research Triangle Institute, NVLAP or AIHA proficiency testing rounds.
  • A bulk asbestos result one range away from the true range was acceptable. A result two or more ranges away was unacceptable, and another quality control sample would then be analyzed.
  • A bulk asbestos quality control result also had to be correct on whether asbestos was present and on its type (for example chrysotile, crocidolite or amosite), as well as on the range.
  • For metal, silica and fiber count quality control samples, the program reports OK, WARNING or OUT. An OUT result means the quality control samples failed and leads to a series of interventions.
  • At the time of writing, the laboratory maintained over 200 different solvent control charts.
• The authors' conclusion: The authors concluded that the program is flexible, user friendly and particularly suitable for small industrial hygiene laboratories.

Topics

Medical terms in this study, explained in our Lexicon: Industrial Hygiene.

Related studies

• Within-laboratory quality control of asbestos counting — T.L. Ogden, T. Shenton-Taylor, et al. (1986)
• A proposal for harmonising laboratory performance assessment criteria in national asbestos fibre counting schemes — M.C. Arroyo, J.M. Rojo (2001)
• Statistical uncertainties in asbestos-laboratory classification through the RICE scheme — T.L. Ogden (1984)
• Analysis of the analytical performance of laboratories participating in two major U.S. bulk asbestos proficiency testing programs — B.W. Harvey, W.G. Winstead (2008)
• Assessing quality of life when planning and evaluating worker notification programs: two case examples — B.E. Meyerowitz (1993)
• Industrial hygiene perspectives in control of asbestos exposure — W. Reitze (1979)

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