The presence of a
quality assurance and quality control (QA/QC) program in the laboratory is an indication
of the laboratory's commitment to producing acceptable results.
The program should be contained in a written document that is available for
examination. When examining a QA/QC program the following items should be considered:
External to the laboratory, other QA activities may indicate additional aspects of
- Is it fully documented?
- Does it address specific aspects of silica analysis?
- Does it require the use of control charts?
- Does it require internal peer review of analytical calculations and results?
- Does it require the analysis of quality control samples with each analytical batch?
- Does it require the evaluation of quality control samples and comparison against control
Compliance with the OSHA standards requires knowing the mass of dust collected on each
sample. This is generally accomplished by the use of pre-weighed filter media. Since the
sample mass is critical to the proper calculation of the PEL and the exposure level
observed, the accuracy of this determination is critical. If the laboratory provides
pre-weighed sample media the following should be considered:
- Does the laboratory participate in proficiency studies (e.g., American Industrial
Hygiene Association Proficiency Analytical Testing (PAT) ) for silica? (These are programs
where several laboratories analyze prepared samples where the "actual" value is
unknown to the laboratories. The results from all of the laboratories are evaluated by the
program administrator against the "actual" values.)
- Is the laboratory proficient in these studies, and what is its proficiency performance
- Does the laboratory examine the cause of outliers (results outside of the study's
control limits) and can they provide a plausible explanation for outliers?
- Is the laboratory accredited or certified for silica analysis? If not for silica, are
they for any similar types of analyses? (Accreditation and certification demonstrate that
the laboratory has met requirements prescribed by an organization.)
- Is the media weighed to constant weight?
- Are quality control samples analyzed with preliminary weighings?
- Are quality control samples analyzed with final weighings?
- Is polyvinylchloride (PVC) or other weight stable media supplied?
- If weight stable media is not supplied, is matched-weight mixed cellulose ester or other
compensating media supplied?