A computer program to promote understanding of the monitoring method evaluation guidelines used at NIOSH.

A computer-based training program has been devised to promote better understanding of the recently revised National Institute for Occupational Safety and Health (NIOSH) test guidelines applicable to methods requiring on-site sample collection and laboratory sample analysis of airborne toxic substances. A statistics section explains the basis of the NIOSH accuracy criterion (NAC); an experiments section provides details on the evaluation experiments; and a calculations section calculates method statistics based on data entered by the user. The statistics section graphically explains concepts such as the NAC and limit of detection, allowing the user to experiment with some parameters to see how the results are affected. This section also provides background material to show how some of the performance criteria evolved. The experiments section provides a summary of the experiments used to generate the data for method evaluation. The calculations section has several screens that work like customized spreadsheets for the entry of data collected during the laboratory evaluation of a method. A separate screen then calculates the precision (relative standard deviation) of analytical results at each of four concentrations, tests to see if the precision values are statistically homogeneous, and combines the homogeneous data for calculation of the relative standard deviation. It does the same for bias, and combines the precision with method bias to arrive at an estimate of method accuracy. Other screens in the calculations section facilitate the determination of method limit of detection and sample storage stability.

Methods used by the United States National Institute for Occupational Safety and Health to monitor crystalline silica.

The National Institute for Occupational Safety and Health (NIOSH) in the United States has four methods for monitoring the concentration of crystalline silica dust. They all employ a cyclone for size-selective sampling in the field, but differ primarily in that the laboratory measurement is based on either infrared spectroscopy, X-ray diffraction, or colorimetry. The limits of detection for these methods are similar, but their accuracy is poor, particularly at low filter loadings near the current recommended exposure limit (50 mu g center dot m-3). Advances in analytical instrumentation have improved measurement precision. Correction techniques to account for X-ray absorption in samples loaded with nonsilica dust have eliminated one source of bias. Direct analysis on collection filters is a convenient technique that should decrease sample manipulation errors, but it has not been shown to improve precision or accuracy significantly.

A sampling and analytical method for the simultaneous determination of multiple organophosphorus pesticides in air.

A sampling and analytical method for organophosphorus pesticides using a combined filter/XAD-2 sorbent sampler and gas chromatography (GC)-flame photometric detection (FPD) was developed. The method was evaluated for 19 organophosphorus pesticides based on the joint Occupational Safety and Health Administration/National Institute for Occupational Safety and Health Standards Completion Program methods evaluation protocol. The evaluation addressed analyte recovery, sampler capacity, sample stability, and precision and accuracy. Additional experiments addressed long-term sample stability (30-day storage), short-term exposure limits, limits of detection, and concentration levels down to 0.1 times an exposure limit value. Samples were stable for 30 days of storage under either ambient or refrigerated conditions. Based on this research, all 19 compounds studied can be successfully determined simultaneously using one method with an accuracy of +/- 25% of the true value 95 times out of 100.

Performance of laboratories measuring silica in the Proficiency Analytical Testing program.

A statistical study was performed on the results reported by laboratories analyzing silica samples in the first 101 rounds of the Proficiency Analytical Testing (PAT) program. Five laboratories participated in the first round of the PAT program in 1972, and participation grew to 130 laboratories before falling to 105 in Round 101. The laboratories use all three of the major methods of analysis: colorimetry, x-ray diffractometry, and infrared spectroscopy. The objectives of the study were to determine bias between methods, the variability associated with the methods, and any changes in bias or variability caused by a number of factors. The colorimetric method has consistently given the lowest results, particularly at higher loadings. X-ray diffractometry results were biased higher than infrared spectroscopy results during one period but not in the following period. Between the two periods, the procedures and materials used to prepare PAT samples changed in a number of ways, but the switch to quartz dust with a smaller particle size is a likely explanation for the bias difference. Generally, silica analyses have improved in precision over time, and this improvement has taken place for all three of the methods. The colorimetric method has shown the poorest precision of the three methods, but, unlike the differences in bias, the differences in precision have diminished considerably over time. Precision estimates from other studies were compared to those from this study to learn more about sources of variability. The largest source of variability, the differences between laboratories, was large even when laboratories used the same method, as they did in a collaborative study of silica methods.

Monitoring the performance of occupational health laboratories.

To monitor the performance of occupational health laboratories analyzing workplace air, the American Industrial Hygiene Association (AIHA), with assistance from the National Institute for Occupational Safety and Health, has established four national quality assurance programs. They are the Proficiency Analytical Testing (PAT) Program, the AIHA Laboratory Accreditation Program, the Asbestos Analysts Registry, and the Bulk Quality Assurance Program. This paper focuses on the PAT program, a quality audit program that provides samples of asbestos, silica, metals, and solvents to laboratories quarterly. PAT data for asbestos, silica, and lead were examined for trends in precision. Simple graphs of coefficient of variation during the 18-yr history of the program provide evidence of improved agreement among laboratories performing these analyses. The improvement took place in spite of growth in the number of laboratories and decreases in the levels being analyzed. The improvement is attributed to several factors, including improved analytical methods and the very existence of the PAT and AIHA Laboratory Accreditation Programs.

An ion chromatographic method for insoluble chromates in paint aerosol.

Potential exposure to Cr(VI) extends to over a million U.S. workers in the plating, paint, steel, tanning and chrome ore processing industries. Historically, Cr(VI) exposure has been monitored using a colorimetric method. This colorimetric method requires acidification of the sample for color development, a step that could cause reduction of Cr(VI) to Cr(III), thus underestimating the Cr(VI) content of the sample. A new method of analysis has been developed that uses ion chromatography (IC) for the measurement and which does not require acidification of the sample. In this method, the same extraction solution of hot 2% NaOH and 3% Na2CO3 as used in the earlier methods is used to dissolve both soluble and insoluble chromates (e.g., PbCrO4, ZnCrO4 and BaCrO4), but it can be carried through the method with only a dilution step before sample injection. Therefore, this method has the advantage of minimizing the potential for Cr(VI) loss by reduction. Another advantage is provided by the IC measurement step, which is not interfered with by colored samples that may affect the colorimetric method. The new method was tested with filter samples of paint aerosol containing PbCrO4 and ZnCrO4. Complete extraction of Cr(VI) from the filter samples was verified by comparison to an independent method in which the filter was completely ashed and analyzed by inductively coupled plasma-atomic emission spectroscopy method. Nothing in the paint samples interfered with the Cr(VI) measurement, nor did five common anions used in a separate test. The method had the sensitivity needed for monitoring at the ACGIH TLV of 0.05 mg Cr(VI)/m3.