Stanley A. Shulman

Evaluation of the Magiscan Image Analyzer for Asbestos Fiber Counting

The Magiscan 2 (M-2) image analysis system with asbestos fiber counting software was evaluated. The M-2 takes a video image from a standard phase contrast light microscope used for human (manual) counting of asbestos fibers, processes the video image and then analyzes the particle shapes to count the number of fibers. Operator attention is required to the extent of placing the slide in the microscope, selecting the areas for analysis and focusing the microscope. A set of Occupational Safety and Health Administration (OSHA) quality control field samples was analyzed by the M-2, and the results were compared to the OSHA counts. The data indicated good precision by the M-2 and reasonably good agreement with the OSHA counts. A subset of these samples also was analyzed by a group of 12 proficient laboratories. The M-2 results agreed well with the inter-laboratory means. Finally, the performance of the M-2 was observed for individual fibers. The M-2 did not always agree with the observer (e.g., sometimes missin...

Use of Tracer Gas Technique for Industrial Exhaust Hood Efficiency Evaluation–Where to Sample?

A tracer gas technique using sulfur hexafluoride (SF6) was developed for the evaluation of industrial exhaust hood efficiency. In addition to other parameters, accuracy of this method depends on proper location of the sampling probe. The sampling probe should be located in the duct at a minimum distance from the investigated hood where the SF6 is dispersed uniformly across the duct cross section. To determine the minimum sampling distance, the SF6 dispersion in the duct in fully developed turbulent flow was studied at four duct configurations frequently found in industry: straight duct, straight duct-side branch, straight duct-one elbow, and straight duct-two elbows combinations. Based on the established SF6 dispersion factor, the minimum sampling distances were determined as follows: for straight duct, at least 50 duct diameters; for straight duct-side branch combination, at least 25 duct diameters; for straight duct-one elbow combination, 7 duct diameters; and for straight duct-two elbow combination, 4 duct diameters. Sampling at (or beyond) these distances minimizes the error caused by the non-homogeneous dispersion of SF6 in the duct and contributes to the accuracy of the tracer gas technique.

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.

Identification and Counting of Asbestos Fibers

A combined analytical electron microscopic/optical count method for the determination of airborne asbestos fibers was tested for precision and bias. A modified phase contrast microscopic count method (NIOSH Method 7400) was used to determine total fiber content. The analytical electron microscope (AEM) procedure was added to identify the fraction of amosite asbestos fibers in airborne, laboratory-generated samples containing amosite and wollastonite fibers. Then this fraction was applied to the routine optical counts of all the samples in the set to estimate the asbestos fiber concentration. The effects of sample to sample, wedge to wedge, within wedge and between and counter variability were examined. In addition, the variabilities of the elemental ratio within a fiber and between fibers was also determined to find their possible influence on the ability to identify the fiber as amosite in the presence of other silicate fibers. A precision of 20.1% relative standard deviation (RSD) and a bias of -9.1% for the AEM count method compared with the optical count procedure were found for these mixed fiber samples.

Comparison of Three Sampling and Analytical Methods for Measureing m-Xylene in Expired Air of Exposed Humans

Three breath sampling and analytical methods were tested following exposure of 12 subjects for 4 hr to 75 ppm m-xylene in a controlled environmental chamber. Mixed-expired breath was sampled for m-xylene from all 12 subjects with a new stainless steel device that permits continuous mainstream or sidestream sampling of the solvents present. The m-xylene was sampled from the mainstream using charcoal cloth and from the sidestream using Tenax TA. Alveolar breath also was sampled for m-xylene from 6 of these subjects using bags. The carbon dioxide concentrations of the mixed and alveolar samples, obtained from these 6 subjects, were also determined and used to assess the accuracy of the mixed-expired sampling and analytical procedures. Breath sampling was conducted over the immediate 240-min postexposure period. All m-xylene samples were analyzed using gas chromatography with flame ionization detection. Carbon dioxide concentrations were determined with an infrared analyzer. Nonlinear regression analysis was used to model the desaturation of m-xylene via the breath. Overall, the desaturation of m-xylene from all subjects by all methods was best described using three-compartment pharmacokinetic models. The precision of each sampling and analytical method, estimated from the residual variabilities of the desaturation curves were 0.13 for alveolar sampling, 0.14 for mainstream-mixed sampling (12 subjects), and 0.23 for sidestream-mixed sampling (12 subjects). For all 12 subjects, the breath m-xylene concentrations determined by sidestream-mixed sampling averaged 83% of those determined by mainstream-mixed sampling; this bias was significant. For the 6 subjects from whom both mixed-expired and alveolar breath samples were obtained, the average m-xylene desaturation rates determined by both mainstream-mixed and alveolar sampling were comparable but substantially different from those determined by sidestream-mixed sampling. For these subjects, comparison of the average and individual mixed to alveolar ratios of m-xylene and carbon dioxide showed that mainstream-mixed sampling was accurate and that sidestream-mixed sampling was not.

Performance of Asbestos Fiber Counting Laboratories in the NIOSH Proficiency Analytical Testing (PAT) Program

Asbestos fiber counting data reported in the NIOSH Proficiency Analytical Testing (PAT) Program are used in this study to evaluate the analytical performance of participating laboratories and to determine if overall performance has improved during a ten-year period. PAT laboratories have achieved intralaboratory precision of 0.18 to 0.28 relative standard deviation (RSD), and interlaboratory precision of 0.33 to 0.44 RSD. In addition, there was higher variability between PAT laboratories from 1974 to 1978, when the program underwent considerable change and growth than the variability found during previous or subsequent time periods. The improvements in interlaboratory precision by approximately one-third since 1974 and the tendency of laboratories with little PAT experience to have poorer interlaboratory precision than more experienced laboratories raises a concern that interlaboratory precision may deteriorate as large numbers of new laboratories start to enroll in the PAT Program with the increased emphasis on asbestos removal in public buildings.

Control of wake-induced exposure using an interrupted oscillating jet.

A problem may arise in ventilation design when the contaminant source is located in the workers wake, where turbulence and vortex formation can carry the contaminant into the breathing zone even though the source is downwind. It was found previously that forced directional variations in the flow can reduce or eliminate the vortex formation that causes these local reversals. Reported here is a simple realization of this concept, in which an oscillating jet of air was directed at a mannequin in an otherwise steady flow of air. A 50th percentile male mannequin was placed in a nearly uniform flow of approximately 0.18 m/sec (36 ft/min). A low-velocity tracer gas source (isobutylene) was held in the standing mannequins hands with the upper arms vertical and the elbows at 90 degrees. Four ventilation scenarios were compared by concentration measurements in the breathing zone, using photoionization detectors: (A) uniform flow; (B) addition of a steady jet with initial velocity 5.1 m/sec (1.0 x 10(3) ft/min) directed at the mannequins back, parallel to the main flow; (C) making the jet oscillate to 45 degrees on either side of the centerline with a period of 13 sec; and (D) introducing a blockage at the centerline so the oscillating jet never blew directly at the worker. At the 97.5% confidence level the interrupted oscillating jet (case D) achieved at least 99% exposure reduction compared with the uniform flow by itself (case A), at least 93% compared with the steady jet (case B), and at least 45% exposure reduction compared with the unblocked oscillating jet (case C).

The Quality of Fiber Count Data

Abstract Optical fiber counts are used to determine asbestos exposure, so it is important to assess, control, and document the quality of those counts. These functions are the responsibility of the quality assurance (QA) coordinator in each laboratory. The QA coordinator must recognize that, compared to the analytical results for other substances, fiber count data are much more variable and have different statistical properties. These data, therefore, warrant special treatment. This article discusses the need to recount some samples, the procedures for determining bias and variability from these recount data, and the use of these statistics to test analytical results or assign confidence limits to them. Three kinds of bias and variability must be considered: intracounter, intra-laboratory, and interlaboratory. As data pairs (count and recount) are obtained, the first consideration is whether bias is present. If bias is detected in a set of data, that data should not be used for any purpose until the sourc...

An Environmental Sampling Model for Combining Judgment and Randomly Placed Samples

In the event of the release of a lethal agent (such as anthrax) inside a building, law enforcement and public health responders take samples to identify and characterize the contamination. Sample locations may be rapidly chosen based on available incident details and professional judgment. To achieve greater confidence of whether or not a room or zone was contaminated, or to certify that detectable contamination is not present after decontamination, we consider a Bayesian model for combining the information gained from both judgment and randomly placed samples. We investigate the sensitivity of the model to the parameter inputs and make recommendations for its practical use.

Summary of the NIOSH guidelines for air sampling and analytical method development and evaluation

Suggested guidelines for the development and evaluation of sampling and analytical methods for industrial hygiene monitoring have recently been published in a NIOSH technical report. These guidelines are based in part on various published approaches for method development and evaluation and serve as an attempt at a more unified experimental approach. This paper presents some salient features of this unified approach for method development and evaluation. The basic goal of the approach is to determine if the method under study meets the criterion to produce a result that fell within 25% of the true value 95 times out of 100 on average, although other factors of method performance are evaluated. The experiments proposed for the evaluation of method performance include determination of analytical recovery from the sampler, sampler capacity, storage stability of samples and effect of environmental factors. Evaluation criteria for the experimental data and procedures for the calculation of method bias, precision and accuracy are also included.