Michael A. McCawley

A Personal Cascade Impactor: Design, Evaluation and Calibration

A cascade impactor has been developed that is suitable for personal sampling. The impactor can be used with four, six, or eight stages with cut points ranging from 0.5 micron to 21 micron aerodynamic diameter. Although the impactor can be operated over a fairly wide flow rate range, it is designed specifically to be operated at 2 L/min so that a personal sampler may be used as the air mover. The nozzles of the impactor are radial slots with six slots per stage for the first six stages. Circular nozzles arranged in a radial pattern are used for the last two stages. On each stage, the area between the nozzles is used as the impaction surface for the stage before it. This design allows for the impactor to be compact, rugged and lightweight (170 gm for the four-stage design). The impactor stages are contained in a mounting bracket that can be clipped to the lapel or pocket. Although the impactor is designed for personal use, it also can be used as a compact impactor for general sampling tasks. The particle cut-off characteristics of each stage and the interstage losses were determined using monodisperse aerosols. The particle losses were found to be low and the cut-off characteristics sharp. Thus, size distributions can be obtained as accurately as with larger cascade impactors.

Mortality among dust-exposed Chinese mine and pottery workers.

A cohort study of approximately 68,000 persons employed during 1972 to 1974 at metal mines and pottery factories in south central China was conducted to evaluate mortality from cancer and other diseases among workers exposed to different levels of silica and other dusts. A follow-up of subjects through December 31, 1989 revealed 6,192 deaths, a number close to that expected based on Chinese national mortality rates. There was, however, a nearly 6-fold increase in deaths from pulmonary heart disease (standard mortality ratio, 581; 95% confidence interval 538 to 626), and a 48% excess of mortality from nonmalignant respiratory diseases (standard mortality ratio, 148; 95% confidence interval, 139 to 158), primarily because of a more than 30-fold excess of pneumoconiosis. Pulmonary heart disease and noncancerous respiratory disease rates rose in proportion to dust exposure. Cancer mortality overall was not increased among the miners or pottery workers. There was no increased risk of lung cancer, except among tin miners, and trends in risk of this cancer with increasing level of dust exposure were not significant. Risks of lung cancer were 22% higher among workers with than without silicosis. The findings indicate that respiratory disease continues to be an occupational hazard among Chinese miners and pottery workers, but that cancer risks are not as yet strongly associated with work in these dusty trades.

Ultrafine Beryllium Number Concentration as a Possible Metric for Chronic Beryllium Disease Risk

Beryllium is a lightweight metal which causes a chronic granulomatous lung disease among workers who become sensitized to it. Recent research has shown a persistence of the disease despite efforts at control with mean exposures below the Occupational Safety and Health Administration (OSHA) occupational exposure limit of 2 microg/m3. Results of our current research confirm a previous finding in certain plants that particle number concentrations are higher in areas where historical estimate of risk showed a high risk of disease despite relatively lower mass concentrations. By providing side-by-side measurements of both particle number and mass, this research adds support to the proposal that particle number rather than particle mass may be more reflective of target organ dose and subsequently a more appropriate measure of exposure for chronic beryllium disease. Our evidence also shows that particle mass exposure measurements and particle number exposure measurements were not correlated.

Rationale and Recommendations for Particle Size-Selective Sampling in the Workplace

Abstract Because many aerosol hazards depend upon particle size, the American Conference of Governmental Industrial Hygienists established an Air Sampling Procedures Committee to “recommend size-selective aerosol sampling procedures which will permit reliable collection of aerosol fractions which can be expected to be available for deposition in the various major subregions of the human respiratory tract.” After reviewing available data on regional deposition of inhaled particles and on the collection efficiencies of sampling instruments, the committee recommends use of three particulate mass fractions for workplace sampling: inspirable particulate mass (IPM), for materials which may be hazardous anywhere in the respiratory tract; thoracic particulate mass (TPM), for materials which may be hazardous anywhere within the lung airways and the gas exchange region; and respirable particulate mass (RPM), for materials which may be hazardous in the gas exchange region of the lung. The mass fractions are defined ...

Estimating historical respirable crystalline silica exposures for Chinese pottery workers and iron/copper, tin, and tungsten miners

Collaborative studies of Chinese workers, using over four decades of dust monitoring data, are being conducted by the National Institute for Occupational Safety and Health (NIOSH) and Tongji Medical University in China. The goal of these projects is to establish exposure-response relationships for the development of diseases such as silicosis or lung cancer in cohorts of pottery and mine workers. It is necessary to convert Chinese dust measurements to respirable silica measurements in order to make results from the Chinese data comparable to other results in the literature. This article describes the development of conversion factors and estimates of historical respirable crystalline silica exposure for Chinese workers. Ambient total dust concentrations (n>17000) and crystalline silica concentrations (n=347) in bulk dust were first gathered from historical industrial hygiene records. Analysis of the silica content in historical bulk samples revealed no trend from 1950 up to the present. During 1988-1989, side-by-side airborne dust samples (n=143 pairs) were collected using nylon cyclones and traditional Chinese samplers in 20 metal mines and nine pottery factories in China. These data were used to establish conversion factors between respirable crystalline silica concentrations and Chinese total dust concentrations. Based on the analysis of the available evidence, conversion factors derived from the 1988-1989 sampling campaign are assumed to apply to other time periods in this paper. The conversion factors were estimated to be 0.0143 for iron/copper, 0.0355 for pottery factories, 0.0429 for tin mines, and 0.0861 for tungsten mines. Conversion factors for individual facilities within each industry were also calculated. Analysis of variance revealed that mean conversion factors are significantly different among facilities within the iron/copper industry and within the pottery industry. The relative merits of using facility-specific conversion factors, industry-wide conversion factors, or a weighted average of the two are discussed. The exposure matrix of the historical Chinese total dust concentrations was multiplied by these conversion factors to obtain an exposure matrix of historical respirable crystalline silica concentrations.

Non-malignant respiratory diseases and lung cancer among Chinese workers exposed to silica.

The objective of this study was to explore whether a medical history for non-malignant respiratory disease contributes to an increased lung cancer risk among workers exposed to silica. We analyzed data from a nested case-control study in 29 dusty workplaces in China. The study population consisted of 316 lung cancer cases and 1356 controls matched to cases by facility type and decade of birth who were alive at the time of diagnosis of the index case and who were identified in a follow-up study of about 68,000 workers. Age at first exposure and cigarette smoking were accounted for in the analysis. Smoking was the main risk factor for both lung cancer and chronic bronchitis. Lung cancer risk showed a modest association with silicosis and with cumulative silica exposure, which did not vary by history of previous pulmonary tuberculosis. Among subjects without a medical history for chronic bronchitis or asthma, lung cancer risk was associated with silicosis (odds ratio [OR], 1.6; 95% confidence interval [CI], 1.1 to 2.2), and it was increased in each quartile of cumulative silica exposure. However, risk was not elevated in the highest quartile (OR, 1.3, 1.6, 1.8, 1.4). Among subjects with a medical history for chronic bronchitis or asthma, lung cancer risk was associated with neither silicosis (subjects with chronic bronchitis: OR, 0.6; subjects with asthma: OR, 0.4) nor with silica exposure. In this study population, we observed a modest association of both silicosis and cumulative exposure to silica with lung cancer among subjects who were not previously diagnosed with chronic bronchitis or asthma, but not among subjects who had a medical history for either disease. Risk of lung cancer associated with silicosis or cumulative exposure to silica did not vary by previous medical history of pulmonary tuberculosis.

Particle Size Distributions in Underground Coal Mines

This paper reports the results of a sampling program undertaken by NIOSH to determine the particle size distributions in underground coal mines. The program made use of newly developed cascade impactors capable of being operated with personal sampling pumps. Particle size distribution samples were collected at selected areas in 10 continuous mining sections in three states. Results plotted as mass frequency distributions indicate that a bimodal distribution may exist in areas away from the operations of the continuous miner. A primary size mode of about 17 micron and a secondary size mode of about 5 micron were measured consistently throughout the 10 mines studied.

Thoracic Dust Exposures on Longwall and Continuous Mining Sections

Abstract Past data on the prevalence of symptoms of chronic bronchitis and decreases in pulmonary function indicate a potential problem due to deposition of coal mine dust in the bronchial airways. Difficulty with dust control in certain jobs indicates that chronic bronchitis may continue to be a problem. Compliance with the respirable dust standard does not equally limit the thoracic dust exposure of all miners. Coal mine dust size distributions indicate that thoracic dust levels may be as high as five times respirable dust levels in some work areas on continuous mining sections and seven times respirable dust levels in some work areas on longwall mining sections. The largest thoracic dust generating sources are the longwall shearer, shield support advancement, and the continuous miner. The worst case scenario for thoracic dust exposure occurs on bidirectional cutting longwall mining sections where some mine personnel are very likely to work downwind of the shearer and/or support advancement for a signif...

Occupational Hygiene around the World

Abstract To conduct a retrospective exposure assessment for a study of silica, silicosis, and lung cancer, current exposure measurements and techniques were compared with industrial hygiene data that had been systematically collected in Chinese industries over the past three decades. Historically, sampling was usually confined to total dust evaluation and bulk silica determinations. For comparison, from 1988 through 1989, several special surveys were conducted in Chinese iron and copper mines in the Huangshi region of Hubei Province. In addition to the total dust and silica measurements using the traditional Chinese sampling system, data were collected using standard National Institute for Occupational Safety and Health (NIOSH) sampling equipment for respirable dust, total dust, particle size distribution, selected trace elements, radon, and fibers. Overall, total dust measurement using NIOSH sampling and analytical procedures were correlated to the corresponding Chinese measurement, r2=0.77. No statistic...

A Microcomputer Spreadsheet Technique for Analyzing Multimodal Particle Size Distributions

Abstract Particle size distributions (PSD) of industrial aerosols are usually described in the literature by a single geometric mean (GM) and geometric standard deviation (GSD) determined using log-probability (probit) analysis, thus implying the existence of a single-mode, lognormal distribution. If a multimodal distribution is suspected, as indicated in log-probability analysis by data points that do not lie upon a straight line, a different method of analysis is necessary in order to estimate the parameters of each of the underlying distributions. A simple method to analyze multimodal PSDs was developed. A microcomputer spreadsheet is used to fit a smooth curve to grouped (histogram) particle size data, e.g., cascade impactor data, scanning electron microscope (SEM) particle counts, and optical device particle counts. This method is based upon the assumption that multimodal PSDs can be adequately described by a linear combination of weighted, lognormal distributions. This method yields a fitted smooth ...