Workplace Aerosols Research Articles

Assessment of particle size distributions in workers' aerosol exposures.

A full description of the regional dosimetry of inhaled workplace aerosols requires information about the particle aerodynamic size distributions of inhaled aerosols for appropriate health-related species. Therefore, since the late 1970s, interest has risen in how to assess workers' aerosol exposures in terms of particle fractions which may be inhaled and penetrate down to different parts of the human respiratory tract. The personal inhalable dust spectrometer (PIDS) was proposed as a versatile sampling instrument for assessing workers' exposures along these lines. Raw data from this cascade impactor-based instrument are obtained initially in terms of discrete particulate masses collected on the individual impactor stages. Recovery of the desired particle size distribution is difficult because the mathematical inversion problem is 'ill-posed' (i.e., there are many possible solutions that would be consistent with the observed masses). However, a routine has been developed that involves considerations of the detailed deposition characteristics of the impactor stages, measurement errors and a priori assumptions about the shape of the expected particle size distribution (e.g., log-normal). These differ from other such routines in that account is taken not only of aerosol deposited at the impactor stages but also that collected inside the entry system. Hence the final result covers the whole inhalable range, for particles up to and exceeding 100 microns in aerodynamic diameter. The PIDS has recently been used in studies in several industries to examine inhalable particle size distributions for individual exposed workers. This paper considers the results of such studies, and discusses how they may be used to provide information not only about the inhalable, thoracic and respirable fractions identified in the latest particle size-selective sampling criteria (upon which it is expected that future aerosol standards will be based), but also other health-related fractions that may be defined numerically (including, for example, alveolar deposition fractions for workers with different breathing patterns relevant to the type of work undertaken).

The performance evaluation of aerosol samplers tested with monodisperse aerosols

Performance requirements are currently being established for instruments used for the particle size-selective sampling of potentially hazardous aerosols in workplaces. In this paper, two are described, for aerosol sampler evaluation data obtained from experiments carried out with monodisperse test aerosols. Application of the methods is illustrated using experimental data for two sampler types, the MRE 113A static respirable sampler and the PM-10 ambient aerosol sampler. Where both methods can be applied to the same data, the estimates obtained using the two methods are in broad agreement. The small number of data points obtained in typical monodisperse-aerosol experimentals leads to large uncertainties i n the estimated performance characteristics.

Technique for Assessing the Electrical Charge Levels of Aerosols

A relatively low-cost and easy-to-use method for estimating the charge level on aerosols has been developed. It uses the properties of an electrostatically enhanced (electret) filter combined with an optical particle counter to obtain size-dependent charge levels of workplace aerosols. The optical particle counter is calibrated to give a “filtration equivalent” particle size. For the size range of the present measurements, this is similar to geometric size. The aerosol concentration is measured before and after neutralization to determine a penetration ratio that can be approximately correlated with particle electrical mobility. For a particle of a given size, the penetration ratio increases with increasing particle charge level. The method was calibrated with monodisperse methylene blue particles charged to a known level. A polydisperse CaCO3 aerosol, characterized as to size-dependent charge levels, also was measured. Finally, the charge level on a copy-machine toner dust was measured to simulate a highly charged workplace aerosol. The method is limited to the size range of 0.1 µm to 0.7 µm by the characteristics of the electret filter. Electrical mobilities ranging from 0.01 to 1 cm2/statV sec can be measured. The charge level on one particle size in a size distribution is proportional to the charge on other sizes, and can thus be an indicator of charge level of the overall aerosol. Although of limited size-range capability, the method can serve as an indicator of the importance of aerosol charge for sampling or for health effects.

Technique for Assessing the Electrical Charge Levels of Aerosols

A relatively low-cost and easy-to-use method for estimating the charge level on aerosols has been developed. It uses the properties of an electrostatically enhanced (electret) filter combined with an optical particle counter to obtain size-dependent charge levels of workplace aerosols. The optical particle counter is calibrated to give a “filtration equivalent” particle size. For the size range of the present measurements, this is similar to geometric size. The aerosol concentration is measured before and after neutralization to determine a penetration ratio that can be approximately correlated with particle electrical mobility. For a particle of a given size, the penetration ratio increases with increasing particle charge level. The method was calibrated with monodisperse methylene blue particles charged to a known level. A polydisperse CaCO3 aerosol, characterized as to size-dependent charge levels, also was measured. Finally, the charge level on a copy-machine toner dust was measured to simulate a high...

Measurement of fine aerosols in workplaces. A review.

The fine aerosol fractions of interest in occupational health are those associated with the regional deposition of inhaled aerosols in the different parts of the human respiratory tract. The recent recommendations of the International Standards Organization, the American Conference of Governmental Industrial Hygienists and the Comité Europeén de Normalisation define the thoracic fraction (inhaled particles which penetrate into the lung) and the respirable fraction (inhaled particles which penetrate further into the alveolar region). Based on the results of inhalation experiments with humans, conventional curves for these fractions are proposed, which provide 'yardsticks' for health-related sampling devices. Samplers for the respirable fraction have been in existence since the early 1950s, and a fairly large range of acceptable instrumentation is available commercially. Recently, however, attention has been drawn to the effect of even small departures from the 'target' curve on the respirable mass sampled. This suggests the need for additional criteria for sampler acceptability, based on sampled mass in addition to particle size selectivity. Samplers for the thoracic fraction may be based on similar physical concepts to those for respirable aerosol. In addition, versatile devices capable of providing information about more than one fraction simultaneously are being proposed and are finding increasing use as investigative tools for industrial hygienists. Finally, measurement of fine fibrous aerosols is recognized as a special case, and so is treated separately.

Measurement of coarse aerosols in workplaces. A review.

Coarse aerosol fractions in workplaces are sampled if it is felt that particles of all sizes may pose a risk to health. Although the so-called 'total' aerosol has been widely used to refer to the relevant coarse fraction, practical measurement has been very dependent on the actual sampling instrument used. This in turn has led to great uncertainty about what was being measured. In the 1980s, the concept of inhalability was proposed, based on the aerosol particle size fraction that enters the human head through the nose and/or mouth during breathing. Now there is substantial agreement by most of the world's major criteria-setting bodies on a quantitative definition taking the form of a single curve describing the probability of inhalation as a function of particle aerodynamic diameter. This definition now forms a truly health-related 'yardstick' against which to assess the performances of practical sampling devices. In turn, more and more countries are beginning to adopt the new criterion for health-related aerosol measurement in their standards, replacing the old 'total' aerosol concept. Experiments in wind tunnels to investigate the performances of previous samplers for 'total' aerosol show that most of them do not satisfactorily match the new inhalability criterion. A small number of samplers designed specifically for the inhalable fraction have been proposed and are available commercially. They include samplers for both static (or area) and personal sampling.

Proposal for Converting “Total” Dust Limits to Inhalable and Thoracic Dust Limits

Abstract One step in the implementation of new particle size-selective sampling definitions of inhalable, thoracic, and respirable dust that are becoming internationally accepted is the establishment of appropriate limits on the concentrations of airborne dusts. The preferable approach is to analyze toxicological and epidemiological studies that incorporate sufficient particle size information to obtain particle size-selective dust limits directly. In the absence of such information but with sufficient information about the collection efficiency of the current “total” dust sampler and about the range of workplace aerosol size distributions for the material being considered, there is a rational approach to converting current “total” dust limits to approximately equivalent inhalable or thoracic dust limits, which is described briefly. Currently, there is very little information about the collection efficiency of the “total” dust personal sampler that is used most commonly in the United States. Because of this, there is insufficient information to take even the second approach outlined above. However, recommendations can be developed for converting current “total” dust limits to tentative inhalable or thoracic dust limits using guidelines presented here. Side-by-side sampling comparisons are strongly recommended to discover discrepancies. To illustrate this approach, formulas are proposed for converting current “total” dust limits established in the United States to tentative inhalable or thoracic dust limits (inhalable particulate matter [IPM]- and thoracic particulate matter [TPM] - threshold limit values [TLVs]), whichever is appropriate for the material under consideration:

Sampling and chemical characterization of aerosols in workplace air

Abstract

Aerosols in Workplace

Aerosols in Workplace

Aerodynamic size measurement of airborne fibers and health effects implications

The constituent particles of many ambient and workplace aerosols of health effects concerns are of fibrous and aggregate geometric shapes. Although the deposition sites of particles in the human respiratory system are primarily related to their aerodynamic diameters, for rod-like and branching forms the dominant deposition mechanism may be interception. A theoretical model has been developed which predicts that natural and synthetic fibers may be preferentially deposited at lung airway bifurcations. Therefore, to assess potential exposure hazards it is necessary to have accurate kinetic classifications of airborne particulate matter. Centrifugal spectrometers can give direct and continuously graded measures of the aerodynamic size distributions of sampled aerosols. Herein, a mathematical description of centrifuge operation is refined to permit the characterization of irregularly shaped particles, with specific application to fibers. Aerosol centrifuge performance therefore can be customized to specific applications and be integrated into health effects studies.

ENTRY CHARACTERISTICS OF PRACTICAL WORKPLACE AEROSOL SAMPLERS IN RELATION TO THE ISO RECOMMENDATIONS

In recent years, new sets of criteria for health-related aerosol sampling in workplaces have been proposed by, for example, the International Standards Organizations (ISO) and the American Conference of Governmental Industrial Hygienists (ACGIH). It is therefore timely to examine the performances of workplace aerosol samplers, both instruments that have been used in the past and ones which are beginning to emerge, in the light of these recommendations. This paper describes the results and conclusions from a study of dust samplers with a view to their possible applications in the mining industry. Their performances are assessed with special reference to their entry efficiencies, based on the philosophy contained in the most up-to-date ISO recommendations, in particular with regard to the concept of inhalability (or inspirability).

Size Characteristics of Machining Fluid Aerosols in an Industrial Metalworking Environment

Abstract In an industrial metalworking environment, workplace aerosols are produced continuously during normal operations as machining fluids flood the cutting or grinding tools at the machined surfaces. Since aqueous, synthetic fluids and soluble oils have replaced straight oils for the most part, the physical characteristics of the machining fluid aerosols should be determined to facilitate the assessment and control of potential health hazards in an industrial metalworking environment. The size distributions and mass concentrations of machining fluid aerosols in an automotive transmission manufacturing plant were determined by cascade impactors, real-time aerosol monitors, and a new area respirable impactor. The aerosols sampled at six sampling sites within the plant were found to be polydispersed with large droplets greater than 8 μm in aerodynamic mass median diameter and fine particles in the 0.1–1 μm size range. The large aerosols were formed from the direct spraying of machining fluids or from emi...

AERODYNAMIC CLASSIFICATION OF FIBERS WITH AEROSOL CENTRIFUGES

ABSTRACT Many ambient and workplace aerosols of health effects concerns are composed of particulate matter having fibrous or aggregate shapes. Aerosols used in medical research for treatment of lung diseases also have rod-like forms. The deposition sites of inhaled particles in the human respiratory system are primarily related to their aerodynamic characteristics. Therefore, to assess potential exposure hazards and prophylactic applications it is necessary to have accurate kinetic classifications of airborne particulate matter. Centrifugal spectrometers give direct and continuously graded measures of the aerodynamic size distributions of sampled aerosols. A mathematical description of particle behavior in spiral channel centrifuges has been presented, and substantiated by comparisons with laboratory calibration data using polystyrene latex spheres. Here, the theory is extended to non-spherical forms by incorporating appropriate dynamic particle shape resistance factors in trajectory equations. This permi...

Exposure characterization of aerosols and carbon monoxide from supplemental inflatable restraint (automotive air bag) systems

The purpose of this study is to determine the characteristics of aerosols inside a passenger car after the deployment of air bags (supplemental inflatable restraints, SIR) for a worst-case situation. Mass concentrations and size distributions of the SIR-aerosols, and the concentration of carbon monoxide were measured. The average total particulate mass concentrations during each of the 25-min observation periods immediately following deployment of three different preproduction SIR-systems, each employing three inflators were 86, 83 and 415 mg m −3, and the average carbon monoxide concentrations were 46, 48 and 180 ppm, respectively. The SIR-aerosols exhibited bimodal size distributions with modes centred at 0.8 and 10 μm. Using ion chromatography, the fine aerosol fraction near 1 μm was found to contain carbonates, while the larger aerosol near 10 μm was not alkaline and was probably derived from corn starch, a dry lubricant which coated the air bag. Currently, very limited human exposure data exist which can be used to assess the respiratory effects from a single acute exposure to such dusts. The absence of short-term exposure limits for workplace aerosols or nuisance dusts with similar properties warrants studies to quantify the human respiratory response to SIR-aerosols.

On the Biologically-Relevant Sampling of Airborne Particles

Abstract This paper describes how the assessment of workplace aerosols should be based on criteria which are directly relevant to health effects. Such criteria are embodied in two recent sets of recommended standards for aerosol sampling: firstly in 1981 by the International Standards Organisation and then in 1985 by the American Conference of Governmental Industrial Hygienists. In occupational hygiene, both static and personal dust samplers are widely used for estimating worker exposure. Although there are arguments for and against each, it is suggested that a well-planned sampling strategy should involve the use of both. We have therefore set out to develop new instruments of both types consistent with the recommended sampling criteria. These include inspirable aerosol samplers for the biologically-relevant measurement of so-called ‘total’ aerosol, and inspirable aerosol spectrometers for providing a wider range of health-related aerosol information.

Recent advances in aspiration theory for thin-walled and blunt aerosol sampling probes

In this paper, an attempt is made to generalize and extend what has already been learned about the physical basis of the aspiration efficiencies of aerosol samplers. It begins with the assumption that all such samplers are, in fact, aerodynamically blunt since their physical presence inevitably imposes some restriction to the movement of the surrounding air. The thin-walled probe, which has already been the subject of much interest, is just such a limiting case. Other forms of blunt sampler have received less attention. The paper describes an improved theoretical model for aspiration efficiency which is derived from knowledge of the broad features—rather than the details—of the distorted air flow near a blunt sampler. Such features include, for example, the location on the sampler body of stagnation, indicating where the airflow divides between that which is sampled and that which passes by outside the sampler. This is dependent not only on the sampling flow rate and wind speed but also on the aerodynamic ‘bluntness’ of the sampler body. The model was tested against experimental results already published for thin-walled probes and a range of less-idealized sampling systems. The comparison is good except for very blunt samplers at orientations other than facing the wind. This is believed to be associated with the fact that we do not yet know how to account for changes in aerodynamic bluntness with increasing yaw angle. In view of the wide practical importance of such work to the development of samplers with characteristics consistent with the latest particle size-selective recommendations for aerosols in workplaces and in the ambient atmosphere, the need for further experimental work is identified.

Critique of 1985 ACGIH report on particle size-selective sampling in the workplace.

The criteria recently proposed by ACGIH for judging the acceptability of respirable and other dust fraction samplers are analyzed. Implications on the sampling of workplace aerosol are determined. With the consideration of both bias and imprecision, the overall accuracy limited by the criteria is estimated for the sampling of coal mine dust as characterized by various researchers. The accuracy limits thus found appear to be excessively broad. As an example with actual workplace dust distributions in the sampling of a single aerosol (mass median diameter = 18.6 micrometers and geometric standard deviation = 2.3) with respirable dust concentration near 2 mg/m3, two samplers acceptable according to the proposed criteria could be found giving respirable dust measurements equal to 0.71 mg/m3 and 4.3 mg/m3 (even after excluding 5% of the low and high measurements from each sampler, respectively). Large variation in samplers acceptable according to the criteria is found for many other distributions as well; this indicates that tighter requirements are necessary. Seldom attained are both the single-sample +/- 25% accuracy at the 95% confidence level required of sampling/analytical methods endorsed by the National Institute for Occupational Safety and Health (NIOSH) and the tighter ISO dust fraction measurement requirement that 67% of the measurements of a sampled dust fall within 10% of a true value. Suggestions are given for sharpening the criteria without eliminating all samplers from acceptability.

Industrial hygiene implications of the static electrification of workplace aerosols

This paper reviews the electrostatic properties and effects of workplace aerosols as they relate to industrial hygiene. It summarises what is known about the nature of the charging of aerosols generated in industrial workplaces, the results of studies in workplaces together with those of relevant laboratory studies, the effects of aerosol charge on the deposition of inhaled particles in the respiratory tracts of humans and animals, the effects on aerosol sampling in the workplace, and the effects on filtration. The main conclusions are that: (a) workplace aerosols are invariably charged to levels substantially above Boltzmann equilibrium (with the distribution between positive and negative polarity usually being approximately symmetrical); (b) effective charging levels are higher for fibrous aerosols (e.g., asbestos) than for most similarly dispersed non-fibrous ones; (c) the effect of aerosol charge is to enhance deposition in the deep lung by the action of electrical image forces (d) the magnitude of deposition for most practical aerosols is insignificant for isometric particles but might not be for fibrous ones; (e) the effects on the aspiration efficiencies of aerosol samplers are small but the effects on particle transport through tubes, cowls, transition sections and onto the filters of samplers may be large; and (f) aerosol charge enhances the particle collection efficiencies of many air filters but, in the case of artificially electrified filters, causes a degradation in performance due to progressive charge neutralisation.

On the practical significance of electrostatic lung deposition of isometric and fibrous aerosols

Evidence from experiments with humans and animals suggests that the lung deposition of inhaled particles is enhanced if the particles are electrically charged. Simple analysis has been carried out by which the practical significance of the problem can be assessed, based on consideration of the physical factors which influence particle movement under electrostatic image forces in the confined spaces of the alveolar region of the lung. The results support the observations in animal studies that electrostatic enhancement of lung deposition is small for inhaled isometric polydisperse mineral dusts, but potentially large for similarly dispersed fine fibrous asbestos aerosols. From measurements of the levels of electrostatic charging of workplace aerosols, it is concluded that the same will be true for human subjects occupationally exposed to airborne dust.

Occupational Lung Diseases.

A Short History of Occupational Lung Diseases. Prevention of Occupational Lung Diseass. The Clinical Approach. Legal Aspects of Industrial Disease. Pulmonary Physiology. Epidemiology and Occupational Lung Disease. The Deposition and Clearance of Dust from the Lungs. Pathological Reactions of the Lung to Dust. The Measurement of Workplace Aerosols. Respiratory Protection. Basic Mechanisms in Occupational Lung Diseases Including Lung Cancer and Mesothelioma. Silicosis. Silicates and Lung Disease. Asbestos-Related Diseases. Coal Workers' Pneumoconiosis. Other Pneumoconiosis. Occupational Asthma. Byssinosis and Related Conditions. Industrial Bronchitis and Other Nonspecific Conditions. Hypersensitivity Pneumonitis. Toxic Gases and Fumes. Barotrauma and Hazards of High Pressure. Infectious Diseases. Occupational Lung Cancer.