Laboratory and field testing of sampling methods for inhalable and respirable dust

Performance of Asbestos Enclosure Ventilation: Laboratory Evaluation of Complex Configuration

The aim of the study was to find out good practices for effective air distribution inside a complex shaped asbestos enclosure and for control of pressure differences between the enclosure and the surroundings. In addition, sufficient pressure difference for asbestos containment was tested. The effect of air distribution was studied in laboratory conditions by constructing an L-shaped asbestos enclosure and connecting it to a negative pressure unit. The efficiency of six different ventilation configurations was compared using a tracer decay method and the local air change indexes as the performance indicator. The sufficient negative pressure for containment was assessed by simulating person traffic to and from the enclosure and recording the pressure difference continuously. The effect of a pressure controller unit in maintaining the target pressure difference was also tested by simulating filter loadings of the negative pressure unit causing changes in the air flow rate. The results showed that high nominal air change rates alone do not guarantee good air distribution. Effective air distribution within an asbestos enclosure can be arranged by locating additional air supply openings far away from the air exhaustion point, using recirculation air with a pressure controller, or extending the exhaust location to the poorly ventilated areas. A pressure difference of at least -10 Pa is recommended to ensure a sufficient margin of safety in practical situations.

Review of Workplace Based Aerosol Sampler Comparison Studies, 2004-2020

We provide a narrative review on published peer-reviewed scientific literature reporting comparisons of personal samplers in workplace settings published between 2004 and 2020. Search terms were developed for Web of Science and PubMed bibliographic databases. The retrieved studies were then screened for relevance, with those studies meeting the inclusion criteria being taken forward to data extraction (22 studies). The inhalable fraction was the most common fraction assessed with the IOM sampler being the most studied sampler. The most common workplace environment where samplers had been compared was that where metals/metalloids were present. The requirements of EN13205 standard (Workplace exposure. Assessment of sampler performance for measurement of airborne particle concentrations) have also been considered, with these requirements not currently being met, or at least referred to, in the included published literature. A number of conclusions have been drawn from this narrative review. For studies that reported correction factors, no discernible trends could be identified. Correction factors also varied between samplers and settings, with correction factors varying from 0.67 for Button/IOM in agriculture settings to a correction factor of 4.2 for the closed face cassette/IOM samplers in aluminium smelters. The need for more detailed and informative data sharing from authors is highlighted, providing more context to both the sampling strategy and methodology, as well as the data analysis. It is recommended that the requirements of EN13205 are taken into account when designing sampler comparison studies at the workplace and that these are also reported. It is also considered that there is a need for a clear standardized workplace sampler comparison protocol to be developed, which can be used by the research and occupational hygiene community to allow more robust and transparent assessment of aerosol samplers and better-quality evidence for use by industrial hygienists, epidemiologists, and occupational safety specialists alike.

Effects of Bedding Material on Equine Lower Airway Inflammation: A Crossover Study Comparing Peat and Wood Shavings

Bedding materials affect stable air hygiene, and thus the development and exacerbation of equine asthma. There is limited knowledge concerning the effects of different types of bedding material on equine lower airway inflammation. The objective of our study was to investigate the effects of bedding materials on respiratory signs, tracheal mucus score, and lower airway cytology in healthy adult horses. The study design was a prospective controlled study, and the subjects were healthy adult riding school horses (n = 32) from a single stable. Wood shavings were compared to peat, which was used as a reference bedding material. Lower airway endoscopy and sampling (tracheal wash and bronchoalveolar lavage fluid) for cytological examination were performed after each 35-day bedding period. No difference between bedding periods was observed in the respiratory rate or tracheal mucus score. Tracheal wash neutrophil percentage with the wood shavings was higher compared to the previous (P = 0.040) or following (P = 0.0045) peat period. Bronchoalveolar lavage fluid neutrophil percentage with the wood shavings was higher compared to the following peat period (P < 0.001). We conclude that, between the two bedding materials used in this study, peat caused less neutrophilic lower airway inflammation in horses. The information gained from this study may assist veterinarians and horse owners in selecting bedding materials, especially for horses suffering from equine asthma.

Estimating Respirable Dust Exposure from Inhalable Dust Exposure

In the sector of occupational safety and health only a limited amount of studies are concerned with the conversion of inhalable to respirable dust. This conversion is of high importance for retrospective evaluations of exposure levels or of occupational diseases. For this reason a possibility to convert inhalable into respirable dust is discussed in this study. To determine conversion functions from inhalable to respirable dust fractions, 15 120 parallel measurements in the exposure database MEGA (maintained at the Institute for Occupational Safety and Health of the German Social Accident Insurance) are investigated by regression analysis. For this purpose, the whole data set is split into the influencing factors working activity and material. Inhalable dust is the most important predictor variable and shows an adjusted coefficient of determination of 0.585 (R2 adjusted to sample size). Further improvement of the model is gained, when the data set is split into six working activities and three material groups (e.g. high temperature processing, adj. R2 = 0.668). The combination of these two variables leads to a group of data concerned with high temperature processing with metal, which gives rise to a better description than the whole data set (adj. R2 = 0.706). Although it is not possible to refine these groups further systematically, seven improved groups are formed by trial and error, with adj. R2 between 0.733 and 0.835: soldering, casting (metalworking), welding, high temperature cutting, blasting, chiseling/embossing, and wire drawing. The conversion functions for the seven groups are appropriate candidates for data reconstruction and retrospective exposure assessment. However, this is restricted to a careful analysis of the working conditions. All conversion functions are power functions with exponents between 0.454 and 0.946. Thus, the present data do not support the assumption that respirable and inhalable dust are linearly correlated in general.

A field evaluation of a single sampler for respirable and inhalable indium and dust measurements at an indium-tin oxide manufacturing facility

Indium-tin oxide production has increased greatly in the last 20 years subsequent to increased global demand for touch screens and photovoltaics. Previous studies used measurements of indium in blood as an indicator of indium exposure and observed associations with adverse respiratory outcomes. However, correlations between measurements of blood indium and airborne respirable indium are inconsistent, in part because of the long half-life of indium in blood, but also because respirable indium measurements do not incorporate inhalable indium that can contribute to the observed biological burden. Information is lacking on relationships between respirable and inhalable indium exposure, which have implications for biological indicators like blood indium. The dual IOM sampler includes the foam disc insert and can simultaneously collect respirable and inhalable aerosol. Here, the field performance of the dual IOM sampler was evaluated by comparing performance with the respirable cyclone and traditional IOM for respirable and inhalable indium and dust exposure, respectively. Side-by-side area air samples were collected throughout an indium-tin oxide manufacturing facility. Cascade impactors were used to determine particle size distribution. Several statistical methods were used to evaluate the agreement between the pairs of samplers including calculating the concordance correlation coefficient and its accuracy and precision components. One-way ANOVA was used to evaluate the effect of dust concentration on sampler differences. Respirable indium measurements showed better agreement (concordance correlation coefficient: 0.932) compared to respirable dust measurements (concordance correlation coefficient: 0.777) with significant differences observed in respirable dust measurements. The dual IOM measurements had high agreement with the traditional IOM for inhalable indium (concordance correlation coefficient: 0.997) but lower agreement for inhalable dust (concordance correlation coefficient: 0.886 and accuracy: 0.896) with a significantly large mean bias (-146.9 µg/m³). Dust concentration significantly affected sampler measurements of inhalable dust and inhalable indium. Results from this study suggest that the dual IOM is a useful single sampler for simultaneous measurements of occupational exposure to respirable and inhalable indium.

Exposure assessment and associated lung deposition calculations for vehicular exhaust in four metropolitan cities of Pakistan

Ambient aerosol concentrations along the roadside of metropolitan cities of Pakistan were measured using a Grimm 1.109 dust monitor. Considering the high ambient aerosol concentrations, regional lung deposition of aerosol particles in the human respiratory tract was calculated to assess extent of exposure. Lung deposition was computed in terms of mass concentration and the associated surface area for 12 male traffic wardens using the latest version of the stochastic lung deposition code Inhalation, Deposition, and Exhalation of Aerosols in the Lung. The results have revealed 4 to 10 times higher concentrations than recommended by WHO guidelines. The deposition results derived from the model disclose that extrathoracic deposition is in the range of 22 to 28 % with total lung deposition ranging from 40 to 44 % for the scanned particle window of 0.25-10 μm. Considering an average 8-h shift per day and an average breathing rate of 1.3 m(3) h(-1), it is approximated that in a worker, up to 1.6 mg of inhalable particle mass can deposit per day.

A novel particle sampling system for physico-chemical and toxicological characterization of emissions

Several studies have shown that combustion-derived fine particles cause adverse health effects. Previous toxicological studies on combustion-derived fine particles have rarely involved multiple endpoints and a detailed characterization of chemical composition. In this study, we developed a novel particle sampling system for toxicological and chemical characterization (PSTC), consisting of the Dekati Gravimetric Impactor (DGI) and a porous tube diluter. Physico-chemical and toxicological properties of the particles emitted from various combustion sources were evaluated in two measurement campaigns. First, the DGI was compared with the High-Volume Cascade Impactor (HVCI) and to the Dekati Low-Pressure Impactor (DLPI), using the same dilution system and the same sampling conditions. Only small differences were observed in the mass size distributions, total particulate matter (PM), and particulate matter with diameter smaller than 1 um (PM(1)) concentrations and geometric mass mean diameters (GMMD) between these three impactors. Second, the PSTC was compared with the HVCI sampling system, which has been optimal for collection of particulate samples for toxicological and chemical analyses. Differences were observed in the mass size distributions, total PM and PM(1) emissions, and GMMDs, probably due to the different sampling and dilution methods as well as different sampling substrates which affected the behavior of semi-volatile and volatile organic compounds. However, no significant differences were detected in the in vitro measurements of cytotoxicity between the samples collected with the PSTC and the HVCI systems. In measurements of genotoxicity, significant differences between the two sampling systems were seen only with the particles emitted from the sauna stove. In conclusion, due to compact size, PSTC is an applicable method for use in particle sampling as part of the toxicological and chemical characterization of particulate emissions from different combustion sources. It offers some advantages compared to the previously used high-volume sampling methods including compactness for field measurements, simple preparation of sample substrates and high extraction efficiency.

Design and computational fluid dynamics investigation of a personal, high flow inhalable sampler

The objective of this research was to develop an inlet to meet the inhalable sampling criterion at 10 l min(-1) flow using the standard, 37-mm cassette. We designed a porous head for this cassette and evaluated its performance using computational fluid dynamics (CFD) modeling. Particle aspiration efficiency was simulated in a wind tunnel environment at 0.4 m s(-1) freestream velocity for a facing-the-wind orientation, with sampler oriented at both 0 degrees (horizontal) and 30 degrees down angles. The porous high-flow sampler oriented 30 degrees downward showed reasonable agreement with published mannequin wind tunnel studies and humanoid CFD investigations for solid particle aspiration into the mouth, whereas the horizontal orientation resulted in oversampling. Liquid particles were under-aspirated in all cases, however, with 41-84% lower aspiration efficiencies relative to solid particles. A sampler with a single central 15-mm pore at 10 l min(-1) was also investigated and was found to match the porous sampler's aspiration efficiency for solid particles; the single-pore sampler is expected to be more suitable for liquid particle use.

The suitability of the IOM foam sampler for bioaerosol sampling in Occupational Environments

Concurrent samples were collected with Andersen and IOM foam samplers to determine whether if the IOM foam sampler can be applied to collect culturable microorganisms. Two different kinds of aerosols were studied: peat dust in a power plant and mist from coolant fluid aerosolized during grinding of blades and rollers in a paper mill. In the power plant, the concentrations of fungi were 2-3 times higher in the IOM samples than in the Andersen samples. However, more fungal genera were identified in the latter case. The methods yielded similar concentrations of bacteria and actinobacteria in the power plant. On the other hand, the performance of the IOM foam sampler was very poor in the paper mill, where stress-sensitive gram-negative bacteria dominated; low concentration of bacteria was detected in only one IOM sample even though the concentration of bacteria often exceeded even the upper detection limit in the Andersen impactor samples. It could be concluded that the IOM foam sampler performs quite well for collecting inhalable fungi and actinobacteria. However, the Andersen sampler provides better information on fungal genera and concentrations of gram-negative bacteria. Personal sampling with the IOM foam sampler provided an important benefit in the power plant, where the concentration ratio of personal to stationary samples was much higher for bacteria than for inhalable or respirable dust.

The real issue with wall deposits in closed filter cassettes--what's the sample?

The measurement of aerosol dusts has long been utilized to assess the exposure of workers to metals. Tools used to sample and measure aerosol dusts have gone through many transitions over the past century. In particular, there have been several different techniques used to sample for beryllium, not all of which might be expected to produce the same result. Today, beryllium samples are generally collected using filters housed in holders of several different designs, some of which are expected to produce a sample that mimics the human capacity for dust inhalation. The presence of dust on the interior walls of cassettes used to hold filters during metals sampling has been discussed in the literature for a number of metals, including beryllium, with widely varying data. It appears that even in the best designs, particulates can enter the sampling cassette and deposit on the interior walls rather than on the sampling medium. The causes are not well understood but are believed to include particle bounce, electrostatic forces, particle size, particle density, and airflow turbulence. Historically, the filter catch has been considered to be the sample, but the presence of wall deposits, and the potential that the filter catch is not representative of the exposure to the worker, puts that historical position into question. This leads to a fundamental question: What is the sample? This article reviews the background behind the issue, poses the above-mentioned question, and discusses options and a possible path forward for addressing that question.

Development of a sampler for total aerosol deposition in the human respiratory tract

Studies that seek to associate reduced human health with exposure to occupational and environmental aerosols are often hampered by limitations in the exposure assessment process. One limitation involves the measured exposure metric itself. Current methods for personal exposure assessment are designed to estimate the aspiration of aerosol into the human body. Since a large proportion of inhaled aerosol is subsequently exhaled, a portion of the aspirated aerosol will not contribute to the dose. This leads to variable exposure misclassification (for heterogenous exposures) and increased uncertainty in health effect associations. Alternatively, a metric for respiratory deposition would provide a more physiologically relevant estimate of risk. To address this challenge, we have developed a method to estimate the deposition of aerosol in the human respiratory tract using a sampler engineered from polyurethane foam. Using a semi-empirical model based on inertial, gravitational, and diffusional particle deposition, a foam was engineered to mimic aerosol total deposition in the human respiratory tract. The sampler is comprised of commercially available foam with fiber diameter = 49.5 microm (equivalent to industry standard 100 PPI foam) of 8 cm thickness operating at a face velocity of 1.3 m s(-1). Additionally, the foam sampler yields a relatively low-pressure drop, independent of aerosol loading, providing uniform particle collection efficiency over time.

Application of PUF foam inserts for respirable dust measurements in the brick-manufacturing industry

Institute of Occupational Medicine dual-fraction samplers equipped with porous polyurethane foam inserts have been introduced as a cheaper alternative to cyclone pre-selectors for measuring respirable dust. Initial data from a variety of industries suggested that the dual-fraction sampler yielded similar results as personal cyclones and that the respirable selection of the foam was not adversely affected by particle loading. We conducted a similar study, but specifically in the brick industry to assess the validity of this dual-fraction sampler as an alternative to personal cyclones in this industry. A total of 72 side-by-side samples using Higgins-Dewell cyclones and dual-fraction samplers were taken in seven UK factories manufacturing a variety of bricks. A priori measurements were assigned to any of the three groups based on the dominant source of the particulates in the exposure matrix (clay, sand or mixed) at the location in the factories where the measurements were taken. After log transformation, Higgins-Dewell cyclone-measured concentrations were on average 1.9 times higher than the concentrations measured by the dual-fraction samplers, with a Pearson correlation of 0.78 (95% confidence interval 0.66-0.85). Stratified analysis by main source of exposure suggested that the correlation was best for silica dust-based exposures r(p) = 0.88 (0.63-0.96), but decreased with the relative importance of clay particulates in the exposure matrix to r(p) = 0.82 (0.59-0.93) in the 'mixed-source' group and r(p) = 0.74 (0.55-0.85) in the 'clay particulates' group. Similarly, performance of the dual-fraction sampler relative to the cyclone sampler was negatively associated with increased relative importance of clay particulates in the exposure matrix and ranged from similar measured concentration beta = 0.96 (0.54-1.39) for silica to 50% under sampling beta = 0.50 (0.33-0.67) for clay particulates. These results suggested that the overall performance of the dual-fraction sampler in the brick industry depends on the relative importance of clay particulates in the exposure matrix. As such, results from occupational hygiene compliance surveys close to the occupational exposure limit can lead to erroneous decisions on compliance.