Assessment of measured respirable dust sampler penetration and the sampling convention for work environment measurement]

The relationship between dust size and penetration for a static horizontal elutriator (Sibata C-30) was measured in calm air. The elutriator as a low-volume air sampler is widely used as a dust size classifier in work environment measurements. The actual penetrations were compared with the theoretical models of the sampler and with sampling convention for respirable dust in work environment measurement. The sampling convention was recently introduced into the Japanese standard for work environment measurement and is based on the ISO 7708 respirable dust convention. The bias of sampled masses from the respirable dust was calculated for two flow rates of the sampler, i.e., 50% cut sizes of 4 microm and 5 microm, from measured penetration curves. The bias of the sampler was overestimated in the 5 microm, 50% cut condition and underestimated in the 4 microm, 50% cut condition for most workplace sampling situations.     

Comparison of measured respirable dust sampler penetration curves with sampling conventions.

Measured sampler penetration curves are presented for British personal cyclone samplers and the MRE 113A static horizontal elutriator in calm air. These curves are compared with previous results for these instruments, and with theoretical models of sampler behaviour. The sampling efficiency of the elutriator when facing a moderate wind is discussed. The penetration curves are assessed by comparison with standard sampling conventions for respirable dust.     

Cotton dust sampling efficiency of the vertical elutriator.

A theoretical model of the vertical elutriator air sampler based upon the phenomenon of flow separation at the inlet was developed at SRRC. The model's equations were simulated by a computer program (VELUT). The model was calibrated by comparison of available experimental results to isokinetic sampling efficiencies calculated by the model. The calibrated model was used to predict integral efficiencies for a systematic assortment of size distributions of cotton dust. Rather than cutting off cleanly at 15 micrometers, the computer model exhibited a 50% differential efficiency at approximately 20 micrometers. Furthermore, the model predicted substantial non-zero collection efficiencies in the aerodynamic size range of individual cotton fibers. Program VELUT represents an objective method whereby the isokinetic sampling efficiency of the vertical elutriator can be explicitly calculated for any known or postulated ambient dust distribution presented to the sampler at its inlet plane.     

Field performance of the RespiCon for size-selective sampling of industrial wood processing dust

The RespiCon sampler is a multistage virtual impactor that simultaneously collects the ISO/CEN/ACGIH size fractions of inhalable, thoracic, and respirable particulate matter. The field performance of the device for measurement of industrial wood processing dust was evaluated against reference size-selective samplers: the IOM sampler (inhalable dust), the GK 2.69 cyclone (thoracic dust), and the SKC aluminum cyclone (respirable dust). Seventy-one sets of area samples were collected from 10 wood processing plants, with the samplers mounted either in the free-field or on a two-dimensional bluff body. The geometric mean (range) dust levels across all plants measured by the reference samplers were: inhalable, 1.35 mg/ m3 (0.11-11.06); thoracic, 0.31 mg/m3 (0.05-1.38); and respirable, 0.10 mg/m3 (0.02-0.54). In comparing the RespiCon with the reference samplers, there was no significant difference between sampling in the free-field versus bluff-body modes. For inhalable dust, there was no significant difference between the RespiCon and the IOM sampler after applying a correction factor of 1.5 to the extrathoracic data obtained from the RespiCon. Without the correction factor, the RespiCon undersample inhalable dust by an average of 23%. For thoracic dust, the RespiCon was shown to oversample the extrathoracic dust fraction resulting in an overall error of 48%. A simple correction based on the inhalable and thoracic dust levels reported by the RespiCon is proposed. For respirable dust, there was a significant difference between the RespiCon and the SKC cyclone, but the data were equivocal due to imprecision in measurement of the low respirable dust concentrations encountered and the likelihood of bias in the reference sampler. Overall, the RespiCon sampler appears to be a suitable size-selective sampling device for industrial wood processing dust, although adjustments should be made to the inhalable and thoracic dust results.     

Determination of large aerosol particle size by elutriation

Inhalable dust fraction determination requires aerodynamic size information for large aerosol particles. Operation of cascade impactors at flows that collect these particles leads to jet Reynolds numbers outside the range of established impactor performance. Horizontal elutriators, designed to match earlier respirable dust curves at a single flow rate, may be used to provide aerodynamic size information for particles larger than 50 microm. Operation of these elutriators at higher than design flow rates and angles other than horizontal provides for particle penetration over the size range of the inhalable dust curve. Equations are provided that relate penetration, flow rate, and angle to aerodynamic diameter to allow for bracketing the desired size and distribution. The use of impactor data reduction methods to determine size distributions with the MRE horizontal elutriator is examined with a spreadsheet model. Comparison of elutriator size determination with an impactor in the 10 to 15 microm range, where both methods could be used, resulted in reasonable agreement. This method provides for determination of aerodynamic characteristics of large aerosols in field sampling conditions.     

Development and testing of a new sampler for welding fume

The development of a new sampler having an inhalable entry and a porous foam plug, which can partition the respirable and non-respirable fractions of the sampled air, is described. The rationale for this partitioning is that welding fume is primarily respirable, where dust generated by other welding related processes is generally non-respirable. The sampler is designed to operate inside the welder's face shield, and its attachment configuration fulfils the requirements stated in the proposed European Standard for welding fume sampling (CEN, 1996). The aspiration efficiency agrees well with that of a breathing mannequin wearing a face shield, although it undersamples compared to the inhalable convention (CEN, 1993) in wind tunnel tests. The penetration of welding fume through the porous foam is consistently around 72%, comparable to that through a conventional personal cyclone. Field trials have indicated that the sampler does not obstruct nodal work activity or vision. Finally, the new sampler has been included in the proposed European Standard.     

Occupational exposure to cotton dust in cottonseed oil mills

Air samples were collected at breathing height in the hulling-separation department of a modern cottonseed oil mill in Uzbekistan. The average elutriated mass concentration measured by standard cotton dust samplers was 4.6 mg/m3, much lower than the average total dust concentration measured by stationary personal samplers, 12.49 mg/m3, and by personal samplers attached to workers, 14.53 mg/m3. Differences in readings among the vertical elutriators, stationary personal samplers, and roving personal samplers are attributed to the distinct sampling nature and dynamics of these samplers. The data suggest that most of the dust consisted of particles larger than 15 microm, the particle size cutoff of the vertical elutriator. Differences in readings among stationary and roving personal samplers are statistically significant, presumably representing biased sampling by the roving personal samplers of regions characterized by high dust concentration (due to machines malfunctioning), the nonstatic nature of the sampling, and the interaction between the sampler and the worker (the personal cloud). Cotton dust concentrations in the hulling-separation room were nonuniform, peaking in front of and between the huller-separator pairs. The high total mass readings show that workers were exposed to very high levels of nonthoracic airborne dust, which upon inhalation tends to deposit in the extrathoracic airways. The high elutriated mass concentrations suggest that workers were exposed to respirable cotton dust at levels higher than 1 mg/m3 mean concentration, the current Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) for cotton dust. Regressions between dust concentrations measured by stationary vertical elutriators and by personal samplers attached to workers serve for estimating the potential occupational exposure to cotton dust of workers in the hulling-separation room.     

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

The performance of four sampling devices for inhalable dust and three devices for respirable dust was tested with different kinds of dusts in the laboratory and in the field. The IOM sampler was chosen as the reference method for inhalable dust, and the IOM sampler provided with the porous plastic foam media was used as the reference method for respirable dust. The other tested instruments were the Button sampler, the optical Grimm aerosol monitor, and the Dekati two-stage cascade impactor with cutoff sizes of 10 and 4 mu m. The study confirmed the applicability of the IOM and Button samplers. The new foam product followed the respirable criteria well. However, the foam sampler was unstable for measuring inhalable dust, probably due to its moisture absorption. In addition, high dust loads should be avoided with the foam sampler due to increase in filtering efficiency. The concentrations of inhalable dust measured with the Button sampler, the Grimm monitor, and the impactor sampler were usually close to those measured with the reference sampler. On the other hand, impactor sampling yielded higher respirable dust concentrations than the reference method in the field, which may have been caused by particle bounce; high dust loads should be avoided while using the impactor. The results also showed that the Grimm monitor enables real-time dust concentration determinations that are accurate enough for routine monitoring of occupational exposure and for testing efficiency of control measures in workplaces.     

Wood dust sampling: field evaluation of personal samplers when large particles are present

Recent recommendations for wood dust sampling include sampling according to the inhalable convention of International Organization for Standardization (ISO) 7708 (1995) Air quality--particle size fraction definitions for health-related sampling. However, a specific sampling device is not mandated, and while several samplers have laboratory performance approaching theoretical for an 'inhalable' sampler, the best choice of sampler for wood dust is not clear. A side-by-side field study was considered the most practical test of samplers as laboratory performance tests consider overall performance based on a wider range of particle sizes than are commonly encountered in the wood products industry. Seven companies in the wood products industry of the Southeast USA (MS, KY, AL, and WV) participated in this study. The products included hardwood flooring, engineered hardwood flooring, door skins, shutter blinds, kitchen cabinets, plywood, and veneer. The samplers selected were 37-mm closed-face cassette with ACCU-CAP?, Button, CIP10-I, GSP, and Institute of Occupational Medicine. Approximately 30 of each possible pairwise combination of samplers were collected as personal sample sets. Paired samplers of the same type were used to calculate environmental variance that was then used to determine the number of pairs of samples necessary to detect any difference at a specified level of confidence. Total valid sample number was 888 (444 valid pairs). The mass concentration of wood dust ranged from 0.02 to 195 mg m(-3). Geometric mean (geometric standard deviation) and arithmetic mean (standard deviation) of wood dust were 0.98 mg m(-3) (3.06) and 2.12 mg m(-3) (7.74), respectively. One percent of the samples exceeded 15 mg m(-3), 6% exceeded 5 mg m(-3), and 48% exceeded 1 mg m(-3). The number of collected pairs is generally appropriate to detect a 35% difference when outliers (negative mass loadings) are removed. Statistical evaluation of the nonsimilar sampler pair results produced a finding of no significant difference between any pairing of sampler type. A practical consideration for sampling in the USA is that the ACCU-CAP? is similar to the sampler currently used by the Occupational Safety and Health Administration for purposes of demonstrating compliance with its permissible exposure limit for wood dust, which is the same as for Particles Not Otherwise Regulated, also known as inert dust or nuisance dust (Method PV2121).     

Study of fifteen respirable aerosol samplers used in occupational hygiene

European and international standards lay down criteria for the size-selective aerosol sampling in occupational hygiene. Aerosol samplers are supposed to match these target sampling criteria. This study focused on 15 aerosol samplers used to sample the conventional respirable fraction. An aerodynamic particle sizer (APS) method was used to measure the sampling efficiency of the samplers in a low-velocity wind tunnel. Polydisperse coal dust was generated as the test aerosol. The data were fitted by an appropriate mathematical model. For some instruments the results show serious deviations from the conventional target curve, whereas other devices meet the convention quite well. The flow rate of certain cyclone-separator-based instruments was optimized to adjust their sampling efficiency. The mass concentration bias and accuracy of the samplers were calculated for a number of ranges of particle size distributions of aerosols commonly found in industrial workplaces. Finally, the performance of each sampler was evaluated using bias and accuracy maps. Most of these samplers are suitable for sampling the CEN-ISO-ACGIH respirable fraction of aerosols, but several require modification of the flow rate. For real industrial situations, the rough knowledge of the aerosol size distribution can guide the choice of an appropriate sampling technique.     

A Simple Device for Gravimetric Sampling

In view of the increased importance attached to the gravimetric sampling of airborne dust in mines and other working places, it was recently decided to start regular gravimetric sampling in the experimental animal dusting rooms in this Unit. As no suitable sampling instrument was available, a Hexhlet dust sampler was modified by fitting it with a probe in place of the elutriator. This instrument has also been used to collect samples of airborne particulate matter from within chimney stacks and exhaust ducts and also unelutriated samples of dust from the air in working places.     

Assessment of personal direct-reading dust monitors for the measurement of airborne inhalable dust

The performances of five portable direct-reading dust monitors were investigated in a wind tunnel for a range of industrial dusts and three sizes of aluminium oxide test dust to mainly determine their suitability for measuring the inhalable fraction of airborne dust in workplaces. The instruments tested were Split 2 (SKC Ltd), Sidepak (TSI Inc.), Dataram (Thermo Electron Ltd), PDS-2 (Sibata Scientific Technology Ltd) and the Respicon TM (Hund Ltd). The instruments' responses were compared with reference dust samplers. These were the IOM sampler for the inhalable fraction and the Casella cyclone sampler for the respirable fraction. All instruments are predominantly responsive to and are designed to measure particles in the respirable size range, although two of the instruments, the Split 2 and Respicon TM, are claimed to be capable of measuring inhalable-sized particles. For the purpose of the tests, major modifications to an existing wind tunnel dust injection system were made to facilitate the generation of uniform concentrations of large inhalable-sized dust particles at low air velocities. Each monitor greatly underestimated the measurement of inhalable concentration for all the dusts tested, although the linearity was good over a wide range of concentrations for any particular size distribution of dust. However, their calibration factors, defined as the ratio of reference inhalable concentration to monitor concentration, were especially sensitive to changes in particle size as the response of the instruments decreased rapidly with increasing particle size. The monitors generally overestimated the measurement of respirable dust concentration by up to a factor of about 2, apart from the PDS-2, which underestimated it by a factor of up to 3. There was, however, a great deal more scatter in the reference respirable concentration measurements owing to the collection of small dust samples. Therefore, monitor linearity and effects of monitor response to changes in particle size could not be accurately investigated for the respirable fraction. The sampling head of the Split 2 monitor incorporates an IOM inlet and filter to gravimetrically collect the inhalable fraction of airborne dust. This can give a concurrent reference measure of inhalable airborne dust concentration. However, poor sealing within the sampling head resulted in some of the sampled dust not reaching the backup filter. This resulted in the Split 2 underestimating the reference inhalable dust concentration, which meant that it could not be accurately used as a calibration standard. Communications with the manufacturers have since revealed that the sampling head has recently been redesigned in order to improve the seal and eliminate leakage. The Respicon sampler gravimetrically underestimated the inhalable dust concentration, and did so increasingly as the particle size increased.     

Applications of low-cost, dual-fraction dust samplers

Porous polyurethane foams provide a low-cost method for separating dust into health-related fractions in accordance with recognized sampling conventions. A number of dust sampling instruments that make use of foam selectors have been described in recent literature, but practical experiences of using these instruments in real workplaces have not been widely reported. An IOM inhalable dust sampler incorporating a respirable-fraction selector foam was evaluated in a range of industries, for general occupational dust monitoring. The key issues addressed were those that determine the practicability of the instrument, such as limitations on particulate loading, losses or movements of particles during transportation of samples, and equivalence with conventional respirable dust sampling methods. The new sampler was found to be satisfactory in all these respects. The minor problems experienced have been addressed during the design of the production version of the foam cassette, which is available as an accessory for the existing IOM inhalable dust sampler. The key advantage of the new dust sampler is that it measures both inhalable and respirable dust concentrations in a single sample (hence the name: dual-fraction dust sampler). Therefore, it saves both time and money in industries where both inhalable and respirable dust are routinely monitored.     

Respirable size-selective sampler for end-of-shift quartz measurement: Development and performance

Aims of this study were to develop a respirable size-selective sampler for direct-on-filter (DoF) quartz measurement at the end-of-shift (EoS) using a portable Fourier transform infrared (FTIR) spectrometer and to determine its size-selective sampling performance. A new miniaturized sampler has been designed to have an effective particle deposition diameter close to the portable FTIR beam diameter (6 mm). The new sampler (named the EoS cyclone) was constructed using a 3D printer. The sampling efficiency of the EoS cyclone was determined using polydisperse glass sphere particles and a time-of-flight direct reading instrument. Respirable dust mass concentration and quartz absorbance levels of samples collected with the EoS cyclone were compared to those collected with the 10-mm nylon cyclone. The EoS cyclone operated at a flow rate of 1.2 l min^?1 showed minimum bias compared to the international standard respirable convention. The use of the EoS cyclone induced respirable dust mass concentration results similar but significantly larger (5%) than those obtained from samples collected with 10-mm nylon cyclones. The sensitivity of the DoF-FTIR analysis in estimating quartz was found increased more than 10 times when the samples were collected with the EoS cyclone. The average particle deposition diameter was 8.8 mm in 60 samples. The newly developed user friendly EoS cyclone may provide a better sampling strategy in quartz exposure assessment with faster feedback.     

Calibration of high flow rate thoracic-size selective samplers

High flow rate respirable size selective samplers, GK4.126 and FSP10 cyclones, were calibrated for thoracic-size selective sampling in two different laboratories. The National Institute for Occupational Safety and Health (NIOSH) utilized monodisperse ammonium fluorescein particles and scanning electron microscopy to determine the aerodynamic particle size of the monodisperse aerosol. Fluorescein intensity was measured to determine sampling efficiencies of the cyclones. The Health Safety and Laboratory (HSL) utilized a real time particle sizing instrument (Aerodynamic Particle Sizer) and polydisperse glass sphere particles and particle size distributions between the cyclone and reference sampler were compared. Sampling efficiency of the cyclones were compared to the thoracic convention defined by the American Conference of Governmental Industrial Hygienists (ACGIH)/Comité Européen de Normalisation (CEN)/International Standards Organization (ISO). The GK4.126 cyclone showed minimum bias compared to the thoracic convention at flow rates of 3.5 l min^?1 (NIOSH) and 2.7–3.3 l min^?1 (HSL) and the difference may be from the use of different test systems. In order to collect the most dust and reduce the limit of detection, HSL suggested using the upper end in range (3.3 l min^?1). A flow rate of 3.4 l min^?1 would be a reasonable compromise, pending confirmation in other laboratories. The FSP10 cyclone showed minimum bias at the flow rate of 4.0 l min^?1 in the NIOSH laboratory test. The high flow rate thoracic-size selective samplers might be used for higher sample mass collection in order to meet analytical limits of quantification.     

Cotton dust sampling: I. Short termed sampling.

A short term sampler for cotton dust is introduced which, when used in conjunction with a correctly designed vertical elutriator, gives equivalent results to the Lumsden-Lynch vertical elutriator. The short termed sampler not only offers results which can be applied to the ACGIH TLV but offers an effective means of environmental surveillance in a byssinosis prevention program with the additional advantages of immediate read-out short termed sampling and truer employee exposure.     

The effects of neutralized particles on the sampling efficiency of polyurethane foam used to estimate the extrathoracic deposition fraction

In addition to chemical composition, the site of deposition of inhaled particles is important for determining the potential health effects from an exposure. As a result, the International Organization for Standardization adopted a particle deposition sampling convention. This includes extrathoracic particle deposition sampling conventions for the anterior nasal passages (ET1) and the posterior nasal and oral passages (ET2). This study assessed how well a polyurethane foam insert placed in an Institute of Occupational Medicine (IOM) sampler can match an extrathoracic deposition sampling convention, while accounting for possible static buildup in the test particles. In this way, the study aimed to assess whether neutralized particles affected the performance of this sampler for estimating extrathoracic particle deposition. A total of three different particle sizes (4.9, 9.5, and 12.8 µm) were used. For each trial, one particle size was introduced into a low-speed wind tunnel with a wind speed set a 0.2 m/s (～40 ft/min). This wind speed was chosen to closely match the conditions of most indoor working environments. Each particle size was tested twice either neutralized, using a high voltage neutralizer, or left in its normal (non neutralized) state as standard particles. IOM samplers were fitted with a polyurethane foam insert and placed on a rotating mannequin inside the wind tunnel. Foam sampling efficiencies were calculated for all trials to compare against the normalized ET1 sampling deposition convention. The foam sampling efficiencies matched well to the ET1 deposition convention for the larger particle sizes, but had a general trend of underestimating for all three particle sizes. The results of a Wilcoxon Rank Sum Test also showed that only at 4.9 µm was there a statistically significant difference (p-value = 0.03) between the foam sampling efficiency using the standard particles and the neutralized particles. This is interpreted to mean that static buildup may be occurring and neutralizing the particles that are 4.9 µm diameter in size did affect the performance of the foam sampler when estimating extrathoracic particle deposition.     

Field testing of a personal size-selective bioaerosol sampler.

Existing samplers for the collection of bioaerosols have been designed with the aim of maintaining biological stability of the collected material, and in general do not select particles in accordance with international conventions for aerosol sampling. Many have uncharacterised sampling efficiencies and few are designed as personal samplers. If standard personal dust samplers are used for bioaerosols the viability of collected microorganisms may be compromised by dehydration. The objective of this study was to evaluate a novel personal bioaerosol sampler designed to collect the inhalable dust fraction and further subdivide the sample into thoracic and respirable fractions. The new sampler was tested to see whether it enhanced the survival of the collected microorganisms, and was assessed for ease of use in the field and in subsequent laboratory analyses. A number of occupation-related field sites were selected where large concentrations of bioaerosols were to be expected. The prototype sampler was found to be simple to use. Analysis could be carried out with similar efficiency either with all three fractions together for a total count, or separately for size selective data. The sampler performed at least as well as the standard IOM filter method but with the added advantage of size fractionation. The field trials showed that for sampling periods lasting several hours, microorganism survival within the sampler was adequate for culture and identification of the organisms present. This new sampler is now commercially available. In addition to bioaerosol sampling, the principle of size selective sampling using porous foams can be applied to other occupational hygiene problems, and also to indoor air monitoring of PM10 and PM2.5 concentrations.     

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.     

A SURVEY OF DUST CONCENTRATIONS IN FLAX MILLS IN NORTHERN IRELAND

The concentrations in the air of total and of respirable (less than 7 microns equivalent diameter) dust were measured in 142 workrooms of 17 Northern Ireland flax spinning mills using a hexhlet air sampler.

Neither the distribution of total nor of respirable dust concentrations (mg./100 m.³ air) measured in each of four large workrooms conformed to the normal (or Gaussian) distribution, but it is shown that the logarithms (to the base 10) of these concentrations are normally distributed. In order to make valid statistical comparisons between the dustiness of the different types of room, mean log. concentrations are therefore used.

The mean log. concentrations of total and of respirable dust, and the 95% confidence limits derived from these, were calculated for each room surveyed. For total and respirable dust the ranges of mean log. concentrations followed in brackets by the respective antilogs. (mg./100 m.³ air) were as follows: [Table: see text] Thus, dust concentrations varied widely within each category of room, although in general the pre-preparing rooms had the highest levels followed by other preparing rooms, other finishing rooms, and wet finishing rooms, in that order.