Size selective dustiness and exposure; simulated workplace comparisons

A simulated workplace study was conducted to investigate the relation between inhalation exposure and dustiness determined with a rotating drum dustiness tester. Three powders were used in the study, i.e. magnesium stearate, representing a very dusty powder, and aluminium oxide and calcium carbonate, representing low and very low dusty powders, respectively. Two scenarios of handling small volume of powders were included; sweeping/cleaning and scooping/weighing/adding. Size-selective dust exposure was assessed using MultiDust (dual-fraction) IOM and RespiCon sampling heads. For the present operation scenarios, dustiness showed itself to be the major determinant of exposure and explained approximately 70% of the exposure variances. The ratios of respirable and inhalable fractions as determined by dustiness tests were comparable with the ratios observed for exposure. The results emphasize the relevance of dustiness as a parameter to characterize substances according to potential for exposure.     

A novel device for measuring respirable dustiness using low-mass powder samples

Respirable dustiness represents the tendency of a powder to generate respirable airborne dust during handling and therefore indicates the propensity for a powder to become an inhalation hazard. The dustiness of 14 powders, including 10 different nanopowders, was evaluated with the use of a novel low-mass dustiness tester designed to minimize the use of the test powder. The aerosol created from 15-mg powder samples falling down a tube were measured with an aerodynamic particle sizer (APS). Particle counts integrated throughout the pulse of aerosol created by the falling powder were used to calculate a respirable dustiness mass fraction (D, mg/kg). An amorphous silicon dioxide nanopowder produced a respirable D of 121.4 mg/kg, which was significantly higher than all other powders (p < 0.001). Many nanopowders produced D values that were not significantly different from large-particle powders, such as Arizona Road Dust and bentonite clay. In general, fibrous nanopowders and powders with primary particles >100 nm are not as dusty as those containing granular, nano-sized primary particles. The method used here, incorporating an APS, represents a deviation from a standard method but resulted in dustiness values comparable to other standard methods.     

The application of dustiness tests to the prediction of worker dust exposure

Laboratory bench tests, known as dustiness tests, have been used to evaluate and compare the potential of various powders to cause occupational dust exposure. Dustiness tests are used to develop products with reduced dust emissions. The correlation between dustiness test results and dust exposures was evaluated at two bag dumping and bag filling operations. At one bag dumping and one bag filling operation, there was evidence of a relationship between dustiness test results and dust exposures. In one case, regression analysis showed that dust exposures could be predicted to within nearly one order of magnitude. The variability in this prediction was caused by the inherent variability in the occupational dust exposures. In the other case, there was evidence of a correlation after the data had been adjusted for the effect of varying drop height. At the remaining two operations, no correlation between dust exposures and dustiness test results were observed. These results indicate that the relevance of dustiness tests to occupational dust exposure needs to be evaluated at each site. Because a better option does not exist, manufacturers should continue to use empirical dustiness tests to develop better products in the laboratory. The conclusions reached in the laboratory need to be validated by dust exposure measurements in the field, however.     

Exposure Assessment of Four Pharmaceutical Powders Based on Dustiness and Evaluation of Damaged HEPA Filters

In this study, we show the different dustiness characteristics of four molecular pharmaceutical powder candidates and evaluate the performance of HEPA filters damaged with three different pinhole sizes and exposed to dust using real industrial powders in a miniaturized EN15051 rotating drum dustiness tester. We then demonstrate the potential use of such data using first-order exposure modeling to assess the potential worker exposure and transmission of active powder ingredients into ventilation systems. The four powders had highly variable inhalable dustiness indices (1,036 – 14,501 mg/kg). Dust particle size-distributions were characterized by three peaks; the first occurred around 60–80 nm, the second around 250 nm, and the third at 2–3 μm. The second and third peaks are often observed in dustiness test studies, but peaks in the 60–80 nm range have not been previously reported. Exposure modeling in a 5 times 20 kg powder pouring scenario, suggests that excessive dust concentrations may be reached during use of powders with the highest dustiness levels. By number, filter-damage by three pinhole sizes resulted in damage-dependent penetration of 70–80 nm-size particles, but by volume and mass the penetration is still dominated by particles larger than 100 nm. Whereas the exposure potential was evident, the potential dust concentrations in air ducts following the pouring scenario above were at pg/m³ levels. Hence, filter penetration at these damage levels was assumed to be only critical, if the active ingredients were associated with high hazard or unique product purity is required.

[Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: An example of a typical particle number time-series of a complete dustiness test. It provides information on the HEPA-filter used including a scanning electron microscopy image of it. It also provides APS-measurements of particles penetrating the damaged HEPA-filter.]     

Factors affecting the Heubach and MRI dustiness tests

The effect of test parameters upon material dustiness measured by the Heubach dust measurement appliance and the MRI dustiness tester was studied. The users of these tests can alter test parameters such as flow rate, sampling time, mass of material tested, bulk density, and vibrator setting. The effect of these parameters upon the aerosol produced in the dustiness tester was experimentally studied. All of the parameters affected in a complicated manner, the amount of dust and the size distribution of the dust generated during these tests. Therefore, dustiness test results should not be adjusted for variations in test parameters. The users of dustiness tests need to carefully control dustiness test parameters in order to have reproducible dustiness tests.     

Occupational exposure to dust in quartz manufacturing industry.

Owing to the abundance of a sedimentary rock, 65 small-scale quartz manufacturing enterprises, employing 650 workers, have been established in the region studied. Quartz powder manufacturing involves various processes and operations, such as manual handling of quartz stones, crushing, grinding, sieving, screening, mixing, storing and bagging. Results demonstrate that each of these operations generates high concentrations of airborne 'total' dust and respirable dust, which contain a very high percentage (> 75%) free silica. The estimated average exposure to airborne 'total' dust was 22.5 mg m-3 (Permissible Limit of Exposure 1.08 mg m-3), and respirable dust 2.93 mg m-3 (PLE 0.36 mg m-3). This shows that 'total' dust exposure was 7.7 times higher than respirable dust. Since the present work systems and practices may pose a serious health risk to the workers, public and the environment, suitable preventive and control measures have been suggested for improvement in the workplace.     

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.     

Redesign of a static horizontal elutriator to perform according to the ISO 7708 respirable convention

A static horizontal elutriator (multi-channel elutriator C-30, Sibata Scientific Instruments Ltd, Tokyo) has been widely used as a dust size classifier for a low-volume air sampler in Japan. The sampler uses the historical criterion defined by the British Medical Research Council (BMRC). However, a new sampling convention based on the ISO 7708 respirable dust convention was recently introduced into the Japanese standard for work environment measurement. It is necessary to modify the multi-channel static horizontal elutriator to satisfy the ISO 7708 respirable convention. We propose a modification of the horizontal elutriator, involving the shortening of 11 of the 36 plates to meet the ISO 7708 respirable convention. The relationship between aerosol particle size and penetration for the elutriator was measured in calm air. The measured penetrations were compared with the calculated performance of the sampler and with the sampling convention for the ISO respirable dust. The calculated bias of sampled masses with respect to the ISO respirable mass was almost zero for the workplace aerosols.     

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.     

Performance of the RespiCon personal aerosol sampler in forest products industry workplaces

The RespiCon is a multistage virtual impactor that can be used as either a personal or an area sampler. Particles collected on the first stage of the RespiCon represent the respirable fraction of airborne particulate matter. Particles collected on the first and second stages represent the thoracic fraction, and particles collected on the first, second, and third stages represent the inhalable fraction. The RespiCon is available in two versions, one with photometric aerosol detection and a gravimetric version. In this study, the performance of the gravimetric version was examined in various forest products industry facilities. The precision of the RespiCon was assessed and its performance was compared with that of both a respirable cyclone and an inhalable dust sampler. In addition, some RespiCon samples were examined using scanning electron microscopy to determine physical particle size distribution. Under the conditions of this testing, the RespiCon appeared to be reasonably precise. For most sampling locations there was a close correspondence between measurements made with the RespiCon and the CIS personal inhalable sampler or the BGI-4 respirable cyclone. The results of microscopic examination of filters from the RespiCon were consistent with expected performance characteristics. The RespiCon is a useful sampling device for those situations in which it is important to simultaneously collect either personal or area samples of the respirable, thoracic, and inhalable fractions of airborne particulate matter.     

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.     

Diacetyl emissions and airborne dust from butter flavorings used in microwave popcorn production

In microwave popcorn workers, exposure to butter flavorings has been associated with fixed obstructive lung disease resembling bronchiolitis obliterans. Inhalation toxicology studies have shown severe respiratory effects in rats exposed to vapors from a paste butter flavoring, and to diacetyl, a diketone found in most butter flavorings. To gain a better understanding of worker exposures, we assessed diacetyl emissions and airborne dust levels from butter flavorings used by several microwave popcorn manufacturing companies. We heated bulk samples of 40 different butter flavorings (liquids, pastes, and powders) to approximately 50 degrees C and used gas chromatography, with a mass selective detector, to measure the relative abundance of volatile organic compounds emitted. Air sampling was conducted for diacetyl and for total and respirable dust during the mixing of powder, liquid, or paste flavorings with heated soybean oil at a microwave popcorn plant. To further examine the potential for respiratory exposures to powders, we measured dust generated during different simulated methods of manual handling of several powder butter flavorings. Powder flavorings were found to give off much lower diacetyl emissions than pastes or liquids. The mean diacetyl emissions from liquids and pastes were 64 and 26 times larger, respectively, than the mean of diacetyl emissions from powders. The median diacetyl emissions from liquids and pastes were 364 and 72 times larger, respectively, than the median of diacetyl emissions from powders. Fourteen of 16 powders had diacetyl emissions that were lower than the diacetyl emissions from any liquid flavoring and from most paste flavorings. However, simulated handling of powder flavorings showed that a substantial amount of the airborne dust generated was of respirable size and could thus pose its own respiratory hazard. Companies that use butter flavorings should consider substituting flavorings with lower diacetyl emissions and the use of ventilation and enclosure engineering controls to minimize exposures. Until controls are fully implemented, companies should institute mandatory respiratory protection for all exposed workers.     

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.

     

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.     

Measuring dust on skin with a small vacuuming sampler--a comparison with other sampling techniques

Airborne skin exposure to allergens and irritants may cause dermatitis. There are few methods for assessing skin exposure to airborne particles. We have modified and tested a vacuuming sampler for removing particles from the skin. The sampler was compared with two other skin and surface exposure sampling techniques. These were based on surrogate skin (a patch sampler-adhesive tape on an optical cover glass) and a tape stripping removal procedure. All three samplers measure the mass of dust on skin. Dust containing starch was deposited onto the skin in a whole-body exposure chamber. Samples were taken from forearms and shoulders and analysed using optical microscopy. With the different sampling techniques small differences in the results were obtained. Agreement between the vacuuming sampler and the tape stripping technique was good. The comparison between patch and tape stripping procedure indicated a slight overestimation for the patch. The three techniques are applicable for assessing skin exposure to particles and for dose-effect studies. The vacuuming method will be further developed and applied in workplace studies. The technique allows for dust sampling from large areas of skin.     

Silica exposure assessment in a mortality study of Vermont granite workers

A study of past silica and respirable dust exposures in the Vermont granite industry was conducted to develop a job exposure matrix (JEM) that used 5204 industrial hygiene measurements made from 1924-2004. The construction of the JEM involved data entry from several original sources into an Excel database that was reviewed later to ensure accuracy. Exposure measurements by job or location were grouped in two broad categories of quarry or shed and then into 22 job classes. Missing exposure data by time period were computed, taking into account improvements in dust control and periods of significant reduction in dustiness. Percent free silica (α-quartz) in respirable dust was estimated to be 11.0% based on previous published studies in Vermont and on data in the current database. About 60% of all measurement data (primarily from years prior to 1972) were obtained using the impinger and expressed in millions of particles per cubic foot (mppcf), which were converted to equivalent respirable free silica concentrations using the conversion of 10 mppcf = 0.1 mg/m(3) of respirable silica. For impinger data, respirable dust was calculated by multiplying respirable silica by a factor of 9.091 to reflect that the respirable silica was 11.0% respirable dust. This JEM has been used in a recent epidemiologic study to assess mortality in Vermont granite workers and to examine the relationships among mortality from silicosis, lung cancer, and other nonmalignant respiratory diseases.     

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.     

Performance testing of the OSIRIS dust monitoring system

OSIRIS is a monitoring system for non-fibrous dusts based on optical scattering methods. It was developed by HSE's Safety Engineering Laboratory primarily for use in the coal-mining industry as an alternative to gravimetric sampling. Up to eight dust monitors can be controlled by a microcomputer via a two-wire telemetry link at distances of up to 8 km. The paper reports the results of comparative tests between OSIRIS and the MRE 113A gravimetric sampler in a calm air dust box, in a wind tunnel and in field trials at two collieries. Results show that OSIRIS can be calibrated against the MRE 113A for a given dust and that the calibration is maintained over the normal working range of 0-40 mg m-3. Results of tests against a variety of available test dusts show that the physical and optical properties of the dust particles have a significant effect on the response of the instrument. OSIRIS therefore needs to be calibrated against a gravimetric sampler for each dust which it will be used to monitor. Once calibrated, OSIRIS would be useful in monitoring respirable dust concentrations in a wide range of industrial or laboratory situations.     

Particle size distribution: A key factor in estimating powder dustiness

A wide variety of raw materials, involving more than 20 samples of quartzes, feldspars, nephelines, carbonates, dolomites, sands, zircons, and alumina, were selected and characterised. Dustiness, i.e., a materials' tendency to generate dust on handling, was determined using the continuous drop method. These raw materials were selected to encompass a wide range of particle sizes (1.6–294 µm) and true densities (2650–4680 kg/m³).

The dustiness of the raw materials, i.e., their tendency to generate dust on handling, was determined using the continuous drop method. The influence of some key material parameters (particle size distribution, flowability, and specific surface area) on dustiness was assessed. In this regard, dustiness was found to be significantly affected by particle size distribution.

Data analysis enabled development of a model for predicting the dustiness of the studied materials, assuming that dustiness depended on the particle fraction susceptible to emission and on the bulk material's susceptibility to release these particles. On the one hand, the developed model allows the dustiness mechanisms to be better understood. In this regard, it may be noted that relative emission increased with mean particle size. However, this did not necessarily imply that dustiness did, because dustiness also depended on the fraction of particles susceptible to be emitted. On the other hand, the developed model enables dustiness to be estimated using just the particle size distribution data. The quality of the fits was quite good and the fact that only particle size distribution data are needed facilitates industrial application, since these data are usually known by raw materials managers, thus making additional tests unnecessary.

This model may therefore be deemed a key tool in drawing up efficient preventive and/or corrective measures to reduce dust emissions during bulk powder processing, both inside and outside industrial facilities. It is recommended, however, to use the developed model only if particle size, true density, moisture content, and shape lie within the studied ranges.     

Inhalable Dust Measurements as a First Approach to Assessing Occupational Exposure in the Pharmaceutical Industry

Occupational exposure to active ingredients in the pharmaceutical industry has been the subject of very few published studies. Nevertheless, operations involving active powdered drugs or dusty operations potentially lead to operator exposure. The aim of this study was to collect occupational exposure data in the pharmaceutical industry for production processes involving powdered active ingredients. While the possibility of assessing drug exposure from dust level is examined, this article focuses on inhalable dust exposure, without taking chemical risk into account. A total of 377 atmospheric (ambient and personal) samples were collected in nine drug production sites (pharmaceutical companies and contract manufacturing organizations) and the dust levels were assessed. For each sample, relevant contextual information was collected. A wide range of results was observed, both site- and operation-dependent. Exposure to inhalable dust levels varied from 0.01 mg/m³to 135 mg/m³. Though restricted to dust exposure, the study highlighted some potentially critical situations or operations, in particular manual tasks (loading, unloading, mechanical actions) performed in open systems. Simple preventive measures such as ventilation, containment, and minimization of manual handling should reduce dust emissions and workers’ exposure to inhalable dust.