Experimental examination of factors that affect dust generation.

A method is presented to examine factors that affect the amount and size distribution of dust generated by falling granular material in still air. This work was conducted by using an apparatus with separate dust generating and dust measuring sections. The dust generated by a falling material was carried into an elutriation column equipped with a slotted Sierra high-volume impactor at the top. This apparatus can measure dust generation rates for particles between 0.4 and 25 microns in aerodynamic diameter as well as the amount of air entrained by the falling material. Four granular materials were tested, and a simple model was developed to describe the dust generation rate of these materials as a function of particle size, drop height, material flow, and moisture content. Moisture content strongly influenced the interparticle binding forces and the amount of dust generated. Drop height and material flow influenced the material separation forces and also significantly influenced the amount of dust generated.     

Combined single-drop and rotating drum dustiness test of fine to nanosize powders using a small drum

A dustiness test has been developed that performs both a single-drop and a continuous rotation test using a 6-g sample. Tests were completed on pigment-grade and ultrafine TiO2, two grades of corundum (Aloxite), yttrium-stabilized zirconia (Y-zirconia) granules, fumed silica, goethite, talc and bentonite. The generated particles were quantified by counting and sizing at 1-s time resolution using the TSI Fast Mobility Particle Sizer and the TSI Aerodynamic Particle Sizer and by collecting the particles on a filter for weighing. The method generated reproducible amounts and size distributions of particles. The size distributions had two more or less separated size modes >0.9 microm and in addition all materials except TiO2 pigment-grade and Aloxite F1200 generated a size mode in the range from approximately 100 to approximately 220 nm. Pigment-grade TiO2 had the lowest dustiness and ultrafine TiO2 the highest dustiness as measured by particle number for both the single-drop and rotation test and as measured by mass for both tests combined. The difference was a factor of approximately 300. Three types of dust generation rate time profiles were observed; brief initial burst (talc, both grades of corundum), decaying rate during rotation period (fumed silica, TiO2 ultrafine and pigment grade, bentonite) and constant rate (Y-zirconia, goethite). These profile types were in agreement with the differences in the ratio of amount of particles generated during the single drop to the amount generated during the single-drop and rotation test combined. The ratio ranged a factor approximately 40. The new test method enables a characterization of dustiness with relevance to different user scenarios.     

An investigation of dust generation by free falling powders.

To identify the dust generation processes, aluminum oxide powder was dropped as a free falling slug in a test chamber. The effect of the slug's mass, diameter, and drop height upon the aerosol concentration and size distribution was measured with an aerodynamic particle sizer. To differentiate between aerosol generated during the free fall and at the end of the fall, the slug was dropped either onto a flat surface or into a container of water that suppressed dust generation associated with the impact at the end of the fall. Aerosol generation occurred during the slug's free fall as well as at the end of the fall. The falling solid induced an airflow that followed the falling solid to the end of the fall. This induced airflow contained the aerosol generated during the free fall. At the end of the free fall, the induced airflow, combined with air jets created on impact, dispersed the aerosol throughout the test chamber. Additional measurements were made by using "neutral buoyancy" helium-filled bubbles to visualize the airflow in the test chamber. The airflow and ensuing turbulence were sufficient to keep large, inspirable particles suspended throughout the test chamber for periods greater than 10 min. During experimental work, the effect of drop height, mass, and slug diameter upon aerosol generation by a single slug of powder was studied. The results indicated that the manner in which a powder is handled may be as important as material dustiness as measured by a dustiness tester. Aerosol generation can be reduced by minimizing the contact between the falling powder and the air.     

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.     

Response characteristics of scattered light aerosol sensors used for control monitoring

The response characteristics of scattered light aerosol monitors used in control monitoring applications were evaluated. In this report, "control monitoring" refers to continuous, fixed point monitoring used to ensure that dust controls are effective. Instruments evaluated included the following: an ATI-722, which uses a white light source; a RAM-S, which uses a LED source; and a PCAM-TX, which uses a LED source and provides a correction for particle size. The linearity of the monitors was evaluated from 0.5-10 mg/m3 with the use of coal dust as an aerosol. This concentration range was broken up into two smaller ranges since it was not possible to generate an aerosol with a constant size distribution over the entire range. All instruments showed a linear response with concentration for constant dust size distribution. The size sensitivity of the instruments was determined by passing a test aerosol through a series of impactor stages and measuring the mass response of each instrument relative to the indicated mass response of an Aerodynamic Particle Sizer (APS). The particle size was varied from 2-14 microns. The mass response of the instruments relative to the APS over this size range varied from as low as 0.1 to as high as about 5. The PCAM provides data that indicate changes in the size distribution of the aerosol being monitored. A simple model was developed to relate the net response of each test instrument to various log normal size distributions. The user of the instruments has to be aware of particle size changes in the aerosol being monitored since changes in the size distribution will affect the relationship between the response of the instruments and the mass concentration. Guidelines for instrument use are given in order to show how the instruments can be applied to the continuous monitoring of dust in the workplace.     

A study on dust emission, particle size distribution and formaldehyde concentration during machining of medium density fibreboard

A study to characterise the quantity, particle size distribution and morphology of dust created during the machining of MDF was carried out. Four different types of MDF boards were included in this study, including a 'zero-formaldehyde' board that contains isocyanate-based resin, rather than urea-formaldehyde resin. In addition, natural softwood (pine) and natural hardwood (oak) were included in the study, for comparison with MDF. The results show that in general, the dust generated by machining MDF is comparable in terms of particle size distribution and morphology with the dust generated by similarly machining hardwood or softwood. The quantity of dust generated during sanding is higher for sanding MDF compared with sanding either hardwood or softwood. However, for sawing there is no significant difference between MDF and natural woods, in terms of the quantity of dust generated. Free formaldehyde in the air was less than 0.17mg m(-3) during machining of the Class B (higher formaldehyde potential) MDF board. There was no measurable isocyanate in the dust generated from the boards.     

Separation efficiency of a wood dust collector-field measurement using a fluorescent aerosol

Given the dangerous nature of the dust emitted in the wood industry, the quality of the recycled air in the work premises after cleaning must be strictly controlled.A method of measuring the efficiency of a wood dust collector as a function of the particle diameter has been developed using a fluorescein tracer aerosol generated upstream of the equipment. The separation efficiency is determined from the particle size mass distribution of the tracer, both upstream and downstream, measured by means of two cascade impactors. The mass efficiency measured by tracer technique was compared on a test rig to the number efficiency measured using a reference method based on optical counting. The agreement between the two efficiencies is quite good; nevertheless, the tracer method leads to results that are slightly below those obtained using the reference method.The method was applied to measure the efficiency of a 11 500 m(3) h(-1) wood dust collector. The results are presented along with those obtained from a sample of plane filter media making up the bags of the dust collector.     

Dust exposures in the Canadian grain industry

Total dust concentrations measured in 8 terminal, 9 transfer and 14 country grain elevators ranged from 0.18 to 781 mg/m3. Results indicate that elevatormen performing housekeeping and maintenance chores or working in transfer galleries are more likely to be exposed to high concentrations. Dust exposures can be related to the amount of grain handled and the extent of dust control measures in effect at a worksite. The respirable mass fraction of grain dust varies according to the type of grain handled. The quartz, inorganic material and fungal spore content and particle size of the dust from specific grains were also studied.     

Comparison of coal mine dust size distributions and calibration standards for crystalline silica analysis

Since 1982 standard calibration materials recommended for respirable crystalline silica analysis by the Mine Safety and Health Administration (MSHA) P7 Infrared Method and the National Institute for Occupational Safety and Health (NIOSH) X-ray Diffraction (XRD) Analytical Method 7500 have undergone minor changes in size distribution. However, a critical assumption has been made that the crystalline silica in ambient mine atmosphere respirable dust samples has also remained essentially unchanged in particle size distribution. Therefore, this work compared recent particle size distributions of underground coal mine dust and the silica component of these dusts with estimated aerodynamic particle size distributions of calibration standard materials MIN-U-SIL 5, Berkeley 5, and SRM 1878 used by two crystalline silica analysis techniques. Dust impactor sampling data for various locations in 13 underground coal mines were analyzed for the respirable mass median aerodynamic diameters. The data suggest that the MSHA P7 method will underestimate the silica content of the sample by at most 7.4% in the median size range 0.9 to 3.6 microm, and that it is unlikely one would obtain any significant error in the MSHA P7 method analysis when the method uses Berkeley 5, MIN-U-SIL 5, or SRM 1878 as a calibration standard material. The results suggest that the NIOSH Analytical Method 7500 would be more appropriate for a dust sample that is representative of the total (no cyclone classifier) rather than the respirable airborne dust, particularly because the mass fraction in the size range below 4 microm is usually a small percentage of the total airborne dust mass. However, NIOSH Analytical Method 7500 is likely to underestimate the silica content of an airborne respirable dust sample by only 5 to 10%. The results of this study also suggest that any changes that may have occurred in the median respirable size of airborne coal mine dust are not significant enough to cause any appreciable error in the current methods used for respirable crystalline silica analysis.     

Types, numbers, sizes, and distribution of mineral particles in the lungs of urban male cigarette smokers

We analyzed the exogenous mineral particle concentration, size, type, and distribution for particles larger than 0.1 micron in the left lungs of 10 long-term male cigarette smokers. The mean number of particles found was 465 +/- 295 X 10(6)/g dry lung, of which 80% were kaolinite, micas, feldspars, free silica, and talc. Lead particles were extremely rare, despite their ubiquity in urban air. Overall there were no differences in particle concentration in upper vs lower lobes or central vs peripheral sampling sites. However, a significant correlation was found for upper lobe (r = 0.68), but not lower lobe (r = 0.08), particle concentration and amount of cigarette smoking. Overall, the geometric mean particle size was 0.6 +/- 2.1 microns; 56% of the particles in the upper lobes were larger than 0.75 micron in diameter, compared to 17% in the lower lobes, and the mean upper lobe particle size was greater than the mean lower lobe particle size for all individual mineral types. There was a remarkable homogeneity of mean particle size from patient to patient (mean intercase arithmetic particle size +/- SD of 0.8 +/- 0.1 micron). Particle size was not affected by the amount of smoking. We conclude that contrary to some published acute deposition data, there are no long-term differences in upper vs lower lobe particle concentration; total upper lobe particle retention is influenced by the amount of smoking as measured by pack-years, whereas total lower lobe particle retention appears to be independent by the amount of smoking; particles retained in the upper lobe are somewhat larger than those retained in the lower lobe, but the amount of smoking does not appear to influence retained particle size; the size of long-term retained particles most likely reflects largely atmospheric particle burden; and in the absence of overwhelming dust loads, the lung is able to regulate retained particle concentration and size in a fairly narrow range.     

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.     

Experimental study on effects of drilling parameters on respirable dust production during roof bolting operations

Underground coalmine roof bolting operators exhibit a continued risk for overexposure to airborne levels of respirable coal and crystalline silica dust from the roof drilling operation. Inhaling these dusts can cause coal worker's pneumoconiosis and silicosis. This research explores the effect of drilling control parameters, specifically drilling bite depth, on the reduction of respirable dust generated during the drilling process. Laboratory drilling experiments were conducted and results demonstrated the feasibility of this dust control approach. Both the weight and size distribution of the dust particles collected from drilling tests with different bite depths were analyzed. The results showed that the amount of total inhalable and respirable dust was inversely proportional to the drilling bite depth. Therefore, control of the drilling process to achieve proper high-bite depth for the rock can be an important approach to reducing the generation of harmful dust. Different from conventional passive engineering controls, such as mist drilling and ventilation approaches, this approach is proactive and can cut down the generation of respirable dust from the source. These findings can be used to develop an integrated drilling control algorithm to achieve the best drilling efficiency as well as reducing respirable dust and noise.     

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.     

Comparison of the Grimm 1.108 and 1.109 portable aerosol spectrometer to the TSI 3321 aerodynamic particle sizer for dry particles

This study compared the response of two optical particle counters with that of an aerodynamic particle sizer. The optical particle counters rely on the amount of incident light scattered at 90 degrees by a particle to measure particle number concentration by optical particle size. Two models of optical particle counters from Grimm Technologies were used: the portable aerosol spectrometer (PAS) 1.108 (0.3-20 microm in 15 channels); and the PAS 1.109 (0.2-20 microm in 30 size channels). With a substantially different operating principle from that employed by the optical particle counters, the aerodynamic particle sizer (APS) model 3321 (TSI, Inc., St Paul, MN, USA) sizes particles according to their behavior in an accelerating flow to provide particle number concentration by aerodynamic size over a slightly narrower size range (0.5-20 microm) in 52 channels. The responses of these instruments were compared for three sizes of monodisperse solid aerosols composed of polystyrene latex spheres and a polydisperse aerosol composed of Arizona test dust. The PASs provided similar results to those from the APS. However, there were systematic differences among instruments in number and mass concentration measurement that depended upon particle size.     

An approach to evaluating and correcting aerodynamic particle sizer measurements for phantom particle count creation.

An aerodynamic particle sizer (APS) can be used to make real-time measurements of the aerodynamic particle size distribution over the range of 0.5 to 32 microns. This instrument is very useful in conducting health-related aerosol measurements involving aerosol generation, respirator efficiency, and particulate sampling efficiency. One of the two signal processors within the APS can create spurious or phantom particle counts that can significantly affect relative measurements and calculated mass distributions. In the APS, particle size measurement is based upon a particle's transit time between two laser beams that are perpendicular to an accelerating airflow. The signal processors measure each particle's transit from the time between the two pulses of scattered light that are generated as the particle passes through the two laser beams. When only a single pulse from a particle is detected, another pulse can cause the recording of a randomly sized phantom particle. The small particle processor (SPP), which measures particle transit from the times in digital increments of 4 nanoseconds, can create phantom particles; the large particle processor (LPP), which measures particle transit times in digital increments of 66.67 nanoseconds, is designed to prevent the creation of phantom particles. These two processors overlap in the range of 5.2 to 15.4 microns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental methodologies and preliminary transfer factor data for estimation of dermal exposures to particles.

Developmental efforts and experimental data that focused on quantifying the transfer of particles on a mass basis from indoor surfaces to human skin are described. Methods that utilized a common fluorescein-tagged Arizona Test Dust (ATD) as a possible surrogate for housedust and a uniform surface dust deposition chamber to permit estimation of particle mass transfer for selected dust size fractions were developed. Particle transfers to both wet and dry skin were quantified for contact events with stainless steel, vinyl, and carpeted surfaces that had been pre-loaded with the tagged test dust. To better understand the representativeness of the test dust, a large housedust sample was collected and analyzed for particle size distribution by mass and several metals (Pb, Mn, Cd, Cr, and Ni). The real housedust sample was found to have multimodal size distributions (mg/g) for particle-phase metals. The fluorescein tagging provided surface coatings of 0.11-0.36 ng fluorescein per gram of dust. The predominant surface location of the fluorescein tag would best represent simulated mass transfers for contaminant species coating the surfaces of the particles. The computer-controlled surface deposition chamber provided acceptably uniform surface coatings with known particle loadings on the contact test panels. Significant findings for the dermal transfer factor data were: (a) only about 1/3 of the projected hand surface typically came in contact with the smooth test surfaces during a press; (b) the fraction of particles transferred to the skin decreased as the surface roughness increased, with carpeting transfer coefficients averaging only 1/10 those of stainless steel; (c) hand dampness significantly increased the particle mass transfer; (d) consecutive presses decreased the particle transfer by a factor of 3 as the skin surface became loaded, requiring approximately 100 presses to reach an equilibrium transfer rate; and (e) an increase in metals concentration with decreasing particle size, with levels at 25 microns typically two or more times higher than those at 100 microns--consistent with the earlier finding of Lewis et al. for the same sample for pesticides and polycyclic aromatic hydrocarbons (PAHs).     

Characterization of Ambient Air Particle Size Fractions in Three German Cities with the Aid of Electron Microscopy

Multistage-filtration samplers offer the opportunity to analyze dust fractions deposited on corresponding stages of the sampler. In this investigation, a typical two-stage sampler was used in the cities of Dortmund (mining and steel industry), Düsseldorf (lesser industrial activities), and Duisburg (steel industry), North Rhine Westphalia. The purpose of this study was to compare the composition of dust fractions with the aid of analytical electron transmission microscopical methods. The particle size distribution was similar in the cities, the 50% value of the equivalent diameter was 0.8 μm. Analytical results are presented for different mineral classes with approximately 30 single minerals in all cities. The highest concentration values in the fine dust fraction were silicate minerals, while the sulfate content was very high in the coarse dust fraction in all cities. Received: 26 July 1996/Revised: 14 September 1996     

The effectiveness of handheld ventilated sanders in reducing inhalable dust concentrations

Ventilated sanders are commonly used during aircraft surface abrasion but there is limited data on their effectiveness in reducing worker exposures. This study compared two handheld ventilated sander brands, DCM and Dynabrade, in a laboratory glovebox. Both sanders collect particulates by drawing air through holes in the sanding pads; the dust subsequently passes into a vacuum collection system. Aluminum panels coated with aircraft epoxy primer and polyurethane paint were abraded and inhalable dust concentrations were measured inside the glovebox with IOM samplers. The results indicate that both sanders effectively control inhalable dust, with the DCM sander reducing mass concentrations by 93 percent, and the Dynabrade by 98 percent, when the ventilation system is used. The Dynabrade unit, however, was more aggressive and produced over four times as much dust per unit time as the DCM unit. In spite of this, the Dynabrade sander adequately collected this additional dust. Varying abrasive grit size did not significantly affect dust generation, although the differences between the grit sizes used (180 and 240 grit) were not great and may have influenced the results.     

An evaluation of the GCA respirable dust monitor 101-1.

The GCA RDM 101-1 has been evaluated using aerosols of coal, Arizona road dust, silica, potash, and rock (copper ore) particles. The effects of the dust mass concentration, particle size distribution, and dust material on the instrument response were investigated. The instrument was found to measure the mass concentrations of respirable dust aerosols up to about 16 mg/m3 for coal and rock dust and about 20 mg/m3 for silica, potash, and Arizona road dust, providing there is not appreciable mass in the size range below approximateley 0.7 micrometer aerodynamic diameter.     

乡镇水泥厂综合防尘适宜技术的研究

目的 研究乡镇水泥厂的适宜防尘技术,以控制尘肺病的发生。方法 采用现场和实验室相结合的综合调研方法。用示踪气体测量抽气罩的效率。按照国家标准（GB／T16157－1996）测定通风管道中的粉尘浓度。采用WY－1型冲击式尘粉分级仪测量各尘源排放粉尘的粉尘粒径分级组成和除尘器的粒径分级除尘效率。结果 （1）工程技术措施方面：提出了破碎、球磨、烘干、烧窑、物料运输和包装等工艺工序的适宜吸尘罩设计（及通用图集）,可有效地控制这些尘源的粉尘外溢。测定不同工序排放烟气的特性（烟气的温度、含水量、粉尘浓度、粉尘粒径分级组成等）,研究了多种除尘器的粒径分级除尘效率、阻力等,提出了各主要工序最适宜方案：破碎、磨机工序除尘以旋风加滤袋或静电等;烘干窑除尘以旋风加静电或冲击喷雾等;立窑除尘以沉降室加静电等;包装工序除尘以滤袋或静电等。（2）组织措施方面：完善职业卫生管理系统,包括建立组织机构、加强职业卫生服务、开展技术培训和职业卫生教育。强调“有效地控制各尘源处的粉尘,防止其向周围扩散”是防止尘肺病发生的最有效方法。结论 提出了乡镇水泥厂适宜综合防尘技术措施,可有效控制水泥尘危害。