Using water sprays to improve performance of a flooded-bed dust scrubber

Supplemental water sprays were placed along the sides of a continuous mining machine to improve suppression and confinement of the dust cloud under the cutting boom to reduce downwind dust levels. Using a full-scale mock-up of a continuous mining machine, preliminary work showed that these side sprays improved suppression of the dust cloud and redistributed this cloud under the cutting head. This led to reductions in dust levels around the machine and in down-wind airways for some positions of the mining machine. This testing also showed that side spray effectiveness was influenced by the distance from the fresh air ventilation device to the cutting surface, termed the ventilation setback distance. These sprays produced larger reductions in machine and return dust levels at smaller setback distances than at larger setback distances. These side sprays then were installed in similar locations on a mining machine at an underground coal mine operation to evaluate their effectiveness for improving suppression and capture of dust by the flooded-bed dust scrubber. Although sampling could not be conducted successfully in the return, sampling around the mining machine and at the machine operator showed that dust levels decreased with use of these sprays. Further analysis showed that these sprays were most effective at the smaller setback distances, a result confirmed by full-scale laboratory testing.     

The use of tracer gases to determine dust dispersion patterns and ventilation parameters in a mineral processing plant.

A study was conducted in a fluorspar milling plant to assess the effectiveness of tracer gases as a reliable supplement to conventional air-monitoring and ventilation measurements. In the course of this study, a tracer gas was used as a surrogate substance to analyze the direction and the rate of spread of contaminants from various potential dust production points in the plant. Time-weighted average and continuous mineral dust concentrations were measured in several areas of the plant; these results were compared and correlated with steady-state tracer gas concentrations in the mill. Time-weighted average dust concentrations varied between 0.18 and 0.57 mg/m3 for total dust and 0.04 and 0.20 mg/m3 for quartz respirable dust, depending on the location. Correlation of these values with steady-state tracer gas concentrations yielded linear relationships with correlation coefficients (R2) of 0.95 and 0.87, respectively, for total and quartz dust. Results from this study, therefore, indicate that tracer gases may help model the spread of airborne respirable dust from point sources. These tracer gas releases also allowed the simultaneous quantitative determination of air residence times and contaminant clearance times from the building. Hence, tracer gases will help industrial hygienists obtain useful data with respect to building ventilation.     

The Evaluation and Quantification of Respirable Coal and Silica Dust Concentrations: A Task-based Approach

Silicosis and coal worker's pneumoconiosis are serious occupational respiratory diseases associated with the coal mining industry and the inhalation of respirable dusts containing crystalline silica. The purpose of this study (funded by the Mine Health and Safety Council of South Africa) was to evaluate the individual contributions of underground coal mining tasks to the respirable dust and respirable silica dust concentrations in an underground section by sampling the respirable dust concentrations at the intake and return of each task. The identified tasks were continuous miner (CM) cutting, construction, transfer of coal, tipping, and roof bolting. The respirable dust-generating hierarchy of the tasks from highest to lowest was: transfer of coal > CM right cutting > CM left cutting > CM face cutting > construction > roof bolting > tipping; and for respirable silica dust: CM left cutting > construction > transfer of coal > CM right cutting. Personal exposure levels were determined by sampling the exposures of workers performing tasks in the section. Respirable dust concentrations and low concentrations of respirable silica dust were found at the intake air side of the section, indicating that air entering the section is already contaminated. The hierarchy for personal respirable dust exposures was as follows, from highest to lowest: CM operator > cable handler > miner > roof bolt operator > shuttle car operator, and for respirable silica dust: shuttle car operator > CM operator > cable handler > roof bolt operator > miner. Dust control methods to lower exposures should include revision of the position of workers with regard to the task performed, positioning of the tasks with regard to the CM cutting, and proper use of the line curtains to direct ventilation appropriately. The correct use of respiratory protection should also be encouraged.     

Novel Approach for Suppressing Cutting Dust Using Foam on a Fully Mechanized Face with Hard Parting

The cutting dust created by the shearer drum is the main source of dust on a fully mechanized coal face. However, overexposure to respirable dust may cause pneumoconiosis in coal workers, while coal dust may lead to serious explosions. The fully mechanized face known as II1051 Face, found at the Zhuxianzhuang Coal Mine located in east China, generates dust by way of the drum on a high-power shear. The coal seam involves hard rock parting so there is a high concentration of cutting dust when the shearer is working. Thus, we developed a new foam dust suppression method with an air self-suction system based on an analysis of the dust generation characteristics that suppressed the shearer cutting dust level. The new foam system was evaluated in a field test where the dust concentration was measured at two points. The results showed that the foam reduced the cutting dust concentration significantly. The respirable dust exposure levels were reduced from 378.4 mg/m³to 53.5 mg/m³and the visibility was enhanced dramatically. Thus, we conclude that our new foam system is highly efficient at capturing cutting dust, and it has a much lower water consumption.

[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: Contact angle of cutting dust sample, migration trajectory of cutting dust, technological process for suppressing shearer cutting dust using foam, the layout of the foam dust suppression system on coal face, real object of the air self-suction type foam generator, the special foam nozzle used for shearers, relevant experimental results of the air self-suction foam system.]     

Assessment of respirable dust and its free silica contents in different Indian coalmines

Assessment of respirable dust, personal exposures of miners and free silica contents in dust were undertaken to find out the associated risk of coal workers' pneumoconiosis in 9 coal mines of Eastern India during 1988-91. Mine Research Establishment (MRE), 113A Gravimetric Dust Sampler (GDS) and personal samplers (AFC 123), Cassella, London, approved by Director General of Mines Safety (DGMS) were used respectively for monitoring of mine air dust and personal exposures of miners. Fourier Transform Infra-red (FTIR) Spectroscopy determined free silica in respirable dusts. Thermal Conditions like Wet Bulb Globe Temperature (WBGT) index, humidity and wind velocity were also recorded during monitoring. The dust levels in the face return air of both, Board & Pillar (B&P) and Long Wall (LW) mining were found above the permissible level recommended by DGMS, Govt. of India. The drilling, blasting and loading are the major dusty operations in B&P method. Exposures of driller and loader were varied between, 0.81-9.48 mg/m3 and 0.05-9.84 mg/m3 respectively in B&P mining, whereas exposures of DOSCO loader, Shearer operator and Power Support Face Worker were varied between 2.65-9.11 mg/m3, 0.22-10.00 mg/m3 and 0.12-9.32 mg/m3 respectively in LW mining. In open cast mining, compressor and driller operators are the major exposed groups. The percentage silica in respirable dusts found below 5% in all most all the workers except among query loaders and drillers of open cast mines.     

小型喷砂机柜式水幕排风罩矽尘防控有效性研究

目的:探究柜式水幕排风罩应用于小型喷砂机防治矽尘的效果,提出粉尘通风防护设施新思路,有效保护劳动者职业健康。方法:于2018年8至10月,选取某研究所喷砂间喷砂工艺配置的柜式水幕排风罩为研究对象,采用职业卫生调查、现场检测和气流组织物理相似模拟的方法,对其改造前后的局部排风设施设置情况、矽尘浓度、控制风速、气流组织进行...     

Dust exposure during small-scale mining in Tanzania: a pilot study

Small-scale mining in developing countries is generally labour-intensive and carried out with low levels of mechanization. In the Mererani area in the northern part of Tanzania, there are about 15000 underground miners who are constantly subjected to a poor working environment. Gemstones are found at depths down to 500 m. The objectives of this pilot study were to monitor the exposure to dust during work processes, which are typical of small-scale mining in developing countries, and to make a rough estimation of whether there is a risk of chronic pulmonary diseases for the workers. Personal sampling of respirable dust (n = 15) and 'total' dust (n = 5) was carried out during three consecutive days in one mine, which had a total of 50 workers in two shifts. Sampling started immediately before the miners entered the shaft, and lasted until they reappeared at the mine entrance after 5-8 h. The median crystalline silica content and the combustible content of the respirable dust samples were 14.2 and 5.5%, respectively. When drilling, blasting and shovelling were carried out, the exposure measurements showed high median levels of respirable dust (15.5 mg/m(3)), respirable crystalline silica (2.4 mg/m(3)), respirable combustible dust (1.5 mg/m(3)) and 'total' dust (28.4 mg/m(3)). When only shovelling and loading of sacks took place, the median exposures to respirable dust and respirable crystalline silica were 4.3 and 1.1 mg/m(3). This study shows that the exposure to respirable crystalline silica was high during underground small-scale mining. In the absence of personal protective equipment, the miners in the Mererani area are presumably at a high risk of developing chronic silicosis.     

Effect of ventilation rate on gradient of aerial contaminants in the confinement pig building

The principal aim of this study was to compare the aerial contaminants concentrations between the levels of ventilation rate and determine the variation pattern of aerial contaminants affected by the ventilation rate. As a result, there was not significant difference in total dust and total airborne microorganisms among three levels of ventilation rate (P>0.05) whereas the increased ventilation rate lowered the levels of respirable dust and gaseous compounds (P<0.05). Based on the results, it was concluded that the suspended gases in the confinement pig building generally followed the air streamline formed by the ventilation whereas the ventilation rate had little effect on the gradient of particulates, especially total dust, due to gravity generated by their size and weight. The findings that the concentrations of total airborne microorganisms were not also significantly different among the ventilation rates could be explained in terms of the fact that airborne microorganisms are easily adsorbed on the surface of dust particle.     

Measurements of the effectiveness of dust control on cut-off saws used in the construction industry

Materials used in the construction industry frequently contain large quantities of silica. When they are cut or shaped with power tools considerable respirable dust can be produced. Three dust control systems for use with cut-off saws have been evaluated on site: wet dust suppression using mains water, the same system using water from a portable water tank, and local exhaust ventilation. The efficiency of water suppression on cut-off saws has been precisely quantified in controlled laboratory conditions by means of measurements with and without dust control. When dust control was used on-site, the mean concentrations of airborne silica were reduced by a factor of between three and seven, the accuracy being limited by the relatively high limit of detection for silica. All controls systems generally reduced respirable dust levels by at least 90%. Although the effectiveness of dust suppression did not depend on blade type, a diamond blade was more effective than a resin-bonded blade with the pressurised water system; cutting a slab with this type of blade could be completed before the water tank required repressurization. In laboratory tests, the application of water reduced the dust concentration to < 4% of its value without control. The method for monitoring the dust concentration was sufficiently sensitive to measure a difference in concentration produced during cutting in different directions. It is important, however, that the pressure in supply reservoirs is properly maintained, that the water is correctly applied and that it is used at the correct rate. If this is done effective dust control can be achieved.     

Effect of hollow bit local exhaust ventilation on respirable quartz dust concentrations during concrete drilling

Drilling large holes (e.g., 10–20?mm diameter) into concrete for structural upgrades to buildings, highways, bridges, and airport runways can produce concentrations of respirable silica dust well above the ACGIH^® Threshold Limit Value (TLV^® = 0.025?mg/m³). The aim of this study was to evaluate a new method of local exhaust ventilation, hollow bit dust extraction, and compare it to a standard shroud local exhaust ventilation and to no local exhaust ventilation. A test bench system was used to drill 19?mm diameter x 100?mm depth holes every minute for one hour under three test conditions: no local exhaust ventilation, shroud local exhaust ventilation, and hollow bit local exhaust ventilation. There were two trials for each condition. Respirable dust sampling equipment was placed on a “sampling” mannequin fixed behind the drill and analysis followed ISO and NIOSH methods. Without local exhaust ventilation, mean respirable dust concentration was 3.32 (±?0.65) mg/m³ with a quartz concentration of 16.8% by weight and respirable quartz dust concentration was 0.55 (±?0.05) mg/m³; 22 times the ACGIH TLV. For both LEV conditions, respirable dust concentrations were below the limits of detection. Applying the 16.8% quartz value, respirable quartz concentrations for both local exhaust ventilation conditions were below 0.007?mg/m³. There was no difference in respirable quartz dust concentrations between the hollow bit and the shroud local exhaust ventilation systems; both were below the limits of detection and well below the ACGIH TLV. Contractors should consider using either local exhaust ventilation method for controlling respirable silica dust while drilling into concrete.     

Retrospective exposure assessment for respirable and inhalable dust, crystalline silica and arsenic in the former German uranium mines of SAG/SDAG Wismut

OBJECTIVES: Starting shortly after the reunification of Germany and lasting up to the end of the 1990s, an extensive series of retrospective exposure investigations for the East German uranium mining industry was performed in order to provide information about the exposure situation of the miners towards respirable dust, inhalable dust, crystalline silica and heavy metals. It should provide the necessary information for legal compensation of miners with potential industrial diseases as well as for epidemiological research. METHODS: Extensive side-by-side measurements using original historic equipments as well as comprehensive evaluation of the time increments of specific jobs with respect to exposure relevant tasks were performed. After attributing average exposures to the tasks, shift exposures for the jobs could be calculated. RESULTS: By the end a comprehensive job exposure matrix for all underground jobs of the German uranium mining industry was developed for the components mentioned, including arsenic where relevant. In the early days of SAG/SDAG Wismut dust and silica exposures were extremely high with respirable dust up to 20 mg/m(3) and respirable crystalline silica well above 2 mg/m(3) as shift averages. Beginning from about the early 1960s dust control measures started to improve conditions dramatically. CONCLUSIONS: It is absolutely necessary to invest sufficient effort for the estimation of exposure situations of past technological environments. Especially, the situation of early mechanised mining, characterised by low ventilation, dry drilling techniques and generally lacking dust control measures was characterized by extreme shift exposures. It is important to keep these in mind when metal mining exposure in different environments is considered.     

High exposure to respirable dust and quartz in a labour-intensive coal mine in Tanzania

Labour-intensive mines are numerous in several developing countries, but dust exposure in such mines has not been adequately characterized. The aim of this study was to identify and quantify the determinants of respirable dust and quartz exposure among underground coal mine workers in Tanzania. Personal respirable dust samples (n = 134) were collected from 90 underground workers in June-August 2003 and July-August 2004. The development team had higher exposure to respirable dust and quartz (geometric means 1.80 and 0.073 mg m(-3), respectively) than the mining team (0.47 and 0.013 mg m(-3)), the underground transport team (0.14 and 0.006 mg m(-3)) and the underground maintenance team (0.58 and 0.016 mg m(-3)). The percentages of samples above the threshold limit values (TLVs) of 0.9 mg m(-3) for respirable bituminous coal dust and 0.05 mg m(-3) for respirable quartz, respectively, were higher in the development team (55 and 47%) than in the mining team (20 and 9%). No sample for the underground transport team exceeded the TLV. Drilling in the development was the work task associated with the highest exposure to respirable dust and quartz (17.37 and 0.611 mg m(-3), respectively). Exposure models were constructed using multiple regression model analysis, with log-transformed data on either respirable dust or quartz as the dependent variable and tasks performed as the independent variables. The models for the development section showed that blasting and pneumatic drilling times were major determinants of respirable dust and quartz, explaining 45.2 and 40.7% of the variance, respectively. In the mining team, only blasting significantly determined respirable dust. Immediate actions for improvements are suggested to include implementing effective dust control together with improved training and education programmes for the workers. Dust and quartz in this underground mine should be controlled by giving priority to workers performing drilling and blasting in the development sections of the mine.     

Comparison of the CAS-POL and IOM samplers for determining the knockdown efficiencies of water sprays on float coal dust

Float coal dust, generated by mining operations, is distributed throughout mine airways by ventilating air designed to purge gases and respirable dust. Float coal dust poses an explosion hazard in the event of a methane ignition. Current regulation requires the application of inert rock dust in areas subjected to float coal dust in order to mitigate the hazard. An alternate method using water sprays, which have been effective in controlling respirable dust hazards, has been proposed as a way to control float coal dust generated on longwall faces. However, the knockdown efficiency of the proposed water sprays on float coal dust needs to be verified. This study used gravimetric isokinetic Institute of Occupational Medicine (IOM) samplers alongside a real-time aerosol monitor (Cloud Aerosol Spectrometer with polarization; CAS-POL) to study the effects of spray type, operating pressure, and spray orientation on knockdown efficiencies for seven different water sprays. Because the CAS-POL has not been used to study mining dust, the CAS-POL measurements were validated with respect to the IOM samplers. This study found that the CAS-POL was able to resolve the same trends measured by the IOM samplers, while providing additional knockdown information for specific particle size ranges and locations in the test area. In addition, the CAS-POL data was not prone to the same process errors, which may occur due to the handling of the IOM filter media, and was able to provide a faster analysis of the data after testing. This study also determined that pressure was the leading design criteria influencing spray knockdown efficiency, with spray type also having some effect and orientation having little to no effect. The results of this study will be used to design future full-scale float coal dust capture tests involving multiple sprays, which will be evaluated using the CAS-POL.     

Dust exposure indices and lung function changes in Longshoremen and Dock workers

A group of Dutch harbor workers involved in loading and unloading bulk products from sea vessels such as coal, cokes, and some other products like alumina, borax, phosphate ore, and vermiculite was studied. Exposures were characterized by personal and environmental monitoring. This information was subsequently used to estimate several dust exposure indices and to study relationships with lung function variables and respiratory symptoms. Average respirable dust exposure levels ranged from 0.3–4.0 mg/m³. Workers involved in unloading products from sea vessels were exposed to the highest dust levels. Supervisors and workers with tasks in the dock had an intermediate to low exposure. Office workers had the lowest exposure to respirable dust. Inhalable dust levels were considerably higher and average exposures ranged from 0.3–80 mg/m³. The ranking of occupational titles by inhalable dust exposure was almost identical to the rank order of respirable dust levels. Workers with higher current and cumulative dust exposures tended to have a lower lung function, and only shortness of breath had a statistically significant relationship with current and cumulative inhalable dust exposure. In general, relationships between lung function and inhalable dust levels tended to be somewhat stronger in terms of statistical significance, because inhalable dust is an estimate of dust deposition in the upper airways and lung function is a measurable parameter of airway obstruction in that region. However, the differences with respirable dust were minimal, and variability in dust exposure levels was extremely large for this population. It was concluded that harbor workers involved in unloading ships containing coal and various kinds of ore can be exposed to high dust levels. Relationships between dust exposure and lung function illustrate that these exposures are a respiratory hazard. Our finding that inhalable dust levels have a somewhat stronger relationship with lung function level than respirable dust levels deserves further attention.     

某煤矿综掘工作面新型高效除尘技术有效性研究与应用

目的研究综掘面防尘新型高效除尘系统的有效性,为煤矿综掘面煤尘防护和管理提供新技术。方法采用现场调查的方法对该综掘面防尘现状、综掘面现有通风设施布置情况、掘进司机接触煤尘情况、新型高效控尘系统布置情况进行分析和评价。结果采用新型高效除尘系统后,综掘面掘进司机位总粉尘降尘率为72.1%,呼吸性粉尘降尘率为85.3%;机尾8、15 m处总粉尘降尘率均高于90%以上,呼吸性粉尘降尘率均高于92%以上;掘进工接触煤尘浓度总粉尘超标率下降了79.8%,呼吸性粉尘超标率下降了87.2%。结论综掘面煤尘浓度较高的场所集中分布在掘进司机位和掘进巷回风侧,作业人员长期处在粉尘浓度较高的场所,引发职业病的风险较高,应作为煤尘防治的重点。新型高效除尘技术与原有通风设施应合理配合控尘、降尘、除尘,能够有效控制综掘工作面粉尘。     

The efficacy of local exhaust ventilation for controlling dust exposures during concrete surface grinding

This study assessed the effectiveness of a commercially available local exhaust ventilation (LEV) system for controlling respirable dust and crystalline silica exposures during concrete grinding activities. Surface grinding was conducted at six commercial building construction sites in Seattle, WA, by cement masons. Time-integrated filter samples and direct reading respirable dust concentrations were collected using a cyclone in line with a direct reading respirable dust monitor. Personal exposure levels were determined with and without LEV, one sample directly after the other. A total of 28 paired samples were collected in which three different dust collection shroud configurations were tested. Data obtained with a direct reading respirable dust monitor were adjusted to remove non-work task-associated dust exposures and was subsequently used to calculate the exposure reduction achieved. The application of LEV resulted in a reduction in the overall geometric mean respirable dust exposure from 4.5 to 0.14 mg/m(3), a mean exposure reduction of 92%. Despite the effective control of dust generated during surface grinding, 22 and 26% of the samples collected while LEV was being used were greater than the 8 h time-weighted average permissible exposure limit (Occupational Safety and Health Administration) and threshold limit value (American Congress of Governmental Industrial Hygienists) for respirable crystalline silica, respectively.     

Crystalline silica dust and respirable particulate matter during indoor concrete grinding - wet grinding and ventilated grinding compared with uncontrolled conventional grinding

The effectiveness of wet grinding (wet dust reduction method) and ventilated grinding (local exhaust ventilation method, LEV) in reducing the levels of respirable crystalline silica dust (quartz) and respirable suspended particulate matter (RSP) were compared with that of uncontrolled (no dust reduction method) conventional grinding. A field laboratory was set up to simulate concrete surface grinding using hand-held angle grinders in an enclosed workplace. A total of 34 personal samples (16 pairs side-by-side and 2 singles) and 5 background air samples were collected during 18 concrete grinding sessions ranging from 15-93 min. General ventilation had no statistically significant effect on operator's exposure to dust. Overall, the arithmetic mean concentrations of respirable crystalline silica dust and RSP in personal air samples during: (i) five sessions of uncontrolled conventional grinding were respectively 61.7 and 611 mg/m(3) (ii) seven sessions of wet grinding were 0.896 and 11.9 mg/m(3) and (iii) six sessions of LEV grinding were 0.155 and 1.99 mg/m(3). Uncontrolled conventional grinding generated relatively high levels of respirable silica dust and proportionally high levels of RSP. Wet grinding was effective in reducing the geometric mean concentrations of respirable silica dust 98.2% and RSP 97.6%. LEV grinding was even more effective and reduced the geometric mean concentrations of respirable silica dust 99.7% and RSP 99.6%. Nevertheless, the average level of respirable silica dust (i) during wet grinding was 0.959 mg/m(3) (38 times the American Conference of Governmental Industrial Hygienists [ACGIH] threshold limit value [TLV] of 0.025 mg/m(3)) and (ii) during LEV grinding was 0.155 mg/m(3) (6 times the ACGIH TLV). Further studies are needed to examine the effectiveness of a greater variety of models, types, and sizes of grinders on different types of cement in different positions and also to test the simulated field lab experimentation in the field.     

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.     

Airborne endotoxin associated with particles of different sizes and affected by water content in handled straw

High exposures to endotoxin are observed in environments where organic materials are handled and lower exposures are found in e.g. indoor air. Inhaled endotoxin contributes significantly to the induction of airway inflammation and dysfunction. The size of an inhaled particle influences the deposition in the airways and the following health symptoms. The objective is to characterise the distribution of endotoxin on airborne particles of different sizes in straw storage halls with high exposure and in other environments with lower exposure levels to endotoxin. Furthermore we have studied the influence of water content of handled straw on the size distribution of endotoxin containing particles. Total, inhalable, thoracic and respirable endotoxin and particles have each been quantified in aerosols from boiler rooms and straw storage halls at 24 power plants, including 21 biofuel plants. Inhalable, thoracic and respirable endotoxin have been quantified in aerosols from offices and outdoor air. The endotoxin concentration was higher in airborne thoracic dust than in airborne ‘total dust’. The median respirable fraction in the straw storage halls, boiler rooms at biofuel plants, boiler rooms at conventional plants, offices and outdoors was respectively 42%, 9%, 19%, 24% and 34%. Thoracic endotoxin per number of thoracic particles was higher than respirable endotoxin per number of respirable particles at the biofuel plants. In straw storage halls the fraction of endotoxin of respirable size was highest on the days with lowest water content in the received straw. Furthermore the exposures to all endotoxin fractions were highest on days with the lowest water content in the received straw. In conclusion the highest exposures and concentrations of endotoxin occur or tend to occur from thoracic dust. A high variation in endotoxin concentrations and in fractions of respirable or thoracic size is found in the different working areas. This is important in the risk assessment and makes attempts to influence the endotoxin exposure a possibility. Water content in straw affected the concentration, exposure level and size distribution of airborne endotoxin.     

Particulate penetration of porous foam used as a low flow rate respirable dust size classifier

Porous foam has been used as a material for classification of particulate matter into various size fractions. The penetration characteristics of a nominal 90 pores per inch porous foam were studied at various flow rates, face velocities, and foam plug diameters and compared to the aerosol penetration of a 10 mm Dorr Oliver cyclone operated at 1.7 L/min. Poly-dispersed triethanolamine spheres were classified through porous foam plugs and the resulting penetration was determined using an aerodynamic particle sizer. Results showed that for a given plug diameter, as face velocity increased from 26 to 39 cm/sec, the 50 percent cut point decreased from 4.5 to 3.8 microns. Furthermore, as the diameter of the plug increased from 4 to 12 mm, the 50 percent cut points were similar to other plug diameters at equivalent face velocities. The best match to the 1.7 L/min cyclone penetration characteristics occurred at a flow rate of 250 ml/min through a 25 mm by 4 mm diameter section of 90 pore per inch foam. Because of the need to provide short-term or real-time estimates of worker respirable dust exposure, porous foam may be a viable classification media for a low flow rate, disposable respirable dust sampler for use in the coal mining industry.