Free Silica Content Research Articles

Coal Workers’ Pneumoconiosis and Related Risk Indices

Coal Workers’ Pneumoconiosis and Related Risk Indices: Qiao Niu, et al. Department of Public Health, Shanxi Medical College—Cross sectional epidemiological studies were carried out in three coal mines (Mines A, B and C), that produce differnt types of coal in order to examine the relationship between the prevalence of coal workers’ pneumoconiosis (CWP) and factors contributing to the development and seriousness of CWP. Seven factors were taken into consideration and two of them were calculated as “risk indices”. They concerned composition (including carbon, ash, volatile content of coal, free silica in coal dust and rock dust) and exposure factors (including dust concentration, duration of exposure and type of operation). Composition factors were: carbon 90%, ash 23.13%, volatile content 13.85%, free silica in coal dusts 2.58% and free silica in rock dusts 32.88% in Mine A. Carbon 82%, ash 8%, volatile content 28.5%, free silica in coal dusts 5.90% and free silica in rock dusts 33.0% in Mine B. Carbon 94%, ash 20.46%, volatile content 10.76%, free silica in coal dusts 2.04% and free silica in rock dusts 24.04% in Mine C. Differences in the coal dust concentration over a period of 20 to 30 years were not significant in the three mines. The rock dust concentration in Mine B was much higher than those in the other two mines. The CWP prevalence was 2.22% in Mine A, 13.20% in Mine B and 1.86% in Mine C. Analysis has shown that both composition and exposure factors were related to CWP prevalence, but the strength of the relationship between the factors was different in the three mines, especially in Mine B, where there was a high CWP prevalence, and the association of CWP with free silica and high volatile content was strong. It was interesting that, though the rank of coal in Mine B was much lower than those in Mine A and Mine C, the prevalence of CWP in Mine B was much higher than those in Mine A and Mine C. This result was in contrast with those reported before. The calculation of risk indices indicated that there was a positive correlation between the risk indices and exposure duration.

Study on quantitative analysis of free silica content in sample dust made by established specific gravity

Study on quantitative analysis of free silica content in sample dust made by established specific gravity

Acid activation of a Spanish sepiolite: physico-chemical characterization, free silica content and surface area of products obtained

AbstractA sepiolite from Vallecas (Spain) was treated with solutions of HC1 (1.25, 2.5, 5.0, 10.0 and 20.0 wt%) at 25°C for 2, 6, 24 and 48 h, respectively. The resulting solids were characterized by XRD, FT-IR and thermal analyses, along with SEM, TEM and nitrogen adsorption isotherms at 77 K. The free silica was digested and determined in all samples. Several samples were seen to have specific surface areas up to 450 m2/g, with a maximum value of 549 m2/g in the sample treated with 1.25 wt% HCl for 48 h. A sudden decrease in specific surface areas was observed when free silica was digested.

Estimating historical exposure to silica among mine and pottery workers in the people's Republic of China

A quantitative retrospective exposure assessment method was developed for use in a nested case-control study of lung cancer among mine and pottery workers exposed to silica dust in the People's Republic of China. Exposure assessment was carried out in 20 mines (10 tungsten, 6 iron/copper, and 4 tin) and nine pottery factories. A job title dictionary was developed and used in both the collection of historical exposure information and work histories of 1,668 (316 cases and 1,352 controls) study subjects. Several data abstraction forms were developed to collect historical and current exposure information and employees' work histories, starting in 1950. A retrospective exposure matrix was developed on the basis of facility/job title/calendar year combinations using available historical exposure information and current exposure profiles. Information on the amount of respirable, thoracic, and free silica content in total dust was used in estimating exposure to silica. Starting in 1950, 6,805 historical estimates had been carried out for 14 calendar-year periods. We estimated the average total dust concentration to be 9 mg/M3, with a range from 28 mg/M3 in earlier years to 3 mg/M3 in recent years. Several exposure indices [such as cumulative dust, average dust, cumulative respirable (< 5 mu in particle size) and thoracic (< 10 mu in particle size) silica dust, average respirable and thoracic silica dust, exposure-weighted duration, and the highest/longest exposure] were calculated for individuals by merging work history and historical exposure matrix for each study subject. We developed these various measures of exposure to allow investigators to compare and contrast different indices of historical exposure to silica.

Relation between exposure to respirable silica dust and silicosis in a tungsten mine in China.

To estimate the quantitative relation between exposure to respirable silica dust and risk of an attack of silicosis, 1151 workers exposed to silica dust and employed from 1958 to 1987 in a tungsten mine in China were investigated. The results showed that the ratio of respirable silica dust concentration to total silica dust concentration was 0.529. Then, the total silica dust concentration in historical surveillance and monitoring data was converted to respirable silica dust concentration. The free silica content in respirable dust determined by x ray diffraction averaged 24.7%. Multiple logistic regression was used for the dichotomous dependent variables (presence or absence of silicosis). The independent variables in the multiple logistic regression with presence of silicosis as the dependent variable were age when first exposed, tuberculosis (presence or absence), and cumulative exposure to respirable silica dust. The partial regression coefficient of individual cumulative exposure was estimated as 0.079. It implied a positive association between exposure to respirable silica dust and risk of an attack of silicosis. The exposure limit for respirable silica dust was estimated as 0.24 mg/m3 under given conditions.

Combined effect of silica dust exposure and tobacco smoking on the prevalence of respiratory impairments among gold miners.

The combined effect of underground gold mining dust with a high content of free silica and tobacco smoking on the prevalence of respiratory impairment was examined among 2209 South African gold miners and 483 nonminers. The subjects were grouped as having normal function; minimal, moderate or marked obstruction; marked obstruction with restriction; or pure restriction on the basis of their lung function profiles. Each profile group was compared with the normal group for exposure prevalences, and additive and multiplicative relative risk models were applied to test for departure from the additivity of individual effects. Departure from additivity was found to increase progressively with the severity of obstructive impairment. The results indicated that approximately 94% of the cases with the most severe respiratory impairment (N = 191) could have been prevented through the elimination of tobacco smoking. In conclusion, tobacco smoking was found to potentiate the effect of dust on respiratory impairments.

Characterization of airborne mineral dusts associated with farming activities in rural Alberta, Canada

The dry and windy climate of the Western Canadian prairie provinces, combined with large scale agricultural activities, results in aerosolization or organic and mineral dusts. The purpose of this study was to conduct an environmental and minerological analysis of these dusts in order to estimate the risk for pneumoconiosis in exposed farmer populations. Two districts in central/southern Alberta were chosen for study. One of these regions was representative of a predominantly grain growing district with minimal use of irrigation; the other region was largely devoted to forage and irrigated crop production. Air pollution statistics showed a bi-modal distribution of total suspended particulates (TSP) with peaks corresponding with maximal farm activities in the spring and early fall. Analysis of bulk dust samples obtained from tractor cab filters showed that the majority of particles from both districts were within the respirable range (less than 5 microns). Samples from the forage-crop region contained more organic material, a greater water soluble fraction and had particles that were, on average, smaller and rounder than particles from the grain district. These differences were thought to reflect differences in irrigation patterns and use of fertilizers between the two districts. Free silica (quartz) content was also very variable and ranged from 1 to 17% on a mass basis. Respirable fibrous minerals were occasionally identified, however, no asbestos fibres, fibrous tremolite, or fibrous zeolites were identified. The results indicate that there is potential risk for mineral dust pneumoconiosis in heavily exposed farmer populations and that this risk will be influenced by local and regional factors.

鋳造床フレームワーク研磨作業で飛散する粉塵に関する産業衛生学的研究

Dental laboratory work includes frequent cutting and polishing, which are always accompanied by scattering of dust. It is well known that microscopic particles are deposited in lung alveoli when inhalated for long periods, so that dentists and dental technicians may have their health affected by inhalation of dust.In a preliminary measurement of cutting dust from various laboratory procedures, I found that polishing cast framework for dentures caused the highest concentration of dust.Chromium-cobalt alloy is commonly used in denture framework. Cobalt exposure can cause interstitial pulmonary fibrosis, and chromium has cell toxicity and exerts corrosive action on mucous membranes.Therefore, I investigated dust from framework polishing from the viewpoint of occupational hygiene.Air samplings during work were performed with a low volume air sampler (flow rate 15 l/min.) at 7 dental laboratories in the Tokyo area, and personal exposure was measured with a size-selective personal dust sampler (flow rate 1.4-1.5 l/min.) which sorted dust particles 7 μm increments.Dust collected by both atmospheric air sampling and personal sampling was measured as dust concentration, and cobalt and chromium concentrations were measured with atomic absoption analysis and neutron activation analysis.The free silica and chromium content of the polishing materials were also analyzed.The following results were obtained:1. The atmospheric dust concentration in polishing workplaces was 0.07-0.26 mg/m3.2. Although a low atmospheric dust concentration was maintained in the workplaces, personaldust exposure was several times higher than the atmospheric dust concentration. The average dust exposure of dental technicians differed greatly according to working conditions, such as the type of work, working posture of the technician, and the use of a local exauster. In 13 cases of dental technicians who polished framework under the condition using local exaust systems, the average concentration of dust did not exceed the threshold limit value (JAIH) in any case, but 8 of 11 cases without local exaust systems exceeded the threshold limit value.3. The atmospheric cobalt concentration in polishing workplaces was from 0.001 to 0.016 mg/m3. Chromium concentration was from 0.001 to 0.008mg/m3.4. The average cobalt exposure of dental technicians was 0.1mg/m3, which ACGIH indicated as the TLV·TWA for cobalt, in 1 of 14 cases with local exaust systems, and more than 0.1mg/m3 in 3 of 10 cases without local exaust systems. Therefore, I suggest that cobalt exposure is hazardous to the health of dental technicians under some polishing conditions.5. The average chromium exposure of dental technicians was less than 0.5mg/m3, which ACGIH indicated as the TLV·TWA for chromium, independently of the use of a local exaust system.6. Free silica content was 11.3% in abrasive for sandblasting, and less than 5% in the other polishimg materials for cast framework.7. Cr2O3 was confirmed as a main component of“green polishing agents”by X-ray diffraction analysis, and buffing with“green polishing agents”caused a high degree of chromium exposure.

Influence of slag substitution on some properties of sand-lime aerated concrete

The effect of substitution of sand with granulated slag on some properties of sand-lime aerated concrete was investigated. The compressive strength, the hydration kinetics and the nature of the hydration products were studied for samples autoclaved under 8 atm for different periods from 0.5 to 24 h. The results indicate that the substitution of slag leads to a marked increase of the compressive strength compared with that of the unsubstituted samples. The extent of hydration, as measured by the chemically combined water, free lime and free silica contents, is enhanced due to the slag substitution. The X-ray diffraction results show that the hydration products are mainly tobermorite-like phases, C4AH13,C3AH6 and CAH10 in the slag-containing samples. Cement notations are used in the text, e.g. C=CaO, S=SiO2, A=Al2O3 and H=H2O.

Evaluation of physical health effects due to volcanic hazards: human studies.

Despite certain gaps in the knowledge that has been gained from the studies done in the aftermath of Mount St. Helens and following previous major volcanic eruptions, we can be confident that the health effects of both short- and long-term exposures to the relatively low levels of airborne volcanic ash that are typical following such a volcanic eruption are minor. These effects seem to relate more to the irritating effect of the ash on mucous membranes and airway epithelia than to the potential of the ash (due to its free crystalline silica content) to initiate a fibrotic response. Nevertheless, common sense dictates that exposures should be minimized whenever possible by use of appropriate preventive measures, such as wetting the sedimented ash before disturbing it, and using commercially available disposable paper masks meeting NIOSH code TC-23 for dusts for light exposures and industrial half- and full-faced respirator and goggles for more extensive and heavy exposure.

A critique of MSHA procedures for determination of permissible respirable coal mine dust containing free silica.

The literature in selected technical subject areas related to the Mine Safety and Health Administration's (MSHA) respirable mine dust control policy was critically reviewed. Specific topics included: (1) the technical aspects of respirable dust sampling, (2) the development of a sampling strategy and (3) currently used analytical techniques for free silica content of respirable coal mine dust. The 2.0 Lpm MSHA respirable dust sampling flow rate does not conform with published results which indicate that to simulate existing pulmonary particle deposition models, the sampling flow rate should range from 1.4 to 1.7 Lpm. MSHA's sampling strategy focuses on controlling respirable coal mine dust with both area and personal samples of workers in selected occupations or activities. Many uncertainties are encountered as area samples are used to estimate personal exposures. Although all of the analytical methods for crystalline free silica are sufficiently sensitive to be able to detect and quantitate free silica at environmentally significant concentrations, they are all plagued with similar difficulties. Analytical standards representing the various forms of silica are not available. Available analytical methods do not differentiate among polymorphs of silica. Recommendations are presented to resolve identified problem areas.

リン酸法による作業環境空気浮遊粉じんの遊離ケイ酸測定方法

Free silica content in airborne dust was measured with a modified procedure collecting sample dust on glass fiber filter and heating the dust together with the filter in phosphoric acid. The insoluble phosphoric acid residue of the glass fiber filter used by us was of small amount. Fifteen mg of dust was enough to determine its free silica content correctly.On dust collected at pottery and foundries works, satisfactory coincidence was found between the values of free silica content by our procedure and by X-ray diffraction. It can be concluded that this is a reliable method for determination of free silica content of airborne dust as well as of deposited one.

Mineralogic Information from a New Airborne Thermal Infrared Multispectral Scanner

A new six-channel aircraft multispectral scanner has been developed to exploit mineral signature information at wavelengths between 8 and 12 micrometers. Preliminary results show that igneous rock units can be identified from their free silica content, and that carbonate as well as clay-bearing units are readily separable on the digitally processed images.

AN EPIDEMIOLOGICAL-INDUSTRIAL HYGIENE STUDY OF TALC WORKERS

Abstract Two-hundred and ninety-nine (299) miners and millers exposed to talc from Montana, Texas and North Carolina were examined in a cross-sectional study of respiratory systems, lung function and chest X-rays. Work histories were taken from personnel records. Personal respirable dust samples were collected for all jobs. Cumulative exposure was calculated by summing the products of the estimated exposure for each job and the length of time worked in that job. The average time worked was 7, 6, and 10 yr and the average exposure (cumulative exposure/total time worked) was 1.2,2.6, and 0.3 mg m~3 in Montana, Texas, and North Carolina respectively. Free silica content of bulk samples was low (below the limit of detection in Montana, 1.5% in North Carolina, and 2.2% in Texas). No fibres were observed under the light microscope. Under the transmission electron microscope, tremolite and antigorite fibres (0.5-3 μm length) were observed on the Texas talc, acicular particles (aspect ratios 5-100 to 1 and some diameters less than 0.1 jum) in North Carolina talc, and no fibres in the Montana talc. The differences in age-corrected symptom prevalences (cough, phlegm, and dyspnea) between regions, when compared by both smoking categories and exposure groups were not statistically significant. None of the symptoms showed any consistent association with years worked or cumulative exposure. Symptom prevalence was not elevated compared with blue collar workers and potash miners. There were two cases (less than 1 %) of grade 1 small rounded opacities. The prevalence of bilateral pleural thickening among workers 40 yr or older was 7,16, and 14% in Montana, Texas, and North Carolina, and 0, 0, and 10% in those less than 40 yr of age. No non-smoker had bilateral pleural thickening and there was a slight tendency for the prevalence to increase with exposure. Workers with bilateral pleural thickening had lung function 10-20% below workers with no pleural thickening. They had also worked twice as long (13 yr) and an average of 13 yr between beginning exposure to talc and the time of the X-ray. The prevalence of bilateral pleural thickening was elevated in workers 40 yr or older compared with blue collar workers and potash miners. There also were no demonstrated differences in prevalence when the subjects in this study were compared with workers exposed to New York talc which contains tremolite and anthophyllite. For the entire study population no association of reduced lung function with exposure was demonstrated. After adjustments for age, height, and smoking, FEVi and FVC were not detectably different compared with potash miners and blue collar workers; however, flow rates at low lung volumes were' reduced 4-19%. There was little difference among these three populations in age coefficients for FEVX, FVC, and flow rates by smoking category. Predicted pulmonary function of the study population was elevated compared with New York talc workers. There were no significant increases in symptoms or pneumoconiosis among the study group of talc workers nor significant reductions in lung function; however, the average amount of time worked by the study group was short. Bilateral pleural thickening was significantly increased and was associated with decreased pulmonary function. The prognostic significance of the pleural thickening awaits prospective evaluation.

Evaluation of occupational exposure to free silica in Alberta foundries.

The Occupational Hygiene Branch of Alberta Workers' Health, Safety and Compensation conducted a comprehensive study of the foundry industry in Alberta. The surveys assessed both the degree of health hazards present and the effectiveness of existing control systems for airborne contaminants. All nine of Alberta's ferrous foundries were surveyed in the course of the project. The foundries varied from those which were small with limited mechanization to those which were large and highly automated. The concentrations of free silica in the work environment are correlated to the different attempts to control silica using substitution and various ventilation systems. The particular foundry processes evaluated for airborne free silica were sand preparation, shakeout, dry sand transport and sand molding. Workers' exposure to free airborne silica was evaluated by personal and area samples. The free silica content of the samples was determined by infra-red spectrophotometry. The results indicated most control systems were inadequate. Effective control methods are described to reduce the health hazard.

Evaluation of occupational exposure to free silica in Alberta foundries

The Occupational Hygiene Branch of Alberta Workers' Health, Safety and Compensation conducted a comprehensive study of the foundry industry in Alberta. The surveys assessed both the degree of health hazards present and the effectiveness of existing control systems for airborne contaminants. All nine of Alberta's ferrous foundries were surveyed in the course of the project. The foundries varied from those which were small with limited mechanization to those which were large and highly automated. The concentrations of free silica in the work environment are correlated to the different attempts to control silica using substitution and various ventilation systems. The particular foundry processes evaluated for airborne free silica were sand preparation, shakeout, dry sand transport and sand molding. Workers' exposure to free airborne silica was evaluated by personal and area samples. The free silica content of the samples was determined by infra-red spectrophotometry. The results indicated most control systems were inadequate. Effective control methods are described to reduce the health hazard.

Analytical methods applied to Portland, Oregon, volcanic ash analysis

The volcanic ash from Mt. St. Helens has, so far, reached Portland, Oregon in three eruptions: May 24–25, 1980; June 12–13, 1980; and October 16–17, 1980. Integrated ash fall samples were collected in a downtown Portland location. The particle-size distribution was determined by dry-sieving. The analysis for crystalline free silica on the respirable and near-respirable fractions of the ash was performed. All ash samples had been pretreated with phosphoric acid to remove silicate interferences and were then analyzed by x-ray diffraction for crystalline silicas. The residue after acid treatment was also examined using optical methods to increase certainty of the free silica identification. The total crystalline free silica content was determined by the Talvitie (colorimetric) method. The colorimetric method was then applied to occupational exposure samples of Portland-area maintenance personnel.

Fibrogenic potential of slags used as substitutes for sand in abrasive blasting operations.

The fibrogenic potentials of coal and copper slags used as substitutes for silica sand in abrasive blasting operations were assessed in rats. The test animals were given a single pulmonary intralobar instillation of 20 mg of test material and were sacrificed 10 months after dosing. Pulmonary fibrosis was seen in the coal slag-treated rats while no fibrosis was seen in the copper slag-treated animals. Granulomas were seen in the lungs from all treatment groups. The results of the study emphasize the need for bioassay of silica sand replacements for fibrogenic potential in spite of the low free silica contents of these materials.

Radiometric assessment of abrasiveness of coal in pulverizers

A laboratory method is described for the measurement under water, of the abrasiveness of a coal as it affects wear in pulverizers. The coal is ground by a rotating blade containing radioactive material. The determination of the level of radioactivity on the ground material provides an indication of the amount of material abraded from the blade. A coal which caused excessive wear in commercial grinding in a pin-disc mill gave an extremely high ‘abrasive index’ when subjected to this laboratory test. Abrasive indices have been determined for a series of New Zealand coals. High values correlate with increased ash level, with a high silica-to-alumina ratio in the ash and especially with a high free-silica content of the coal.

The relation of silica dust to accelerated silicosis

More than 130 cases of silicosis among sandblasters with an average exposure to free silica of 10 years have been studied in Louisiana. The mortality was approximately 25%. Examination of 180 gravimetric respirable dust samples from the breathing zones of sandblasters and other associated workers in two steel fabrication yards showed extensive dust exposure (up to 42.8 times the threshold limit value). The silica fraction of the respirable dust was determined either by X-ray diffraction or by a modified colorimetric technique based on that of Talvitie and Hyslop ( Amer. Indust. Hyg. Assoc. J. 19, 54–58, 1958). Sandblasters wearing non-air-supplied defective hoods were at the greatest risk. Their exposure to silica dust varied greatly depending on the type of hood, maintenance, proper fit, and atmospheric dust concentrations during nonblasting periods when they were unhooded. The development of so-called accelerated silicosis is related to ordinary and faulty characteristics of sandblasting: high free-silica content of sand, use of inadequate or faulty protective devices, carelessness, and incomplete safety training.