Relationship of pulmonary impairment in simple coal workers'' pneumoconiosis to type of radiographic opacity

Seaton, A., Lapp, N. L., and Morgan, W. K. C. (1972).Brit. J. industr. Med.,29, 50-55. Relationship of pulmonary impairment in simple coal workers' pneumoconiosis to type of radiographic opacity. From a group of 1 461 working coal miners who participated in an epidemiological study, 223 men with simple pneumoconiosis were selected on the basis of the type of small rounded opacity noted to be present in their chest films. No differences in spirometry or lung volumes were found between those with the micronodular (q) and those with pinhead (p) opacities. Twenty-five non-smoking miners with category 2 or 3 simple coal workers' pneumoconiosis were subsequently selected for further pulmonary function testing. Studies of lung volumes and pulmonary mechanics showed no difference between those with the pinhead and micronodular types of opacity; however, transfer factor was somewhat lower in those with the former.     

Life Expectancy of Pennsylvania Coal Miners Compensated for Disability

From December 1965 through December 1967, 13,000 Pennsylvania coal miners were awarded compensation for complete disability due to coal workers’ pneumoconiosis (CWP). Standardized mortality ratios compare all deaths occurring in a sample of 4,004 of these men with deaths expected (1959 to 1961) of white men in Pennsylvania; similar ratios are shown for anthracite and bituminous miners by category and stage of CWP and, in some cases, according to whether the ratio of forced expiratory volume during the first second of a forced exhalation after maximum inhalation to vital capacity (FEV₁/FVC) was greater or less than 55%. Excess deaths were found primarily in subjects with a reduced ventilatory capacity, and secondarily with complicated CWP of stage C or, for anthracite miners, stage B. No excess deaths were found for simple CWP or stage A complicated with FEV₁/FVC more than 55%.     

Histocompatibility antigens in coal miners with pneumoconiosis.

Twenty-five histocompatibility antigens have been measured in 100 coal miners with pneumoconiosis attending a pneumoconiosis medical panel and the results compared with a panel of 200 normal volunteers not exposed to dust. Chest radiographs were read independently by three readers according to the ILO U/C classification. On a combined score, 40 men were thought to have simple pneumoconiosis and 60 men complicated pneumoconiosis. The number of antigens tested and associations between antigens caused difficulties in assessing the statistical significance of differences in prevalence of antigens between groups of men. Using stringent criteria for statistical significance, no significant differences were found in antigen prevalences between miners and controls, or miners with simple or complicated pneumoconiosis. When a less stringent statistical approach was applied, three antigens appeared to have abnormal prevalences in these 100 miners by comparison with the normal volunteers. More detailed examination of these antigen prevalences in relation to radiographic category of pneumoconiosis did not provide any supportive evidence that these slight associations were of statistical or clinical significance. Reports on histocompatibility antigens in miners with pneumoconiosis are reviewed briefly and the results compared. There is no good evidence that any of the histocompatibility antigens so far tested are associated with a clinically important altered risk of simple or complicated pneumoconiosis when dust is inhaled.     

Histocompatibility antigens in coal miners with pneumoconiosis

Twenty-five histocompatibility antigens have been measured in 100 coal miners with pneumoconiosis attending a pneumoconiosis medical panel and the results compared with a panel of 200 normal volunteers not exposed to dust. Chest radiographs were read independently by three readers according to the ILO U/C classification. On a combined score, 40 men were thought to have simple pneumoconiosis and 60 men complicated pneumoconiosis. The number of antigens tested and associations between antigens caused difficulties in assessing the statistical significance of differences in prevalence of antigens between groups of men. Using stringent criteria for statistical significance, no significant differences were found in antigen prevalences between miners and controls, or miners with simple or complicated pneumoconiosis. When a less stringent statistical approach was applied, three antigens appeared to have abnormal prevalences in these 100 miners by comparison with the normal volunteers. More detailed examination of these antigen prevalences in relation to radiographic category of pneumoconiosis did not provide any supportive evidence that these slight associations were of statistical or clinical significance. Reports on histocompatibility antigens in miners with pneumoconiosis are reviewed briefly and the results compared. There is no good evidence that any of the histocompatibility antigens so far tested are associated with a clinically important altered risk of simple or complicated pneumoconiosis when dust is inhaled.     

Changes in Ventilatory Function in Coal Miners After a Work Shift

Ninety-three coal miners and 42 nonminers underwent studies of ventilatory capacity before and after a work shift. Small, but significant, decreases in ventilatory capacity occurred among the miners; in contrast, significant increases in ventilatory capacity occurred among the nonminers. These decreases in the miners were most evident in the expiratory flow at low lung volumes, viz, forced expiratory flow at 75% of the vital capacity exhaled. Proportionately greater decreases in expiratory flow at low lung volumes occurred in men exposed to the higher dust levels. Degree and extent of exposure to coal mine dust is the most likely explanation for these findings; however, other factors peculiar to the miners’ working environment cannot be definitely excluded from consideration.     

Relation between content and composition of coalworkers'' lungs and radiological appearances

Rossiter, C. E. (1972).Brit. J. industr. Med.,29, 31-44. Relation between content and composition of coalworkers' lungs and radiological appearances. The relation between radiological category of simple pneumoconiosis and dust content of the lung has been studied on a mixed group of 221 miners, of whom 76 had progressive massive fibrosis radiologically.

The average radiological scores based on 11 independent readings for the films showing simple pneumoconiosis only were related, by multiple regression, to the coal, mineral, quartz, and iron contents of the lungs. Three subgroups were found which showed differing relations. Films of poor technique tended to be read in the middle categories whatever the content of the lungs. The lungs of Scottish miners all contained soot, from working in naked light pits, and their radiological scores were much higher than expected from the lung dust contents. The few films showing nodular sized small opacities were also over-read, suggesting that nodularity may be some response to dust other than simple accumulation. There were 98 subjects in the resulting homogeneous group of cases with simple pneumoconiosis only. On a revised scale to correct for slight non-linearity, the regression coefficients of radiological score on the total mineral and coal contents of the lung were in the ratio of 3·8 to 1. The iron content did not add much to this regression relation even though by itself it correlated well with the amount of simple pneumoconiosis. Probably most of the variation of radiological appearance with iron reflects variation with coal and mineral. The mineral and quartz contents were highly correlated (r = 0·96), but relations including quartz were not as close fitting as those including mineral. There was a small, but significant, residual relation of radiological score to years in coalmining.

The background categories of simple pneumoconiosis in the 76 radiographs showing some evidence of progressive massive fibrosis were generally read higher than expected from the relation to dust content derived from the simple pneumoconiosis cases only. This was most true for those showing most evidence of progressive massive fibrosis.

     

Respiratory Status of Surface Coal Miners in the United States

The United States Public Health Service examined 1,438 surface coal miners to determine the prevalence of coal worker’s pneumoconiosis (CWP), chronic bronchitis, and ventilatory impairment among them. Four percent (fifty-nine individuals) showed some roentgenographic evidence of pneumoconiosis, but only seven miners had films interpreted as CWP of category2 or greater (according to the UlCC/Cincinnati classification system). Moreover, most of the affected miners had worked in underground coal mines for prolonged periods. Significant decrements in pulmonary function to increasing exposure to surface mine dust were demonstrated only in the forced vital capacity of smokers. Increased prevalence of chronic bronchitis with increasing exposure was found in all smoking categories. However, significant airway obstruction was an uncommon finding (6.6%) in nonsmoking miners. Employment in surface mining was not likely to cause either the development of CWP or clinically significant respiratory impairment.     

煤工尘肺并发肺癌患者C-erbB-2基因表达的研究

目的　检测C erbB 2癌基因在煤工尘肺并发肺癌患者的表达与单纯肺癌患者的差异及与临床病理的关系。方法　采用免疫组织化学方法分别检测 32例煤工尘肺并发肺癌者及 30例单纯肺癌者的C erbB 2表达。结果　煤工尘肺肺癌组患者C erbB 2阳性表达率为 5 3.13% ,单纯肺癌组患者C erbB 2阳性表达率为 2 6 .6 7% ,差异有显著性 (P <0 .0 5 ) ;两组中有淋巴结转移者C erbB 2阳性表达率 (尘肺组 70 .5 9%、单纯肺癌组 5 0 .0 0 % )与无淋巴结转移者 (尘肺组 33.33%、单纯肺癌组 11.11% )的差异有显著性 (P <0 .0 5 ) ;C erbB 2阳性表达者预后差 ,与病理组织学类型无关。结论　C erbB 2是煤工尘肺并发肺癌的重要的调控基因之一 ,可作为判断有无淋巴结转移及预后的参考指标。     

Dust concentrations and respiratory risks in coalminers: key risk estimates from the British Pneumoconiosis Field Research

To help inform the setting of dust control standards in coalmines, this brief review summarises the most recent and reliable exposure-response relations, for damaging respiratory effects, derived from the Pneumoconiosis Field Research (PFR). Collecting data over 38 years in the British coal industry, this was a programme of prospective research on the respiratory health of coal miners, characterised by regular health surveys and detailed measurements of dust and silica concentrations in the workplace. Exposure-response relations are presented for coal workers' simple pneumoconiosis category II, progressive massive fibrosis, defined deficits of lung function (FEV₁), and category II silicosis. This simplified overview provides a guide to the most recent and most reliable estimates from the PFR of dust-related risks of substantial pulmonary disease, and to the magnitude of the effects. Control of dust sufficient to prevent category II simple pneumoconiosis should prevent most cases of progressive massive fibrosis and most dust related large lung function deficits. Where the dust contains high proportions of silica, control to low levels is essential, and even quite brief excursions of silica to high levels must be avoided.     

CT和高分辨CT对煤工尘肺小阴影和阴影融合及肺气肿诊断的价值

目的 探讨CT和高分辨CT(HRCT)早期检测煤工尘肺小阴影、阴影融合与肺气肿的敏感性和准确性.方法 77例煤工尘肺患者、36例无尘肺煤工和37例健康非煤工接受多层螺旋CT机无间隔胸部容积扫描及HRCT扫描,对所获得的CT图像进行煤工尘肺小阴影密集度分级、平均肺密度值和肺气肿指数测定,并与其X线胸片诊断结果对照.结果 对77例煤工尘肺患者CT和HRCT诊断的尘肺小阴影密集度分级与X线胸片尘肺分期一致性较好(Kappa=0.771,P＜0.01).CT和HRCT诊断尘肺的敏感性达到98.70％,在X线胸片确诊的77例煤工尘肺患者中,CT和HRCT评估76例为煤工尘肺,可疑1例.CT和HRCT从36例X线胸片无尘肺煤工中检出8例(22.22％)达到小阴影密集度1级;从73例Ⅰ～Ⅱ期煤工尘肺患者中,检出26例(35.62％)阴影密集度≥3级,其中3级密集度阴影20例,4级密集度阴影6例;对4例X线胸片Ⅲ期煤工尘肺患者,CT和HRCT与X线胸片诊断结果相同.从113例煤工中,X线胸片检出肺气肿7例(6.19％),CT检出36例(31.86％).CT尘肺小阴影密集度1～2级组的CT平均肺密度值最高,明显高于健康对照组、无尘肺组和小阴影密集度4级组,差异有统计学意义(F1=-45.73、F2=-23.00和F3=57.72,P＜0.01或P＜0.05).结论 从多层螺旋CT获得的CT和HRCT影像,与X线胸片比较,对煤工尘肺小阴影、阴影融合与肺气肿识别的敏感性和准确性均较高,可为煤工尘肺及其并发症的早期诊断提供更先进的手段.     

Role of dust in the working environment in development of chronic bronchitis in British coal miners

Rogan, J. M., Attfield, M. D., Jacobsen, M., Rae, S., Walker, D. D., and Walton, W. H. (1973).British Journal of Industrial Medicine, 30, 217-226. Role of dust in the working environment in development of chronic bronchitis in British coal miners. In the course of a long-term prospective study of chronic respiratory disease in British coal miners the effects on pulmonary ventilatory function of exposure to airborne dust, of simple pneumoconiosis, and of chronic bronchitis have been examined in a group of 3581 coalface workers.

The men were employed in 20 collieries throughout the British coalfields. Their cumulative exposures to coal mine dust in the respirable range (1-5 μm) were calculated from detailed dust sampling results at their work places during a 10-year period and from estimates of earlier exposures based on records of their industrial histories.

A progressive reduction in FEV_1·0 with increasing cumulative exposure to airborne dust has been demonstrated. This effect was evident also in a subgroup of the men studied who reported no signs of mild bronchitic symptoms (cough and phlegm for at least three months in a year).

Among men with pneumoconiosis there was no evidence of a reduction of FEV_1·0 in excess of that attributable to their dust exposures, smoking habits, age, and physique.

Increasing severity of bronchitic symptoms was associated with a loss in FEV_1·0 greater than that expected from the effects of dust exposure as measured, smoking, age, and physique. Possible explanations for this phenomenon are discussed. It is suggested that the results may indicate that once early bronchitic symptoms are present the disease may progress and ventilatory capacity may deteriorate independently of factors initiating the disease process.

     

The Attack Rate of Progressive Massive Fibrosis

A radiological follow-up of the miners and ex-miners in two Welsh mining valleys whose chest radiographs showed simple pneumoconiosis in 1950/51 has been carried out to study the factors associated with the attack rate of progressive massive fibrosis. The radiographs were read in pairs, and also with the pairs separated, the radiographs being randomized and identifying features concealed. The relative value of these two types of reading is discussed.

An attempt to investigate the importance of exogenous tuberculous infection by comparing the attack rate in the two mining valleys, in one of which great efforts had been made to eradicate tuberculosis, failed. The reasons for the failure are discussed.

No evidence was found of any association between the attack rate of progressive massive fibrosis and age, energy expenditure at work, smoking habits, body type, exogenous tuberculous infection, or endogenous infection as measured by the presence of primary complexes in the first radiographs. The only factor related to the attack rate was the average category of simple pneumoconiosis. The attack rate is zero at category ½ and rises to 30 or more per 100 in eight years for category 3. It is argued from this that the logical way to control the appearance of progressive massive fibrosis is to concentrate on preventing miners reaching category 2 of simple pneumoconiosis. Evidence is also presented that considerable progression of simple pneumoconiosis has been occurring during the past eight years amongst coal-face workers at the collieries in this area.

     

Airways obstruction, coal mining, and disability.

It has recently been suggested that the inhalation of coal in the absence of complicated coal workers' pneumoconiosis (CWP) or smoking can lead to disabling airways obstruction. The cause of such obstruction has been variously attributed to emphysema or bronchitis. The frequency of significant airways obstruction in a group of United States coal miners seeking compensation for occupationally induced pulmonary impairment was therefore determined. In a sample of 611 "Black Lung" claimants there was only one subject who was a non-smoker and who in the absence of other non-occupationally related diseases,--for example, asthma and bronchiectasis--had sufficient airways obstruction to render it difficult for him to carry out hard labour. An alternative explanation for his reduced ventilatory capacity other than coal dust or smoking may be available. If the inhalation of coal dust in the absence of smoking and complicated CWP ever induces sufficient ventilatory impairment to preclude a miner from working, it is indeed rare.     

Does Coal Workers Pneumoconiosis Predict to Lung Cancer? Some Evidence from a Case-Control Study

Previous reports on the relationship between coal workers' pneumoconiosis(CWP) and lung cancer mortality have shown widely differingresults. Concern has centred especially around whether or notthere is an aggregation of complicated CWP, or Progressive MassiveFibrosis (PMF), with lung cancer. This paper evaluates, amongUS coal miners, the CWP-lung cancer relationship by computingthe lung cancer mortality risk of simple and complicated CWPas well as the interactions with cigarette smoking and ventilatoryfunction. Two case-control studies based on 317 white male lungcancer mortality cases are presented. A one-to-one matched-casedesign allows examination of the lung cancer mortality riskof CWP and cigarette smoking. A two-to-one matched-case designcontrols on smoking status. Based upon these data, no evidenceof a CWP-lung cancer risk was found, although the expected increasedrisk for lung cancer mortality in cigarette smokers was observed.No relationship was found between PMF and lung cancer mortalityrisk. Finally, no evidence was found of interaction effectsbetween cigarette smoking or ventilatory function and CWP aspredictors of lung cancer mortality risk. Requests for reprints should be addressed to: R. G. Ames, Appalachian Laboratory, US National Institute for Occupational Safety and Health, 944 Chestnut Ridge Road, Morgantown, West Virginia 26505, USA.     

Respiratory impairments due to dust exposure: A comparative study among workers exposed to silica,asbestos, and coalmine dust

We conducted a comparative study of pulmonary dysfunction among workers who were exposed to silica, asbestos, or coalmine dust. The results showed that all three groups of dust-exposed workers, even those without radiographic signs of pneumoconiosis, had decreased spirometric parameters and diffusing capacity (DLco) in both nonsmokers and smokers. Pulmonary function was further decreased when pneumoconioses were present in the three groups. In accord with increasing radiographic categories, pulmonary function in the workers' pneumoconiosis (CWP), it changed relatively little. Workers with mild to moderate (radiographic category I–II) silicosis or asbestosis showed similarly decreased DLco, but those with silicosis showed lower FEV₁/FVC than those with asbestosis. The workers with CWP also showed a lower FEV₁/FVC than those with asbestosis. The major impairment patterns for silica workers, asbestos workers, and coal miners were mixed, restrictive and mixed, and obstructive, respectively. Smoking obviously increased the prevalence of obstruction for all the groups. We conclude from the present study that all the three dusts cause functional abnormalities that precede radiographic changes of pneumoconiosis. We should pay more attention to respiratory impairment in the initial stage of silicosis and CWP. Am. J. Ind. Med. 31:495–502, 1997. © 1997 Wiley-Liss, Inc.     

Presence of Stable Coal Radicals in Autopsied Coal Miners' Lungs and Its Possible Correlation to Coal Workers' Pneumoconiosis

Stable coal radicals (SCRs) were detected by electron spin resonance (ESR) spectroscopy in the lung tissue of autopsied coal miners. The SCR concentrations were measured in the lung tissues from 98 coal miners with and without (a) coal workers' pneumoconiosis (CWP), (b) cancer, and (c) a history of cigarette smoking. Concentrations of SCRs were also determined in the lungs of nonminer controls. The SCR concentration was related to longer mining tenure, CWP disease severity, lung cancer, and cigarette smoking. The mean concentration of SCRs in the lung tissues of miners with 30 ± 1.4 y of coal mining exposure was 5.3 ± 1.3 × 10¹⁷ spins/g versus controls who had a nondetectable level (< 10¹⁵ spins/g). An increase in disease severity was accompanied by a progressive increase in SCR concentration. A SCR concentration of 4.8 ± 0.7 × 10¹⁷ spins/g was found for simple CWP (with moderate coal macules) versus 7.8 ± 4.6 spins/g lung tissue for complicated CWP (with progressive massive fibrosis). Significantly higher (i.e., 10 × 10¹⁷) concentrations of SCR in the coal miners' lung tissues were associated with an exposure history in the anthracite regions of northeastern Pennsylvania. These results indicate a possible role for SCRs in the disease process. Furthermore, ESR appears to be an adequate methodology for the quantitation of coal dust retained in the lung and for distinguishing exposures to anthracite and/or bituminous coal.     

Surveillance data on US coal miners'' pneumoconiosis, 1970 to 1986.

OBJECTIVES. Statistics on prevalence of pneumoconiosis among working underground coal miners from data collected as part of a large national radiographic surveillance program between 1970 and 1986 are presented. The main intent was to examine the time-related trend in prevalence over this period, which coincides with historically low dust levels mandated by federal act. METHODS. Tenure-specific prevalence rates and summary statistics derived from them for four consecutive time intervals within the 16-year period were calculated and compared. RESULTS. The results indicate a reduction in pneumoconiosis over the life of the program. This trend is similar to that seen in epidemiologic studies undertaken concurrently. CONCLUSIONS. Although low participation in the surveillance program and other problems complicate the findings, it appears that reductions in dust exposure mandated by federal act in 1969 have led to lower prevalence of pneumoconiosis among underground coal miners.     

A cross sectional study of the independent effect of occupation on lung function in British coal miners.

BACKGROUND: Chronic bronchitis and emphysema are now recognised complications of occupational exposure to coal dust, and since 1992 compensation has been available for miners with impaired lung function provided that they also have x ray film evidence of pneumoconiosis. However, many miners with heavy exposure to coal dust and impairment of lung function therefore do not qualify for compensation because they do not have simple pneumoconiosis. In the present study attempts were made to determine whether coal mining is an independent risk factor for impairment of lung function in a group of Nottinghamshire miners with no evidence of simple pneumoconiosis, by comparing these men with a group of local controls who were not occupationally exposed. METHOD: Forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were obtained on 1286 miners with no evidence of pneumoconiosis on x ray film. Lung function data were also obtained from a random sample of 567 men aged between 40 and 70 living in a district of Nottingham and who had never worked in the mining industry or in any other dusty occupation. Multiple linear regression in SPSS was used to estimate the mean independent effect of mining on FEV1 and FVC after adjustment for age, height, and smoking, in all miners and controls, and in a subgroup of men of 45 and under. In men of 45 and under, the independent effects of mining and smoking on the probability of a deficit of one litre or more from modelled predicted FEV1 values were computed with logistic regression in EGRET. RESULTS: There was a significant mean effect of mining on FEV1 after adjustment for age, height, and smoking of -155 ml (95% confidence interval (95% CI) -74 to -236 ml, P < 0.001), but the size of effect was inversely related to age such that in men of 45 and under the estimated mean effect of mining was -251 ml (95% CI -140 to -361 ml, P < 0.001). In this subgroup of younger men, 4.7% of miners and 0.7% of controls had a deficit of one litre or more from predicted FEV1 values, and in logistic regression, there was a marginally significant independent effect of both smoking (P = 0.05) and mining (P = 0.07) for a deficit of this magnitude. CONCLUSIONS: Occupational exposure to coal dust is associated with a small mean deficit in lung function even in the absence of simple pneumoconiosis, and independently from the effects of smoking. The requirement that miners should have evidence of pneumoconiosis to qualify for compensation for impaired lung function is therefore unjustified.     

Pneumoconiosis and advanced occupational lung disease among surface coal miners--16 states, 2010-2011

Coal workers' pneumoconiosis (CWP) is a chronic occupational lung disease caused by long-term inhalation of dust, which triggers inflammation of the alveoli, eventually resulting in irreversible lung damage. CWP ranges in severity from simple to advanced; the most severe form is progressive massive fibrosis (PMF). Advanced CWP is debilitating and often fatal. To prevent CWP, the Coal Mine Health and Safety Act of 1969 established the current federal exposure limit for respirable dust in underground and surface coal mines. The Act also established a surveillance system for assessing prevalence of pneumoconiosis among underground coal miners, but this surveillance does not extend to surface coal miners. With enforcement of the exposure limit, the prevalence of CWP among underground coal miners declined from 11.2% during 1970-1974 to 2.0% during 1995-1999, before increasing unexpectedly in the last decade, particularly in Central Appalachia. Exposure to respirable dust is thought to be less in surface than underground coal miners. Although they comprise 48% of the coal mining workforce, surface coal miners have not been studied since 2002. To assess the prevalence, severity, and geographic distribution of pneumoconiosis among current surface coal miners, CDC obtained chest radiographs of 2,328 miners during 2010-2011 through the Coal Workers' Health Surveillance Program of the National Institute for Occupational Safety and Health (NIOSH). Forty-six (2.0%) of 2,257 miners with >1 year of surface mining experience had CWP, including 37 who had never worked underground. Twelve (0.5%) had PMF, including nine who had never worked underground. A high proportion of the radiographs suggested silicosis, a disease caused by inhalation of crystalline silica. Surface coal mine operators should monitor worker exposures closely to ensure that both respirable dust and silica are below recommended levels to prevent CWP. Clinicians should be aware of the risk for advanced pneumoconiosis among surface coal miners, in addition to underground coal miners, to facilitate prompt disease identification and intervention.     

Exposure-response analysis of mortality among coal miners in the United States

The quantitative relationship between exposure to respirable coal mine dust and mortality from nonmalignant respiratory diseases was investigated in a study of 8,878 working male coal miners who were medically examined from 1969 to 1971 and followed to 1979. Exposure-related mortality was evaluated using Cox proportional hazards modeling for underlying or contributing causes of death and modified lifetable methods for underlying causes. For pneumoconiosis mortality, the lifetable analyses showed increasing standardized mortality ratios (SMRs) with increasing cumulative exposure category. Significant exposure-response relationships for mortality from pneumoconiosis (P < 0.001) and from chronic bronchitis or emphysema (P < 0.05) were observed in the proportional hazards models after controlling for age and smoking. No exposure-related increases in lung cancer or stomach cancer were observed. Pneumo coniosis mortality was found to vary significantly by the rank of coal dust to which miners were exposed. Miners exposed at or below the current U.S. coal dust standard of 2 mg/m³ over a working lifetime, based on these analyses, have an elevated risk of dying from pneumoconiosis or from chronic bronchitis or emphysema.