NIOSH Programs > Respiratory Diseases > Evidence Package > 4. Airways Diseases > 4.2 Obstructive Airways Disease
4.2a) Establishing the Work-relatedness of COPD4.2 Obstructive Airways Disease | 4.2b) Assess the Extent, Severity, and Burden of Work-Related COPD and Identify Industries, Occupations, and Occupational Exposures Associated with Potential High-Risk of COPD
In 1966, the British Medical Research Council issued a report of a select committee which concluded that occupationally-induced bronchitis did not play a significant part in the etiology of airways obstruction in dust-exposed men.130 In the U.S., an editorial on black lung benefits stated, “Disability, even when it exists, is rarely caused by coal particles alone, but is usually the result of other factors (italics added) such as cigarette smoking . . . .”131 Yet today the occupational-relatedness of COPD is well accepted (1, A4-50).132
RDRP research findings on coal miners (chapter 3.1a) played a large role in this major change in opinion. RDRP included one of the first concerted efforts to systematically examine COPD-related health outcomes in the occupational setting, using quantitative measures of workplace dust exposure. As such, it provided much novel information and, owing to the high technical standards and large population size, also provided information of high quality and reliability. For this reason, the findings have been relied upon heavily in debates on the work-relatedness of COPD.
Although a primary focus of RDRP’s research on coal miners was CWP, another major objective was assessment of COPD-related health outcomes, based on respiratory symptoms and lung function measurement, and their relationship with coal mine dust exposures. This research was undertaken in a large industry-wide epidemiologic study, the National Study of Coal Workers’ Pneumoconiosis (NSCWP), initially involving over 9,000 coal miners studied in 30 mines.
At first the focus of the research was on assessment of exposure-response based on cross-sectional and longitudinal analysis. In this, quantitative measures of dust exposure were related to absolute indices of pulmonary function or to pulmonary function declines derived from differences in absolute measurements undertaken serially over a number of years. Further research looked at patterns in pulmonary function change, particularly after starting work in mining, and related to ex-miners as well as current miners.
Later, from 1996 onwards, the RDRP focus on coal miners turned to identifying and assessing occupational and non-occupational risk factors for excessive declines in lung function and their implications for future health and mortality. In these, the data from the NSCWP were supplemented by information collected in other studies tailored to the specific hypotheses.
Laboratory studies also contributed to the body of knowledge on mechanisms and burden of disease. The largest part of these involved pathological examinations using data collected by the National Coal Workers’ Autopsy Program, but also included toxicological, physiologic, and clinical studies.
Outputs and Transfer
RDRP scientists published 17 scientific publications on epidemiologic investigations of COPD-related outcomes among coal miners. One of these described an exposure-response using cross-sectional pulmonary function and was the first to show a relationship of pulmonary function with dust exposure in U.S. coal miners, and contradicted earlier published findings that had been based on a flawed analysis (2, A4-51). This study was supplanted by a major study of pulmonary function change, and was one of the first published occupational health studies relating longitudinal decline and quantitative dust exposure estimates (3, A4-52). Together, these papers for the first time revealed the high burden of respiratory disease in the U.S. coal miners and provided the first scientific evidence that U.S. underground coal miners, including never smokers, suffer from obstructive airways disease caused by their work.
Our studies also showed exposure-response relationship for airflow obstruction and cumulative dust exposures that suggested that the current coal mine dust PEL of two mg/m3 is inadequate in protecting coal miners from the development of lung function impairment. In combination with other findings, they were instrumental in NIOSH concluding that a REL of one mg/m3 was appropriate for underground coal miners. This conclusion was disseminated in “Criteria for a Recommended Standard. Occupational Exposure and Respirable Coal Mine Dust,” published by NIOSH in 1995. (A3-2) The document provides RELs for respirable coal mine dust and respirable silica of 1mg/m3 and 0.05mg/m3, respectively, and recommends screening for respiratory disease in coal miners. Equally as important, the findings established the need for further research and disease surveillance for COPD related outcomes other industries.
A more recent RDRP study looked at the implications of selection into mining and work involving dust exposure (4, A4-53). This report showed that miners tended to self-select jobs based on their nonspecific bronchial reactivity to methacholine; (i.e., those with nonspecific bronchial hyperreactivity tended to seek jobs with lower dust exposures). A subsequent study showed that coal miners with excessive FEV1 declines were more likely to retire due to chest illnesses. Cases had twice the risk of dying with cardiovascular and non-malignant respiratory diseases and a 3.2-fold risk of dying with COPD, compared to referents (5, A4-54).
Further proof that coal mine dust exposure has a non-trivial impact on the lung in terms of airways disease was offered in an RDRP analysis of coal miner mortality. In this, a significant exposure-response relationship for mortality from chronic bronchitis or emphysema was observed controlling for age and smoking. Together with the pathology findings, these results indicate that the morbidity observations imply permanent changes to the lung having adverse consequences for mortality (6, A4-55).
RDRP laboratory investigations, particularly involving analysis of autopsy material supplemented the field studies, and provided evidence of structural damage to the lung and the extent to which emphysema was related to the degree of dust exposures (7, A4-56).
As a result of RDRP’s research on coal miners, it is now recognized that there is an occupational risk of COPD in the coal mining industry. In fact, the Report of the Secretary of Labor’s Advisory Committee on the Elimination of Pneumoconiosis Among Coal Mine Workers, published October 1996, acknowledged that “… the Committee members believe that airways diseases are likely associated with at least as great morbidity and mortality as CWP or silicosis,” and that “chest x-ray program enhanced by pulmonary function testing has the potential to be useful in the surveillance for coal miner airways disease” (A4-57).
Scientific evidence produced by RDRP scientists relating to COPD in coal miners provide additional stimulation and motivation (over and above that forthcoming from studies of CWP) to industry, labor, and government to achieve and maintain low dust levels. The reduction in dust exposures mandated by the 1969 Coal Mine Health and Safety Act is expected to reduce all occupational lung disease among underground coal miners. Although enacted to prevent CWP, the lower exposures should lead to a marked reduction in occupational COPD. In fact, one RDRP-authored paper indicates that compliance with the dust levels mandated by the 1969 Act should reduce pulmonary function decline among those most heavily exposed to one-third of the decline expected to occur from dust exposure levels existing before the Act (3, A4-52).
Progress Towards End Outcomes
As noted in the chapter 3.1a, reductions in dust levels in coal mines since 1969 have led to a major reduction in pneumoconiosis in the last 30 years. Concomitant improvements in health arising from less occupational COPD among miners should be expected. However, owing to termination of further data collection under the NSCWP in 1988, it has not been possible to evaluate reliably the progress made towards elimination of occupational COPD in underground coal miners. In this, it must be borne in mind that full evaluation of the benefits of dust exposure reduction on COPD may be difficult to evaluate because of the predominant effect of smoking and its own temporal changes in exposure over the same period.
In 2005 RDRP acquired a mobile medical unit equipped with modern radiological and spirometry equipment. RDRP is using this for medical screening and surveillance of coal miners, including both lung imaging and lung function measurements. In terms of COPD, the planned objective of the medical screening is to identify miners with signs of early disease. Such miners will be informed about their health status and provided with educational material endorsing reductions in both occupational dust exposure and (if applicable) smoking. Cases will be advised to discuss their health with their physician. Over time, lung function data from this screening program may permit reliable assessment of the prevention of work-related COPD among coal miners.