3.1 Respiratory Diseases Induced by Coal Mine Dust3. Interstitial Lung Diseases | 3.1a) Verification that the Enacted Coal Mine Dust Standard Protects Miners
In 2004, there were 74,000 people, mostly males, employed as coal miners in the U.S., of which 57 percent were underground miners. Despite a long secular trend of decreasing employment in coal mining associated with mechanization, the number of coal miners has very recently been increasing because of enhanced production of coal due to high prices in energy markets associated with high energy demands in general. Coal mining operations vary in size from small operations employing fewer than 10 people to operations with several hundred employees. There is evidence that larger coal mining operations generally do better at protecting their workers from disease development.17
Both surface and underground coal miners suffer from dust exposure and associated lung diseases. In general, levels of dust in underground mines are greater than at surface mines, but certain occupations at surface mines are at high-risk for silicosis.18 Among underground coal miners, those who work where the coal is cut from the coal seam are at highest risk. This is especially true for the longwall19 mining method, where production levels are high, leading to dust levels that are hard to control. Dust levels in tipples where coal is sorted and cleaned may be high, but most others who handle coal in other settings (e.g. power station workers and dock loaders) do not appear to be at especially high risk of respiratory disease.
Coal mine dust has long been known to cause chronic respiratory disease but for many years little was done in the U.S. to prevent overexposure. For the 20 or so years following World War II, a period when mine mechanization grew rapidly, a population of between 150,000 and 500,000 underground miners regularly suffered exposures up to 6 - 8 mg/m3 of coal mine dust (compared to the current NIOSH Recommended Exposure Limit [REL] of 1 mg/m3).20
As a result of these exposures, there was an epidemic of occupational lung disease in underground coal miners. In nine studies undertaken in various regions of the U.S. in the 1960s, the prevalence of CWP among those with 30 or more years in mining ranged between 10 percent and 60 percent depending on the coal field. The underlying cause of this broad range of prevalence by coal field is probably the type (rank) of coal mined at that time.21
Apart from the obvious benefits from reducing ill-health, impairment, and disability; reduction in dust exposures in underground coal mining should correlate with reduction in compensation costs. In 2005, there were 104,503 beneficiaries of the federal Black Lung Program for coal miners. The total amount awarded to these beneficiaries in 2005 exceeded $675 million. Although these numbers are trending downward, in large part due to long-term downward trends in overall employment, RDRP remains vigilant to changes and is working to minimize the number of coal miners who will become disabled in the future as a result of coal mine dust exposure.
A number of activities conducted by RDRP were initiated and continue under federal mandate. The Federal Coal Mine Health and Safety Act was enacted in 1969, following a massive coal mine explosion at Farmington, West Virginia and the resulting public outcry and concern about high levels of injury and occupational disease in the coalfields. The Act mandated a battery of prevention-related measures, which included: strict dust control to a specific standard, a program of research into lung diseases related to coal mining, and implementation of worker medical monitoring of miners (with a voluntary medical removal program for miners with chest x-ray evidence of dust-induced disease). At the same time, Congress appropriated funding for a program of research and development of tools and methods for helping mining companies assess and reduce dust exposures in their mines.
Virtually all of the occupational health research relating to disease prevention among coal miners and coal mining operations in the U.S. over the last 35 years has been undertaken by RDRP, complemented by engineering and control technology research conducted by NIOSH Mining Research Program (formerly the U.S. Bureau of Mines). Coal mining-related laboratory and field investigations formed a major part of our activities from 1970-1990. Following the accumulation of a wealth of epidemiologic knowledge, the focus in human studies for RDRP has moved largely to ongoing disease surveillance and prevention. Laboratory investigations have continued to a lesser extent to the present, but a robust research program on dust assessment and control continues.
RDRP work addresses three objectives directed at disease assessment and prevention of occupational lung disease in coal miners: a) research into disease causation with the aim of verifying that the enacted coal mine dust standard protects coal miners; b) disease surveillance and monitoring to track the success (or otherwise) of the standard and to identify ‘hotspots’ of disease to effectively target focused prevention efforts; and c) research to improve coal mine dust measurement and control aimed at reducing dust levels in coal mines.
In summary, the three objectives are:
RDRP research showed that the current Permissible Exposure Limit (PEL) of 2 mg/m3 (MRE equivalent) for respirable coal mine dust does not fully protect U.S. coal miners. Publication of this research in the 1995 criteria document, “Occupational Exposure to Respirable Coal Mine Dust,” (3.1a) was acknowledged by MSHA. Subsequently, MSHA implemented some improvements to the relevant regulations and increased enforcement (3.1c). RDRP’s Coal Workers X-ray Surveillance Program has identified miners with radiographic evidence of pneumoconiosis and provided them with information that helps them seek work in less dusty environments. RDRP’s development of the personal dust monitor provides real-time exposure measures to miners and will help with ongoing and future disease prevention.
Although MSHA has yet to reduce the PEL to match the current NIOSH REL of 1 mg/m3, the activities of RDRP, MSHA, and other stakeholders have resulted in significant reductions in the percentage of dust samples exceeding the MSHA PEL (from 44 to 49 percent c1970 to 9 to 12 percent c2000) despite large increases (up to 7-fold) in coal production. The prevalence of pneumoconiosis in underground miners with 25 or more years mining tenure fell from 35 percent in the years 1973-1978 to four percent in 1997-1999. However, CWP (including the potentially disabling advanced form of the disease known as progressive massive fibrosis) continues to occur and novel approaches undertaken by the Coal Workers X-ray Surveillance Program has recently identified counties in the coalfields with high rates of rapid pneumoconiosis progression among active miners. The reasons for this apparent rapid progression and continuing occurrence of progressive massive fibrosis are unclear. It may result from a combination of inadequacies in the present dust limit and its method of enforcement. These occurrences point to the need for continued surveillance and monitoring activities to track disease decline and to target enhanced exposure assessment and dust control.
17. Pon MRI, Petsonk EL, Wang ML, Castellan RM, Attfield MD, Wagner GR . Pneumoconiosis prevalence among working coal miners examined in federal chest radiograph programs - U.S., 1996-2002. Morbidity and Mortality Weekly 336-340.
19. Longwall mining comprises a cutting head that moves from side-to-side across a coal-seam for distances of up to 1450 feet. The cut coal falls onto a conveyor belt for removal from the mine. The machinery is protected by hydraulic roof supports, which advance behind the cutter as it moves through the seam. The result is immediate roof collapse and associated surface subsidence. Today, approximately 90 longwall operations account for 20 percent of U.S. coal production.