The Centers for Disease Control and Prevention (CDC) released July 6 the results of studies prompted by reports that underground coal miners are still experiencing unusual occurrences of black lung disease despite federal regulations to prevent exposure to coal dust. The "clusters of rapidly progressing and potentially disabling pneumoconiosis," or black lung disease, were found in 2005 and 2006 in some eastern Kentucky and southern Virginia miners, according to CDC's Morbidity and Mortality Weekly Report (MMWR).

In response to the 2005 and 2006 reports, the CDC's National Institute for Occupational Health and Safety (NIOSH) conducted surveys of miners in three Kentucky counties and in four Virginia counties. The results of the NIOSH testing of 975 miners indicated that four percent (37 miners) of those tested had advanced cases of black lung disease.

According to MMWR, the 37 miners with advanced cases of pneumoconiosis were categorized into two groups of workers — those who worked in jobs exposing them to silica dust (roofbolters) and those who were exposed to coal dust (coal-face workers). Both groups of miners had worked in these jobs an average of nearly 30 years.

The results, according to NIOSH, were unusual. Sixty-four percent of the coal dust workers and 42 percent of the roofbolters developed black lung. What was unexpected was the rapid advancement, in less than 10 years, of the disease among the workers exposed to coal dust. There were more cases of advanced black lung disease among these workers than among the roofbolters who were exposed to silica dust. Silica is more toxic to the lungs, and silicosis, one type of black lung disease, develops more quickly.

NIOSH proposed several possible explanations for the unexpected results. There might be inadequacies in the dust exposure standards, failures to comply with existing regulations and missed opportunities for miners to be screened for early disease detection through voluntary chest radiographs (a type of x-ray). The NIOSH study, however, made no attempt to determine why these unusual disease results occurred.

Ellen Smith, Owner and Managing Editor of Mine Safety and Health News, wondered why the NIOSH team that conducted the surveys did not include an examination of the working conditions in the mines they visited. "Did anyone look at the history in these mines of ventilation, dust control, and water spray violations?" she asked in a telephone interview.

Federal laws have regulated exposure to coal mine dust since 1969, with amendments in 1977, and are credited with a reduction of black lung among underground coal miners. According to MMWR, the "prevalence of all pneumoconiosis…among underground miners with [at least 25] years on the job dropped from approximately 30% in the early 1970s to [less than] 5% in the late 1990s."

Legislation introduced in the House (H.R. 2769) in June would revise the 1977 standards for respirable coal dust to those NIOSH recommended in 1995. (See the Watcher article on the legislation.) In addition, according to MMWR, NIOSH is examining mining environments to evaluate current exposure levels and conducting investigations to gather more data on disease clusters.