Mines operate under stringent federal and state regulations established to protect workers and the environment.
The Federal Mine Safety and Health Act of 1977 gives the U.S. Department of Labor the authority to issue and enforce health and safety standards for working conditions in underground and surface mining, milling, and related operations. Within the Department of Labor, the Mine Safety and Health Administration (MSHA) is responsible for oversight and enforcement of the mine safety act; the Occupational Safety and Health Administration has authority over occupational health and safety matters not regulated by MSHA.
Requirements for mine safety include limiting worker exposure to radon, a common, naturally occurring gas that may be present in any type of underground mine. Radon has been linked to lung cancer and is especially hazardous for smokers, who already have a higher risk of lung cancer. Workers are exposed to radon decay products in various underground mining operations, including uranium, fluorspar, iron and tin. The federal government first established limits on radon in mines in 1967.
The U.S. mining industry works closely with employees and regulators to enhance worker safety, investing in advanced technology, training and systematic analysis of the causes of injuries with the goal of eliminating areas of potential risk. The industry has invested more than $850 million over the past four years to improve mine safety. In 2011, lost time injuries declined 39 percent over 2010.1
Safety standards and improved operating practices have lowered radon exposure among workers dramatically since the early years of uranium mining. Concentrations of radon gas in mines are monitored by the MSHA. The most effective measures for controlling radon gas are dilution of the air and ventilation. All underground uranium mines have extensive ventilation systems, incorporating multiple vertical shafts and fans, to bring fresh air into the mines.
In 2009, the National Mining Association, Northwest Mining Association and Uranium Producers of America entered an agreement with the National Institute for Occupational Safety and Health to collaborate and identify research needed to improve health, safety and training of a new generation of uranium miners.
Federal Regulations Protect Worker Safety
Because radon is so common, federal regulations require the owners of all types of underground mines to test for the presence of radon in the air.
In underground uranium mines specifically, the air in work areas—including lunch rooms and other areas where workers congregate—must be sampled at least every two weeks. If the concentration of radon particles exceeds a threshold level, sampling must be conducted weekly until five successive samples show a level below the threshold. Exhaust mine air must be sampled at least monthly. Sampling is less frequent where uranium is not being mined—for example, in coal mines.
Mining regulations also require operators to keep records of worker exposures to the decay products of radon gas. Regulations limit the exposure of miners to radon.
Background on US Uranium Mining
The U.S. government took steps in the late 1940s to develop domestic supplies of uranium to support the development of the nation’s atomic weapons arsenal, spurring a boom in uranium mining on the Colorado Plateau. Hundreds of uranium mines opened in the Four Corners area of Arizona, New Mexico, Utah and Colorado. Although some of the early uranium mines were open pits, most were underground.
For mining activities, the U.S. Nuclear Regulatory Commission only oversees in situ recovery, in which uranium ore is chemically altered underground before being pumped to the surface for further processing. The states and the U.S. Interior Department’s Office of Surface Mining regulate mining where uranium ore is removed from deep underground shafts or shallow open pits.
However, the NRC regulates all uranium mills and the disposal of waste from uranium recovery operations (including mill tailings). Currently, the NRC regulates uranium recovery operations in Wyoming, New Mexico and Nebraska. The NRC does not directly regulate the active uranium recovery operations in Texas, Colorado and Utah, which have entered into agreements with the NRC to exercise regulatory authority.
Scientists Observe Health Effects From Radon
Scientists have observed a link between lung cancer and underground miners for more than a century. Following a review of the literature on European miners, a scientist with the National Cancer Institute suggested in 1942 that radon gas may contribute to the development of lung cancer in underground miners.
Radon is a naturally occurring gas that results from the radioactive decay of radium-226, which is a decay product of uranium-238. Both radium and uranium are present in most soils and rocks and, consequently, “radon is ubiquitous in indoor and outdoor air,” according to the National Academy of Sciences. Concentrations vary depending on geography and the makeup of rock formations.2
The principal health concern associated with radon is alpha radiation. Alpha particles may become attached to dust, smoke or water vapor particles and be inhaled deep into the lungs, where they can harm sensitive lung tissue and potentially lead to lung cancer. The most effective way to manage radon exposure is dilution of the particles in the air and ventilation.
Radon Amplifies Lung Cancer Risk for Smokers
In the late 1990s, the sixth Committee on Biological Effects of Ionizing Radiation studied data on 11 cohorts of underground miners from seven countries in an effort to assess the health effects of radon exposure to the general public. The mines included eight uranium mines, along with tin, fluorspar and iron mines. All the miners were male; most were smokers.
The committee concluded that smoking poses a much greater risk of lung cancer than exposure to radon. However, it also found that radon exposure multiplies the lung cancer risk for smokers.
“The risk of lung cancer caused by smoking is much higher than the risk of lung cancer caused by indoor radon. Most of the radon-related deaths among smokers would not have occurred if the victims had not smoked,” the committee said. “Furthermore, there is evidence for a synergistic interaction between smoking and radon. In other words, the number of cancers induced in ever-smokers by radon is greater than one would expect from the additive effects of smoking alone and radon alone.”3
Studies Look at Uranium Miners
A study of uranium miners in New Mexico supports the conclusion that there is a link between radon and lung cancer as well as the observation that smoking significantly increases the health risk.
In 2008, the Journal of Radiological Protection reported on a study of workers who were engaged in uranium mining and milling near Grants, N.M., from 1955 to 1990. The study found an increased incidence of lung cancer and increased mortality among underground miners. “The lung cancer excess likely is attributable to the historically high levels of radon in uranium mines of the Colorado Plateau, combined with the heavy use of tobacco products. … For uranium mill workers exposed to uranium dusts and mill products, there was no clear evidence of uranium-related disease.”4
In 2012, a French study explored the role of uncertainty in measuring radon exposure and found that “the total size of the uncertainty decreased from about 47 percent in the period 1956–1974 to 10 percent after 1982, illustrating the improvement in the radiological monitoring system over time.”5
In fact, significant improvements in mine safety over the past several decades make it difficult to compare the health effects on contemporary miners with historical data. In Canada, for example, a group of scientists concluded in a 2004 report that it would not be feasible to conduct a study of workers in Saskatchewan uranium mines from 1975 to the present. “Today’s Saskatchewan uranium miners have radon exposures that are between 100 and 1,000 times lower than those of past uranium miners … because of dose limits, improved mining techniques, and other radiation protection practices. Any higher-than-normal rates of lung cancer from such workplace exposures would be virtually impossible to measure.”6
1 “Compliance at metal and nonmetal mines improving, says MSHA assistant secretary,” Feb. 16, 2012, Mining Safety and Health Administration.
2 “Comparative Dosimetry of Radon in Mines and Homes,” National Academy of Sciences, 1991.
3 “Health Effects of Exposure to Radon: BEIR VI,” 1999.
4 “A cohort study of uranium millers and miners of Grants, New Mexico, 1979-2005,” John D. Boice Jr. et al., Journal of Radiological Protection, Vol. 28, No. 3, 2008.
5 Assessment of uncertainty associated with measuring exposure to radon and decay products in the French uranium miners cohort, Rodrigue S Allodji et al., Journal of Radiological Protection, Vol. 32, No. 1 , 2012.
6 “Update: Saskatchewan Uranium Miners’ Health Studies,” news release, June 18, 2004, Canadian Nuclear Safety Commission.