Preventing occupational disease and injury, second edition. Levy BS, Wagner GR, Rest KM, Weeks JL, eds. Washington, DC: American Public Health Association, 2005 Jan; :166-169
Coal workers' pneumoconiosis (CWP) is one of the lung diseases arising from inhalation and deposition of respirable coal mine dust in the lungs, and from the reaction of the lungs to the dust. It is a chronic, irreversible disease of insidious onset, usually-but not always-requiring 10 or more years of dust exposure before appearing on chest x-ray. It is characterized by abnormalities visible as small or large opacities (spots) on chest x-ray. When only small opacities are present, the condition is called chronic or simple CWP. Complicated CWP or progressive massive fibrosis (pMF) are the terms used when opacities greater than 1 centimeter attributable to coal dust exposure are present on x-ray. Obsolete terms applied to the same conditions include anthracosis, anthracosilicosis, miners' phthisis, and miners' asthma. For purposes of compensation, various jurisdictions define pneumoconiosis differently. For example, in the U.S. federal compensation system for miners, pneumoconiosis is defined as "a chronic dust disease of the lung arising out of employment in an underground coal mine" [Federal Mine Safety and Health Act, Section 402(b)]. Thus, eligibility for benefits under the federal act is not limited to dust effects visible on chest x-ray. Disease definitions delineating eligibility for state workers' compensation benefits also vary from state to state. The ILO disseminates a conventional method for x-ray classification that is employed in the recognition and categorization of the pneumoconioses, including CWP. This method classifies opacities according to their shape, size, location, and profusion. Profusion is determined by comparing the miner's film with "standard" ILO films. There are four major categories of increasing profusion of opacities: 0, 1, 2, and 3. Whichever standard film most closely matches that of the miner determines the "major category" of profusion. If the film is in a border area between two major categories, both categories are noted, with the category most like the film noted first. For example, a film that shows a higher profusion of opacities than the category 1 standard film, but that is more like the 1/1 standard than like the 2/2 standard, is classified 1/2. PMF is classified as category A, B, or C, depending on the size of the large opacities. The ILO system was originally established to achieve consistency in film interpretation during the conduct of health surveillance or epidemiological investigations. In the United States, readers trained in this method of interpretation who pass a competency test administered by NIOSH are designated as B readers. However, despite efforts to achieve standardized interpretations of chest x-rays through use of the ILO system, significant variability is often found between and within readers regarding the presence of severity of CWP. Coal workers' pneumoconiosis has characteristic pathological features, which can be seen on autopsy or biopsy and are described in standard reference works. Tissue examination is not necessary for the diagnosis of the disease.