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Coalworker's pneumoconiosis

Coalworker's pneumoconiosis

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Coal workers' pneumoconiosis
Pneumoconiosis is an occupational lung disease and a restrictive lung disease caused by the inhalation of dust, often in mines.-Types:Depending upon the type of dust, the disease is given different names:...

(CWP), colloquially referred to as black lung disease, is caused by long exposure to coal dust
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

. It is a common affliction of coal miners and others who work with coal, similar to both silicosis
Silicosis, also known as Potter's rot, is a form of occupational lung disease caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in forms of nodular lesions in the upper lobes of the lungs...

 from inhaling silica dust, and to the long-term effects of tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...

 smoking. Inhaled coal dust progressively builds up in the lungs and is unable to be removed by the body; that leads to inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

, fibrosis
Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...

, and in worse cases, necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...


Coal workers' pneumoconiosis, severe state, develops after the initial, milder form of the disease known as anthracosis (anthrac - coal, carbon). This is often asymptomatic and is found to at least some extent in all urban dwellers due to air pollution. Prolonged exposure to large amounts of coal dust can result in more serious forms of the disease, simple coal workers' pneumoconiosis and complicated coal workers' pneumoconiosis (or Progressive massive fibrosis
Progressive massive fibrosis
Progressive Massive Fibrosis , characterized by the development of large conglomerate masses of dense fibrosis , can complicate Silicosis and Coal worker's pneumoconiosis...

, or PMF). More commonly, workers exposed to coal dust develop industrial bronchitis, clinically defined as chronic bronchitis
Chronic bronchitis
Chronic bronchitis is a chronic inflammation of the bronchi in the lungs. It is generally considered one of the two forms of chronic obstructive pulmonary disease...

 (i.e. productive cough for 3 months per year for at least 2 years) associated with workplace dust exposure. The incidence of industrial bronchitis varies with age, job, exposure, and smoking. In nonsmokers (who are less prone to develop bronchitis than smokers), studies of coal miners have shown a 16% to 17% incidence of industrial bronchitis.

History and prevention efforts

Black lung is actually a set of conditions and until the 1950s its dangers were not well understood. The prevailing view was that silicosis was very serious but it was solely caused by silica and not coal dust. The miners' union, the United Mine Workers of America
United Mine Workers
The United Mine Workers of America is a North American labor union best known for representing coal miners and coal technicians. Today, the Union also represents health care workers, truck drivers, manufacturing workers and public employees in the United States and Canada...

, realized that rapid mechanization meant drills that produced much more dust, but under John L. Lewis
John L. Lewis
John Llewellyn Lewis was an American leader of organized labor who served as president of the United Mine Workers of America from 1920 to 1960...

 they decided not to raise the black lung issue because it might impede the mechanization that was producing higher productivity and higher wages. Union priorities were to maintain the viability of the long-fought-for welfare and retirement fund, and that required higher outputs of coal. After the death of Lewis, the union dropped its opposition to calling black lung a disease, and realized the financial advantages of a fund for its disabled members. In the Coal Mine Health and Safety Act of 1969, the U.S. Congress set up standards to reduce dust and created the Black Lung Disability Trust. The mining companies agreed to a clause, by which a ten-year history of mine work, coupled with X-ray or autopsy evidence of severe lung damage, guaranteed compensation. Equally important was a "rate retention" clause that allowed workers with progressive lung disease to transfer to jobs with lower exposure without loss of pay, seniority, or benefits. Financed by a federal tax on coal, the Trust by 2009 had distributed over $44 billion in benefits to miners disabled by the disease and their widows. A miner who spent 25 years in underground coal mines has a 5-10% risk of contracting the disease.

21st century

There are currently about 130,000 underground coal miners actively working in the United States. The mining and production of coal is a major part of the economy in several developed countries. In the past ten years, over 10,000 American miners have died from CWP. Although this disease is preventable, many miners are still developing advanced and severe cases.

In 1966 Doctors I.E. Buff, Hawey Wells, and Donald Rasmussen started studies on effects of working in coal mines. They soon had the first miner who would allow experimental tests to find out how his lungs were affected, Earl Stafford, then a 48 year old miner who had been forced to leave the mines due to his lung condition.

In the following years, Doctors Buff, Wells, and Rasmussen, and Mr. Stafford, continued to lobby for action to provide help and develop preventive measures to eliminate this disease. Mr. Stafford along with a group of disabled miners lobbied congress. Mr. Stafford later testified before the U.S. congress about the conditions to which miners were subjected. He later lead this band of miners to conduct local strikes and work stoppages to bring attention to miners suffering from Black Lung, its effects and possible preventative measures. In addition he lectured at several universities, including Berea College in 1974.

By January 1986, Mr. Stafford was considered a lay expert on the cause and effect of the disease. Less than 20 years after being forced to leave the industry he loved, at the age of 68, Earl Stafford passed away quietly as a result of black lung.

In the 40 years since the Federal Coal Mine Health and Safety Act of 1969 became law, the proportion of miners with black lung disease has gone down by about 90%. But the downward trend of this disease in coal miners has not continued. Rates of black lung are on the rise, and have almost doubled in the last 10 years. The US National Institute for Occupational Safety and Health (NIOSH) reported that close to 9 percent of miners with 25 years or more experience tested positive for black lung in 2005-2006, compared with 4 percent in the late 1990s.

The National Institute for Occupational Safety and Health (NIOSH), with support of the Mine Safety and Health Administration (MSHA), has started a Mobile Health Screening Program. This Mobile Unit travels to mining regions around the United States. Miners who participate in the Program receive health evaluations once every five years, at no cost to themselves. Chest x-rays can detect the early signs of and changes in CWP, often before the miner is aware of any lung problems. The screening program is only available to current miners.


Pioneering work to investigate the relationship between respirable dust exposure and coal worker's pneumoconiosis was carried out in Britain by the Institute of Occupational Medicine
Institute of Occupational Medicine
The Institute of Occupational Medicine was founded in 1969 by the National Coal Board as an independent charity. The IOM is a major independent centre of scientific excellence in the fields of occupational health and environmental health, occupational hygiene and occupational safety...

. This research was known as the Pneumoconiosis Field Research (PFR). The research underpinned the recommendations for more stringent airborne dust standards in British coalmines and the PFR was ultimately used as the basis for many national dust standards around the world.

Following observations on industry workers in Lucknow
Lucknow is the capital city of Uttar Pradesh in India. Lucknow is the administrative headquarters of Lucknow District and Lucknow Division....

 (India), experiments on rats found that jaggery
Jaggery is a traditional unrefined non-centrifugal whole cane sugar consumed in Asia, Africa, Latin America, and the Caribbean. It is a concentrated product of cane juice without separation of the molasses and crystals, and can vary from golden brown to dark brown in color...

 (a traditional sugar) had a preventive action against the harmful effects of coal dust.


Coal dust is not as fibrogenic as is silica dust. Coal dust that enters the lungs can neither be destroyed nor removed by the body. The particles are engulfed by resident alveolar or interstitial macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

s and remain in the lungs, residing in the connective tissue or pulmonary lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...

s. Coal dust provides a sufficient stimulus for the macrophage to release various products, including enzymes, cytokines, oxygen radicals, and fibroblast growth factors, which are important in the inflammation and fibrosis of CWP. Aggregations of carbon-laden macrophages can be visualised under a microscope as granular, black areas. In serious cases, the lung may grossly appear black. These aggregations can cause inflammation and fibrosis, as well as the formation of nodular lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...

s within the lungs. The centres of dense lesions may become necrotic due to ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...

, leading to large cavities within the lung.


Simple CWP is marked by the presence of 1-2mm nodular aggregations of anthracotic macrophages, supported by a fine collagen network, within the lungs. Those 1-2mm in diameter are known as coal macules, with larger aggregations known as coal nodules. These structures occur most frequently around the initial site of coal dust accumulation - the upper regions of the lungs around respiratory bronchiole
Respiratory bronchiole
The respiratory bronchioles are interrupted by alveoli which are thin walled evaginations. Alveolar ducts are distal continuations of the respiratory bronchioles.-External links:*...

s. The coal macule is the basic pathological feature of CWP, and has a surrounding area of enlargement of the airspace, known as focal emphysema.

Continued exposure to coal dust following the development of simple CWP may progress to complicated CWP with progressive massive fibrosis
Progressive massive fibrosis
Progressive Massive Fibrosis , characterized by the development of large conglomerate masses of dense fibrosis , can complicate Silicosis and Coal worker's pneumoconiosis...

 (PMF), wherein large masses of dense fibrosis develop, usually in the upper lung zones, measuring greater than 1 cm in diameter, with accompanying decreased lung function. These cases generally require a number of years to develop. Grossly, the lung itself appears blackened. Pathologically, these consist of fibrosis with haphazardly-arranged collagen and many pigment-laden macrophages and abundant free pigment. Radiographically, CWP can appear strikingly similar to silicosis
Silicosis, also known as Potter's rot, is a form of occupational lung disease caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in forms of nodular lesions in the upper lobes of the lungs...

. In simple CWP, small rounded nodules (see ILO Classification
ILO Classification
ILO Classification is a system of classifying radiographs for persons with pneumoconiosis. The intent was to provide a means for describing and recording systematically the radiographic abnormalities in the chest provoked by the inhalation of dusts.-History:Since 1946, the International Labour...

) predominate, tending to first appear in the upper lung zones. The nodules may coalesce and form large opacities (>1 cm), characterizing complicated CWP, or PMF.


There are three basic criteria for the diagnosis of CWP:
  1. Chest radiography consistent with CWP
  2. An exposure history to coal dust (typically underground coal mining) of sufficient amount and latency
  3. Exclusion of alternative diagnoses (mimics of CWP)

Symptoms and pulmonary function testing relate to the degree of respiratory impairment, but are not part of the diagnostic criteria. As noted above, the chest X-ray appearance for CWP can be virtually indistinguishable from silicosis. Chest CT, particularly high-resolution scanning (HRCT), are more sensitive than plain X-ray for detecting the small round opacities.

See also

  • Black Lung Benefits Act of 1973
    Black Lung Benefits Act of 1973
    The Black Lung Benefits Act is a U.S. government program. It provides monthly payments and medical benefits to coal miners totally disabled from pneumoconiosis arising from employment in or around the nation's coal mines...

  • Caplan syndrome is a nodular condition of the lung occurring in dust-exposed persons with either a history of rheumatoid arthritis
    Rheumatoid arthritis
    Rheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints. The process produces an inflammatory response of the synovium secondary to hyperplasia of synovial cells, excess synovial fluid, and the development...

    (RA) or who subsequently develop RA within the following 5–10 years. The nodules in the lung typically occur bilaterally and peripherally, on a background of simple CWP. There are usually multiple nodules, varying in size from 0.5 to 5.0 cm. The nodules typically appear rapidly, often in only a few weeks. Nodules may grow, remain unchanged in size, resolve, or disappear and then reappear. They can cavitate, calcify, or develop air-fluid levels. Grossly, they can resemble a giant silicotic nodule. Histologically, they usually have a necrotic center surrounded by a zone of plasma cells and lymphocytes, and often with a peripheral inflammatory zone made of macrophages and neutrophils.

External links