SILICOSIS, or miners' phthisis, has been known to occur among miners in certain districts for centuries. This disease is found among metal miners in New Zealand, Australia, South Africa, Great Britain, and in many of the states of the United States. Silicosis is due to breathing very fine rock dust. Rock dust high in free silica is found to be most injurious.
Some physicians have thought that silica dust by its sharpedged and needle-like particles injures the lung tissue mechanically. Another belief is that the silica, being soluble in water and weakly alkaline liquids, injures lung tissue by its poisonous action.
The rate of development of silicosis depends upon the character of the dust, the amount breathed, length of exposure, past illness (especially tuberculosis), and physical fitness of the men.
Among gold miners in South Africa the average length of exposure to silica dust before silicosis develops is seven and a half years, the shortest period of exposure for like results is two and a half years.
Silicosis is usually divided into three stages: The first shows symptoms and physical signs of damage to lung tissue caused bv exposure to dust, but capacity for work is not impaired. The second stage shows definite signs of silicosis and capacity for work is impaired, although not seriously or permanently. The third stage shows that specific signs of silicosis are or have been present and the capacity for work has been seriously and permanently impaired by the disease.
The cardinal symptom of silicosis is shortness of breath, especially on exertion. The cardinal sign is diminished expansion of the chest. Both .are slight in the early stages and increase gradually with development of the disease. Other symptoms and signs, as coughing, frequent colds, pains in the chest, and X-ray findings, are very important in making a diagnosis.
Men having silicosis are more susceptible to tuberculosis than normal men.