Silica

General Description

Silica is a fine dust which is found in granite, sandstone, and sand. The primary source of silica is quartz. Silica has the potential to damage the lungs. Over time, it may lead to a disease known as silicosis.

Health Effects

Silicosis is a fibrotic disease of the lungs. It is caused by breathing in silica particles which stay trapped in the lungs. The silica particles in the lungs cause the body to produce a scarring of the lung tissue and eventually results in massive fibrosis. Chronic reactions usually take years to develop, but there is also an acute silicosis that is caused by being exposed to huge amounts of silica.

Early symptoms include a dry cough that becomes worse and may include phlegm as the disease advances. Shortness of breath and later breathlessness are also symptoms. In the late stages, lung function may be lower than usual. The scarring of the lungs makes breathing hard since the lungs are not able to expand to take in air. Massive exposure to silica particles may cause acute silicosis, although this is rare. It usually appears within one to three years after exposure.

Sometimes there is also bronchitis or emphysema with silicosis. This may be due to cigarette smoking in addition to the silica exposure. Also, there may be tuberculosis at the same time. There is no specific treatment for silicosis. Treatment is often for the other illnesses, such as tuberculosis and heart problems, that sometimes go along with silicosis.

Silicosis is diagnosed by chest x-rays and pulmonary function tests, but it may go undetected since it takes a long time to develop. It is not known how much exposure will lead to disease, but there is a relationship between how long a worker is exposed and whether he will develop silicosis. Studies have found that workers with five years of exposure or less were not affected, while workers with 30 or more years of exposure had a prevalence rate of 60%. Also, disease may develop although exposure has stopped.

As with most medical conditions, there are other factors that affect the outcome, for example, personal differences in smoking habits, work practices, and other work exposures.

Exposure Limits

OSHA has set a limit of 5 mg/m3 of respirable dusts. The NIOSH limit for respirable quartz is 0.05 mg/m3.

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