Silicosis

The commonest form of pneumoconiosis is due to the inhalation of free silica. The condition is known as silicosis. Silicosis is an occupational lung disease that develops over time when dust-containing silica is inhaled into the lungs. Silica in crystalline form is toxic to the lining of the lungs. When the two come into contact, a strong inflammatory reaction occurs. Over time this inflammation causes the lung tissue to become irreversibly thickened and scarred - a condition known as fibrosis.

Free silica (SiO²) or crystalline silica occurs in three common forms in industry: quartz, tridymite and cristobalite. There is also a cryptocrystalline variety in which the 'free silica' is bound to an amorphous silica (non-crystalline). This includes tripolite, flint and chert. Diatomine is the most common form of amorphous silica capable of producing lung disease. Some of these forms can be altered by heat to the more dangerous crystalline varieties such as tridymite and cristobalite.

Common sources of crystalline silica dust include:

• sandstone
• granite
• slate
• coal
• pure silica sand

People who work with these materials, as well as foundry workers, potters and sandblasters, are most at risk. Industrial exposure occurs in mining, quarrying, stone cutting, sand blasting, some foundries, boiler scaling, in the manufacture of glass and ceramics and, for diatomite, in the manufacture of fluid filters.

What is silicosis?
Silicosis is an occupational lung disease that develops over time when dust-containing silica is inhaled into the lungs. Inhalation of free silica is the most commonest form of pneumoconiosis.

Damage to the lung tissue means the lungs don't perform as well as they should. The symptoms include a cough, shortness of breath and tightness about the chest. There is no cure for silicosis and the damage suffered by the lungs means that a person might become more susceptible to lung infections and to tuberculosis (TB). There is treatment available to reduce inflammation and improve lung function which may help.

Types of silicosis

• Chronic silicosis - is the most commonest form of the disease and the symptoms develop over many years from long-term exposure to silica dust. The lung tissue becomes damaged by fibrosis and nodules of chronic inflammation and scarring provoked by the silica dust form in the lungs and chest lymph nodes.
• Acute silicosis - this rare condition results from short-term exposure to very large amounts of silica dust. The lungs become very inflamed and may fill with fluid, causing severe shortness of breath and low blood oxygen levels. This condition is often fatal.
• Accelerated silicosis - occurs after exposure to large amounts of silica over a shorter period of time. Inflammation, scarring, and symptoms progress faster in accelerated silicosis than in simple silicosis.
• Progressive massive fibrosis
• Conglomerate silicosis

Who is at risk?
People who work with these materials, as well as foundry workers, potters and sandblasters, are most at risk. Other forms of silica, such as glass, are less of a health risk as they aren't as toxic to the lungs.

It usually takes years of exposure before the gradually progressive lung damage becomes apparent.