Silicosis is a respiratory disease caused by breathing in (inhaling) silica dust.

Silica is a common, naturally-occurring crystal. It is found in most rock beds and forms dust during mining, quarrying, tunneling, and working with many metal ores. Silica is a main part of sand, so glass workers and sand-blasters are also exposed to silica.

Three types of silicosis exist:

• Simple chronic silicosis -- results from long-term exposure (more than 20 years) to low amounts of silica dust. Swellings caused by the silica dust form in the lungs and chest lymph nodes. This disease may cause people to have trouble breathing.
• Accelerated silicosis -- occurs after exposure to larger amounts of silica over a shorter period of time (5 - 15 years). Swelling in the lungs and symptoms occur faster than in simple silicosis.
• Acute silicosis -- results from short-term exposure to very large amounts of silica. The lungs become very inflamed and can fill with fluid, causing severe shortness of breath and low blood oxygen levels.

Progressive massive fibrosis can occur in either simple or accelerated silicosis, but is more common in the accelerated form. Progressive massive fibrosis is caused by severe scarring and destroys normal lung structures.

People who work in jobs where they are exposed to silica dust are at risk. These jobs include:

• Abrasives manufacturing
• Mining
• Quarrying
• Road and building construction
• Sand blasting
• Stone cutting

Intense exposure to silica can cause disease within a year, but it usually takes at least 10 - 15 years of exposure before symptoms occur. Silicosis has become less common since the Occupational Safety and Health Administration (OSHA) created regulations requiring the use of protective equipment, which limits the amount of silica dust workers inhale.