Silica is a common, naturally-occurring crystal. It is found in most rock beds. Silica dust forms during mining, quarrying, tunneling, and working with certain metal ores. Silica is a main part of sand, so glass workers and sand-blasters are also exposed to silica.
Three types of silicosis occur:
- Simple chronic silicosis, which results from long-term exposure (more than 20 years) to low amounts of silica dust. The silica dust causes swelling in the lungs and chest lymph nodes. This disease may cause people to have trouble breathing. This is the most common form of silicosis.
- Accelerated silicosis, which occurs after exposure to larger amounts of silica over a shorter period of time (5 to 15 years). Swelling in the lungs and symptoms occur faster than in simple silicosis.
- Acute silicosis, which 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 causes severe lung 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
- Glass manufacturing
- 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 to 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.