When workers inhale crystalline silica, the lung tissue reacts by developing fibrotic nodules and scarring around the trapped silica particles.  This fibrotic condition of the lung is called silicosis. If the nodules grow too large, breathing becomes difficult and death may result. A worker's lungs may react more severely to silica sand that has been freshly fractured, as happens when silica containing products are sawed, hammered, or treated in a way that produces airborne dust. This factor may contribute to the development of acute and accelerated forms of silicosis.

A worker may develop any of three types of silicosis, depending on the airborne concentration of crystalline silica:

Chronic silicosis, which usually occurs after 10 or more years of exposure to crystalline silica at relatively low concentrations

Accelerated silicosis, which results from exposure to high concentrations of crystalline silica and develops 5 to 10 years after the initial exposure

Acute silicosis, which occurs where exposure concentrations are the highest and can cause symptoms to develop within a few weeks to 4 or 5 years after the initial exposure

Complications

Initially, workers with silicosis may have no symptoms. As silicosis progresses, there may be difficulty in breathing and other chest symptoms such as cough. Individuals with silicosis are also at high risk of developing tuberculosis, which causes fever, weight loss, and night sweats. Tuberculosis or other infections are believed to result when the lung cells (macrophages) that fight these infections are overwhelmed with silica dust and are unable to kill the TB bacteria. About half of the mycobacterial infections are caused by Mycobacterium tuberculosis (TB), with the other half caused by M. kansasii and M. avium-intracellulare. Nocardia and Cryptococcus may also cause infections in silicosis.

Evidence indicates that crystalline silica is a potential occupational carcinogen.

The relationship between silica exposure and development of silicosis is well known, and there is an OSHA standard for silica and a NIOSH recommended exposure limit of 0.05 mg/m3.

Research currently underway has shown that use of controls tested for cutting block reduced silica exposure by over 90%. Mean exposure without use of controls was 57 times the NIOSH Recommended Exposure Limit (REL). Use of controls for cutting brick reduced exposures by 81 – 91% with mean exposure 19 times the REL without use of any control. NIOSH has produced some documents that provide extensive detail on the exposure-disease relationship: 

Preventing Silicosis and Deaths in Construction Workers (NIOSH Pub# 96-112)

Health Effects of Occupational Exposure to Respirable Crystalline Silica (NIOSH Pub# 2002-129)