NIOSH Issues Hazard Review for Respirable Crystalline Silica

The NIOSH Hazard Review, Health Effects of Occupational Exposure to Respirable Crystalline Silica, describes published studies and literature on the health effects of occupational exposure to respirable crystalline silica among workers in the United States and many other countries.

The review indicates a significant risk of chronic silicosis for workers exposed to respirable crystalline silica over a working lifetime even at the current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL), or the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL). It discusses three recent studies that estimated that the risk of silicosis for a 45-year working lifetime is 47% to 90% for cumulative silica exposure levels at concentrations equal to the current PEL.

In addition to the risk of silicosis, workers exposed to respirable crystalline silica have an increased risk of developing lung cancer, pulmonary tuberculosis, and airway diseases (bronchitis and emphysema). The latest scientific information also indicates possible associations of occupational exposure to silica dust with autoimmune diseases, which include lupus, rheumatoid arthritis, and chronic renal disease.

Until improved sampling and analytical methods are developed for respirable crystalline silica, NIOSH will continue to recommend:

• an exposure limit of 0.05 mg/m3 as a time-weighted average (TWA) for up to a 10-hr workday during a 40-hr workweek.
• substituting less hazardous materials for crystalline silica when feasible,
• using appropriate respiratory protection when source controls cannot keep exposures below the REL, and
• making medical examinations available to exposed workers.

Ordering Information

To order a copy of the review contact the National Institute for Occupational Safety and Health (NIOSH) at

NIOSH Publications Dissemination
4676 Columbia Parkway
Cincinnati, OH 45226-1998

Telephone: 1-800-35-NIOSH (1-800-356-4674)
Fax: 1-513-533-8573
E-mail: pubstaft@cdc.gov