Department of Energy, Labor & Economic Growth
Andrew S. Levin
Acting Director

Silica Exposure - It's Not Just Dust!

Silica is the second most common mineral in the earth's crust and is a major component of sand, rock and mineral ores. Some of the activities that pose the greatest potential for worker exposure are: abrasive blasting, masonry work, jack hammering, cutting of concrete, and rock drilling.

Silicosis

Silicosis is a disabling, nonreversible and sometimes fatal lung disease caused by over-exposure to respirable crystalline silica. Overexposure to dust that contains microscopic particles of crystalline silica can cause fibrotic nodules and scar tissue to form in the lungs that reduces the lungs' ability to extract oxygen from the air we breathe. In addition to silicosis, inhalation of crystalline silica particles has been associated with other diseases, such as bronchitis and tuberculosis. Some studies also indicate an association with lung cancer.

Exposure Limits

The MIOSHA Permissible Exposure Limit (PEL) for respirable crystalline silica depends upon the amount of silica in the sample. The formula for determining the PEL is as follows:

For example: If an employee is monitored for silica exposure and the amount of silica in the sample is 20% then the PEL = 0.45 mg/m3. The sample result would then be compared to the PEL to determine if the employee was over-exposed. The National Institute for Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists (ACGIH) both recommend a PEL of 0.05 mg/m3.

How to Avoid Hazards

The best way to prevent over-exposure to respirable crystalline silica is to install and maintain engineering controls to eliminate or reduce the hazard. Remember, nearly all concrete, block, brick and other masonry material contains silica. If you cut it, drill it, jack-hammer it, or break/crush it, you can create hazardous exposure to silica. Examples of engineering and other controls include:

· Employees must be trained on the hazards of exposure to silica in accordance with Part 430, Hazard Communication.
· In the case of abrasive blasting, utilize abrasive blasting materials with <1% crystalline silica. Materials such as steel-shot or iron-shot can be used for abrasive blasting instead of silica sand.
· Use exhaust ventilation and dust collection systems. For example, power tools used for cutting masonry materials can be equipped with dust collection systems.
· Use wet methods to keep dust to a minimum when cutting/drilling silica containing materials (water sprays, wet drilling, etc.).
· Enclose cabs on machinery to prevent operator exposure.
· Do not dry sweep or use compressed air to clean work areas, use wet methods or a vacuum equipped with a high efficiency particulate (HEPA) filter.
· Use work practice controls such as opening doors and windows to provide general ventilation and stay up-wind of a dusty operation.
· If engineering and work practice controls cannot be used or do not reduce the dust to an acceptable level, then the employer must provide respiratory protection. For operations other than abrasive blasting, the protection recommended is an air-purifying respirator with HEPA filters. Air supplied type CE abrasive blasting respirators are the only respirators suitable for abrasive blasting operations. Remember, the employer must then implement a respiratory protection program as required by MIOSHA Part 451, Respiratory Protection.
· If respirators are used to protect employees, then a regulated area should be established to prevent unprotected employees from entering the exposure area.

For more information visit the NIOSH web site at: www.cdc.gov/niosh/topics/silica.

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