The Occupational Safety and Health Administration (OSHA), and the National Institute for Occupational Safety and Health (NIOSH) each have guidelines and exposure limits for work environments that may contain silica dust. It is well documented that exposure to silica dust causes silicosis, an incurable lung disease.
Exposure limits are determined by measuring millions of particles per cubic foot (MPPCF). Dust is measured by determining how many silica particles are present in a sample. This is calculated using the formula PEL† = 250 mppcf / % silica +5.
OSHA Exposure Limits
OSHA mandates that employees must not be exposed to airborne silica dust in excess of permissible exposure limit (PEL) of 50 μg/m3 . Respirable dust that contains silica must meet the following general industry guidelines:
- PEL = 10 mg/m3 / % silica +2
- PEL = 250 mppcf / % silica +5
Employees who are exposed to silica dust must be further monitored using one of two assessment methods:
- Performance Option – Employers assess 8-hour time-weighted average (TWA) exposure for any employee exposed to silica dust. This is based on a combination of objective data and air monitoring data, and is used to accurately characterize each employee’s exposure level.
- Scheduled Monitoring Option – Employers conduct initial monitoring of the 8-hour TWA exposure of each employee. This is based on samples from the personal breathing zone, and reflects exposure levels based on the shift, job classification, and work area. Follow-up monitoring can be done and compared to the initial assessment.
In addition to exposure limits, OSHA also has specific guidelines for compliance with health and safety standards.
NIOSH Exposure Limits
NIOSH recommends that exposure to silica dust be limited to 0.05 mg/m3 (50 µg/m3). This limit is based on a 10-hour workday and a 40-hour work week.
In addition to setting limits, NIOSH has also recommended specific respirators and personal protective equipment (PPE) that will reduce the risk of exposure to toxins, including probable carcinogens. NIOSH recommends the following respirators based on exposure levels:
- Up to 0.5 mg/m3: Respirators equipped with filters N95, R95, or P95.
- Up to 1.25 mg/m3: Respirators that are powered or supplied-air, that have a high-efficiency particle filter.
- Up to 2.5 mg/m3: A respirator that is air-purifying and full-face. Use filters N100, R100, or P100.
- Up to 25 mg/m3: Supplied-air respirator that uses a pressure-demand or positive-pressure mode.
How to Prevent Silicosis
Silicosis is completely preventable. By following guidelines and limiting exposure, you can protect yourself and your family from harmful contamination. Follow these tips for preventing silicosis:
- Know the sources of silica dust at work.
- If dust is visible, you are at risk.
- When working in confined structures or environments, do the following:
- Use water to wet dust and prevent it from becoming airborne.
- Use saws or machinery that adds water to the blade.
- Use cleaning machines that control dust.
- Always use a respirator (Your employer is required to provide one).
- Never consume open food or drinks in dusty areas.
- Change clothing before you leave the worksite (silica dust can be transferred to your car or home).
- Shower and change clothes before contact with others.
Even though silicosis is 100 percent preventable, the Centers for Disease Control and Prevention (CDC) estimates that 2.3 million workers in the United States are exposed to respirable silica dust. This is an alarming number of exposed workers who are at risk for silicosis.