Crystalline silica is a common mineral found in the earth’s crust. Materials like sand, stone, concrete, and mortar contain crystalline silica. It is also used to make products such as glass, pottery, ceramics, bricks, and artificial stone. Respirable crystalline silica – very small particles at least 100 times smaller than ordinary sand found on beaches and playgrounds – is created when cutting, sawing, grinding, drilling, and crushing stone, rock, concrete, brick, block, and mortar.
Activities such as abrasive blasting with sand; sawing brick or concrete; sanding or drilling into concrete walls; grinding mortar; manufacturing brick, concrete blocks, stone countertops, or ceramic products; and cutting or crushing stone result in worker exposures to respirable crystalline silica dust. Industrial sand used in certain operations – such as foundry work and hydraulic fracturing (fracking) – is also a source of respirable crystalline silica exposure. About 2.3 million people in the United States are exposed to crystalline silica at work.
Workers who inhale these very small crystalline silica particles are at increased risk of developing serious silica-related diseases – including silicosis, an incurable progressive lung disease that can lead to disability and death; lung cancer; chronic obstructive pulmonary disease (COPD); and kidney disease.
Silica Exposure Levels and OSHA Rules
The Occupational Safety & Health Administration (OSHA) has set forth regulatory requirements for preventing and controlling workplace crystalline silica hazards. To protect workers exposed to respirable crystalline silica, OSHA has issued two standards: one for Construction (29 CFR 1926.1153) and the other for General Industry & Maritime (29 CFR 1910.1053).
OSHA standards require employers to protect workers from respirable crystalline silica at exposures above the permissible exposure level (PEL) of 50 micrograms per cubic meter of air (50 µg/m3) averaged over an eight‐hour work shift. In addition, it requires employers to safeguard workers at or above an action level (AL) of 25 µg/m3 – which is set forth to protect workers against exposure above 50 µg/m3.
The standard also provides flexible alternatives, which OSHA expects will be especially useful for small companies. Employers can either use the control methods laid out in the construction standard, or they can measure workers’ exposure to silica and independently decide which dust controls work best to limit exposures to the PEL in their workplaces.
Regardless of which exposure control method is used, all construction employers covered by the standard are required to:
- Establish and implement a written exposure control plan;
- Designate a competent person to implement the written exposure control plan;
- Restrict housekeeping practices that expose workers to silica;
- Offer medical exams-including chest X-rays and lung function tests – every three years for workers who are required by the standard to wear a respirator for 30 or more days per year;
- Train workers on work operations that result in silica exposure; and
- Keep records of exposure measurements, objective data, and medical exams.
Construction employers must have complied with all requirements of the standard by September 23, 2017.
Silica Hazards: Evaluating the Workplace
An exposure assessment is conducted to assess the eight-hour time-weighted average (TWA) exposure of each employee who is or may reasonably be expected to be exposed at or above the OSHA AL and the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) of 25 µg/m3 (ACGIH, 2017). Any combination of air monitoring data or objective data sufficient to accurately characterize employee exposures to respirable crystalline silica may be used to assess the eight-hour TWA exposure. Initial monitoring shall be performed to assess the eight-hour TWA exposure on the basis of one or more personal breathing zone air samples that reflect the exposures of employees on each shift, for each job classification, in each work area.
Once measurements are made on workers and worker exposure is characterized, they must be protected from respirable crystalline silica exposures above the 50 µg/m3 PEL, averaged over an eight-hour day.
Exposure Control Measures
Engineering controls must always be considered first when determining exposure control measures, followed by administrative controls, and then personal protective equipment (PPE).
Engineering controls include dust suppression with water; providing local exhaust ventilation; using HEPA‐filtered vacuums; providing enclosed cabs on equipment; substituting non‐silica products for those with silica; and using shrouds connected to HEPA-filtered vacuums to capture particles at point of generation – all of which are effective in reducing exposures.
Administrative controls (e.g., work practices) are used to control and limit workers’ exposure time by such measures as: working upwind; providing work area access controls; and operating/maintaining tools in accordance with manufacturer’s instructions to minimize dust emissions.
PPE, such as respiratory protection, is required when engineering and administrative controls are not sufficient to reduce exposures to or below the OSHA Action Level and TLV of 25 µg/m3.
For more information on OSHA required Specified Exposure Control Methods for respirable crystalline silica in construction activities, please reference OSHA 29 CFR 1926.1153, part c.
HETI…Helping Evaluate and Control Silica Hazards
HETI can assist facilities facing the challenges of assessing and controlling worker silica exposure. Our experienced and trained industrial hygienists can apply the OSHA crystalline silica standard to ensure that the workplace is properly evaluated for silica hazards and recommend proper exposure control measures to reduce the risk of overexposure.
References:
Occupational Safety and Health Administration, Department of Labor, OSHA Fact Sheet, DSG FS-3681 03/2016: OSHA’s Crystalline Silica Rule – Construction
Occupational Safety and Health Administration, Department of Labor, OSHA Fact Sheet, DSG FS-3683 03/2016: Workers’ Exposure to Respirable Crystalline Silica – Final Rule Overview
OSHA standards require employers to protect workers from respirable crystalline silica at exposures above the permissible exposure level (PEL) of 50 micrograms per cubic meter of air (50 µg/m3) averaged over an eight‐hour work shift. In addition, it requires employers to safeguard workers at or above an action level (AL) of 25 µg/m3 – which is set forth to protect workers against exposure above 50 µg/m3.
The standard also provides flexible alternatives, which OSHA expects will be especially useful for small companies. Employers can either use the control methods laid out in the construction standard, or they can measure workers’ exposure to silica and independently decide which dust controls work best to limit exposures to the PEL in their workplaces.
Regardless of which exposure control method is used, all construction employers covered by the standard are required to:
Establish and implement a written exposure control plan;
Designate a competent person to implement the written exposure control plan;
Restrict housekeeping practices that expose workers to silica;
Offer medical exams-including chest X-rays and lung function tests-every three years for workers who are required by the standard to wear a respirator for 30 or more days per year;
Train workers on work operations that result in silica exposure; and
Keep records of exposure measurements, objective data, and medical exams.
Construction employers must have complied with all requirements of the standard by September 23, 2017.
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