Silica (Respirable Crystalline Silica)

Respirable crystalline silica (RCS) is the very fine dust created when materials containing crystalline silica, such as sand, stone, concrete, brick, mortar and engineered stone, are cut, ground, drilled, crushed or otherwise disturbed. The particles are small enough to reach deep into the lungs, where they can cause silicosis, lung cancer and other serious diseases.

Silica exposure is one of the oldest known occupational hazards, and it is still common today in construction, manufacturing, mining, foundries, oil and gas, and countertop fabrication. In the United States, OSHA regulates RCS exposure through two standards, one for general industry and maritime and one for construction.

What Is Respirable Crystalline Silica?

Crystalline silica is a common mineral found in many natural and manufactured materials. Quartz is the most common form. Large pieces of silica-containing material are not a breathing hazard, but when the material is broken down, it releases particles that can be inhaled. "Respirable" refers to particles small enough to penetrate to the gas-exchange region of the lungs.

Common tasks that can create RCS dust include:

• Cutting, grinding or drilling concrete, brick, block and stone.
• Abrasive blasting with silica sand.
• Jackhammering and chipping concrete.
• Fabricating and finishing stone and engineered stone countertops.
• Foundry work such as sand casting, shakeout and finishing.
• Handling sand during hydraulic fracturing.
• Manufacturing glass, ceramics, brick and other silica-containing products.

Health Effects of Silica Exposure

Breathing RCS can cause:

• Silicosis: an incurable lung disease in which silica particles cause scarring that reduces the lungs' ability to take in oxygen. It can develop after years of exposure, or more quickly after very high exposures.
• Lung cancer: crystalline silica is classified as a human carcinogen.
• Chronic obstructive pulmonary disease (COPD).
• Kidney disease.

Silicosis cannot be reversed, so prevention through exposure control is essential. Public health agencies, including the CDC, have reported cases of severe silicosis among workers who fabricate engineered stone countertops, a reminder that new materials and tasks can create high exposures.

OSHA Silica Standards

OSHA published its respirable crystalline silica rule on March 25, 2016, creating two standards:

• General industry and maritime: 29 CFR 1910.1053, with most requirements in effect since June 23, 2018.
• Construction: 29 CFR 1926.1153, with enforcement beginning September 23, 2017.

Exposure Limits

• Permissible exposure limit (PEL): 50 micrograms per cubic meter of air (50 µg/m³), averaged over an 8-hour day.
• Action level: 25 µg/m³, averaged over an 8-hour day. Reaching the action level triggers certain requirements, such as periodic exposure monitoring and, in general industry, medical surveillance.

Key Requirements in General Industry and Maritime (1910.1053)

• Exposure assessment: assess exposures for employees who are or may reasonably be expected to be exposed at or above the action level, using either a performance option or a scheduled monitoring option. Under scheduled monitoring, repeat monitoring within six months when results are between the action level and the PEL, and within three months when results are above the PEL. Monitoring may stop after two consecutive measurements, taken at least 7 days apart, are below the action level.
• Regulated areas: establish regulated areas wherever exposures exceed, or can reasonably be expected to exceed, the PEL.
• Controls: use engineering and work practice controls to keep exposures at or below the PEL, and provide respirators when those controls are not enough.
• Written exposure control plan: describe the tasks that involve exposure, the controls and respiratory protection used for each task, and housekeeping measures. Review the plan at least annually.
• Housekeeping: do not allow dry sweeping or dry brushing where it could contribute to exposure, unless wet sweeping, HEPA-filtered vacuuming or other methods are not feasible. Restrict the use of compressed air for cleaning.
• Medical surveillance: offer medical exams at no cost to employees exposed at or above the action level for 30 or more days per year, with exams at least every three years or more often if recommended by the examining health care professional.
• Training and recordkeeping: train employees on silica hazards and controls, and keep exposure and medical records.

Key Requirements in Construction (1926.1153)

The construction standard covers the same core topics, with some important differences. According to OSHA's construction guidance:

• Table 1: employers that fully and properly implement the engineering controls, work practices and respiratory protection listed in Table 1 for a task do not need to assess exposures for that task or separately show compliance with the PEL.
• Alternative exposure control methods: for tasks not on Table 1, or where Table 1 is not fully implemented, employers must assess exposures and keep them at or below the PEL.
• Written exposure control plan: required for each worksite, describing tasks, controls, housekeeping and procedures to restrict access to work areas. It must be evaluated at least annually.
• Competent person: the employer must designate a competent person to make frequent and regular inspections of job sites, materials and equipment to implement the plan.
• Medical surveillance: offered at no cost to workers required to wear a respirator under the standard for 30 or more days per year, with follow-up exams at least every three years.

Understanding Table 1

Table 1 lists common construction tasks, such as using handheld power saws, jackhammers, drills and grinders on silica-containing materials. For each task it specifies dust controls, such as integrated water delivery or a shroud connected to a dust collection system, along with operating requirements and any required respiratory protection. Some entries require different respiratory protection depending on whether the task is performed for four hours or less, or more than four hours, in a shift, and whether the work is indoors or outdoors.

Table 1 can save contractors the time and cost of air monitoring, but only if every element listed for the task is followed. If the water flow is inadequate, the dust collector does not meet the specifications or the shroud is damaged, the employer is no longer following Table 1 and must use the alternative exposure control methods instead.

How to Build a Silica Exposure Control Program Step by Step

1. Identify silica sources. Review safety data sheets and product information to find materials that contain crystalline silica.
2. List the tasks. Identify every task that disturbs those materials and who performs it.
3. Choose a compliance approach. In construction, decide which tasks will follow Table 1. For other tasks, and in general industry, plan exposure assessments.
4. Apply controls. Use the hierarchy of controls, favoring substitution, wet methods, local exhaust ventilation and enclosed cabs before respirators.
5. Write the exposure control plan. Document tasks, controls, housekeeping and access restrictions.
6. Set up respiratory protection and medical surveillance. Where respirators are needed, follow your respiratory protection program and track who qualifies for exams.
7. Train workers. Explain silica hazards, the specific controls for each task and how to report problems.
8. Inspect and review. Check that controls work as intended and review the plan at least annually.

Best Practices for Controlling Silica Dust

• Use tools with integrated water delivery or vacuum dust collection whenever possible.
• Maintain dust collectors, filters and water systems so they work as designed.
• Use HEPA vacuums or wet methods for cleanup, never dry sweeping or compressed air.
• Position workers upwind and keep bystanders out of dusty areas.
• Provide PPE and respirators as required, and make sure respirator users are fit tested and medically cleared.
• Include silica controls in job hazard analyses and pre-task briefings.

How SMS360 Helps

The SMS360 Risk Assessment module helps teams identify silica-generating tasks, document the controls required for each one and track corrective actions when gaps are found. Keeping assessments, control requirements and reviews in one system makes it easier to maintain an accurate exposure control plan and show how silica risks are being managed across sites.

Frequently Asked Questions

What is the OSHA PEL for respirable crystalline silica?

The OSHA permissible exposure limit for respirable crystalline silica is 50 µg/m³ as an 8-hour time-weighted average. The action level is 25 µg/m³. The same limits apply under both the general industry and maritime standard (29 CFR 1910.1053) and the construction standard (29 CFR 1926.1153).

What is Table 1 in the OSHA silica standard?

Table 1 is part of the construction standard. It lists common construction tasks with specified engineering controls, work practices and respiratory protection. Employers that fully and properly implement those controls for a listed task do not need to perform exposure assessments for that task.

Who needs medical surveillance for silica?

In general industry and maritime, employers must offer medical exams to employees exposed at or above the action level for 30 or more days per year. In construction, exams must be offered to workers required to wear a respirator under the standard for 30 or more days per year. In both cases, exams are repeated at least every three years.

Is a written exposure control plan required?

Yes. Both silica standards require a written exposure control plan that describes tasks involving exposure, the controls and respiratory protection for each task, and housekeeping measures. In construction, the plan must also describe procedures to restrict access to work areas, and it must be implemented by a competent person.