Respirable Crystalline Silica Exposure Monitoring

What is Respirable Crystalline Silica?

Crystalline silica is a basic component of soil, sand, granite, and many other minerals. Quartz is the most common form of crystalline silica, while cristobalite and tridymite are two other naturally occurring forms. When workers chip, cut, drill, grind, sand, or polish materials containing crystalline silica, respirable-sized particles become airborne and can be inhaled deep into the lungs.

Prolonged exposure to respirable crystalline silica causes silicosis, an incurable and sometimes fatal lung disease. Silica exposure is also linked to lung cancer, chronic obstructive pulmonary disease (COPD), and kidney disease. Because these health effects develop gradually over years of exposure, proactive monitoring and control are essential.

Cal/OSHA Section 5204: Occupational Exposures to Respirable Crystalline Silica

Employers must perform initial monitoring to assess exposures for each employee based on personal breathing zone air samples that reflect exposures on each shift, for each job classification, in each work area. In representative sampling, employers must sample the employees expected to have the highest exposure to respirable crystalline silica.

Cal/OSHA Section 5204 does not apply if the employer has objective data demonstrating that employee exposure to respirable crystalline silica will remain below 25 µg/m³ under any foreseeable conditions. However, most stone fabrication, construction, and manufacturing operations require monitoring due to the high-exposure nature of cutting, grinding, and polishing tasks.

Common Exposure Scenarios

Respirable crystalline silica exposure occurs across a wide range of industries and operations. Any task involving cutting, grinding, drilling, sanding, or polishing materials containing silica generates respirable dust. Below are typical exposure scenarios:

Silica Content by Material Type

The percentage of crystalline silica in materials varies significantly, directly impacting exposure potential during fabrication or construction tasks. Understanding silica content helps predict exposure levels and prioritize monitoring efforts:

When compared across materials with differing silica levels, exposures while working with quartzite or quartz are expected to be significantly higher on average than granite or marble. Fabricators working primarily with high-silica materials face elevated exposure risk and require more stringent controls.

Real-World Example: Stone Fabrication Shop

EHS Analytical Solutions recently conducted silica exposure monitoring at a stone fabrication facility in San Marcos, California. The shop primarily works with quartzite and marble, followed by quartz and granite. On the day of monitoring, quartzite and quartz were the materials being fabricated and polished.

Despite the use of wet cutting and polishing methods, which reduce but do not eliminate airborne silica, the fabricator's exposure exceeded the PEL due to the high silica content in quartzite (90%) and the duration of cutting operations. Polishers, who primarily use wet methods with minimal visible dust generation, maintained exposures below the Action Level.

When is Silica Monitoring Required?

Cal/OSHA Section 5204 requires initial exposure monitoring to assess employee exposures whenever operations involve respirable crystalline silica. Initial monitoring establishes baseline exposures and determines the frequency of ongoing monitoring. Key triggers include:

• New Operations: When starting stone fabrication, construction, or manufacturing tasks involving silica-containing materials
• High-Exposure Trigger Tasks: Tasks such as cutting, grinding, polishing, abrasive blasting, drilling, or demolition involving silica materials
• Process or Equipment Changes: When new equipment, materials, or work practices are introduced that may affect exposure levels
• Employee Reports: When workers report respiratory symptoms or express concerns about dust exposure
• Regulatory Compliance: To fulfill Cal/OSHA's requirement for representative exposure data for each job classification and work area

Monitoring Frequency Based on Results

Cal/OSHA Section 5204 establishes specific requirements for repeat monitoring based on initial results:

Employers must notify employees of monitoring results within 15 working days after completing the exposure assessment. Notifications must be provided individually in writing or posted in an accessible location. When exposures exceed the PEL, the notification must describe the corrective actions being taken to reduce exposure.

What Happens After Monitoring?

Once silica exposure monitoring is completed and results are analyzed, employers must take specific actions based on exposure levels. Cal/OSHA Section 5204 establishes a hierarchy of controls prioritizing engineering and work practice controls over respiratory protection:

Engineering and Work Practice Controls

Employers must use engineering and work practice controls to reduce and maintain employee exposure to or below the PEL unless such controls are not feasible. Even when controls are insufficient to reach the PEL, they must still be implemented to reduce exposures to the lowest feasible level, supplemented by respiratory protection.

Common engineering controls include:

• Local Exhaust Ventilation (LEV): Capture silica dust at the source using downdraft tables, overhead hoods, or on-tool dust extraction systems
• Wet Methods: Use water to suppress dust generation during cutting, grinding, or drilling. Water must be applied continuously to be effective
• Process Enclosure: Isolate high-dust operations within enclosed spaces with separate ventilation
• Tool Modifications: Use saws, grinders, and drills equipped with integrated water delivery or dust collection systems

Work practice controls include positioning workers to face ventilation systems, minimizing dry cutting or grinding, reducing the duration of high-exposure tasks, and implementing proper housekeeping to prevent dust accumulation and re-entrainment.

Respiratory Protection

When engineering and work practice controls are insufficient to reduce exposures to or below the PEL, employers must provide respiratory protection at no cost to employees. Respiratory protection must comply with Cal/OSHA Section 5144 (Respiratory Protection) and be selected based on the level of airborne silica.

For silica exposures, NIOSH-approved respirators with appropriate assigned protection factors are required:

• Half-Mask Respirators with P-100 Filters: Assigned Protection Factor (APF) of 10, protecting up to 10× the PEL (500 µg/m³)
• Full-Facepiece Respirators with P-100 Filters: APF of 50, protecting up to 50× the PEL (2,500 µg/m³)
• Powered Air-Purifying Respirators (PAPR): APF of 25 (half-mask) or 1,000 (full-facepiece with tight-fitting), providing greater protection and comfort
• Supplied-Air Respirators: APF up to 1,000 or higher for extremely high exposures such as abrasive blasting

Employers must establish a respiratory protection program that includes medical evaluations, fit testing, training, and proper maintenance and storage of respirators.

Written Exposure Control Plan

Cal/OSHA Section 5204 requires employers to establish and implement a written exposure control plan containing:

• A description of tasks in the workplace that involve exposure to respirable crystalline silica
• Engineering controls, work practices, and respiratory protection used to limit exposure for each task
• Housekeeping measures used to limit employee exposure

The written exposure control plan must be reviewed and updated at least annually and made readily available for examination by employees, their designated representatives, and Cal/OSHA officials.

Housekeeping Requirements

Proper housekeeping is essential to prevent silica dust accumulation and re-entrainment into the air. Cal/OSHA Section 5204 prohibits:

• Dry Sweeping or Dry Brushing: Prohibited where such activity could contribute to employee exposure unless wet sweeping, HEPA-filtered vacuuming, or other methods that minimize exposure are not feasible
• Compressed Air: Prohibited for cleaning clothing or surfaces where such activity could contribute to silica exposure

Employers should use HEPA-filtered vacuums for all silica dust cleanup operations. Standard shop vacuums without HEPA filtration shall not be used, as they re-entrain fine silica particles into the air.

Medical Surveillance

Employers must offer medical surveillance to employees who are exposed to respirable crystalline silica at or above the Action Level for 30 or more days per year. Medical surveillance includes:

• Initial and periodic medical examinations, including chest X-rays
• Pulmonary function testing
• Tuberculosis (TB) testing
• Evaluation by a physician or other licensed healthcare professional (PLHCP)

Medical surveillance ensures early detection of silica-related health effects and allows for timely intervention and exposure control adjustments.

Why Use a Certified Industrial Hygienist?

Accurate silica exposure monitoring requires specialized knowledge of sampling methods, analytical techniques, Cal/OSHA regulations, and exposure control strategies. A Certified Industrial Hygienist (CIH) provides critical expertise that ensures compliance and protects employee health:

• Proper Sampling Equipment: CIHs use calibrated personal sampling pumps with SKC Parallel Particle Impactor (PPI) cassettes designed to capture respirable-sized silica particles at precise flow rates (2.0 L/min)
• Representative Sampling Strategy: CIHs identify employees with the highest expected exposures and select appropriate sampling durations to capture worst-case scenarios
• AIHA-Accredited Laboratory Analysis: Samples are analyzed by accredited laboratories using X-ray powder diffraction (XRD) techniques to quantify quartz, cristobalite, and tridymite with high accuracy
• Exposure Calculation and Interpretation: CIHs calculate 8-hour TWA exposures, account for variability in work tasks, and determine compliance with Cal/OSHA standards
• Comprehensive Reporting: Detailed industrial hygiene survey reports include methods, results, regulatory requirements, and actionable recommendations for exposure control
• Engineering Control Guidance: CIHs assess the feasibility and effectiveness of ventilation systems, wet methods, and other engineering controls to reduce exposures
• Regulatory Compliance Assurance: CIHs ensure all aspects of Cal/OSHA Section 5204 are addressed, including written exposure control plans, employee notifications, regulated area signage, and medical surveillance

Attempting silica monitoring without proper expertise and equipment can result in inaccurate exposure data, regulatory violations, inadequate employee protection, and increased liability. A CIH ensures the assessment is conducted correctly, meets all legal requirements, and provides a solid foundation for an effective silica control program.