Risk assessment for silica in CA

In California, a silica exposure risk assessment should identify whether employees are exposed to respirable crystalline silica—quartz, cristobalite, and/or tridymite in respirable airborne particles—and whether the work falls under general industry (§5204) or construction (§1532.3). Under §5204, the standard applies to occupational exposures unless construction, agriculture, or certain sorptive clay processing exceptions apply, and it applies to high-exposure trigger tasks regardless of objective data. High-exposure trigger tasks include machining, cutting, drilling, grinding, polishing, and cleanup of dust or debris from artificial stone containing more than 0.1% crystalline silica or natural stone/products containing more than 10% crystalline silica. [12] [4] [4]

Hazard identification should focus on materials and tasks with significant silica content and dust generation potential. Artificial stone commonly contains more than 90% crystalline silica, quartzite about 95%, sandstone about 60%, and granite about 10 to 45%. Tasks such as grinding, cutting, routing, drilling, chipping, and polishing can generate hazardous airborne dust. Health effects include silicosis, lung cancer, kidney and autoimmune disease, decreased lung function, and increased susceptibility to tuberculosis; silicosis is progressive and irreversible and can be fatal. [6] [2] [10] [2]

For exposure assessment, California requires employers to assess each employee who is or may reasonably be expected to be exposed at or above the action level of 25 µg/m³ as an 8-hour TWA. The permissible exposure limit is 50 µg/m³ as an 8-hour TWA. Under §5204 and §1532.3, employers may use either a performance option based on air monitoring/objective data or a scheduled monitoring option, except that high-exposure trigger tasks must be assessed by scheduled monitoring. Initial monitoring must use personal breathing zone samples representing each shift, job classification, and work area, with sampling focused on employees expected to have the highest exposure. [4] [1] [1] [1]

• If initial monitoring is below the action level, monitoring may be discontinued for represented employees, except high-exposure trigger tasks.
• If results are at or above the action level but at or below the PEL, repeat monitoring within 6 months.
• If results are above the PEL, repeat monitoring within 3 months.
• If non-initial results are below the action level, repeat within 6 months until two consecutive measurements taken 7 or more days apart are below the action level.
• Reassess whenever changes in process, controls, personnel, production, or work practices may create new or additional exposures.
• Use a laboratory that analyzes respirable crystalline silica samples according to Appendix A procedures.
• Notify affected employees of assessment results in writing or by posting; under §5204 this must be within 15 working days, and if above the PEL the notice must describe corrective action.

[5] [5] [5] [5] [5] Control measures must follow the hierarchy of controls. Employers must use engineering and work practice controls to reduce exposures to or below the PEL unless infeasible, and if those controls are insufficient they must still be used to reduce exposure to the lowest feasible level and be supplemented with respiratory protection. For high-exposure trigger tasks, effective wet methods are mandatory regardless of measured exposure. California specifically defines wet methods as applying constant, continuous, appropriate water to the point of contact, submersing the workpiece, or water-jet cutting, with water covering the entire surface where the tool contacts the work object. [9] [9] [1] [1]

• Use water-fed tools or directed water application at the point of operation whenever possible.
• Use local exhaust ventilation at the dust generation source.
• For indoor or enclosed construction tasks, provide exhaust as needed to minimize visible airborne dust accumulation.
• Maintain enclosed cabs/booths under positive pressure with filtered intake air and good seals where those controls are used.
• Avoid homemade or poorly designed controls; use controls designed, maintained, and operated according to manufacturer instructions.

[2] [2] [3] [3] [7] Housekeeping is a critical part of worker protection because cleanup activities can create severe secondary exposures. For high-exposure trigger tasks, wastes and dust must be promptly cleaned up and placed in leak-tight containers, with at least end-of-shift cleanup and more often as needed to prevent visible dust buildup. Wet methods or HEPA-filtered vacuums must be used. Dry sweeping, dry shoveling, disturbing dry dust, and compressed air cleaning are prohibited for high-exposure trigger tasks, and employee rotation cannot be used as an exposure-control method. [9] [9] [9] [11] [15]

Respiratory protection is required when engineering and work practice controls cannot keep exposure at or below the PEL, during installation of controls, for certain non-feasible tasks, and whenever employees enter regulated areas. For general §5204 situations, respirators must comply with Section 5144. For high-exposure trigger tasks, California generally requires a full-face tight-fitting PAPR, helmet/hood PAPR with APF 1000, or equivalent/higher protection with HEPA, N100, R100, or P100 filters, unless the employer qualifies for a limited exception based on repeated representative air sampling below the action level and other conditions. Workers with confirmed or suspected silicosis may require supplied-air respirators. [14] [14] [14] [2]

Cal/OSHA also requires regulated areas wherever exposure exceeds or can reasonably be expected to exceed the PEL, and all high-exposure trigger tasks must be conducted within a regulated area regardless of measured exposure. Access must be limited to authorized persons and observers, warning signs must be posted, and employees entering regulated areas must be provided appropriate respirators. A written exposure control plan is required and must describe silica-generating tasks, controls, respiratory protection, and housekeeping; for high-exposure trigger task workplaces it must also address PPE donning/doffing to prevent take-home exposure, training procedures, medical surveillance, and medical removal procedures if necessary. [5] [9] [11] [11]

Worker protection procedures should include training, medical surveillance, symptom reporting, and recordkeeping. Employees must be trained on silica health hazards, symptoms, exposure-generating tasks, controls, respirator use, the medical surveillance program, and the increased risks from smoking and latent tuberculosis. Employers must encourage symptom reporting without reprisal. Medical examinations must be made available at no cost to employees exposed at or above 25 µg/m³ as an 8-hour TWA for 30 or more days per year, and broader surveillance is encouraged for workers exposed more than 30 days per year. Employers must maintain air-monitoring records and report confirmed silicosis or silica-related lung cancer cases to CDPH and the Division within 24 hours. [8] [8] [10] [8] [13]

• Determine whether the work is covered by §5204 general industry or §1532.3 construction.
• Inventory silica-containing materials and identify high-exposure trigger tasks.
• Conduct personal breathing-zone monitoring or use valid objective data; use scheduled monitoring for high-exposure trigger tasks.
• Compare results to the action level of 25 µg/m³ and PEL of 50 µg/m³, both as 8-hour TWAs.
• Establish regulated areas where required and post warning signs.
• Implement wet methods, local exhaust ventilation, and other engineering/work practice controls before relying on respirators.
• Prohibit dry sweeping and compressed-air cleanup where silica exposure can result; use wet cleanup or HEPA vacuums.
• Provide appropriate respirators, fit testing, training, and a full respiratory protection program under Section 5144.
• Maintain a written exposure control plan, train employees, provide medical surveillance when required, and keep monitoring records.
• Promptly investigate symptoms or diagnoses suggestive of silicosis and complete required reporting within 24 hours for confirmed silicosis or silica-related lung cancer cases.

[12] [4] [4] [1] [14]