Dry-Cutting Concrete: Table 1, Exposure Above the PEL, and Interim Controls
A 28-employee concrete contractor is cutting control joints and block openings in a new warehouse with a 14-inch gas-powered handheld saw. Four workers dry-cut 6-inch concrete block and poured walls about six hours per day, five days a week. A visible dust plume drifts past the operator and helper. No water feed, no vacuum shroud, no respirators, and no written exposure control plan are in use. Personal sampling over one shift gives the saw operator a respirable crystalline silica 8-hour time-weighted average of 0.12 mg/m3; the PEL is 0.05 mg/m3 and the action level is 0.025 mg/m3. The company has no air-monitoring program for other tasks, no medical surveillance, and no training documentation beyond a toolbox talk stating that silica is in concrete. Work continues for four months. The saw is the only unit available; a water kit is on backorder for three weeks.
1. May the employer use Table 1 of 1926.1153 and skip exposure assessment for this cutting operation? Explain.
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No. Table 1 is a compliance option, not a safe harbor that applies to any task involving silica. 1926.1153(c)(1) requires the employer to comply with Table 1 only when the task is listed and the specified engineering control, work practice, and respiratory protection are fully and properly implemented. The entry for a handheld power saw requires either a water-fed saw or a saw equipped with an integrated dust collection shroud and HEPA vacuum. This crew is dry cutting with neither, so the task as performed is not a Table 1 task.
Because Table 1 does not cover the operation, the employer must comply with 1926.1153(d): assess the exposure of each employee who may be exposed, use engineering controls and work practices to reduce exposure to the PEL, and supplement with respiratory protection only where engineering controls are not feasible or cannot achieve the PEL. The sampling result of 0.12 mg/m3 is 2.4 times the PEL and 4.8 times the action level, so the employer has actual knowledge of overexposure and cannot wait for the backordered water kit. Interim controls plus respirators are required immediately.
The employer also cannot declare the assessment complete on the basis of one sample if the results are not representative. A single personal sample above the PEL is enough to trigger the full program, and the employer should reassess after controls are installed.
2. Given the 0.12 mg/m3 result, what hierarchy of controls and respiratory protection is required, and what minimum respirator is acceptable?
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Engineering controls. Water-fed cutting is the preferred control and is the Table 1 method; the employer should rent or borrow a water-fed saw, or use a shroud with a HEPA vacuum, rather than wait three weeks. Local exhaust ventilation at the point of cut is an alternative. Dry sweeping and compressed air are prohibited as cleanup methods; use wet methods or HEPA vacuums under the housekeeping provisions of 1926.1153.
Respiratory protection. Because the measured exposure is 2.4 times the PEL, a respirator with an assigned protection factor of at least 10 will reduce the effective exposure below the PEL (0.12 / 10 = 0.012 mg/m3). A NIOSH-approved half-mask air-purifying respirator with P100 filters meets this. The full 1910.134 program applies: written program, medical evaluation, fit testing, training, cartridge or filter change schedule, and storage and inspection. Voluntary use is not available because exposure exceeds the PEL.
Regulated area. 1926.1153(e) requires warning signs and restricted access where exposures exceed the PEL.
Monitoring. Reassess whenever there is a change in equipment, process, or controls, and after the water kit is installed to confirm the controls are effective. If the controls bring exposure below the action level, respirators can be discontinued after confirming with sampling.
3. Which program elements and records are triggered, and by when?
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- Written exposure control plan under 1926.1153(g): describe the tasks, engineering controls, work practices, and respirators; identify a competent person; review and update at least annually.
- Training under 1926.1153(j): before assignment and annually. Content must include health effects, tasks that cause exposure, engineering controls and work practices, respirators, and the exposure control plan.
- Medical surveillance under 1926.1153(i): offer exams to employees exposed at or above the action level for 30 or more days per year. The crew works six hours a day, five days a week, so this is triggered. Offer within 30 days of assignment and every three years thereafter, with a written medical opinion.
- Recordkeeping under 1926.1153(k): exposure records for 30 years; medical records for the duration of employment plus 30 years. Training records are not specifically required by the silica standard but should be kept to prove compliance.
- Communication: labels and safety data sheets for products containing crystalline silica under 1910.1200, plus warning signs in regulated areas.
The plan, training, and medical surveillance should be in place before the crew continues dry cutting, with interim respirators and engineering controls while the water kit is on backorder.