Dry Concrete Cutting and Silica Overexposure
At a concrete bridge deck project, a worker uses a 14 in. gas-powered cut-off saw to dry-cut control joints for 6 hours per shift. Personal air sampling on two consecutive days shows respirable crystalline silica (quartz) at 0.18 mg/m3 and 0.16 mg/m3 as 8-hour time-weighted averages. The OSHA permissible exposure limit is 0.05 mg/m3, and the action level is 0.025 mg/m3. The crew has no water attachment, no vacuum shroud, no respirators, and no written exposure control plan. Workers wear safety glasses and hearing protection. The saw has a manufacturer-provided water port, but the water tank was removed to save weight. The foreman proposes that everyone wear a dust mask and continue until the end of the month. A worker reports shortness of breath, but he has smoked for 20 years and says it is not work-related.
1. Evaluate the exposure results and specify the engineering controls that must be implemented before cutting continues.
Read the worked answer
Both samples exceed the 0.05 mg/m3 PEL and the 0.025 mg/m3 action level. The higher result is 0.18 divided by 0.05, or 3.6 times the PEL. The average is also well above the PEL. The employer must implement an exposure control plan and use engineering controls before relying on respirators.
Engineering controls:
- Reattach the water tank and use wet cutting. Water suppression is the preferred control for a hand-held cut-off saw.
- If water is not feasible, use a vacuum dust-collection shroud designed for the saw.
- Use the saw outdoors or with local exhaust ventilation; do not dry-cut in an enclosed area.
- Limit the number of workers exposed and the duration of cutting where possible.
- Clean up dust with wet methods or HEPA vacuums, not dry sweeping or compressed air.
The foreman's dust mask is not a NIOSH-approved respirator and is not acceptable. Dry cutting must stop until controls are in place.
2. Select the minimum respirator class needed if engineering controls do not reduce exposure below the PEL, and list the program elements.
Read the worked answer
The minimum assigned protection factor is the exposure divided by the PEL: 0.18 / 0.05 = 3.6. A half-face air-purifying respirator with particulate filters has an assigned protection factor of 10, so it is adequate for 3.6 if the program is complete. A full-face respirator would provide a higher protection factor if exposures are higher or if eye irritation is a concern.
Required program elements:
- Written respiratory protection program.
- Medical evaluation before fit testing and use.
- Annual fit testing and training.
- NIOSH-approved particulate filters, properly selected and changed.
- User seal checks and proper storage.
- Evaluation of exposure and of the respirator program.
The respirator is a supplement, not a substitute for wet cutting or dust collection.
3. What medical surveillance and exposure control plan requirements apply to this crew?
Read the worked answer
The employer must have a written exposure control plan that identifies the tasks, controls, housekeeping methods, and procedures to restrict access. Because exposures are at or above the PEL, medical surveillance must be offered to employees who are exposed at or above the PEL for 30 or more days per year. The medical surveillance includes a medical and work history, physical examination, chest X-ray, spirometry, and tuberculosis testing, with follow-up as needed. The worker with shortness of breath should be referred for medical evaluation even though he smokes; the employer should not attribute the symptom to smoking without a medical evaluation.
Also provide training on silica health effects, controls, and the importance of wet cutting. Keep exposure records and medical records as required. Reassess exposure after controls are installed to confirm they are effective.