Safety and health newsletter for the Oregon construction industry


September 18, 2012

Dry-cutting concrete

Respirable hazard of the month: silica dust

On many construction projects, some unsafe practices are obvious to a passerby. Working on a steep roof without fall protection, working in an unshored trench, and using a stepladder on a scaffold to gain a few extra feet are examples. But there’s one unsafe practice that literally calls attention to itself with ear-splitting noise and clouds of dust: dry-cutting concrete without respiratory protection.

The saw blade may be well maintained, properly positioned, and the correct one for the job. And the saw operator may be wearing safety glasses and hearing protection. But unless the operator is protected from breathing the dust, there’s a serious health hazard in the making. Unfortunately, the operator may not show any symptoms of long-term overexposure to the hazard – silica dust –for 10 years or more. By then, the damage to the operator’s lungs is complete and the result is the incurable lung disease, silicosis.

Oregon OSHA’s permissible exposure limit (PEL) to silica is 0.1 milligrams per cubic meter of air (mg/m3 ) averaged over an eight-hour period. This limit is for the respirable fraction of the dust, which is microscopic; particle sizes are 1 to 10 microns. Operating a handheld masonry saw outdoors, for example, without dust controls can produce silica exposures as high as 14 times the PEL.

What should this mean to the saw operator? Control the dust. The best method is to cut wet. Cutting wet controls the dust at its source because the dust is less likely to become airborne. Wet cutting, when done properly, can keep exposures to silica dust exposures below the PEL.

Using a vacuum dust collection system is another way to control the dust, but it’s generally not as effective as wet cutting in reducing silica levels. For outdoor work, using an effective vacuum dust collection system with an efficient filter may reduce exposures below 1.0 mg/m3, but not necessarily below the PEL. In that case, the saw operator must wear a properly fitted, NIOSH-approved half-facepiece or a disposable respirator equipped with an N-, R-, or P-95 filter.

What you can’t see might still harm you

If you’re cutting concrete and generating dust, chances are that respirable silica levels are too high. But just because you can’t see any dust doesn’t mean that you’re not breathing silica into your lungs. Those 1-10 micron-sized respirable silica particles (the ones that damage your lungs) are invisible. When you’re cutting concrete, the best safe practice is to cut wet.

While we’re on the subject of invisible hazards, never use gas-powered concrete saws in poorly ventilated areas. In July, an Oregon construction worker using a gas-powered saw in a manhole was overcome by carbon monoxide and lost consciousness.


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