Given the silica content of concrete and mortar, silicosis is an enduring scourge of concrete and masonry construction. The damaging effects of ongoing exposure to airborne silica were familiar even to the ancient Greeks and Romans. When inhaled, the tiny abrasive particles damage a person’s lungs and over time reduce breathing capacity, leaving the person chronically gasping for breath. Nor is silicosis the only danger: studies link exposure to airborne crystalline silica to COPD, tuberculosis and lung cancer.
Little wonder that OSHA has proposed strengthening standards protecting workers from silica exposure, including a table of suggested engineering controls for reducing airborne dust. Our current study of silica exposures during concrete cutting focuses on one of those controls.
Dust and Noise
The research is part of a multi-year examination of controls for dust and noise hazards on construction sites. While dramatic fatal accidents capture the news, far larger numbers of construction workers suffer from hearing loss or respiratory illness as a result of chronic dust inhalation and noise exposures. Our team here at the University of Massachusetts Lowell Department of Work Environment has partnered with construction contractors and labor organizations to seek practical controls to eliminate these dangers and the debilitating occupational illnesses they produce.
The study at hand focused on the use of gas-powered portable concrete saws to cut reinforced concrete pipe, measuring the content of airborne silica dust generated each time. We aimed to find out: could wet concrete cutting, a favored engineering control, indeed drastically reduce respirable levels of silica dust in the worker’s environment?
Since we wanted the results to resemble a variety of conditions seen on a construction site, we did not attempt our work in a sterile lab environment but at the New England Laborers’ Training Center. We ran some tests in a semi-enclosed warehouse setting, and others outdoors; new apprentices operated the saws for one series of tests, while experienced journeymen did so in others.
In the end we employed 31 different operators in the series of tests over a period of months. The tests were performed using a gas powered concrete saw with a 14 inch diameter blade and a water connection. The water feature could be activated either by connecting a hose or a portable pressurized spray canister – we measured results using each alternative. The operators were asked to make cuts for the entire 8’ length of the concrete pipe (not the typical direction for cutting but necessary for consistent sampling technique).
The Results: Wetter is Better
The results confirmed what common sense has told us: if you want to keep dust out of the air when cutting concrete, wetter is better. The geometric mean respirable dust concentration produced by dry cutting trials was 14.396 milligrams per cubic meter – more than 10 times higher than the concentrations created while using water-based controls. (The average trial using the water hose hookup generated just under 1.1 milligrams per cubic meter; the spray control trials put an average of 1.2 milligrams of silica dust per cubic meter into the ambient air.)
To control for any differences between individual operators and/or individual saws, we matched up the results into 79 pairs. Each pair compared the dust concentrations generated by the same worker operating the same saw, once cutting dry and another time using the wet method. The results were categorical and striking. Using water reduced respirable dust concentration by 85%. The contest between the two methods, in other words, was no contest at all. Anyone cutting concrete who is concerned about respiratory health should take note, and use water.
Indeed, we note with some alarm that even though the concrete cutting exercise we performed was a brief one, over in a matter of minutes, it was enough time to push the airborne crystalline silica levels above the OSHA Permissible Exposure Limits in ten of the dry cutting trials – and even one of the wet ones!
Dry cutting with gas-powered concrete saws should not be allowed under any circumstances, unless the firm is prepared to perform personal air sampling to ensure that exposure levels do not exceed acceptable limits. When exposure levels are known, selection of the appropriate respirator can be an effective way to reduce personal exposures, although the dust can still fill the work area and expose other workers and the neighborhood. The regular use of water controls on gas-powered concrete saws is a clear and effective way to reduce the level of respirable dust altogether: for operators, other project workers and the community.
The complete report, “Controlling Dust from Concrete Saw Cutting,” can be found in the February 2013 edition of the Journal of Occupational and Environmental Hygiene. The study was made possible with support from CPWR – the Center for Construction Research and Training.
Susan Shepherd, ScD CIH CSP is currently an industrial hygiene consultant at the On-site OSHA Consultation Program in Massachusetts.
Susan Woskie, PhD, CIH, is a professor at the University of Massachusetts Lowell Department of Work Environment and director of the Occupational and Environmental Hygiene Program there.