NIOSH-Supported Study Examines Substitutes for Silica Sand to Further Efforts in Silicosis Prevention

Contact: Fred Blosser (202) 260-8519
March 25, 1997

It is a research project that involves true grit -- literally. In a study initiated by the National Institute for Occupational Safety and Health (NIOSH), scientists are gathering comprehensive data about dusts generated from abrasive blasting processes using 41 different gritty materials as abrasive agents. Results of the study will advance efforts to protect workers from silicosis, a serious and sometimes fatal occupational lung disease, by helping users and others identify appropriate substitutes for silica sand in abrasive blasting.

In the first phase of the research, performed by KTA/SET Environmental, Inc., Pittsburgh, Pa., with NIOSH funding, scientists simulated abrasive blasting in a carefully monitored laboratory setting. Individually, 41 grits were applied to a row of steel plates at identical pressures. The grits represented 10 different types of abrasives other than silica sand: garnet, olivine, coal slag, steel grit, treated sand (silica sand treated with a dust suppressant), copper slag, nickel slag, specular hematite, staurolite, and crushed glass. To obtain more than one sample of each material, the researchers used products from different manufacturers or suppliers.

The laboratory simulations, now completed, will be followed by field research at a selected site. Eight different types of abrasives used in the laboratory setting will be applied to steel plates at identical pressures in the field research. The laboratory research allowed scientists to collect consistent data on the performance of the materials, avoiding random factors that could make it diffcult to compare and analyze the findings. With that consistent baseline, the field research then will help researchers identify factors that could influence the performance of the materials in real-life applications.

In abrasive blasting, high-pressure streams of grit are projected against a hard surface, usually with compressed air or steam. The process is used to clean foundry casings, remove rust and other impurities from steel surfaces such as girders, and scour stone buildings, among other applications. In the U.S., these operations most often use silica sand as the abrasive agent. Workers may be at risk of silicosis from exposure to silica dust generated when high-velocity impact shatters the sand into smaller, breathable dust particles.

One way to reduce this risk is to replace silica sand with an abrasive that does not contain crystalline silica, but substitution can be complex and expensive. It is difficult for users to determine if potential substitutes will work as effectively as silica sand for their purposes, because little research has been done to study the applications of these materials under identical conditions. Also, little data exist for evaluating whether the uses of alternative abrasives may themselves pose health concerns. Results of the NIOSH-initiated study will help fill these critical gaps in knowledge.

Data being gathered in the study include areas vital for identifying potential health effects from exposures during abrasive blasting. The researchers are measuring the airborne levels of dust generated by each application, and identifying the composition and size of the airborne particles.

Additionally, the researchers are gathering data that can be combined with information such as the price per ton of each type of abrasive, and disposal costs for spent materials, to compare the overall costs of using one type versus another. The researchers are evaluating:

• The rates at which different abrasives are consumed. At equal pressures, some abrasives will be used up faster than other abrasives.
• The blasting rates for different abrasives in units of square feet of surface blasted per minute. Some abrasives can blast more square feet of a particular surface in the same time period (using the same blasting pressure), due to the fact that physical properties such as shape, density, and hardness differ among the various materials.
• The number of times each abrasive can be recycled.

Researchers completed the laboratory work in late 1996. The pending field study is expected to be completed by September 1997. A report is expected to be published after both phases of research are completed. The study is one of several ongoing efforts by NIOSH to protect workers from the risk of silicosis.

For further information on currently available publications from NIOSH relating to prevention of silicosis, contact toll-free 1-800-35-NIOSH or visit the NIOSH site.