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NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

NIOSH Programs > Respiratory Diseases > Evidence Package > 3. Interstitial Lung Diseases > 3.2 Silica-Induced Respiratory Diseases

3.2b) Promotion of Substitutes for Silica Sand in Abrasive Blasting

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Issue

In 1992, NIOSH published an Alert “Request for Assistance in Preventing Silicosis and Deaths from Sandblasting” (A3-35). This Alert described the very high silica dust levels produced during sandblasting and noted that workers in this occupation were at extremely high risk of developing silicosis. The Alert recommended the use of abrasive substitutes for sand. However, at that time the economic feasibility of substitute use and the potential toxicity of substitute abrasives were not fully understood. These factors were obstacles to the adoption of substitute abrasives for sand by industry.

Approach

RDRP scientists used many of the same elements that are described in chapter 3.2a to address the substitution of abrasive for silica sand sandblasting. However, additional activities were part of this approach. In response to the inputs described in chapter 3.2a, RDRP scientists developed two research projects to resolve the following questions:

  • Are substitute materials commercially available in sufficient quantities to serve industry?
  • Are these substitutes effective and cost-efficient abrasives?
  • What is the pulmonary toxicity of these substitutes compared to silica sand?

RDRP scientists started the evaluation of substitute materials with a literature search of data concerning the toxicity of abrasive substitutes. Significant knowledge gaps were noted. Therefore, in vitro testing of toxicity was conducted and acute in vivo testing of toxicity. Data were published in the peer-reviewed literature and presented to industrial stakeholders and other interested parties.

The evaluation of substitute materials for silica sand in abrasive blasting proceeded through conducting controlled test blasting. The costs of substitute materials were evaluated and the effectiveness of the substitute materials as abrasives was determined. Airborne elemental metals generated during use of the substitutes were also measured.

Outputs and Transfers

RDRP results of determinations of costs and effectiveness of substitute materials and the comparative toxicities with silica sand were disseminated through at least seven publications. The publications included four key reports published in the peer-review literature (1-4, A3-45, A3-46, A3-47, A3-48) and three NTIS publications (A3-49, A3-50, A3-51). These key publications provided data on the blasting effectiveness and costs of abrasive substitutes, evaluations of the airborne metals generated during the use of various blasting substitutes and details of differential pulmonary toxicities of abrasive substitutes (specular hematite and steel grit were less toxic than sand; while coal, slag, and olivine were more toxic). Other substitutes (garnet, staurolite, nickel slag, copper slag, crushed glass, and treated sand) exhibited toxicity in the same range as sand.

Communication of these results to industry, industrial hygienists, and governmental regulatory agencies is evidenced by 23 direct communications to partners (A3-52). Results were disseminated to industrial stakeholders and other interested parties via RDRP presentations at numerous trade association and other meetings.

Intermediate Outcomes

RDRP, through direct communication to industrial stakeholders of its research findings on cost effectiveness, abrasion effectiveness, and toxicity of various blasting materials, has played a role in substituting the use of alternative abrasives for sand in abrasive blasting operations. Between 1996 and 2004, the use of abrasive substitutes for sand increased as the use of silica sand for sandblasting decreased by 47 percent. The “U.S. Geological Survey Minerals Yearbook” documented use of silica sand for sandblasting decreased from 1,470,000 metric tons in 1996 to 784,000 metric tons in 200452 (A3-53). It is anticipated that this intermediate outcome will eventually result in reduction of silicosis incidence in sandblasters.

OSHA considered information concerning the toxicity of sandblasting substitute abrasives to be critical to its ongoing effort to review its silica standard. Through an Interagency Agreement, OSHA partially funded RDRP’s research effort evaluating the relative toxicity of blasting materials in an acute study in 1999-2000 (Perry letter A3-54).

The National Toxicology Program (NTP), upon review of RDRP findings, accepted the nomination of toxicology evaluation of selected abrasive blasting substitutes for a sub-chronic inhalation study in 2002.

What’s Ahead

RDRP scientists will consult with the NTP on experimental study design for a short-term inhalation study comparing the pulmonary responses to silica sand and various substitute abrasives. Toxicology data pertaining to substitute abrasives will be provided to OSHA to support ongoing efforts to review the OSHA silica standard. In addition, substantial enhancement of information concerning silica exposure and silicosis risk among sandblasters is planned for the NIOSH Web-based “Silica” Topic page and/or for a separate “Abrasive Blasting” Topic page to be developed.

52. Dolley TP [2004]. U.S. Geological Survey - Minerals Yearbook  Silica. Table 6 p13.
External link: http://minerals.usgs.gov/minerals/pubs/commodity/silica/silcamyb04.pdf

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