Exposure to silica and metals among painters using specular hematite abrasive.

This work was conducted through a cooperative agreement between the National Institute of Occupational Safety and Health and the Center to Protect Workers’ Rights (grant no. U60/CCU317202). S ince 1993, the Center to Protect Workers’ Rights, the research arm of the Building and Construction Trades Department, AFL-CIO, has developed and used a task-based approach to assessing and controlling occupational health hazards in construction. The Task-Based Exposure Assessment Model (T-BEAM) approach, which has been previously described,(1) was applied to characterize silica exposures among trades engaged in abrasive blasting, masonry work, and milling operations beginning in 1999. Baseline exposure data (without controls), collected in 1999 and 2000 on job sites where silica sand was used as an abrasive and/or sites with concrete substrates being blasted, showed that painters were exposed to silica at concentrations well above recommended and legal exposure limits.(2) On four sites surveyed, seven shift samples collected among abrasive blasters ranged between 0.26 and 26.2 mg/m3, or approximately 5 to 524 times the National Institute of Occupational Safety and Health’s (NIOSH) recommended exposure limit (REL) of 0.05 mg/m3. Within the trades sampled, silica exposure concentrations among industrial painters were the highest. Since the T-BEAM approach emphasizes the identification and evaluation of engineering and work practice controls, we sought to assess a substitute abrasive that conformed to NIOSH’s 1974 recommendation to prohibit the use of silica sand or other substances containing more than 1% silica.(3) Abrasive blasting is a widely used technique for removing existing paint from surfaces prior to applying new paint. Paint must be reapplied periodically and/or maintained to prevent rusting and failure of steel structures such as bridges. Paint is removed by propelling an abrasive agent under high pressure on coated surfaces, generating large amounts of inhalable, toxic dust. For new paint to bond effectively to steel, abrasive blasting must achieve a desired surface profile. The construction work force is made up of over 7 million workers employed in a large number of specialized trades.(4) Several trades may engage in abrasive blasting. However, the trades with the most significant exposure risks are painters, laborers, and masonry workers. Proportionate mortality ratios from silicosis for these trades are also among the highest.(5) Silica sand has been widely used as an abrasive in the past because of its low cost and ability to effectively remove paint while leaving the desired surface profile.(6) However, extremely high concentrations of respirable silica are generated that can lead to silicosis,(7) autoimmune problems,(8−10) and possibly cancer.(7,11,12) Other types of abrasives include steel shot and grit, coal and metallurgical slags, and synthetic abrasives. Laboratory studies have suggested specular hematite may generate significantly lower airborne concentrations of respirable silica and toxic agents other than silica sand and other common abrasives.(13) However, to the best of our knowledge, this abrasive has not been evaluated for these agents in an actual work setting. Specular hematite