The Evaluation of Worker Exposure to Airborne Silica Dust During Five OSHA Table I Construction Tasks

Abstract

Fifty-one (51) personal silica air samples were collected over 13 days on 19 construction employees while they performed five different construction tasks found in the Occupational Safety and Health Administration's (OSHA) respirable crystalline silica standard for construction, Table 1, which specifies engineering, work practice, and respiratory protection controls that employers can use in lieu of exposure monitoring to adhere to the standard. The average construction task time was 127 min (range: 18-240 min) with a mean respirable silica concentration of 85 μg m-3 (standard deviation [SD] = 176.2) for all 51 measured exposures. At least one OSHA-specified silica dust control measure was used during all 51 samples collected. The mean silica concentrations for the five tasks were: core drilling 11.2 μg m-3 (SD = 5.31 μg m-3), cutting with a walk-behind saw 126 μg m-3 (SD = 115 μg m-3), dowel drilling 99.9 μg m-3 (SD = 58.7 μg m-3), grinding 172 μg m-3 (SD = 145 μg m-3), and jackhammering 23.2 μg m-3 (SD = 5.19 μg m-3). Twenty four of 51 (47.1%) workers were exposed above the OSHA Action Level (AL) of 25 μg m-3 and 15 of 51 (29.4%) were exposed above the OSHA Permissible Exposure Limit (PEL) of 50 μg m-3 when exposures were extrapolated to an 8-h shift. When silica exposures were extrapolated to 4 h, 15 of 51 (29.4%) of workers sampled were exposed over the OSHA AL and 8 of 51 (15.7%) were exposed over the OSHA PEL. A total of 15 area airborne respirable crystalline silica samples were collected on days where the personal task-based silica samples were taken, with an average sampling time of 187 min. Of the 15 area respirable crystalline silica samples, only four were greater than the laboratory reporting limit of 5 μg m-3. The four area silica samples with reportable concentrations revealed background silica concentrations of 23 μg m-3, 5 μg m-3, 40 μg m-3, and 100 μg m-3. Odds ratios were used to analyze the apparent association between dichotomous background construction site exposures to respirable crystalline silica (detectable or not detectable), and personal exposure category (over or not over the OSHA AL and PEL) when exposure times were extrapolated to 8 h. The associations were strongly positive and significant between detectable background exposures and personal overexposures for workers conducting the five Table 1 tasks with engineering controls in place. The results of this study suggest that exposure to hazardous levels of respirable crystalline silica may be present even when OSHA-specified engineering controls are implemented. The current study findings also suggest that background construction site silica concentrations may potentially cause task-based overexposures, even when the OSHA Table 1 control methods have been put in place.

Keywords: OSHA Table I; OSHA silica permissible exposure limit; construction; silica controls; silica exposure.