Assessment of silica exposure and engineering controls during tuckpointing.

Abstract

Exposures to crystalline silica in the construction industry are widespread. This report documents exposures to crystalline silica and describes the effectiveness of a commercially available dust collection system designed for tuckpointing tools. Exposure to respirable crystalline silica (quartz) can result in silicosis, a serious and often fatal disease with symptoms including shortness of breath, weight loss, weakness, and the onset of autoimmune diseases. The American Conference of Governmental Industrial Hygienists (ACGIH©R ) regards silica as a suspected human carcinogen, and the National Toxicology Program (NTP) and the National Institute for Occupational Safety and Health (NIOSH) have designated crystalline silica as a potential occupational carcinogen. NIOSH estimates that more than one million workers are at risk for silicosis, with the majority of them in construction trades.(1) The NIOSH Recommended Exposure Limit (REL) and ACGIH©R Threshold Limit Value (TLV©R ) for respirable quartz are 0.05 mg/m3. The Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) for respirable dust containing crystalline silica for the construction industry is measured in millions of particles per cubic foot (mppcf) and is calculated using the following formula: PEL = 250 mppcf/% silica + 5.(2) However, OSHA compliance officers use the general industry PEL for respirable silica to test for compliance on construction sites, calculating the allowable exposure based on the measured quartz percentage for each sample in accordance with the following equation: 10 mg/m3/(% quartz + 2).(1) In this article, we used the NIOSH REL and the ACGIH TLV as the evaluation criteria, as these values reflect more current research on the health effects of silica exposure. Construction workers are routinely exposed to silica-containing dust without any engineering controls. One study showed that tuckpointing workers were exposed to silica-containing dust at levels 17 to 116 times higher than the OSHA PEL and 212 to 4300 times higher than the NIOSH REL.(3) According to NIOSH, non-powered air purifying respirators are not recommended for workers who are exposed to greater than 10 times the NIOSH REL.(4) In cases such as this, engineering controls, not only respirators, are required to reduce the exposure to the workers. OSHA also requires that engineering controls be used to the extent feasible for reducing exposures to regulated agents.(5) Exposures in construction are closely related to task.(6) For the grinding process during tuckpointing, personal silica exposures can vary substantially between the component tasks a worker conducts. Exposure assessment and the design of effective control technology require knowledge of each task component’s relative contribution to the total exposure. Detailed work task–exposure analysis using a combination of direct reading monitor and videotaping is well suited to assess the exposure associated with each task component in the mortar grinding process.(7) The goals of this study were as follows: 1) to evaluate the efficiency of engineering controls by calculating the respirable dust reduction as the ratio of exposure, both with and without the engineering control; 2) to determine the contribution of each component task to the total exposure in the grinding process based on the detailed task-exposure analysis; 3) to suggest improvements to the engineering control based on the data analysis and the comments of the journeyman bricklayers participating in the evaluation; and, 4) to evaluate the suitability of the disposable half-mask respirators typically used in this process.