Experimental Evaluation of Respirable Dust and Crystalline Silica Controls During Simulated Performance of Stone Countertop Fabrication Tasks With Powered Hand Tools

Abstract

Objectives: Workers who fabricate stone countertops using hand tools are at risk of silicosis from overexposure to respirable crystalline silica. This study explored the efficacy of simple engineering controls that can be used for dust suppression during use of hand tools by stone countertop fabricators.

Methods: Controlled experiments were conducted to measure whether wet methods and on-tool local exhaust ventilation (LEV) reduced respirable dust (RD) exposures during use of various powered hand tools on quartz-rich engineered stone. RD samples collected during edge grinding with a diamond cup wheel and a silicon carbide abrasive wheel were analyzed gravimetrically as well as by X-ray diffraction to determine silica content. A personal optical aerosol monitor was used simultaneously with the RD samples and also for rapid assessment of controls for polishing, blade cutting, and core drilling.

Results: On-tool LEV and sheet-flow-wetting were effective in reducing exposures, especially when used in combination. Sheet-flow-wetting with LEV reduced geometric mean exposures by as much as 95%. However, typical water-spray-wetting on a grinding cup was less effective when combined with LEV than without LEV. Mean silica content of RD samples from grinding operations was 53%, and respirable mass and silica mass were very highly correlated (r = 0.980). Optical concentration measures were moderately well correlated with gravimetric measures (r = 0.817), but on average the optical measures during a single trial using the factory calibration were only one-fifth the simultaneous gravimetric measures.

Conclusions: Sheet-flow-wetting combined with on-tool LEV is an effective engineering control for reducing RD exposures during engineered stone edge grinding and blade cutting. On the other hand, addition of LEV to some water-spray-wetted tools may reduce the effectiveness of the wet method.

Keywords: crystalline silica; dust suppression; engineering controls; local exhaust ventilation; stone dust.

Figure 1

Tools used in the experiments. A: drilling with a core bit using a “water ring” made of plumber’s putty; B: steel cup edge grinding with jet spray; C: SiC dry edge grinding; D: grinder fitted with a cutting blade; E: edge polishing.

Figure 2

Experimental setup for wet operations using sheet flow wetting via a perforated water distribution manifold.

Figure 3

Scatter plot of paired data from the TSI SidePak optical aerosol monitor with Dorr-Oliver cyclone and gravimetric analysis of respirable dust > LOQ collected using cyclone samplers. Solid circles: GK4.162 cyclone samples; solid diamonds: GS-3 cyclone samples. The solid line represents the least-squares fit with zero intercept. A dotted line with unit slope is provided for comparison. The squares with crosses represent the mean of the replicated aerosol monitor measures for a given tool/condition plotted against the corresponding geometric mean of the replicated gravimetric measures.