Modelling the health risks of exposure to respirable crystalline silica from hydraulic fracturing operations in the USA shale plays

Abstract

Respirable crystalline silica (RCS) is a known human carcinogen and a contaminant of potential concern. Proppants are used during the process of well stimulation (hydraulic fracturing) as additives in the fluid cocktail and sand is often used as a proppant which contains high percentage of silica determined by the quartz content. Empirical occupational exposure risk models were employed in this study to assess the potential health consequences from chronic RCS exposures based on RCS data from NIOSH and risk assessment formulas. Evaluating the lifetime (LT) excess cancer risk (LCR) potential, based on a risk target of 10⁵, the job titles that are likely to experience any substantial potential effect of cancer induction are the sand mover (LCR = 16.1 × 10⁵) and transfer belt (LCR = 19.2 × 10⁵) operators. The sand truck driver and data Van operators are among the job functions with a cumulative disease burden of 7.2% that are unlikely to be affected by < 2% carcinogenic disease burden.  The chemical truck, sand mover and transfer belt (T-belt) operators may potentially be at risk of other occupational nonmalignant respiratory diseases with hazard quotient (HQ) of 0.65, 1.79, and 2.13 respectively. It is recommended that continuous occupational health monitoring of potentially exposed workers should be included as part of the project plan and the engineering risk controls that have been put in place should be ranked to highlight the effectiveness of any risk reduction/prevention methodology employed.