Workers’ exposure to airborne particulate and crystalline silica (quartz) during the excavation of a geognostic tunnel with a full - face machine

The underground construction operations require special attention to Occupational Safety and Health - OS&H aspects. In such situations, the presence of some ubiquitous pollutants (e.g. silica) further contributes to the already critical environment due to narrow operating spaces, high concentration of great power machinery, production of airborne particulates from excavation activities. Moreover, the geological variability of rock formations may challenge the design decisions, and affect the exposure of workers to noxious pollutants. In this context an ongoing and continuous monitoring of the workers’ exposure conditions and of the working environment quality can provide useful information about the possible correlation between geo-mechanical parameters of the rock formations, erformance parameters of the used technologies and techniques, and production or release of pollutants. The paper summarizes the results of a study carried out at “La Maddalena” pilot tunnel of the Turin-Lyon railway line. The excavation by an open Tunnel Boring Machine -TBM- takes place in a geological environment of rocks with a content of crystalline silica (quartz) ranging from 30 to 80%. Hence, ongoing and continuous measurements (personal and stationary) in compliance with the up to date reference standards were scheduled from the very early stages of the excavation, to monitor the content of airborne particulate (respirable fraction) and crystalline silica. The study discusses factors and parameters possibly affecting the content of airborne silica: • the geological aspects; • the state of fracturing of the rock (in terms of Rock Mass Rate - RMR); • the water seepage; • the TBM’s Performance parameters (thrust, head rpm, and daily progress rate); • the micro-climatic conditions in the tunnel. Due to the great variability of activities involved by the tunnel driving macro-phases, the evaluations on workers were conducted by homogeneous groups, divided by work area and with specific indication of the different jobs. The results proved that for almost all the groups the crystalline silica levels exceeded 0,025 mg·m-3, Threshold Limit Value - Time- Weighted Average - TLV-TWA for the pulmonary fibrosis Risk suggested by the American Conference of Governmental Industrial Hygienists - ACGIH (coherently with the ACGIH’s approach to provide information on the risk involved by substances with reference only to health impairments other than cancer, and to include clear information on the possible carcinogenic class). The achieved results will be helpful to improve the Chemical Risk Management in the future Base Tunnel construction.