Ann. Occup. Hyg., 2016, Vol. 60, No. 2, 263–269 doi:10.1093/annhyg/mev067 Advance Access publication 23 September 2015
Occupational Exposure to Respirable Dust, Respirable Crystalline Silica and Diesel Engine Exhaust Emissions in the London Tunnelling Environment Karen S. Galea1*, Craig Mair2, Carla Alexander1, Frank de Vocht3 and Martie van Tongeren1 1.Centre for Human Exposure Science, Institute of Occupational Medicine (IOM), Research Avenue North, Riccarton, Edinburgh, EH14 4AP, UK; 2. IOM, Suite D, Quay West Park Lane, Salamander Quay, Harefield, Uxbridge, UB9 6NZ, UK; 3.School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK *Author to whom correspondence should be addressed. Tel: +44(0) 131 449 8034; e-mail: [email protected]
,org Submitted 18 June 2015; revised 20 August 2015; revised version accepted 24 August 2015.
A B ST R A CT Personal 8-h shift exposure to respirable dust, diesel engine exhaust emissions (DEEE) (as respirable elemental carbon), and respirable crystalline silica of workers involved in constructing an underground metro railway tunnel was assessed. Black carbon (BC) concentrations were also assessed using a MicroAeth AE51. During sprayed concrete lining (SCL) activities in the tunnel, the geometric mean (GM) respirable dust exposure level was 0.91 mg m−3, with the highest exposure measured on a back-up sprayer (3.20 mg m−3). The GM respirable crystalline silica concentration for SCL workers was 0.03 mg m−3, with the highest measurement also for the back-up sprayer (0.24 mg m−3). During tunnel boring machine (TBM) activities, the GM respirable dust concentration was 0.54 mg m−3. The GM respirable elemental carbon concentration for all the TBM operators was 18 µg m−3; with the highest concentration measured on a segment lifter. The BC concentrations were higher in the SCL environment in comparison to the TBM environment (daily GM 18–54 µg m−3 versus 3–6 µg m−3). This small-scale monitoring campaign provides additional personal data on exposures experienced by underground tunnel construction workers. K E Y W O R D S : construction; Crossrail; crystalline silica; diesel exhaust; personal sampling; respirable
I N T RO D U CT I O N Substantial exposure to total dust, respirable dust (RD), and α-quartz has been previously reported during tunnel construction work. In Norway, Bakke et al. (2002) indicated that 15% of total dust, 5% of RD, and 21% of quartz measurements exceeded the
Norwegian occupational exposure limits. Exposures to elemental carbon (EC) [as an index of exposure to diesel engine exhaust emissions (DEEE)] ranged from 100 to 340 μg m−3 in this study indicating that even the lowest measured concentrations were above those considered to have an impact on health (van Tongeren
© The Author 2015. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.
264 • Occupational exposure to respirable dust, RCS and DEEE in London tunnelling environment
et al., 2013). More recently, Bakke et al. (2014) shows that measured levels for some agents and tasks had reduced (e.g. for DEEE). Crossrail is a 118-km railway line under construction across Greater and Central London and is currently Europe’s largest infrastructure project. Tunnel boring machines (TBMs) are used to construct 42 km of tunnels. As the TBM advances the cutter head excavates the ground. Concrete segments (as well as personnel, other materials) are transported to the TBM by diesel powered ‘Schoma CHL-200G’ locomotives (fitted with a diesel particulate filter and catalytic exhaust cleaner). The precast concrete segments are built into 23 tonne rings to line the tunnels. Crossrail also involves the construction of tunnels using a sprayed concrete lining (SCL) technique (e.g. when expanding tunnels for station platforms, cross passages, etc) whereby the ground is excavated using mobile plant and then rapidly sprayed with concrete to support the surrounding soil. The aim of the project described here was to measure operator’s personal exposure to RD, DEEE [as respirable elemental carbon (REC)] and respirable crystalline silica (RCS) for workers involved in Crossrail tunnelling activities. Direct reading measurements of black carbon (BC) were also obtained to inform within-shift temporal patterns in DEEE concentrations during tunnelling. The COSHH definition of a substance hazardous to health includes RD of any kind when present at a concentration in air equal to or >4 mg m−3 as 8-h timeweighted averages (TWA) (HSE, 2011). BOHS, IOM, and others consider that the current British limit value is unsafe and that employers should attempt to reduce exposures to help prevent further cases of respiratory disease amongst their workers by keeping exposure to RD below 1 mg m−3 (BOHS, 2012; IOM, 2011). The current 8-h TWA workplace exposure limit (WEL) for RCS is 0.1 mg m−3 (HSE, 2011). M ET H O D O LO G Y Four 3-consecutive day measurement surveys were completed, two during TBM activities and two during SCL activities. It was agreed a priori, following discussion with Crossrail and their contractors’ health and safety and occupational hygiene personnel that RD and RCS were to be sampled during SCL activities,
whereas RD and REC were to be sampled during TBM activities. Personal inhalation exposure measurements were obtained using Higgins Dewell cyclones in accordance with MDHS 14/4 (HSE, 2014). Those operators a priori expected as potentially being more highly exposed due to their work activities were primarily targeted for sampling, although convenience sampling was also employed. Cyclones were loaded with either a polyvinyl chloride (PVC) or heat-treated filter for RCS and REC measurements, respectively. A MicroAeth AE51 aethalometer equipped with a microCyclone (time base 60 s, flow rate 50 ml min−1) measured BC concentrations in a fixed location. In the first SCL survey, the MicroAeth was located on a raised access way outside the restricted working zone (where only designated SCL personnel are permitted to work); during the second survey it was located within the restricted zone. In the TBM, the MicroAeth was positioned at the grout pump operator station, which had been expected a priori as potentially experiencing the highest DEEE exposure. The PVC filters were analysed to determine the RD and RCS concentrations (HSE, 2014, 2005). The heat-treated quartz filters were analysed for RD and REC (HSE, 2014; NIOSH, 2003). The analytical limits of detection (LOD) were 0.05 mg for RD, 0.02 mg for RCS and 1 µg for EC. Results were field blank corrected and reported as 8-h TWA. A random imputation method was used to substitute those RCS values below the LOD [26/49 values (53%)] (Helsel, 2005). Since the data were not normally distributed, measurements were log(e)transformed prior to analysis. For each value below the LOD, a number between 0 and the LOD was randomly generated from the log-normal distribution. The results were summarized in terms for geometric mean (GM) and geometric standard deviation (GSD). R E S U LTS Engineers’ shift work reports were made available; summaries of the activities and control measures in place during each survey are provided in detail in Galea et al. (2015). SCL activities involved the formation of expansions for station platforms and also cross passages, linking platforms, and running tunnels. Wet concrete was applied using a remote controlled nozzle application. Concrete was delivered to the pump via a
Occupational exposure to respirable dust, RCS and DEEE in London tunnelling environment • 265
small diesel powered mixer. Forced air was supplied to the workface. In summary, the activities involved tunnelling through areas of clay; 25 SCL operators participated with 49 personal measurements being collected and 44% of SCL operators provided one sample, with 16 and 40% providing two or three samples respectively. In the TBM environment, 20 operators participated, with 36 personal measurements being obtained; 45% of the TBM operators provided one sample, with 40, 5, and 10% of operators providing two, three, or four samples respectively. The results of the individual personal samples are presented by job group in Fig. 1 for the SCL exposure measurements and Fig. 2 for the TBM measurements. Figure 3 presents the GM exposure measurement results by job group for both environments. In the SCL environment the GM RD exposure was 0.91 mg m−3 (GSD 1.98; range 0.30–3.20 mg m−3) compared to 0.54 mg m−3 (GSD 2.08; range 0.07– 1.79 mg m−3) in the TBM environment. A two-sample t-test (assuming unequal variances) shows that these are statistically different (P > 0.005). Operators that experienced the highest RD exposures were the (backup) sprayers (SCL) and conveyor extenders (TBM). GM average RCS exposure during all SCL activities was 0.03 mg m−3 (GSD 2.59; range