Airborne asbestos fibres monitoring in tunnel excavation

Our plain-English summary of Airborne asbestos fibres monitoring in tunnel excavation, by L. Gaggero, E. Sanguineti, A. Yus González, et al (Journal of Environmental Management, 2017).

The study

• Authors: L. Gaggero, E. Sanguineti, A. Yus González, G.M. Militello, A. Scuderi, G. Parisi
• Journal: Journal of Environmental Management
• Published: 2017;196:583-593
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Tunnelling across ophiolitic formation with Naturally Occurring Asbestos (NOA) can release fibres into the environment, exposing workers, and the population, if fibres spread outside the tunnel, leading to increased risk of developing asbestos-related disease. Therefore, a careful plan of environmental monitoring is carried out during Terzo Valico tunnel excavation. In the present study, data of 1571 samples of airborne dust, collected between 2014 and 2016 inside the tunnels, and analyzed by SEM-EDS for quantification of workers exposure, are discussed. In particular, the engineering and monitoring management of 100 m tunnelling excavation across a serpentinite lens (Cravasco adit), intercalated within calcschists, is reported. At this chrysotile occurrence, 84% of 128 analyzed samples (from the zone closer to the front rock) were above 2 ff/l. However, thanks to safety measures implemented and tunnel compartmentation in zones, the asbestos fibre concentration did not exceed the Italian standard of occupational exposure (100 ff/l) and 100% of samples collected in the outdoor square were below 1 ff/l. During excavation under normal working conditions, asbestos concentrations were below 2 ff/l in 97.4% of the 668 analyzed samples. Our results showed that air monitoring can objectively confirm the presence of asbestos minerals at a rock front in relative short time and provide information about the nature of the lithology at the front. The present dataset, the engineering measures described and the operative conclusions are liable to support the improvement of legislation on workers exposure to asbestos referred to the tunnelling sector, lacking at present.

Copyright © 2017 Elsevier Ltd. All rights reserved.

In plain English

This study reported air monitoring for asbestos fibres during the digging of tunnels for the Terzo Valico railway in northern Italy. The tunnels pass through rock that can contain naturally occurring asbestos. Between September 2014 and July 2016, 1,571 air samples from the tunnel works were analysed by electron microscopy. In the routine monitoring during excavation, the authors reported that 86.7% of measurements were below 1 fibre per litre (ff/l). During excavation under normal working conditions, 3.6% of samples were above 2 ff/l. In the Cravasco adit, digging crossed serpentinite rock, and chrysotile fibres appeared in the air. Work was stopped, and the tunnel was later divided into three zones with dust controls. From January to May 2016, 84% of samples in the zone nearest the rock face exceeded 2 ff/l, compared with 24% and 4% in the two zones further out. All samples from the outdoor square were below 1 ff/l. The authors reported that the daily workplace limit of 100 ff/l was never exceeded, which they credited to protective equipment and shorter shifts. They noted that dust-overloaded filters were the main sampling problem. The authors concluded that air monitoring at the rock face proved effective for immediately detecting asbestos in the rock.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Occupational air-monitoring study: airborne asbestos fibre measurements, analysed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), taken during the first phase of tunnel excavation
• Who was studied: 1,571 air samples from the Terzo Valico railway tunnel works (Genoa to Milan, northern Italy), September 2014 to July 2016. These were made up of 668 samples taken during excavation in rock not containing asbestos, 32 taken during other construction activities, and 871 taken during the Cravasco dedusting installation and serpentinite excavation. The authors describe the samples as collected inside tunnels, but the Cravasco data also include samples from the outdoor square outside the tunnel.
• Exposure: Airborne asbestos fibres released from naturally occurring asbestos in rock during tunnelling. The fibre types identified on filters were actinolite, tremolite and chrysotile. Chrysotile was found at the Cravasco serpentinite lens.
• Main results:
  • In the routine excavation monitoring across the tunnels (the dataset shown in Fig. 5, discussed before the separate Cravasco intervention results), 86.7% of measurements were below 1 ff/l, and 67.5% were below the detection limit (no fibres found). The article does not state that this applies to all 1,571 samples.
  • During excavation at normal working conditions, 3.6% of analysed samples were above 2 ff/l.
  • In the interconnection tunnels, Polcevera, Campasso and Southern Valico (209 samples), concentrations were below the detection limit in 85.6% of samples and between the detection limit (0.3 ff/l) and 1 ff/l in 10.1%.
  • In Northern Valico, excavated in marls (120 samples): 52.5% of results were between the detection limit and 1 ff/l, 16.7% were between 1 and 2 ff/l, and 5.7% exceeded 2 ff/l.
  • At Cravasco, 77% of 103 results were below 1 ff/l. Chrysotile fibres appeared occasionally in June 2015 and rose above 2 ff/l in late July 2015.
  • At Cravasco, during the safety works with excavation stopped, 2.7% of measurements near the rock face were above 2 ff/l, compared with 33.3% in July. The authors reported this difference as statistically significant.
  • From January to May 2016, with the Cravasco tunnel divided into zones, concentrations were above 2 ff/l in 84% of samples from zone A (nearest the rock face), 24% in zone B and 4% in zone C.
  • All values from the outdoor square (zone D) were under 1 ff/l. The authors interpreted this as no release of fibres outside the tunnel.
  • Although most zone A samples largely exceeded 2 ff/l, the authors reported that the daily working exposure limit of 100 ff/l was never exceeded. They attributed this to protective equipment and shorter work shifts.
  • In a 16-day comparison, personal samplers gave a mean of 15.57 ff/l (SD 11.63). This was significantly lower (t-test p = 0.013) than static sampling in zone A during excavation, which gave a mean of 25.37 ff/l (SD 13.69).
  • Inside the drivers' cabs of the large vehicles at Cravasco, values below 1 ff/l made up 83% of samples for the dumper, 24% for the wheel loader and 5.8% for the drilling excavator.
• The authors' conclusion: The authors concluded that air monitoring carried out at the rock face proved effective for immediately detecting asbestos in the rocks.
• Limitations the authors state:
  • Overloading of filters with mineral dust was the most significant sampling problem. Heavy dust obscured fibres, lowered counts or made counting impossible.
  • The authors acknowledged that low fibre counts have very poor precision.
  • There is no specific regulation for air monitoring in tunnels. The available Italian method was designed for closed environments after remediation.
  • No current technology removes the delay between fibres becoming airborne and their detection.

Topics

Medical terms in this study, explained in our Lexicon: naturally occurring asbestos (NOA), Serpentinite, Chrysotile, Occupational Exposure, Air Sampling, Asbestos.

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