Direct by Design
In-tunnel PSV fire incident report TunnelTalk reporting
November 2022
A
s was promised, the report into the fire that destroyed a PSV passenger service vehicle on the HS2 Chilterns high speed rail TBM drive in the UK in May 2022 is published and made available to the wider industry by HS2 Ltd, the client, and Align JV, the contractor. An exact cause of the fire is inconclusive as the burnedout vehicle was too damaged to allow deeper forensic study. The report reveals that the vehicle was running on HVO, hydrotreated vegetable oil, fuel in place of standard diesel and in efforts to run a environmentally friendly, low carbon foot print project. The fire broke out in the engine bay of the vehicle and one scenario is that a frayed fuel line allowed HVO to spill onto hot surfaces and ignite. Another scenario was that fuel pipes covered with steel wire could have caused arcing if in contact with live electrical terminals.
Burned-out PSV that was too damaged to provide an exact cause of the fire
The dry powder fire suppression system in the engine compartment and dry powder fire extinguisher on the vehicle were said to comply with the BS6164:2019 Health & Safety in tunnelling in the construction industry regulations, but that no specific discussions were held by the construction JV and the vehicle supplier as to what the regulation should include or how the retro-fitted system should operate.
It is to the industry’s benefit and to the credit of HS2 Ltd and the Align JV that the report into the incident is made available to the British Tunnelling Society and through it to the wider international industry. The experience and the lessons learnt are shared so that vital safety regulations and standards can be revised as necessary and for all to appreciate the value of well-devised and well-rehearsed life safety emergency practices and procedures in tunnelling and underground construction. The hope is that a similar sharing of the investigation and findings of another fire incident on a tunnelling project in the UK will follow the same example. It was in September, at the start of the TBM drive under the River Thames for the Silvertown highway tunnel project to the east of London that part of the conveyor haulage system caught fire and brought six fire engines and about 40 firefighters to the site at about 10.30pm to manage the incident. The fire was on a section of the conveyor at the portal where muck transitions to a vertical conveyor for onward transfer to surface muck management systems. A photo taken of the night scene by a passer-by has been shared on social media and by UK construction magazines. Finding of the investigation into what caused the fire and the reparation measures taken by Riverlinx, the construction consortium, and TfL, Transport for London, the client, as a result is yet to be published or made publicly available. n Silvertown tunnel conveyor belt fire in the working portal job site lights the night sky
All the MSVs, multi-service vehicles, on the Align JV contract run on HVO and all were inspected thoroughly and upgraded as required. Discussion on the use of HVO in the tunnelling industry and the appropriate fire suppression systems therefore required are now part of current discussions within the BSI British Standards Institution in the UK and in CEN, the Comité Européen de Normalisation, European Committee for Standardization, that are preparing and revising applicable standards for the application of MSVs in the underground construction industry. The fire occurred in May 2022 as the PSV was transporting the crew to the TBM on one of the twin rail tunnels through the Chiltern Hills. It broke out as the vehicle stopped to pick up a maintenance worker at about 2.6km from the portal. When the fire became too fierce for any firefighting efforts, all those with the vehicle left the scene and walked safely to the portal. Three maintenance crew on the TBM at about 1.5km further into the drive were ordered to enter one of the refuge chambers on the TBM backup, start up its support systems and stay there overnight until they could walk the 4km to the portal after the fire had burnt out and visibility and the air had cleared. There was little structural damage to the segmental lining of the tunnel with localised damage to a high-voltage electrical cable, the ventilation duct and to the invert concrete slab needing replacement and repair. A full copy of the published report is available for download and a report about the initial incident was published by TunnelTalk in May.
TunnelTalk references • Improving TBM fire safety - June 2014 • TBM projects fuel refuge chamber demand - June 2015 • Sprinkler limitations for tunnel fire fighting - September 2011 • Mobile furnace for in-situ fire safety testing - August 2012 • Smart safety for Seattle underground highway - May 2018 • Managing safety under Sydney Harbour - August 2017 • Evacuating on elevated running tunnel walkways - May 2018 • TTS and BTS supporting safety awareness - April 2020 The references below are hotlinked to articles in the Archive of the TunnelTalk.com web magazine. The web magazine link currently show a security warning as we undertake every effort to regain control of the magazine and restore it to serve the industry and the readers. Although the warning is there, it is the genuine TunnelTalk.com site and we hope to regain access to apply the new SSL certificate just as soon as possible. 1