Search

Fire life safety (FLS) risk during construction of Watercare's Central Interceptor wastewater project in Auckland, New Zealand, is increased due to the combustible high-density polyethylene (HDPE) plastic used to fully line the main tunnel and link sewers. With the single-bore main tunnel having a length of 14.7 km, fire risk is compounded, as opportunities for egress and smoke management are limited, and so there is increased risk to Tunnel Boring Machine (TBM) crews and to workers in the smaller link sewers. It is the extensive use of polymer linings that make the Central Interceptor project an interesting FLS case study, and a unique construction project in Australasia. The project invested in fire testing to understand the HDPE combustion hazard during construction, and to assess the benefits of water mist suppression as a potential risk mitigation measure. It was found that the material was difficult to ignite and did not promote fire spread. Misting was demonstrated to be effective at suppressing a fire involving HDPE liner. Outcomes of the testing informed a wider risk assessment. A suite of engineering and operational controls was developed. To complement "business as usual" measures, other novel controls were implemented, including a misting system behind the TBM trailing gear and innovative misting "fire breaks" distributed along the length of the tunnel at 1500 m intervals. With the efforts made to minimise the hazard of fire and the potential for localised flashover and spread, and to facilitate self-evacuation, it was concluded that the plastic liner materials do not unacceptably increase risk to life or asset, relative to other tunnels without a combustible liner. [ABSTRACT FROM AUTHOR]