Speaking at a Onehunga explosion press conference (front left) Derrick Adams, CEO of HEB Contractors, Mark Ford, CEO of Watercare Services and Auckland mayor Len Brown
Emergency services are mystified at how an explosive gas came to be present at the site of yesterday's fatal blast in Auckland.
The type of gas and its origin are unknown.
Gas levels were still at an explosive level late last night following the early morning tragedy in Onehunga.
A police spokeswoman said emergency services were continuously pumping air into the tunnel but the site was too dangerous to enter for closer inspection.
The spokeswoman said the type of gas remained unidentified and no one knew how it had come to be in the pipe. "It is a mystery to everybody," she said.
Fire Service staff would remain at the scene until it was safe, and nearby residents were able to stay in their homes because the gas is not toxic.
The Mt Smart Rd site is part of the Hunua 4 watermain that will eventually run for 28km from Manukau to Auckland's CBD.
The $245 million project is aimed at catering for population growth and Watercare Services, an Auckland Council company, had engaged HEB Construction to carry out the work.
The Hunua 4 pipes are between 1.3m and 1.9m in diameter and the steel is 12mm thick. Most are being laid using an open trench system but tunnelling is employed for areas such as busy intersections.
The HEB workers were yesterday at the intersection of Mt Smart Rd, Victoria St and Athens Rd, installing apipe linking the new Hunua 4 pipe to the existing Hunua 3 watermain.
The Mt Smart Rd section of the project started in January, and yesterday's "critical cross connection work" was deliberately scheduled for Queen's Birthday Weekend when traffic flows and water demand would be lower.
At 7.15am a section of Hunua 3 was removed in preparation for the new connection. Watercare Services says that a short time later a small inspection team trained to operate in confined spaces entered the tunnel.
They were only a few metres along when the explosion occurred. Two of them were blown outside by the force of the blast.
Shortly after the blast, firefighters using gas detection equipment found gas levels in the tunnel were at dangerous levels.
Auckland fire acting area commander Steve Lakin said seven specialist appliances were sent to the scene.
Lakin said they do not know what gases were in the tunnel or what had ignited them but did say the limits were "beyond our normal safe procedures".
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