A court has been told it may never be known what caused a fatal gas explosion in Auckland.
Philomen Gulland was killed and another worker lost both legs in the blast in 2011. Prosecutors say harm would have been averted if procedures were followed.
The summary of facts in the case against Watercare was read in court on Wednesday after the Auckland Council owned company entered a surprise guilty plea on Monday.
The Ministry of Business, Innovation and Employment says Watercare failed to ensure monitoring was done by contractors.
Prosecutors say it should also have made sure there was enough ventilation and the company's own procedures were not followed once gas was found by the entry team.
The ministry says it is not possible to say with absolute certainty what caused the explosion.
Watercare is yet to be sentenced.
A hearing for contractor Canadian Pacific is ongoing.
