The Department of Labour has laid five charges over a gas explosion in the Auckland suburb of Onehunga which killed a worker.
Watercare Services staff member Philomen Gulland died and six others were injured in the incident in June.
Five charges were laid in Auckland District Court against Watercare, the regional water company, and its contractor Canadian Pacific Ltd under the Health and Safety in Employment Act.
Contractors were working on joining two large watermains when the explosion occurred.
Watercare says it was a tragic accident and it will continue to cooperate with the department.
The company has found that reticulated gas had entered an empty water pipe, which it says was unprecedented.
The Department of Labour says its investigation looked at whether legal obligations were complied with, what caused the accident and how to prevent it happening again.
Watercare says it is committed to ensuring all possible lessons are learnt.
Gas company Vector says it is working with the department.