“That’s things like people’s memories, any evidence that can get washed away.”
Cook said there is a lot of rain in the capital, so investigators will try to collect any at-risk evidence as soon as possible.
TAIC inquiries can take 18 months to two years, depending on how complex the accidents are.
However, if initial evidence suggests something requires urgent attention, the commission can issue an “urgent safety recommendation to those that can make a change”.
“At this stage, we have no idea of the complexity of the inquiry.”
Investigators were on site last night and will be back in the coming days, Cook said.
The Metlink train derailed just after 7pm yesterday.
Six patients were taken to Wellington City Hospital, four in a minor condition and two in a serious condition, Wellington Free Ambulance said.
All passengers made it off the train, with no need for extrications.
Wellington City Councillor Diane Calvert was at home when she heard “a huge boom”.
“I wasn’t sure what on earth what it was,” said Calvert, “It was like an earthquake, but there was no shaking.”
Metlink senior operations manager Paul Tawharu said his immediate thoughts were “for the safety and well-being of the passengers and Metlink staff on board.
“I’d also like to thank the emergency responders for their fast and excellent response.”