The blaze that gutted a factory in Kaiapoi started accidentally, Fire investigators have found.
The Sutton Tools factory in the north Canterbury town went up in flames last month, flushing about 3000 litres of oil into three nearby rivers.
The company employs 100 staff.
Fire and Emergency New Zealand (Fenz) said it had finished examining the factory and was finalising an investigation report.
FENZ did not reveal exactly how the fire started, but it did not appear to be intentional.