"They must have assumed it was safe. It was probably unlucky they didn't smell the gas."
He said the explosion, from a gas cylinder similar to a can of fly spray, may have prevented the three local men from passing out from the fumes in the enclosed cab "so perhaps they escaped serious injury".
Wairoa volunteer fire brigade Chief Fire Officer Grant Duley said he was called to the hospital to make sure the men's ute was not a fire risk. He said there was evidence of seat covers having burned but there was no fire danger.
"It must have been like a flash and put itself out," he said.
"By the time we got there, it was all out bar the shouting."
The men were flown by the Lowe Corporation rescue helicopter to Hawke's Bay Regional Hospital, where a spokesperson said they were in a stable condition but likely to be transferred to Hutt Hospital.
The men were not in a condition to talk, the spokesperson said last night.