The very last person to see the coal face deep inside the Pike River Mine told the Royal Commission of Inquiry on Thursday "at some stage it was going to collapse".
Former monitor deputy Stephen Wylie had done hydro mining at Solid Energy's Spring Creek underground mine, near Greymouth, but was moved to a similar position at Pike River without training - or even applying for the post, the Royal Commission of Inquiry was told.
He was on the shift before the November 19 explosion, and was the last person to view the area being mined by high-pressure water.
The commission regards the hydro monitor being used to cut the coal as its 'prime suspect' for causing the explosion that killed 29 men. It is considering whether a collapse at the coal face had pushed a wave of explosive gases through the mine.
Mr Wylie's crew was far less experienced than the incoming shift, who all lost their lives - Peter O'Neill, Allan Dixon and Richard Valli.
"I noticed nothing in the goaf that was any different (the day of the disaster)," Mr Wylie told the hearing.
Methane levels were low, and there were no unusual smells or sounds.
The goaf - the cavity left by mining coal - was up to 9m high that night. Somewhere in the back, there would have been 100 per cent methane, he said.
"At some stage it was going to collapse."
However, the coal left holding the roof up was very hard and it was unlikely the incoming crew would disturb the goaf.
Mr Wylie finished work at 8am on November 19.
There was never enough time at shift changeover, and his boss was arranging a meeting about this at the time of the explosion.
"If there is an explosion somewhere else in the mine and you are able to put your rescuer on, what would you do?" families lawyer Richard Raymond asked.
Mr Wylie said he had no particular training, but would have headed to the box of self-rescuers, and then made his way out.
He became monitor deputy in October 2010, eight months after joining Pike River as an 'out-bye' deputy.
He transferred there without any training: "I didn't apply for the position, and I was just told. I managed the situation as best I could."
His trainee Craig Reyland had worked for Chris Yeats Builders and had no face mining experience.
Mr Wylie had to leave the hydro area to do gas checks, but would "zip" back as soon as possible.
He would relieve the operator, who was sitting in the cold wind just pulling levers for a whole 12-hour shift. The person could get complacent, whereas at Spring Creek staff alternated hourly.
It took three days to take out a piece of coal that the continuous monitor would have done in an hour.
"It was well known we weren't producing anything, we just carried on it wasn't looking real flash."
He was working in the early hours of October 30, when there was a large rockfall in the mine.
The stump which had been holding up the roof beforehand was like a "44-gallon drum holding up the AMI Stadium roof".
He was concerned at the lack of a second escapeway, and thought more stone dusting (covering the roadways to reduce the risk of explosion) could be done in some areas, something he kept reporting.
Earlier today, the commission heard that hydro mining co-ordinator George Mason was previously the under-manager at two Australian mines that had exploded, claiming 23 lives.
He was at Moura No 4 Mine in 1986, which claimed 12 men, and in 1994 he was at the Moura No 2 Mine, where 11 died.
Mr Mason voluntarily surrendered his certificate of competency in 1995.
In 2007, he re-entered the industry as a miner, after a stint as a professional fisherman and in an aluminium refinery.
He did not relay an international mining expert's concerns about ventilation to managers.
Engineering, Printing and Manufacturing Union lawyer Nigel Hampton QC said criticism after the 1994 Moura disaster related to failures to communicate things to management.
"I thought things were under control," said Mr Mason, who still works for Pike River Coal (in receivership) as the mining co-ordinator.
He said he told mine manager Peter Whittall during a phone interview for the job that he had no experience in hydro mining.
Before he started at Pike River he tried to research hydro mining on the internet but could not find much.
The Royal Commission will resume on December 5, when it will look at the management of the company, and its contractors.