Pike River Coal's former hydro mining co-ordinator was previously the under-manager at two Australian mines that exploded, killing 23 men.
George Mason worked at Moura No 4 Mine in 1986, where an explosion killed 12 men. In 1994, he was at Moura No 2 Mine which exploded, killing 11.
According to his written evidence to the royal commission of inquiry yesterday, he surrendered his certificate of competency a year later.
In 2007, he re-entered the industry as a miner after stints as a fisherman and in an aluminium refinery.
Engineering, Printing and Manufacturing Union lawyer Nigel Hampton, QC, said Mr Mason did not have his New Zealand competency certificates, although some of the Pike River miners thought he did.
Mr Mason had started at Pike River months before the fatal explosion a year ago. He had not relayed an international expert's concerns about ventilation to managers. Criticism after the 1994 Moura blast related to failures to communicate with management, Mr Hampton said.
Mr Mason, who still works for Pike River Coal (in receivership) as the mining co-ordinator, had told former mine manager Peter Whittall during a phone interview for the job that he had no experience in hydro mining but was confident he could upskill.
Once at Pike River, he'd received no formal training, learning on the job. He'd tried to research it on the internet but couldn't find much, and management had supplied no documents.
Hydro mining was "all very high-tech" and he'd initially felt over-whelmed, although he'd had no qualms about managing the process later.
About half the crews operating the hydro machine had no formal training but three of the men who died in the explosion - Peter O'Neill, Keith Valli and Allan Dixon - were experienced in it.
Mr Mason had thought staff should be familiar with operations underground before starting hydro training. He was concerned at the number of inexperienced staff.
"[But] they were all placed there with deputies and experienced people around them."
Mr Mason revealed that in the early hours of October 30, three weeks before the disaster, there was a significant rockfall in front of the hydro machine. The steel mesh bent down a few metres in front and rubble fell on the machine.
In early November, struggling to mine the coal, the company moved to shot-firing to loosen up the coal because the men thought it too hard.
"That was carried out without my prior knowledge," he said.
Mr Mason confirmed international expert Masaoki Nishioka relayed concerns about the lack of ventilation.
Mr Mason had found him hard to understand, and he didn't tell management "because I understood the situation was being addressed".
All haste was being made to get hydro mining started and the main fan commissioned.
Mr Mason couldn't access methane readings through the computer system.
Asked why he didn't raise that with management, he said: "Pass".