Pike River families have reacted strongly to evidence at the Royal Commission from an experienced tunneller about the mine's effect on his health.
Twenty-nine men were killed in a series of explosions that began at the Pike River Coal mine on the West Coast on 19 November last year.
The inquiry resumed its third phase in Greymouth on Tuesday with a focus on health and safety systems in place at the mine.
On Tuesday, the Pike River families' legal team called as a witness Alan Houlden, the leading hand for drilling and tunnelling contractor McConnell Dowell for six months until April 2010.
Mr Houlden says he left the mine in April because he feared the inexperience of the workers at Pike River would lead to an explosion.
He says the lack of ventilation and its poor management left him with headaches and feeling sick due to the carbon monoxide he was being exposed to.
A spokesperson for the Pike River families, Bernie Monk, says that was a tearful moment, because his son who worked at the mine was often ill and also had headaches, but did not realise until now that it was because of poor ventilation.
Mr Monk says if the family had known the cause, it might not be in the predicament it is today.
Alan Houlden did not inform management at Pike River Coal about the carbon monoxide poisoning and the company has stated it was not aware of safety concerns.
But Mr Monk told Checkpoint on Tuesday it should not be up to workers to alert management, and those in charge should have been actively monitoring the workplace for safety issues.
Alan Houlden said when he started mining in Britain 37 years ago he was trained slowly in gradual steps and not allowed to work on the coal face for at least two years.
But he says at Pike River Coal contractors with little or no previous experience were working in the mine, with little induction training and very light supervision.
He says he found it very hard with the young workforce, because they did not appreciate the dangers.
Safety not compromised - former board chair
The former chairperson of Pike River Coal's board says it never put production ahead of workers' safety.
The mine's former training coordinator, Adrian Couchman, gave evidence that a drive for coal production became more important than mine safety.
Mr Couchman told the inquiry that morale had been falling among staff due to changing shift patterns and working conditions. Training courses were increasingly cancelled last year because of growing staff absenteeism and a drive for production over safety.
Mr Couchman said the pressure on safety manager Neville Rockhouse was so great he would come back with a visibly grey face from management meetings and twice had tried to resign.
But giving evidence for the first time on Tuesday, John Down, chair of the board's directors at the time of the disaster, strongly disagreed that production was more important.
"Senior management on site always had a safety first approach. I'm not aware of any circumstance in which production was prioritised over safety and I would be surprised if it was."
Mr Dow says only one major safety concern was ever raised with him and he dealt with that immediately.
The Royal Commission was told that former Pike River Coal chief executive Gordon Ward had been the project's "main man" since the late 1990s and its architect. Mr Dow says he had more to do with Mr Ward than any other manager at Pike River.
Gordon Ward left his job less than two months before the disaster, but is refusing to return from Australia for the inquiry.