A vital Pike River mine escape route would have been extremely difficult to use in an emergency, and virtually impossible in a fire, an inquiry into 29 deaths at the mine has heard.

Pike River Coal chief executive Peter Whittall was yesterday forced to defend apparent inadequacies in safety at the mine as he gave evidence for a second day to a Royal Commission of Inquiry.

The inquiry heard criticisms of one of only two options for escape from the mine, and how systems to handle gas in the "gassy mine" had been insufficient.

Gas explosions at the mine last November killed the 29 workers.

Aside from the single tunnel into the mine, the only other option for getting out of it was a ladder up the vertical ventilation shaft leading from the mine. Another planned exit was never built.

In an audit in 2009, the Mines Rescue Service found the capability for escape from the mine was an area of serious concern. In the event of fire in the main intake, workers would have to try to climb out through the ventilation shaft.

"This would be extremely difficult under normal circumstances, but in the event of fire would, in my view, become virtually impossible," the audit read.

Asked if there had been trial evacuations up the ventilation shaft, Mr Whittall said not to his recollection.

He said it had been envisaged that in an emergency, workers could gather at a "fresh air base" in the mine - but he accepted this was not a way out.

"There's not a lot of scenarios whereby you would need to egress from the mine other than straight down the tunnel. So that's the primary egress from the mine."

Reports last year on gas management and drainage at the mine found a pipeline and other equipment to remove gas were not sufficient and needed upgrading.

Mr Whittall said he knew of the reports, but the issues were for his operational team, rather than him, to deal with.

He said he was not aware which of the mine's gas sensors were operating at the time of the deadly explosion.

The inquiry also heard how the expected cost of developing the mine blew out from $207 million to $350 million by the middle of last year.

Mr Whittall said the lack of cash had become an issue.

He described the coal from the mine as hard coking coal, but earlier Solid Energy chief executive Don Elder described it as being of a lesser quality.

Mr Whittall said: "I have no idea what he's based that on, or his motives for making those comments."

The first phase of the inquiry hearings will conclude today with further questioning of Mr Whittall.