Full ventilation was restored to the mine and mining recommenced in June 2009, some four months after the rockfall in the $NZ7 million 108-metre ventilation shaft.

Methane levels at the New Zealand mine reached dangerous levels several times and peaked three weeks ago as the company strived to make up for lost time, according to unnamed experts.

An Australian gas drainage engineer with knowledge of the mine and a New Zealand mine safety expert, neither of whom wished to be identified, told The New Zealand Herald the explosion at Greymouth could have been avoided.

The company reported in its September quarter that commissioning of the first of two underground ventilation fans had been completed, which will provide greater ventilation capacity underground and allow for faster dilution of gases liberated during the mining process.

However, any disruption to the supply of electricity could impair the operation of the ventilation fan and increase the percentage of methane in the mine, the unnamed ventilation expert said.

Pike River had been under pressure to proceed with hydro mining and become a 1 million tonne per annum operation after delays with its Waratah continuous miner set back its production targets. Production forecasts for 2011 were halved before the disaster.

Peter Whittall, who was Pike River’s general manager mines for five years prior to taking up the managing director’s position last month, had been responsible for all operational aspects of the business including mine design and development and safety and environment.

Pike River Coal had experienced its “fair share of challenges” he told shareholders at last week’s annual general meeting.

“The geological challenges we had been facing for some time continued to have a negative impact on our production forecasts, affecting the rate of underground mine development and ultimately progression to full production,” he said.

“The second shipment [of 21,000t] was, overall, a month behind schedule, reflecting the difficulty in accurately forecasting the production profile in these early stages of mine development.

“It was becoming increasingly clear that we needed to take steps to improve the mine’s ability to reach its stated production target – which was, at the time, 620,000 tonnes of saleable coal for this year to 30 June 2011. With that in mind, we contracted additional mining equipment and labour as well as hiring additional engineering and mining staff.”

Pike is targeting 60,000t of saleable coal production per month in the June quarter of 2011 and 80,000tpm by the December quarter of that year.

The magnitude of Pike’s production revisions “surprised” Goldman Sachs.

“Longer term, the investability of PRC is a challenging question. It is certainly not a stock for investors with a lower risk tolerance,” Goldman analysts said after the move.