Police today described the conditions at the Pike River coal mine as volatile.
Tasman District Commander, Superintendent Gary Knowles said, while flames were no longer visible at the vent, conditions inside the mine were still extremely dangerous and any attempt at a recovery operation was a long way off.
"Even if there is no flame for a period, conditions remain volatile.
"We know the mine is extremely hot - in the range of 600degC. Despite the GAG operating for more than a week now we know there is still oxygen getting into the mine and the risk of further combustion still exists. Our experience to date shows the environment can change very quickly."
Superintendent Knowles said work was progressing to analyse the risks associated with putting a cap on the vent.
"One of the new risks identified is that capping could cause the GAG to stall and expert advice indicates that would likely prompt further explosions.
"Despite no flames being visible at the vent there is still a significant quantity of gas escaping, which poses a huge risk to helicopters flying overhead."
Superintendent Knowles said the next phase would involve using nitrogen-generating equipment to pump the gas into the mine in an attempt to lower the temperature. Machines capable of doing this are available in New Zealand and Australia, and assessments are being carried out as to whether either of these could be operated at the site.
"The situation remains the same. All of the evidence to hand confirms this would be an extremely high-risk operation."