He defends the length of time it has taken to decide to drill the shaft.
"We're doing everything we can.
"We've tried a lot of more obvious things to understand the conditions. You don't do these kinds of things unless you absolutely have to."
Mr Dow says the 150m drill shaft is expected to be complete this evening, but could take as long as two days.
It will enable more accurate and regular samples of air quality in the tunnel where the 29 miners are trapped.
Rescue efforts have so far been hampered by fluctuating levels of methane and carbon dioxide down the mine.
"If we can show that the quality of air is stable then it assures rescuers it will be safe for them to enter the mine," says Mr Dow.
"It is about making a judgement call."
He maintains measurements showing an unstable atmosphere do not mean the miners are dead.
"They could still have plenty of air. We won't be able to make any official pronouncement. That's not what this is about. It's all about search and rescue."
Pike River Coal CEO Peter Whittall announced a rig will drill 150m into the mine shaft in a press conference this morning.
He hinted that the rig could be used in future rescue efforts.
"In parallel to that I've asked my team... what else we can use that for, whether we can use that hole primarily for one thing and then move the rig a couple of metres away and start drilling another hole for another reason."
Families of the some of those men trapped in the Pike River coal mine near Greymouth on the West Coast have arrived at the site this morning as rescuers attempt to drill down into the mine.
Mr Whittall said Air New Zealand had offered employee support people to help the families, which Pike River had accepted.
"They've mobilised nearly 30 people to Greymouth and we will be allocating one support person to each of the families, so they will have a direct communication, a direct update, someone to help with the logistics and they will have direct communication with us."
Buses will take a few representatives from each family to the site this morning and it will be explained to them what is going on with the rescue effort.
"They'll be able to get off, walk around, have a look at the emergency services that are being set up - just have a touch and feel and...understand what's going on."
View Pike River coal mine in a larger map
- NZ HERALD STAFF / NZPA
