(CNN) -- A toxic mix of gases inside a New Zealand coal mine kept frustrated rescue workers on the sidelines again Monday, as they waited for the go-ahead to try to reach 29 miners trapped underground.
No one has heard from the men -- ages 17 to 62 -- since an explosion inside the mine around 4 p.m. Friday afternoon. Officials hope they are alive, though they do not know if the men found a safe haven or whether parts or all of the mine collapsed.
To gather more information, rescue workers are planning to send a high-tech robot inside the mine, which is located on New Zealand's west coast between Greymouth and Reefton.
"We owe it to the men that are underground, that in undertaking the rescue we do it in a way that doesn't endanger their lives any further," Prime Minister John Key told reporters. "We're going to get through this and do everything we possibly can to get the men out alive."
Police on Monday released for the first time the names, ages and nationalities of the 29 men. Most of the missing are from New Zealand, but there are also miners from Australia, Scotland and South Africa in the group.
Two of their colleagues -- Daniel Rockhouse and Russell Smith -- escaped the mine soon after the explosion by walking out through a tunnel, the mouth of which is about 2.2 kilometers (1.4 miles) from where the 29 missing men might be.
"(We) will be utilizing, if possible, a robot on site to go into the tunnel when the opportunity arises," said Gary Knowles, superintendent of the Tasman Police District, who stressed that safety is paramount.
He said he would not send the robot in if he thought it could create a spark that could trigger an explosion and cause the tunnel to collapse.
As they did during the weekend, those in charge of the mine and rescue operation said tests of air quality inside the mine indicated that conditions were not safe enough to send in rescuers. They have cited elevated carbon monoxide and methane levels.
"They're still not consistent," said Knowles, in response to a question about the most-recent air quality test results.
While drinking water is available inside the mine, the trapped men likely only brought enough food for a single day. The mine is ventilated, and rescuers are holding out hope that the men are breathing fresh air in a ventilation shaft.
"The situation still remains grave, given we have not had contact with the men now for three days. Every effort is being made to carry out a rescue," said Knowles, adding: "We remain optimistic."
Meanwhile, rescuers were working to drill a small bore hole, which is expected to reach its intended target later Monday, said Pike River Coal CEO Peter Whittall. The hole should dig down around 150 meters (492 feet) and be about six inches wide, he said.
Once the hole breaks through, rescue workers will be able to collect gas samples and other data from a new area of the mine, providing information that could aid in the rescue. Workers also expect to put laser imaging gear down the hole to create a real-time image of what the mine looks like, said Whittall, who added that rescuers so far have been working with a lot of unknowns.
"All information is gold," he said.