The rescue effort at a New Zealand mine that exploded Friday is on hold because workers fear there might be a second blast, since the mine is known to leak methane gas. Twenty-nine men, ranging from a 17-year old believed to be on his first shift to a 62-year-old veteran of the job, have been missing since the first explosion. Police say they are conducting tests on gases in the mine, and would not send rescuers inside until at Sunday at the earliest. "We will still look for that window of opportunity to get underground and get those men out," said the regional police commander. "We still remain positive and we believe that once that window of opportunity opens, we are ready to go."