19 November 2010. Methane may have accumulated in a void formed during earlier mining activities, then been expelled into the rest of the mine by a roof fall, or it may have accumulated directly in working areas of the mine. It is not known what sparked the explosion, but a working mine contains several possible ignition sources. Two miners managed to walk from the mine later the same day, having been in the access tunnel, or just off it, some distance from the source of the explosion. Both were taken to Greymouth Hospital suffering moderate injuries. Initial media reports were unclear as to the number of miners and contractors remaining within the mine, with various numbers between 25 and 33 being mentioned. It was eventually ascertained that there were 16 miners and 13 contractors trapped. The names of the missing workers were released on 21 November 2010. Mine officials noted that every worker carried a self-rescue device providing 30 minutes of air, and fresh air bases were provided within the mine for them to escape to in the event of an emergency; however, the refuges were empty and there was no evidence of miners attempting to reach them. When a borehole was drilled into the area where the miners were thought to be, a level of 95% methane was found, with the remainder primarily carbon monoxide. It appeared there was little chance that any of the miners who may have survived the blast could still be alive. Although families had held out hope that some of the miners may have survived, it was believed by the rescue team that all had been killed by the initial explosion. The mine had not collapsed and air was blowing freely throughout the tunnels indicating that there were no obstructions to survivors leaving the mine or indicating their presence by tapping on pipes or calling for help. A second explosion occurred at 2:37 pm on 24 November 2010. Police Superintendent Gary Knowles stated that he believed no one could have survived. According to the CEO of the Pike River mine, Peter Whittall, the explosion was not caused by anybody working in or around the mine. The second explosion sent smoke, soot and explosive gases up a mine shaft where a team of rescue staff had been taking samples; the noise of the rising explosion provided them enough warning to get clear, evacuating the area