After drilling the 6 1/4 inch bore hole, they examined the air quality inside of the section on the mine they drilled into. The O2 (Oxygen) reading was 20% (very good) however the CO (Carbon Monoxide) readings were 1300 parts per million. At 400 PPM CO is which is considered a very dangerious, you will notice head aches after 1 - 2 hours and unconsciousness or death after 3 - 5 hours of exposure. My CO meter publishes alerts after 5 PPM and most house detectors will alert after 50 - 100 PPM.
Hopefully the miners who are trapped are located in a different location of the mine than where the bore hole was drilled. The self rescuers which these miners are equipted with convert the elevated levels of CO (carbon monoxide) to carbon dixoide only last about 7 hours. These miners are not equipted with any other source of O2.
Rescue workers were sent in the mine to look for the trapped miners, however high levels of CO prevented the workers from reaching the area of the mine where the miners would have been trapped. As a result, a robot has been sent down to look around in areas of the mine inaccessible.