blackdamp, the mixture of carbon dioxide and nitrogen is released from the decay of organic meterials........ie coal in our case. blackdamp is heavier than oxygen there fore displacing it near the floor first. if in a tunnel blackdamp should be checked for regularly by walking with the flame safety lamp low or holding your oxygen metering device low. slopes are dangerous in blackdamp seasons..... yes there are seasons. since blackdamp sinks it will fill the whole mine up at the bottom of a slope or anywhere along the slope. youll not enter it slowly from the floor up but youll walk right into a high level of it where the mines filled up. we have run across this in many trips. the only time we found CO in a mine was when i "released some" into gregs passport in the diamond drift!
chris
also watch this video.....
http://www.ironminers.com/mineforum/viewtopic.php?t=840