Our guide explains the use of various pieces of safety equipment used in the mines over the years. He is currently explaining the use of a safety lantern that can show the presence of methane gas before it reaches explosive proportions, and carbon dioxide before it suffocates you. Before the safety lantern, miners used canaries to detect gasses. If the canary dropped dead, you had a problem and better get out. Unfortunately the dead canary didn't give any indication if it was methane or CO2 that killed it, where the safety lantern will tell you exactly what you're dealing with.
These days, air in the mines is monitored electronically with sensors placed at strategic intervals.