One common cause of the accidents was a build-up of dangerous gases like methane and carbon monoxide in the mine shafts. Large amounts of these gases could lead to violent explosions. Methane and carbon monoxide have no color and no odor. The miners of the 1800s didn t have the special equipment scientists have today to measure chemicals in the air, so it was impossible to tell if the gases were building up to dangerous levels. Miners started to use canaries to test the air quality in the mines.
Canaries are very sensitive to carbon monoxide.
The canaries would chirp and sing and make noise all day long. But, if the carbon monoxide levels got too high, the canaries would have trouble breathing, and maybe even die. When the canaries were no longer singing, miners would know the levels of the gases were too high. They would leave the mine quickly to avoid being caught in an explosion. This is how canaries acted as a warning system for miners.