DEyncourt wrote: Cages used by British miners as late as 1987 had oxygen tanks that would revive canaries affected by carbon monoxide:
In 1987 such cages were replaced by electronic gas detectors.
BUT WHAT ABOUT THOSE NOW-UNEMPLOYED CANARIES!Today, the National Mining Museum Scotland has thirteen canaries and they are unsurprisingly very popular with visitors!
Hmm, Seems like it be cheaper to just have a whole bunch of canaries.