From WILLIAM EDWARDS
Re ‘Leaking light stops methane build-up’ (Technology, 13 February).
Canaries were never used to ‘warn miners of a build-up of methane gas’.
They were used to detect the presence of highly lethal gases such as carbon
monoxide which occurred usually after an explosion, and were carried by
men wearing breathing apparatus. Small, fast-breathing birds are many times
more susceptible to CO than man and during rescue operations, if the canaries
showed any signs of distress, the rescuers (and the bird) could retreat.
William Edwards Oldham, Lancashire
