In 1896, John Scott Haldane descended into the Tylorstown Colliery in South Wales and found four dead miners beside a lit oil lamp. Plenty of oxygen. Their blood was cherry red. Carbon monoxide.
His solution was a canary. Its respiratory system, a unidirectional loop of air sacs, absorbed poison roughly twenty minutes before a human body registered anything. And the warning was graded: agitation, then quiet, then stillness. Silence itself was the alarm.
On December 30, 1986, Britain retired the last colliery canaries for electronic catalytic sensors. Cheaper, multi-gas capable, humane. Miners objected anyway. A catalytic sensor can be silently poisoned by compounds common underground, and a poisoned sensor looks exactly like a functioning one. A dying canary, at least, had the decency to show you it was dying.