On the historical use of canaries in coal mines

The use of canaries as a means of warning against the presence of firedamp in coal mines is mentioned in many references. Firedamp, composed mainly of methane and carbon dioxide, was the cause of suffocations and explosions. The use of certain animals as a means of warning, more sensitive than humans to the presence of low concentrations of dangerous gases in the air, appears referred to on several occasions, especially in the nineteenth and early twentieth centuries. It is worth remembering, by way of anecdote, the case of the Grotta del Cane (Cave of Dogs), in Italy, where small animals faint due to the high concentration of carbon dioxide at ground level. The canaries, very sensitive to the presence of harmful gases in the air, have been engraved in popular culture by this type of use, and until today we get colloquial expressions that refer to the canary as a means of early warning against danger. In the May 20, 1918 issue of the Spanish magazine “Alrededor del Mundo”, there is mention of an attempt to systematize the use of canaries in North American coal mines:

Flammable gases from coalfields cause formidable explosions of firedamp in mines, and it is logical that coal mining companies have long been concerned about seeking some remedy or at least to find something indicating the presence of gas and the danger of the explosion. The simplest is to lower the wick of the safety lamp to three millimetres and cover the body of the flame with your finger. In the event of danger, the flame reduces its brightness and is then…