"About ten minutes, without being really put to the bad, though twenty minutes of it would make him mighty sick. You see, that gives a party six minutes clear before any harm's done. Any time a canary gives a warning, if the miners turn back right then and there, nobody'd be hurt. Isn't that a great little alarm, though?"
"It is that," Eric agreed. "But what happens to the canary?"
"Oh, he comes around again in about five minutes. If a bird gets too much 'white damp,' though, he loses some of his value, because he gets immune and can stand almost ten minutes. So you see, Eric, the 'yellow machine with feathers' can be a real help sometimes."
Courtesy of U.S. Bureau of Lighthouses.
A Beacon Masked in Ice.
Racine Reef Light, in the Great Lakes, where navigation has perils unknown to the open sea.
"Great!" said Eric, "I'll always look at a canary with respect after this. But I've been taking you away from the yarn, Ed, with all my questions. You were telling about the drill."
"So I was. Well, as soon as all the men are fitted up and the teams are ready, a signal is given. All the men are examined for their general health, their heart, pulse, breathing and all that sort of thing, and then they are made to get into the special helmet and sent into a smoke-house filled with the worst kind of fumes. They have to be there ten minutes. When they come out, the doctor examines them again. If any man shows poor condition, his team is penalized.