but I was at Grandma's in the 1970s when she was canning and the safety plug blew out and put a hole in the ceiling. The safety plug back then were little round chunks of metal and made quite the ballistic projectile.
The newer canners I've seen have round rubber plugs that begin to seal as the pressure increase, and presumably would cause less damage if they blew out. Some even have an interlock that prevents removing the lid while it's still pressurized.
My wife does the canning, and would recommend choosing a canner with the "jiggle" weight instead of a pressure gauge. That way you can hear when the pressure comes up to start timing your batch. And if the noise stops - you have a problem (burner blew out, orifice clogged, etc.). And the jiggle weights don't need to be regularly re-calibrated like the dials. I know - more than you wanted to know about canning.
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