Slightly sobering website with broken cranks-- http://pardo.net/pardo/bike/pic/fail/FAIL-001.html
In twenty five years plus I have never seen a Campagnolo crank break at the spider. I have seen them break in the middle of the arm where Colnago has panto'd their name in the milled out groove. Usually cranks fail at the pedal eye. NOTICE THAT THE WEBSITE SHOWS ALL BRANDS OF CRANKS FAILING!!! Keep your bike clean and do periodic visual checks of your highly stressed parts and you won't have a problem. And yes, even steel cranks can fail.
South Pasadena, California