When metal fails, it leaves an irrefutable story about the failure. In the case of a steel frame, the likely failure places (the most common by far) are, probably in this order:
1. Right rear dropout. The failure is almost always caused by riding on a broken rear axle, which flexes the dropout and ultimately fatigues it about halfway through, at which point the rest of it may give away "suddenly." But the failure itself is not sudden. Cassettes and unbreakable rear hub axles prevent this, absolutely.
2. Tie between A. Bottom of the seat tube B. Top part of down tube, underside, behind the lug.
The seat tube failure is always a fatigue failure, which again, by definition, takes place over time and is catchable by paying attention to noise; and by looking down there once in a while. Light colored frames without splatter paint jobs are easiest to check out, since cracks collect dirt and show up dark. I'm not suggesting anybody forgoe a dreamy Diamondback roadframe-from-the-late-'80s paint job, if that's what they're seeking; just pointing out that light plain paint shows cracks better.
The down tube is flexed (or at least stressed a bit) every time you apply the front brake. The fork is forced rearward, leveraging against the frame, and the stress falls on the upper underside of the down tube. If the lug has a sharp point there, your frame MAY suffer a "can opener" failure. That is the term for it, but it is misleading, since you open a can suddenly and get a hole in the shape of the canopener. But in a bike frame, the "failure" starts as a crack emanating from the point of the lug, and creeps around the down tube. Far from happening suddenly, you can (and people have, and are now) ride on a downtube that's cracked more than halfway around, without even knowing it. I've seen a fellow finish a race in the top three with about 3/4 of an inch left to his downtube (he didn't even know it, and was..Cat's Hill Criterium, a hilly one in CA). Bottom head lugs ought to have rounded spoons down there on the underside; that distributes stress better than does a sharp point.
Every now and then you hear of a steel frame failing someplace else, but those are the freak ones, and the ones I've listed are the most common. None is what I'd consider dangerous in the sense that it's just going to happen in an instant, and down you go.
I'm with Dave Bohm on this one. Anything can break, but knowing what to look for and knowing something about the causes should let you sleep better. One other thing, though: Super thin tubes are more likely to break than thick tubes, almost regardless of the quality of the steel. In other words, a frame made with 0.55mm butts (the tubes are out there), even if it's Jetson-age tubing with wonderful metallurgical scores, is closer to death than is a frame made with Hi-Ten steel that's 1.2mm at the butts. (My opinion, just from what I've seen in the past 20 years.)
One last thing: Let's consider dropping the Eisentraut thing. Albert is a superbe builder and has contributed so much to the sport we all love, and has been an inspiration and a teacher to so many. He builds a fantastic frame, and there was a time when he was IT, at least here in America. He ought not to have his name associated with sudden failures. I know there's no mean intent here, I'm just throwing that out, not scolding.
Grant Petersen
Walnut Creek, CA