There is a place at the seal that will fail if the pressure gets too high so that the top will not blow up. The new ones are very safe. They will not open when under pressure too.Not sure if that one had a air vent blow out thingy. Or how ancient it might have been.
I'm pretty sure our four qt and my MIL's old big canner is older than 30yrs, both prob 1970s ish they do have the air vent blow out thingy that has to build pressure to seal, our new big canner is built the same way. Now when you say the newer ones are designed to fail at the seal do you mean the main seal? Or the little air vent thingy?
I know there is certain things your not supposed to cook in them cause they can foam up or something and plug the vents, or maybe it was expand, like beans or rice.
I have been using pressure cookers for 15 years and have never had an issue
, send him for coffee and donuts 
