I have a very old ('50's) Mirro Matic Pressure Cooker which is sitting on my bench  that blew the lead (blowout) seal and covered the kitchen ceiling with beef stew a couple years ago.  It was a thrilling experiencefor all involved to say the very least.  Believe it or not I think I have a new seal for it somewhere.  Back in the day they came with a spare seal and gasket. 
That's the brand! Maybe the seal blew out on our neighbor's instead of opening the lid. 
I was just a little kid at the time, and I know everyone laughed, so she wasn't burned.
Those old ones didn't have a top that rocked back and forth to maintain steady pressure. 
They had a stationary top with a little rod that extended, with scribe marks to indicate pressure.
You had to regulate heat carefully to maintain the desired pressure.