Originally Posted by havasu
I like your thinking. Make sure you consider the water penetration, keeping it dry without moisture, and well ventilated. I'm sure you can search old bank vault doors or check out Cleveland home/business recycling in Los Angeles with finding the vault door.
we did prisons..fresh air intake/ ac duct
use a steel plate as your register, with bars welded on it.
put a smoke detector at the opening of your fresh air.
to monitor, any funny bidness
run a 4'' fresh air vent out the roof..even tho, you will have fresh air duct.
if someone were to trap you inside,,and seal off the duct, they do not know you have back up
i like your idea...