Good point - all the hyperbaric chambers I've been in had inwards-opening doors.
One man chambers often open outwards, which does make you nervous.
Here is a pretty medical example with a "Intrinsically safe two-way communications system"
http://www.perrybaromedical.com/sigma-40-hyperbaric-chamber.html
I was in a one man chamber once, all steel, outward opening, its emergency communication system was a hammer.
If you had a problem you could attract attention!
The example above only takes you to about 2 bar above ambient but even so the door locking mechanism is quite susbtantial.
At only 2 bar the door hinges and lock have to contain 28lbs/inch2 of pressure on the door. Since it has a 40" dia door dia it has an area of 1256inches2 and so must contain 35,158lbs or 17 tons.
The original post looks very pretty but it cannot be containing much pressure.