There is nothing to pressurise, they tend not to explode as such, if the water housing goes faulty or the gas valve sticks in the open position then you get steam very quickly, it will blow the weakest link.......I think the biggest danger with this old thing other than problems with leaky seals etc is if it starts to work!
You will then be successfully heating water in a boiler of unknown condition. If the pressure does not vent as the water starts to boil, it could explode.
Have you tried pressurising the vessel to see if it will vent correctly?? Is there a safety release valve somewhere? Do all the valves operate as intended, especially any pressure release valves!!
They are very reliable units when working.