Thinking about a cheap low presure air tank. pic here is of a 2 litre drink bottle pumped up with hydraulic pump set up. bottle filled with water the only air is in the tube feeding the gauge, so while there might be lots of pressure there is no volume, therefore little danger. Bottle blew at 110 psi plus. the bottle swallowed more than 120ml as it expanded. The pump set up came from a testing program for sub miniature steam boilers, 2" dia mostly, Went over 1000psi. Only 1/4" ram, tried 3/8" to find it too hard.