Negodki,
Jim has it right, I'm afraid. What Jim was getting at, is that gases, _because_ they are compressible, store a great deal of energy to get them under pressure.
Think of how long an air compressor must run in order to build up 30 psi in a bladder. All that time represents energy being stored up, just as if one were compressing a spring. If a failure occurs, that energy isn't released in the same gradual way it was stored, it comes out immediately & explosively. Water, of course, doesn't compress and reaches a pressure soon after filling its container. If a hydraulic failure occurs, the only energy being released comes from the elasticity of the container, not the medium. It's really an astounding difference between the two. It's also somewhat counterintuitive, so convincing people is difficult.
A while back, someone here wrote that he once arrived at a winery just after an air-filled bladder press ruptured, presumably under normal pressures. It shattered the thick, 3" wide oak staves of the press and hurled pieces & must for about 50 feet, as I recall. It was remarked that a person in the way would have been killed. This jives with what I know about compressed gas: it's amazingly dangerous.
Please don't take these comments as criticism. It's just that a lot of people were never taught how different the two are, and learn too late.
Besides, we need to keep all the good winemakers on this group alive & posting. ;)
Luck, Mike MTM