While working in a dealership many years ago we had a mechanic add some hydraulic oil to the in-ground automotive lift. Success! The lift didn't jump anymore the last two inches where it ran on just air when the oil was low. He decided to help the mechanic in the next bay and top off his lift as well. He stuck a 3/4" impact gun in the plug and zip out came the plug along with several gallons of oil powered by a whole bunch of air pressure.
Dave
Loosening a hydraulic connector when the system is already bled is undramatic, and pretty safe if the connection is of the type that indirectly leaks to a side hole. BUT .. if there is still air in there, it stores energy like a spring! Not quite like death by diesel injector, but it is true that a squirt of hydraulic oil into below the skin is pretty much the end of all.
My direct experience with trying to vent Argon from a HIP (Hot Isostatic Press) out into the exhaust pipe...
From cooling back from 900C to below 300C, the pressure had reduced a bit, but was still at 800Bar (11,600psi).
The vent valve opens into only 1mm hole, which then ends up in a sort of "communal" exhaust about the diameter of a spray can.
The final vent pipe was 1/2", meaning it was 3/4" OD, in stainless 316. The problem was with the "communal" part being shared by a oil filled vacuum pump.
I never would have thought that one could blow hard enough through a tiny 1mm hole to make enough pressure in a 1/2" pipe open exhaust to blow back through the gaskets of a vacuum pump, and generate an expanding mist of white oil fog - that is oil bubbles filled with Argon.
Panic! It spread through the whole lab, filling up from the floor. I reached down into the fog, and spun the needle valve shut, but by the time we had made our way out, it was waist high, and I was tripping over all sorts of machinery under it. In 30 minutes with loading bay doors wide open - it was all gone, but the fright has stayed with me! Breathing reaction is driven by CO2. A lungful of Argon will stop you breathing!
Gas under pressure is just dangerous stored potential energy. The work the compressor has to do to get it there could have driven you somewhat far down the road. High pressure gas is something that you treat with very, very special care - as if it was dynamite!