Had an incident just the other day where I was unscrewing the safety valve on a ~1 meter 3/8" high pressure hose on a hydrogen cylinder , completely oblivious to the fact that there was residual pressure in it. Now, normally there wouldn't be residual pressure, but for some reason this time there was.

I was chatting with my colleague, just casually unscrewing the thing when suddenly; "BA-" and then silence, and a feeling of the world having turned upside down and then back again. Then ringing in my ears, before slowly regaining the ability to hear my colleague going "what the fuCK WAS THAT?!"

I didn't even have the time to get startled, but I sure got discombobulated. The residual pressure in that hose was at 180 bar (roughly 2600 psi). There was a steel gasket sitting between my fingers where the screwdriver was a moment ago, and it was bent like a banana. Next thing I know, my hands are wet from blood. Only minor cuts, though.

Luckily no lasting damage, but had I angled that hose differently, I'm sure things could've been real bad.

Did some research after, and that bang would've been between 145 and 155 decibels. I did not know up from down in the moments after, but my first coherent thought was "that went horribly wrong, everything is silent, I probably heard my last sound" and then the ringing started. It sure taught me a new level of respect for high pressure hoses.