Nor is hardware protection enough. The injector of a large tandem Van de Graaff generator damn near killed me. That injector ran at about 150 KV, with some decent capacitors, and lived inside a steel cage with a locked metal door so the electricity couldn't get out. There was a switch on the lock so as soon as the door was unlocked, the injector would be turned off, and it would be safe to go into the cage to service it.
This was Monday, maintenance day, and at the end of the day the accelerator would be turned back on to run straight through until the next Monday, Murphy willing. That day I was the operator to turn the machine on for the week's run. Had to do some fiddling around with the injector first, though. So I went, unlocked that door, and opened it. Bolts of electricity jumped from the injector to the door, frightening me so badly that after is stopped quivering I called the lab director at home, after hours, and told hi9m I was
not going in there. And he grumped and persuaded, but I remained adamant. Lightning bolts, even small ones, were not part of my daily routine.
Fortunately, I was paranoid working around high voltage. I didn't push open the door I kicked it open. And it turned out that this was maintenance day, and they'd had to work on the injector, so the crew had bypassed the safety switch and forgotten to take out the bypass at the end of the day.
The injector is way off at the other end, but here's an idea of the sizes involved. If you look carefully you can see a person climbing up a ladder at the widest part of the machine.
A similar accident happened to my thesis advisor, years before he became my advisor. They were finishing up construction and tuning of a three-tank proton linac. I'm not sure of the voltage it was running at -- 40 or 58 MeV -- but it was turned off at the time and my advisor was working at the end of the beamline. Some fool, not knowing my advisor was there, set the machine going; and my advisor ended up with a sunburn (or worse) all the way from one side of his hand to the other. I think the hardware protection was bypassed there, also.
Software and hardware can both improve your safety. But never overlook the human touch. NOTHING can be made foolproof, because fools are so ingenious.