I have personal experience of a safety briefing planned work involving an active high pressure/temperature piece of equipment.
Just before we started the work we heard a loud & persistent banging noise coming from the depths of the equipment - we found someone trying to dislodge a valve with a sledgehammer - had he succeeded he would have opened an 11,000 psi 250C gas system 3 ft in front of him...........................
As you can imagine the Elf & Safety guys went ape... we were able to show that not only did we have his signature that he'd attended the briefing & understood it but there was a video of it him clearly paying attention with everyone else.. He wasn't mad, a member of ISIS or low IQ - in fact he was an experienced, well regarded hand.......
All we could get out of him was that he didn't think what he was doing had anything to with the procedure and "he thought it would save time later"