Physical Danger
Have you ever seen those famous pictures of skyscraper construction workers eating their lunch on the end of a loose girder ninety stories up? Those guys have nothing on their aquatic counterparts. While it's admittedly not so scary to fall off your working platform when you're under the sea, pretty much everything else about it is terrifying.
Commercial diving puts you in an extreme environment in a special suit that, provided it's functioning correctly, allows you to survive where you normally can't. That should be your first red flag. Construction work is full of perils, but those perils quickly become much more perilous when you're simply trying to breathe and your equipment isn't working.
Things get even more dangerous when you up the stakes and start working in HazMat gear. Divers can be asked to jump feet-first into everything from liquid cement to raw sewage or oil sludge. We're talking about risking hepatitis while moving through invisible broken glass or discarded needles. Worst of all, you don't get to see all of those colorful little fishies while you're down there. Scary stuff.