Recreational divers don't normally do this, but it might be useful to go through in your mind exactly what you would do when each piece of equipment fails. I actually do this myself, I do NOT like betting my life on any one piece of equipment or system.
None of us can survive all dives if everything fails, but we should be able to survive single item failures.. so WWYD:
Reg freeflows
Reg stops
BC starts inflating by itself.
You notice that you are at 100 feet and it is getting hard to breath and the guage is in the red.
mask strap breaks
regulator mouth piece falls off and you start choking
weight belt falls off (or if you are lucky you catch it on the back of your knees)
you get tangled in fishing line around the first stage and can't see it.
Fins strap breaks and you lose a fin.
You lose your buddy
You get lost underwater and have no idea where the anchor line is.
You jumped in and you forgot to turn your air on.
You are caught in a current that is taking you where you don't want to go.
You computer stops working or you can't understand it.
Your computer says you are in deco.
Your BC is leaking bad and not holding air.
Your dry suit gets ripped.
You are trying to make an exit on a rocky shore and the seas have increased dramatically.
A few sharks come around and appear agitated and aggressive.
A Moray eel tries to bite you (or does bite you)
You've totally exerted yourself and now find yourself gasping for air on the bottom and you begin to feel a strong (and natural) urge to bolt for the surface.
You've pulled yourself down an anchor line and when you get to the bottom, you find that you are drastically under-weighted.
You crawled under a ledge to catch a lobster and now you are wedged and seem stuck.
You come to the surface and there ain't no boat where you left it.
You've gone way deeper than you intended and you are scared and narced.
Then we can go into scenarios where your buddy has problems, does stupid things, requires help etc.
It probably helps to at least envision what you would do when stuff like this happens. And if you keep diving long enough, probably a lot of those things will happen sooner or later.
Whoa, that's a bunch but I'll try and please someone tell me where I go wrong
1. Keep it in my mouth, clear it in an attempt to correct the problem, get buddies attention, turn tank off then on again, abort the dive if all else fails
2. Switch to alternate, abort via cesa if air wont work
3. hold deflator button, hang on to buddy, abort dive
4. Get buddies attention, give ooa signal and get his reg, start controlled ascent
5. Manually hold mask to face, clear it, assess
6. This one is tricky, it depends on if i have any breath left and which is faster, first try to get aas, but I suppose I press the regs free flow button and hold it up to my mouth to breath manually
7. Put it back on, grab buddy to control ascent
8. Don't panic, calm down, remove knife cut myself free
9. Cuss, keep diving on one fin
10. Look for a minute iaw the dive plan, surface and deploy smb
11. Same as above
12. Put snorkel in, turn it on
13. Let buddy know, swim out of it, reassess
14. Use other instruments, forget computer, ??
15. I don't know for sure but I would do a series of stops at ascending depths prior to safety stop
16. Fin my way to surface, if too negative, dump eights, of course always let buddy know
17. ??? Never dive dry
18. Tough, I might try to get to an alternate exit point with fewer rocks, go as far as I can subsurface
19. Try not to turn my back to them and get big and defensive in an attempt to deter them, make my way out of the water
20. If he tries, leave it be, if he does, assess the damage and get out of his ao
21. Stop, think, look at gauges to reassure myself, surface in control
22. Let buddy know and thumb dive
23. Don't panic, if necessary, remove bc and free myself, bang tank to alert others of my problem
24. Inflate bc, deploy smb, wait, if within a couple miles, start finning for shore
25. Don't panic, ascend, reassess, at least that's the idea