@DX: Ben commented on the lack of pressure-rated 3"-4" fittings before; it's an iffy matter, but it's worth re-reading what he said about it here:
I've also read a source over here: http://www.spudfiles.com/forums/nsf-pw- ... 15265.html
Now, I'm fairly certain that all of the 3" fittings I use are NSF-DWV as I've just had a look. With that, I'd say the fittings are safe enough to continue using that I wouldn't need to spend a ton of time and money replacing them. I'm also unlikely to go out of my way to look for fittings that give an actual number on their PSI rating. People have used these fittings for a long time without any reports of incidents, and I've used them on WBL's for a long time too.
I have a strict 80 PSI maximum rule on my WBL's. (Especially since one of them has a modded sprinkler valve blowgun rated at only 90 PSI.) I usually don't make shots over 60 PSI anyway, and they're more likely to pre-pop at this point. (Though that may be due to bad sabots and I have yet to test [or even finish some of] my new ones.)
Regarding sunlight exposure, my homemades are rarely exposed to sunlight due to rare use and the fact that they're ALWAYS stored indoors. If exposure is a concern, a good coat of paint should solve the issue.
That said, if I could press a button to turn all my launchers to those fittings (i.e. bushing and coupler connections that are obviously rated) and for all the stores to carry them, I would. However, I'm just not convinced that the risk is high enough to be worth the trouble.
Regarding sound, I'd only be concern if someone puts their ear up to the muzzle of a modded sprinkler valve based launcher. Outside of that, the sound levels are not loud enough to cause any damage that I'm aware of. The shots are made outside and there are no openings on the launcher to direct the sound in a way that would be harmful to your hearing. If you're using a ball valve, I wouldn't even think at all about ear protection. Worry about what actually matters, like the projectile launching or pressurization.
I did hear that you can fire guns outdoors without ear projection, but not sure how accurate that is. I have however, had some slight damage to my hearing as of late after going to a concert and I intend to never repeat that experience.