Okay let's talk about what we CAN do:
1) deafening the sounds. Actually OFP does it for us, be you could use fadesound command
(ever launched a barrage from a low flying Heli (maybe 30 m), right in front of you? Sounds almost gone, and takes a while to come back
2) visual effects. Possible, for a cheap version you could use something like the White Out
3) Detecting that an explosion actually occured close enough (and for a Flashbang, so that you actually saw it...I might also add that a flashbang doesn't make is so you don't see anything as in Rainbow Six, and CS):
Now that the actually hard part, and IMO not really possible at the moment, unless you are able to attach an eventhandler to the Shells, which isn't easy, but theoretically possible.
4) Confronting the fact with reality, we already have the sound fading build into flashpoint, and in reality you don't get the funky visual effects.
Maybe Interesting would be flying debries...
but the bottom line is, you don't really need such a script
-Fishion