I believe that better catch the explosion sound as v3x said, because it indicates exact the moment of explosion.
Kraugh's method seems less precise since grenades thinks not instantly but with something like 0.1sec delay.
Here is grenades explosion sound list:
Code:
HE Grenade
weapons/debris1.wav
weapons/debris2.wav
weapons/debris3.wav
Flashbang
weapons/flashbang-1.wav
weapons/flashbang-2.wav
Smoke Grenade
weapons/sg_explode.wav