I know frags didn't kill you instantly in Halo 3. You CAN survive a plasma/spike grenade if they miss sticking you. And you can survive a them sometimes. I can remember a few times where I stick someone and they don't die. Grabbing the OS and having it charge makes you invincible from everything.
Frags aren't supposed to kill you instantly. That's why I'm happy that they nerfed them in Halo: Reach.
Then we will leave it at that. Frags don't kill you instantly at full shields/health.
Plasma has a certain kill radius, shields or not. Spikes are different; Standing over it, or having it stick a wall behind you within a certain cone will kill you no matter what shield/health you're at.
Just saying.
It seems to go like this for blast radius;
(___) Frag
(__) Plasma (but can stick and deals more damage than frag)
[___]
.[__]
...V
That's some terrible editing on my part...
Anyway, the spike grenade is like a shotgun; cone effect, deadly stuck, doesn't expand outward like the plasma and frag.
Plus they're fun to drop in a bubble shield. XD