What is the best thing to do when a grenade is thrown at you?: originally appeared on Quora: The best answer to any question. Ask a question, get a great answer. Learn from experts and get insider knowledge. You can follow Quora on Twitter, Facebook, and Google+.
The generally accepted fragmentation radius for a frag grenade is 30-35 feet, and the fuse length will be between 3-5 seconds. So usually running isn't going to be an option for you. If you can take cover, do so. If not, hit the deck and get as low as possible, as the majority of the fragmentation will go upwards. Beyond that, there's not a whole lot to be done.
Frequently asked followup questions:
Head first, sideways, or feet first? Head first. Your Kevlar helmet is specifically designed to stop shrapnel, and your plate carrier generally is going to only protect you in three spots -- straight on from the front, straight on from the back, and over the shoulders (with shoulder pads, which most troops deploy with these days). By presenting a minimal cross-section to the grenade, you're minimizing the fragments that can hit you, and by presenting your most armored front to the grenade, you're protecting yourself from what fragments do hit you. Feet first is a bad idea -- you don't have any significant protection there, and it's a great way to get your femoral artery severed. Leg and intestinal wounds are both incredibly painful, and incredibly dangerous in the field. Sideways is even worse; your plate carrier won't have any protection under the arms, and you're maximizing the frontage of your body that is exposed to the blast.
Pick it up and throw it back? Not a chance. There's no way you have enough time. Assuming a 4 second fuse length, two of which are spent in flight, you have just two seconds to notice the grenade, react, reach down, pick it up, plant your feet, lift up, and throw it far enough that you're clear of the blast radius. Not going to happen except in the ultra-rarest of situations. Plus, while you're faffing about with that, whoever threw the grenade at you is still putting fire down on your position.
Back in 2003, when I was in Iraq, we were executing a cordon and search operation in Baghdad. There was one particular house that we had a pretty good idea had some insurgents in it. I was outside, just down the block, when a team from our Bravo company went in to clear the house. They took fire immediately on entering the door, and someone from upstairs threw a Russian RGD-style grenade down the stairs. It clunked down to the bottom as everyone freaked out and dove for cover.......and it didn't explode. I think they eventually managed to finish clearing that building by climbing over from the next roof; nobody wanted to walk up the stairs with unexploded ordnance sitting on them and insurgents the next floor up.