1. Most people can’t swallow a frag grenade, and if it’s stuck in someone’s mouth, the cheek flesh isn’t going to slow down the fragments much, so it would tend to be about the usual “safe” distance, which really depends on whether you get hit by fragments or not. 2. The time needed to get a grenade into someone’s stomach, would I imagine tend to be longer than the fuse delay, so that’s an issue. 3. If a frag grenade is in someone’s stomach and explodes, I think you could probably stand right next to them and not die – I imagine there would be some fragments going out in some directions, and not in others. So it depends on what odds of not dying count. If your spectators are above or below such a person who is standing, that could help, since the torso above and below would tend to absorb most/all of the fragments. 4. Really you’re better off using something transparent and fragment proof, rather than relying on distance. 5. Distance also depends on the model of frag grenade. 6. Yes the more fat between you and flying fragments, the better. 7. As one example, the data listed for the M67 frag grenade specifies a lethal radius of 5 meters, so I’d want to be well outside that radius even with a grenade in someone’s stomach. Actually I’d want to be well outside the 15 meter casualty radius, and hiding behind cover with ear protection. 8. Really it depends, and “without dying” can’t be guaranteed without much more distance, and is up to whether you actually get hit with a fragment or not. As the M67 spec sheet warns, and applies to all other frag grenades if with slightly different ranges: “ALTHOUGH THE KILLING RADIUS IS 5 METERS AND THE CASUALTY PRODUCING RADIUS OF THIS GRENADE IS 15 METERS, FRAGMENTS CAN DISPERSE AS FAR AWAY AS 230 METERS.”