How far must you be from an exploding hand grenade to avoid injury?
You aren’t completely safe at any distance you can throw the grenade.
In basic, we were taught that the average soldier can throw the grenade about 35 meters and it has a ‘burst’ radius of 40m.
Wikipedia reports injury at 15m, fragments at 250m, fatality at 5m.
M67 grenade - Wikipedia
The M67 can be thrown 30 to 35 metres (98 to 115 ft) by the average male soldier. Its fuze delays detonation between 4 and 5 seconds after the spoon is released. Steel fragments (not to be confused with shrapnel) are provided by the grenade body and produce an injury radius of 15 metres (49 ft), with a fatality radius of 5 metres (16 ft), though some fragments can disperse as far out as 250 metres (820 ft).
The key point from this is that whenever possible you would throw the grenade from cover and take further cover with your head down.
One of those ‘little grenades’ (they are smaller than a baseball) will SHAKE THE GROUND a half mile or more away.
In a near ambush where you were about to die unless immediate action was successful — you throw the grenade and keep fighting, hoping the enemy takes a LOT MORE damage than you do.