The F1 grenade is a defensive fragmentation grenade, designed to be thrown in cover and at range in close quarter situations as this grenade will fragment upon explosion, sending hundreds of hot shrapnel flying at different directions. The F1 has an even bigger damage output and radius than the RGD-5 so one should not be surprised if the grenade wounds the player at ranges where one is safe from an RGD-5 blast.
Shadow of Chernobyl
A defensive hand grenade with a large radius of splinter damage. It is recommended to throw it only from behind cover.
In Call of Pripyat grenades' shrapnel can seldom hit the player well outside its declared blast radius, resulting in severe bleeding or, on higher difficulties, instant death. In-game, it is best used against tougher but slower mutants (controllers, for example). When engaging other stalkers it is best used in open areas (since in game grenades can be thrown across a considerable distance) where its fragments can easily kill a whole group of densely packed enemies, in contrast to RGD-5s which work better in room clearing situations.
Hawaiian and Owl sell as well as buy this type of grenade.