Grenades are fun for sure, but jail isn't a war zone and on top of that, it'd do more harm than good when someone miscalculates their throw and the nade reflects back on his group, due to the very cramped interior layout. It sure also would be very OP against large groups of cops, and in jail you'll never see cops spread out, because the layout is so cramped and the amount of safespots is tiny, so nades would be the most effective weapons to take out the entire force. Given it's easier for criminals to maintain control of jail during a jailbreak, I would aim for body armor, combat shotgun, teargas, sniper rifle spawns in jail for cops to equip even before suggesting grenades to work for criminal side.