[headquarters]

they can be locked from the inside by a manual bolt in most cases - at least the few hatches I have had hands on experience with.

Even with tools you would have a hard time /use a lot of time popping the hatch.

Of course - careless mechie types and armoured bullywagon types can forget the lock in their eagerness to run over yet another enemy combatant on foot. I suppose its possible then to rip it open and throw the frag inside.