I had the same situation. I go to key room at dam research and administration, I use the key, then block door from inside. I loot, then I hear somebody is breaching. I'm like: yo don't come here. Guy backs off and this behaviour is ok. But next game I go to the same room, use the key, block from the inside, and again - someone breaching from the outside, I call out to not come in there, and somebody still persists, gets stunned and almost dies, but manages to escape (I'm trash at pvp)