I did a search on the forums, but did not find a post about this yet. So here it is.
Typically I don’t kill friendly NPCs, but I was messing around in QE after I had already beaten the game. In my devious endeavors to kill as many living organisms as possible, I noticed that the 3 scientists you meet in QE are impervious to a few weapons/weapon features, such as the secondary charge for the Tau Cannon and the crossbow.
They also appeared to have super human strength when It took more than a few headshots with the .357 to put them down.
check it out https://www.youtube.com/watch?v=qDDc2MkLu6U&feature=youtu.be