I have spent a fair bit of time trying to break into a lab. It’s a new type that I haven’t seen before (I haven’t played for around six months) and after trying the lift and fleeing quickly from the horde of Hulks and Corrosives waiting to say ‘Hello’ I had to come up with a plan.
I 'm playing a more ranged focused character, bow’s mostly and reasonable armour but not nearly capable of surviving a mass pile on in tight quarters with no room to run. I
So I built a stair downwards at the side of entry building and then another because it was actually two levels down, thinking I would be able to entice them up a few at a time. It didn’t quite work out that way; mostly they couldn’t/wouldn’t follow me up the stairs (not always though which was a bit of a shock when it first happened and I was no longer expecting it…). It wasn’t that much of a problem though, I have a spear as my melee weapon of choice and I had enough skill to gradually chip away at this horde. Standing on the stairs evading the odd blow also trained my dodge :-). So, that’s how the party went. And kept on going. And going.
I used to dash down the stairs and pulp the corpses whenever I had a chance but I was surprised at the huge number of Kevlar Hulks and SkJs. They took ages to kill (although it got a bit faster as my skill improved from all of the unending combat). I also was a bit puzzled at the lack of bodies to pulp - when I had the chance I would do my best to find the corpses but they didn’t seem to be showing. I eventually concluded that they must be slipping down the second stair into the lab proper which was annoying because it was difficult to go down there without being swamped. I did risk it a couple of times to kill a necromancer and a master which I thought might be responsible for the constant stream of full health top tier zombies.
Today I worked it out. As a floor tile only has 1000 volume and all these large zoms soon fill it up, I couldn’t pulp them and somehow they revive on full health! Two SkJs take up all the available space and everything else slips in between the dimensions only to come back and laugh at me next time I show up. Cheeky sods 
I’m sure I would have worked it out sooner but playing with a Winter start and x2 monster spawn means that I was expecting Labs to be pretty painful regardless. Oh well, it’s done my melee skills the world of good. And my first aid.