Going through the lab's pipe section can be nasty if you mess up the timing. Start with full stamina and clear out any mutants lurking around first, makes life way easier. The whole sequence is pretty straightforward once you know what's up - you need all three valves turned or that radiation starts flooding in fast. Here's something interesting: if you get caught in the radiation it's basically instant death and you'll need to reload your last save. The door stays locked until all valves are working properly, so get comfortable with those climbing spots between pipes. Tip: might be worth saving right before you start the valve sequence, especially if your equipment loadout is making you move slower than usual.