Kill a cacodemon to your right then a wraith, maggot, imp and finally a hellknight. Use the medical station and then take the door on the right.
Go up the stairs and kill the archvile that spawns in before taking out the imps, grab the pick ups by the candles and then go through the door marked lab. There’s a maggot and a revenant waiting to your right and an imp behind you.
Use the medical station on your left and then go up the stairs. There’s a wraith behind the next door, take the ladder on the left down, kill some imps and a maggot and grab Richard Davis’s PDA from the ground in front of the large screen and some pick ups from the shelves on your right.
There’s a revenant and an imp ahead and a maggot will spawn in behind you, take the left fork and kill another imp, grab armor and a medkit from the dark spot at the end then climb the ladder, follow the passage round and drop down.