Clear out the lab, then head upstairs and the log is round the corner to your right. Climb up a couple of steps immediately to your left, then jump across to the green-tinged rock and follow the walkway ahead.
After leaping, turn left and climb into an alcove, jump onto the box, and pull yourself up. Drop into the room and the log is on a barrel to the right. After a while you'll have to climb up a wall to proceed - from the top, turn left and look through the opening straight ahead and you should see markings on the floor saying 'CAUTION: STAND CLEAR'.
Make your way to it and follow the passageway.
