It's been a while since I took my class, but I seem to remember the above applying ONLY if the confined space is not vertical entry. So if you're monitoring the air and something goes south, or your attendant notices the entrant acting funny they can get the entrant out without exposing themselves to the hazardous atmosphere. The only situation that is feasible is if the attendant can pull the entrant out, which is not possible with vertical entry and is why it requires a permit as well as equipment to necessitate a safe and timely extraction. I definitely recommend taking a class on confined space, it will clear a lot of things up. It is also not something to screw around with, as if something does happen and you aren't following safety protocol, you are not only going to kill yourself but likely the person that finds you. A class is well worth the couple hundred bucks it will cost, and many places have confined space attendants you can hire out for the day (they have monitoring and extraction equipment too) which makes way more sense if you're cleaning infrequently.