Been listening to the show from the beginning but this is the first time I've come on the forums...I love Sark's DMing most of the time, but I think he made a mistake here. I say that because I think he meant there to be only a remote chance of one of the characters falling (at least, that's what it seemed like from his reaction to what was happening), but in fact the way he set things up on the fly made it more likely than not that one of the characters would fall. If there is a 7% chance of something happening on one dice roll, but you repeat the dice roll 12 times (4 characters X 3 floors), you end up with more than a 58% chance of one of the players missing a roll at least once. I know that's kind of nitpicky, but it's come up a few times before, where by repeating something that is very low percentage over and over you end up making it more likely to happen than not.
Something to keep in mind for the future, maybe: if you repeat a low-percentage chance a bunch of times, it becomes a high-percentage chance.