I just put two plus two together on how the CIA decided what "limits" to apply to sleep deprivation as part of its torture program.

The May 10 Techniques memo reveals that, when CIA’s IG reviewed the program in 2003 and 2004, the maximum allowable time which a detainee could be subject to sleep deprivation was 264 hours–an amazing 11 days straight.

The IG Report described the maximum allowable period of sleep deprivation at that time as 264 hours or 11 days. See IG Report at 15. You have informed us that you have since established a limit of 180 hours, that in fact no detainee has been subjected to more than 180 hours of sleep deprivation, and that sleep deprivation will rarely exceed 120 hours. To date, only three detainees have been subjected to sleep deprivation for more than 96 hours. 

Elsewhere the same memo explains,

As discussed [in the book Why We Slept], the longest documented period of time for which any human has gone without sleep is 264 hours. … The longest study with more than one subject involved 205 hours of sleep deprivation.

So what they did, apparently, to set an "upper limit" to the amount of time they can shackle someone up so they can’t sleep was simply to look up the longest recorded incident of sleep deprivation and use that!

And then when someone–presumably the IG and the CIA’s own doctors–pointed out (1) that expecting detainees subject to incredible stress to be able to withstand what one single person once withstood under radically different conditions is just nuts, and (2) sleep deprivation had already been tied to deaths in US custody, they toned it down. And how they picked their new, eminently reasonable standard of 180 hours (7.5 days)? 

Well, from the looks of things, they just figured out the longest they had kept any one detainee awake, and made that their new standard. They had to, of course, to ensure that the new standard still considered everything that had been done to be legal. 

These psychopaths were trying to set a new world record with their little science experiment on detainees, it looks like.