It is amusing to read this thread and realize that in an emergency everyone is fiddling around with harnesses, carabiners, and rappelling devices. Back when the earth had just cooled and climbing was in a more primitive state, everyone learned the dulfersitz. It is very simple and quick. All you need is a well anchored rope and your (hopefully well padded) bod. You can finish a 100 foot rappel before the average person has donned a harness and rigged up. I dulfered back in the day and I had the scars to prove it, but still used it from time to time on SAR operations in subsequent years. When I taught rappelling, I made sure the student was at least aware of the technique and the situations in which it might be employed. If I recall the Surviving Disaster episode, the dulfersitz was briefly demonstrated.

Rappelling on para cord is insane. An edition of Accidents in American Mountaineering sometime around 1954 unequivocally stated that para cord had no place in climbing (well, maybe shoelaces). That statement was based on analysis of several climbing accidents that occurred that year.

If I were in a tall building and considering emergency rappelling,I would stash the right amount of proper rope, consult the revised edition of On Rope, by Bruce Smith and Allen Padgett, 1996, and get TRAINING and then PRACTICE. I would figure out how to rig my anchor (a pretty critical step) and get through the window. Proper padding of the edge would be critical.

Rappelling looks easy, and while it doesn't require any significant physical strength, a lot can go wrong, and the results of an accident are nightmarish. Trust me.