There are escape rappelling kits sold to the fire department industry. 75' of high strength, low diameter, low stretch rope with a figure 8 and carabiner stored in a pouch.

They assume that you are already wearing a harness or one of the fancy belts that can be used as a harness in theory. The belts are made of 2 inch webbing with a parachute grade buckle. The figure eight would connect to the buckle. The webbing and buckle are strong enough but would be painful and potentially compromise your airway if you get stuck while rappelling.

A belt around the waist can cinch down on the abdomon, or pull out the belt loops of your pants and ride up on your rib cage and cinch down preventing you from inhaling. Hopefully you rapell to the ground before either of these things happen. Pants loops are not designed to support the weight of the wearer being suspended from them, only to counter act the weight of pants against gravity.

Additionally you need to secure your rappel line to something in the burning building that will withstand the weight of you and your rappel. Granted it only has to hold you unti you reach the bottom, and if it doesn't you will reach the bottom anyway. This anchor point may not be next to the window so allow some extra length to reach across the room and to tie/secure the rope to your anchor when deciding on length of rope.

Rope is bulky. Even 75' of small diameter rope fills a pouch about size of a leg pocket on BDU's. As you increase the length, the larger the pouch. Storage may not be a problem but cost may be. These escape kits typically cost $150 or more. The rope is made of Kevlar which is high dollar.

Are you familar with rapelling? It is not that difficult but if you plan on rappelling out of an office building, you might want to have rappelled at least once before so you know how to operate the devices. Rappelling anything over about 150 ft requires different equipment from a figure 8 because the rope weighs so much that it provides a braking effect to the point you may not be able to rappel at all.

Different rope diameters and materials provide differing amount of friction through figure 8's. You also need to take in to account body weight. Anything over about 250lbs and the figure 8 does not always provide enough fricition to control a rapppel. I weigh about 230 and double wrap my figure 8 when rapelling to get enough friction on an oversized figure 8 and 1/2" rope. A smaller figure 8 with small diameter slick Kevlar rope and I would be zooming down like on a greased pole.

I am not saying rule it out altogether. I would say you need to identify an anchor point or points. You would need to have a relaible means of breaking open your windows (window punch ). You would want some sort of padding system to cover the broken window glass so it does not cut your rappell line. You want to have enough rope to reach the ground from the floor you are most likely to rappel from. You need to have a harness or belt system that will effectivly work as a harness. And you probably should have rappelled at least once before, ideally with the equipment you plan on using. Swinging out an open window anything over a couple of stories and you will get some good pucker going on your backside.

I teach rappelling to fire fighters and rescue personnel. These guys and gals work on ladders and go into burning buildings. Getting some of them to even go out a second story window in a training environment for the first time can be a challenge. I have rappelled from about 200' feet and spent a day working on a 15x15 platform at 800ft. I had butterflies in my stomach all day and was not to keen on looking over the side even though I had on my harness and was tied in.

On the other side, most fire department ladder trucks and arials only reach 85'-100' feet. There are a few 110' ladders but 85'-100' are the most common. That is about 7-8 stories by the time they park the truck away from the building and angle it towards the building. They can be moved but it takes some time for the truck to place its outriggers and raise the ladder. They will have to lower the ladder, retrack the out riggers, move the truck and then reset the out riggers and raise the ladder.