This is an interesting question, and the posts are awesome!!

I have been dong Vertical Rope Rescue off and on since 1990. I have received training from Schools like F.I.R.E.S and applied what I learned teaching S.W.A.T. teams in Mass as well as local SAR teams in Mass. Latter I worked doing SAR and High Angel rescue in Alaska. While I feel confident in my knowledge on this, I do NOT consider myself the all knowing PUBA of Rappelling. With that said here is my two cents.

An emergency Rappel means that you have no option to take a safer or more practical route out of what ever got you into that position.

With the thought of preparing for an emergency rappel means that you are packing tubular webbing to make a Swiss seat and have taken the time to learn how to do put it on. And you are packing rope that is applicable for rappelling. You are hopefully packing locking carabineers, or at the least load rated carabineers that haven’t been banged around (we use to throw them out, or put them to non life load tasks if they were so much as dropped on concrete or rock).

Believe it or not, with the materials listed above you can accomplish a true emergency rappel. Safety will be at a minimal but you can do it.

I have tested a rappel with a harness carabineer, figure 8 device and parachute cord. Before you freak out, it was high quality true parachute cord that was doubled over and doubled, so it was 4 strands gonig through my figure 8 device, NOT what you buy at Wal-Mart that has a very low strength. My cord was rated at a true 550. The endeavor allowed me to go down 50 feet of vertical free fall (there was a safety line just incase) but it took a serious bite into the aluminum of the figure 8 and was very intense. After several rappels the best way was to triple wrap the parachute cord around the figure 8 device and move slowly and smoothly.

Speaking to the use of the Rappelling Instructor belts. I wear one made by Black Hawk (no affiliation, but wish to be specific due to manufactures deviations in build and design) I have done several rappels to test the system. As long as I was against a wall or surface the belt was actually not too bad. Fee hanging would require me to add leg loops to prevent the belt from slipping up and suffocating me around my lower chest cavity.

One thing that I like about it is that if you have to do an emergency, under the armpits, haul of a person or a lower of a person the belt is quite helpful and offers a solid connection point.

If you were concerned about ever having to do an impromptu rappel, I would strong suggest that you pack prussic cord of the 6 to 7 mill diameter or a 1/2 inch tubular webbing, and a "SWAT" harness (they are normally just nylon webbing sewn into a seat formation, that can take a multitude of sized people) a figure 8 device, and a set of 4 locking carabineers. While the cost will be about $110 for all of that but it will fit into a pretty small sized pack.

I have not given suggestion to techniques here intentionally, that is something you should get in person from someone whom is qualified to teach you how to do rappelling and how to do impromptu rappelling.

Regarding the person who is not able to climb, you can still get classes on rappelling that would not require doing any climbing.

I hope that helps.