For years I was very active in two nationally-rated USAR teams - NASA DART, and FEMA's California Task Force-3. Both were deployed to the Oklahoma City Bombing and the New York Trade Center after I left.

This was part of the training required to become certified to the Rescue Systems-1 level. This was actually beginner-level training.  Here, we are using the high rise section of the Dunbarton Bridge to practice basic rappelling.  It was a great long way to that concrete below, but I'm hooked to two separate lowering systems - each rated for a 600 pound load, with a 10x safety factor.  I'm controlling the rope I'm holding on to and a second person is controlling the second line as a backup.

Once you master the basics then the drills become more and more complex - pick off an injured person half way down, assess his injuries, render first aid, package him in a stokes stretcher, then lower him down.  What's that you say?  There's a HAZMAT spill directly below and we can't bring him back up either?  No problem.  Rig another rope system and bring him out sideways.