Simple equations really. 2 Firefighters lost their lives in London playing with bits of string rather than use hose lines. By the time the the bits of string were used alongside hose lines, confusion reigned. Even with procedures for use, firefighters would rather go in a building with something tangible to fight a fire if it should break out, in front or behind them. Also, I doubt very much if fires antwhere in the world are different, they will still kill or injure all types of people from the trained to the non trained. By the way, how difficult is it to tie off that guideline and keep it taunt so that those entering behind have something to follow. Do all buildings have nice height tie off points at the right place, not by the ties, and what happens when a short tie comes undone. (Just a point, I haven't looked at a guideline for too many years so I might have the wrong info here).