I think he has already been persuaded not to do it and to wait in the burning building for the emergency services.

What he could consider doing is learning to rappel and then with the knowledge learnt reassess his original idea. it would be foolish to wait till an emergency to try it out.

When I escort groups in the jungles I carry a 7mm line but no harness. this is to save weight and that is as critical as the potential safety issues.I have never had to rappel to assist anyone but did once descend a steep section using the CLASSIC ABSEIL to save time.

Don't fool around with back packs and slings, learn to tie an improvised harness.

Personally, I don't think I'd use it