I probably wouldn't bother with fireproofing spray (a little overkill IMO) on welding gloves... Leather doesn't burn very well.I welded for over five years and a welding arc is much hotter than any butane flame will get, and never had any gloves actually catch on fire.
Bonny your probably right, heat from a welding arc is much hotter than any butane flame will get, its not so much the blow torch aspect im concerned with, its some of the idiots who don`t understand the dangers of working closely with fireworks that bothers me!
It maybe overkill, but wearing long welders gloves with a flame retardent is in my opinion a good idea as a compromise in not having the arms length protection of a portafire in your hand.
I once visited a hospital burns-unit a few days after bonfire night in the UK, you should see and hear some of the victims stories, some of these were pyro-hobbyists who thought they were safe by not wearing any suitable clothing and protection, also you should see the burns from sparklers (mostly children) - they are now going to be in and out of hospital for the rest of there lives!
stay safe!