Of course it's a personal choice, up to the point that the welder is burning himself due to lack of sensible protection. There are many levels of welding protection from the green jackets to full leather jackets, most welders will wear the correct amount of protection in self defense. Not many folks want to be burned. No one I know wears personal protection against explosions. It sounds like you've been talking to lawyers, trying to put the onus on the welder? The bottom line is, using the info provided in your previous post, your company is seriously on the hook for what OSHA used to call an Immediate Threat to Life Infraction. You are lucky the man wasn't killed. You are searching the web for information on how to do the job safely AFTER almost killing someone, I would suggest you search for that info BEFORE ignorantly proceeding with a dangerous task next time. If not for the humanitarian reasons, at least to limit your liability.
JTMcC.