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Safety glasses a must...and he usually wears them. So far as the infra red.. I consider the most auspicious time for them, would be when forge welding.
When forge welding, one is concentrating upon the white hot steel in the middle of the fire, which is already formed into a "torch"..
Back when forge welding was a common practice, smiths who regularly did that task, developed a blind spot in the middle of their vision.
At blade heat, I don't consider it a visual danger.