Per hundred workers. Your link is in absolute units of fatalities, their claim is a rate. At the very least, you need the number of workers (which is also available in BLS data) to refute their claim.

The data shows roughly 454k workers in the welders, solderers, and brazers occupation series. With their claim of 3.5 severe injuries per 100 worker-careers, that's about 16k severe injuries. If you assume an average career is about 25 years, that's about 636 severe injuries per year, compared to the 48 fatalities per year. So it's an order of magnitude higher (which I think is the direction most people would expect).

thanks for tracking that down! I stand corrected.