A nice short article on the dangers of photographing bright objects over on PetaPixel:
https://petapixel.com/2017/09/01/photos-cameras-lenses-got-destroyed-solar-eclipse/If the light source you are directly filming is bright enough to burn things with just a magnifying glass it's best to look into protection, especially if you're expecting to be looking at it for a long period of time. I'd also think the near infrared radiation would be more of a hazard to the lens and camera than UV. Modern lenses usually have UV blocking coatings, as well as the glass itself being not very transmissive to UV. Near infrared on the otherhand will pass through and while the bandpass filter in front of the sensor will reflect most of it, it will heat anything it shines on.
Regular photographic ND filters are not designed to block near infrared, and as such are not suitable for solar photography. For this reason I wouldn't recommend using them for photographing welding either. A solar filter might work if you want more true colours, but I can't say how well they would work. Welding lenses are made for looking at welding arcs and are thus probably the best choice protection wise.
Welding shades are cheap insurance against lens and sensor damage, and not terrible to have extra of if you've got welding equipment already. A no.7 or 8 shade should be fine, it's about a 9-10 stop reduction and thus is approximately equivalent of going from F/2 to F/45 - F/64, or going from 1000μs to 2μs - 1μs exposure. If this is too dark for your needs a no.6 lens is a whole 3 stops faster, or 1000μs down to ~20μs.