Yet it appears that those often happen without people noticing. Of course, only specific people, 4th degree burn is a trauma associated with metalworking, super small bits of molten metal burn right through and too fast for nerves to register and those burns are small enough to not bother
You also have the issue that deep burns like that destroy the nerves that would report pain, so you only feel it at the margins of the wound. If they're of significant size you'll also possibly go into shock, further dulling the sensation, if only temporarily.