I don’t really have an answer to your question other than “a lot”! I grew up in Wyandotte, MI which is a Downriver suburb of Detroit. There were two large steel mills within a 2 mile radius. Back in the 60’s, long before the EPA, you could drive down the street and tell who worked at the mill. Their car was covered in a rust colored ash that many wouldn’t bother to wash off because it would just get covered again in a day or two. After high school, the two easiest jobs to get were pushing a broom around the mill or banging out car parts in a stamping plant. I went to the stamping plant. It was louder but cleaner.