No owner or operator shall cause emissions exiting from a shop due solely to operations of any affected submerged arc furnace, to exceed 20 percent opacity for more than one 6-minute period during any performance test, with the following exceptions:

(a) Visible particulate emissions from a shop due solely to operation of a semi-closed submerged arc furnace, may exceed 20 percent opacity, measured as a 6-minute average, one time during any performance test, so long as the emissions never exceed 60 percent opacity, measured as a 6-minute average.

(b) Blowing taps, poling and oxygen lancing of the tap hole; burndowns associated with electrode measurements; and maintenance activities associated with submerged arc furnaces and casting operations are exempt from the opacity standards specified in this section.