Taking 200 cfm out of your workspace means you need 200 cfm of fresh
air coming in.
If your w/shop is fairly air tight, you wont get 200cfm. Just over
3cfsec isnt really enough, a min should be 5 for brazing and 6 for
Work out whats the cube of your w/shop in air. that will tell you
how many air changes an hour you might get.
That aside, working with only artificial light is not good. Glad you
appreciate the health hazards in our trade. Brazing fumes polishing
dust sanding particles etc then eye strain.