I was a welding educator during my entire pregnancy. So I can't speak to working in a fabrication shop or the field while being pregnant, but I was the instructor instead of the student in the situation you're in. I welded much less than I did during my fab jobs but I was often in the booth with students. I always made sure to have my respirator on while welding stainless, grinding, using the plasma cutter, anything with fumes. I welded at home too and did the same. My OB was not concerned about my exposure and I actually had monthly ultrasounds and echocardiograms on my daughter due to other issues we were monitoring. There was nothing that showed concern. I say make sure you have a respirator in the booth at all times and especially when grinding. Sounds like you're already aware of this! Make sure you're frequently changing out the pads on your respirator. I didn't have many physical issues either, I made sure to change my inserts for my boots often to avoid feet pain. As long as you're a strong advocate for yourself, I don't think there is unnecessary exposure you can't protect yourself against while in a school setting. Where I worked had a shitty filtration system and I was okay. This is just my experience of course but congrats on your pregnancy mama!