I've worked as a fitter & turner in heavy manufacture including the BHP & Rio Tinto workshops at Dampier, Port Hedland and Cape Lambert and have never heard of double eye protection as being mandatory. I will say that it's been about 6 years since I left the trade and things may have changed.
Personally I don't wear safety glasses when turning as I find they fog up, the face shield however has plenty of ventilation and rarely fogs up (maybe I'm just an unusally heavy breather

).