Here's my logic:
OSHA requires compliance with NFPA 70E (Electrical Safety Standard), NFPA 70E has 5 levels of protective clothing that may be worn when working on energized circuits/equipment. The appropriate level/category is chosen based on the amount of arc flash incident energy available at the equipment and your proximity to the energized part.
Category 0, is essentially required for many residential situations. Category 0 is natural fiber clothing and other accessories. So if your going to buy company clothes, it might as well be category 0 or higher. A 50/50 shirt is not even category 0, as the non-natural fiber portion will melt on the skin during the heat of an arc blast.