When you are near, or working with a potentially poisonous substance that can become airborne, protect yourself by wearing protective gear and keeping the area a. dim b. well-ventilated c. sealed d. brightly lighted

I think it's B. Because if you're wearing something that filters oxygen (E.g. gas mask) and the substance becomes airborne, the filters in the protective gear might be overworked if the substance density is greater than the filtering capacity.

Can you list the drugs that you want answered for? i think maybe your answer could be a or b. but i’ll never know till you post the rest of this question.

It would be 23 beats per second