When should a respirator be used?

A respirator should be used whenever the label requires it because pesticide labels provide specific instructions on safety equipment necessary for handling and application. These labels are designed to ensure user safety by outlining the potential hazards associated with the chemicals, including whether a respirator is required to protect against inhalation of toxic substances.

Using a respirator only when applying herbicides, on windy days, or during equipment maintenance does not encompass all situations where a respirator may be needed. The label is the most authoritative source, as it takes into account the specific product, the active ingredients, and the potential risks involved in its application or handling. This makes option B the most comprehensive and appropriate choice in determining when to use a respirator.