When is it appropriate for an applicator to use gas masks?

Using gas masks is specifically appropriate when an applicator is exposed to toxic fumes in heavy concentrations. Gas masks are designed to filter out harmful substances from the air, protecting the respiratory system from inhalation of these dangerous chemicals. In situations where toxic substances are present in high amounts, the use of a gas mask becomes crucial to ensure the applicator's safety and health.

The other choices do not warrant the use of gas masks. For example, non-toxic fumes do not require the same level of respiratory protection. Additionally, working indoors does not automatically necessitate a gas mask unless toxic fumes are involved; therefore, the context of exposure to hazardous materials is key. Lastly, using a gas mask when working without any protective gear is not a standard safety procedure, as proper personal protective equipment (PPE) should always be utilized, including adequate clothing and other protective measures.