When is it appropriate for Alex to safely use a respirator?

The appropriate time for Alex to safely use a respirator is after receiving proper training on respirators. This training ensures that she understands how to correctly select, fit, use, and maintain the respirator, as well as how to recognize the limitations of the device. Proper training involves learning about the types of respirators available, the specific hazards present in her work environment, and the necessary procedures for ensuring the respirator offers the intended protection. Without this training, even if the respirator fits well or the air quality seems acceptable, Alex may not be adequately protected against airborne contaminants. It's essential that anyone using a respirator has a clear understanding of its functionality and the environmental conditions in which it is necessary.