At which level of protection can an air-purifying respirator be used?

An air-purifying respirator is designed to filter out harmful substances from the air, making it suitable for use in situations where the contaminant levels are known and can be effectively filtered. Level C protection is specifically for situations where airborne concentrations of substances are known and they are only present in lower doses, allowing for the use of air-purifying respirators. This level also requires the use of additional protective gear to ensure the safety of the worker.

Level A and Level B protection are necessary when dealing with highly hazardous substances, where the type and concentration of contaminants are unknown, or where there is a risk of encountering life-threatening concentrations. These levels require more comprehensive and specialized respiratory protection than what air-purifying respirators can provide.

Level D is used for work situations that do not require any respiratory protection, typically in environments free of hazardous materials. Hence, air-purifying respirators have no application in this context either.

Overall, air-purifying respirators are appropriate for environments that align with Level C protection criteria, where they can effectively filter out airborne contaminants without the need for more complex protection measures.