What type of respirator requires a continuous supply of air from an external source?

A supplied-air respirator is designed to provide a continuous flow of clean, breathable air from an external source, rather than filtering the air around the user. This type of respirator is essential in environments where the air may be contaminated with harmful substances, or where there is insufficient oxygen, such as confined spaces or areas with hazardous gases. The external air supply can come from a variety of sources, including a dedicated air compressor or a compressed air cylinder.

In contrast, self-contained breathing apparatus units contain their own air supply, allowing the user to be independent of external air sources but typically for limited durations. The options related to cartridges and air-purifying respirators rely on filters or chemical scrubbers to remove contaminants from the air rather than supplying fresh air. Thus, the proper equipment choice in situations needing continuous air supply is the supplied-air respirator, as it addresses safety needs effectively by sourcing air from a controlled environment.