Which type of breathing apparatus recycles the user's exhaled air?

The correct choice is a closed-circuit breathing apparatus. This type of apparatus is designed to recycle the exhaled air of the user. In a closed-circuit system, the exhaled air passes through a chemical scrubber that removes carbon dioxide and can be enriched with oxygen before being reintroduced to the user. This recycling process enables the user to utilize the air more efficiently, extending the duration of air supply and making it suitable for applications where conserving air is critical, such as in hazardous environments or confined spaces.

Closed-circuit breathing apparatus is particularly valuable in firefighting and other emergency response scenarios because it allows the user to operate longer without needing to resupply, making it advantageous in situations where quick escape or prolonged activity is required. The mechanism also reduces the release of exhaled gases into the surrounding environment, which can be particularly beneficial in tactical operations.

In contrast, the other types of systems mentioned have different operational principles that do not involve recycling exhaled air. Single-stage breathing apparatus typically refers to simpler systems that do not incorporate advanced management of exhaled air, while open-circuit systems release exhaled air into the environment, thus not recycling it. Non-rebreathing systems similarly prevent the re-inhalation of ex