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

The type of breathing apparatus that recycles the user's exhaled air is the closed circuit system. Closed circuit breathing apparatus, also known as rebreathers, operate by taking the exhaled air, removing carbon dioxide, and then enriching the air with oxygen before it is inhaled again. This system allows for a more efficient use of oxygen, as it minimizes the amount of fresh gas required to sustain the user, making it particularly advantageous in controlled environments, like diving or extended operations in hazardous areas.

In contrast, open circuit systems exhaust the exhaled air directly into the atmosphere, relying on a continuous supply of fresh breathing gas. Options such as Emergency Escape Breathing Apparatus and Positive Pressure Respirators also follow this principle but are not designed to recycle air. Therefore, the distinction of closed circuit systems lies in their ability to allow the user to breathe the same air multiple times with the necessary treatment for safety, making it an ideal option for scenarios where conserving breathable air is essential.