What is a defining feature of an open circuit SCBA?

An open circuit SCBA (Self-Contained Breathing Apparatus) is characterized by the way it handles exhaled air. In an open circuit SCBA, when the wearer exhales, the exhaled air is vented directly to the outside atmosphere rather than being recycled or reused. This means that the air the user inhales comes from a supply of compressed air stored in a tank, while exhaled air is expelled without any filtration or recycling process.

This feature is vital for maintaining a safe and breathable environment for the user since the exhaled air can contain carbon dioxide and other contaminants that need to be vented without re-entering the breathing circuit. In contrast, other systems may have different mechanisms for handling exhaled air, but in an open circuit SCBA, the focus is straightforward: inhale clean air, exhale directly outside. This ensures optimal oxygen supply and safety for the user in hazardous environments.