What distinguishes open-circuit SCBA from closed-circuit SCBA?

• A. Open-circuit vents air to the environment.
• B. Open-circuit recycles exhaled air after CO2 removal.
• C. Closed-circuit vents air to the environment.
• D. Closed-circuit purges the regulator automatically.

Answer: (A)

The essential difference is what happens to the breathing gas after you inhale and exhale. In an open-circuit SCBA, the air from the cylinder is breathed in, and the exhaled gas is vented to the surrounding environment through an exhaust valve, with no gas being reused. This means the amount of usable gas is tied to the cylinder’s capacity and your breathing rate. In a closed-circuit SCBA, the exhaled air is routed through a carbon dioxide scrubber to remove CO2 and then recycled for inhalation (with oxygen replenishment as needed), so the breathing gas is reused until the scrubber or oxygen supply runs out. That venting-to-environment vs recycling of gas is the defining distinction, which makes open-circuit the setup that vents air to the environment.