Which color of light will flash slowly when the air capacity is at half?

The correct answer is yellow, which is significant as it serves as an important visual alert for users of the Scott Air-Pak X3 Self-Contained Breathing Apparatus. When the air supply reaches half capacity, the yellow light is designed to flash slowly to notify the wearer that their air supply is diminishing, allowing them to take necessary actions such as exiting a hazardous environment or preparing to switch to a backup air supply.

This function is critical in maintaining safety during firefighting or emergency response situations. The yellow light acts as a clear and immediate indicator, ensuring that the wearer is aware of the remaining air supply and can make informed decisions regarding their continued operation and safety. The other color options do not serve this specific purpose, as they are associated with different operational states of the SCBA.