Which SCBA component allows two firefighters to share air from one cylinder without removing their facepieces?

The component that allows two firefighters to share air from one cylinder without removing their facepieces is the air transfer valve. This device enables the transfer of air from one SCBA cylinder to another, providing an essential lifeline in emergency situations where one firefighter may need to assist another who is low on air.

The air transfer valve is specifically designed for this purpose, ensuring that both firefighters can maintain their protective facepieces while sharing air, which is critical for safety in hazardous environments. This feature can be vital during rescue operations or when breathing apparatus failure occurs.

In contrast, while an emergency escape breathing support system is important for providing an additional means of air during evacuation, it does not facilitate sharing air between two firefighters in the way the air transfer valve does. The other options, such as the two-way communication device and pressure gauge, serve different purposes related to communication and monitoring the air supply, respectively.