Which safety feature is commonly integrated into modern gas furnaces?

A thermocouple is a safety device commonly found in modern gas furnaces. It serves an essential role in monitoring the flame status of the furnace. When the furnace is operating, the thermocouple generates a small voltage due to the heat produced by the flame. This voltage signals the gas valve to remain open, allowing gas to flow into the burner. If the flame goes out, the thermocouple stops generating voltage, which causes the gas valve to close, preventing unburned gas from escaping into the environment. This feature is crucial for ensuring safe operation and minimizing the risk of gas leaks or potential explosions.

In contrast, the other choices do not serve the same safety function. An expansion valve is primarily used in refrigeration systems to regulate refrigerant flow, a zone damper is utilized in zoned HVAC systems to control airflow to specific areas, and a compressor is a component found in air conditioning systems that pressurizes refrigerant but does not relate directly to the safety of gas furnaces. Each of these components plays a different role in HVAC systems but does not pertain to the specific safety measures integrated into modern gas heating systems.