What feature must portable heaters be equipped with to ensure safety in case of flame extinguishment or combustion failure?

Portable heaters must be equipped with an automatic shutoff feature to ensure safety in the event that the flame is extinguished or if combustion fails. This mechanism is crucial because it immediately stops the flow of gas to prevent dangerous situations, such as gas buildup that could lead to explosions or fires. The automatic shutoff acts as a fail-safe, enhancing the overall safety profile of the heater, especially in residential or enclosed environments where adequate ventilation may not be available.

Other options, such as a manual control valve, are used to start and stop the flow of gas but do not automatically respond to unsafe conditions. A pressure relief valve is designed to prevent excessive pressure buildup in gas systems, which, while important for system integrity, does not directly address the issue of flame extinguishment. A thermostatic regulator helps maintain a consistent temperature but does not function in the context of flame safety. Hence, the automatic shutoff feature is essential for portable heaters to mitigate risks associated with gas combustion failures.