The gas safety valves I've read about aren't physical, but are actually electric. They use a thermocouple to power an electromagnet in the (sprung) safety valve

The gas safety valves I've read about aren't physical, but are actually electric. They use a thermocouple to power an electromagnet in the (sprung) safety valve. Presumably this allows the safety valve to be located further away from the heat source reducing the risk of thermally-induced failure modes.