Embodiments of the invention include a system and method for controllably delivering hydrocarbon gas to a hydrocarbon gas-fueled device. According to one embodiment, a valve having an open state and a closed state is used to control the flow of hydrocarbon gas from a pressure vessel to a supply line. A hydrocarbon gas sensor detects airborne hydrocarbon gas and generates a signal in response. A controller automatically moves the valve to the closed state in response to the signal from the hydrocarbon gas sensor while the valve is in the open state. The controller automatically releases liquid sealant to the supply line in response to a continued signal from the hydrocarbon gas sensor after at least attempting to move the valve to the closed state.