A system comprising a refrigeration engine (132) and regulator (250, 350, 450, 550, 650) positioned within a housing (144, 244), the regulator (250, 350, 450, 550, 650) controlling fuel to the engine through a fuel line (354), a lock-off valve connected to the regulator (250, 350, 450, 550, 650) to shut off fuel supply through the regulator (250, 350, 450, 550, 650), a controller operably connected to the lock-off valve and/or the regulator (250, 350, 450, 550, 650), a guide (462, 562) positioned within the housing (144, 244) and proximate to the refrigeration engine (132), the regulator (250, 350, 450, 550, 650), and/or the fuel line (354) to direct gases leaking from the refrigeration engine (132), regulator (250, 350, 450, 550, 650), and/or at least one fuel line (354), and a methane sensor (566, 666A) positioned within the guide (462, 562) to detect the presence of methane within the guide (462, 562) that is directed by the guide (462, 562), the methane sensor (566, 666A) in communication with the controller and configured to transmit a signal to the controller when methane is detected by the methane sensor (566, 666A). The controller performs a safety action when the signal from the methane sensor (566, 666A) is received.