Abstract: The invention comprises a plurality of fluid actuated members for interrupting the ignition circuit and stopping the operation of an internal combustion engine in the event of a malfunction of the engine or components driven thereby. A tank containing air under pressure is connected with an electrical current conducting master switch interposed in the engine ignition circuit and comprising a hollow housing divided by a diaphragm which, by the tank air pressure, normally maintains the master switch closed. Loss of the air pressure opens the master switch. Other similar diaphragm type fluid pressure operated members respectively connected with and responsive to radiator coolant level and temperature, engine oil pressure and sprinkler system water pressure vents the pressurized air from the tank in the event of a malfunction.