Abstract: A safety air supply for use in combination with pneumatic shutdown systems of the type connected to an existing air supply source and cooperative through electromechanical control means with the fuel injectors of Diesel engines for moving the fuel injectors between operative an inoperative positions. The safety device comprises an enclosed air reservoir tank connected between the air supply source and the air cylinder of the shutdown system by heavy duty armored conduit. A tee fitting is sealed in the top wall of the tank and a one-way check valve secured in the top of the tee fitting allows air to enter the tank from the existing source up to a predetermined pressure and thereafter closes to contain a supply of air within the tank independent from the existing source. The outlet of the tee fitting is connected to the inlet of the existing pneumatic shutdown system.