Abstract: A pressure gas engine such as a compressed air turbine having a variable speed device for controlling the speed of a rotor and also having an overspeed safety device to prevent damage to the engine in the case of excess speed through malfunction. The overspeed safety device includes speed responsive elements that force the rotor against braking elements that are successively operated to brake the rotor to a complete stop in successive gentle braking actions and with the speed responsive elements including means for preventing resumed rotation of the rotor until the engine has been partially dismantled and the cause of the malfunction corrected.