Abstract: An automatic fire prevention system provides failsafe features as well as the capability of checking the operation of associated fire sensors. Multiple fire sensors, including thermal and optical types, are continually checked by a test circuit which simulates fire conditions. Detection of an actual fire causes an automatic control circuit, after a predetermined time delay, to activate a fire extinguishing device such as a dry powder chemical extinguisher. Logic circuitry distinguishes between true fires and fires simulated by the aforementioned test circuit. An operator can by-pass the automatic activation of the fire extinguishing device by means of a manual switch during the time delay period and can also manually discharge the fire extinguisher. Applications include the protection of mine haulage trucks so as to provide automatic fire extinguisher activation, continued self-checking and manual override features for a driver.