Built-in emergency safety device of tank car tank or storage tank and use method

The invention relates to a built-in emergency safety device of a tank car tank or a storage tank and a use method. Four built-in emergency safety devices are welded to the upper end wall and the lowerend wall of the tank car tank correspondingly, correspond to four valves outside the tank car tank correspondingly and are connected with a nitrogen gas cylinder through line pipes. When any one of the valves breaks down to cause leakage of a high-pressure medium in the tank car tank, the nitrogen gas cylinder is opened, clearance pistons move upwards to push gravity balls to compress conical hard sealing faces to form one-way sealing pair linear sealing with the conical hard sealing faces, and the aim of emergency danger prevention is achieved. When the tank car tank is turned over due to accidents, or any one of the valves breaks down to be out of control after turnover, the gravity balls in the built-in emergency safety devices can roll down to the conical hard sealing faces correspondingly to form one-way sea