The avoidance of disruptions is essential for the next generation tokamaks. The dangerous consequences of disruptions are excessive heat loads, high forces, creation of high-energy runaway electrons, and a bad conditioning for the start of the following discharge. In order to mitigate these effects, a fast valve has been developed on TEXTOR with a response time to full opening of 1 ms after a trigger pulse. The fast injection of helium by such a valve suppresses runaway electron production and even removes them if present. The reaction time of the valve is fast enough to apply it even after the start of a disruption. The fast gas injection has been applied to a nearly stationary runaway discharge and it was successfully shown that the energetic electrons are quickly expelled.