Abstract: A separable fastener includes a fastener body having a head end and a shank nd. The head end defines a generally cylindrical open ended cavity in which a cylindrical punch is disposed. The cavity is sealed and closed by a gas generator that develops an increasing fluid pressure against the punch. The punch is restrained within the cavity by a retaining ring which yields once a preselected gas pressure is reached. The release of the punch causes it to rapidly accelerate in a short distance to impact the shank end of the fastener body. The shank end is thereby sheared from the body with the void created in the body being sealed by the impacting punch.