Pressure-Actuated Safety For Well Perforating

A safety mechanism and method for downhole perforating are disclosed. In one example, a mechanical firing head includes a firing pin carried on a pin carrier within a housing. The firing pin is movable from a retracted position to a firing position for striking an explosive initiator. A retention member retains the firing pin in the retracted position with the safety member in the armed position. A safety member is biased to a safety position that additionally blocks movement of the firing pin. The safety member is moveable to an armed position that unblocks movement of the firing pin in response to an arming pressure supplied to the housing bore. The retention member releases the firing pin in response to a firing pressure supplied to the housing in excess of the firing pressure.