Role of Oxygen in Cystic Fibrosis Transmembrane Conductance Regulator Expression and

A perforating gun having no firing head and no primary explosives is attached to a tubing string and the tubing string is run into a borehole. A new well apparatus, having a firing head, is run into the tubing string until the firing head is adjacent the perforating gun. The firing head in the well apparatus detonates, firing the perforating gun. If the firing head fails to detonate, one need only remove the well apparatus from the tubing string in order to gain access to the firing head, for repair and replacement thereof. One need not remove the tubing string to gain access to the firing head.