Firing head assembly, well completion device with a firing head assembly and method of use

A firing head assembly for use with a perforating gun is described. The firing head assembly includes a tubular housing, first and second pistons, and a compressible member arranged within a lumen of the tubular housing and positioned between the first and second pistons. According to an aspect, the assembly includes a plurality of upper locking arms and lower locking arms that engage with locking members formed in the tubular housing. The firing head assembly further includes upper and lower shear washers arranged at the second opening of the tubular body, in a sandwich type configuration with respect to the second piston. Pressures within the firing head assembly may be adjusted to activate the firing head assembly to either trigger an explosive reaction or to not trigger the explosive reaction.