reduces the amplitude of a vibration to a level lower than that which would otherwise be expected u201c damping chamber u201d refers to the u201c air gap u201d between the front and back panels contained within the metal frame that acts as an air spring to slow the inward movement of the front panel when hit with a blast wave but also has built in pressure relief to provide additional protection for the back panel as the air pressure rises within the damping chamber u201c film u201d refers to transparent polymer sheeting also referred to as u201c safety film u201d u201c film tail u201d is the edge of the polymer sheeting that extends beyond the outer edge of each panel u201c film tail anchoring u201d refers to the mounting of the panels within the window frame by attaching the film tails to the window frame using friction or an adhesive u201c flexible u201d refers to the ability of a material to deform in at least one direction under a load without suffering a brittle structural failure u201c front panel u201d refers to the panel in the window structure of the invention facing external of the structure in which the window is installed u201c internal pressure u201d refers to the buildup in pressure in the gap between the two sealed panels as the front panel deflects inwardly under externally applied incident pressure u201c leaking u201d refers to the inability of a.