Explanation: >After more than 50 years of high intensity use the building was ageing. Plans for refurbishment were hastily modified in the light of the 1995 Oklahoma bomb. > >This meant protection against external explosions was rapidly incorporated: **Kevlar mesh reinforced the masonry infill wall panels and modern blast resistant windows were installed.** > >But only one ‘wedge’ of the building had been refurbished before the terrorists struck, and it was the reinforced outer walls and window frames of this refurbished section that took the initial impact. Source: https://www.newcivilengineer.com/latest/structural-strength-saved-pentagon-lives-on-9-11-13-02-2003/