Before countless violent episodes forced schools and universities to view visitors as potentially dangerous intruders, building security was not a constant concern, and doors were considered a means of ingress and egress, not necessarily a first line of protection from threats.
If a classroom door was closed, it was probably because of too much noisy traffic in the hallway; if an exit door was propped open, it was most likely to bring some fresh air into a stuffy building. But in the 21st-century reality that has made the names Columbine, Sandy Hook and Parkland instantly recognizable symbols of unspeakable school tragedies, a door propped open or left unsecured is a safety breach that could lead to a deadly attack on students and staff. And a closed and locked classroom door could be the factor that slows down or halts an intruder’s attack and saves lives.
