Maybe someone who lives near a chemical plant can fill in more details but I believe that was part of a fairly common strategy called shelter in place. If, for example, a chemical plant has a leak authorities do not want people to get in their cars tie up traffic and become exposed to a cloud of toxic gas. Instead they would like people to shelter in place, blocking up their windows and doors as best as they can with plastic and duct tape.
Of course the media spun this as duct tape is the only thing protecting us from an AQ attack.
Very interesting information. Thank you for taking the time to explain.