ing ▁and ▁machine ▁condition , ▁to ▁find ▁the ▁root ▁cause ( s ) ▁of ▁the ▁problem ( s ). ▁Once ▁changes ▁to ▁the ▁process , ▁or ▁machine ▁rep airs ▁that ▁may ▁include ▁adjust ments ▁and / or ▁replacement ▁are ▁effect ed , ▁a ▁sample ▁run ▁is ▁initi ated ▁and ▁evaluated . ▁If ▁the ▁results ▁of ▁the ▁validation ▁are ▁within ▁the ▁required ▁specific ations , ▁the ▁area ▁lock down ▁is ▁lifted ▁and ▁production ▁is ▁res umed . ▁Follow ▁up ▁sampling ▁is ▁conducted ▁subsequently ▁to ▁ensure ▁continu ity ▁of ▁the ▁lock down ▁results . ▁ ▁Historical ▁events ▁▁ ▁In ▁the ▁w ake ▁of ▁the ▁September ▁ 1 1 ▁attacks ▁( 2 0 0 1 ), ▁a ▁three - day ▁lock down ▁of ▁American ▁civil ian ▁air space ▁was ▁initi ated . ▁ ▁In ▁December ▁ 2 0 0 5 , ▁the ▁New ▁South ▁Wales ▁Police ▁Force ▁( NS W ▁Police ▁Force ) ▁initi ated ▁a ▁lock down ▁of ▁the ▁S uther land ▁Sh ire ▁and ▁other ▁beach ▁areas ▁of ▁New ▁South ▁Wales ▁to ▁contain ▁race ▁ri oting ▁( and ▁ret ali ative ▁strik es ). ▁▁ ▁An ▁example ▁of ▁a ▁campus / school ▁lock down ▁was ▁demonstrated ▁at ▁the ▁University ▁of ▁British ▁Columbia ▁( U BC ) ▁on ▁January ▁ 3 0 , ▁ 2 0 0 8 , ▁when ▁an ▁unknown ▁threat ▁was ▁made ▁and ▁the ▁Royal ▁Canadian ▁Mount ed ▁Police ▁( RC MP ) ▁issued ▁a ▁lock down ▁on ▁one ▁of ▁the ▁buildings ▁on ▁campus ▁for ▁six ▁hours , ▁cord oning ▁off ▁the