s ▁population . ▁By ▁late ▁April , ▁around ▁ 3 0 0   mill ion ▁people ▁were ▁under ▁lock down ▁in ▁nations ▁of ▁Europe , ▁while ▁around ▁ 2 0 0   mill ion ▁people ▁were ▁under ▁lock down ▁in ▁Latin ▁America . ▁Near ly ▁ 3 0 0   mill ion ▁people , ▁or ▁about ▁ 9 0 ▁per ▁cent ▁of ▁the ▁population , ▁were ▁under ▁some ▁form ▁of ▁lock down ▁in ▁the ▁United ▁States , ▁and ▁ 1 . 3   b ill ion ▁people ▁have ▁been ▁under ▁lock down ▁in ▁India . ▁ ▁Typ ical ▁scenarios ▁▁ ▁School s ▁ ▁Lock down ▁procedures ▁vary ▁by ▁school ▁district . ▁Gener ally , ▁a ▁lock down ▁means ▁that ▁interior ▁and ▁exterior ▁doors ▁are ▁locked , ▁and ▁all ▁students ▁and ▁staff ▁must ▁remain ▁in ▁their ▁location ▁from ▁the ▁time ▁the ▁lock down ▁is ▁announced . ▁Windows ▁are ▁covered , ▁and ▁students ▁stand ▁at ▁the ▁back ▁of ▁the ▁class room ▁or ▁away ▁from ▁windows . ▁ ▁Since ▁the ▁Columb ine ▁Sho oting ▁in ▁ 1 9 9 9 , ▁lock down ▁procedures ▁in ▁schools ▁have ▁been ▁constantly ▁changing . ▁Some ▁schools ▁direct ▁teachers ▁to ▁continue ▁with ▁standard ▁procedures ▁while ▁remaining ▁quiet , ▁while ▁some ▁recommend ▁an ▁active ▁approach ▁against ▁thre ats . ▁ ▁Pr isons ▁In ▁its ▁most ▁common ▁usage ▁in ▁corre ctions ▁units , ▁the ▁term ▁lock down ▁can ▁be ▁defined ▁as ▁a ▁course ▁of ▁action ▁to ▁control ▁the ▁movement ▁of ▁in m ates . ▁Conf ining ▁all ▁prisoners , ▁except ▁workers ,