lapsed , ▁destroy ing ▁the ▁sc aff old ▁st air way ▁and ▁str and ing ▁workers ▁on ▁the ▁remaining ▁sections ▁above . ▁Work ers ▁on ▁Unit ▁ 4 ▁were ▁cr ushed ▁to ▁death ▁when ▁the ▁section ▁f li pped ▁and ▁land ed ▁ups ide - down ▁while ▁desc ending ▁due ▁to ▁t ension ▁in ▁the ▁c ables . ▁ ▁Sur v iving ▁construction ▁workers ▁brought ▁in ▁a ▁cher ry ▁pick er ▁to ▁rescue ▁the ▁remaining ▁workers ▁str and ed ▁on ▁the ▁r amp , ▁but ▁five ▁minutes ▁after ▁the ▁initial ▁collapse , ▁Unit ▁ 5 , ▁the ▁neighbor ing ▁section , ▁also ▁col lapsed . ▁Tw elve ▁workers ▁in ▁total ▁were ▁killed ▁instantly ; ▁a ▁ 1 3 th ▁died ▁two ▁weeks ▁after ▁the ▁collapse , ▁and ▁the ▁ 1 4 th ▁worker ▁died ▁of ▁inj uries ▁suffered ▁during ▁the ▁collapse ▁two ▁years ▁later . ▁The ▁accident ▁remains ▁Indiana ' s ▁dead liest ▁industrial ▁or ▁construction ▁accident . ▁ ▁Investig ators ▁from ▁the ▁National ▁Bureau ▁of ▁Stand ards ▁for ▁the ▁Occ up ational ▁Saf ety ▁and ▁Health ▁Administration ▁( OS HA ) ▁discovered ▁several ▁errors ▁that ▁caused ▁the ▁collapse ▁of ▁the ▁bridge ▁section . ▁The ▁most ▁likely ▁cause ▁of ▁the ▁collapse ▁was ▁" the ▁crack ing ▁of ▁a ▁concrete ▁pad ▁supporting ▁a ▁leg ▁of ▁the ▁sh oring ▁to wers ". ▁The ▁failure ▁of ▁the ▁concrete ▁pad , ▁built ▁too ▁thin ly , ▁led ▁to ▁another ▁finding ; ▁ ▁bol ts ▁that ▁were ▁supposed ▁to ▁connect ▁key ▁string ers ▁to ▁cross - be ams