10/17/01 2000hrs.-Dover Fire Dept. Receives Phone call from Large Chemical plant in city's southwest section reporting a release of an unknown corrosive. Dover E-1 goes enroute, request New Phila E-17. app. 1 block from plant, a large cloud is noted moving across street towards resiential area and hospital. E-1 orders New Phila T-11 for elevated streams and 2nd and 3rd alarms. E-1,E-17 and T-11 deploy master streams for vapor suppression.IC orders evacuation of 2 block area. IC orders county HazMat Team call-down. HM Team makes entry in level B splash and shuts valve. IC calls under control at app. 0100 hrs.