Hundreds of residents were forced to flee Saturday after a chemical leak in Petrolia , Pennsylvania . NEW : Environmental official says when surveyed , no traces of chemical remain . Toxic smoke forms Saturday after chemical spill at the plant . Three residents taken to hospital ; extent of injuries not known .
NEW : Environmental official says when surveyed , no traces of chemical remain . Toxic smoke forms Saturday after chemical spill at the plant . Three residents taken to hospital ; extent of injuries not known .