EMB145 FLT CREW HAS SMOKE IN THE CABIN DURING CLBOUT; DECLARES AN EMER AND RETURNS TO DAY.

Narrative

WHILE CLBING OUT OF DAYTON; A LOUD BANG WAS HEARD FOLLOWED BY THE 'LAVATORY' SMOKE MASTER WARNING. FLT ATTENDANT CALLED TO ADVISE US OF SMOKE IN THE CABIN. WE DECLARED AN EMER AND INITIATED A RETURN TO THE FIELD. FLT ATTENDANT WAS ASKED IF SHE COULD SEE ANY SIGNS OF A FIRE IN THE LAVATORY AND SHE SAID NO. ON SHORT FINAL; AN 'ENG #2 BLEED LEAK' WARNING WAS RECEIVING AFTER WHICH THE FO DESELECTED THE #2 ENG BLEED. AFTER LNDG; WE STOPPED ON THE RWY TO ASSESS THE SIT IN THE CABIN AND WE WERE ADVISED BY THE FLT ATTENDANT THAT SHE HAD THE PAX UNDER CTL AND THAT THE SMOKE HAD DIMINISHED. ONCE WE REACHED THE GATE AREA; WE WERE ADVISED BY THE FLT ATTENDANT THAT THE SMOKE WAS GETTING WORSE; SO I MADE THE DECISION TO EVAC THE ACFT UTILIZING ALL EXITS. 50 PAX; 3 CREW AND 1 JUMPSEATER WERE DEPLANED WITHOUT INCIDENT. CAUSE OF THE NOISE AND PERCEIVED SMOKE WAS A RUPTURED HIGH PRESSURE BLEED LINE RUNNING UNDER THE FLOOR BOARDS; RESULTING IN DUST AND INSULATION BEING FORCED AROUND THE CABIN. REDUCING VISIBILITY AND MAKING IT HARD TO BREATH FOR THE PAX.