B767 CREW HAD SMOKE; FUMES IN CABIN.

Narrative

I WAS THE FO ON A B767-300 DEPARTING SFO ON MAR/XA/00. DURING THE TKOF ROLL; I BEGAN HEARING A HIGH PITCHED BEEPING NOISE COMING FROM THE FORWARD CABIN. ONCE ABOVE 1000 FT BOTH THE CAPT AND I COMMENTED ON THIS NOISE. SHORTLY THEREAFTER; THE CABIN CALL RANG. THE FLT ATTENDANT IN THE FORWARD CABIN INFORMED US THAT ONCE OF THE FORWARD LAVATORY SMOKE ALARMS HAD GONE OFF; AND THAT HAZE AND SMOKE WAS BEGINNING TO FILL THE CABIN. THIS WAS CONFIRMED BY FLT ATTENDANTS STATIONED IN THE MID AND AFT CABIN ALSO. I ASKED THE FLT ATTENDANTS IF THEY HAD IDENTED THE SOURCE OF THE SMOKE. THEY RESPONDED THAT THEY HAD NOT. THE CREW IN THE AFT CABIN WERE NOW COMPLAINING OF NAUSEA AND HEADACHES. AFTER FOLLOWING COMPANY PROC AND A SHORT DISCUSSION WITH THE CAPT; WE DECIDED TO RETURN TO SFO. DUE TO LIMITED INFO; WE WERE ABLE TO GATHER AND THE TYPE OF SIT THAT WAS DEVELOPING; WE DECIDED TO LAND IN SFO 12000 LBS OVERWT. MAX GROSS LNDG WT IN THE B767 WE WERE FLYING WAS 320000 LBS. WE TOUCHED DOWN AT APPROX 332000 LBS. OUR DECISION TO LAND OVERWT WAS BASED ON THE NATURE OF THE EMER; THE GOOD WX IN SFO; AND THE LENGTH OF RWY AVAILABLE ON RWY 28R.