Narrative:

During cruise over water; we started to smell an odor that couldn't be idented but had an acrid smell to it. Shortly thereafter; the first officer crew rest smoke alarm went off with the associated EICAS. The relief pilot and I were in the cockpit at the time and donned our masks; established communications and called the captain; who was in the crew rest facility. The captain did a cabin walkaround before coming up to the cockpit and noticed a slight haze. The captain came into the cockpit and took command of the aircraft and I ran the smoke/fumes air conditioning checklist. The odor remained but lessened when we isolated the right side. I then ran the smoke/fumesecond officerdor removal checklist and when I selected the equipment cooling override switch to override the odor seemed to lessen. While I was running the checklist the captain was communicating with the company and after I finished with the smoke removal checklist we decided to divert to ZZZ. The odor never completely left the cabin or cockpit. When we landed and took the masks off; I noticed I had a slight cough from irritation. It seemed to improve as I breathed clean air. Callback conversation with reporter revealed the following information: the reporter stated that the source could not be identified; and the fumes were present for the remainder of the flight. Oxygen masks were donned and worn until touchdown. An emergency was declared.

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Original NASA ASRS Text

Title: OVERWATER B777-200 DEVELOPED SMOKE AND FUMES IN THE CABIN. THE SOURCE COULD NOT BE IDENTIFIED; BUT THE INTENSITY DID NOT INCREASE. THE FLT CREW DECLARED AN EMER AND DIVERTED.

Narrative: DURING CRUISE OVER WATER; WE STARTED TO SMELL AN ODOR THAT COULDN'T BE IDENTED BUT HAD AN ACRID SMELL TO IT. SHORTLY THEREAFTER; THE FO CREW REST SMOKE ALARM WENT OFF WITH THE ASSOCIATED EICAS. THE RELIEF PLT AND I WERE IN THE COCKPIT AT THE TIME AND DONNED OUR MASKS; ESTABLISHED COMS AND CALLED THE CAPT; WHO WAS IN THE CREW REST FACILITY. THE CAPT DID A CABIN WALKAROUND BEFORE COMING UP TO THE COCKPIT AND NOTICED A SLIGHT HAZE. THE CAPT CAME INTO THE COCKPIT AND TOOK COMMAND OF THE ACFT AND I RAN THE SMOKE/FUMES AIR CONDITIONING CHKLIST. THE ODOR REMAINED BUT LESSENED WHEN WE ISOLATED THE R SIDE. I THEN RAN THE SMOKE/FUMES/ODOR REMOVAL CHKLIST AND WHEN I SELECTED THE EQUIP COOLING OVERRIDE SWITCH TO OVERRIDE THE ODOR SEEMED TO LESSEN. WHILE I WAS RUNNING THE CHKLIST THE CAPT WAS COMMUNICATING WITH THE COMPANY AND AFTER I FINISHED WITH THE SMOKE REMOVAL CHKLIST WE DECIDED TO DIVERT TO ZZZ. THE ODOR NEVER COMPLETELY LEFT THE CABIN OR COCKPIT. WHEN WE LANDED AND TOOK THE MASKS OFF; I NOTICED I HAD A SLIGHT COUGH FROM IRRITATION. IT SEEMED TO IMPROVE AS I BREATHED CLEAN AIR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT THE SOURCE COULD NOT BE IDENTIFIED; AND THE FUMES WERE PRESENT FOR THE REMAINDER OF THE FLT. OXYGEN MASKS WERE DONNED AND WORN UNTIL TOUCHDOWN. AN EMER WAS DECLARED.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.