Narrative:

Approximately two hours following our departure; the flight attendants (flight attendant) notified me of smoke emanating from the aft lavatory (aircraft right) immediately following its use by a passenger. Additionally the passenger reported he saw smoke emanating from the overhead panel in the lavatory. Uncharacteristic of him simply smoking in the lavatory; but possibly something much more serious and potentially life-threatening; an actual aircraft fire. The smoke alarm was activated and projecting an extremely loud and piercing tone throughout the cabin. This caused distress among passengers as well as the flight attendant's. Communicating with the flight attendant's over the interphone was very difficult due to the combined chaotic nature of the alarm and the chaos surrounding its activation. The flight attendant's were having difficulty extinguishing the alarm. I did not know if this was due to continued smoke; or some delay in extinguishing the alarm. Our collective belief was the situation could be much more serious. The flight attendant's asked me for assistance in evaluating the situation. I knew my assistance in the aft of the aircraft would be a departure from our standard protocol. However; based on the information we received at the time; I concluded my assistance might very well mitigate a further degradation in the cabin and secure a safe condition as quickly as possible. The first officer had demonstrated confidence and technical competence; thus I had no reason to doubt her ability to navigate and control the aircraft; as well as communicate with outside agencies while I assisted the flight attendant's with what appeared and sounded to be a rapidly deteriorating situation. In the interest of time and consequently safety; I elected to personally inspect and evaluate the severity of the incident. I did this in order to determine the most expeditious course of action regarding continuing to [our destination] or turning back.as we were mere minutes from the critical point on our flight plan there was only one flight attendant present in the forward part of the aircraft during the time I exited the flight deck. I shut the flight deck door before the forward flight attendant could enter the flight deck. After working with the flight attendant's to silence the alarm and after inspecting the lavatory and it's overhead panel; I determined there was no immediate threat of an actual aircraft fire; as there was no evidence of heat; burning; or residual smoke. I instructed the flight attendant's to lock the lavatory; and reassess every few minutes. After I returned to the front of the aircraft; I established communication with the first officer via interphone; and advised her I was ready to return to the flight deck; (after approximately 4-5 minutes). The smoke did not continue; so I opted to continue to [our destination]; as long as the condition didn't reappear. For reasons unknown to me; the first officer left her seat to open the door rather than pushing the unlock button. About twenty minutes later; the flight attendant's found an electronic cigarette in the toilet that was discarded in what appears to be an attempt to conceal its presence and cause for the smoke. After the passenger (who reported the smoke emanating from the overhead portion of the lavatory) was asked about the device; he did admit it was the cause for the smoke and activation of the smoke detector. I felt in the interest of safety; it was best to leave the flight deck and assess the situation personally; and that would be the most expeditious way to evaluate an overall course of action.at no time during the above events did I intentionally disregard standard procedure; rather I utilized my authority as the captain to bring the situation to safe conclusion while being mindful of [company policies].

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Original NASA ASRS Text

Title: B737 Captain reported leaving the flight deck to evaluate smoke in the aft lav caused by a passenger's electronic cigarette.

Narrative: Approximately two hours following our departure; the Flight Attendants (FA) notified me of smoke emanating from the aft lavatory (aircraft right) immediately following its use by a passenger. Additionally the passenger reported he saw smoke emanating from the overhead panel in the lavatory. Uncharacteristic of him simply smoking in the lavatory; but possibly something much more serious and potentially life-threatening; an actual aircraft fire. The smoke alarm was activated and projecting an extremely loud and piercing tone throughout the cabin. This caused distress among passengers as well as the FA's. Communicating with the FA's over the interphone was very difficult due to the combined chaotic nature of the alarm and the chaos surrounding its activation. The FA's were having difficulty extinguishing the alarm. I did not know if this was due to continued smoke; or some delay in extinguishing the alarm. Our collective belief was the situation could be much more serious. The FA's asked me for assistance in evaluating the situation. I knew my assistance in the aft of the aircraft would be a departure from our standard protocol. However; based on the information we received at the time; I concluded my assistance might very well mitigate a further degradation in the cabin and secure a safe condition as quickly as possible. The First Officer had demonstrated confidence and technical competence; thus I had no reason to doubt her ability to navigate and control the aircraft; as well as communicate with outside agencies while I assisted the FA's with what appeared and sounded to be a rapidly deteriorating situation. In the interest of time and consequently safety; I elected to personally inspect and evaluate the severity of the incident. I did this in order to determine the most expeditious course of action regarding continuing to [our destination] or turning back.As we were mere minutes from the critical point on our flight plan there was only one FA present in the forward part of the aircraft during the time I exited the flight deck. I shut the flight deck door before the forward FA could enter the flight deck. After working with the FA's to silence the alarm and after inspecting the lavatory and it's overhead panel; I determined there was no immediate threat of an actual aircraft fire; as there was no evidence of heat; burning; or residual smoke. I instructed the FA's to lock the lavatory; and reassess every few minutes. After I returned to the front of the aircraft; I established communication with the First Officer via interphone; and advised her I was ready to return to the flight deck; (after approximately 4-5 minutes). The smoke did not continue; so I opted to continue to [our destination]; as long as the condition didn't reappear. For reasons unknown to me; the First Officer left her seat to open the door rather than pushing the unlock button. About twenty minutes later; the FA's found an electronic cigarette in the toilet that was discarded in what appears to be an attempt to conceal its presence and cause for the smoke. After the passenger (who reported the smoke emanating from the overhead portion of the lavatory) was asked about the device; he did admit it was the cause for the smoke and activation of the smoke detector. I felt in the interest of safety; it was best to leave the flight deck and assess the situation personally; and that would be the most expeditious way to evaluate an overall course of action.At no time during the above events did I intentionally disregard standard procedure; rather I utilized my authority as the Captain to bring the situation to safe conclusion while being mindful of [Company policies].

Data retrieved from NASA's ASRS site 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.