Date: 201812
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: Mixed
Weather elements / visibility: 10
Light: Night
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Integrated Audio System
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Anomaly: Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Flight Deck / Cabin / Aircraft Event Passenger Electronic Device
Detector: Person Flight Attendant
When detected: In-flight
Result: General Physical Injury / Incapacitation
Contributing factors: Aircraft; Equipment / Tooling; Human Factors
Primary problem: Human Factors

Narrative: We were cruising at FL390 about 75 minutes into the flight when we received a four-chime call from the cabin. We were informed that there was smoke in the cabin from an unknown source. Per non-normal guidance; we donned our oxygen masks and established communication. I was Pilot Flying so I maintained aircraft control as the Captain notified ATC of our situation and requested a landing at the nearest suitable airport. Center pointed out [a possible alternate] at 1 o'clock and 60 miles. We were immediately cleared to 8000' and began an emergency descent. The Captain was forced to shed his headset because the oxygen mask would not fit over it. As a result; he used the cockpit speaker to listen and kept hot MIC on.The sounds of breathing made it very difficult to understand what was being said. We deployed the speedbrakes and extended the landing gear (on speed) in order to increase our descent rate and expedite a landing at [the alternate]. I took over the radios while the Captain coordinated with the cabin crew. This allowed me to listen to and understand what ATC was saying. Next; the Captain ran the Smoke; Fire or Fumes Non-normal Checklist. While descending through FL270; we received a call from the cabin that a USB battery device was found to be the source of the smoke. It had been placed in the containment bag and was no longer smoking. They also indicated that the smoke was clearing out from the cabin. We elected to level off near FL250 and await confirmation that the situation was safe. With this confirmation received; we removed our oxygen masks and reviewed the remainder of the [procedure] per QRH guidance. We elected to cancel the [divert]; climb; and continue to [destination]. The Captain gave a PA explaining the situation and that we were continuing to the destination. A non-Company FA (Flight Attendant) was onboard and assisting our Flight Attendants with the situation. Being a fluent Spanish speaker; she also repeated all of the Captain's PAs in Spanish; which was extremely helpful in keeping the customers calm. We asked that [ground personnel] meet us at the gate to inspect the containment bag. Additionally; EMS was requested because one of our FAs had received an injury to her hand while securing the device. A normal landing ensued and our aircraft was escorted to the gate by [ground personnel]. With the device in the aft galley area still secure in the containment bag; we decided to deplane the customers. Once this was accomplished; the Fire Crew tended to the containment bag while EMS attended the injured FA who was treated briefly. We were given the 'all clear' by the Fire Crew and the event was concluded. This situation was successfully handled because of the professionalism and teamwork demonstrated by our crew. Our Flight Attendants (including the other airline FA) reacted quickly and assertively. Because of their actions; this flight had a successful outcome. Our situation was clearly mitigated by the containment bag. Without it; we would have diverted and emergency egressed at [the alternate].Difficulty that we encountered in the cockpit was an inability to communicate clearly with the oxygen masks on. The Captain's mask would not fit over his headset; so it was quickly shed and communication was established by use of the speaker and hot mike. This technique works well in the simulator however; in the airplane; descending rapidly with the landing gear down; there was too much background noise mixed with regulator sounds to allow easy communication. In hindsight; a better technique would have been to not use the speaker; but put the headphones on over the mask straps. Additionally; only using the yoke push to talk interphone switch when speaking would have also reduced the noise level in the cockpit and on the radios.




Synopsis: B737-700 First Officer reported initiating; then terminating a diversion for smoke in the cabin and difficulty with flight deck communication using oxygen masks.