The incident occurred shortly after landing in Chicago as the aircraft made its way to the gate. A spokesperson at American Airlines said that the e-cig fire was the result of a "thermal runaway event." A thermal runaway event is when an increase in temperature creates conditions that will further increase the temperature. Essentially, a thermal runaway event is a type of positive feedback loop in which one thing (initial temperature increase) leads to a more severe thing (additional temperature increase). In the case of the passenger's e-cig, the temperature of the device reached a level hot enough that the device ignited. This led to a small in-flight fire.
Flight attendants quickly extinguished the fire without additional incident or injuries. The flight continued to taxi to the gate and passengers disembarked without issue.
An American Airlines spokesperson released the following statement regarding the quick response from flight attendants: "We are thankful for our flight attendants who quickly put their training to use to keep our passengers safe. Our crews are trained on fighting high energy battery fires. As part of safety management and risk mitigation, we always evaluate additional ways to enhance existing procedures to ensure cabin safety."
Per protocol, American Airlines will report the incident to the Federal Aviation Administration (FAA), which tracks thermal runaway events and in-flight incidents. E-cigs are not currently banned from carry-on luggage in the United States, however, their use in-flight is. E-cigs were permanently banned from checked luggage in 2016. At the same time, the charging of e-cigs in-flight was also banned. The 2016 ban went into effect after multiple small fires ignited in-flight.
H/T: WGN 9
