An e-cigarette battery set fire to an air passenger's luggage while it was being loaded into the hold of a United Airlines flight. Baggage handlers at Seattle-Tacoma International Airport spotted smoke coming from a bag as they stowed it in an aircraft destined for Houston, said Seattle's Komo News.Firefighters extinguished the flames and traced the source of the fire to a vape cigarette battery connected to a charger. The owner of the bag was identified and the flight was slightly delayed.E-cigarettes are powered by lithium-ion batteries - a particularly volatile type of rechargeable cell that has been linked to spontaneous fires in smartphones and other electronic devices.The US Department of Transportation and the UK's Civil Aviation Authority prohibit the transportation of electronic cigarettes in checked-in baggage because of the volatility of their lithium-ion batteries. They must be carried in hand luggage, but using vapes in the cabins of commercial flights is also illegal.This is not the first incident of its kind. In 2014 firefighters at Logan International Airport in Boston, Massachusetts, were called to extinguish a passenger's vape that had ignited inside a cargo hold. In March this year a Delta Airlines flight from Atlanta International to St Louis was delayed when a passenger's e-cigarette set light to his carry-on bag during boarding. ..