Modern ambulances are typically powered by internal-combustion engine, which can be powered by any conventional fuel, including diesel, gasoline or liquefied petroleum gas, depending on the preference of the operator and the availability of different options. Colder regions often use gasoline powered engines, as diesels can be difficult to start when they are cold. Warmer regions may favor diesel engines, as they are thought to be more efficient and more durable. Diesel power is sometimes chosen due to safety concerns, after a series of fires involving gasoline powered ambulances during the 1980s. These fires were ultimately attributed in part to gasoline's higher volatility in comparison to diesel fuel. The type of engine may be determined by the manufacturer: in the past two decades, Ford would only sell vehicles for ambulance conversion if they are diesel powered. Beginning in 2016, Ford will sell its ambulance chassis with a gasoline engine in order to meet emissions requirements.