There are different sources from which a fire could start during a flight The most common causes of fires on board include: 1 the engines, due to fuel leaks or cracked parts, 2 electrical failures, such as short circuits or faulty wiring, 3 passenger electronics, like overheated lithium batteries, 4 and undeclared dangerous goods in the hold. Dangerous goods include items like explosives, flammable liquids, poisonous chemicals, radioactive materials, and corrosive substances. These materials can cause fires, explosions, or other accidents if they aren't handled correctly, especially in the closed space of an airplane. If something leaks, spills, or catches fire, it can quickly become a big problem because there is not much space to escape or fix the issue. For example, if two chemicals that shouldn't mix come into contact, they could explode or make poisonous gas.