Insulation degradation—Carbon Tracking
Most insulators are made of organic compounds, thus they contain carbon. When heat is applied on such insulators with the exception of glass, ceramic, mica and asbestos insulators, they degrade to form carbon char. This carbon char conducts electricity, thus when the pyrolysis of the insulator occurs over a large area, called carbonization or pyrolyzation, the insulator gets slowly converted into a conductor. One thing to note about materials selected for insulation is that they were selected on the basis of providing insulation under thermal conditions during normal use. This means that wires in abnormal thermal conditions that trap heat, such as being under a thick insulating carpet, or abnormally hot conditions may cause the wire’s insulation to degrade.
Another scenario is the formation of carbon char forming in an area between conductors called carbon tracking or arc tracking. If there is heat generated to initiate the start of carbon degradation, such as the heat produced by a current on a wet insulator, enough carbon may be generated to form in between the conductors conducting a current through the carbon path. Localized heating will then occur, causing even more carbon char to be created. Eventually, enough heat may be produced to reach the ignition temperature of the insulator and start a fire. Carbon tracking might be able to reach other fuels, but only through the carbon degradation of the wire itself first before extending to those of electrical hardware such as switches and plugs.
Ordinary tap water contains dissolved salts, neutral ionic compounds composed of cations and anions, thus enabling water to conduct electricity. When water enters electrical appliances, it may cause electricity to flow along unplanned paths in addition to the danger of causing electric shocks. Current flowing along areas where current is not designed to flow may cause heating to occur at problematic areas, as in the case of carbon degradation, and become a potential ignition source