Muck fires are fires that burn underground. They're usually started when decomposing vegetation catches fire, often as a result of the heat generated by lightning strikes. As muck fires take place underground they seldom represent a threat to human life. Nevertheless, they are virtually impossible to put out, and cause discomfort to anyone in the vicinity by emitting an unpleasant, noxious stench into the atmosphere.
A lightning strike is responsible for igniting the muck fire near Paul's house in Tangerine. The nearby field is full of lignite—kind of like coal—which is highly flammable. All it took was for one bolt of lightning to stir things up. The muck fire's been raging for as long as anyone can remember, but it's much more intense now that lightning has struck. Paul's mom is shocked to discover that the muck fire will never go out. She wants to complain to the Homeowners' Association, but the fire fighter advises her that she'll just have to learn to live with the muck fire like everyone else in the neighborhood.