Oil and water don't mix: it's an old saying, but it's never more true than when you're talking about a pot of hot cooking oil and the moisture condensed on the surface of a frozen turkey. it's pretty incredible the amount of fire that simple combination can create.
Cooking oil is flammable, but it doesn't catch fire in a deep fryer because it never approaches the approximately 800°F required. Even if you drop a match in the fryer, the heat is conducted away from the flame and dissipates into the oil, and the fire goes out.
But oil dispersed into fine droplets is another beast entirely. individual droplets heat up very quickly, and the burning of one drop creates enough heat to ignite the one next to it, and so on, making a cloud of oil droplets extremely flammable. Where might a cloud of oil droplets come from? From that big, frozen bird.
The recommended oil temperature for a deep fryer is 350°, well above the boiling point of water. When you drop food in, you immediately see bubbles; that is the water in the food boiling off. Put too much moisture in by lowering in a frozen turkey, and the vaporization of the water throws oil droplets into the air. a few of the droplets hit the burner under the pot and catch on fire, beginning a chain reaction that ignites a large cloud of droplets. The result is the smell of a county fair-and a towering inferno that can ignite everything around it.