The duration of a jet fuel fire is determined by the fuel’s chemical properties and the specific environmental conditions of the accident. The time a fire lasts depends entirely on whether the fuel is consumed naturally in an uncontained pool fire or is quickly extinguished by specialized response teams. This article examines the variables that dictate the persistence of accidental fires resulting from spills or crashes.
The Composition and Combustion Characteristics of Jet Fuel
Jet fuel, primarily Jet-A or Jet-A1 in commercial aviation, is a highly refined form of kerosene. This hydrocarbon composition contains molecules with typically eight to sixteen carbon atoms, giving it distinct characteristics compared to lighter fuels like gasoline. The high-energy density of this kerosene-based fuel means that once combustion is established, it provides a substantial and intense heat source.
A major difference lies in the flash point, which is the lowest temperature at which the fuel produces enough vapor to ignite. Gasoline has a flash point far below freezing, around -45°F (-42°C), meaning it is highly volatile and its vapors are easily ignitable at ambient temperatures. In contrast, Jet-A has a minimum flash point of 100°F (38°C), making it significantly less volatile and safer to handle under normal conditions.
Because the liquid fuel itself does not burn—only the vapor directly above the surface does—jet fuel requires sustained heat to maintain a fire. This lower volatility means that a cold spill of jet fuel is relatively difficult to ignite. Once a fire is established, however, the heat from the flame continuously vaporizes the liquid fuel below, leading to a persistent and steady “pool fire” that will continue to burn until the fuel source is exhausted or suppressed.
External Factors Determining Fire Duration
The actual time a jet fuel spill burns is dictated by its mass burning rate—the speed at which the fuel is consumed per unit of surface area. This rate is heavily influenced by the physical geometry of the spill, often studied as a “pool fire.” A key variable is the surface area exposed to the air, since a wider, shallower pool maximizes the area where heat feedback from the flame can vaporize the fuel.
The depth of the pool, past a certain minimum, has a negligible effect on the burning rate, but it directly affects the total duration. For example, a four-inch-deep pool of aviation fuel may be consumed in approximately 20 minutes because the fire burns at a steady rate. A larger quantity of fuel spread over the same area will simply last longer, as the burn rate is limited only by the surface area and the heat transfer back to the liquid fuel.
Wind speed is a significant environmental factor, affecting flame geometry and heat transfer. A crosswind can tilt the flame, increasing heat feedback to the fuel surface downwind and potentially increasing the burn rate. Excessive wind can also disrupt the thermal boundary layer, which may increase the burning rate for large fires while sometimes decreasing it for smaller spills. Ambient temperature influences the initial rate of vaporization, though the fire quickly becomes self-sustaining and less dependent on outside heat.
Containment or confinement dramatically alters the fire’s duration and intensity. If the fuel is contained, such as within a fuselage or a drainage trench, the fire will burn with a reduced surface area, potentially extending the total burn time but limiting the spread. Conversely, if the fire occurs at a high altitude or in a low-pressure environment, the mass burning rate decreases due to reduced oxygen availability and less efficient heat feedback to the fuel surface.
Suppression Tactics and Termination of Jet Fuel Fires
The duration of most large-scale jet fuel fires is determined by the speed of human intervention rather than the time it takes for the fuel to be naturally consumed. The primary goal of Aircraft Rescue and Fire Fighting (ARFF) teams is to rapidly extinguish the flames to enable rescue operations. This is accomplished using specialized agents designed for flammable liquid fires.
The most effective agent historically is Aqueous Film-Forming Foam (AFFF), which creates a thin, aqueous film that floats on the fuel surface. This film serves two purposes: it smothers the fire by separating the fuel vapor from oxygen, and it cools the fuel. This separation prevents the flammable vapors from reigniting.
As environmental regulations evolve, fire services are transitioning to fluorine-free foams (F3) that work by forming a physical barrier of bubbles. While highly effective, these newer foams must be applied deliberately to ensure they form a complete, dense blanket over the fuel, as they lack the self-sealing film property of AFFF. When a proper volume of foam is applied quickly and correctly, the fire duration is reduced to minutes or even seconds, preventing the fire from burning to fuel exhaustion.