Is Airplane Fuel Flammable?
Yes, all the many different grades of airplane fuels are flammable. In fact, the word fuel is usually used for materials that can produce heat when burned. Aircraft fuel has similarities and differences with automotive fuel.
Some general properties of aircraft fuel are:
- The flame temperature of aviation fuel is, many times, higher than ground fuel.
- Flammable in the liquid and in the gaseous state.
- Vapor is capable of traveling a considerable distance and remaining dangerous.
- Fire hazards are present in the storage, inside the aircraft and in the transportation from the storage to the airplane.
General Facts About Airplane Fuel
Airplane fuel, from now on referred to as aircraft fuel, can be mainly of two kinds.
- Aviation gasoline (commonly called avgas) used in piston engines.
- Aviation turbine fuel, also called AVTUR, AVJET, paraffin or kerosene, is used in gas turbine engines.
Aircraft fuel components may contain up to thousands of different substances (different hydrocarbons with similar molecular weight). The main component of aircraft fuel is a blend of hydrocarbons.
Small amounts of alcohol may be present as well as others. And, pretty much all of the substances that constitute the fuel are flammable.
Aircraft fuel also contains additives and dyes to help in the quick identification of the fuel grade.
Additives are used to improve the fuel performance and/or safety. The most common additives use organic lead compounds, which are flammable and highly toxic.
Aviation Gasoline (Avgas) and its Fire Hazards
The main avgas constituent is a blend of iso-octane isomers. All these isomers are highly flammable.
This blend of iso-octanes is commonly referred to as just gasoline. The amount of gasoline in a given aircraft fuel is variable. The concentration of gasoline can range from up to 92% (weight/weight) to as low as less than 50%.
The constituintes of avgas besides gasoline are hydrocarbons and organometal additives (organometal additives rarely exceed 1%).
The hydrocarbons besides the iso-octanes are mostly unsaturated hydrocarbons, including toluene, xylene isomers, alkylated benzenes, naphthalene and some saturated hydrocarbons (n-hexane and cyclohexane).
The most commonly used avgas nowadays is avgas 100LL (LL stands for low lead, meaning it has a low amount of lead additive). The 100LL is highly flammable and can ignite with small sparks.
Some important properties of Avgas 100LL are listed in the table below.
| Property | Value at normal pressure |
| Flash point | -37 ºC or lower (estimated) |
| Autoignition temperature | 440 ºC |
| Explosive limits | 1% to 8% (volume in air) |
| Appearance | Blue (dye) |
| Vapor density | Lower than air |
| Chemical reactivity? | Not chemically reactive |
Avgas is less volatile than automotive gasoline. Reid pressure for avgas stays in the range of 35 kPa to 48 kPa, while automotive gasoline stays between 55 kPa and 96 kPa.
The lower vapor pressure of avgas compared to automotive gas helps to prevent vapor lock in the engine.When avgas is at high altitudes, where the pressure is lower, the vapor pressure of the avgas will be higher.
Although 100LL is the most commonly used avgas, there are other grades that may be used depending on the locale or the aircraft model.
Other avgas grades:
| Avgas grade | Colour |
| Avgas 100 (or Avgas 130) | Green |
| UL 91 | None |
| B91 | Green |
The majority of avgas grades contain a small amount of a highly toxic tetraethyl lead (TEL), ((CH3CH2)4Pb). This substance is necessary to prevent premature detonation in the airplane internal combustion engine. There is research on the development of a replacement for TEL.
Jet Fuel and its Fire Hazards
Jet fuels are the fuels used to power gas turbine engines. The most used jet fuels are Jet A (in the U.S.) and Jet A-1 (international). Unlike avgas that has a blend of iso-octanes as the main fuel constituent, jet fuels have kerosene as the main constituent.
Kerosene is a blend of hydrocarbons with a number of carbons in their molecules ranging from 6 to 20. Kerosene used in jet fuels typically have a more strict range of carbons in the hydrocarbon molecules, ranging from 9 to 16.
In comparison with avgas, jet fuel is less dangerous to handle, having a flash point of 38 ºC or less (avgas has a flash point of -37 ºC or less).
Here some important data of Jet Fuel A is summarized:
| Property | Value at normal pressure |
| Flash point | 38 ºC (it may be lower depending on specific fuel composition) |
| Autoignition temperature | ~200 – 250 ºC |
| Explosive limits | – |
| Appearance | Clear liquid |
| Vapor density | >3 (air density = 1) |
| Chemical reactivity | Not chemically reactive |
Another commonly used jet fuel is Jet B, this fuel poses a higher fire hazard than Jet A with a flash point of -18ºC. This fuel is more oftenly used in cold environments for it is far more resistant to freezing than Jet A.
In military aircraft, additional safety margins are necessary, therefore fuels with higher flash points are used in military airplanes. Most commonly used fuels are JP5 and JP7. Both these grades have a flash point of 60 ºC or more.
Fire Hazards During Fuelling and Defueling of Aircraft Tanks
When handling fuel, the major risk is accidental ignition of fuel vapor, which can occur by a single spark.
Fuel vapor can be in the air at a high enough concentration to pose a high risk ignition under the following events:
- Aircraft tank venting.
- Failure of pressurized fuel lines or their couplings.
- Leaks.
- Spillage arising from procedural errors.
Electric sparks with enough energy to ignite fuel vapor can result from the discharge of electrostatic energy (static) created either from the movement of the fuel in the aircraft tank during the fuelling process, or its accumulation on the surface of aircraft or vehicles.
Fuel movement during fueling procedures may cause static charge accumulation in the fuel. If this charge is of sufficiently high electrostatic energy, a sparking can occur within the aircraft tank or within the storage tank.
Some fundamental precaution measures to avoid fuel ignition by sparks originated from static charges in the fuel are the following:
- Use of static dissipater additives in fuel can contribute materially to reducing the risk involved.
- Make sure to connect all exposed metals not designed to carry electricity as protection from electric shock. This practice is called electrical bonding.
- Only perform the coupling/uncoupling of hoses after the proper electrical bonding is in place.
- Avoid any exposure of the fuel to rain storms or thunderstorms.
What is Fire in the Air and is it Dangerous?
Fire in the air is a fire that starts during a flight. A fire on board a flying aircraft is an extremely dangerous situation. It has been the cause of a number of aircraft accidents.
A fire on board a flying aircraft can lead to complete loss of the aircraft within a few minutes. Fast and effective work of the flight crew is the only way a catastrophe happens after a fire in air starts. The main focus should be landing as soon as possible.
Recommended Fire Extinguisher Media for Aircraft Fuel Fires
Below the suitable fire extinguisher for fire caused by aircraft fuel.
- Alcohol-resistant foam.
- Carbon dioxide (CO2).
- Dry chemical.
Some Less Commonly Used Aircraft Fuel Grades
Besides the above mentioned fuel grades, there are many others. Here is a list of some of them along with their respective field of application.
| Area of use and fuel grade name | |
| Civil Jet fuels | Military jet fuels |
| TS-1 | JP-4 |
| Biofuel | JP-8 |
Common Aircraft Fuel Dyes and Their Importance
Dyes are used in some aircraft fuels in order to aid pilots and ground crews in identifying the fuel grade. They are organic molecules and are present in very small amounts in the fuel.
Below, some dyes are represented along with their respective name and chemical denominations.
| Colour | Dye | Chemical name formula formula |
| Blue | Oil Blue A | 1,4-Diaminoanthraquinone derivatives |
| Orange | Sudan I | 1-(Phenyldiazenyl)naphthalen-2-ol (C16H12N2O) |
| Red | Sudan III derivatives | Sudan III: 1-{[4-(Phenyldiazenyl)phenyl]diazenyl}naphthalen-2-ol |
| Yellow | Solvent Yellow 56 | p-Diethylaminoazobenzene (CH3CH2)2NC6H5) |
Conclusions
Some general aspects of aircraft fuel and its associated fire hazards have been presented. Fuels in general pose a significant danger of fire and explosions. Over the years, many developments have been made to improve the safety of users of transports.
Nonetheless the risks are not negligible, the appropriate safety measures must always be properly followed.
Frequently asked questions (FAQ): Is Airplane Fuel Flammable?
Does jet fuel explode or burn?
Jet fuel can burn and it can cause explosions. For it to burn, a source of ignition must be put in contact with the vapors of the fuel. In the case of jet fuel liquid, a small spark or flame may or may not be enough to cause the fuel to catch on fire. This will depend on the conditions of the fuel in the moment as well as the intensity of the flame or spark.
An explosion will happen if a sufficient amount of vapor is ignited in a sufficiently small room or container.
Is aviation fuel more flammable than gasoline?
Aviation gasoline, used in piston engines, has approximately the same risk of catching on fire as automotive gasoline. Jet fuel, used for turbine engines, have a somewhat lower risk of catching on fire than ground gasoline. The main reason for that is because the primary constituent of jet fuel (kerosene) is less volatile than the gasoline commonly used in cars.
Can I put jet fuel in my car?
Diesel and kerosene are reasonably similar to each other. So cars that have diesel engines could work with jet fuels that have kerosene as the main source of energy.
Can a plane explode in the air?
Only under severe circumstances. If a fire does happen midair and it is not dealt with quickly and effectively the plane will likely either have to perform an emergency landing or crash.
Why do airplanes explode when they crash?
In the event of a strong impact, the metal and other materials cause sparks or flames, which causes the fuel to burn. Airplanes usually carry large amounts of fuel, when a portion of it is ignited, it will usually be enough to cause all of the fuel to catch on fire. These events can happen in a fraction of a second.
Is diesel fuel flammable?
Yes diesel is flammable, but it needs more heat than gasoline to catch on fire.
References
https://skybrary.aero/operational-issues/fire-smoke-and-fumes https://skybrary.aero/articles/fire-smoke-and-fumes