By Frank L. Fire
Commercial jet fuel is essentially kerosene that has been hydrotreated to improve its burning properties. Hydrotreatment is a process proprietary to the producer of the fuel utilizing a particular catalyst. It will contain some additives to produce the anti-icing, anti-oxidation, anti-corrosion, and anti-static properties required.
Kerosene is a mixture of aliphatic (straight-chain alkanes or saturated) hydrocarbons, usually beginning with octane (eight carbons in the chain) and going up to hexadecane (16-carbon hydrocarbon). Alkanes have the general formula CnH2n+2. The n stands for the number of carbons in the chain, so hexadecane’s molecular formula would be C16H34. Kerosene is formulated to fit the definition of a combustible liquid rather than a flammable liquid. The flash point of kerosene is controlled to be 100°F, or 37.8°C, to be classified as a combustible liquid.
Commercial jet fuel has many synonyms and trade names, including Jet A or JP-8. It is also known as aviation kerosene, Jet A-1, Jet A-50, Jet B, jet kerosene, jet kerosine, Turbo fuel A, and Turbo fuel A-1. Kerosene may also be called kerosine.
Commercial jet fuel is a pale yellow liquid with a petroleum odor. It has an auto-ignition temperature of 410°F (210°C). Its explosive limits are from 0.6 to 4.7 percent by volume in air. Coupled with its flash point, this means that at 100°F there is enough vapor in the air to reach the lower explosive limit so that even if an ignition source is not present and the fuel reaches a temperature of 410°F (and this is considerably below all common ignition sources), an explosion will occur.
Commercial jet fuel has a vapor density of 5.7 (where air = 1.0), which means the vapors are extremely heavy relative to air and will fall to the lowest point in the terrain and “hang” together for a long time where there is no appreciable breeze. These vapors will flow a considerable distance as if they were seeking an ignition source. They always find one.
Its specific gravity is 0.87, and it is not soluble in water. This means that the liquid will float on top of any water it contacts.
A flash point of 100°F means that it must be warmed to that temperature before it will produce enough vapors to burn (or explode). Any airplane with fuel in it is a flying bomb. If it crashes accidentally into the ground or on purpose as at the World Trade Center (WTC), the friction of the crash produces enough heat energy to ignite the fuel (which has been released by the crash) in a spectacular explosion. Even though the explosion is violent, all of the fuel is not involved, since much of it will be hurled away from the original point of energy release. At the WTC, after the initial explosion, some of the fuel was expelled from the building, but the remaining walls and windows confined much of it.
Hydrocarbons are essentially all fuel, since both the carbon and hydrogen will burn. There is a tremendous amount of energy tied up in the covalent bonds holding the hydrogen atoms to the carbon atoms in the hydrocarbon chain. When these bonds are broken, the energy is released in the fire as the fuel’s heat of combustion. This is defined as the total amount of energy released as a fuel burns completely. Jet fuel has a heat of combustion of more than 19,000 Btus per pound of fuel, or more than 128,000 Btus per gallon of fuel. Multiply this by the amount of fuel in the airliner, and even though some of it was involved in the original explosion, you can understand that there was a tremendous amount of energy released in a short period of time during the ensuing fire of the remaining fuel. The burning jet fuel, plus whatever combustibles were present in the area of impact, produced more than enough heat to raise the temperature of the structural steel above its softening point, causing the floor or floors above the fire to collapse pancake style. There probably can be no tall building built that would withstand the heat generated by the quantity of jet fuel present in the WTC attack. If one can be built, no one would be able to pay for it.
Many victims probably were incinerated in the fireballs of jet fuel that roared through the upper floors of the towers. Many others were dismembered in the crashes or the collapses that followed. Firefighters and others at the scene have reported finding few intact bodies.
“The heat of the fire—estimated by FEMA at 1,700 degrees—would make identification difficult because it consumed smaller body parts,” said Dr. Steven Symes, a professor of forensic pathology at the University of Tennessee.—“NY Shifts from Rescue to Recovery,” Richard Pyle, AP writer with contribution from AP reporter Diego Ibarguen, Sept. 17, 2001
FRANK L. FIRE is executive vice president, marketing and international, for Americhem, Inc. in Cuyahoga Falls, Ohio. He is an instructor of hazardous-materials chemistry at the University of Akron as well as an adjunct instructor of haz mats at the National Fire Academy. Fire is the author of Common Sense Approach to Hazardous Materials (first and second editions) and an accompanying study guide; The Combustibility of Plastics; and Chemical Data Notebook: A User’s Manual, published by Fire Engineering. He is an editorial advisory board member of Fire Engineering.