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JP-4, or JP4 (for "Jet Propellant") was a jet fuel, specified in 1951 by the U.S. government (MIL-DTL-5624). It was a 50-50 kerosene-gasoline blend. It has lower flash point than JP-1, but was preferred because of its greater availability. It was the primary U.S. Air Force jet fuel between 1951 and 1995. Its NATO code is F-40. It is also known as avtag.
JP-4 is a mixture of aliphatic and aromatic hydrocarbons. It is a flammable transparent liquid with clear or straw color, and a kerosene-like smell. It evaporates easily and floats on water. Although it has a low flash point (0 °F (−18 °C)), if a lit match is dropped into JP-4, ignition does not occur. JP-4 freezes at −76 °F (−60 °C), and its maximum burning temperature is 6,670 °F (3,688 °C).
JP-4 is a nonconductive liquid, prone to build up static electricity when being moved through pipes and tanks. As it is volatile and has a low flash point, the static discharge may cause a fire. Since the mid-1980s, an antistatic agent was added to the fuel to lower the charge buildup and decrease the corresponding risk of fires. Flow rates must be controlled, and all the equipment used must be electrically interconnected and well grounded.
The desire for a less flammable, less hazardous fuel led the U.S. Air Force to phase out JP-4 in favor of JP-8; the transition was completed by the fall of 1996.
- Faroon, Obaid; Mandell, Diane; Navarro, Hernan. Toxicological Profile for Jet Fuels JP-4 and JP-7. Agency for Toxic Substances and Disease Registry, Atlanta, June 1995.