SPECIFIC GRAVITY The specific gravity is the ratio of the weight of a given volume of a fuel to the weight of an equal volume of distilled water. Normally, the gravity of petroleum products is converted to degrees API, according to the API (American Petroleum Institute) scale. All gravity determinations are correlated with a specific tempera- ture of 60°F by use of ASTM Standard D1250-80. The specific gravity of petroleum products must be determined to correct the volume at different tempera- tures when gauging the liquid content of storage tanks, tankers, and barges. The specific gravity of JP-5 is also used to select the proper discharge ring on the centrif- ugal purifier. A change of the specific gravity of a fuel may indicate a change of composition caused by the mixing of different fuels, or even mixing different grades of the same fuel. VISCOSITY Viscosity is the measure of a liquid’s resistance to flow. The significance of viscosity depends on the intended use of the product. For application and per- formance, proper viscosity is highly important since specified minimum and maximum flow rates of flow are required for all fuels and lubricating oils. In fuel, viscosity determination serves as an index of how it will flow to the burners, the extent to which it will be atomized, and the temperatures at which the fuel must be maintained to be properly atomized. SOLVENCY OF FUELS All petroleum fuels have the characteristic of being able to dissolve some materials. They can dissolve common lubricants, such as oils and greases in pumps, valves, packing, and other equipment. This charac- teristic requires the use of special lubricants for gasoline services. Gasolines also cause serious deterioration of all rubber materials except those synthetic types designed especially for gasoline service. It is very important, therefore, that only hose specially made and designated for gasoline be used in this service. This also applies to packing, gaskets, and other materials that must be used in gasoline systems. Like gasoline, jet engine fuels have certain solvent properties that dissolve greases and cause deteriora- tion of some rubber materials. Therefore, only spe- cially designated greases and synthetic materials should be used for jet engine fuel service. Another important solvent property of jet engine fuels is their ability to dissolve asphalt used for aircraft runways and pavements. Jet engine fuels seriously damage asphalt pavements, and even small spills of this fuel on asphalt pavement should be avoided. FREEZING POINTS OF FUELS The freezing point of a fuel is the temperature at which solid particles begin to form in the fuel. These particles are waxy crystals normally held in solution in the fuel. These particles can readily block the filters in an aircraft fuel system. The fuel almost always becomes cloudy before the solid particles form. This cloud is due to the presence of dissolved water in the fuel coming out of the solution and freezing. The freezing point of JP-5 is – 51°F. The fuels used by other NATO countries and by commercial users vary widely. FLASH POINTS OF FUELS The flash point of a fuel is the lowest temperature at which the fuel vaporizes enough to form a combus- tible vapor. These temperatures vary according to the fuel in question. The flash point of a fuel is an index of the fuel’s potential safety when being handled or when in stor- age. JP-5 must have a flash point of at least 140°F to have the high safety factor required for storage aboard an aircraft carrier in unprotected tanks. F-40 (JP-4) and F-34 (JP-8) fuels flash at any normal temperature and are in danger of ignition any time they contact a hot surface. Therefore, these fuels must be handled with caution from a safety standpoint. HEALTH HAZARDS OF AVIATION FUELS Most people are aware of the explosive and fire potential of aviation fuels. Furthermore, there is a danger to the health of the individual who must work where hydrocarbon vapors are present. Prolonged in- halation of hydrocarbon vapors can cause dizziness, intoxication, nausea, and death. Consequently, ap- proved safety procedures that minimize the dangers to the health of fuel-handling personnel must be fol- lowed meticulously. Gasoline The concentration of gasoline vapors that can be tolerated by man is far below that required to produce combustible or explosive mixtures with air. Even one- tenth of the amount necessary to support combustion or to form an explosive mixture is harmful if inhaled for more than a short time, causing dizziness, nausea, and 3-3