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Jet fuel additives are always extensively evaluated and tested, as anything added to the fuel could adversely affect engine performance and safety (metals, in particular, are something you don't want to add to jet fuel; even trace amounts can have disastrous effects on the thermal stability of the fuel).
For this reason, producers hew to the jet fuel standards set by ASTM International (formerly known as the American Society for Testing and Materials), known as the ASTM D1655, and/or the Defence Standard 91-91. Jet A must meet the ASTM D1655 specifications, while Jet A-1 has to meet the specifications for Defence Standard 91-91, ASTM D1655, and the specifications of the International Air Transport Association (IATA) Guidance Material (Kerosine Type), NATO Code F-35. (5) Jet A-1 is a high-quality fuel. If it doesn't pass purity and quality tests, it is sold off to ground-based consumers rather than being used in jets. (6)
Currently, the ASTM D1655 specifications allow for the following additives to be added to jet fuel (often these are added in extremely small quantities, measurable in parts per million):
Antioxidants to prevent gumming. These are usually based on alkylated phenols.
Antistatic agents to prevent sparking. Stadis 450 is the most widely-used agent, and is speculated by some chemtrail researchers to be the source of the barium allegedly present in chemtrails (see, for instance, this video).
Biocides to inhibit microbial growth in fuel systems. Fungi and bacteria can pose serious problems to planes. In 2009, Australian airline Qanta grounded all three of its Airbus A380s due to fuel tank leaks reportedly caused by fungus. Currently, only two biocides are approved for use in jet engines: Kathon FP1.5 Microbiocide and Biobor JF.
Corrosion inhibitors
Fuel system icing inhibitor agents. As jets reached higher altitudes and stayed at them for longer periods, ice in the fuel became a deadly hazard. In 1958, a B-52D crashed in South Dakota due to ice blockage in the fuel system, killing 5 of the 6 men on board. Studies indicated fuel icing was the probable cause of over 200 previous aircraft losses. (7) Beginning in the '60s, anti-icing agents were added to military jet fuel. I find it very interesting that it took the military 20 years and over 200 crashes to figure out that fuel icing could be a problem.
Metal deactivators to mitigate the effects of trace metals. The only allowable deactivator is N,N’-disalicylidene 1,2-propanediamine, and it is seldom used.
Aside from the Stadis 450, which we'll examine in another post, note that there isn't anything on this list that would account for the metals thought to be in chemtrails (barium, aluminum, titanium, and strontium). Nor does the fuel itself contain them.
But it must be noted that aviation fuel emissions do contain toxic pollutants. The combustion of jet fuel during flight causes aircraft engines to emit carbon dioxide, nitrogen oxides (in small amounts), carbon monoxide, sulfur gases, and soot. (8) Jet emissions have also been found to contain particles of zinc, beryllium, lead, vanadium, and copper. (9) Note that these are heavy metals, unlike the alleged chemtrail metals.
I ask you, how is this any better than what's supposedly being found in chemtrails?
In 2007, the Discovery Channel program Best Evidence examined chemtrails. A team led by Dr. Gregory W. Davis at Kettering University's Automotive Engine Research Laboratory tested five gallons of randomly selected jet fuel from a Flint airport, running it through a small jet turbine. They ran an array of tests on the fuel itself and the emissions, looking for aluminum (the metal most frequently mentioned in connection with chemtrails). They found none. They did find some sulfur in the emissions, though."
http://swallowingthecamel.blogspot.com/2012/06/chemtrails-i-jets.html