Gasoline is known to be a volatile fuel. Specific instructions are many times provided with respect to refueling procedures. Almost no information is provided about the potential for gasoline to erupt from the fuel filler neck when the gas cap is removed or dislodged. Temperatures higher than the boiling point of gasoline can be expected with the use of tractors and lawn mowing equipment, particularly when the machines are used in the summer and have gas tanks exposed to the sun. In the past many tractors and lawn mowers used a small hole to allow vapor pressure in the tank to try and equalize with the atmosphere either as gas was used from the tank or due to heating of the gasoline. This small vent hole can become plugged due to the intake of dirt and debris from use in the field, as well as, from corrosion. Some caps have a screw that can be closed to prevent any venting. When the venting provided by the cap can no longer keep up with the production of vapor the pressure in the tank builds up causing the lighter hydrocarbons in gasoline to superheat. If the cap is dislodged or removed the superheated gasoline will suddenly expand and force gasoline to erupt from the filler neck. Gasoline must be prevented from super-heating to avoid the risk associated with this hazard. Design steps to address this hazard will be presented and discussed.

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