Safety on the Ground - Using Plastics in Refueling
Static electricity can be a shocking experience! An electrostatic charge is generated as aircraft fuel or any flammable fluid flows through pipes, hoses, pumps, or filters. The amount of charge is dependent upon factors such as rate of flow (faster flow makes more static) and conductivity of materials used.
Previous articles in SAFETY NET on "Bonding and Grounding" (Summer/Fall, 1991), and "Observations during inspections" (Summer, 1992) covered the use of metal containers, funnels, and other conductive items used in fueling aircraft, along with precautions which must be taken to prevent possible fires due to static electricity. What about the use of nonconductive plastic items such as fuel containers and funnels?
UL Classified "Jerry" Cans
These ANSI/ASTM approved plastic containers, sometimes red, are not eleccrostatically conductive, and are no better from a static electricity standpoint than any other plastic "can." By rubbing it with various kinds of cloth it is possible to generate up to 18,000 volts, which is similar to voltage on clear, white, or yellow plastic jugs which contain paint thinner, antifreeze, or windshield cleaner, etc. So, except for the approval stampings, there is no static safety advantage to these red jerry cans. There are also large white plastic jugs, 2/30 liters, which are in the same non-conductive category. Though metal containers, properly bonded grounded, are recommended, the plastic items ran be used with relative safety if the procedures outlined below are strictly followed.
Non-Conductive Plastic Funnels
Some plastics can be made conductive by adding carbon-black or other chemicals in the process. Many of these products will be black, but some semi-conductive containers will have a special pink color.
A black plastic funnel is currently being used by several mission aviation groups. "Mr. Funnel," from American Product Development, Inc., is made from electrostatic-conductive black polypropylene. We have tested this funnel from a static and conductivity standpoint; it can be safely used, provided it is properly bonded/grounded as any metal funnel or container. Flammable liquids, such as Avgas, and combustible liquids, like kerosene, did not cause static of concern.
Bonding alone, and bonding with grounding, were employed during the tests. In most tests the grounded funnel was in a grounded can, as the fluids were poured from plastic (properly treated, see below) and metal cans. With the grounded funnel placed on an untreated plastic can the can had static but Mr. Funnel did not. From these tests, we conclude that this type of conductive plastic funnel can be safely used, if properly bonded to the receiving vessel. One interesting note: stamped inside, and printed on the outside of Mr. Funnel, are these words of warning: "Not Certified for Aviation Fuel."
A standard, non-conductive, white plastic funnel was subjected to the same tests as noted above. It did not pass! Over 12,000 volts were generated on this non- conductive funnel when Avgas was poured through it! For this reason, we suggest that only metal funnels or the type of conductive funnel just described should be used, and they should be properly bonded or grounded.
Correct Use of Plastic Containers
There is a procedure that can make the use of most non-conductive plastic containers relatively safe to use when handling Avgas. Static is made on these "cans" by pouring into, or out of them, and by brushing against pants or other clothing. This static can build up to 20,000 volts!
We have found that this high static can be reduced to less than 1 KV with a very simple procedure. Just before pouring from this kind of container, wipe down and around the can with a water-dampened rag. This "wipes off' the accumulated static. The rag needs to be just damp, not dripping wet. It works! When the moisture dries off, the plastic will again be able to build up static, so if much time has gone by after first wiping it, wipe it again before using the container. Because it is non-conductive, it will do no good to bond/ground the container, even though the static is "removed" by wiping with water.
The above procedure will reduce the static to an acceptable level. It is still best to use metal funnels and containers, well bonded and/or grounded. If it is necessary to use plastics, use conductive plastic or treat the plastic as described above.
Safety on the Ground is a Prerequisite to Safe Flying!