Metal or Plastic — Portable Fueling for Airplanes

In the flurry of messages that came in the wake of the story on fuel tank explosions during fueling, one of our readers had a really good question. Mark asked what type of containers would be best to fuel his plane at remote locations — metal or plastic cans. The answer depends a lot on when the plane is fueled, but lets look at the factors involved.

Metal cans are heavier than plastic, but the metal can is a good conductor. While a metal can will hold a static charge and a metal nozzle will allow a spark to jump, metal cans can also to be grounded (bonded for those purists out there) to the aircraft via a wire or ground (bonding) strap. This means that a difference in electrical potential can’t occur, which means that you can’t get a spark from the can to cause a fire at the airplane fuel tank.

THE BASICS — Plastic
Plastic tanks are generally lighter than their metal counterparts, which means they will be easier to handle. Due to this difference in weight, a pilot of an average build and strength can often lift a 5-gallon plastic tank over their wing and fill the fuel tank with less effort than they would with a metal can. Winter Warning: Many winter coats are made of synthetic materials, which are great generators of static electricity when they come in contact with plastic. Since plastic is an insulator (tell that to my wife, who gets zapped every time she slides out of her car in the winter and closes the metal car door!) it doesn’t conduct electricity all that well. Translation: A static charge could be imparted on the fuel container as you lift it to the wing, as it rubs against your coat.

Good: If it is hot outside, the air generally holds more moisture. This means that in the summertime, or in areas where temperatures stay warm year round, the chance of a static discharge is minimized (NOT ELIMINATED) … so long as there is enough humidity in the air. Bad: Then again, hotter temperatures are worse, since the fuel is closer to the vapor temperature, there will be more vapors. When it comes to fuel explosions, vapors are a prime culprit, which is why hot weather is a mixed blessing.

Good: If it is cold outside, the fuel is typically further away from its vapor pressure, which means less vapors floating around in the fuel tank. This helps to reduce (NOT ELIMINATE) the risk of a fuel explosion during fueling.
Bad: Again, colder temperatures mean the air can’t hold as much moisture. This means the air is dryer, and more likely to conduct an electrical spark between fuel vessels.

So, all weather is bad… Go figure.

Disclaimers aside, a recommendation: In our opinion, metal cans for metal airframes (provided they are grounded to one another) are the way to go. A proper ground eliminates the potential for a significant electrical potential difference between the fuel container and the airplane.

Yes, some folks have figures out how to ground plastic cans. The methods include a metal band around the mid-section of the tank and a connection at the tip of the fuel nozzle to help siphon off the electric charge. And don’t make the mistake of underestimating the risk of fueling your airplane, just because you use a 5-gallon container. The risk is the same as it is with a fuel truck. The trick is getting it right — because all it takes is one wrong connection and KA BOOM!

…And before you write in. I am sure there will be many of our readers that have used plastic fuel containers for years without a problem, and some may also have worked out the whole grounding/bonding thing to perfection. That’s swell. But the metal can is more foolproof than anything you can do with plastic containers when you are dealing with fuel.

Some simple procedures to reduce risk of refueling metal aircraft:

  1. Establish a ground (bond) between the fuel container and the fuselage. This is done with a good quality, stranded wire, which is PHYSICALLY CONNECTED to the fuel container and the airplane. This does not mean a wire is looped around the handle — this works best when a lug or connector is welded to the tank, to provide a positive connection.
  2. Open the fuel cap on the airplane.
  3. Get the fuel nozzle in contact with the airplane’s fuel tank filler ring as the fueling gets underway.
  4. Allow all the fuel to drain into the tank if possible, then remove the container, and replace the airplane cap.
  5. Repeat steps with the next fuel container.

Remember — Driving to the airport with the bed of your truck full of fuel will cause the fuel to slosh around in the tanks. This will create a static charge (do you ever remember getting a shock when you picked up one of the fuel tanks — now you know why!) Thus, it is critical to ground the tanks before you start fueling.

THE BOTTOM LINE: DON’T BE FUELISH. Follow the safety tips and rules, and you will be able to fuel your plane from small containers safely. For more safety tips, review the applicable National Fire Protection Association (NFPA) and fuel handling codes, and contact your local Fire Marshall.