Static Discharge / Equipotential Bonding of Fuel Truck 1

[jbond]

Hi Guys, I'm designing the earthing system at a fuel re-fill station where trucks (tankers) will be filled with a fuel

I think that the equipotential leads that earth the truck/tanker when its filling have a switch on them so that you can (I guess) control when or not the truck/tanker is floating and when it's grounded

Does anyone have any info on the purpose of that switch or can you shed some light onto the usefulness of it?

Also, if the fuel is diesel, which I believe is combustible but not flammable, then is there any need to worry about static discharge?

 

[waross]

The switch would be to allow connection to the truck while avoiding a spark in the vicinity of the truck. Connect with the switch open, then ground by closing the switch. Your control interlocks should prevent fuel transfer when the switch is open.
You may want to consider a two ground safety system. The control scheme sends an intrinsically safe level of current out on one ground cable to the truck chassis and the current returns via the second cable. The control logic prevents fuel transfer until ground continuity through the truck chassis is proved.

Definition of Combustible
1. Classification of liquid substances that will burn on the basis of flash points. A combustible liquid means any liquid having a flash point at or above 37.8°C (100°F) but below 93.3°C (200°F), except any mixture having components with flash points of 93.3°C (200°F) or higher, the total of which makes up 99 percent or more of the total volume of the mixture.

Definition of Flammable
1. A liquid as defined by NFPD and DOT as having a flash point below 37.8°C (100°F).

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[alehman]

#2 diesel fuel is considered combustible, not flammable. I don't think grounding is necessary for combustible liquids.

 

[burnt2x]

Depends on where you are! Flammability tests are done in a laboratory environment. At different temperatures (high enough), no one can discount vapors from being released from the fuel surface and into the filling hose/ truck tank.

 

[alehman]

I'm thinking in terms of NFPA codes. Diesel fuel is a Class 2 combustible liquid. NFPA 30 "Flammable and Combustible Liquids" specifically excludes tank cars and trucks carrying exclusively class 2 and class 3 liquids from bonding and grounding requirements provided no class 1 liquids are handled at the facility, or where closed connections are used exclusively.

As with all codes, check with your local authority.