Static cling in clothing and that jarring shock that sometimes happens when you touch a doorknob in the winter are two of the consequences of built-up static electricity. While these events range from embarrassing and annoying to slightly painful, static electricity can be life threatening when it comes to handling and transferring flammable liquids.
One of the primary hazards of flammable liquids is their vapors. Properly bonding and grounding containers reduces the risk of a spark igniting these vapors.
Bonding and grounding often go hand-in-hand, and some people use the terms interchangeably, but each has a slightly different purpose.
Recognizing the differences and using each correctly minimizes risks. Read on to learn the differences between bonding and grounding.
What is Grounding?
Like your clothing and a doorknob, static electricity can build up on many different types of surfaces including drums, containers and tanks.
Grounding the drum, container or tank gives that energy a safe path to flow to the earth. Metals are good conductors of electricity and can be grounded easily. Most plastics are insulators and cannot be grounded.
Metal items can be grounded directly to a grounding rod or to a grounding system. Items that are stored outdoors are usually grounded to a grounding rod. Items stored indoors are usually grounded to a water piping system that also is grounded.
How to Ground an Item
To ground an item, start at the grounding rod or grounded pipe. Attach a metal grounding wire to the rod or pipe, then attach the other end of the wire to the item being grounded. If either the pipe or the item being grounded is painted, be sure to sand or scratch off the paint in the area where the connection will be made to create a good metal-to-metal bond.
When sanding or scratching off paint, be sure that all containers holding flammable liquids are closed and there are no harmful levels of flammable vapors present.
In some parts of the world, this process is called “earthing” instead of “grounding.” The two terms are used interchangeably because both drain energy to the ground or earth. Note that there is a slight technical difference between the two: “grounding” drains static electricity from items that don’t normally carry an electrical charge, whereas “earthing” is used to safely discharge electrical circuits.
What is Bonding?
Remember that static electricity can’t be eliminated. It’s on surfaces waiting for something with a different electrical potential to come near it. When it finds another conductor with a different electrical potential, it is drawn toward it, sometimes creating heat and a spark as it moves. When two conductors are bonded, any difference in their electrical potentials is eliminated. When the electrical potential between two conductors is the same, electrical discharges (sparks) cannot occur.
Bonding completes circuits. Let’s say that you want to pump a gallon of paint thinner from a drum into a metal pail. The drum is properly grounded and the pump is bonded to it. To complete the circuit and make sure that no spark is generated when the paint thinner is dispensed, the pail will need to be bonded to the pump.
Having all of the items bonded (or connected) equalizes any potential energy among the conductors, completing the circuit and giving that energy a safe path to the earth.
Like grounding, bonding assemblies need to make metal-to-metal contact to be effective. Paint, coatings, grease or dirt needs to be removed from the areas being connected.
Bonding and Grounding Connections
Bonding and grounding can be done with the same types of cables. Usually, bonding and grounding cables (or wires) are made of copper or another highly conductive metal. Each end has a clamp, clip or eyelet to facilitate bonding or grounding. Jumper cables are not reliable as bonding/grounding assemblies and should not be used for bonding or grounding.
The following clips and clamps are commonly used for bonding and grounding:
- Good for both bonding and grounding
- Very durable
- The heavy spring in the clamp helps to ensure strong connections
- Commonly used for bonding
- Easier to manipulate than hand clamps
- Can be dislodged more easily than hand clamps
- Commonly used for grounding to pipes or over the top rims of drums
- Most often used in areas where the container or item won’t be moved often
- Has a bolt that helps to keep the clamp and cable from being dislodged
- Most often used to ground machinery, cabinets or things that aren’t moved or replaced often
- Facilitates the use of a screw to more permanently attach a bonding or grounding assembly
Wires or Cables
Like “grounding” and “earthing,” the terms “wires” and “cables” are used interchangeably when referring to bonding and grounding devices. As mentioned, the wires are usually copper because it’s durable and conductive. Wires can be insulated or uninsulated.
Most organizations use non-insulated wires because they are easier to inspect. But in areas where there are abrasive materials in use or in corrosive environments, insulation will help to protect the wires while they are in use. NFPA 77, Chapter 188.8.131.52 clarifies that either type may be used for bonding and grounding.
Channeling static electricity by bonding and grounding drums, tanks and containers takes away more than just that tingly feeling after a shock. It provides a safe path to channel static energy, preventing sparks and avoiding explosions.
Have a question about bonding and grounding? Ask us in the comments section.