I am sure this article will ruffle a few feathers, but honestly, I am surprised and disappointed by that. But I do a lot of work in flammable liquid processing, and this topic always comes up during audits, PHAs, and accident investigations. Some folks will swear that only grounding is “required.” They get this from OSHA’s 1910.106(e)(6)(ii) Grounding section. However, although the title of that section is indeed “Grounding,” it literally uses the word “bond” twice. This is my attempt to make clear that in flammable liquids, the two practices WORK TOGETHER to control the generation and dissipation of static electricity.
The correct and legally required method for transferring Class I flammable liquids is Grounding and Bonding used together. Using one without the other leaves a gap in the static mitigation circuit, which can lead to a catastrophic spark inside the flammable vapor-air mixture. Here is the mechanical breakdown of why both are required by OSHA’s 1910.106 and NFPA 30:
Bonding (Equalizing Potential between containers)
Bonding is the physical connection of two conductive containers with a wire to equalize their electrical potential. As liquid flows from a drum into a receiving can, friction generates a static charge. If the two (2) containers are not bonded, one container will accumulate a higher charge than the other. Bonding ensures that both containers maintain the exact same electrical voltage. Because there is no difference in potential between them, a static spark cannot jump from the dispensing nozzle to the receiving container.
Grounding (Dissipating to Earth)
Grounding is the physical connection of the bonded system to the earth (a driven ground rod, building steel, or grounded water pipe). Even if two containers are bonded and share the same electrical potential, that shared potential might be 10,000 volts higher than the surrounding environment. If an unbonded worker reaches for the container, or if a tool is brought near it, a spark will jump from the charged system to the grounded object. The ground wire acts as a safe, continuous bleed path, draining the accumulated static charge from the entire bonded system safely into the earth as fast as the flowing liquid generates it.
Critical Order of Operations
When transferring liquids, the sequence of making these connections is CRITICAL. A static spark can occur at the exact moment a metal clamp touches a charged container. If a vessel is already open to the atmosphere, that attachment spark can act as the ignition source.
1 Attach the Ground
Must be done before any containers are opened
Connect the ground wire from a known earth ground to the dispensing vessel (the source container).
2 Attach the Bond
Connect the bonding wire from the grounded dispensing vessel to the receiving vessel.
The system is now equalized and drained to zero potential.
3 Open Containers and Transfer
Open the lids or valves and begin the fluid transfer.
4 Close Containers
Once the transfer is complete, securely close all caps, lids, and valves to eliminate the flammable atmosphere.5 Disconnect Wires in Reverse Order
Remove the bonding wire first, followed by the ground wire. Any spark generated during disconnection will now occur safely outside of a flammable atmosphere.