Grounding and bonding is the practice of connecting conductive containers and equipment to each other and to earth so static charge cannot spark and ignite flammable vapors, gases or dusts.
Grounding and bonding are two related methods of connecting conductive objects so static electricity cannot build up to a spark that ignites flammable vapors, gases or dusts. Bonding connects two or more conductive objects to each other so they sit at the same electrical potential. Grounding connects an object, or a bonded set of objects, to earth so the charge drains away.
Static builds whenever materials move against each other: liquid flowing through a hose, powder sliding down a chute, a worker walking across a floor. On its own the charge is harmless. The danger is the discharge. A spark from a charged drum to a nozzle can carry enough energy to ignite gasoline vapor or a cloud of fine powder. Bonding removes the voltage difference that drives the spark. Grounding removes the charge itself.
When a metal drum and a metal safety can are bonded with a wire, charge can still build, but both objects rise and fall together. With no difference in potential between them, no spark can jump across the gap where the liquid flows. Bonding alone does not drain charge to earth.
Grounding gives the charge a path to earth. A dispensing drum is typically grounded to a building ground bus or a verified grounding point, and the receiving container is bonded to the drum. Together they keep everything at earth potential. Most transfer operations need both.
The phrase "grounding and bonding" also appears in the National Electrical Code, Article 250, where it refers to connecting electrical equipment so fault current trips breakers and metal enclosures do not become energized. That is shock and fault protection, covered under electrical hazard. Static grounding uses some of the same hardware but serves a different purpose. A grounded equipment frame does not mean a hose or drum resting on it is grounded for static.
OSHA's flammable liquids standard, 29 CFR 1910.106(e)(6)(ii), says Category 1 or 2 flammable liquids, and Category 3 liquids with a flash point below 100°F, shall not be dispensed into containers unless the nozzle and container are electrically interconnected. Bonding the fill stem to the container with a bond wire, or standing the container on a metal floor plate connected to the fill stem, meets that requirement. Similar interconnection rules apply at service stations. For the categories behind these rules, see flammable liquids and flash point.
NFPA 77, Recommended Practice on Static Electricity, is the main US reference on how static is generated and controlled. The current edition is 2024. It covers liquids, powders, gases, people and equipment, and it is the source most engineers use when designing bonding and grounding systems. NFPA 30 covers flammable liquid storage and handling more broadly and refers to static control in several places.
A path of around one megohm is generally enough to dissipate static charge. In practice, metal bonding and grounding connections are expected to read far lower, commonly under 10 ohms, which shows the connection is metal-to-metal and not degraded. A reading much higher than that usually means paint, rust or a broken strand.
Plastic cannot be bonded the way metal can. A metal funnel or fill stem in a plastic container can be bonded, but the liquid inside the plastic can still hold a charge. Use approved metal or static-dissipative containers for low flash point liquids, and avoid plastic liners in metal drums unless the liner is rated as conductive or dissipative.
Pneumatic conveying, bag dumping and filling of flexible intermediate bulk containers (FIBCs) generate large charges. Conductive parts of conveying systems need to be bonded and grounded, including hoses with internal wire helixes. Type C FIBCs require grounding during filling and emptying. Workers handling powders near a flammable atmosphere may need static-dissipative footwear and flooring. See combustible dust for the wider dust hazard.
A specialty chemical plant transferred toluene from a grounded 55-gallon drum into 5-gallon metal pails with a hand pump. During one transfer, a flash fire started at the pail opening. The operator stepped back and used a nearby extinguisher. No one was hurt. The investigation found the bonding clamp had been attached to a painted lifting handle on the pail. A resistance check through that handle read well into the megohm range.
The plant replaced its alligator clips with heavy-duty clamps that pierce coatings, added a bare-metal bonding tab to every pail, and moved transfers to a grounded metal floor plate. Operators now attach the clamps and confirm the indicator light before opening any container, and the weekly area inspection includes a meter check of every cable. The explosion hazard assessment for the area was revised to treat static discharge as a primary ignition source.
For flammable liquids covered by 1910.106(e)(6)(ii), the nozzle and receiving container must be electrically interconnected. With small metal containers in hand contact, the person, can and receiving container may already be connected, but it is not reliable, especially with gloves or a plastic receiver. Bond whenever the receiving container is metal and the liquid is low flash point.
Fuel flowing into a tank truck compartment generates charge on the liquid and the tank. The ground cable keeps the truck at earth potential so a spark cannot jump between the truck and the loading arm. Many loading racks use ground monitoring systems that will not allow pumps to start until a verified connection to the truck is detected.
Not by itself. Ordinary rubber is insulating. Static-control hoses contain a conductive wire or a conductive rubber layer, which must be connected to the nozzle and the supply end to work. Check the hose marking and test end-to-end continuity, since internal wires can break without visible damage.
No. Higher humidity can help charge leak away from some surfaces, which is why static is worse in dry winter air. It is not dependable enough to control ignition risk. Low-conductivity liquids such as toluene and many fuels can hold charge regardless of the humidity around them. Treat humidity as a minor help, never a control.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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