Static grounding during fuel loading

Static grounding during fuel loading is the practice of connecting the tank truck to the loading rack's grounding system. The electrostatic charge generated by flowing fuel then drains to earth before it builds up and sparks near fuel vapour. A grounding verification system adds a check that the connection is sound before loading can start.

This guide explains where the charge comes from, how bonding differs from grounding, what the verification system does at a bay and what a grounding assessment looks at. It builds on the interlock ideas in ESD, SIS and interlock and the zones in hazardous areas and Ex equipment.

Static charge is what builds up when two surfaces rub or separate, like a balloon on hair. Fuel moving through a pipe does the same thing at the boundary between the liquid and the metal.

Charge separates at the pipe wall, at filters, valves and the nozzle, and the fuel leaves the hose carrying it.

Gasoline, diesel, kerosene and jet fuel conduct electricity poorly, so the charge fades slowly. Standards call such liquids static accumulators. In a truck compartment the charged liquid raises the voltage of its own surface. A spark can then jump between that surface and a conductive object such as a gauge probe or a loose metal item. The vapour space above the liquid may sit inside the flammable range, which is how a spark becomes a fire.

API RP 2003, NFPA 77 and IEC TS 60079-32-1 describe the controls. Grounding and bonding come first. Limiting flow velocity at the start of filling, until the outlet is covered, comes next, and so does keeping the outlet low in the compartment. Switch loading is a known high-risk case. A high-vapour-pressure product such as gasoline goes into a compartment that last carried a low-vapour-pressure product such as diesel, which can leave a flammable mixture above a charged liquid.

A truck standing on rubber tyres is not reliably earthed. Dry tyres insulate, and the chassis can float at a voltage well above ground. That is why the clamp is required even when the truck is parked on a concrete apron next to a grounded rack. The same goes for a truck fresh from a workshop, whose chassis may be freshly painted so the old contact point is no longer bare.

The verification unit is both a safety device and an interlock input. Without its OK signal the batch controller will not accept a preset, and if the signal drops during loading the valve closes. The exact reaction belongs in the safety requirements specification of the bay. Read how the controller handles permissives in the batch controller guide, and how the bay is laid out in the filling shed and loading rack guide.

The sequence below is typical and follows the intent of API RP 2003 and NFPA 77. It does not replace the procedure of your terminal, which also covers wheel chocks, permits and the vapour recovery connection. A driver new to the terminal should be guided by the bay operator on the first loading, because the sequence differs slightly from one terminal to another.

A grounding permissive that leaves no trace cannot be audited. The batch controller and the TAS can record what happened without extra hardware, as long as the signal reaches them.

Review these records with the safety team on a fixed schedule. A bay with many short signal losses is telling you something about its clamp, and a bay with none for months may be reporting OK whatever happens. The CATALYST batch controller interface passes bay data to the terminal system, and INTEGRA TAS keeps a history for every transaction. Whether the grounding status lands in that record depends on how the signals are configured at your site.

Static grounding at the bay is not lightning protection and not stray current control, although API RP 2003 covers all three. The bay earthing is normally tied into the plant earthing network, and the electrode design and resistance targets come from the earthing design of the site, not from this article.

Citia carried out a grounding system assessment at the LPG terminal in Balongan, Indramayu, in 2026 under a batch controller scope. The technical field analysis reached four conclusions. The module was completely dead and had passed its ideal service life. Its reliability no longer met the working standard. A failed grounding system leaves static electricity that can cause fire and explosion.

The recommendation was to service the module: fit a temporary jumper for grounding while it is repaired, check the grounding module and check the module's power supply. A temporary jumper is a change to a safeguard, so record who fitted it, why, and when it must come off.

How often to check depends on the owner's procedure and the manufacturer's instructions. The usual pattern is a visual check of the clamp and cable at each loading. The verification unit gets a functional test on a fixed schedule, and the earthing system a test at a longer interval. Test again after a repair, a lightning strike or a change to the bay. Earlier results are the best comparison, because a slowly rising trend says more than a single passing value.