Static earthing and bonding solutions provider, Newson Gale, outlines what is required to ensure an earthing system meets the requirements for safe product transfer from road tankers and tank trucks.
Carrying out a product transfer with an ungrounded road tanker/tank truck is a static electricity hazard capable of causing extreme damage to plant and personnel.
The design and manufacture of a road tanker/tank truck must ensure that all metal items are bonded together. International standards and recommended practices state that this bonding/continuity must be <1Ω and others <10Ω between metal items. Designated earth points must also be welded onto the vessel or body of the truck and be clearly marked and manufactured from a corrosion-resistant material.
Drivers must be educated to attach the grounding clamp and system to the designated earth point on the truck as soon as they leave the cab and before they start any other operation or product transfer. The clamp must be connected to the designated earth pin on the vehicle before any other equipment, bonded or associated with the tanker, (e.g. transfer hose, landing legs) comes into contact with the ground.
The dedicated earthing system needs to confirm a good ground connection before the product transfer can begin. After the product transfer and all other activities have been completed, the driver can then remove the earthing clamp and store it away on the earthing system stowage point before driving off.
To protect against the static electricity hazard, some operators of road tankers/tank trucks fit a simple hand wind or retractable single core cable reel and clamp assembly to protect their trucks. Unfortunately, the single-core cable reel and clamp assembly is only a basic introductory method that does not meet international standards and recommended practices when protecting the trucks, because it cannot alert the driver to any of the following dangers:
- It cannot provide a visual indication of a GOOD or BAD ground connection.
- It does not provide true earth verification, e.g. is the system connected to an earth that is capable of dissipating static electricity.
- Because it is not a monitored circuit, it cannot automatically shut down the product transfer if the ground connection is lost.
- It does not comply with the relevant International Standards and Recommended Practices.
Therefore, the recommended and safest way to protect a product transfer is to use a dedicated truck earthing system that is gantry mounted. A dedicated earthing system would:
- Provide the driver with a visual indication of a GOOD or BAD ground connection (GREEN flashing LEDs).
- Detect if the earthing system is attached to a road tanker/tank truck by its capacitance and at the same time check that the resistance of the verified true earth connection is capable of dissipating static electricity.
- Utilise an intrinsically safe (ia) monitored circuit that can automatically shut down the product transfer if the ground connection is lost.
- Provide an earthing method that fully complies with the relevant international standards and recommended practices, i.e. monitoring between the teeth of the clamp on the designated earth point of the truck back to the verified true earth point close to the gantry is less than 10Ω.
However, a two-core cable reel is suitable for this application if used in conjunction with a dedicated earthing system.
The verified true earth connection located close to the gantry and connecting the dedicated earthing system to true earth must be checked regularly by a responsible person.