This updated animation illustrates the dangers of static build up and how, by using this system, road tankers can correctly be identified to ensure loading and unloading of hazardous materials can be carried out safely.
Our patented Tri-mode technology allows the Earth-Rite RTR to achieve continuous monitoring of the road tanker throughout the loading procedure with visual indication of a verified path to ground. This ensures the highest levels of safety available for operators, road tankers and valuable plant equipment, through protection from ignitions caused by electrostatic spark discharges.
Standards and recommended practice governing the static control of road tanker product transfers
Regulators are extremely cautious about the ignition hazards presented by static electricity in road tanker product transfer operations. Three standards, in particular, provide clear guidance on what precautions should be taken. NFPA 77, API RP 2003 and IEC 60079-32 state that grounding of the road tanker should be the first procedure carried out in the transfer process. Grounding effectively creates an electrical circuit that connects the road tanker to the Earth and it is this connection to earth which prevents static charges accumulating on the road tanker’s container. The reason the charges can transfer from the road tanker to earth is because the Earth has an infinite capacity to absorb and redistribute static charges, with the positive effect of removing the ignition source from a potentially combustible atmosphere.
The electrical resistance of this circuit from the road tanker to the “ground source” (or “grounding point”) which is in contact with the earth, is a key performance indicator of the entire grounding circuit’s capacity to provide a secure and safe product transfer operation. NFPA 77 and API RP 2003 state the resistance in a healthy metal circuit should never exceed 10 ohms, therefore the entire circuit between the truck and grounding point should be measured and be equal to, or less than, 10 ohms. If a resistance above 10 ohms is measured this will indicate problems with parts of the grounding circuit including the road tanker connection, the ground point connection or the condition of the conductor cable.
Road Tanker Recognition
Because resistance monitoring systems operate when connected to conductive metal objects, additional features can enhance the protection of drivers, product and equipment. A “road tanker recognition” feature can be utilised to ensure that drivers can only operate the feed system when the grounding system detects it is connected to a road tanker. A system like the Earth-Rite RTR will analyse the capacitance of the road tanker as part of the grounding circuit. If the capacitance presented is in the normal range for road tankers, the grounding system will recognise that it has made a positive connection to a road tanker.
From the site operator’s perspective, this eliminates the risk of drivers unknowingly connecting the grounding clamp to parts of the truck chassis that are electrically isolated from the truck’s container. This isolation may be due to original design oversight like isolated mud guards or paint coatings insulating conductive parts like truck light enclosures from the chassis. In addition drivers have been known to attach the grounding system’s clamp to the loading rack in order to obtain a permissive state for the feed system to “speed up” the transfer. So while a permissive state for the feed system can be obtained with a standard resistance based monitoring system it does not necessarily mean the grounding clamp is electrically connected to the road tanker’s container.
Specifying a grounding system with a road tanker recognition feature ensures the road tanker is safely grounded before drivers are in a position to begin filling it with product. Once the system has verified it is connected to a road tanker it should then monitor the road tanker’s connection to the grounding point to 10 ohms or less.
Picture: Two workers on a tanker top from Carbis Loadtec Group Limited
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