Specifying a Static Grounding System for rail tanker loading/unloading operations.
One of the main problems with static electricity is that it is not something the operators can see, smell or hear. This characteristic of static electricity can, unfortunately, promote an attitude of “it can’t happen to me” or “it doesn’t exist” amongst personnel operating loading gantry systems. A grounding system that combines a simple visual “GO / NO GO” communication via a traffic light model of indication with interlock control capability is the most effective means of controlling the risk of ignitions caused by static electricity during rail tanker product transfer operations. Interlocking the transfer system with the grounding system is probably the ultimate layer of protection equipment specifiers and designers can take to ensure the rail tanker is grounded.
Newson Gale recommends the Earth-Rite PLUS for bonding rail tankers to rail tanker loading gantries. Along with demonstrating the full range of ATEX and IECEx certification for all gas and liquid vapour groups, it also ensures there is a 10 ohm, or less, connection between the rail tanker and the product transfer system. By simply connecting the grounding clamp to the rail tanker the Earth-Rite PLUS automatically verifies if the rail tanker is connected to the loading gantry by delivering an Intrinsically Safe monitoring circuit to the system’s Factory Mutual approved grounding clamp. The Factory Mutual approved stainless steel heavy duty grounding clamp ensures that a strong initial connection, via a pair of tungsten carbide teeth, is made to the rail tanker, and is then maintained for the duration of the product transfer operation, resisting movement caused by vibration or accidental dislodging.
Fig. 2 The Earth-Rite PLUS uses an intrinsically safe signal (Zone 0 / Zone 20) to ensure there is continuity through the tank of the railcar, through the chassis, through the wheels, through the bonded connection back to the gantry. The signal returns to the Earth-Rite PLUS via the G1/G2 connections to the gantry. The entire circuit is monitored for the duration of the transfer operation ensuring there is a continuous dissipation path between the tank of the railcar and the earthed gantry.
Unlike standard grounding systems that rely on the their non-monitored electrical ground connection to dissipate the static charges generated by the transfer, the Earth-Rite PLUS ensures that its dedicated static grounding connection to the loading gantry is always monitored, via the static ground connections G1 and G2 (ref. Fig. 2). This ensures there is a monitored connection directly between the rail tanker and the loading gantry. This is an important feature as we are depending on the loading gantry’s verified ground connection to dissipate static charges from the rail tanker to the general mass of earth.
When the Earth-Rite PLUS verifies the rail tanker is connected to the loading gantry superstructure, a cluster of attention grabbing green LEDs pulse continuously to inform the operator that the system is actively monitoring the integrity of the ground loop.
A pair of volt-free double pole, double throw, contacts can be interlocked with the power delivered to the pump or PLCs to halt the product transfer operation if the Earth-Rite® PLUS detects a resistance of more than 10 ohms in the ground loop between the rail tanker and the product transfer system. Shutting down the transfer operation ensures the generation of static electricity is stopped thereby eliminating the risk of the rail tanker accumulating a voltage and discharging a static spark which could ignite combustible flammable or dust atmospheres present in the spark discharge gap.
Fig. 3 Earth-Rite PLUS ground status indicators
pulse continuously when grounding is in place.
Mike O’Brien, Managing Director for Newson Gale
If you have any questions relating to the topics discussed in this article,
please contact Newson Gale.