2.3 Assessing the required Layers of Protection in the context of Question C:
As highlighted already, there are many operations carried out in the hazardous process industries that require static earthing protection but the nature of the operation and the environments they are conducted in can vary greatly. Different zoning requirements coupled with the characteristics of the operation and the scale of the hazard, particularly the amount of flammable or combustible material at risk of ignition, can influence the kind of solution specified. This generally means that a “one-size-fits-all” off-the shelf earthing solution will not provide you with the layers of protection and installation flexibility you may require. The following examples help illustrate how different processes can have unique characteristics that can influence the type of earthing solution employed by your company.
2.3.1 Drumming operations require the repeated filling of drums on a continuous basis where the drums can be filled with fixed pumps that can fill four drums to a pallet, can be filled with fixed pumps on a rolling conveyor system or can be filled with portable pumps. Because such operations are typically carried out indoors, a number of Ex locations ranging from Zone 0 right through to Non-Hazardous areas could reflect a matrix of installation options and required layers of protection that provide the best fit for your static earthing application.
Fig. 3: Pulsing green ground status indicators provide operators with a visual reference point to ensure the equipment they are operating is grounded prior to, and during, the operation.
Imagine a scenario where up to 10 drums can be filled with portable pumps at a dedicated solvent filling location at any one time. Because the pumps are held by the operators and require the operators to continuously “eyeball” the liquid level in the drum, when management analyse the trade-off between interlocking the pumps with that of a manual shutdown by the worker operating the pump, they deem it OK for the operator to both start and stop the pump in response to a visual indication of each drum’s ground connection. An ancillary benefit of determining this operation’s required layers of protection, which is ground circuit monitoring in combination with a visual I.D. of the ground status of the drum, is that a solution like the Bond-Rite® REMOTE can be specified to monitor multiple drums off a single power supply on a 24/7 basis.
The benefit of this type of solution is that it closes the gap between no visual indication via “passive” earthing clamps and “off-the-shelf” earthing solutions with interlocks that require a 230 V AC mains supply or 24 V DC supply delivered to 10 separate earthing systems operating in the hazardous location. A solution like the Bond-Rite® REMOTE, which only requires a single 230 V AC or 24 V DC feed to its Zone 2/21 mounted power supply, can deliver Intrinsically Safe power to the 10 Zone 0 / 20 ground status indicators, which can then independently monitor the earthing status of each individual drum. If filling is carried out on a less routine basis, installation time can be reduced by specifying ground status indicators that are powered by their own internal battery.
2.3.2 Vacuum trucks
Vacuum trucks provide a multitude of services to the hazardous process industries, with the primary role of cleaning out storage tanks and sucking up spills from loss of containment incidents. They also present one of the most complex problems in terms of assigning layers of protection that can control an electrostatic hazard in a safe and repeatable way. They process and transport large quantities of volatile flammable liquids and powders, often in less than perfect circumstances when it comes to controlling the presence of flammable atmospheres.
They operate in many different locations, often in a remote setting, where there will be no ground monitoring systems in place for them to connect to and the speed at which material is transferred, which increases the rate of charge generation, can be very high. In short, the risk profile is pretty high and until recently all drivers could do was connect a passive earthing clamp to a metal object, like a tank shell, or piping, in the hope that he/she could ground the truck safely and reliably, without monitoring the earthing circuit or even knowing if the object he/she connected the clamp to had a verified true earth ground connection (see Fig. 1).