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Mobile Static earthing protection for Road and Vacuum Tankers.
This article will explore the methods used to providing static earthing protection for vehicles operating in locations that do not have installed, or correctly specified, static earth monitoring systems. Although primarily designed to provide all tankers with mobile ground (earth) verification capability, the Earth-Rite® MGV has proven to be a success for vacuum tankers used by contractors providing cleaning, spill and material recovery services to companies with classified hazardous areas. The MGV is also utilized on tankers that must collect from, or deliver product to, locations that do not have satisfactory static earthing protection for road tankers in place.
Reading time: approximately 10 - 15 minutes.
A PDF version can be downloaded from the last page of this article.
Vacuum tankers provide a wide range of services to the hazardous process industries ranging from storage tank cleaning to the recovery of combustible materials resulting from leaks and spills. A key feature of this type of service is the recovery of materials in locations with potentially combustible atmospheres.
Vacuum tanker transferring product out of storage tank.
Static electricity is a well known ignition source within the hazardous process industries and because the generation and accumulation of static electricity is not visible to the naked eye, this “below the radar” characteristic, makes it an exceptionally precarious and dangerous hazard. Normally, the only evidence of static electricity being present during a transfer operation is when somebody sees or hears a static spark discharge. By then it may be too late to prevent the ignition of the surrounding atmosphere if it is in its combustible range.
Earthing vacuum tankers operating in hazardous areas eliminates the threat posed by static electricity and is an action that effectively connects the tanker to the general mass of the Earth, which is sometimes called “True earth ground”. The voltage induced on the tanker by the charged material is the key factor in a static spark discharge. Earthing ensures that no voltages are generated and permitted to accumulate on the tanker.
A solution that is appropriate to the potential hazard.
For over twenty years dedicated static earth monitoring systems have replaced basic earthing reels on the road tanker loading gantries of petrochemical and chemical sites, pharmaceutical sites, tank farms and food and beverage manufacturing sites. Due to the combination of the large quantities of combustible material being processed, the amount of charge that can be induced on tankers and the potential outcome of the ignition of the atmosphere, bonding reels were replaced with earth monitoring systems that were designed to monitor the integrity of the road tanker’s connection to earth so that electrostatic charge could not accumulate on the tank or chassis of the road tanker while product was being transferred. To enhance the safety of transfers at these locations, gantry mounted earth monitoring systems normally have an interlock function that stops the movement of product if the earthing system is disconnected from the road tanker.
Even though the potential and consequences of fires is, at the very least, the same for road tankers at dedicated loading gantries, vacuum tanker service providers have not been in a position to provide this level of safety and protection of their personnel and tankers, or for their customer’s personnel and property.
Road tanker static earthing system for a petrochemical loading gantry.
Until now, vacuum tanker service providers have had to rely on very basic devices to earth their vehicles. This is simply because technology that is capable of verifying the quality of static earthing points in a mobile, quick and user-friendly way has not been available to drivers and operators. The method currently used consists of a simple earthing clamp attached to single core braided cable wound onto a reel.
Very often, vacuuming operations will be carried out on facilities and remote locations where “designated” earthing points may not be tested on a regular basis, are not accessible or do not exist. (More detail on earthing points is provided on page 3 of this article).
Bulk transportation companies can also have the same difficulties when they deliver product to customer sites where earthing systems are not up to current specifications, or worse still, are not installed. When compared to the performance and safety of static earth monitoring systems, single core bonding reels have several major drawbacks.
Example of basic bonding reel
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Bonding reels cannot inform the driver that the clamp has penetrated through potential resistors to the flow of static electricity. Rust and paints coatings can prevent clamps from making a solid, low resistance connection to the metal of the object performing the earthing function.
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Bonding reels cannot monitor the tanker’s connection to the earthing point for the duration of the transfer process. If the clamp’s connection to the earthing point is compromised, the drivers and operators will have no way of knowing this as they will be concerned with the safe and secure transfer of material.
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When the driver needs to connect the reel to secondary earthing points (e.g. pipe or structural support beam), the bonding reel cannot verify that the earthing point actually has a verifiable connection to a True earth ground.
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On many customer sites electricians are required to perform resistance readings with multi-meters to verify that the tanker has a 10 ohm or less bonded connection to a designated earthing point, via the bonding reel. This method has several major drawbacks.