Earth-Rite® MGV
Newson Gale’s dedicated truck-mounted static grounding system
Learn more about Industry Standards and Guidelines relating to static electricity in explosive atmospheres:
- Gain insights into the specification of HAZLOC-certified equipment.
- Understand standards referenced in the industry.
- Learn about the selection of HAZLOC equipment.
- Evaluate competency requirements for personnel.
- Navigate HAZLOC equipment documentation.
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P1 = one GRP enclosure
Static Grounding for Vacuum Truck Transfer Operations
The Earth-Rite® MGV system runs two essential system checks, allowing the vehicle to dissipate static charges for the duration of the transfer process.
The Earth-Rite® MGV System Checks:
- Static Ground Verification: The MGV system ensures the connection resistance of the object that is identified as the ground source to earth is low enough to safely dissipate static charges from the truck.
- Continuous Ground Loop Monitoring: When the Static Ground Verification process is confirmed, the Earth-Rite® II MGV system continuously monitors the connection resistance of the truck to this verified grounding point for the duration of the transfer process. This connection resistance must be maintained at 10 ohms or less for the duration of the transfer process.
Remember to always follow a “Clamp On First, Clamp Off Last” protocol by attaching the grounding clamp before starting any operation, and keep it connected until all transfer activities are complete.
Overview of the Earth-Rite® MGV
The Earth-Rite® MGV is a truck-mounted static grounding system that provides vacuum and tanker truck operators, and bulk distributors with a means of connecting their trucks to ground to mitigate the effect of electrostatic charge generation caused by the transfer of materials in hazardous locations.
The transfer of flammable materials into and out of tanker trucks normally takes place at dedicated tanker truck loading gantries, where static grounding systems are installed at the gantry. However, the transfer of flammable materials can take place in less controlled circumstances.
For example, vacuum tankers can be used in scenarios ranging from storage tank cleaning to the recovery of spills at multiple locations around refineries and large chemical manufacturing complexes.
To have static grounding systems installed at every location on large sites where vacuum truck operations are carried out would most likely be cost-prohibitive. Bulk distributors may have to deliver products to locations where effective static grounding measures are not in place.
For mobile grounding applications, many fleet operators utilize basic clamps and cable reels; however, basic methods like this cannot test the grounding point to assess if it has a connection to the general mass of the earth, nor can they monitor the tanker’s connection to the grounding point for the duration of the material transfer operation.
Some sites, like refineries and large chemical manufacturing complexes, will only permit transfers to take place after one of their Qualified Electrical Personnel (QEP) has carried out a resistance meter test between the designated grounding point local to the transfer operation and the tanker.
Some drawbacks of this method are:
- The vacuum truck team can be waiting for long periods until a QEP is available to perform resistance reading checks.
- The tanker’s ground connection cannot be monitored for the duration of the transfer operation, as the vacuum tanker team is engaged in tasks to transfer the material.
Having a truck-mounted static grounding system that possesses the same capability as grounding systems typically used at loading gantries provides a higher level of flexibility. At the same time, it enhances the method of verifying and monitoring the connection to the grounding point when compared with basic clamps and cable reels, and enhances safety to the plant and personnel.
It should be noted that all metal parts should be bonded together. This ensures that electrostatic charge cannot accumulate on isolated components (e.g., cabinets, man lid covers, etc.) when grounded by the Earth-Rite® MGV.
Operation of the Earth-Rite® MGV
Operating parameters
Primary: Permanent ground rod/network
Secondary: Permanent “man-made” structure
Temporary ground rods
The threshold resistance of ≤ 1000 ohms is advised in NFPA 77 “Recommended Practice on Static Electricity”*. This publication cites that HAZMAT teams engaged in material recovery operations, like tanker truck fuel and chemical spills, may need to install temporary ground rods in soil or ground local to the recovery operation. Testing of the resistance to the general mass of the earth is a one-time check, as there should be no disturbance to permanently installed ground electrodes or temporary electrodes buried in soil during the material transfer operation.
The next step is to monitor the connection between the Earth-Rite® MVG’s connection to the truck and the verified grounding point. The purpose of this function is to determine if there is a low-resistance path between the truck and the verified grounding point for the duration of the material transfer operation. The resistance monitoring threshold of ≤ 10 ohms is selected from a wide range of industry guidance for controlling static electricity in Ex operations. Independent bodies like the National Fire Protection Association (NFPA), the International Electrotechnical Commission (IEC), and CENELEC (CEN) recommend resistance levels of 10 ohms or less between the object requiring static grounding and the verified grounding point. The reason for this is that a resistance higher than 10 ohms in the circuit between the object, in this case the truck, and the verified grounding point, indicates potential compromise of the grounding circuit, like a poor initial connection to the grounding point via the grounding clamp, or loose/corroding connections that could otherwise prevent the passage of static charges to earth. In the vast majority of applications, the object requiring static grounding will be made of metal, as will the verified connections to earth. Given that the static charge is dissipating from the truck through metal connections from the tanker to the tungsten carbide teeth on the grounding clamp, 10 ohms or less resistance is an appropriate benchmark.
It is important to emphasize that the Earth-Rite® MGV is the point of contact between the tanker and the grounding point, where any static charge will be dissipated.
When both input parameters (≤1000 ohms and ≤10 ohms) are met, the Earth-Rite® MGV’s LED indicators switch from solid red to flashing green. The indicators continue to flash for the duration of the time the clamp is connected to the grounding point. When the system becomes permissive, a pair of NO/NC dry/volt-free contacts changes state.
*NFPA 77 2024 “Recommended Practice on Static Electricity”
7.3.1.6.1
“Where the bonding/grounding system is all metal, resistance in continuous ground paths is measured to verify mechanical integrity. (See A.3.3.2.) Such systems include those having multiple components. Greater resistance usually indicates that the metal path is not continuous, usually because of loose connections or corrosion. A permanent or fixed grounding system that is acceptable for power circuits or for lightning protection is more than adequate for a static electricity grounding system. Static grounds should be made to the building steel, if possible. Grounding to power grounds or lightning protection systems is not recommended.”
7.3.1.6.1.1
“In field-based situations such as HAZMAT response operations or flammable/combustible material spill control and transfer, it might be necessary to establish a temporary or emergency grounding system in a remote location in order to dissipate electrostatic charges. In such situations, various types of conductive grounding electrodes can be used, such as rods, plates, and wires, which are sometimes used in combination to increase surface area contact with the earth. If the purpose of the temporary grounding system is to dissipate static electricity, a total resistance of up to 1 Kiloohm (1000 ohms) in the ground path to earth is considered adequate. This can be measured using standard ground resistance testing instruments and is realistically and quickly achievable in most types of terrain and weather conditions.”
7.3.1.9
“Permanent bonding or grounding connections can be made by brazing or welding. Temporary connections can be made using bolts, pressure-type bonding clamps, bonding balls, or other special clamps or means of connection. Pressure-type bonding clamps should have sufficient pressure to penetrate any protective coating, rust, or spilled material to ensure contact with the base metal. When making connections through any surface that is compromised (e.g., by debris, by corrosion), the connection should be verified with a low voltage ohmmeter or similar device (see A.3.3.2).”
A.3.3.2 Bonding
“A resistance not exceeding 10 ohms for copper wire or 25 ohms for stainless steel or other metals is typically found in practice. Higher resistances could indicate a lack of mechanical integrity.”
IEC 60079-32-1 “Explosive Atmospheres Part 32-1 Electrostatic Hazards – Guidance”.
8.8.4 Vacuum trucks
“Vacuum trucks should be connected to a designated site earth before commencing any operations. In areas where site earths are not present, i.e. where portable earthing rods are required, or there is doubt regarding the quality of site earths, the resistance to earth should be verified prior to any operation. When the truck is connected to a verified earth, the connection resistance between the truck and verified earth should not exceed 10 Ω for pure metallic connections or 1 MΩ for all other connections.”
13.2.2 Practical criteria
“Although a value of up to 1 MΩ is acceptable for static dissipation, values above 10 Ω may give an early indication of developing problems (e.g. corrosion or a loose connection) and should be investigated. It is important that all connections are reliable, permanent and not subject to deterioration”.
Intrinsically safe (IS) circuits
Because the truck is engaged in the transfer of hazardous materials in hazardous locations, the system uses an intrinsically safe signal with the highest level of protection ‘ia’.
The benefit associated with this feature is that the energy in the electrical circuit that verifies and monitors the resistance of the grounding point will not exceed levels that have the potential to ignite all classifications of gases, vapors, and dust. This is particularly relevant for scenarios where containment of gases, vapors, and dust may be difficult to enforce due to the complexity of some operations (e.g., tank cleaning, spill recovery).
At a minimum, any electrical equipment used in classified hazardous locations must carry the appropriate level of hazardous location system certification.
Output contacts
A pair of dry/volt-free NO/NC contacts and an optional single intrinsically safe output contact can be selected for controlling equipment like pumps or valves to prevent material transfers from taking place if the tanker is not grounded. Additional equipment, like strobe lights, can also be interlocked with the Earth-Rite® MGV, especially for scenarios where the drivers/operators may need a secondary method of indication, as their view of the primary indicators on the MGV may be obstructed during material transfer operations.
Please note that in an emergency shutdown scenario, e.g., the connection to ground has been compromised during the material transfer procedure, the product may continue to flow into or out of the tanker once the transfer process has begun. This could lead to the accumulation of static electricity on the tanker or objects connected to the tanker, e.g., hoses. If a HAZOP assessment highlights the potential for such a scenario to occur, additional measures may need to be put in place. For example, it may be possible to determine the charge relaxation time of the material and issue an SOP to operators so that they do not approach the tanker or hoses during the specified time period. Site operators should retain the services of a static control consultant if this scenario could arise.
Installation
The Earth-Rite® MGV is simple to install and operate. Unlike many other static grounding systems, the Earth-Rite® MGV is designed to operate “out of the box”. It does not require any calibration at the point of installation nor throughout its time in use. Because the tanker truck is electrically isolated from the ground by its tires, it has a capacitance relative to ground. A simplified model of tanker truck capacitance is the parallel plate capacitor, and tanker trucks are generally thought to have a capacitance value of greater than 1000 picofarads (pF). Newson Gale’s own research into tanker truck capacitance shows high variations of capacitance depending on several variables. It is for this reason that the Earth-Rite® MGV, via its patented method of operation, can cater to such variables, thus eliminating the need to calibrate the system at the point of installation or throughout its period in use.
Testers can be purchased with the system to ensure it is operating within the required design parameters highlighted above (see Operating parameters section). It should be noted that the system must be installed in accordance with the accompanying Instruction Manual, as failure to do so will invalidate the HAZLOC certificate of the system.
Depending upon the model selected, an installation kit consisting of glands and cabling can be specified with the system.
The Earth-Rite® MGV is powered by the tanker’s 24v/12v DC battery.
Please note that a HAZLOC-qualified person is required to carry out the installation of HAZLOC-certified products, as per the product manual. If you have any doubts with respect to the installation requirements of Newson Gale equipment in hazardous locations, one of our hazardous location-experienced engineers will be happy to support you.
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