Grounding Multiple Containers in a Hazardous Atmosphere
Without suitable grounding provisions on site, electrostatic charges can accumulate on metal containers, such as drums and hazardous area suitable Ex IBCs during the handling of flammable liquids in Ex/HAZLOC areas. Once such handling operations begin, these metal containers can quickly generate enough voltage for an electrostatic discharge to occur. Implementing suitable electrostatic grounding & bonding measures is a critical step to mitigating against the risks posed to plant personnel and assets from ignitions caused by electrostatic discharges.
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Preventing Flammable Liquid Ignition
The storage and handling of flammable liquids is a necessity for many chemical companies’ daily operations. Once a hazardous area classification has been assigned to the area(s) in question, attention should turn to the control of potential ignition sources in these areas.
When completing a risk assessment or hazard and operability (HAZOP) analysis of such operations, many can and will identify electrostatic discharges as a potential ignition source. Whilst best practice guidance such as IEC TS 60079-32-1:2013+AMD1:2017 ‘Electrostatic hazards, guidance’ provides advice on the use of insulating and semi-conductive materials, a common challenge plant managers and personnel face is the grounding of potentially isolated metal plant equipment within a hazardous area.
If metal plant equipment is not suitably grounded prior to commencing work involving the handling of flammable liquids, electrostatic charges can quickly accumulate on the equipment once an operation begins. This causes voltage levels to increase, and once an object reaches a critical ‘breakdown voltage’ the risk of an electrostatic discharge is present. Provided the concentration of flammable gas and/or vapor is within the upper and lower explosion limits of the material(s) in question, and the energy level of the discharge exceeds the minimum ignition energy (MIE) of the surrounding hazardous atmosphere, an ignition can occur.
Target ≤ 10 Ω
The immediate priority is to ensure the presence of a local plant ground point, typically a pre-verified ground bar capable of safely dissipating electrostatic charges to ground. Once verified, attention can turn to ensuring all metal plant equipment shares an equipotential bond to the nominated ground point, taking it to “earth/ground potential” for the safe dissipation of electrostatic charges.
Best practice guidance such as IEC TS 60079-32-1:2013 +AMD1:2017 & NFPA 77 ‘Recommended Practice on Static Electricity, (2019 Edition)’ can be used to establish what constitutes a repeatable and reliable ground connection for metal plant equipment. Although, ≤ 1 megohm (1 x 106 Ω) is generally considered “adequate” (NFPA 77, 7.4.1.3) for the purpose of electrostatic charge dissipation, this should not be confused as being indicative of a repeatable and reliable connection to ground for all metal connections. In fact, both IEC TS 60079-32-1 & NFPA 77 conclude that any ground connection exceeding 10 Ω for metal plant equipment can be a sign of “loose connections or corrosion” that requires further investigation.
Most fixed plant equipment will typically possess a structural ground connection that can be relied upon if properly maintained and tested. However, ensuring a ≤ 10 Ω ground connection for portable metal containers such as drums, hazardous area suitable Ex or stainless steel IBCs, mixing pans and buckets can be far more of a challenge with several portable containers being used simultaneously.
Multiple Metal Containers
Many users will opt for a grounding system that continuously monitors the connection as far as the designated ground point in order to mitigate against loose or corroded connections. A system that monitors to a 10 Ω permissive threshold provides continuous indication of a connection that adheres to best practice recommendations.
Multi-Channel Ground-Monitoring System
When multiple electrostatic ground monitoring connections are required in a process area, the use of “traditional” single channel monitoring systems that would each require power in the 110/230 V AC range may not be the most cost effective, or flexible option in terms of installation requirements. Therefore, the use of a multi-channel ground monitoring system such as the Earth-Rite® MULTIPOINT II should be considered. This system allows for the simultaneous monitoring of up to eight items of process equipment to a 10 Ω permissive threshold from a single ATEX, IECEx, NEC & CEC certified monitoring control unit, and a 110/230 V AC power supply unit.
Earth-Rite® MULTIPOINT II features and benefits:
- Monitors to a 10 Ω permissive threshold: Demonstrates compliance with internationally recognized best practice guidance such as IEC TS 60079-32-1 & NFPA 77.
- Continuous Monitoring: Continually monitored connections with visual indication reduce the need for costly and time consuming electrical continuity checks. These checks should be undertaken by qualified hazardous area specialist personnel who may not always be accessible.
- Application Flexibility: A simple, easy-to-use dipswitch on the monitoring unit PCB allows the user to add/remove channels should their application requirements change.
- Indication Flexibility: Additional remote indicator stations can be positioned local to each monitoring connection, so the operator has an easily accessible indication as to a specific channel’s current state via the red (non-permissive) and green (permissive) LEDs local to each process. This enables a single system to monitor multiple metal containers within a broad plant area.
- Installation Flexibility: The indicator stations are powered by intrinsically safe Ex ia circuits distributed from a single in-line marshalling junction box (supplied with the system). This can be advantageous for equipment installers who may otherwise face the prospect of installing several individually powered single-channel systems in an Ex/HAZLOC area. If you combine the installation flexibility afforded by the Earth-Rite® MULTIPOINT II system and the expected upfront saving of purchasing one multi-channel ground monitoring system over several individual units, the overall value differential can be favorable.
- Process Interface Flexibility: The voltage-free contacts located in the power supply unit enable the user to interface with process control devices such as pumps, PLCs and valves to inhibit their operation until a permissive output is obtained from the corresponding channel(s) (see Fig. 1). Each channel is allocated a single volt-free contact to enable complete segregation between distinct processes. Meanwhile, an additional group relay allows for several or all eight channels to be grouped using a simple dipswitch on the power supply unit, thus ensuring that all grouped channels must be permissive for the group relay to energize.
Note – Process interface / interlock configurations should always be risk assessed by a suitably qualified entity, taking all process parameters into consideration.
- Reliability: The Earth-Rite® MULTIPOINT II uses secure and reliable software based on the MISRA C protocol. Watchdog circuits located on both the monitoring and power supply units can activate a fail-safe relay also located in the power supply unit.
You can read the associated Case Study here, where a customer specializing in the production of resins, improved process safety and efficiency by installing the Earth-Rite® MULTIPOINT II.
Newson Gale
Newson Gale has been providing static grounding and bonding solutions to the hazardous process industries for over 40 years. In that time we have developed a wide range of solutions, and many “industry firsts”, to cater for a wide range of industry processes, installation settings and end user preferences. Our hardware is designed to support our customers in demonstrating compliance with industry guidance like IEC TS 60079-32-1 and NFPA 77 and all possess the necessary and most up to date ATEX, IECEx and North American hazardous area approval certificates.
Find out more about out Bond-Rite® or Cen-StatTM Range of products.
Whether your communication preference is through e-mail, video conferencing or by phone our global team of sales engineers will be more than happy to discuss your processes and outline the range of grounding and bonding solutions that match your requirements.
If you have any questions relating to the topics discussed in this article, please contact Newson Gale.
Newson Gale
Newson Gale has been providing static grounding and bonding solutions to the hazardous process industries for over 40 years. In that time we have developed a wide range of solutions, and many “industry firsts”, to cater for a wide range of industry processes, installation settings and end user preferences. Our hardware is designed to support our customers in demonstrating compliance with industry guidance like IEC TS 60079-32-1 and NFPA 77 and all possess the necessary and most up to date ATEX, IECEx and North American hazardous area approval certificates.
Whether your communication preference is through e-mail, video conferencing or by phone our global team of sales engineers will be more than happy to discuss your processes and outline the range of grounding and bonding solutions that match your requirements.
If you have any questions relating to the topics discussed in this article, please contact Newson Gale.