Industries such as pharmaceuticals, food and beverage, chemicals and paints and coatings, where powders and solvents are used in key processes, are at particular risk due to the hazardous nature of the materials. Fires and explosions can occur as a result of uncontrolled static discharge from plant, people and materials, and these commonly result in civilian injuries and fatalities, as well as significant financial losses in direct property damage and plant downtime.
In facilities where flammable or combustible materials are being transferred from one container to another, both vessels should be effectively bonded and grounded to prevent discharge sparks of static electricity. Accumulation of charge is always prevalent when you have moving fluids or solids and the potential for discharge is always a risk. The generated charge only becomes a problem in hazardous areas when it is allowed to accumulate on objects that are not at ground (earth) potential. The most important action an operator can take to control static electricity is to ensure any conductive objects are connected to a verified earth. Those who ignore the dangers of electrostatic discharge in hazardous environments jeopardise people and the plant alike. Flowing material can charge isolated conductors such as metal containers to unsafe levels in a short amount of time. Due to the flow of product, static charge can build up on both the materials being transferred from a drum and an equal and opposite charge on the container itself. A build-up of electrostatic charge will eventually develop enough to discharge a spark onto an object held at a different potential in an attempt to equalise the charge. This spark could cause a dust cloud to ignite in a pharmaceutical plant during transfer, or liquid in a paint mixing facility, resulting in an explosion or fire.
Eliminate the Risk; Remove the Charge
Product build-up and protective coatings on process equipment can impede the integrity of grounding clamp connections to verified earth. As a result, material on an isolated conductor such as a drum can, on occasion, be thick enough as to avoid electrostatic charge dispersion. Paint deposits have the potential to isolate the clamp connection, which means the resistance to ground is not guaranteed. You must have metal-to-metal contact between the clamp tips and the surface of the vessel to be able to achieve a low resistance to earth.
To reliably penetrate built up layers of material like rust or paint, a purpose built grounding clamp should have the ability to bite through inhibitors using pointed tips that maintain their point during their use within a heavy industrial environment. Tungsten Carbide teeth tips are powerful enough to continuously bite through coatings, rust or product deposits that a basic alligator clip or welding clamp would struggle with. Ultimately, although a clamp and cable is a suitable initial layer of protection in mitigating against the risk of an electrostatic discharge, it is based on the assumption that there is a path to earth. The optimum solution is to provide operators with a visual means of verifying a connection to equipment at risk of static charge accumulation with a resistance of 10 Ohms or less, as stated by the IEC 60079-32-1 “metallic items in good contact with earth should have a resistance to it of less than 10 Ohms”.
Visual indication and continuous ground circuit monitoring are two fundamental layers of protection that go hand in hand. Whilst Newson Gale’s Cen-Stat range of ATEX/FM approved clamps and cables provide continuity to earth, pulsing green ground status indicators provide operators with a verified visual reference point to ensure that equipment they are operating is grounded prior to, and during, the process. Monitoring proves a connection on repeated use, verifies the integrity of the grounding cable and the green light indicator enables operators to take responsibility for ensuring the equipment does not pose a static ignition risk.
“Newson Gale systems do not use arbitrary values of resistance. When our ground status indicators go green, your operators are working in compliance with NFPA, IEC, API and CENELEC industry codes of practice.”
Whilst the Bond-Rite range of systems provides visual indication of when grounding is present or lost, and continuous monitoring of the equipment’s ground resistance, it is still very much operator-dependent and susceptible to human error.
In a drum mixing application, operators may not be present throughout the duration of the process, the loss of grounding when unattended may result in hazardous levels of charge to be accumulated on the process, presenting a very real risk of static ignition. To mitigate this risk, employing a system with the ability to interlock with the process, can execute an automatic shutdown of the process equipment if a compromised ground connection is detected. Shutting down the flow of materials within the mixer will stop any further generation of static electricity and remove any risk of static ignition until operators return to resolve the earthing connection issue.
The Earth-Rite range has interlocking capability, reducing operator dependency to have constant clear line of sight to identify when the system has gone non-permissive (LED has gone red) and perform a manual shutdown. The ground loop monitoring system ensures a positive connection resistance of 10 ohms or less, as displayed on the monitoring unit via a pulsing green LED.
Despite the ever-present dangers, by eliminating the charge and the potential for an uncontrolled electrostatic discharge, the resulting ignition is eradicated. The primary mind set should be to source a grounding solution that provides the best fit for your objectives. The more layers deployed to protect against an ignition source, the more likely static will be controlled in a safe, repeatable and reliable way, day in and day out.
To help control these risks, Newson Gale offers a wide range of static grounding and bonding equipment which is made to provide optimum safety in explosive atmospheres and other hazardous environments. The Newson Gale range prevents static charge accumulating by using practical and innovative designs to ensure effective static control on three levels:
- Earth-Rite® series of static ground indicators and interlock systems
- Bond-Rite® series of self-testing static grounding clamp units
- Cen-Stat™ series of static grounding and bonding clamps, cables, reels and test instruments
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