The Importance of Static Control in Hazardous (Ex) Environments

Figure 1: Image of static electricity explosion which occurred at Barton Solvents, Kansas²

Key Findings: The Chemical Safety Board determined that several factors likely combined to produce the initial explosion:

• The tank contained an ignitable vapour-air mixture in its head space.
• Stop-start filling, air in the transfer piping, and sediment and water (likely present in the tank) caused a rapid static charge accumulation inside the VM&P naphtha tank.
• The tank had a liquid level gauging system float with a loose linkage that likely separated and created a spark during filling.
• The MSDS for the VM&P naphtha involved in this incident did not adequately communicate the explosive hazard.

Good Examples of Methods of Static Control

Finch has found some good examples across different sites and industries to help control static discharge. Below are some examples which we have seen:

• Use of an Earth-Rite unit manufactured by Newson Gale (other equivalent manufacturers of similar technology have also been seen). The Earth-Rite unit has typically been used for earthing road tankers, mobile vessels, or drums and there is a red and green light present to show negative and positive ground connection. The light stays red when an earth hasn’t been found and turns green when the clamp has been properly earthed. Typically, there is an interlock in the system so the tanker offload cannot be completed unless the earth is connected and turns green. This is great visibility for the operators to help support them to identify whether the tanker or drum is properly grounded or not.

Figure 2: Example of Earth-Rite unit by Newson Gale for grounding connection³

• Use of suitable bonding across flanges of pipework when non-conducting gaskets are used to reduce the likelihood of static build up within the pipework. See the example in Figure 2 below. It is a common but incorrect assumption that bolted flange connections provide sufficient electrical continuity between pipework sections. Often the metal-to-metal contact between the flange bolts can be unreliable due to corrosion or rust on bolts, paints or coatings and contaminants on the mating surfaces. Without bonding, static charge can build up on one side of the flange and discharge as a spark. Bonding straps ensure a low resistance path (<0.1 Ω is typical) across the joint. This is why it is important to check the electrical continuity as part of a preventative maintenance programme to ensure there is still a low resistance electrical path.
• 

Figure 3: A good example of pipe flange jumper with non-conducting gasket⁴

Best Practices for effective Static Control

To ensure effective static control in Ex environments:

• Undertake detailed hazard assessments across all processes, explicitly addressing ignition risks associated with static electricity.
• Ensure all key equipment and pipework are effectively bonded and grounded to prevent the accumulation of static electricity.
• Implement a programme of routine inspection and testing of grounding and bonding systems to confirm their integrity, continuity, and ongoing effectiveness in controlling static electricity hazards.
• Train personnel on electrostatic risks.
• Use certified Ex equipment suitable for hazardous areas.
• Anti-static / dissipative clothing and footwear for personnel working in Ex areas
• Follow applicable standards and guidelines.

Conclusion

Static control is a critical process safety component in hazardous (Ex) environments. While often invisible, electrostatic hazards can have devastating consequences if ignored. By implementing proper grounding and bonding, using appropriate materials, following regulatory standards, and maintaining awareness, organisations can significantly reduce the risk of ignition and ensure safe operations.

In Ex environments, controlling static electricity is not just about managing charge, it is about protecting lives, assets, and the integrity of industrial processes.

References

1. Chemical Safety Board (CSB) – Barton Solvents Case Study – pdf
2. One Spark Article from NFPA – One Spark | NFPA Journal
3. Newson Gale Grounding and Bonding Handbook Volume 5 – Leading the way in hazardous area static control
4. Research Gate Practical Bonding of Industrial Piping in Hazardous Areas: Standards, Implementation, and Field Examples: Field-based grounding methods for safety in oil & gas operations Flange jumper bonding schematic across non-conductive gasket (per IEC… | Download Scientific Diagram