Assessing suitability of earthing arrangements

HSE inspections


Our client is one of the largest bulk liquid storage companies in the UK, handling a wide range of hazardous and non-hazardous liquids, such as chemicals and fuels. It operates more than 5.8 million cubic metres of storage capacity in numerous locations across Europe.

As an operator of COMAH Upper Tier sites, it is subject to regular HSE inspections, and, following a recent visit, was left with actions to verify that their earthing arrangements at nine of their main substations were suitable for ongoing operations. Without the in-house skills to address the problems, the client sought Covol’s expertise to ensure compliance within the 60-day deadline.


Following the HSE inspection, the client was left with two actions to undertake to ensure compliance:

  • To determine if the HV and Primary LV distribution system earthing arrangements meet the functional and safety criteria within the relevant British Standards and best practice.
  • Following the assessment, to ensure relevant documentation reflects the calculated earth resistance values, and providing such documentation to the HSE as proof of completion.


Following a site survey to understand the scale of their operations and the specifics of what was required to ensure compliance, we conducted an earthing study at each terminal.

Results obtained from the earthing study indicated that the existing arrangement was in reasonable condition, and the calculated step and touch potential values were below the maximum permissible values.

We also found that the earth fault protection installed on the switchgear would limit the duration of any earth fault, isolating the source of supply and protecting the system.

The step and touch potentials calculated within the study were for the main HV switchroom/transformer compound areas. The substation’s step and touch potentials were below the respective safety criteria as defined in the relevant standards and guidance and therefore were not considered to be a safety issue.

For the purpose of the study, all earth rods/matrixes installed at each substation were considered to be interconnected. As such, appropriate PPE, including correct footwear, was worn when accessing these areas.


Following our assessment of the sites, Covol worked closely with the client to ensure all locations met the requirements of the standards and satisfied HSE concerns, and to support them in ensuring that this would remain the case.

For each of the relevant sites, we:

  • Carried out an earthing study report for each of the substations and provided calculations of earth fault levels, ground potential rise, and step and touch potential limits, including safety measures to be taken when accessing these areas.
  • Tabulated the resistance of each of the earth grids for the substations, along with specifying the maximum allowable resistance for each of the earth grid, to meet safety limits.
  • Advised as to whether the above met the functional and safety criteria specified in the relevant standards.
  • Advised that the earthing arrangements/grid resistance can change due to environmental factors and therefore, the range of resistance values provided can be utilised as part of the periodic testing of the arrangement.

In total, the period of Covol’s involvement was two months, followed by a project handover and addressing any potential gaps and observations that required our further attention or support.


The client can now be assured they are operating a safe and compliant plant, and also has the tools to continually assess their arrangements independently.

No matter how well prepared a client is, knowledgeable, well-trained HSE inspectors can and will uncover weak points, gaps and potential safety hazards or issues on a plant, and will often find regulations some clients may have limited knowledge and experience of.

The Covol Engineering team are proud to offer a proactive service, working with clients to resolve issues before they arise, and ensuring safety and compliance across site all year round.