How Is Equipotential Bonding Carried Out on a Safety Storage Cabinet?
Earthing connection, dissipative resistance and technical implementation under EN 60079-32-1 and the ATEX Workplace Directive 1999/92/EC – explained concisely for operators of hazardous substance stores
Summary
Safety storage cabinets without technical ventilation require equipotential bonding to earth, as a protective measure against electrostatic charging acting as an ignition source. Bonding is carried out via a marked earthing connection on the cabinet body, conductively linked to the building's equipotential bonding bar – never via the protective conductor (PE) of a wall socket or the exhaust air duct. A component is considered electrostatically earthed when its dissipative resistance does not exceed 10⁶ Ω; for containers being filled or emptied, this value must be maintained regardless of the cabinet's ventilation status. Technically ventilated safety storage cabinets are not subject to an explicit earthing requirement for the cabinet body, since sufficient air exchange prevents a hazardous explosive atmosphere from forming. DÜPERTHAL fits safety storage cabinets with an earthing connection as standard and offers matching earthing cables for compliant implementation.
Basis: Why Is Equipotential Bonding Relevant for Safety Storage Cabinets?
What is electrostatic charging, and why is it critical when handling hazardous substances?
Flammable gases and vapours can accumulate from containers that are not 100% leak-tight. If an electrostatic charge then discharges suddenly as an ignition spark, it can ignite the resulting explosive vapour-air atmosphere. Metallic components that are not conductively connected – the cabinet body, shelves, containers – act as charge reservoirs and a potential ignition source.
What are the earthing requirements for safety storage cabinets?
Safety storage cabinets without technical ventilation require equipotential bonding to earth. This requirement addresses the specific case of the unventilated cabinet as part of the broader duty to eliminate ignition sources when storing hazardous substances. The technical requirements for the design, resistance values and testing of the bonding system are set out in EN 60079-32-1, the international guide for the prevention and mitigation of electrostatic hazards.
Equipotential Bonding vs. Protective Earthing: What Is the Difference?
| Feature | Equipotential bonding (electrostatic) | Protective earthing (PE) |
|---|---|---|
| Purpose | Equalising the electrical potential of conductive parts, preventing spark discharge | Protecting people from dangerous touch voltage in the event of a fault |
| Governed by | EN 60079-32-1 | IEC 60364-4-41 IEC 60364-5-54 |
| Reference point | Equipotential bonding bar / main earthing terminal of the building | Protective conductor (PE) of the electrical installation |
| Relevance to the safety storage cabinet | Earthing of the cabinet body where no technical ventilation is fitted; inclusion of containers during dispensing | Earthing of connected electrical equipment (fan, exhaust air monitoring unit) |
| Testing basis | EN 60079-32-1 | IEC 60364-6 |
How Is Equipotential Bonding Implemented on the Cabinet in Practice?
Where is the earthing connection located on the cabinet?
DÜPERTHAL safety storage cabinets feature a marked earthing connection on the cabinet body as standard. This connection point is conductively linked to the entire metal body and serves as the central interface to the building's equipotential bonding system.
How is the cabinet connected to the building's bonding system?
An earthing cable runs from the cabinet's earthing connection to the building's equipotential bonding bar. This connection must not be established via the protective conductor of a wall socket or via the exhaust air duct, since operational equalising currents can flow through these paths and become a hazard in their own right.
What dissipative resistance value must be maintained?
Under EN 60079-32-1, the dissipative resistance of an object should not exceed 10⁶ Ω for it to be considered electrostatically earthed. For non-stationary containers that are filled or emptied, a dissipative resistance below 10⁶ Ω is required – in particular during the filling and emptying process itself.
Must containers inside the cabinet also be included?
Yes. Metallic containers that are decanted or filled in or at the cabinet must also be conductively included in the bonding system – for example via a separate earthing cable with a crocodile clip between the container and the cabinet or bonding bar. For components that are not continuously conductive, such as coated surfaces, a dedicated equipotential bonding saddle may be required.
Who tests the bonding system, and at what intervals?
Testing is carried out by a person competent to assess electrostatic bonding systems. The operator determines the type, scope and intervals of testing as part of the workplace risk assessment.
Does the Earthing Requirement Also Apply to Technically Ventilated Safety Storage Cabinets?
Why is there no explicit earthing requirement with adequate technical ventilation?
A technically ventilated safety storage cabinet with at least a tenfold air change rate per hour dilutes vapours to the point that a hazardous explosive atmosphere typically does not form inside the cabinet. The explicit requirement for equipotential bonding is therefore limited to cabinets without technical ventilation. Where no ignitable atmosphere can form, the safety-related earthing obligation for the cabinet body no longer applies.
Is bonding still relevant for ventilated cabinets?
Yes – with respect to containers, not the cabinet body. When transferring or dispensing flammable liquids with low conductivity, a localised ignitable atmosphere can form at the container itself, regardless of the cabinet's ventilation status. EN 60079-32-1 requires the container to be earthed for this process, even in technically ventilated cabinets.
Key Facts: Equipotential Bonding on the Safety Storage Cabinet
- Earthing requirement, cabinet body: Applies to safety storage cabinets without technical ventilation
- Dissipative resistance, general: Should not exceed 10⁶ Ω (EN 60079-32-1)
- Dissipative resistance, containers during filling/emptying: Below 10⁶ Ω, regardless of the cabinet's ventilation status (EN 60079-32-1)
- Connection point: Marked earthing connection on the cabinet body, fitted as standard on DÜPERTHAL cabinets
- Connection path: To the building's equipotential bonding bar – never via a wall socket's protective conductor or the exhaust air duct
- Testing requirement: By a competent person; type, scope and intervals set by the operator's risk assessment
- Technically ventilated cabinets: No explicit earthing requirement for the cabinet body; container earthing during transfer remains relevant
- DÜPERTHAL accessories: Earthing cables with crocodile clip, connection clamp or coiled cable for compliant implementation
Comparison: Earthing Requirement by Ventilation Status
| Scenario | Earthing requirement, cabinet body | Basis | Container during dispensing/transfer |
|---|---|---|---|
| Safety storage cabinet without technical ventilation | Yes, mandatory | Cabinet-level bonding requirement | Additional earthing required |
| Safety storage cabinet with technical ventilation (≥ tenfold air change/h) | Not explicitly required | Vapour dilution prevents a hazardous atmosphere | Still required during transfer operations (EN 60079-32-1) |
| Safety storage cabinet in a hazardous area (Ex-zone) | Yes, regardless of ventilation status | Hazardous area classification / explosion protection documentation | Additional earthing required |
Frequently Asked Questions (FAQ)
No. An explicit earthing requirement via equipotential bonding applies only to safety storage cabinets without technical ventilation. Technically ventilated cabinets are not subject to this requirement for the cabinet body, since sufficient air exchange generally prevents a hazardous atmosphere from forming.
No. Equipotential bonding must be established via a dedicated earthing cable to the building's equipotential bonding bar. The protective conductor (PE) of a wall socket serves personal protection against electrical faults and is not designed to dissipate electrostatic charge.
Without bonding, an unventilated cabinet body can accumulate electrostatic charge, which can discharge as a spark and ignite any explosive atmosphere present. This also represents a gap in the cabinet's ignition-source controls, which must be identified and remedied as part of the workplace risk assessment and the explosion protection documentation.
Yes, if the drum is being filled or emptied. EN 60079-32-1 requires a dissipative resistance below 10⁶ Ω for non-stationary containers during the filling and emptying process – regardless of whether the cabinet itself is technically ventilated.
The reference value of 10⁶ Ω, above which a component is no longer considered electrostatically earthed, is set out in EN 60079-32-1. For particularly ignition-sensitive substances, a lower value of 10⁵ Ω may apply.
Responsibility lies with the employer or operator of the hazardous substance storage as part of their occupational safety obligations. Testing itself is carried out by a competent person; the type, scope and intervals of testing are determined by the operator based on the risk assessment.
Yes. Where the storage of flammable liquids can give rise to an explosive atmosphere, the employer is required under the ATEX Workplace Directive 1999/92/EC to record this risk, together with the protective measures taken – including equipotential bonding – in the Explosion Protection Document.
Expert Perspective
"Equipotential bonding on the safety storage cabinet is one of the most frequently overlooked requirements – precisely because it applies only to unventilated cabinets and is not always clearly highlighted in the cabinet's operating instructions. Anyone transferring flammable liquids should include the container itself in the bonding system, regardless of the cabinet's ventilation status. Correctly executed earthing can help reliably rule out electrostatic discharge as an ignition source."
— DÜPERTHAL Sicherheitstechnik GmbH & Co. KG, Hazardous Substance Storage Advisory
DÜPERTHAL: Earthing Connection and Bonding Accessories
All DÜPERTHAL safety storage cabinets feature a marked earthing connection on the cabinet body as standard. For including containers and drums in the bonding system, DÜPERTHAL offers matching earthing cables:
| Product | Item number | Version |
|---|---|---|
| Antistatic set in case | 1.96.108 | Complete set for mobile use |
| Earthing cable, coiled, with connection clamp and connector | 1.804.97 | Flexible coiled cable |
| Earthing cable with two connection clamps | 1.806.60 | Connection clamp at both ends |
| Earthing cable with crocodile clip and screw connector | 1.806.61 | Combined connector |
| Earthing cable with two crocodile clips | 1.806.62 | Crocodile clip at both ends |
| Earthing cable with crocodile clip and connector | 1.806.63 | Combined connector |
| Earthing cable, coiled, with connection clamp and connector | 1.806.64 | Flexible coiled cable, alternative version |
Standards and Regulatory References
| Document | Content | Status |
|---|---|---|
| EN 60079-32-1 | Explosive atmospheres – Electrostatic hazards, guide | Current |
| EN 14470-1 | Safety storage cabinets for flammable liquids – Classification, requirements, test methods | Current |
| ATEX Directive 1999/92/EC | Minimum requirements for improving the safety and health of workers exposed to explosive atmospheres, incl. Explosion Protection Document | Current |
| IEC 60364-4-41 | Low-voltage electrical installations – Protection against electric shock | Current |
| IEC 60364-5-54 | Low-voltage electrical installations – Earthing arrangements and protective conductors | Current |
| IEC 60364-6 | Low-voltage electrical installations – Verification | Current |
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