1. The Risk Landscape: Fugitive Emissions and Explosive Atmospheres
In any facility handling flammable liquids or gases, the primary safety objective is to prevent the formation of an Explosive Gas Atmosphere. However, industrial operations inherently involve Fugitive Emissions—small, chronic leaks from process equipment such as valve packings, pump seals, and flanges.
Statistics indicate that major leaks (>10,000 ppmv) occur in approximately 1.18% of gas plant components annually. Without regular ATEX inspections, these minor leaks can go undetected, eventually reaching the Lower Flammable Limit (LFL)—the minimum concentration of a gas in air that can ignite.
2. Standardized Framework: IEC 60079-10-1 and IEC 60364
An effective audit must bridge the gap between hazardous area protection and general electrical safety:
- IEC 60079-10-1 (Hazardous Area Classification): This standard provides the methodology for identifying the Source of Release and determining the Grade of Release (Continuous, Primary, or Secondary). It dictates the extent of Zone 0, 1, and 2.
- IEC 60364 (Low-Voltage Installations): While IEC 60079 focuses on the “Ex” protection, IEC 60364 ensures the fundamental electrical infrastructure is sound. This includes verifying Earthing and Bonding to prevent static discharge and ensuring Protection Against Overcurrent so that cables do not reach their Auto-Ignition Temperature (AIT).
3. Critical Audit Components: Ventilation and Dilution
A central pillar of electrical safety in depots and fuel stations is the use of ventilation to mitigate hazards.
- Adequate Ventilation: This is defined as air movement sufficient to keep gas concentrations below 25% of the LFL.
- Air Changes per Hour (ACPH): For enclosed locations, a minimum of 6 ACPH is often required to maintain a safe environment.
- Degree of Dilution: Annual audits evaluate the Ventilation Velocity to determine if the dilution is High, Medium, or Low. If an audit finds that ventilation has been obstructed or fans have degraded, a Secondary Grade release that was previously classified as Zone 2 might dangerously escalate to a Zone 1 or Zone 0.
4. Technical Documentation and Equipment Selection
A comprehensive Electrical Safety Audit verifies that the “as-built” facility matches the Hazardous Area Classification (HazLoC) drawings. Key data points that must be confirmed annually include:
- Gas Groups: Ensuring equipment is rated for the correct gas (e.g., Group IIA for gasoline/methane).
- T-Codes (Temperature Class): Verifying that the maximum surface temperature of electrical equipment is safely below the AIT of the stored fuel.
- Ingress Protection (IP Rating): Checking that seals and enclosures prevent the entry of moisture or dust which could cause internal sparking.
5. Personnel Competency: The IECEx Scheme
The reliability of an inspection is only as good as the inspector. The IECEx Scheme provides a global benchmark for Personnel Competence. Annual audits should be conducted or overseen by individuals holding specific Units of Competence:
- Unit Ex 007: Visual and Close Inspection (identifying obvious surface defects).
- Unit Ex 008: Detailed Inspection (in-depth checks requiring enclosures to be opened).
- Unit Ex 010: Performing Audit Inspections of electrical installations.
6. Conclusion: Reducing the Cost of Ownership
Annual ATEX inspections and electrical safety audits are not merely a “check-the-box” regulatory exercise. They are essential for managing the Cost of Ownership by identifying equipment degradation early and preventing catastrophic explosions. By strictly adhering to the quantitative methods of IEC 60079-10-1 and the installation requirements of IEC 60364, operators of fuel stations and oil depots ensure that Ignition Sources are strictly controlled, protecting both personnel and infrastructure from the ever-present risks of explosive atmospheres.