Documenting Zone Classification
Zone classification only protects workers if it's properly documented and communicated. The ATEX Workplace Directive requires employers to document their zone classifications as part of the Explosion Protection Document. This documentation serves multiple purposes: demonstrating compliance, guiding equipment selection, informing maintenance activities, and providing a basis for future reviews.
What Must Be Documented
Article 8 of Directive 1999/92/EC requires the EPD to demonstrate "those places which have been classified into zones in accordance with Annex I." This means documentation must include:
- Identification of all hazardous areas and their zone classification
- The extent (boundaries) of each zone
- The basis for the classification decisions
- The substances present and their relevant properties
- The relationship between zones and equipment requirements
Zone Drawings
Zone drawings are the primary means of communicating classification. Effective zone drawings should show:
- Plan views showing horizontal extent of zones at relevant elevations
- Elevation views or sections showing vertical extent (critical for heavier/lighter than air vapours)
- Clear zone boundaries with dimensions or reference points
- Zone identification (Zone 0, 1, 2 for gases; Zone 20, 21, 22 for dusts)
- Source of release identification where relevant
- Equipment locations relative to zones
Colour coding is conventional: Zone 0/20 often shown in red, Zone 1/21 in yellow, Zone 2/22 in blue—though this isn't mandated. The key is consistency and clarity.
Zone Schedule
Complement drawings with a zone schedule listing each classified area, its zone type, the substances present, relevant flammability parameters, gas/dust group, temperature requirements, and the basis for classification. This tabular format aids systematic review and equipment selection.
Example schedule headings:
| Area | Zone | Substance(s) | Gas/Dust Group | T-Class/Max Temp | Basis |
|---|---|---|---|---|---|
| Pump house | Zone 1 | Petrol vapour | IIA | T3 (200°C) | Primary release from pump seals |
Classification Basis and Assumptions
Document the reasoning behind classification decisions, including:
- Sources of release identified and their grades
- Ventilation assessment (natural/mechanical, availability, effectiveness)
- Release rate estimates or calculations
- Standards or guidance used (e.g., EN 60079-10-1 methodology)
- Assumptions made (e.g., "ventilation continuously available")
- Any deviations from standard guidance and their justification
This documentation is crucial for future reviews—without understanding why a classification was made, it's impossible to assess whether changes affect its validity.
Linking to Equipment Requirements
Classification documentation should clearly connect zones to equipment requirements. For each zone, specify the minimum equipment category, required ATEX markings, and any specific requirements (gas group, temperature class). This enables straightforward verification during equipment selection and inspection.
Warning Signs
Article 7(3) requires hazardous areas to be "marked with signs at their points of entry in accordance with Annex III" where necessary. The warning sign (triangular, yellow background, "EX" letters) should be placed at entry points to classified zones. Document sign locations and ensure they're maintained.
Revision Control
Zone classification documents need revision control—version numbers, dates, approval signatures, and change history. When classifications change, old versions should be archived (for historical reference if incidents occur) and current versions clearly identified. All relevant personnel should be notified of changes.
Integration with Other EPD Elements
Zone classification doesn't stand alone—it integrates with the complete Explosion Protection Document:
- Risk assessment provides the basis for identifying hazards
- Zone classification determines equipment requirements
- Equipment registers confirm appropriate equipment is installed
- Inspection schedules ensure ongoing compliance
- Training records show personnel understand the hazards
Accessibility
Classification documentation must be accessible to those who need it: maintenance personnel selecting replacement equipment, contractors planning work in hazardous areas, inspectors verifying compliance, and emergency responders understanding hazard locations. Consider how documentation is distributed and kept current across the organisation.