Working in environments containing flammable gases, solvent vapours, combustible dusts, or sewage methane requires specialised explosion-protection methodology governed by the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) and the BS EN 60079 standards series. A standard non-Ex switch or loose terminal can trigger an immediate catastrophic explosion.
A hazardous area is any workplace location where flammable gases, vapours, mists, or combustible dusts can mix with air to create an explosive atmosphere. In these environments, ordinary electrical equipment cannot be installed because normal switching sparks, frictional heat, or a loose wiring connection can ignite the surroundings. Specially certified explosion-protected (Ex) apparatus is required to eliminate potential ignition sources, contain internal explosions, or restrict electrical and thermal energy below dangerous thresholds.
What are the ATEX Zone 0, 1, and 2 classifications?
Hazardous area zoning categorises plant locations based on how often an explosive atmosphere is present and how long it persists. This classification dictates the minimum equipment protection category and equipment protection level (EPL) required for safe operation.
What is the difference between Zone 0, 1, and 2?
Gas, vapour, and mist hazards are divided into three zones, based on how likely an explosive atmosphere is and how long it lasts.
| Zone | How often the atmosphere is present | Equipment category | EPL | Typical example |
|---|---|---|---|---|
| Zone 0 | Present continuously, or for long periods (> 1,000 hours/year) | Category 1G | Ga | Inside fuel storage tanks, inside sewage digesters |
| Zone 1 | Likely to occur in normal operation (10 to 1,000 hours/year) | Category 2G | Gb | Around tanker fill points, spray paint booths, pump room sumps |
| Zone 2 | Not likely to occur in normal operation and, if it does, will persist for a short period only (< 10 hours/year) | Category 3G | Gc | Flanges and valve stations in open ventilated areas |
What are combustible dust Zones 20, 21, and 22?
Combustible dust hazards are classified into three zones, according to whether a dust cloud or layer is continuous, occasional or abnormal.
| Zone | What it means |
|---|---|
| Zone 20 | Continuous dust cloud (common in grain silos, flour mills, timber workshops, and powder coating facilities) |
| Zone 21 | Occasional dust cloud (common in grain silos, flour mills, timber workshops, and powder coating facilities) |
| Zone 22 | Abnormal dust layer (common in grain silos, flour mills, timber workshops, and powder coating facilities) |
What are the main Ex explosion protection concepts?
Equipment installed in hazardous areas relies on specific engineering protection concepts to prevent ignition. The primary concepts for electrical apparatus include:
How does flameproof protection (Ex d / Ex db) work?
Flameproof protection (Ex d / Ex db) is designed on the principle of containment. The enclosure is engineered to withstand an internal explosion without igniting the surrounding external atmosphere.
When an internal ignition occurs, escaping hot gases pass through precision-machined flame paths (such as machined flat flanges, spigots, or threaded joints). These flame paths cool the escaping gases below the ignition temperature of the external gas mixture before they can reach the surrounding environment.
How does increased safety (Ex e / Ex eb) work?
Increased safety (Ex e / Ex eb) is an explosion prevention method used for non-arcing equipment (such as terminal boxes, LED luminaires, and squirrel-cage motors).
This concept employs high-integrity terminal blocks, extended creepage and clearance distances, and specialised insulation materials. These design measures prevent arcs, sparks, and excessive surface temperatures under both normal and abnormal operation.
How does intrinsic safety (Ex i / Ex ia / Ex ib) work?
Intrinsic safety (Ex i / Ex ia / Ex ib) is an energy-limiting technique used in low-energy instrumentation circuits (such as 4-20 mA sensors and RTDs).
Electrical energy within the hazardous area is restricted below the minimum ignition energy (MIE) of the gas mixture using Zener barriers or galvanic isolators located in the safe area. Ex ia provides the highest protection level and is the only protection concept permitted in Zone 0.
When are cable barrier glands and Ex inspections required?
Safe operation depends not only on certified apparatus, but also on correct cable installation and rigorous ongoing maintenance under the BS EN 60079 series.
Cable Glanding Best Practice (BS EN 60079-14):
When entering an Ex d enclosure with non-compact or flexible multicores, flammable gas can travel along cable fillers. Always use compound-filled barrier cable glands to create an airtight gas seal around individual insulated cores.
Inspection and Maintenance Schedules (BS EN 60079-17):
All Ex inspections must be documented under BS EN 60079-17 across four designated inspection grades: Initial, Visual, Close, and Detailed inspections.