In industries where flammable gases, vapors, or combustible dusts are present, understanding zone classification in explosion protection is critical. ATEX (Atmosphères Explosibles) and IECEx (International Electrotechnical Commission System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres) provide frameworks for classifying hazardous areas to ensure safe operation and compliance.
What is zone classification in explosion protection?
Zone classification is the process of identifying and categorizing areas where explosive atmospheres may occur. This helps determine the type of equipment and protection methods required to operate safely in those environments. ATEX and IECEx use a similar zone-based system but may differ slightly in terminology and regional adoption.
There are two main categories:
Gas/vapor hazardous areas
Dust hazardous areas
Each is divided into zones based on the frequency and duration of the explosive atmosphere.
Gas Hazardous Areas
Zone 0
Definition: Area where an explosive gas atmosphere is present continuously or for long periods.
Example: Inside storage tanks with flammable liquids.
Protection Requirements: Equipment must be “Ex ia” rated (intrinsically safe with two faults considered).
Zone 1
Definition: Area where an explosive gas atmosphere is likely to occur during normal operation.
Example: Areas around filling points, pump seals.
Protection Requirements: Flameproof (Ex d), increased safety (Ex e), or intrinsically safe (Ex ib).
Zone 2
Definition: Area where an explosive gas atmosphere is not likely to occur, and if it does, it will exist only for a short time.
Example: Surroundings of Zone 1 areas.
Protection Requirements: Equipment rated for occasional exposure, such as Ex n or Ex ec.
Dust Hazardous Areas
Zone 20
Definition: Area where combustible dust is present continuously or frequently.
Example: Inside dust collectors or silos.
Protection Requirements: Equipment must prevent dust ingress and avoid surface temperatures that could ignite dust.
Zone 21
Definition: Area where explosive dust atmospheres are likely during normal operation.
Example: Around bagging or mixing equipment.
Protection Requirements: Dust-tight equipment with temperature control (Ex tb).
Zone 22
Definition: Area where dust atmospheres are not likely, or only for short periods.
Example: Near dust extraction points.
Protection Requirements: Equipment suitable for infrequent exposure (Ex tc).
Summary Table: Gas vs. Dust Zones
Zone Type Zone Number Description Typical Location Equipment Protection Gas Zone 0 Continuous presence of gas Inside tanks Ex ia (intrinsically safe) Gas Zone 1 Likely presence of gas Near flanges/pumps Ex d, Ex e, Ex ib Gas Zone 2 Rare and short gas presence Adjacent to Zone 1 Ex n, Ex ec Dust Zone 20
Continuous dust presenceInside hoppers Ex ta (dust-tight) Dust Zone 21 Likely dust presence Filling/bagging areas Ex tb Dust Zone 22 Rare and short dust presence Near conveyors Ex tc
Why Proper Classification Matters
Accurate zone classification in explosion protection is not just about compliance—it’s about safety. Misclassification can lead to inadequate equipment being installed, which increases the risk of ignition and catastrophic incidents. It also affects insurance, legal liability, and operational integrity.
Working with competent professionals and conducting thorough risk assessments ensures that each zone is correctly identified and protected, aligning with both ATEX and IECEx standards.
Conclusion
Understanding and implementing the right zone classification for explosive atmospheres is essential in hazardous industries. Whether dealing with gases or dust, classifying areas appropriately helps mitigate risk, ensures compliance, and protects people, assets, and the environment.