What Are Zone 0, Zone 1 and Zone 2? Their Impact on Exproof Fan Selection
The first step in selecting an exproof fan for a hazardous area is not the fan model but the Zone classification of the location. Zone classification describes how often an explosive atmosphere may occur and directly affects the protection level required from the equipment.
Why is zone classification carried out?
Areas where an explosive atmosphere may form because of gas, vapour or mist are classified as Zone 0, Zone 1 and Zone 2. The objective is to define the area according to the likelihood and persistence of the explosive atmosphere and then ensure that equipment used there provides an appropriate protection level.
A similar approach is used for combustible dust with Zone 20, Zone 21 and Zone 22. Project documentation should therefore state more than “exproof area” or “hazardous zone”; it should identify whether the hazard is gas/vapour/mist or dust and specify the applicable zone.
Zone classification is not information that the fan manufacturer should estimate. It must be established by competent persons using process conditions, possible release sources, ventilation conditions and the plant risk assessment. Fan selection is built on this classification.
Difference between Zone 0, Zone 1 and Zone 2
Zone 0 describes an area in which an explosive gas atmosphere is present continuously, for long periods or frequently. Zone 1 describes an area in which an explosive atmosphere is likely to occur occasionally during normal operation. Zone 2 describes an area in which an explosive atmosphere is not likely during normal operation and, if it occurs, exists only for a short time.
These definitions classify the likelihood and duration of the explosive atmosphere rather than assigning a simple “danger score”. Zone 2 therefore does not mean “risk-free”. Equipment must still be selected for the protection level permitted for that zone.
The same basic logic applies to Zone 20, 21 and 22 for combustible dust. Gas and dust markings are different, so equipment suitable for a gas atmosphere is not automatically suitable for a combustible-dust atmosphere.
How do ATEX equipment categories match the zones?
There is a general relationship between ATEX equipment categories and zone classifications. For Group II gas applications, Category 1G equipment may be considered for Zones 0, 1 and 2; Category 2G for Zones 1 and 2; and Category 3G for Zone 2. A similar relationship exists between 1D, 2D and 3D and dust Zones 20, 21 and 22.
This mapping is only the first check. Even when the category or EPL is suitable, the gas/dust group, temperature class, protection concept, ambient temperature and any special certificate conditions must also be verified.
For example, a product described as suitable for Zone 1 is not automatically suitable for every Zone 1 installation. If the site requires gas group IIC or a particular temperature class, the product must satisfy those requirements as well.
How is zone information used in fan selection?
Zone information is a fundamental input for determining the required protection level. The gas/dust group of the substance, required temperature class, ambient temperature and certificate conditions are then assessed. On the aerodynamic side, airflow, total pressure and system losses from ductwork, filters, dampers and other components are calculated.
Fan location is also important. The fan itself may be inside the hazardous area, or it may convey a hazardous process stream through ductwork. These scenarios can affect product and system design differently, so the quotation request should state where the fan will operate and what air or process stream it will convey.
The motor, fan casing, impeller, electrical accessories and connection parts should be considered within the same safety approach. Suitability of a single component does not automatically make the complete system suitable.
The most common mistake
One of the most common mistakes is the assumption that “the motor is exproof, so the fan is exproof”. Motor certification is important, but it covers only one part of the system. Mechanical sparking risks, impeller/casing relationship, earthing, connections and documentation for the complete fan must also be checked.
Another common problem is omitting the zone information at quotation stage. The fan may then be selected for performance, but its hazardous-area suitability cannot be verified. A sound selection should include at least the zone, gas/dust information, temperature class, ambient temperature, airflow and pressure.
The next step is to understand why IIA, IIB and IIC gas groups must still be checked separately even within the same zone.