ATEX Concepts: What is BS EN 14986:2017?

Even though Britain has left the European Union, there are still European laws, legislative pieces and standards that have been adopted as a British standard or as formal guidelines. One example is the European standard EN 14986:2017 which has the status of a British standard through BS EN 14986:2017.   EN 14986:2017 is known as the “Design of fans working in potentially explosive atmospheres” legislation and specifies the constructional requirements for ATEX fans constructed in Group IIG (Suitable for non-mining gas environments) of explosion groups IIA, IIB and hydrogen,  categories 1 (zone 0), 2 (zone 1) & 3 (zone 2), and Group IID (Suitable for non-mining dust environments) categories 2 (zone 21) and 3 (zone 22) for use in explosive atmospheres.  

What does BS EN 14986:2017 cover?

The standard sets out the requirements for the design, construction, testing and marking of complete fan units intended for use in potentially explosive atmospheres in air containing gas, vapour, mist and/or dusts. These atmospheres may exist inside, outside or both inside and outside of the fan.   The standard is applicable to fans working in ambient atmospheres and with normal atmospheric conditions at the inlet, having: — absolute pressures ranging from 0.8 bar to 1.1 bar, — and temperatures ranging from −20 °C to +60 °C, — and maximum volume fraction of 21 % oxygen content, — and an aerodynamic energy increase of less than 25 kJ/kg.   So you don’t have to read the entire standard, we’re covering a small section in this article to assist you in ensuring the ATEX fan you purchase is designed, built, and specified in line with the legal guidelines.  

BS EN 14986: 2017 Standards: Mechanical Design Criteria of Fans for Explosive Atmospheres

Section 4.4.1 of the standard describes how industrial fans should be designed to make them suitable for placement on the EU or UK market, in explosive atmospheres.  

“Fans for operation in potentially explosive atmospheres shall be of rigid design.”  

There’s lots of aspects that cover rigid design, and to test this fan, manufacturers should complete impact tests. “Impact testing should be undertaken on casings, supporting structures, guards, protective devices, and other external parts. Then if the deformation resulting from these tests at the most vulnerable point is so small that the moving parts of the fan do not come into contact with the casing, then the component is classed as having a rigid design.” Therefore, any fan design that’s placed on the market will have been impact tested using approved testing procedures and these results will have been sufficient to pass the tests.  

Clearance between Rotating Elements and the Fan Casing

The most important safety feature of any industrial fan construction, to minimise ignition, is the clearance between the rotating elements and the fan casing. This is clearly stated in BS EN 14986 at clause 4.4.2. “The minimum clearances between rotating parts such as the impeller and fixed parts, such as the fan casing, shall be at least 0.5% of the relevant contact diameters (diameter of the rotating part at the point where it can contact a stationary part) of the finished component, but shall not be less than 2mm in the axial or radial directions nor need be more than 13mm.” The fan manufacturer should design and construct the fan ensuring that the clearances are well maintained under all conditions covered by the intended use.  Clearances may change with rotation, temperature and due to vibrations or belt drive tension. Clearances should be adhered to in application considering potential casing distortion, ductwork and pressure drops that may affect.  

Fan Casing

To satisfy the mechanical design requirements specified in the standard, the fan casing should be of a substantially rigid design with leakage protection, adequate shaft seals and fully welded joints. As shaft seal leakage rate may increase over time, on request the manufacturer should provide information about the maintenance requirements for the seals. The fan should be capable of withstanding the lowest inlet pressure that can be generated by the fan itself when the inlet is closed, without causing contact between the casing and moving parts. Leakage declaration is compulsory when the internal and external zones of the fan are different.  

Impellers

Impellers shall be of a rigid design and shall be able to withstand a test run at a minimum of 115 times the maximum operational rotating speed for at least 60 seconds without causing an ignition risk, i.e. the impeller shall not contact the casing. An impeller design that enables a primary stress calculation based on 2/3 of the yield stress shall be deemed to satisfy the requirements for a rigid design without testing. The security coefficient at the rotating element in our tests is a minimum of 20%. This information is recorded in the technical record.   If you’re unsure about the type of explosion proof zone you require and you have the hazardous area classification to hand, give our technical explosion proof fan experts a call or email [email protected] and we’ll talk you through the concepts, jargon and if we have the necessary information, we’ll supply a fan suitable for your application.

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