In this article we look at important ATEX zones for gases and dust to dig a little deeper into understanding how we go about ATEX Fan selection. If you are not sure whether you need an explosion proof ATEX fan or need to know the ATEX zone in which your application is classified, please consult an official authority in your country.
ATEX is an acronym derived from the words “Atmospheres Explosibles” and forms part of a European equipment directive known as ATEX 2014-34 EU. Since the departure of the UK from the European Union, the UK is getting ready to transition to the term UKEX under its own statory instrument. Both directives are basically the same and cover comprehensive manufacturing standards to ensures that people are protected against the risk that may be caused by dangerous substances. An application will require an explosion proof ATEX fan if there are flammable, combustible gases or dusts present at any time in the airstream.
In many industrialised countries, during manufacturing, treatment, transport and in the storage of goods, gases, vapours or mists are produced or leaked into the environment. In industrial manufacturing processes, flammable dust can also be produced which in combination with the oxygen in the air can create a potentially explosive atmosphere that can cause an ignition inducing a dust explosion. Other sources of ignition are common and can happen as a result of electronic failure, for example in switches or mechanical failure, for example the friction of an impeller with the inlet.
An explosive atmosphere is defined as a mixture in atmospheric conditions caused by the activity of manipulating of the air and flammable substances (gas, vapour or dust). These explosive atmospheres can occur in many industrial activities that surround us such as the chemical industry, power plants, landfills, food processing factories and metallurgical industries.
There are two types of ATEX atmosphere:
Explosive Gas Atmosphere
Mixture of the flammable substance with the air. Combustion is spread to the entire unburned mixture on ignition. Gas groups allow us to identify the explosive nature of a gas, so therefore there are a set of sub groups to collectively categorise gases based on their characteristics including their minimum ignition current and their maximum experimental safety gap. Gas groups can be seen below; IIC being the most dangerous, IIB and IIA. Fans must be rated as safe for the gas group in which they will be operating.
Explosive Dust Atmosphere
Mixture of the air with flammable substances in the form of dust or fibres. On ignition the combustion propagates through the rest of the unburned mixture. Dusts are also divided into sub groups because the types of dust. IIIC dusts are the most dangerous while IIIB dusts are classed as more dangerous when there is possible electrostatic charge.
In ATEX marking GB relates to Gas explosion equipment protection and Db relates to the dust explosion equipment protection.
This is not applicable when the risk of explosion comes from unstable substances such as explosives and pyrotechnic substances, or when the explosive mixture is outside of what is understood as normal atmospheric conditions.
Depending on the presence of the explosive gas or dust, these are classified into different zones and categories as detailed below:
Zone 0 (gases/vapours) or Category 1G: an area in which an explosive mixture is continuously present or present for long periods.
Zone 1 (gases/vapours) or Category 2G: an area in which an explosive mixture is likely to occur in normal operation.
Zone 2 (gases/vapours) or Category 3G: an area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time.
Zone 20 (dusts) or Category 1D: an area in which an explosive mixture is continuously present or present for long periods.
Zone 21 (dusts) or Category 2D: an area in which an explosive mixture is likely to occur in normal operation.
Zone 22 (dusts) or Category 3D: an area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time.
Our collection of ATEX Centrifugal and ATEX Axial fans are available in references capable of handling ATEX Gas and Dust in one reference. ATEX polypropylene fans are available in zone 2 gas environments. Ask us for the configuration you need in your project and we’ll supply the correct fan to suit the gas and dust zone correctly.
In addition to understanding the ATEX gas and dust zones, it is important to be aware of the temperature classes of each ATEX fan in line with the flammable gas present in the application.
Gas or Dust Group: Determines the explosive level of the gas
Type of Temperature: Determines the highest acceptable surface temperature on the motor. Going over the maximum temperature risks ignition of either the gas or dust present.
Learn more about temperature classes for ATEX explosive environments here or for more information on EX fans and EEX definitions such as Ex nA and Ex eb view here.
The Axair team have undertaken extensive training in ATEX regulations but have a duty of care to ensure we supply a suitable fan based upon a customer’s correct ATEX coding specifications. ATEX has to be understood as an ever-evolving subject requiring competence and training that is now provided by UK notified bodies and consultancies. We advise that if anyone requires additional training in ATEX that they contact an independent body for assistance. Axair can supply fans suitable for ATEX applications within zone 1 & zone 2 manufactured from either metal or corrosion resistant polypropylene depending on the specification. To help with your understanding of ATEX atmospheres and accurate fan selection, view our article featuring the main ATEX concepts, here.