Add My Company
An explosive atmosphere can be created with the presence of gases, vapours, mists or dusts, which have the potential to ignite under certain operating conditions. Potentially explosive atmospheres are found in many areas of industry, from mines, battery rooms releasing the IIC Gas hydrogen, chemical, oil and gas, pharmaceuticals industries, processing plants handling cereal, animal feed, paper, wood, coal, sugar, flour or other petro-chemical fumes and more. All these have the potential to produce gas, dust or fumes which can be ignited by even a small spark or flame.
Ex fans are labelled according to their capability of handling these potentially explosive gases or dusts without creating an explosion. The gas or dust zone classification of the potentially explosive atmosphere depends on the frequency with which potentially explosive atmospheres may exist along with the capability of the gas or dust to create an explosion. Explosive gas and dust is classified according to its likelihood to be ignited and other important characteristics such as: Minimum ignition energy Minimum ignition temperature Auto-ignition temperature Layer ignition temperature.
Ex Fans and ATEX as a concept is ever evolving and engineers should stay up to date with changes to ATEX directives, legislation and ATEX marking. In this article we’ll look at EEx definitions used within ATEX specifications for fans and motors.
Ex eb Increased Safety – Explosion Protected. Equipment is designed and manufactured with components which prevent ignition sources being generated internally such as static discharges or high temperatures. Suitable for zone 1 area use. The enclosure is certified and constructed as Explosion protected according to the increased safety standard. The philosophy with ex eb is to provide an impact resistant enclosure and also to ensure that its contents are certified such that they will never produce sparks, temperatures or current creepage that could ignite the flammable atmosphere which may enter the enclosure. Ex eb rated enclosures are therefore explosion protected but are not flameproof.
EExde – flame proof but with increased safety terminal box A flameproof motor with the terminal box of an increased safety motor, combining the superior safety of a “d” protection with the less stringent electrical connection requirements of Eexe motors. EExe in Increased Safety Increased safety motors that do not allow any sparking components inside, for Zone 1. Prevent sparks, arcs or hot spots during service, including starting, by a number of constructional or dimensional provisions, and by the use of special protection devices, designed to trip within a specified time.
To reduce the temperature rise, this type of motor typically has a special winding that effectively de-rates the motor; for instance a motor that normally delivers 5.5 kW output may only deliver 5 kW in its increased safety design. This type of motor has never been widely used in the UK, although it is very popular on the continent, where it is used both as an alternative to non-sparking, as well as an economical alternative to flame proof. The type designation under ATEX for this type of motor is EExe, which supersedes the designation Exe. Increased safety motors are designed for Zone 1, but can also be used in Zone 2.
EExp – Pressurised – keeping dangerous atmosphere outside by overpressure. Large AC machines are available with a pressurised enclosure that can be purged and filled with an inert gas to prevent an explosion. They meet the most stringent safety requirements for hazardous areas in the chemical and mineral oil industries.
EEi – Intrinsic Safety Limitation of energy in the entire electrical circuit. Suitable for zone 0 or 20, category 1. This is achieved through limiting the energy of sparks and surface temperatures through very low power requirements.
Ex db – Flameproof ( Zone one Area Use) The product incorporates mechanical features which are designed to contact an explosion and not allow any flame to escape. db versions are suitable for Zone 1 are use. The enclosure or junction box is constructed and certified as explosion protected according to the flameproof standard. The flameproof philosophy is that should an explosion occur with the enclosure, it will either be contained or the escaping flame will be cooled by a flamepath thus mitigating the risk of igniting an explosive outside atmosphere. The enclosure of this motor type will prevent an internal explosion, or flame, from being transmitted to the explosive atmosphere surrounding the machine, hence the name flameproof.
The enclosure must withstand any pressure levels caused by such an internal explosion. Its design includes a flame path, a route for exploding gas to escape by whilst cooling off. The motor also has flameproof joints with long spigots that form part of the flame path. Every cast iron part must be pressure tested to ensure explosions will be contained. The designation under ATEX for this type of motor is EExd, which supersedes the earlier designation Exd. To summarise in flameproof Exd equipment, the housing will contain a flame without allowing it to escape to the hazardous atmosphere. Suitable for zones 1 and 2, category 2 and 3 unless they have a second character a, b or c which further limits this.
Key Changes to Ex Markings
One of the International Electrotechnical Commission’s (IEC’s) most popular explosive atmospheres standards has recently undergone a full technical revision. These standards work by setting out requirements which do one of three things: prevent flammable gases and dust from getting into electrical equipment in the first instance by manufacturing and designing equipment that reduces the potential of a strong enough spark to create an explosion or by manufacturing equipment that can contain or cool the combustion internally. These standards were created following electrically initiated explosions that were first discovered in coal mines.
When ATEX marking standards change, manufacturers should be aware of the changes and bring their certifications up to date accordingly. The change to IEC standards affecting ATEX products is a key change and we’ll highlight this below as well as discussing older ATEX markings.
Ex nA is now Ex ec ( Suitable for Zone 2 Only ) The former Ex nA ATEX (non-sparking protection), is now Ex ec , and this ATEX option is suitable for Zone 2 and Zone 22 Non-Conductive Dust. Ex nA is now Ex ec Ex nA / Ex ec – Non sparking electrical equipment The lowest level of Ex protection, also known as reduced risk protection, for motors is non-sparking, so called because the design aims to prevent an internal malfunction from creating sparks in normal operation and therefore is not capable of causing an explosive atmosphere to ignite. It also aims to prevent excessive heating during starting. The EHSR (Essential Health & Safety Requirements) introduced by ATEX now make this design safer against the risk of sparks during starting.
Ex nA (non arcing) motors can be fitted with thermistors or other thermal devices that cut the power if the temperature rises above certain limits. This level of protection provides an economical compromise between high safety requirements and normal industrial standards. They are for use in zone 2 only, i.e. for areas where explosive atmospheres occur abnormally, but not during normal duty. The letter “n” stands for non-sparking equipment according to EN50021 which has now been superseded by the IEC 60079-15 standard.
Following IEC standard changes, products complying with the 4th edition of IEC 60079-15 are still able to bear the mark Ex nA, but this Standard has been updated with a new requirement in Ed 5. The new edition of IEC 60079-15 explosive atmospheres: Equipment protection by type of protection “n” does not contain Ex nA anymore following its complete revision. The new edition, called IEC 60079-7, introduced the “Ex ec” marking which basically replaces the “Ex nA” marking. Both markings indicate the same degree of protection and compliance. Both illustrate use of the non-arcing, sparking or overheating protection technique to achieve compliance with the Standards, therefore making the risk of explosion minimal. Installed products that are already in compliance are still safe and no action is mandatory for them, based on the old markings. Manufacturers who continue to build the same devices, however, should once again prove compliance (with the new Standard) and obtain the new marking (Ex ec) as they go forward.
Such updating of the marking is seen as critical to remaining competitive and will give end-users confidence that the products comply with latest technical knowledge and Standards. So in zone 2 the probability of an explosive atmosphere is extremely low. For this reason, products for zone 2 are cheaper than Ex d zone 1 products. This characteristic, combined with the fact that zone 2 is the most widespread hazardous area within an industrial plant, has allowed over the years to register a constantly growing trend for the products suitable for this area.
Right now there is no specified timeline of when Ex Na marking must be replaced but Axair and our fan manufacturers have worked to update our certification and ATEX marking to ensure our product meets the current standards. An example of our ATEX Fan marking is shown below: Typical ATEX Marking Please note the following changes have been made to the ATEX markings on our Casals range of ATEX fans; Ex “d” (dc & db (Flameproof) classifications are now Ex eb (enhanced protection/increased safety with protection level b), suitable for Zone 1 and Zone 22 Conductive Dust. The Ex db version is available on request. Equipment protection Levels The Equipment Protection Level is the last part of the coding for Gas or Dust. Gas – Ga, Gb, Gc or Dust – Da, Db, Dc are the possible levels with Ga or Da being the highest protection.
Axair's EX fans are labelled clearly to show the gas and dust zone that each can operate in. Please check the ATEX labelling carefully before processing your order.
For more information on Understanding ATEX Definitions for Ex Fans – Ex ec, Ex Na, Ex eb talk to Axair Fans UK Ltd