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Fans for ATEX (Explosive environments)

It is not always easy to understand the entire ATEX directive and what applies to your particular application.
As part of the fan hub training, we have a short course about what ATEX is and what need to be taken into consideration in connection with the installation of fans in explosive environments.

ATEX is an abbreviation that stands for “Atmosphére Explosible” which is French for explosive atmosphere.
The ATEX classification was developed to be able to classify machines and equipment that can be used in potentially explosive environments, such as mines, refineries, offshore platforms and a variety of other industrial applications.

An explosive atmosphere occurs when there is a risk of a mixture of air and flammable gas/dust being created. The gas mixture, when ignited, would spread a combustion in the mixture, which leads to an explosion.

An explosive environment does not only have to be a gas mixture in air, but can also consist of liquids or dust, and for these cases there are separate divisions in the directive.

Fans and other equipment that are ATEX-classified are designed and manufactured to avoid creating ignitions in potentially explosive areas. In our case, this means that our fans must not be able to generate sparks, have any hot surfaces, arcs or static electricity that could lead to ignition and thus an explosion.

ATEX Zones

Depending on how the application is designed and where it is placed, there is of course a varying degree of risk that an explosive atmosphere will occur.
This also gives us the opportunity to adapt the fans to actual conditions and thus avoiding overcompensation with unnecessarily advanced solutions for applications with relatively low risks.

The zones into which potentially explosive areas are divided are as follows for gases:

Risk AreaDescription
Zone 0Risk area in which an explosive gas mixture occurs constantly or for a long time.
Zone 1Risk area in which an explosive gas mixture is expected to possibly occur during normal operation.
Zone 2Hazardous area in which an explosive gas mixture is not expected to occur during normal handling, and if it does occur, in that case only rarely or briefly.

And as below for dusts and particles:

Risk AreaDescription
Zone 20Risk area in which an explosive dust mixture occurs continuously or for a long time.
Zone 21Risk area in which an explosive dust mixture is expected to possibly occur during normal operation.
Zone 22Hazardous area in which an explosive dust mixture is not expected to occur under normal handling, and if it does occur, then only rarely or for a short time.

Examples of Zone 0 / Zone 20 are inside cisterns or vessels.

Examples of Zone 1 / Zone 21 are pump rooms, sampling rooms, filling stations, etc.

Examples of Zone 2 / Zone 22 are often outdoors around e.g. valves, pumps or near Zone 1 / Zone 21 surfaces.

Temperature classes for gases

In the same way that the application is divided into different zones depending on the operating situation, the application is also divided into different temperature classes depending on which substance is in question.
The ignition temperature is the lowest temperature that a surface can have and cause a spontaneous ignition of the substance or the gas when it comes into contact with the surface.
Higher temperature class means that a lower surface temperature is required for self-ignition, i.e. greater risk.
Flammable gases are divided into the following classes:

Temperature ClassIgnition Temperature
T1t > 450 °C
T2300 < t < 450 °C
T3200 < t < 300 °C
T4135 < t < 200 ° C
T5100 < t < 135 ° C
T685 < t < 100 ° C

Explosion group

In addition to temperature classes, flammable products are also divided into explosion groups that indicate how
explosive they are.
The groups are IIA, IIB and IIC, where lower ignition energy gives higher explosion group.
There is also another explosion group I, which is used for coal mines where there may be methane and coal dust in the air.
By dividing flammable materials into explosion groups, it is possible to standardize the properties of the fans against a certain group without having to carry out new investigations for each application.

Some examples of materials and explosion groups are as follows:

SubstanceTemperature ClassExplosion Group
Fuel oilT3IIA
Carbon disulfideT6IIC
Carbon monoxideT1IIB

Groups for dust

Dusts are classified in a similar way to gases by examining whether it is combustible and, among other things, at what mixture, temperature and particle size.
These are then divided into dust groups as below:

Dust GroupProperties
IIIADust and fiber > 0.5 mm
IIIBFine dust < 0.5 mm
IIICConductive fine-grained dust  < 0.5 mm

Design of fans for ATEX

When it comes to our design of fans for operation in ATEX zones, there are two major parts that need to be adapted to the application. On the one hand, it is the design of the fan itself and its parts such as spark protection, seals and flame arrestors. And the second thing is choosing the right motor and motor supplier for the application.

Electric motors

Electric motors have clear standards when it comes to environments with explosive atmospheres and it is important to choose the right motor for the application and zone.

Just like for all fans, the first step is to find the correct dimensioning of the fan, this gives us our power requirement in kW and how many poles, i.e. how many rpm, the motor should be equipped with.

In order to then choose the right specification for operating the motor in ATEX environments, the zones, classes and groups above are used to find the right equipment level on the motor as below:

ZoneGroup (according to ATEX Directive 2014/34/EU)Equipment category (according to the ATEX directive 2014/34/EU)Equipment protection level (EPL) according to IEC 60079-0
1II2G or 1GGb or Ga
2II3G, 2G or 1GGc, Gb or Ga
21II2D or 1DDb or Da
22II3D, 2D or 1DDc, Db or Da

The equipment protection level (EPL) then determines the design of the motor according to the table below:

Classification acc. to EPL.

Flammable materialProtection principleProtection typeVery high safetyHigh safetyIncreased safety
Gases and vapors (G)Makes it impossible for an explosion to spread from the inside to the outsideFireproof enclosureEx daEx dbEx dc
Gases and vapors (G)Avoid arcs, sparks and excessive temperatureIncreased safetyEx eb (Old Ex e)Ex ec (Old Ex nA ”Non-sparking”)
Dust and particles (D)Create distance between atmosphere and ignition sourceProtection by encapsulationEx taEx tbEx tc
Gases and vapors (G) and Dust and particles (D) Create distance between atmosphere and ignition sourcePressurizationEx pxb, Ex pybEx pzc
Gases and vapors (G)Create distance between atmosphere and ignition sourceEncapsulationEx maEx mbEx mc

For example, a motor that is to be used in a fan for a methanol room in zone 1 needs at least the following ATEX classifications:

Group II / 2G / Ex db eb / IIA / T2 / Gb

Depending on the motor suppliers’ standards, we choose the closest available standardized ATEX motor, which may mean that certain requirements are met to a higher degree than what is needed for the application.

Fan control with frequency converter

For fans that are to be used at different operating points and controlled using frequency converters, it is especially important that this is mentioned early in the selection of the motor.

Motors that are classified Ex ec (formerly Ex nA) or Ex e (Increased safety), the temperature requirements apply to all parts of the motor – both inside and outside.

This means that these motors are not suitable for operation with frequency converters unless there are tests that approve the exact combination of frequency converter and motor.

For motors with Ex d and Ex t, the temperature requirements only apply to all external surfaces, which means that the temperature protection, e.g. PTCs in the windings or thermistors in the motor provide adequate protection even when operating with a frequency converter.

Therefore, our absolute recommendation is that motors for fans in ATEX environments with multiple operating points must be equipped with Ex d or Ex t motors.

Fan design

We design and manufacture fans for explosive environments in both axial and radial fan designs, what decides the choice of fan type is the application’s needs and layout.

For really tough ATEX applications, however, higher system pressures, flame arrestors and similar accessories are often required, which means that only centrifugal fans can perform in the application.

In the Witt-group, we have worked with ATEX fans since 1985 and since 1999 one of our sister companies is one of the few in the world that manufactures fans approved for zone 0.

Hoffman La Roche (Basel, CH) – 1985

  • Transportation of explosive, posionous and corrosive gases
  • 2000 m³/h
  • 70 mbar
  • T° : – 50°C … + 200°C
  • Systempressure: 8 bar
  • 12 bar explosion resistance

Hofstetter (CH) – 1985

  • Transportation of biogas (metane)
  • Max 2000 m³/h
  • 180 mbar
  • 6 or 10 bar explosion resistance

Sanofi Synthélabo (F) – 1999

  • Zone 0
  • Transporation of steam from solvents
  • 1500 Nm³/h
  • System ER10

Depending on the application, the design of the fans can be varied endlessly with material thicknesses, different sealing systems and flame arresters. But generally for all fans are two points.

Spark protection for fan impeller and shaft

The impeller spark protection is a copper or brass shield that is installed on the inside of the fan shroud. This means that if the impeller should for some reason hit the fan cover, no sparks will occur.

The spark protection for the shaft is a copper shield or brass shield that is located between the motor shaft/coupling shaft and the fan cover to prevent sparks from occurring when they come into contact.

If you have very low rotation speeds and large distances between moving and fixed part, you can do without spark protection. Certain combinations of materials may mean that spark protection is not needed.

Shaft seals

When there are different zones inside and outside the fan, these two zones must be separated with a shaft seal.

If possible (depending on the material in question) the fan can be manufactured with the same design both inside and outside and thus avoid the shaft seal.

For axial fans, we also adapt the external junction box for ATEX.

Name plates

Below is a short guide on how to decipher a nameplate on an existing ATEX fan.

Group II

Inside fan:                1G
External Fan:         2G
G:               Gas
IIA                             Explosion Group IIA
T4                             Max surface temperature 135 °C
Motor:                     EEx d IIB T3
(EEx d is with the new designation Ex eb db)

I.e. better requirements than what the application requires = Ok

ATEX checklist

For every fan we manufacture that is certified according to ATEX, we need a signed ATEX checklist, which you can find on our website.
This is to have guarantees that the fan will be used according to what it was designed for and not outside of its performance and safety level.
When it comes to ATEX, it is always extra important to do the right selection and make sure that your equipment is well adapted for your operating conditions.

Contact us at FläktComp for your ATEX needs.

Or read more about our ATEX fans.

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