Ex Certification: Standards, Marking and Meaning

Introduction: the Risk of Explosion

In many industries, dangerous gases (or dusts) are needed for or result from processes. When the use of such compounds is not avoidable, the risk of explosion must be minimized by following the existing regulations (ATEX directives in Europe) and international standard best practices (IECEx).

The risk of explosion comes from the combination of three factors:

• Combustible material (the process gas or dust under examination)
• Oxygen from the environment (which can react with the combustible)
• Ignition source (an initial source of energy which can spark a chain reaction, usually coming from process equipment and machines)

If one of these elements is not present, the risk of explosion is minimized. For example, most potentially explosive gases need a certain concentration to cause an explosion. If the gas is too diluted in air, the chain reaction won’t start, if the gas is too concentrated, not enough oxygen is present and the reaction won’t self sustain. A gas, to be explosive, must have a concentration between its Lower and the Upper Explosion Levels (LEL and UEL).

The risks posed by the gas mixture and by the ignition source can be quantified (e.g. the gas concentration and the temperature of the ignition source increase the risk of explosion) and categorized.

The ATEX directives and IECEx standards take into account the level of risk posed by the gas mix and equipment (the type of gas, its risk of ignition, the frequency of the presence of such gas, the protection concept of the sources of ignition, etc..), and provide guidelines on which pieces of equipment are compatible with the processes under scrutiny.

The machines are analyzed and rated, the industrial environments are audited for their explosion risk, and with these elements the user has to ensure that the machine rating matches the atmosphere rating.

Levitronix BFS ATEX/IECEx Rating

Many Levitronix products are certified with respect to their likelihood to cause an explosion of a dangerous mix of gases or dust. This certification follows the European Directive (ATEX) and the International IECEx Standard. These two codes overlap in most sections, therefore occasionally only one code is expressed in the labeling, since the counterpart from the other code can be directly extrapolated (for example, the IECEx Zone codes and the corresponding ATEX Category codes are shown in Table 1).

In this topic, there is a description of what each section of the marking means, the other existing options, and an example of a comparison of two Levitronix products, from the Ex perspective.

Let’s take as an example the Ex marking on the Levitronix BFS-i06 :

• II 2G Ex h mb IIC T6 Gb (rating of the risk of igniting a dangerous gas mixture)
• II 2D Ex h mb IIIC T85 Db (rating of the risk of igniting a dangerous dust mixture)

The first distinction is that there are two separate codes, the first related to gases (some sections contain a G) and the second to dusts (some sections contain a D). Let’s analyze block by block their meaning:

• II : Equipment group. The options available are I (equipment used in mines) and II (any other equipment). I is more restrictive, but most of industrial applications only require II.
• 2G (and 2D): ATEX Category code. It expresses in which zones the equipment can be used. Categories are classified based on the likelihood that a dangerous gas or dust mixture is present. The options are 1, 2, and 3 (1 being the strictest, dangerous mix always present, 3 the least strict, mixture rarely present and only for a short time). The categories correspond to zones in IECEx standard. For gases, the zones are coded 0, 1, 2 (0 the strictest); for dusts, the zones are 20, 21, 22 (20 the strictest). A “category 2G/2D” corresponds to “Zone 1/21” (dangerous gas and dust mixtures often present during normal operation).
• Ex: marking related to the risk of explosion
• h, mb: codes related to the protection concept (they express why a certain machine is not a risk of ignition). There are more than 40 option codes available, more than one can be present, and they relate to the protection against mechanical sources of ignition (e.g. a gearbox generating heat due to friction) and against electrical sources (risk of short circuits in explosive atmosphere..). Levitronix products have intrinsic mechanical safety (no friction, no risk of ignition from mechanical sources) and have encapsulated motor (protection against the electrical sources of ignition).
• IIC (and IIIC): express the level of risk of the gas (II) or dust (III) mixtures. The options available are A, B, C, with C as the strictest (the easiest mixture to ignite, the most dangerous). Most Levitronix products are rated for the most dangerous gas and dust mixtures.
• T6 (and T85): temperature rating. It expresses the maximum temperature range reached by any exposed surface of the the machine. For gas related ratings, the temperature ranges are expressed on a scale from 1 to 6 (6 refers to the lowest allowed maximum temperature, hence its the strictest class). For dust, the temperature is explicitly written in degrees Celsius (85 in this case). Levitronix products are typically rated in classes between 4 and 6 (the three strictest classes). The end user has to verify that the rated temperature is well below the flash point of the gas mixture present in the area.
• Gb (and Db): Equipment Protection Level (EPL). EPL expresses the overall likelihood that a machine will be a source of ignition of a mix of gas (G_ rating) or dust (D_ rating). For both gas and dust protection, there are three levels: a, b, c (a being the strictest, corresponding to a very high level of protection, even in the case of rare malfunctions). A separate coding is used for Equipment Group I machines (those used in mines), but they are not relevant to this training.

As shown in Figure 2, the same zone rating applies to both the inside and the outside of the fan. This means that the dangerous gas (or dust) mixture can be both the process fluid being pumped, or the surrounding fluid (e.g. in case of a failure somewhere else in the system), and in neither case the fan will cause an explosion.

IECEx and ATEX Ratings for other Levitronix Products

Not only fans are Ex rated. Levitronix pumps often have a rating which reflects the explosion risk of the motor and pump head. The controllers and external interfaces are not in the scope of the rating in these cases.

Typically more pump heads are compatible with the same motor, and usually a selection of motors – pump heads combinations are included in the same Ex certification. In the certificate itself it is possible to see all rated combinations (as an example, see Figure 3).

The Ex certificate has a unique identifier number, which is reported on the sticker present on the pump drive. The code can end with “X”, meaning that the rating is valid if some special requirements are fulfilled (see Figure 4). The requirements are written in the manual, and refer for example to the fact that the pump head should be filled with liquid. If this requirement is fulfilled, it is clear that the inside of the pump head contains no gas, and therefore it is not a Explosion Risk rated zone.

Comparison of two Levitronix Ex rated Products

As an example, the Ex rating of another Levitronix products is compared against the fan.

Levitronix BPS-i100 pump reports the following Ex marking:

• II 3G Ex ec h mc IIC T4 Gc (rating of the risk of igniting a dangerous gas mixture)
• II 3D Ex h tc IIIC T90 Dc (rating of the risk of igniting a dangerous dust mixture)

The equipment group is II (as for the fans), meaning that the pump is not rated to be used in mines.

The category is 3GD (Zones 2/22), a class lower than the fans. This is because the pumps are made to transport liquids, and are not usually exposed to explosive gas mixtures (unless it’s for temporary conditions or accidents). Fans have a higher rating because their function is to transport said gas mixtures during standard operation.

The protection concept is similar to the fan: the motor is encapsulated (protection against electrical sources of ignition), and there are no mechanical sources of ignition (intrinsic safety).

The gas and dust mixture level of danger (ease of ignition) is the same as for the fan. Both products in fact have a IIC/IIIC rating. As explained, the difference is in the likelihood of being exposed to such gases (the zone rating).

The temperature rating is T4 (T90 for dust), meaning a lower rating than for fans. This indicated that some surface of the pump drive might reach higher temperatures than the fan, hence posing a higher risk of ignition.

For all these reasons, the EPL is Gc/Dc, a class lower than for the fans.

Fans therefore pose a lower risk of explosion, and can be used in more challenging environments.