Explosion Protected Equipment Marking For Safe Use In Hazardous Areas

Published 21 Oct 2019

R Stahl – The Explosion Protection Experts

• By Chris Dodds : estimated reading time 9 minutes

Devices for use in potentially explosive atmospheres have to be marked. The requirements on markings come from different sources. So EU Directive 94/9/EC (ATEX 95) stipulates in Europe, which information has to be given on the type label.

These are the minimum requirements that have to be supplemented by further information required for safety. The required safety-relevant data and their order on the type label are stipulated in the European standards.

The requirements on electrical devices for use in explosive gas atmospheres are included in standard series EN 60079. For devices that are intended for use in areas with combustible dust standard series EN 61241 has to be applied.

For many years now these standards have been prepared on an international level by the IEC and then adopted as European standards.

Up to now marking has been specified in IEC 60079-0  / 2004 and in IEC 61241-0 / 2004. To clearly identify the device, the type identification and the serial number have to be stated as well as, the manufacturer’s name or his trademark.

For devices subject to certification the name of the notified body issuing the certificate and the certification number have to be given. Additionally, a special coding is required that describes the applicable use of the device:

• the symbol  for an Ex explosion-protected device
• the symbol of each type of protection that has been applied
• group IIA, IIB or IIC for explosive gas atmospheres
• temperature class for explosive gas atmospheres or the maximum surface temperature in °C for areas with combustible dust.

Examples:

Ex d e IIC T4
Ex d [ia] IIB T5
Ex pD21 T120 °C

With associated electrical equipment in type of protection intrinsic safety that is to be installed in the safe area, the symbols for this type of protection have to be put into square brackets, e.g. [Ex ia] IIC.

If the equipment is to be mounted in hazardous areas it has to be protected by another type of protection. Then only the mark for intrinsic safety is put into square brackets, e.g. Ex d e [ib] IIC T6.

In the past, the marking pursuant to the European standard changed from ›Ex‹ to ›EEx‹. This was done to relate to the European standards (EN 50014 serie) that then differed from the IEC-standards.

With the current state of the standards this is no longer required so that in Europe the new devices are only marked ›Ex‹ as well.

From the previous marking the protection level of the device in regard to explosion protection cannot be clearly seen right away.   Only knowledge of the possible application of the different types of protection indicates the application of the device in the respective zones.

This problem was noticed in Europe at an early stage. So with the European Directive 94/9/EC (ATEX 95) the equipment categories 1, 2 and 3 were introduced. Transfer of these categories from the Directive to the standards, however, has only been done in the EN-standards and not in the IEC-standards.

Table 1: Marking and definition of Equipment Protection Level EPL

New marking

In the IEC 60079-0 / 2007 the devices for use in explosive dust atmospheres have been included. So the general requirements on devices for use in explosive gas and dust atmospheres are covered in this standard.

Marking has now been supplemented with the protection level of the equipment. This equipment protection level (EPL) consists of two letters. The first one gives information on the type of explosive atmosphere: G for gas, D for dust.

The actual protection level is defined by the letters a, b or c (table 1). These letters are already used for some types of protection to mark the respective protection level: ia, ib, ic.

The symbol for the equipment protection level is added to the existing standard marking: example: Ex d e IIC T4 Gb. With associated electrical equipment, the EPL-symbol has to be mentioned after the type of protection: example: [Ex ia Ga)] IIC.

When an associated electrical equipment with an intrinsically safe circuit ia has been fitted into a flameproof enclosure, for example, make it possible to install it into Zone 1, the following marking is required: Ex d [ia Ga] IIC T4 Gb.

Groups

The suitability of devices for use in different hazardous areas is determined by groups. Up until now two groups have been defined: devices intended for use in mines at risk through firedamp belong to Group I.

Group II stands for devices that may be used in areas other than mines, specifically areas that are at risk through flammable gas.

Further sub-division of this Group II into three sub-groups IIA, IIB and IIC determines which type of gas the device is suitable for. With the IEC 60079-0 / 2007 a new group III has been introduced.

It stands for devices that are intended for areas in which an explosive dust atmosphere may be expected. Devices have to meet different requirements for different dusts. So, similarly to Group II, further sub-division are also planned for Group III:

> IIIA: combustible flyings
> IIIB: non-conductive dusts
> IIIC: conductive dusts

Thus the devices can be assigned to the different types of dust and their different requirements.

Example: Ex tb IIIC T120°C Db.

Table 2: Comparison of the different markings according to IEC 60079-0

Alternate marking

Standard IEC 60079-0 / 2007 allows alternative marking to the one described in the previous chapter, which gives information twice in some cases.

With the introduction of Group III the suitability of a device for gas atmospheres (II) or dust atmospheres (III) can be seen directly through the group number. So the letter G or D in the equipment protection level does not give additional information.

With some types of protection the protection level is marked by supplementing the letters a, b or c to the symbol of the type of protection. Alternate marking intends to add this distinguishing letter to all types of protection.

E.g., flameproof enclosures ›d‹ will then be marked ›db‹. This then clearly shows the application range of a device in regards to the potentially present explosive atmosphere and the protection level without stating the EPL. So EPL marking can be omitted.

Example:

Ex db eb IIC T4
Ex db [ia] IIB T5
Ex tb IIB T120°C

Table 3 shows the currently possible alternate marking of the different types of protection. Old, new and alternate marking is shown in table 2.

The manufacturer may decide which marking he will use. However, the alternate marking seems to be more coherent as redundant information are eliminated.

Table 3: Symbols of the type of protections according to the alternate marking

Marking according to ATEX 95

In Europe, in addition to the marking according to standard, the requirements according to EC Directive 94/9/EC (ATEX 95) have to be fulfilled.
ATEX 95 Directive Annex II requires the following marking:

• name and address of the manufacturer
• serial number, year of manufacture
• mark  with the identification number of the notified body
• Ex and category 1, 2 or 3
• and for Group II the letter G (gases) or D (dust)

Example:  Ex 2 II G

Example for marking according to ATEX Directive and standard EN 60079-0: CE 0158 Ex 2 II G Ex db eb IIC T4

On devices that are marketed within the EU, marking according to the Directive has to be added to the required marking of an international standard.

Table 4: Marking of the types of protection of non-electrical equipment

Non-electrical devices

Standards for non-electrical devices have up until now only been prepared by CEN for Europe. On an international level only the first steps towards standardisation have been taken.

Marking strongly follows the definitions for electrical devices.

Exceptions:

• ›Ex‹ is not stated as the marking according to ATEX Directive already includes the Ex symbol which indicates explosion protection.
• Equipment protection level is not stated as this has not been defined in the respective standards up until now. By stating the category as required by the Directive it can be seen which protection level the device has and in which zone it can be mounted.
• Marking of the different types of protection for non-electrical devices is given in table 4.

Example for marking according to Directive and standard EN 13463-1:

Ex 2 II G d IIB T4

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