Selection of Electrical Equipment's for Hazardous Area.

In continuation to my previous article published on Jun 6, 2021 (Explosion Protection - Basics , I have further added few more pointers about selection of electrical equipment for hazardous area.

Hazardous Area Classification

Area classification is the method of analyzing and classifying the environment where explosive gas atmospheres may occur so as to facilitate the proper selection of the electrical equipment.

Equipment group classification

• Group I equipment applies to equipment used in underground operations, such as mines.
• Group II equipment applies to surface-processing industries. The petrochemical, chemical, pharmaceutical as well as food industries are typical processing industries.

Figure 1: Definition of equipment groups and categories according to ATEX 2014/34/EU

The equipment groups are further sub-divided into categories as shown in the Table 1. Group I is divided?into categories M1 and M2. Group II is sub-divided into equipment categories 1, 2 and 3.

Table 1: Equipment group and category classification according to ATEX 2014/34/EU

Gas and Dust Substance Group

Up to this point, explosion-proof equipment has been divided into:

• Equipment Group I (underground, for mine workings at risk) and
• Equipment Group II (surface equipment, for areas at risk of explosion excluding mines workings).

Lets focus on Equipment Group II only which is further segregated due to gases, vapors, mist and dust.

Table 2: ATEX substance group classification

Area Classification

Equipment Group II, which is intended to be used in hazardous areas, is divided into three zones for gases and three zones for dust substances.

Table 3: Zone classification according to ATEX 1999/92/EC

A methodology for potentially explosive area classification is also available in European Standards EN 60079-10.?The methodology applied in the standards is based on the concept of three “sources of release,” namely continuous, primary and secondary.

Figure 2 shows the classification of the Zones based on the above mentioned standards.

Figure 2: Zone classification according to IEC EN 60079-10 -1 (Gas) and ATEX 1999/92/EC, respectively NEC500

The classification of hazardous areas is based on the degree of emission:

• Continuous emission generates zone 0/20,
• Primary emission generates zone 1/21,
• Secondary emission generates zone 2/22

Although there is no fixed rule regarding the presence (duration and probability) of an explosive atmosphere?in relation to zones 0/20, 1/21, 2/22, the table and graphic represent a useful reference.

• For continuous emission, the overall duration of the explosive atmosphere is more than 1,000 hours per?year.
• For primary emission, the overall duration of explosive atmosphere is between 10 and 1,000 hours per?year.
• And, for secondary emissions, this parameter is less than 10 hours per year.

Figure 3: Duration and presence of hazards compared to risk (Zone)

A competent person or certified body must carry out the zone classification process and related explosion risk assessment, and determine what protective measures are necessary.

ATEX 2014/34/EU equipment categories and IECEx equipment protection level

Equipment to be used must correspond to the assigned equipment categories and equipment protection levels?(EPL) as prescribed by the zone classification. These equipment requirements are categorized in relation to the?European equipment categories on the basis of EU Directive 2014/34/EU; the EPL, introduced by the IEC, applies?on an international level. Both classifications can be used when marking equipment. This classification tells us?about the probability of ignition, taking into account potentially explosive gas and dust atmospheres.

Table 4 presents the definitions of equipment categories and equipment protection levels (EPL) and their differences. The definition of EPL is usually used in the IECEx marking system

Table 4: Definition of ATEX 2014/34/EU equipment categories and IECEx equipment protection level

Auto Ignition temperature and Temperature class

The auto ignition temperature or the ignition temperature is?the minimum temperature at which a substance in air must be heated to initiate or cause self-sustaining combustion independent of the heating source.

A Temperature Class is a term that is allocated within a hazardous area or zone to instruments and equipment. The classification or rating signifies the levels of thermal energy allowed in a particular area or produced by specific equipment.

Table 5: Ignition Temperature class

Ignition Protection Methods

Table 6. Protection methods

Marking of Electrical Equipment for Hazardous Area

ATEX CE marking

Marking is mandatory and must be placed on equipment before it is assigned to be distributed in the market?or put into service. The intention is to facilitate the free movement of equipment within the European Union by signifying that essential health and safety standards have been met. It is a declaration that the product was?produced in conformity with all applicable provisions and requirements of the Directive 2014/34/EU and that?the product has been the subject of the appropriate conformity assessment procedures.

Figure 4: Marking example of electrical equipment for Zone 1/21

To clearly identify the device, the type of identification and the serial number have to be stated as well as the?manufacturer’s name or trademark. Electrical equipment needs to be tested and approved by an appropriate?certified body, so the name of the notified body issuing the certificate and the certification number has to be?stated. The applicable use of the device is described through special coding. The following example refers to?equipment marking for gas atmospheres.

Figure 5: Typical electrical equipment marking (gas) according to ATEX 2014/34/EU

For equipment certified for use in the hazardous areas with the dust atmosphere following marking is used:

Figure 6: Typical electrical equipment marking (dust) according to ATEX 2014/34/EU

Conclusion:

The above article is general guideline for selection of electrical equipment used in hazardous equipment's. Readers are encouraged to refer respective IEC and ATEX standards or various literatures available on internet for more information on this topic.

Reference:

1. 30388484_B_MAR_BR_Hazardous_Area_Guide_EN