Useful information for manufacturers and users

Explosion protection is the safety technology deployed to protect people, plant and machinery in hazardous areas. There are various technical and organisational measures to prevent explosive atmospheres and an ignition, along with limiting the effects of explosions.

In Europe the directive 2014/34/EU defines binding and standardised quality requirements pertaining to explosion protection for equipment and components. Manufacturers therefore need to develop and design equipment for explosion protection so that they do not become a source of ignition, also taking into consideration possible human errors.

You can find detailed information on the technical bases on the following pages, or in our "Essential Explosion Protection" brochure.

Zone classification: Basis for risk assessment

Potentially explosive atmospheres are classified into zones in order to facilitate the selection of appropriate electrical equipment as well as to design suitable electrical installations. The zone classification reflects the probability of the occurrence of an explosive atmosphere.

The maximum risk potential for each area must be taken into account when dividing the potentially explosive areas into zones and determining the necessary protective measures. If the company does not have a suitable person to carry out the risk assessment and determine suitable measures, an authority must be deployed for it.

Ex zone classification basis for risk assessment R. STAHL

Zone classification for gas

Zone 0* defines an area in which a hazardous explosive atmosphere as a mixture of air and combustible gases, vapours or mists is present continuously, for long periods or frequently.

Zone 1* describes an area in which a hazardous explosive atmosphere as a mixture of air and combustible gases, vapours or mists is likely to occur under normal operating conditions.

Zone 2* refers to an area in which a hazardous explosive atmosphere as a mixture of air and combustible gases, vapours or mists is normally not present, or is only present for a short period of time, under normal operating conditions.

Zone classification for dust

Zone 20* defines an area in which a hazardous explosive atmosphere in the form of a cloud containing combustible dust in air is present continuously, for long periods or frequently.

Zone 21* describes an area in which a hazardous explosive atmosphere in the form of a cloud containing combustible dust in air is likely to occur under normal operating conditions.

Zone 22* refers to an area in which a hazardous explosive atmosphere in the form of a cloud containing combustible dust in air is normally not present, or is only present for a short period of time, under normal operating conditions.
 

* Definitions from the German Ordinance on Hazardous Substances (Gefahrstoffverordnung, GefStoffV)


You can find further information in our "Essential Explosion Protection" brochure.

Useful information – Equipment categories and EPL (Equipment Protection Level)

The various safety requirements for the equipment used depend on the probability of the occurrence of an explosive atmosphere. The safety level for equipment is coordinated with the risk potential in the various zones.

In Europe, explosion-protected equipment is classified in categories in accordance with 2014/34/EU (ATEX). At an international level, the IEC 60079-0 standard determines the EPL (Equipment Protection Level). Equipment should be designed with explosion protection measures of various levels of protection depending on the equipment category or EPL.

Equipment categories

Categories 1 (very high level of safety), 2 (high level of safety) and 3 (required level of safety) are defined for equipment for use in potentially explosive atmospheres – except in mines susceptible to firedamp.

The additional letters "G" and "D" refer to the use of equipment in potentially explosive gas atmospheres (G = gas) or for atmospheres with combustible dust (D = dust).

For equipment used in mines susceptible to firedamp, a distinction is made between the two categories: M1 (very high level of safety) and M2 (high level of safety).

Equipment Protection Level (EPL)

In accordance with IEC 60079-0, equipment for potentially explosive atmospheres is classified into three protection levels: EPL Ga or Da (very high level of protection), EPL Gb or Db (high level of protection) and EPL Gc or Dc (enhanced level of protection).

For equipment in mines susceptible to firedamp, two protection levels are defined: EPL Ma (very high level of protection) and ELP Mb (high level of protection).

The additional letters "G" and "D" are used here to indicate the use of equipment in potentially explosive gas atmospheres (G = gas) or for atmospheres with combustible dust (D = dust).

Application of equipments in specific category/EPL in hazardous areas is shown in the table below.
 

You are also welcome to download our "Essential Explosion Protection" brochure.

Zone classification and assignment of equipment

ZoneDuration of presence of explosive atmosphereEquipment categoryEquipment protection level (EPL)

Gases, vapours, mist

0continually, in the long term, permanently1GGa
1occasionally2GGb
2rarely3GGc


Dusts


20continually, in the long term, permanently1DDa
21occasionally2DDb
22rarely3DDc

Selection of equipment groups

Gases, vapours and dusts are subdivided into various groups according to their characteristics, which are assigned to individual material groups, that are designed for correct selection of equipment. The equipment groups therefore describe the level of protection and the application range of the equipment.

Classification in accordance with Directive 2014/34/EU (ATEX)

Equipment Group I applies to equipment intended for use in underground parts of mines as well as parts of surface installations of mines susceptible to firedamp and/or combustible dusts. This equipment group is subdivided into the categories M1 and M2.

Equipment Group II applies to equipment intended for use in other industries susceptible to explosive gas or dust atmospheres. Depending on the occurrence of a hazardous atmosphere, the Equipment Group II is subdivided into categories 1, 2 and 3 and is marked according to the explosive gas (G) or dust (D) atmosphere.

In addition, electrical equipment in Group II (Gas) is, subdivided into Groups IIA (Propane), IIB (Ethene) and IIC (Hydrogen).

Classification in accordance with IEC 60079-0

In 2007, the IEC 60079-0 international standard divided Group II again, into the following three equipment groups: 

  • Group I:   Equipment for mines susceptible to firedamp
  • Group II:  Equipment for all potentially explosive gas atmospheres except for mines susceptible to firedamp
  • Group III: Equipment for potentially explosive dust atmospheres except for mines

The equipment in Group III is intended for use in potentially explosive dust atmospheres. Electrical equipment in Equipment Group III is subdivided according to the type of dust into Groups IIIA (combustible flyings), IIIB (non-conductive dust) and IIIC (conductive dust).

Subdivision of Group II in accordance with IEC

GroupTypical gasSafe gap
(MESG) in mm
Minimum inhibitory concentration* (MIC)
IIAPropane> 0.9> 0.8
IIBEthene0.5 … 0.90.45 ... 0.8
IICHydrogen< 0.5< 0.45
* Minimum inhibitory concentration based on methane

Criticality of temperature factor

The ignition temperature of an explosive gas atmosphere or dust cloud is the lowest temperature of a heated surface at which, under specified conditions, either a combustible in the form of gas or vapour, or as a dust/air mixture, ignites.

The ignition temperature of gases, vapours and dusts is therefore a crucial criterion for the selection of equipment in potentially explosive atmospheres.

Explosive gases

Combustible gases and vapours are classified in temperature classes according to their inflammability. The maximum surface temperature of electrical equipment must always be lower than the ignition temperature of the gas/air or vapour/air mixture in which it is used. Equipment which correspond to a higher temperature class (e.g. T5) are, also permitted for use in applications in which a lower temperature class is required (e.g. T2 or T3). Note: In North America, there is a system incorporating further classification into temperature subclasses.

Temperature classes

Ignition temperature
of gases and
vapours in °C

Temperature class

Maximum surface
temperature of
the equipment in °C

> 450

T1450

> 300 bis 450

T2300

> 200 bis 300

T3200

> 135 bis 200

T4135

> 100 bis 135

T5100

> 85 bis 100

T685

 

 

 

Overview of temperature classes

Substance nameIgnition temperature in °CTemperature classExplosion group
1,2-dichloroethane440T2IIA
Acetaldehyde155T4IIA
Acetone535T1IIA
Acetylene305T2IIC3
Ammonia630T1IIA
Petrol fuels220 to 300T3IIA
Benzene (pure)555T1IIA
Cyclohexanone430T2IIA
Diesel fuels220T3IIA
Acetic acid485T1IIA
Acetic anhydride330T2IIA
Ethene515T1IIA
Ethyl acetate470T1IIA
Ethanol400T2IIB
Ethyl chloride510T1IIA
Ethene440T2IIB
Ethylene oxide435 (self-decomposing)T2IIB
Diethyl ether175T4IIB
Ethyl glycol235T3IIB
Fuel oil EL, L, M, S220 to 300T3IIA
Amyl acetate380T2IIA
Carbon monoxide605T1IIA
Methane595T1IIA
Methanol440T2IIA
Methyl chloride625T1IIA
Naphthalene540T1IIA
n-Butane365T2IIA
n-Butanol325T2IIB
n-Hexane230T3IIA
n-Propyl alcohol385T2IIB*
Phenol595T1IIA
Propane470T1IIA
Carbon disulphide95T6IIC1
Hydrogen sulphide270T3IIB
Toluene535T1IIA
Hydrogen560T1IIC2
*The explosion group for this substance has not yet been determined.
1 Also explosion group IIB + CS2. 2 Also explosion group IIB + H2. 3 Also explosion group IIB + C2 H2.

Combustible dusts

Combustible dusts are not divided into temperature classes and so the ignition temperature of the dust cloud must be compared with the maximum permissible surface temperature of the equipment. However, since dusts can build up on the equipment, the ignition temperature of the dust layer (glow temperature) must also be taken into account. In both cases, the specified safety factors must be considered. Higher layer thicknesses also increase the thermal insulation, which is why maximum permissible surface temperature on the equipment must be further reduced. Further considerations are needed here, which we explain in our "Essential Explosion Protection" brochure.

Types of protection – Avoid explosions by efficient protection

In areas in which an explosive atmosphere is likely to occur only explosion-protected equipment should be used. Electrical equipment for potentially explosive atmospheres can be designed in various types of protection in accordance with the building regulations of the IEC 60079 series of standards. Types of protection for non-electrical equipment are defined in the ISO 80079 series of standards. The latter replaces the EN 13463 series of standards which is currently valid.

The type of protection which the manufacturer applies to equipment largely depends on the type and function of the equipment. Some types of protection are available in different protection levels. These correspond to the equipment categories in accordance to ATEX Directive 2014/34/EU and/or the equipment protection level (EPL) in accordance with IEC 60079-0. From a safety point of view, all standardised types of protection within a category and/or an equipment protection level should be considered equally.

The following tables provide an overview of the standardised types of protection and describe the basic principle and the normal applications. By integrating the types of protection for potentially explosive dust atmospheres in the IEC 60079 series of standards, the symbols for the types of protection are also simplified.

Types of protection for electrical equipment in hazardous areas

Type of protection according to IEC, EN and ULBasic principleMain application
General requirements
IEC 60079-0
EN 60079-0
UL 60079-0
This standard sets out the general requirements for explosion-protected electrical equipment. The equipment marking is also described in this standard. 
Flameproof enclosure "d"
IEC 60079-1
EN 60079-1
UL 60079-1
Parts which can ignite an explosive atmosphere are surrounded by an enclosure which withstands the pressure of an explosive mixture exploding inside the enclosure and prevents the transmission of the explosion to the atmosphere surrounding the enclosure.Switching equipment and switchgears, control and indicating equipment, control systems, motors, transformers, heating equipment, light fittings
da = Use in Zone 0, 1, 2
db = Use in Zone 1, 2
dc = Use in Zone 2
Pressurised enclosure "p"
IEC 60079-2
EN 60079-2
UL 60079-2
The formation of an explosive atmosphere inside an enclosure is prevented by maintaining a positive internal pressure of inert gas in relation to the surrounding atmosphere and, where necessary, by supplying the inside of the enclosure with a constant flow of inert gas which acts to dilute any combustible mixtures.Switching and control cabinets, analytical instruments, large motors
pxb = Use in Zone 1, 2 or Zone 21, 22
pyb = Use in Zone 1, 2 or Zone 21, 22
pzc = Use in Zone 2 or Zone 22
Powder filling "q"
IEC 60079-5
EN 60079-5
UL 60079-5
Filling the enclosure of an item of electrical equipment with a fine granular packing material has the effect of making it impossible for an electric arc created in the enclosure under certain operating conditions to ignite an explosive atmosphere surrounding the enclosure. Ignition must not result either from flames or from raised temperatures on the surface of the enclosure.Sensors, electronic ballasts, transmitters
q = Use in Zone 1, 2
Oil immersion "o"
IEC 60079-6
EN 60079-6
UL 60079-6
Electrical equipment or parts of electrical equipment are immersed in a protective fluid (such as oil), such that an explosive atmosphere present over the surface or outside of the enclosure cannot be ignited.Transformers, starting resistors 
o = Use in Zone 1, 2
Increased safety "e"
IEC 60079-7
EN 60079-7
UL 60079-7
Here, additional measures are taken to increase the level of safety, thus preventing the possibility of inadmissibly high temperatures and the occurrence of sparks or electric arcs within the enclosure or on exposed parts of electrical equipment, where such ignition sources would not occur in normal operation.Terminal and connection boxes, control boxes for installing Ex-components (which have a different type of protection), squirrel-cage motors, light fittings
eb = Use in Zone 1, 2
ec = Use in Zone 2
Intrinsic safety "i"
IEC 60079-11
EN 60079-11
UL 60079-11
Equipment that is used in a potentially explosive atmosphere only contains intrinsically safe electric circuits. An electric circuit is intrinsically safe if no sparks or thermal effects are produced under specified test conditions (which include normal operation and specific fault conditions) which might result in the ignition of a specified explosive atmosphere.Measuring and control technology, fieldbus technology, sensors, actuators
ia = Use in Zone 0, 1, 2 or Zone 20, 21, 22
ib = Use in Zone 1, 2 or Zone 21, 22
ic = Use in Zone 2 or Zone 22
[Ex ib] = associated electrical equipment – installation in the safe area
Type of protection "n"
IEC 60079-15
EN 60079-15 
UL 60079-15
Electrical equipment cannot ignite an explosive atmosphere surrounding it (during normal operation and under defined abnormal operating conditions).All electrical equipment for Zone 2
nA = non-sparking equipment
nC = sparking equipment and components
nR = restricted breathing enclosures
Encapsulation "m"
IEC 60079-18
EN 60079-18 
UL 60079-18
Parts which may ignite an explosive atmosphere are embedded in sealing compound such that the explosive atmosphere cannot be ignited.ma = Use in Zone 0, 1, 2 or Zone 20, 21, 22
mb = Use in Zone 1, 2 or Zone 21, 22
mc = Use in Zone 2 or Zone 22
IEC 60079-25
EN 60079-25
UL 60079-25
Intrinsic safety evaluation for defined systems (equipment and cables).Intrinsically safe systems
Optical radiation "op" 
IEC 60079-28
EN 60079-28
UL 60079-28
Suitable measures prevent ignition of an explosive atmosphere by optical radiation.Fibre optics/use in potentially explosive gas atmospheres. There are three different methods:
Ex op is = inherently safe optical radiation
Ex op pr = protected optical radiation
Ex op sh = optical radiation with interlock

Protection by enclosure "t"
IEC 60079-31
EN 60079-31

UL 60079-31  

Thanks to the tightness of the enclosure, dust cannot penetrate at all or the amount which can is limited to a safe level. For this reason, ignitable equipment can be installed in the enclosure. The enclosure's temperature must not ignite the surrounding atmosphere.Switching equipment and switchgears, control, connection and terminal boxes, motors, transformers, light fittings
ta = Use in Zone 20, 21, 22
tb = Use in Zone 21, 22
tc = Use in Zone 22

 

Types of protection for non-electrical equipment in hazardous areas

Protective type pursuant to ISO or EN

Basic principleMain application

General requirements
ISO 80079-36
(formerly EN 13463-1)

This standard specifies the general requirements for explosion-protected
electrical equipment and also details equipment marking.
 

Constructional safety “c”
ISO 80079-37
(formerly EN 13463-5)

Proven technical principles are applied to equipment types which do not
have any ignition source in normal operation, so that the risk of mechanical
faults causing incendive temperatures and sparks is reduced to a
negligible degree.

Couplings, pumps,
gear drives, chain drives,
conveyor belts

Control of ignition source “b”
ISO 80079-37
(formerly EN 13463-6)

Sensors are integrated into the equipment to detect imminent hazardous
conditions and adopt countermeasures at an early stage before potential
ignition sources become effective. The measures can be initiated automatically
by means of a direct connection between the sensors and the
ignition protection system or manually by issuing a warning to the operator
of the equipment.

Pumps, conveyor belts

Liquid immersion “k”
ISO 80079-37
(formerly EN 13463-8)

Ignition sources are rendered ineffective by immersion in a protective
liquid or by constant moistening with a liquid film.

Submerged pumps, gears

Flameproof enclosure “d”
IEC 60079-1
(formerly EN 13463-3)

Parts that can ignite an explosive atmosphere are housed in an enclosure
which withstands the pressure of an explosive mixture exploding inside
the enclosure and prevents transmission of the explosion to the atmosphere
around the enclosure.

Brakes, couplings

Pressurised enclosure “p”
IEC 60079-2
(formerly EN 60079-2)

The formation of an explosive atmosphere inside an enclosure is prevented
by maintaining a positive internal pressure of inert gas in relation
to the surrounding atmosphere and, where necessary, by supplying the
inside of the enclosure with a constant flow of inert gas to dilute combustible
mixtures.

Pumps

Protection by enclosure “t”
IEC 60079-31

Thanks to its tightness, dust cannot penetrate the enclosure or reduces
it to a negligible degree. Ignitable apparatus can now be mounted in the
enclosure. The enclosure temperature must not be sufficient to ignite
the surrounding atmosphere.

Equipment exclusively for
dust explosion hazardous areas

 

Combination of types of protection

If necessary, combinations of different types of protection can also be applied in order to provide an optimum solution from the safety, functional and economical point of view. Modern explosion-protected equipment generally combine with multiple types of protection. By using different types of protection on one item of equipment, smaller and more cost-effective designs can be implemented on the one hand. On the other, it means that construction types are possible that make operation and maintenance easier for the user.

Our "Essential Explosion Protection" brochure clearly sets out detailed information on types of protection, equipment groups, physical and technical bases, legal specifications and standards as well as erecting and operating systems in potentially explosive atmospheres.

Know what the markings mean

Equipment produced for potentially hazardous atmospheres is marked accordingly. The marking requires certain details depending on the certification and country-specific use.

Worldwide (IEC and ISO)

The marking for electrical equipment is set out in IEC 60079-0. In addition to the name of the manufacturer or their trademark, the type designation, serial number and the test body with certificate number, a special coding is required which describes the intended use of the equipment:

  • Ex symbol.
  • Symbol of any type of protection (e.g. q) or protection level (e.g. ib) used.
  • Equipment Group IIA, IIB or IIC for potentially explosive gas atmospheres and Equipment Group IIIA, IIIB or IIIC for potentially explosive dust atmospheres.
  • Temperature class for potentially explosive gas atmospheres and max. surface temperature in degrees Celsius for potentially explosive dust atmospheres.
  • Equipment Protection Level (EPL).

The marking for non-electrical equipment is specified in ISO 80079-36. It largely identical to that of electrical equipment. However, instead of various symbols for the protection types, the letter “h” is always used.

Europe (ATEX)

In Europe, the marking of electrical equipment in accordance with the IEC standard must meet additional requirements in accordance with ATEX Directive 2014/34/EU and must include the following data:

  • Manufacturer's address.
  • CE marking (where applicable, with identification number of the notified body).
  • Symbol and Equipment Group (e.g. II) as well as Category 1, 2 or 3 and the letter G (gas) or D (dust).

The marking of non-electrical equipment has now been adapted even more closely to that of electrical equipment. In Europe, the EN ISO 80079 series of standards has been applicable since 2016. An "h" is always specified as a symbol for the type of protection.

North America

In addition to the normal data (manufacturer, model, serial number and electrical data), any data relating to explosion protection must be shown on the equipment marking. The specification for this is laid out in the NEC for the USA, in the CEC for Canada and in the relevant building regulations of the test bodies.

Traditional classification of potentially explosive atmospheres in North America

Gases, vapours or mist
Class I classification
Dusts
Class II classification
Fibres and flyers
Class III classification
NEC 500
CEC J18
NEC 500
CEC J18
NEC 500
CEC J18
Division 1Division  1Division 1
Areas in which hazardous concentrations of ignitable gases or vapours
  • Are likely to occur under normal operating conditions.
  • Are likely to occur in the event of repair and maintenance work.
  • May occur in the event of disruptions to operation or under fault conditions and at the same time faults on electrical equipment occur which result in a source of ignition.
Areas in which hazardous concentrations of explosive dust atmospheres
  • Are likely to occur under normal operating conditions.
  • May occur in the event of disruptions to operation or under fault conditions and at the same time faults on electrical equipment occur which result in a source of ignition, as well as areas with hazardous quantities of conductive dust (Group E).
Areas in which combustible fibres and flyers are created or processed.
Division 2Division 2Division 2
Areas in which hazardous concentrations of ignitable gases or vapours are kept in closed containers or systems and can only be released under specific fault conditions.Areas in which combustible fibres are stored or handled differently from within the production process.Areas in which combustible fibres and flyers are created or processed.


 You can find further information in our "Essential Explosion Protection" brochure.

 

Overview of marking of electrical and non-electrical equipment

Marking of electrical equipment

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Marking of non-electrical equipment

pdf 331 KB