Explosion Protection

R. STAHL explosion protection
The basics of
explosion protection

preface
It is a fact that gases, vapours and mists escape during the production, processing,
transportation, and storage of flammable substances in the chemical and petrochemical
industries, as well as during the production of mineral oil and natural gas, in mining and in
many other sectors. During many processes, especially in the food industries, combustible
dusts are also created. These flammable gases, vapours, mists, and dusts form an explosive
atmosphere with the oxygen in the air. If this atmosphere is ignited, explosions take place,
which can result in severe harm to human life and property. To avoid the danger of
explosions, protective specifications in the form of laws, regulations, and standards have
been developed in most countries, which are aimed at ensuring that a high level of safety is
observed. Due to the growing international economic link, extensive progress has
been made in harmonizing regulations for explosion protection. The conditions for a
complete harmonization were created in the European Union through the 94/9/EC and 99/92/EC
Directives. There are also efforts to achieve a global harmonization with the IECEx-scheme,
but much work still needs to be done in this area world-wide. The aim of
this brochure is to provide both experts and interested laymen with an overview of the field
of explosion protection, in conjunction with electrical apparatus and installations. It does
not replace the study of the relevant statutory regulations and applicable standards.
In mining, miners underground have always lived under the threat of firedamp explosions.
Herein lies the origins of explosion protection, which has been consistently developed
in industrialized countries, and which now provides a high level of safety.

contents
Statutory Regulations and Standards
3.1 World-wide
3.1.1 General
3.1.2 Devices
3.1.3 Erection and operation
3.1.4 IECEx
3.2 European Union
3.2.1 Directives
3.2.2 Standards
3.2.4 Selection of devices
3.3 North America
3.3.1 General
3.4 Russia
3.4.1 General
Technical Principles
4.1 Zone classification
4.2 Categories and Equipment Protection Level EPL
4.2.1 General
1 Preface
The Basic Physic Principles and Definitions
2
3
4
2
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9
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11
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15
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28
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6.1 Safety Characteristics of Flammable Gases and Vapours
6.2 Constructional Requirements for Explosion Protected Electrical equipment for
gas-atmospheres
6.3 Degrees of Protection according to IEC 60529 – IPXX
6.4 Degrees of Protection according to NEMA Standards
Literature
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37
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39
44
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24
24
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25
25
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33
34
6
7
5.1 Duties of Installer, Manufacturer and Employer
5.2 Classification of Zones and Selection of Apparatus
5.3 Methods of Installation
5.4 Maintenance
5
4.2.2 Categories
4.2.3 Equipment protection level EPL
4.3 Groups
4.3.1 General
4.3.2 Classification
4.4 Ignition temperature and temperature classes
4.4.1 General
4.4.2 Explosive gases
4.4.3 Combustible dusts
4.5 Types of protection
4.5.1 Applications of Type of Protection »Intrinsic Safety«
4.5.2 Applications of Type of Protection »c«
4.5.3 Application and Combination of Types of Protection »d« and »e«
4.6 Marking
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41
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Installation and Operation of Electrical Equipment 36
Appendix
21
22

2. The Basic Physic Principles and Definitions
of Explosion Protection
An explosion is the sudden chemical reaction of a
flammable substance with oxygen with the
simultaneous release of high energy. Flammable
substances may be present in the form of gases,
vapours, mists or dusts. An explosion can only take
place,when three factors are present simultane-
ously (fig. 1):
1. Flammable material (in ignitable quantities)
2. Oxygen (in the air)
3. Ignition source
Certain characteristic properties of these materials
are required for safety considerations. The flash
point of a flammable liquid is the minimum
temperature at which a liquid gives off vapour in
sufficient concentration to form an ignitable
mixture with air near the surface of the liquid (at
normal air pressure). If the flash point of a flamma-
ble liquid is well above the maximum tempera-
tures that arise, an explosive atmosphere can not
be formed. The flash point of a mixture of various
liquids may be lower than that of the individual
components. In addition to the boiling point, the
flash point of a liquid serves to classify liquids as
highly flammable, easily flammable, and flamma-
ble liquids in the Council Directive 98/24/EC »risks
Fig. 1: An explosion can only occur, when these three
factors come together
Table 1: Classification of flammable liquids
Designation of the flammable liquid at flash point and boiling point °C
Highly flammable Flash point < 0°C and boiling point < 35°C
Easily flammable Flash point < 21 °C and boiling point > 35°C
Flammable 21°C < Flash point < 55°C
6
related to chemical agents«.
To form an explosive atmosphere, the flammable
substance must be present in a certain concentra-
tion (fig. 2).
If the concentration is too high (rich mixture) or
too low (lean mixture), no explosion occurs.
Instead, there is just a steady-state combustion
reaction or none at all. It is only in the range
between the lower and upper explosion limit that
the mixture reacts explosively when ignited. The
explosion limits depend on the ambient pressure
and the proportion of oxygen in the air (table 2).
Explosion protection
2. the basic physic principles and definitions

Mixture
too lean
no
combustion
Mixture
too rich
Deflagration
no explosion
Explosion range
Explosion
lower limit higher
Concentration of air100 Vol % 0 Vol %
Concentration of
combustible substance in air0 Vol % 100 Vol %
Fig. 2: Explosion limits
Table 2: Explosion Limits of selected Gases and Vapours
Substance
designation
Lower explosion limit
[Vol. %]
Upper explosion limit
[Vol. %]
Acetylene 2,3 100 (self-decomposing!)
Ethylene 2,4 32,6
Gasoline ~ 0,6 ~8
Benzol 1,2 8
Heating oil/diesel ~0,6 ~6,5
Methane 4,4 17
Propane 1,7 10,8
Carbon disulphide 0,6 60,0
Hydrogen 4,0 77,0
Extract from the table »Sicherheitstechnische Kenngrößen, Band 1: Brennbare
Flüssigkeiten und Gase« (Safety characteristics, vol. 1: flammable liquids and gases) by
E. Brandes and W. Möller as well as by T. Redeker and G. Schön – (6 th addendum)
7
Depending on the speed of combustion, we speak
of deflagration, explosion or detonation. An atmos-
phere is described as hazardous or explosive if
there is danger to human life or property by an
explosion. An explosive atmosphere of even just a
few litres can be dangerous in an enclosed space.
Ignition source
Ignition of an explosive atmosphere can be caused
by various sources:
> hot surfaces
> flames and hot gases
> mechanically generated sparks
> electrical installations
> equalizing currents, cathodic corrosion
protection
> static electricity
> lightning
> electromagnetic waves (high-frequency)
> optical radiation
> ionising radiation
> ultrasonics
> adiabatic compression and shock waves
> exothermal reactions

1
2
3
Preventing the
formation of an explosive
atmosphere
Avoidance of the
ignition of an explosive
atmosphere
Mitigation of the effects
of an explosion to
an acceptable extent
Integrated explo-
sion protection
Fig. 3: Basic principles of explosion protection
8
Preventing explosive atmospheres
(Primary Explosion Protection)
The term primary explosion protection refers to all
precautions, which prevent a hazardous explosive
atmosphere from being created. This can be
achieved by:
> avoiding flammable substances
(replacement technologies)
> inerting (addition of nitrogen,
carbon dioxide etc.)
> limitation of the concentration by means of
natural or technical ventilation
Avoiding ignition of explosive atmospheres
If the danger of explosion cannot be completely
or only partly avoided by measures of preventing
the formation of an hazardous explosive atmos-
phere, then measures must be taken that
avoid the ignition of the explosive atmosphere.
The required safety level of these measures
depends on the possible danger potential in the
installation location. The hazardous areas
are therefore divided into zones, according to
the probability of an explosive atmosphere being
formed (see Section 3.2.2).
Mitigation of the explosion effects
(Constructive Explosion Protection)
If hazardous explosive atmospheres cannot be
safely avoided and their ignition cannot be exclud-
ed, then measures must be taken which limit the
effect of explosions to a safe degree,
for example, through the use of:
> flameproof or pressure surge resistant design
> explosion relief devices
> explosion suppression by means of
extinguishers
The principle of integrated explosion protection
requires following explosion protection measures
in a certain sequence.
2. the basic physic principles and definitions

3.1 World-wide
3.1.1 General
The International Electrotechnical Commission
(IEC) is responsible for the global standards on the
field of electrical engineering.
IEC publications dealing with the explosion protec-
tion of electrical devices and installations are de-
veloped by the Technical Committee TC31 and can
be seen as recommendations which are a basis for
almost all standards. Up until a few years ago, re-
quirements for areas with potentially explosive
gases have been stipulated in standard series
60079 and for areas containing combustible dusts
in series 61241. As numerous requirements are
similar for both areas, the two standard series will
be combined in series IEC 60079. For some stand-
ards this step has already been taken, others will
follow.
National regulations, however, may differ from
these standards. Based on this, it is necessary to
examine the extent to which the IEC-standards
may be applied in the different countries.
3.1.2 Equipment
The different methods of ensuring ignition protec-
tion of devices are called types of protection.
These are described in different parts of the IEC-
series 60079 or 61241. These are construction reg-
ulations that are acknowledged in many countries
(see table 3).
Equipment used in hazardous areas has to be clas-
sified in zones, according to the degree of danger
in regard to the probability of the occurrence of a
potentially explosive atmosphere (please also see
4.1). For this purpose IEC developed two standards.
IEC 60079-10-1:
Classification of areas – explosive gas atmos-
pheres
IEC 60079-10-2:
Classification of areas – combustible dust atmos-
pheres
Further standards are available for erection and op-
eration of electrical installations:
IEC 60079-14:
Design, selection and erection of electrical instal-
lations
IEC 60079-17:
Inspection and maintenance of electrical installa-
tions
IEC 60079-19:
Equipment repair, overhaul and reclamation
3. statutory regulations and standards
9

10
Table 3: Electrical Equipment for Explosive Atmospheres
IEC EN
General requirements IEC 60079-0 EN 60079-0
Equipment protection by flameproof enclosures »d« IEC 60079-1 EN 60079-1
Classification of areas – Explosive gas atmospheres IEC 60079-10-1 EN 60079-10-1
Classification of areas – Combustible dust atmospheres IEC 60079-10-2 EN 60079-10-2
Equipment protection by intrinsic safety »i« IEC 60079-11 EN 60079-11
Equipment protection by pressurized room »p« IEC 60079-13 EN 60079-13
Installations design, selection and erection IEC 60079-14 EN 60079-14
Equipment protection by type of protection »n« IEC 60079-15 EN 60079-15
Electrical installations inspection and maintenance IEC 60079-17 EN 60079-17
Equipment protection by encapsulation »m« IEC 60079-18 EN 60079-18
Equipment repair, overhaul and reclamation IEC 60079-19 EN 60079-19
Equipment protection by pressurized enclosure »p« IEC 60079-2 EN 60079-2
intrinsically safe systems IEC 60079-25 EN 60079-25
Equipment with equipment protection level (EPL) Ga IEC 60079-26 EN 60079-26
Fieldbus intrinsically safe concept (FISCO) IEC 60079-27 EN 60079-27
Protection of equipment and transmission systems using optical radiation IEC 60079-28 EN 60079-28
Gas detectors – Performance requirements of detectors for flammable gases IEC 60079-29-1 EN 60079-29-1
Gas detectors – Selection, installation, use and maintenance of detectors for flammable gases and oxygen IEC 60079-29-2 EN 60079-29-2
Gas detectors – Performance requirements of open path detectors for flammable gases IEC 60079-29-4 EN 61241-1
Electrical resistance trace heating – General and testing requirements IEC 60079-30-1 EN 60079-30-1
Electrical resistance trace heating – Application guide for design, installation and maintenance IEC 60079-30-2 EN 60079-30-2
Equipment dust ignition protection by enclosure »t« IEC 60079-31 EN 60079-31
Equipment protection by powder filling »q« IEC 60079-5 EN 60079-5
Equipment protection by oil immersion »o« IEC 60079-6 EN 60079-6
Equipment protection by increased safety »e« IEC 60079-7 EN 60079-7
Protection by intrinsic safety »iD« IEC 61241-11 EN 61241-11
Type of protection »pD« IEC 61241-4 EN 61241-4
Artificial ventilation for the protection of analyser(s) IEC/TR 60079-16
Methods for determining the minimum ignition temperatures of dust IEC 61241-2-1 EN 50281-2-1
Method for determining the electrical resistivity of dust in layers IEC 61241-2-2 EN 61241-2-2
Method for determining minimum ignition energy of dust/air mixtures IEC 61241-2-3
Safety devices required for the safe functioning of equipment with respect to explosion risks EN 50495
3.statutory regulations and standards

3.1.4 IECEx
Like the technical and organisational procedures
and measures for the prevention of explosions, the
physiochemical principles for the development of
explosions are equally valid all over the world, de-
spite minor differences.
Therefore, as a natural next step it was necessary
to regulate the conditions for approval of electrical
devices on a global basis and to make free global
trade possible with the certificates valid in differ-
ent countries and regions. So the IEC introduced a
procedure whose objective is standardization: the
IEC-Ex-scheme.
Throughout the world there are now 35 acknowl-
edged IECEx certification bodies (ExCB = Certifica-
tion Body) and 36 acknowledged IECEx test labora-
tories (ExTLs) that are accredited according to high
uniform benchmarks and that are controlled regu-
larly. IECEx follows the rule that a certificate is on-
ly issued when the type tests of the samples have
been passed and existence of an effective quality
management system has been verified with an au-
dit. Currently there are still regional and national
approval procedures all over the world, such as,
the ATEX Directive in the European Union or na-
tional approvals in the USA (UL, FM).
After having established the IECEx scheme for
testing and certification of new products, another
important field of explosion protection has been
covered with a suitable certification scheme:
maintenance and repair of explosion-protected de-
vices. This certification procedure was named
»IECEx Certified Service Facilities Program«
Depending on the maintenance and repair work,
experienced assessors establish during an audit if
the required personal competences in regard to
the function of the respective product and the ap-
plied types of protection are available , if a suffi-
cient amount of correct test devices are available,
if measures for identification and retraceability
have been fixed and executed accordingly and if
subcontractors are trained and controlled.
The basis for this evaluation is given in standards
»IEC 60079-19: Equipment repair, overhaul and rec-
lamation«, the »Operational Document OD 013:
IECEx Operations Manual – Assessment and Certi-
fication of Ex Repair and Overhaul Service Facili-
ties« and »OD 014: IECEx Operational Document:
Quality System Requirements for IECEx Service Fa-
cilities involved in Repair, Overhaul and Modifica-
tion of Ex Equipment«.
The third component of the IECEx scheme aims in a
similar direction, dealing with the certification of
the personal competences of the experts working
in hazardous areas. This is also meant to give oper-
ators working world-wide the security that the em-
ployed personnel has the required qualifications
and experiences to do the different, sometimes
very complex work in hazardous areas correctly.
11

Table 4: Non-Electrical Equipment for Explosive Atmospheres
EN
Basic method and requirements EN 13463-1
Protection by flow restricting enclosure »fr« EN 13463-2
Protection by flameproof enclosure »d« EN 13463-3
Protection by constructional safety »c« EN 13463-5
Protection by control of ignition source »b« EN 13463-6
Protection by liquid immersion »k« EN 13463-8
3.2 European Union
3.2.1 Directives
Already in 1976, the Council of the European
Community established the prerequisite of
free trade of explosion protected electrical equip-
ment within the European Union by ratifying
the »Directive on the harmonization of the laws
of the member states concerning electrical
equipment for use in potentially explosive atmos-
pheres (76/117/EEC)«. This directive has since
become state of the art by means of
execution and adaptation directives on
electrical equipment.
Complete harmonization and extension to all types
of equipment, electrical and non-electrical, was
completed with the new Directive 94/9/EC in 1994.
In 1999 Directive 99/92/EC (ATEX 137) followed,
which regulates operation in hazardous areas and
defines safety measures for the concerned person-
nel.
3.2.2 Standards
The European Standards EN 50014 - EN 50020 on
electrical equipment were issued in 1978 and
replaced the national standards for this equipment
which had been valid up until then Europe-wide. In
addition to
the standards for electrical equipment published
by the CENELEC, standards for non-electrical
explosion-protected equipment have since been
developed by the CEN.
According to an agreement between the European
Committee for Electrotechnical Standardization
CENELEC and the International Electrotechnical
Commission IEC, the European standards for
electrical equipment have been adopted un-
changed by the IEC for several years. The European
Standard series EN 50014, which defines the re-
quirements on equipment to be used in explosive
gas atmospheres, has been gradually replaced by
the European Standards series EN 60079.
These standards have been issued as VDE 0170
in Germany. The requirements on types of protec-
tion for areas where combustible dust may occur
are specified in the standard series IEC 61241. In
Europe, these standards replace the existing series
EN 50281. Since many requirements are identical
to the standards for explosive gas atmospheres,
both standard series will be summarized in the se-
ries IEC or EN 60079 (table 3).
After publication of Directive 94/9/EC the construc-
tion regulations for non-electrical devices have al-
so been fixed in Europe with standard series EN
13463 (see table 4). Some protection principles for
electrical devices have been adopted. However,
some adjustments have been made to fulfil the
special demands on non-electrical devices.
12
GrundlagenExplosion protection

The Directive 99/92/EC (ATEX 137)
The 99/92/EC Directive »Minimum requirements
for improving the health and safety protection of
worker potentially at risk from explosive atmos-
pheres« refers to the operation of potentially ex-
plosive installations, and is therefore intended for
the employer.
According to the 99/92/EC Directive, it is the
duty of the employer to verify where there is a
risk of explosion, classify the hazardous areas into
zones accordingly, and document all measures
taken to protect the personnel in the explosion
protection document:
Assessment of explosion risks
When assessing the risks of explosion, the
following factors are to be taken into account:
> the likelihood that explosive atmospheres
will occur and their persistence
> the likelihood that ignition sources, including
electrostatic discharges, will be
present and become active and effective
> the installations, substances used, processes,
and their possible interactions
> the scale of the anticipated effects
Zone Classification
The employer has to classify the areas in which
explosive atmospheres may be present into zones,
and to ensure that the minimum organisational
and technical requirements of the Directive are
observed (see 4.1).
Explosion protection document
An explosion protection document has to be
generated, which contains at least the following
information:
> assessment of the explosion risk
> protective measures taken
> zone classification
> observance of minimum requirements:
These are divided into organisational measures
(instruction of workers, etc.) and technical
measures (explosion protection measures).
This directive lays down the minimum requirements
that may be tightened by national regulations in
the individual countries.
The Directive 94/9/EC (ATEX 95)
The EC Directive 94/9/EC »on the approximation of
the laws of the Member States concerning equip-
ment and protective systems intended for use
in potentially explosive atmospheres« was issued
in 1994 to further standardize explosion protection
in the EU and make corresponding adjustments in
line with a new directive approach. It specifies the
requirements for explosion protected equipment
and protective systems (e.g. with specifications in
regard to design, certification, manufacturing and
quality assurance, marking, operating instructions
and declaration of conformity) by prescribing es-
sential health and safety requirements, which have
to be observed by the manufacturer and the import-
er.
The directive guarantees free trade within the Euro-
pean Community, as agreed in Article 95 (former
100 a) of the Treaty established between the Euro-
pean Community member states. This is also
where the term generally used amongst experts,
ATEX 95 or 100 a (ATEX as the abbreviation of the
French designation for explosive atmosphere »at-
mosphères explosibles«), comes from.
13

The directive had to be implemented into national
law without any changes/exceptions.
It applies to all industrial potentially explosive are-
as including mining, and also covers dust explo-
sion protection.
Definitions
> »Equipment« means machines, apparatus,
fixed or mobile devices, control components
and instrumentation thereof, and detection or
prevention systems which, separately or jointly,
are intended for the generation, transfer,
storage, measurement, control, and conversion
of energy for the processing of material and
which are capable of causing an explosion
through their own potential sources of ignition.
> »Protective systems« is the definition for design
units, which are intended to halt incipient
explosions immediately and/or to limit the
effective range of explosion flames and
explosion pressures. Protective systems may be
integrated into equipment separately and
placed on the market for use as autonomous
systems.
> »Components« means any item essential to the
safe functioning of equipment and protective
systems but with no autonomous function.
> An »explosive atmosphere« is a mixture with air,
under atmospheric condition, of flammable sub-
stances in the form of gases, vapours, mists,
or dusts in which, after ignition has occurred,
combustion spreads to the entire unburned
mixture.
> A »potentially explosive atmosphere« is an
atmosphere which could become explosive due
to local and operational conditions.
Scope
The directive applies to equipment and protective
systems for use in potentially explosive
atmospheres.
Safety devices intended for use outside potentially
explosive atmospheres but required for or contrib-
uting to the safe functioning of equipment with
respect to the risk of explosion are also covered
by the scope of this Directive. The Directive does
not include a reference to mandatory standards,
whereas it specifies the essential health and
safety requirements to be maintained, and which
are mandatory for design and construction.
Protection against other hazards (e.g. electric
shock) that could be caused by this equipment,
is also required.
Equipment categories
The manufacturers of equipment that includes its
own potential ignition sources, and therefore
could cause an explosion, have to ensure that the
equipment undergoes an ignition hazard assess-
ment procedure, and takes measures according to
the essential safety requirements to exclude the
risk of ignition. In the directive, Group II apparatus
are divided into three categories with various
levels of safety (for mines Group I has two catego-
ries). The required protective measures suit the
required level of safety (see 4.2.2).
Certification
Equipment for use in hazardous areas has to
undergo the conformity assessment procedure
defined in the directive prior to being placed on
the market. Category 1 and M1 equipment must
undergo an EC type examination carried out by a
Notified Body. The same applies to electrical
equipment and I.C.-engines of Category 2 and M2.
For non-electrical equipment of this category,
as well as for those of Category 3, the manufactur-
er is authorized to assess and document
conformity with the requirements of the directive.
The certificates from a Notified Body are recog-
nized throughout the European Community.
14

Marking
In addition to the usual data such as the name
of the manufacturer, type, serial number, and
electrical ratings, any data relating to explosion
protection must be contained in the marking
(see also 4.6).
The CE marking of the equipment confirms that it
is designed and manufactured in compliance with
all applicable EC Directives. For example, an
explosion protected luminaire marked with the CE
conformity mark must comply with both the
ATEX 95 Directive as well as the »EMC Directive«.
Operating instructions
The manufacturers operating instructions
must clearly define the intended use of the
equipment by the operator.
The minimum requirements for the operating in-
struction are include amoungst other things,
Information on safe:
> putting into service
> use
> assembly and dismantling
> maintenance (servicing and emergency repair)
> installation
If necessary, special conditions for safe use have
to be specified and should include notes on
possible misuse that may occur as shown by expe-
rience.
Manufacturer’s EC-Declaration of Conformity
Equipment and systems can be placed on the
market, only if marked with the CE mark and com-
plete with operating instructions and the manufac-
turer’s EC-declaration of conformity. The CE con-
formity marking and the written EC-declaration of
conformity confirm that the product complies with
all requirements and assessment procedures spec-
ified in the EC Directives.
3.3. North America
3.3.1 General
The basic principles of explosion protection are the
same all over the world. However, technologies
have developed in North America in the field of ex-
plosion protection for electrical equipment and in-
stallations which deviate considerably from those
of the IEC (International Electrotechnical Commis-
sion). The differences from IEC technologies are
among others the classification of hazardous loca-
tions, the construction of apparatus and the instal-
lation of electrical systems.
For electrical equipment and installations that are
used in potentially hazardous areas in the USA the
National Electrical Code (NEC) is applicable, and in
Canada the Canadian Electrical Code (CEC) applies.
These codes regulate facilities for electrical instal-
lations in all areas and refer to a series of Stand-
ards from other institutions that also regulate the
installation and construction of equipment.
For potentially explosive atmospheres the term
»hazardous (classified) locations« is used in
North America. These are defined in Articles 500
and 505 of the National Electrical Code (NEC)
in the USA and in Section 18 and Annex J of the
Canadian Electrical Code (CEC) in Canada.
Hazardous locations are locations, where fire or
explosion hazards may exist due to flammable
gases, vapours or mists (Class I), combustible
dusts (Class II), or ignitable fibres or flyings
(Class III).
15

Based on the likelihood or risk that an ignitable
concentration of a flammable substance will be
present the hazardous locations are traditionally
subdivided into Division 1 and Division 2.
In 1996 the IEC classification system was intro-
duced as a parallel system to the existing system
for Class I in the USA. This system was implement-
ed through the new Article 505. This now gives the
end user the possibility to choose the system that
best suits his needs. In 2005, Article 506 intro-
duced Zones 20, 21 and 22 for areas with combus-
tible dust.
The IEC zone classification for Class I was also
introduced in Canada (CEC, 1988 edition).
All newly built facilities in Canada need to be
classified according to this principle.
The traditional North American classification
system divides Class I flammable gases, vapours,
mists and liquids into Gas Groups A, B, C and D,
and Class II combustible dusts into Groups E, F
and G. Group A is the most hazardous gas group in
the traditional NEC system whereas Group IIC is
the most hazardous group in the IEC system in
Article 505 of the NEC. In Canada both gas group-
ing systems may be used with the zone classifica-
tion system.
The determination of the maximum surface tem-
perature according to Article 505 in the NEC takes
place in 6 temperature classes T1 to T6 in agree-
ment with the IEC. This also includes an additional
subclassification into temperature classes within a
division system. After the CEC in 1998 the existing
system for temperature classification was not
changed.
The installation method for the zone concept ac-
cording to the NEC 505 complies with the tradi-
tional class/division systems. New to the NEC
along with the use of fixed pipelines and mineral
isolating cables Type MI in class 1, division 1 re-
spectively zone 1, is also the use of approved list-
ed Type MC cable.
A significant advantage of the CEC is the increased
application possibility of cables and lines. In con-
trast to the USA, Canada has for some time al-
lowed the application of special cables that are
similar to the ringle wire armoured cables in the
IEC areas.
Further, there are different norms and standards
for the construction and testing of explosion pro-
tectes electrical facilities and equipment in North
America. In the USA these are predominately the
Standards of the International Society for Meas-
urement and Control (ISA), respectively the Under-
writers Labratories Inc. (UL) or Factory Mutual Re-
search Corporation (FM). In Canada it is the
Canadian Standards Association (CSA).
Degrees of Protection provided by Enclosures
As standard IEC 60 529 defines the degrees
of protection provided by enclosures, as the
NEMA Publication No. 250 (National Electrical
Manufacturing Association) defines the degree of
protection in the USA. These enclosure types can-
not be exactly equated with the IEC enclosure clas-
sification designation since NEMA takes
additional environmental influences (such as cool-
ing lubricant, cutting coolant, corrosion, icing, hail)
into account. The tables 7.5 and 7.6 in the appen-
dix illustrate the types of protection according
to both standards.
Certification and Marking
Equipment which has been developed and
manufactured for use in hazardous locations is
tested and approved in the USA and Canada by a
notified testing authority. In the USA, this is for
16

example, the Underwriters Laboratories or Factory
Mutual, and in Canada the Canadian Standards
Association.
In addition to data such as manufacturer, type,
serial number, and electrical data, any data relat-
ing to explosion protection must be shown on
the marking of the equipment. The requirements
for this are specified in the NEC, the CEC as
well as, the relevant apparatus regulations of the
testing authority (see 4.6).
17
Table 6a: Classification of Hazardous Locations in North America
Gases, vapors or mists
Classification Class I
Dusts
Classification Class II
Fibers and Flyings
Classification Class III
NEC 500
CEC J18
NEC 500
CEC 18
NEC 500
CEC 18
Division 1
A location, in which ignitable concentrations of
flammable gases, flammable liquid-produced va-
pors, or combustible liquid-produced vapors
- can exist under normal operating conditions, or
- may exist frequently because of repair or
maintenance operations or because of leakage
failure of electrical equipment
- might be released during breakdown or faulty
operation of equipment or processes.
Division 1
A location, in which combustible dust is in the air
in quantities sufficient to produce explosive or igni-
tible mixtures,
- under normal operating conditions
- due to mechanical failure or abnormal operati-
on of machinery or equipment and might also
provide a source of ignition through simultane-
ous failure of electric equipment, through ope-
ration of protection devices, or from other
causes, or
- a location in which Group E combustible dusts
may be present in quantities sufficient to be ha-
zardous.
Division 1
A location in which easily ignitible fibers/flyings are
handled, manufactured, or used.
Division 2
A location in which volatile flammable gases, flam-
mable liquid–produced vapors, or combustible li-
quid–produced vapors are handled, processed, or
used, but in which the liquids, vapors, or gases will
normally be confined within closed containers or
closed systems from which they can escape only in
case of accidental rupture or breakdown of such
containers or systems or in case of abnormal ope-
ration of equipment.
Division 2
A location in which combustible dust due to abnor-
mal operations may be present in the air in quanti-
ties sufficient to produce explosive or ignitible mix-
tures.
Division 2
A location in which easily ignitible fibers/flyings are
stored or handled other than in the process of ma-
nufacture.

One of the main tasks when establishing these
standards has been the harmonization with the in-
ternational standards series IEC 60079. However,
most Russian standards show national deviations
compared to the international standards.
Hazardous areas
All hazardous areas where potentially explosive
mixtures consisting of gases or vapours and air or
combustible dusts or where fibres in the air may
occur, are evaluated from two points of view with
regards to hazard:
> Probability of the occurrence of a potentially
explosive atmosphere in the respective area.
> Safety-relevant key figures of the substances,
gases, vapours dusts that are used and of the ig-
nition sources that may be found.
For evaluation of the possible use of explosion pro-
tected equipment in an installation, the safety-rele-
vant parameters of the explosion protection of the
devices and the parameters of a potentially explo-
sive atmosphere in this area of the installation
3.4 Russia
3.4.1 General
Prerequisite for the use of explosion-protected
electrical equipment in Russian plants is the avail-
ability of an approval by an acknowledged test
and certification centre of the Russian Federation
that confirms the compliance with the require-
ments stated in the Russian standards.
Since 01/01/2001 a new series of standards
which regulates the requirements on the design of
explosion-protected electrical equipment, the clas-
sification of hazardous areas and the application
of explosion-protected equipment in different pro-
tection levels in hazardous areas is effective in
Russia.
18
Table 6c: Temperature classes
Ignition temperature of
gas or vapour in °C
Temperature
class
Max. surface
temperature on
the equipment
°C
> 450 T1 450
> 300 up to 450 T2 300
> 280 up to 300 T2A 280
> 260 up to 280 T2B 260
> 230 up to 260 T2C 230
> 215 up to 230 T2D 215
> 200 up to 300 T3 200
> 180 up to 200 T3A 180
> 165 up to 180 T3B 165
> 160 bis 165 T3C 160
> 135 bis 200 T4 135
> 120 bis 135 T4A 120
> 100 bis 135 T5 100
> 85 bis 100 T6 85
Table 6b: Groups
Gas Dust
A (Acethylene) E (metal)
B (Hydrogen) F (carbon)
C (Ethylene) G (flour plastic)
D (Propane)

have to be in tune. In this context it is necessary to
classify the hazardous area in zones according to
the probability of the occurrence of hazardous po-
tentially explosive atmosphere.
Currently there are two possibilities of classifica-
tion in effect in Russia: the new classification ac-
cording to GOST R 51330-99 and the old classifica-
tion according to the long standing erection
regulations for electrical installations. The reason
behind this is the long-time use of classification of
Ex-zones pursuant to the hitherto valid standard.
So this classification does not only apply to many
currently existing installations but also to those in-
stallations that are reconstructed.
Explosion protection level
Electrical devices are classified according to their
explosion protection level. The term »explosion
protection level« basically corresponds to the de-
termination in regard to equipment category given
in the European Directive 94/9/EC, respectively
the equipment protection level pursuant to IEC
60079-9, but with a different numbering, a differ-
ent classification into types of protection, and a
different grading of the underground areas. Direct
assignment of protection level 0, 1, 2 to Zone 0, 1,
2 does not exist. Erection regulations GOST R
51330.13-99 stipulates what type of protection
may be used in which zone and this corresponds
to the definition given in IEC 60079-14.
Protection level 2
Electrical equipment with a normal degree of ex-
plosion protection (for marking of explosion pro-
tection figure 2 for equipment of Group II and the
Cyrillic letters PB for Group I are added). This is ex-
plosion-protected electrical equipment with which
explosion protection is guaranteed under normal
operating conditions. This explosion protection
level can be ensured with the following types of
protection: ia, ib, ic, px, pz, q, e, m, d, o, s.
Protection level 1
Explosion-protected electrical equipment with a
high degree of explosion protection (for marking of
explosion protection figure 1 for electrical equip-
ment for Group II and the Cyrillic letters ΡΠ for
Group I are added). This is explosion-protected
electrical equipment with which explosion protec-
tion is ensured in normal operating conditions and
when device errors or error conditions occur that
may normally be expected. This explosion protec-
tion level can be guaranteed with the following
types of protection: ia, ib, px, d, s.
Protection level 0
Special explosion-protected electrical equipment
with a very high degree of explosion protection (for
marking of explosion protection the figure 0 for
electrical equipment of Group II and the Cyrillic let-
ters PO for Group I are stated). It is explosion-pro-
tected electrical equipment for which additional
protection measures have been taken within a
standardized type of protection. This explosion pro-
tection level can be ensured with the following
types of protection: ia, s.
Marking
The marking specifications are given in standard
GOST R 51330.0-99 and in the standards for the
different types of protection (see 4.6).
19

4.1. Zone classification
Hazardous areas are classified into zones to facili-
tate the selection of appropriate electrical appara-
tus as well as the design of suitable electrical
installations. Zone classification is a reflection of
the probability of a potentially explosive atmos-
phere occuring again. Information and specifica-
tions for zone classification of potentially explo-
sive gas areas can be found in IEC 60079-10-1,
and for areas with potentially combustable dust in
IEC 60079-10-2.
When classifying hazardous areas into zones and
determining the required protection measures, the
highest possible hazard potential has to be taken
into account. If there is no qualified person availa-
ble in the company for evaluation of explosion haz-
ard and determination of the required measures, a
qualified body should be employed. The devices
used in the defined danger area have to fulfil the
requirements of the respective equipment catego-
ry or equipment protection level.
A survey on zone classification and the assessment
of devices according to their category is shown in
table 8.
Gas
Zone 0
A place in which an explosive atmosphere consisting of a mixture of air with flammable substances in the form of gas,
vapour or mist is present continuously or for long periods or frequently.
Zone 1
vapour or mist is likely to occur in normal operation occasionally.
Zone 2
vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only.
Dust
Zone 20
A place in which an explosive atmosphere in the form of a cloud of combustable dust in air is present continously, or
for long periods or frequently.
Zone 21
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal
operation occasionally.
Zone 22
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in nor-
mal operation but, if it does occur, will persist for a short period only.
Table 7: Zone Classification
20
4.technical principles

4.2 Categories and Equipment Protection
Level EPL
4.2.1 General
Depending on the probability of the occurrence of
a potentially explosive atmosphere, different safe-
ty requirements are posed on the equipment that
is used. Safety level of the devices is adjusted to
the hazard potential in the different zones.
With EC-Directive 94/9/EC (ATEX 95) explosion-
protected devices are classified in categories in
Europe. On an international level, equipment pro-
tection level EPL has been introduced with IEC
60079-0 of 2007.
Equipment has to be designed in such a way that
explosion protection measures on different protec-
tion levels (degree of protection) are included, de-
pending on the category or EPL.
4.2.2 Categories
For devices for use in potentially explosive areas –
excluding firedamp mines – three categories are
provided:
Category 1:
Very high degree of safety. Safe even when infre-
quent device errors occur. Two independent explo-
sion protection measures, or safe even, when two
failures occur independently.
Category 2:
High degree of safety. Safe even when there are
frequent device errors that may usually be expect-
ed. Even safe when a failure occurs.
Category 3:
Normal degree of safety. Safe during normal oper-
ation. Additional letter »G« or »D« refers to the use
of the device in areas with potentially explosive
gases (G) or in areas with combustible dust (D).
Table 8: Zones and allocation of equipment according to the category and the quipment protection level
Zone
Duration of the occurrence of
an explosive atmosphere
Equipment category Equipment protection level EPL
Gases, vapours, mists
0
continuously, for a long period fre-
quently
1G Ga
1 occasionally 2G Gb
2 rarely and for a short period 3G Gc
Dusts
20
continuously, for a long period,
frequently
1D Da
21 occasionally 2D Db
22 rarely and for a short period 3D Dc
21

Devices for use in firedamp mines are classified in
two categories:
Category M1:
Very high degree of safety. Safe even when infre-
quent device errors occur. Devices may still be op-
erated when a potentially explosive atmosphere
occurs.
Category M2:
High degree of safety. Safe during normal opera-
tion, even under difficult operating conditions.
Devices must be turned off in case of potentially
explosive atmosphere.
4.2.3 Equipment protection level EPL
Pursuant to IEC 60079-0 (2007), devices for poten-
tially explosive areas are classified into three pro-
tection levels (for devices used in firedamp mines
two protection levels are determined):
EPL Ga or Da:
Devices with a »very high« protection level for use
in hazardous areas where there is no ignition haz-
ard during normal operation and in case of fore-
seeable or infrequent faults/malfunctions.
EPL Gb or Db:
Devices with a »high« protection level for use in
hazardous areas where there is no ignition hazard
during normal operation or in case of foreseeable
faults/malfunctions.
EPL Gc or Dc:
Devices with »extended« protection level for use in
hazardous areas where there is no ignition hazard
during normal operation and where some addition-
al protective measures are applied to ensure that
the usually foreseeable malfunctions of the devic-
es do not cause ignition hazard.
The letters »G« and »D« determine whether the de-
vice is suitable for use in areas with potentially ex-
plosive gases (G) or for areas with combustible
dust (D).
Devices for firedamp mines:
EPL Ma:
Device with a »very high« protection level for
mounting in firedamp mines, which ensures the re-
quired degree of safety so that no ignition hazard
occurs during normal operation, or in case of fore-
seeable or infrequent faults/malfunctions, even if
the device is still in operation during a gas leak.
EPL Mb:
Device with a »high« protection level for mounting
in firedamp mines, which ensures the required de-
gree of safety so that there will be no ignition haz-
ard during normal operation or in case of foreseea-
ble faults/malfunctions, during the period between
gas leak and turning-off of the device.
Range of application of equipment of a certain cat-
egory or EPL in the respective danger zones in po-
tentially explosive areas is shown in table 7.
22

4.3 Groups
4.3.1 General
Equipment Groups according to European
Directive 94/9/EC (ATEX 95)
The ATEX-Directive classifies the equipment for
use in potentially explosive Atmospheres in two
groups:
Equipment group I:
Equipment intended for use in underground parts
of mines, and in those parts of surface installa-
tions of such mines, liable to be endangered by
firedamp and/or combustible dust.
Equipment group II:
Equipment intended for use in other places liable
to be endangered by explosive atmospheres.
Up until now explosion-protected equipment has
been divided in two groups:
Groups according to IEC 60079-0
Group I:
Equipment for use in mines susceptible to
firedamp.
Group II:
Equipment for use in places with an explosive gas
atmosphere other than mines susceptible to fire-
damp..
Electrical devices for mines, where, in addition to
firedamp, proportions of gases other than methane
may occur, have to fulfil the requirements for
group II as well as those for group I.
Devices of group II are further divided, depending
on their intended field of application, into devices
for areas that are hazardous because of gases, va-
pours or mists and those for areas that are hazard-
ous because of dust.
With the publication of IEC 60079-0 in 2007 group
III for potentially explosive areas due to dust was
introduced. Group II is reserved for equipment for
use in areas with explosive gases.
Group II:
Devices for areas with explosive gases, excluding
mines.
Group III:
Devices for areas with combustible dusts, exclud-
ing mines.
Electrical devices of group II (gas) are divided in
group IIA, IIB and IIC, depending on the properties
of the potentially explosive area they are intended
for (see table on page 9). This classification con-
cerns types of protection Flameproof Enclosure and
Intrinsic Safety. For type of protection Flameproof
Enclosure it is based on the maximum experimental
safe gap (MESG) which is a measure for the dis-
charge behaviour of a hot flame through a narrow
gap, and for Intrinsic Safety it is based on the mini-
mum ignition current (MIC), which is a measure for
the minimum ignition energy of the gases and va-
pours that occur.
Table 9: Subdivision of group II
Explosion group typical gas
maximum experi-
mental safe gap
Minimum ignition
current ratio*
IIA Propan > 0,9 > 0,8
IIB Ethylen 0,5 … 09 0,45 ... 0,8
IIC Wasserstoff < 0,5 < 0,45
* rel. to methane = 1
23

Devices for areas with combustible dust (group III)
are subdivided in groups IIIA, IIIB and IIIC, depend-
ing on the type of dust:
IIIA: combustible flyings
IIIB: non-conductive dust
IIIC: conductive dust
4.3.2 Classification
The substances and thus the explosive areas in
which those substances occur are classified in
groups according to these criteria. The devices that
are used have to be designed to fulfil the require-
ments of the group, which increase from IIA to IIC
and from IIIA to IIIC. A device that fulfils the crite-
ria for IIC can be used in areas that are classified
as IIC, IIB and IIA, devices that fulfil the criteria for
IIB can be used in areas IIB and IIA, while devices
for IIA may only be used in area IIA. Devices for
groups IIIA, IIIB and IIIC can be handled likewise.
4.4 Ignition temperature and temperature
classes
4.4.1 General
Ignition temperature of a combustible gas, vapour
or dust is the lowest temperature of a heated sur-
face, which may ignite the gas/air or vapour/air
mixture. It is virtually the lowest temperature at
which a hot surface may ignite the respective ex-
plosive atmosphere.
4.4.2 Explosive gases
Combustible gases and vapours are classified in
temperature classes according to their ease of igni-
tion (see table 10). Maximum surface temperature
of an electrical device always has to be lower than
the ignition temperature of the gas or vapour/air
mixture in which it is used. Of course, equipment
that complies with a higher temperature class (e.g.
T5) is also permissible for applications for which a
lower temperature class is required (e.g. T2 or T3).
In North America a system with further division in
sub-temperature classes exists.
Table 10: Temperature Classes
Ignition temperature of
gases and vapors in °C
Temperature class Maximum Surface tempera-
ture on the equipment in °C
> 450 T1 450
> 300 up to 450 T2 300
> 200 up to 300 T3 200
> 135 up to 200 T4 135
> 100 up to 135 T5 100
> 85 up to 100 T6 85
24
GrundlagenGrundlagenExplosion protection

4.4.3 Combustible dusts
Combustible dusts are not classified in tempera-
ture classes. Minimum ignition temperature of a
dust cloud has to be compared to the maximum
surface temperature of the equipment. A safety
factor has to be allowed for. The maximum sur-
face temperature of the equipment must not ex-
ceed 2/3 of the minimum ignition temperature of
the dust cloud. As dusts may also deposit on the
equipment, the minimum ignition temperature of
the dust deposit also has to be considered (smoul-
dering temperature). The smouldering temperature
is the lowest temperature of a hot surface at
which a 5 mm dust layer may ignite. Comparison
to the maximum surface temperature of the equip-
ment has to be done with a safety factor of 75 K.
Thermal insulation increases with higher layers.
The dust layer may ignite with lower temperatures.
That is why a reduced surface temperature on the
equipment is permissible.
It is determined according to the diagram shown
in picture 4 (EN 60079-14). If the layer is more
than 50 mm thick the smouldering temperature
has to be determined through a laboratory test.
This also applies to a layer thickness of more than
5 mm when the smouldering temperature at a lay-
er thickness of 5 mm is lower than 250 °C. Labora-
tory tests are also required when the equipment is
completely covered with combustible dust.
4.5 Types of protection
In areas in which an explosive atmosphere may still
be expected despite the implementation of preven-
tative measures, only explosion-protected equip-
ment may be used. Electrical explosion-protected
equipment for use in areas with explosive gases
can be designed in different types of protection,
pursuant to the construction regulations of stand-
ard series IEC 60079. If electrical equipment is
meant to be used in areas with combustible dust,
standard series IEC 61241 has to be applied.
Types of protection for non-electrical equipment
are stipulated in standard series EN 13463. The
type of protection a manufacturer employs for a
certain device mainly depends on the type and
Ignition
temperature of a
5mm thick layer
Thickness of layer [mm]
Max.permissiblesurfacetemperature[°C]
100
200
300
10 20 30 40 50
≥ 400°C
≥ 320°C
≥ 250°C
Fig. 4: Determination of the max. Surface Temperature of Dust Layers of 5 mm to 50 mm
25

corresponds to category 2 or EPL Gb which is suita-
ble for Zone 1. With regards to safety all standard-
ized types of protection within a category or an
equipment protection level can be considered as
being equal.
Tables 11 – 15 show an overview of the standard-
ized types of protection and describe the basic prin-
ciple and the customary fields of application.
function of the device. For some types of protec-
tion there are several protection levels. These cor-
respond to the equipment categories pursuant to
Directive 94/94/EC, or to the equipment protection
levels EPL according to IEC 60079-10 published in
2007. Therefore, there is design Ex ia for Intrinsic
Safety, which is classified as being category 1 or
EPL Ga. It can be installed in Zone 0. Design Ex ib
Table 11: Types of Protection for Electrical Apparatus in Explosive Gas Atmosphere, Part 1
Type of protection in accor-
dance in IEC, EN, ISA
and NFPA
Presentation
(diagram)
Basic principle Main application
Increased safety »e«
EN 60079-7 ISA 60079-7
IEC 60079-7
Here additional measures are applied to increase the
level of safety, thus preventing the possibility of inad-
missibly high temperatures and the occurrence of
sparks or electric arcs within the enclosure or on ex-
posed parts of electrical equipment, where such igni-
tion sources would not occur in normal service.
Terminal and connection boxes, control boxes
for installing Ex-components (which have a
different type of protection), squirrel cage
motors, light fittings
Flameproof enclosure »d«
EN 60079-1 ISA 60079-1
IEC 60079-1
Parts which can ignite a potentially explosive atmo-
sphere are surrounded by an enclosure which with-
stands the pressure of an explosive mixture exploding
inside the enclosure and prevents the transmission of
the explosion to the atmosphere surrounding
the enclosure.
Switchgear and control gear, display units,
control systems, motors, transformers, heating
equipment, light fittings
Pressurized enclosure »p«
EN 60079-2 NFPA 496
IEC 60079-2
The formation of a potentially explosive atmosphere in-
side an enclosure is prevented by maintaining a
positive internal pressure of protective gas in relation
to the surrounding atmosphere and, where necessary,
by supplying the inside of the enclosure with a constant
flow of protective gas which dilutes any com¬bustible
mixtures.
Switching and control cabinets, analysers,
large motors
px = use in Zone 1, 2
py = use in Zone 1, 2
pz = use in Zone 2
Intrinsic Safety »i«
EN 60079-11 ISA 60079-11
IEC 60079-11
Equipment that is used in a potentially explosive area
only con¬tains intrinsically safe electric circuits. An
electric circuit is intrinsically safe if any spark or ther-
mal effect produced under specified test conditions
(which include normal operation and specifiied fault
conditions) is not capable of causing ignition of a given
explosive atmosphere.
Measurement and control technology, field bus
technology, sensors, actuators
ia = use in Zone 0, 1, 2
ib = use in Zone 1, 2
ic = use in Zone 2
[Ex ib] = associated electrical apparatus —
installation in the safe area
EN 60079-25
IEC 60079-25
Intrinsic Safety evaluation for defined systems (equip-
ment and cables)
Intrinsically safe systems
EN 60079-27 ISA 60079-27
IEC 60079-27
FISCO Ex ia IIC T4 Definition of the physical and electrical limit values of
the intrinsically safe bus string
Intrinsically safe field bus systems (FISCO)
for Zone 1
26
GrundlagenGrundlagenExplosion protection

Table 12: Types of Protection for Electrical Apparatus in Explosive Gas Atmosphere, Part 2
dance IEC, EN and ISA
Presentation
(diagram)
Ölkapselung »o«
EN 60079-6 ISA 60079-6
IEC 60079-6
Electrical equipment or parts of electrical equipment
are immersed in a protective fluid (e.g. oil) in such a
way that a potentially explosive atmosphere existing
above the surface or outside of the encapsulation
cannot be ignited.
Transformers, starting resistors
Powder filling »q«
EN 60079-5 ISA 60079-5
IEC 60079-5
Filling the enclosure of electrical equipment with a
fine grained packing material has the effect of mak-
ing it impossible for an electric arc created in the en-
closure under normal operating conditions to ignite a
potentially explosive atmosphere surrounding the en-
closure. Ignition must neither be caused by flames
nor by elevated temperatures on the enclosure sur-
face.
Sensors, electronic ballasts, transmitters
Encapsulation »m«
EN 60079-18 ISA 60079-18
IEC 60079-18
Parts that are capable of igniting an explosive
atmo¬sphere are enclosed in a compound in such a
way that ignition of an explosive atmosphere is pre-
vented.
ma = use in Zone 0, 1, 2
mb = use in Zone 1, 2
Type of protection »n_«
EN 60079-15 ISA 60079-15
IEC 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 apparatus
nC = fittings and components
nR = restricted breathing
nL = limited energy
Optical radiation »op_«
EN 60079-28
IEC 60079-28
Appropriate measures prevent ignition of an explo-
sive atmosphere by optical radiation.
Optical fibre
There are three different methods:
Ex op is = inherently safe optical radiation
Ex op pr = protected optical radiation
Ex op sh= optical system with interlock
27

Table 13: Electrical Apparatus for Use in the Presence of Combustible Dust
dance in IEC, EN and ISA
Presentation
(Diagram)
Protection by enclosure »t«
IEC 60079-31
EN 60079-31
IEC 61241-1
EN 61241-1
ISA 61241-1
Tightness of the enclosure prevents ingress of dust or limits
it to a nonhazardous amount.
So ignitable equipment can be fitted into the enclosure. The
surface temperature of the enclosure must not ignite the
surrounding atmosphere.
Switchgear and control gear, connection and
terminal boxes, motors, light fittings
IEC 61241-4
EN 61241-4
ISA 61241-2
The formation of a potentially explosive atmosphere inside
an enclosure is prevented by maintaining a positive internal
pressure of protective gas in relation to the surrounding at-
mosphere and, where necessary, by sup¬plying the inside of
the enclosure with a constant flow of protective gas which
dilutes any combustible mixtures.
Switching and control cabinets, motors
Intrinsic Safety »i«
IEC 60079-11
EN 60079-11
IEC 61241-11
EN 61241-11
ISA 61241-11
Equipment that is used in a potentially explosive area only
contains intrinsically safe electric circuits. An electric cir-
cuit is intrinsically safe if any spark or thermal effect pro-
duced under specified test conditions (which include normal
operation and specified fault conditions) is not capable of
causing ignition of a given explosive atmo¬sphere.
Measurement and control technology, field-
bus technology, sensors, actuators
[Ex ibD] = associated electrical apparatus —
installation in the safe area
Encapsulation »m«
EN 60079-18
IEC 60079-18
IEC 61241-18
EN 61241-18
ISA 61241-18
Parts that are capable of igniting an explosive atmo¬sphere
are enclosed in a compound in such a way that ignition of an
explosive atmosphere is prevented.
Display units, sensors
Type of ignition protection for areas with combustible dust are integrated into the series of standards 60079. The symbols for these ty-
pes of ignition protection are simplified in standard IEC 60079-0 (Table 14).
Tabelle 14: Kennzeichnung nach Normenreihen IEC 61241 und IEC 60079
Normenreihe 61241 Normenreihe 60079 Einsatzbereich
Norm Symbol Norm Symbol Zone
Schutz durch Gehäuse
IEC 61241-1
tDA20, tDB20
tDA21, tDB21
tDA22, tDB22
IEC 60079-31
ta 20
tb 21
tc 22
Überdruckkapselung
IEC 61241-4
pD21
pD22
IEC 60079-2
pb 21
pc 22
28

Table 15: Types of Protection for Non-electrical Apparatus used in Explosive Gas Atmosphere and in the Presence of Combustible Dust
dance in IEC or EN
Presentation
(Diagram)
Constructional safety »c«
EN 13463-5
Proven technical principles are applied to equipment types which
do not have any ignition source under normal operating condi-
tions, so that the risk of mechanical failures which may cause ig-
nitable temperatures and sparks is reduced to a minimum
Couplings, pumps, gear drives,
chain drives, belt conveyors
Flameproof enclosure »d«
EN 13463-3
Parts which can ignite a potentially explosive atmo-sphere are
surrounded by an enclosure that with-stands the pressure of an
explosive mixture exploding inside the enclosure and prevents the
transmission of the explosion to the atmosphere surrounding the
enclosure.
Brakes, couplings
EN 600079-2
The formation of a potentially explosive atmosphere inside an en-
closure is prevented by maintaining a positive internal pressure of
protective gas in relation to the surrounding atmosphere and,
where necessary, by supplying the inside of the enclosure with a
constant flow of protective gas which dilutes any combustible
mixtures.
Pumps
Control of ignition source »b«
EN 13463-6
Sensors are integrated in the equipment to detect emerging haz-
ardous conditions and to take countermeasures at an early stage,
before potential ignition sources become effective. The applied
measures can be initiated automatically by means of a direct con-
nection between the sensors and the ignition protection system
or manually by issuing a warning message to the operator of the
equipment.
Pumps, belt conveyors
Liquid immersion »k«
EN 13463-8
Ignition sources are rendered inactive by immersion in a protec-
tive liquid or by constant moistening using a liquid film.
Submersible pumps, gears,
liquid immersion
Flow restricting enclosure »fr«
EN 13463-2
The effective sealing of an enclosure can reduce ingress of ex-
plosive atmosphere to such an extent that no potentially explosive
atmosphere can form inside. Pressure differences between the
internal and the external atmo¬sphere because of change in tem-
perature have to be taken into account. Application is limited to
equipment category 3.
Equipment exclusively for Zone 2
or Zone 22
29
Intrinsic safety
IEC 61241-11
iaD20
iBD21
IEC60079-11
ia 20
ib 21
Encapsulation
IEC 61241-18
maD20
maD21
IEC 60079-18
ma 20
mb 21
mc 22

4.5.1 Applications of Type of Protection
»Intrinsic Safety«
The type of protection »Intrinsic Safety« is based
on the principle of energy limitation within an
electric circuit. The energy from a power circuit
capable of causing an explosive atmosphere to
ignite is thus limited to such an extent that the
surrounding explosive atmosphere cannot ignite
as a result of sparks or inadmissible surface heat-
ing of the electrical components.
The type of protection »Intrinsic Safety« is particu-
larly used in measurement and control technology,
as no high currents, voltage and power are re-
quired here.
Terms and Definitions
Intrinsically safe electrical circuit
An electric circuit in which neither a spark nor
the effect of heat can cause a defined explosive
atmosphere to ignite.
Intrinsically safe apparatus
Electrical apparatus in which all circuits are
intrinsically safe.
Associated apparatus
Electrical apparatus which contains circuits, some
of which are intrinsically safe and some are not,
and which is constructed such that the non-intrinsi-
cally safe circuits cannot adversely
affect the intrinsically safe circuits (table 16).
An essential aspect of the type of protection
»Intrinsic Safety« is reliability with regard to the
observance of voltage and current limit values,
even if determined faults may occur. Intrinsically
safe apparatus and intrinsically safe components
from related equipment are classified in different
levels of protection »ia«, »ib« or »ic« with regard
to infallibility. The various protection levels are at-
tuned to the different zones. Intrinsic safety »ia« is
suitable for use in Zone 0, protection level »i« for
use in Zone 1 and protection level »ic« is suitable
for use in Zone 2.
Table 16: Difference between intrinsically safe and associated apparatus
Intrinsically safe apparatus Associated apparatus
These contain intrinsically safe circuits only. These contain both intrinsically safe and non-intrinsically safe electric circuits.
Ex ib IIC T6 [Ex] ib IIC T6 Ex de [ib] IIC T6
All necessary information such as category,
explosion group and temperature class is
provided.
The square brackets indicate that the associated electrical apparatus contains an intrinsically safe electric,
circuit that may be introduced into Zone 1, gas groups IIA, IIB and IIC.
The apparatus may be used in Zone 1 The apparatus has to be installed outside of the
potentially explosive area.
Thanks to being integrated in a flameproof enclosure
»d«, the apparatus may be used in Zone 1.
30

31
Fig. 6: Electric Isolators IS pac
Isolation of Intrinsically Safe Circuits from
An important measure for intrinsically safe circuits
is the safe isolation of all intrinsically safe
circuits from non intrinsically safe circuits (fig. 6).
Safe electrical isolation is always required, with
the exception of safety barriers.
Electric isolation is generally recommended for
Zone 0. Zener diodes, used for limiting voltage,
as well as other semiconductor components are
considered to be fallible and must therefore be
safeguarded by means of redundant components.
Wire wound or sheet resistors for current limita-
tion are considered to be infallible components
(they have high resistivity in the event of a fault).
Therefore one single component is sufficient.
Single fault safety
If one safety-relevant component fails, a second
component has to perform the task (protection lev-
el »ib«: a redundant component).
Double fault safety
If safety-relevant components fail, a third compo-
nent has to perform their task (level of protection
»ia«: two redundant zener diodes).
Zone 2 and Division 2
Intrinsic safety »ic« - energy-limited circuits
»nL« - non incendive »NI«
In the USA the principle of energy limitation is
treated differently, depending on the field of appli-
cation. The demands on devices for Class I Zone 2
correspond to a large extent to the IEC-require-
ments. Intrinsic safety type ic will replace the ener-
gy-limited circuits type nL, as stipulated in the IEC-
standards. For Class I Division 2, energy limitation
will be implemented as >non-incendive< (NI) cir-
cuits. The difference of the various methods is
shown in tables 17 and 18.

4.5.2 Applications of Type of Protection »c«
Non-electrical apparatus are often realised with
the type of protection “Constructional safety”. The
risk of failure, which may cause ignition sources in
an apparatus, is reduced to a low level by means
of constructional measures for this type of protec-
tion. To do so, for example, for hot surfaces, me-
chanically
Table 18: Installation and maintencance
Ex ic Ex nL NI
Cabel IEC 60079-14 US-standard
Marking Yes.
If colored, blue
No requirements No requirements
Isolation to non-Ex i/nL Circuits 50 mm No (50 mm to I.S.) Separation
Clearance to blank conducting mate-
rial
to non-Ex i: 50 mm;
to separate Ex i: 6mm;
to earth: 3mm
No special requirements Separation
Verification of intrinsic safe circuits Yes Yes Yes
Operational maintenance *) Yes Yes Yes
Corrective maintenance *) Yes Yes No
*) NEC 500 differentiates between servicing and repair. For example, during repair the replacement of defective non-incendice components is not allowed.
32
Table 17: Standards
Ex ic Ex nL NI
Description Intrinsic safety Energy limited „Non incendive“
Classification area (gas) Zone 2 Zone 2 Class I Div. 2
Classification area (dust) Zone 22 (Ex icD) Zone 22 (Ex nL) Class II + III Div. 2
Standard IEC 60079-11 IEC 60079-15 NEC500
Fieldbus IEC 60079-27-FISCO IEC 60079-27-FNICO --
Maintenance IEC 60079-17 IEC 60079-17 ANSI/ISA 12.12.01
Note: Ex nL will be replaced by Ex ic.
generated sparks, and electrostatic discharges are
examined. The measures depend mainly on the
equipment type and may vary significantly. Here,
the examined material combination, dimensioning,
tolerances, and lubricants of moving parts play
a role. Even servicing intervals and monitoring of
the service life may be of vital importance.
The manufacturer defines the intended use in the
operating instructions. By doing so, ambient and

operating conditions, as well as the admitted
operating parameters are specified. The operator
has to observe the operating instructions.
4.5.3 Application and Combination of
Types of Protection »d« and »e«
The most important type of protection for switch-
gear is »Flameproof Enclosures«, usually in
conjunction with »Increased Safety«. Switchgear
does produce sources of ignition in normal use and
therefore »Increased Safety« alone is not applica-
ble as type of protection for switchgear, since
»Increased Safety« is based on the principle of
avoiding sources of ignition through additional
measures.
However, »Increased Safety«, in conjunction with
»Flameproof Enclosures«, cut a fine figure for
33
Ex e Ex eEx em
Ex eEx e
Ex em
Ex ed
Ex d
Ex ed
Ex ed
Fig. 5: Combination of Types
of Protection Emergency
Light Fitting C-Lux 6108
switchgear and control gear. Modern, explosion
protected luminaires also use a combination
of several types of protection to achieve the best
results with regard to safety, function, and econmy
(fig. 5).

4.6 Marking
IEC
Marking of electric devices is defined in IEC
60079-0 issued in 2004 for explosive gas atmos-
pheres and in IEC 61241-0 issued in 2004 for areas
with combustible dusts. In addition to the manu-
facturer’s name or trade mark, type designation,
serial number, and the test centre with certificate
number, a special coding is required that describes
the intended use of the device:
> Ex-symbol
> Symbol of every type of protection that has
been applied
The associated electrical devices that are
meant to be installed in the hazardous areas,
have to be marked with the symbols for the
type of protection in squared brackets, e.g. Ex
d[ia] IIC T4.
> Group II, IIA, IIB or IIC for potentially explosive
gas atmospheres
> Temperature class for areas with potentially ex-
plosive gas atmospheres or max. surface tem-
perature in °C for areas in which combustible
dusts may be present.
Examples:
 Ex d e IIC T4
 Ex d [ia] IIB T5
 Ex mbD T120°C
The types of protection have to clearly show which
level they achieve. Some types of protection al-
ready contain the appropriate symbol (e.g. ia):
With others the letter a, b or c has to be added
d -> db
Example:
Ex db eb IIC T4
Ex db [ia] IIB T5
The second variant (called alternate marking in the
standard) is preferentially used.
With this standard, groups for areas where poten-
tially explosive dusts may be present have been in-
troduced as well:
IIIA: combustible flyings
IIIB: non-conductive dust
IIIC: conductive dust
Example for marking of dust:
Ex tb IIIB T120°C
Europe
In Europe, in addition to the marking according to
the standard the requirements pursuant to EC-Di-
rective 94/9/EC (ATEX 95) have to be met as well:
> Manufacturer’s address
> Symbol and the identification number of
the notified body
> and category 1, 2 or 3, as well as group II and
the letter G (gases) or D (dust)
Example: 2 II G
Previously, »Ex« was replaced by »EEx« in Europe, if
the marking was done pursuant to the standard.
Reference has thus been made to the European
Standards (EN 50014 ff), which differed from the
IEC-standards at that time. With the current edi-
tions of the standards this is no longer required,
thus devices in Euope are only marked »Ex« now as
well.
Up until now standards for non-electrical devices
have only been developed by CEN in Europe. Such
standards do not yet exist on an international level.
Marking closely follows the marking of electrical
devices.
Exceptions:
> Ex is not stated, as with ATEX the -sign al-
ready refers to explosion protection
34

35
> Ignition protection level is not given. Alternative
marking is not used either. The equipment pro-
tection level has to be defined with the
category.
A summary of the topic marking of electrical and
non-electrical devices can be found in the enclo-
sure 7.7 and 7.8.
North America
In addition to such data as for example, manufac-
turer, type, serial number and electrical data, data
concerning explosion protection must be included
in the marking of the equipment. Specifications
are given in NEC, CEC and the respective construc-
tion regulations of the test centres.
Class I, II & III, Division 1 and 2
Approved electrical equipment for Class I, Class II
and Class III, Division 1 and Division 2 has to be
marked with the following data:
1. Class(es), Division(s)
(optional, except for Division 2)
2. Gas-/dust-group(s)
3. Operating temperature or temperature class
(optional for T5 and T6)
Example: Class I Division 1 Groups C D T4
Class I, Zone 0, 1 and 2
For equipment for use in Class I, Zone 0, Zone 1 or
Zone 2 a difference is made between »Division
Equipment« and »Zone Equipment«.
(1) Division Equipment
Equipment approved for Class I, Division 1 and/or
Class I, Division 2 may be marked with the follow-
ing data:
1. Class I, Zone 1 or Class I, Zone 2
2. Gas group(s) IIA, IIB or IIC
3. Temperature class
4. Types of protection
Example: Class I Zone 1 d,e IIC T4
(2) Zone Equipment
Equipment complying with several types of protec-
tion pursuant to Article 505 of NEC and section 18
of CEC have to be marked as follows:
1. Class (optional in Canada)
2. Zone (optional in Canada)
3. Symbol AEx (USA) or Ex or EEx (Canada)
4. Symbol of the type(s) of protection that have
been applied
5. Group of the electrical equipment II or gas
group(s) IIA, IIB or IIC
6. Temperature class
Example: Class I Zone 0 AEx ia IIC T6
Russia
Marking of explosion-protected electrical equip-
ment is done according to GOST R 51330.0-99 and
according to the standards for the individual types
of protection.
Marking of explosion protection contains:
> the level of explosion protection
> Ex-symbol
> symbol of the types of protections that have
been applied
> equipment group (I, II or IIA, IIB, IIC)
> temperature class
symbol X, when special conditions have to be
observed for safe use or if the product is an Ex-
component.

36
5.installation and operation of electrical equipment
The installer must observe the installation
requirements, and select and install the electric
apparatus correctly for its intended use.
Manufacturers of explosion protected apparatus
are responsible for routine testing, certification
and documentation and are required to ensure that
each device manufactured complies with the
approved design.
5. Installation and Operation of Electrical
Equipment in Hazardous Areas
5.1 Duties of Installer, Manufacturer
and Employer
Safety in potentially explosive areas can only be
guaranteed by a close and effective working
relationship amongst all parties involved (fig. 7).
The employer is responsible for the safety of his
installations. It is his duty to verify where there
is a risk of explosion and then divide areas into
Zones accordingly. He must ensure that the instal-
lation is installed in accordance with regulations
and that it is inspected before initial use. The in-
stallation must be kept in a regular and correct
state through periodic inspection and maintenance.
The requirements for the operation of facilities in
hazardous areas are defined in national regula-
tions. In Europe the minimum regulations are stipu-
lated in Directive 99/92/EC (ATEX 137). In Germany
the Health and Safety at Work Regulations (BetrSi-
chV) must be maintained. They are specifically de-
fined with the different TRBS (technical rules for
operational safety) – please also see table 5 on
page 14. On an international level and on the Euro-
pean level, different standards have been estab-
lished which can be used as sources of information
in Germany (see table 19). However, this only ap-
plies if it does not contradict the German Health
and Safety at Work Regulations or a TRBS.
Fig. 7: Co-operation of all parties involved
Employer
Manufacturer
Installer
Standardization
Authority
Testing authority
Table 19: Explosive atmospheres (gas and combustible dust)
IEC EN
Electrical installations design, selection and erection IEC 60079-14 EN 60079-14
Electrical installations inspection and maintenance IEC 60079-17 EN 60079-17
Equipment repair, overhaul and reclamation IEC 60079-19 EN 60079-19

37
5.2 Classification of Zones and
Selection of Apparatus
The question of possible risks of explosion must
be addressed at the early stages new facility
planning. When classifying potentially explosive
areas, the influence of natural or technical
ventilation must be considered in addition to the
quantity of flammable substances being released.
Furthermore, the explosion safety characteristics
must be ascertained for the flammable substances
being used (see Appendix 7.2). Only then can a de-
cision be reached on the classification of potential-
ly explosive areas into Zones and the selection of
suitable apparatus.
Equipment shall only be used within the ambient
temperature range stipulated in its marking.
If the marking does not contain any information,
the standard range of between –20 °C and +40 °C
applies.
Electrical apparatus with the types of protection
»d« and »i« must correspond to an explosion group
IIA, IIB or IIC. Electrical apparatus must be selected
and installed such that it is protected against
external influences which may adversely affect the
explosion protection measures.
5.3 Methods of Installation
Essentially, three systems are used for electrical
installations in hazardous areas:
> 1. Cable system with indirect entry
> 2. Cable system with direct entry
> 3. Conduit system
The technical design of the electrical apparatus
used with the individual types of installation is ac-
cordingly different.
Only the conduit system or mineral insulated
cables (MI) are permitted in the USA for all appli-
cations in Class 1, Division 1 in accordance with
NEC 501-4, whereby the mineral insulated cables
are mainly used as heating lines and fire resistant
signal and control lines. Certain types of cable
and line are also permitted in Division 2. A com-
parison of the various systems is shown below.
Cable systems
Cable systems are mainly used in Europe. For this,
high-quality cables are laid uncovered. It is only
in areas in which mechanical damage could
be expected that they are laid in conduits that are
open at both ends.

38
5.installation and operation of electrical equipment
Fig. 8: Methods of Installation
worldwide: Left: Cable sys-
tem with indirect entry; Cen-
tre: Cable system with direct
entry; Right: Conduit system
In the case of indirect entry, the cables and lines
are conducted via cable glands into a connection
chamber in the type of protection “Increased
Safety” and connected to the terminals also pro-
vided in “Increased Safety”. From here, the
individual wires are conducted via flameproof
bushings into the flameproof enclosure.
The cable bushings are installed by the manufac-
turer, with the result that, by contrast with
direct entry, a routine test of the factory wired
flameproof enclosure can be made.
The installation engineer need only open the
connection chamber for the connection, not the
flameproof enclosure.
In the case of direct entry, the connecting
cables are entered directly into the flameproof
enclosure. Only cable glands that have been
specially certified for this purpose may be used
for this type of entry.
The flexible gasket and the cable sheath must
form a flameproof joint through which no flames
can penetrate. For this reason, attention must
be paid to the appropriate selection of cable gland
depending on both the type and structure of
cable and installation location. If the flameproof
enclosure has to be used in a IIC atmosphere
or if a flameproof enclosure with a volume bigger
than 2 dm³ has to be applied in Zone 1, the gaskets
or cable glands have to be sealed. The flameproof
enclosure primarily depends here on the
care taken by the electrician when connecting the
cables.

39
Before corrective maintenance, it must be ensured
that there is no danger of explosions occurring
during this work. Normally, formal written permis-
sion for this should be acquired from the
company management. On completion of the work,
documentation should be kept of what work
was carried out, and confirmation given that all
relevant regulations have been observed.
Once work is completed it should be documented
what work was done and confirmed that all rele-
vant regulations were adheared to.
In case of overhaul which may impair explosion
protection, an examination by a qualified person,
acknowledged by the authorities, or an examina-
tion by the manufacturer has to be done in Germa-
ny (TRBS 1201 part 3).
When replacing components or complete equip-
ment the technical explosion and equipment speci-
fications are to be observed. This inspection may
be done by an approved inspection agency.
Conduit System
In the case of installation using the conduit system,
the electrical lines are drawn as single wires
into enclosed metal conduits. The conduits are
connected to the housings by means of fittings
and equipped with a seal at each entrance point.
The entire conduit system is flameproof. The aim
of the seal is to prevent explosions which may
occur inside the housing from transmitting into
the conduit.
Otherwise, extremely high explosion pressures
would be created as a result of precompression in
long cylindrical tubes. For this reason, it is recom-
mended that seals be installed not just at the en-
trance points but at specific intervals. Drains must
be installed at low points at which condensate can
accumulate.
5.4 Maintenance
Periodic maintenance is required to maintain the
safety of electrical installations in hazardous
areas. Personnel who carry out such maintenance
work should work under the guidance of an
explosion protection expert and should be in-
formed of the particular hazards involved (skilled
person, IEC 60079-17).

Table 20: Safety Ratings: Ignition Temperature, Temperature Class and Explosion Group
Material Ignition Temperature °C Temperature Class Explosion Group
1,2-Dichloroethane 440 T 2 II A
Acetaldehyde 155 T 4 II A
Acetone 535 T 1 II A
Acetylene 305 T 2 II C ³
Ammonium 630 T 1 II A
Petrol fuels 220 bis 300 T 3 II A
Benzene 555 T 1 II A
Cyclohexanone 430 T 2 II A
Diesel fuels 220 T 3 II A
Acetic acid 485 T 1 II A
Acetic anhydride 330 T 2 II A
Ethane 515 T 1 II A
Ethyl ethanoate 470 T 1 II A
Ethanol 400 T 2 II B
Ethyl chloride 510 T 1 II A
Ethylene 440 T 2 II B
Ethylene oxide 435 (self-decomposing) T 2 II B
Diethyl ether 175 T 4 II B
Ethyl glycol 235 T 3 II B
Fuel oil EL, L, M, S 220 to 300 T 3 II A
i-Amyl acetate 380 T 2 II A
Carbon monixide 605 T 1 II A
Methane 595 T 1 II A
Methanol 440 T 2 II A
Methyl chloride 625 T 1 II A
Naphtalene 540 T1 II A
n-Butanol 365 T 2 II A
n-Butanol 325 T 2 II B
n-Hexane 230 T 3 II A
n-Propyl alcohol 385 T 2 II B*
Phenol 595 T 1 II A
Propane 470 T 1 II A
Carbon disulphide 95 T 6 II C
1
Hydrogen sulphide 270 T 3 II B
Toluene 535 T 1 II A
Hydrogen 560 T 1 II C
2
* The gas group for this substance has not yes been determined.
1
Also gas groups II B + CS2
2
Also gas groups II B + H2
3
Also gas groups II B + C2 H2
6.1 Safety Characteristics of Flammable Gases and Vapours
40
6. Appendix
6.appendix

Table 21: Constructional Requirements in Europe, USA, Canada, and International Compariosn, Part 1
Type of ignition protection Abbreviation Region Installation location Standard
General requirements
AEx
Ex
Ex (EEx)
Ex
US
US
CA
EU
IEC
Class I, Division 1 & 2
Class I, Zone 0, 1 & 2
Class I, Zone 0, 1 & 2
Zone 0, 1 & 2
Zone 0, 1 & 2
FM 3600
ISA 60079-0
CSA E60079-0
EN 60079-0
IEC 60079-0
Increased safety AEx e
Ex e
Ex e (EEx e)
Ex e
US
CA
EU
IEC
Class I, Zone 1
Class I, Zone 1
Zone 1
Zone 1
ISA 60079-7
CSA E60079-7
EN 60079-7
IEC 60079-7
Non-incendive (NI)
(NI)
US
CA
Class I, Division 2
Class I, Division 2
FM 3611
C22.2 No. 213
Non-sparking apparatus AEx nA
Ex nA
Ex nA (EEx nA)
Ex nA
US
CA
EU
IEC
Class I, Zone 2
Class I, Zone 2
Zone 2
Zone 2
ISA 60079-15
CAS E60079-15
EN 60079-15
IEC 60079-15
Explosion-proof (XP)
(XP)
US
CA
Class I, Division 1
Class I, Division 1
FM 3615
C22.2 No. 30
Flameproof enclosure AEx d
Ex d
Ex d (EEx d)
Ex d
US
CA
EU
IEC
Class I, Zone 1
Class I, Zone 1
Zone 1
Zone 1
ISA 60079-1
CSA E60079-1
EN 60079-1
IEC 60079-1
Powder filling AEx q
Ex q
Ex q (EEx q)
Ex q
US
CA
EU
IEC
Class 1, Zone 1
Class I, Zone 1
Zone 1
Zone 1
ISA 60079-5
CSA E79-5
EN 50017
IEC 60079-5
Protected facilities and components AEx nC
Ex nC
Ex nC (EEx nC)
Ex nC
US
CA
EU
IEC
Class I, Zone 2
Class I, Zone 2
Zone 2
Zone 2
ISA 60079-15
CSA E60079-15
EN 60079-15
IEC 60079-15
Intrinsic Safety (IS)
(IS)
AEx ia
AEx ib
Ex ia
Ex ib
Ex ia (EEx ia)
Ex ib (EEx ib)
Ex ia
Ex ib
US
CA
US
US
CA
CA
EU
EU
IEC
IEC
Class I, Division 1
Class I, Division 1
Class I, Zone 0
Class I, Zone 1
Class I, Zone 0
Class I, Zone 1
Zone 0
Zone 1
Zone 0
Zone 1
FM 3610
C22.2 No. 157
FM 3610
FM 3610
CSA E60079-11
CSA E60079-11
EN 50020
EN 50020
IEC 60079-11
IEC 60079-11
6.2 Constructional Requirements for Explosion Protected Electrical equipment for gas atmospheres
41

Table 21: Constructional Requirements in Europe, USA, Canada and International Comparision, Part 2
Type of ignition protection Abbreviation Region Installation location Standard
Energy-limited apparatus AEx nC
Ex nL
Ex nL (EEx nL)
En nL
US
CA
EU
IEC
Class I, Zone 2,
Class I, Zone 2
Zone 2
Zone 2
ISA 60079-15
CSA E60079-15
EN 60079-15
IEC 60079-15
Pressurized enclosure Type X
Type X
Type Y
Type Y
Type Z
Type Z
AEx px
US
CA
US
CA
US
CA
US
CA
EU
IEC
US
CA
EU
IEC
US
CA
EU
IEC
Class I, Division 1
Class 1, Divison 1
Class I, Division 1
Class I, Division 1
Class 1, Division 2
Class 1, Division 2
Class I, Zone 1
Class I, Zone 1
Zone 1
Zone 1
Class I, Zone 1
Class I, Zone 1
Zone 1
Zone 1
Class I, Zone 2
Class I, Zone 2
Zone 2
Zone 2
FM 3620
NFPA 496
FM 3620
NFPA 496
FM 3620
NFPA 496
ISA 60079-2
CSA E60079-2
EN 60079-2
IEC 60079-2
ISA 60079-2
CSA E60079-2
EN 60079-2
IEC 60079-2
ISA 60079-2
CSA E60079-2
EN 60079-2
IEC 60079-2
Purged/pressurized AEx nR
Ex nR
Ex nR (EEx nR)
Ex nR
US
CA
EU
IEC
Class I, Zone 2
Class I, Zone 2
Zone 2
Zone 2
ISA 60079-15
CSA E60079-15
EN 60079-15
IEC 60079-15
Encapsulation Ex ma (EEx ma)
Ex ma
AEx m
Ex m
Ex mb (EEx mb)
Ex mb
EU
IEC
US
CA
EU
IEC
Zone 0
Zone 0
Class I, Zone 1
Class I, Zone 1
Zone 1
Zone 1
EN 60079-18
IEC 60079-18
ISA 60079-18
CSS E60079-18
EN 60079-18
IEC 60079-18
Oil immersion AEx o
Ex o
Ex o (EEx o)
Ex o
US
CA
EU
IEC
Class I, Zone 1
Class I, Zone 1
Zone 1
Zone 1
ISA 60079-6
CSA E79-6
EN 50015
IEC 60079-6
42
6.anhang

Table 22: Degrees of Protection according to IEC 60529 – IPXX
Digit
First digit
Physical protection
Foreign body protection
Second digit
Water protection
0 No protection No protection No protection
1
Protection against back of hand
contact
Protection against solid foreign bodies 50 mm Ø Protection against water drops falling vertically
2 Protection agains finger contact Protection against solid foreign bodies 12,5 mm Ø Protection against water drops falling at an angle (15°)
3 Protection against contact from tools Protection against solid foreign bodies 2,5 mm Ø Protection against water-spray at an angle up to 60°
4 Protection against contact with a wire Protection against solid foreign bodies 1,0 mm Ø Protection against water spray from all directions
5 Protection against contact with a wire Protection against dust Protection against water jets
6 Protection against contact with a wire Dust-tight Protection against strong water jets
7 Protection against intermittent immersion in water
8 Protection against continuous immersion in water
6.3 Degrees of Protection according to IEC 60529 – IPXX
Table 23: Degree of Protection provided by Enclosures according to NEMA (Publication No. 250 Enclosures for Electrical LEuqipment 1000 Volts Maximum)
Digit Degree of Protection Use
Type 1 Protection against incidental contact with the enclosed equipment. Indoor
Type 2 Protection against limited amounts of falling water and dirt. Indoor
Type 3 Protection against rain, sleet, windblown dust, and damage from external ice formation. Outdoor
Type 3R Protection against rain, sleet, and damage from external ice formation. Outdoor
Type 4 Protection against, rain, splashing water, hose directed water, and damage from external ice formation. Indoor or outdoor
Type 4X Protection against, rain, splashing water, hose directed water, and damage from external ice formation.
Protection against corrosion.
Indoor or outdoor
Type 5 Protection against settling airborne dust, falling dirt, and dripping non-corrosive liquids. Indoor
Type 6 Protection against hose directed water, penetration of water during occasional temporary submersion at a li-
mited depth, and damage from external ice formation.
Indoor or outdoor
Type 6P Protection against hose directed water, penetration of water during prolonged submersion at a limited depth,
and damage from external ice formation.
Indoor or outdoor
Type 7 For use in locations classified as Class I, Groups A, B, C or D as defined in the NEC. Indoor
Type 8 For use in locations classified as Class I, Groups A, B, C or D as defined in the NEC. Indoor or outdoor
Type 9 For use in locations classified as Class II, Groups E, F, or G as defined in the NEC. Indoor
Type 10 Constructed to meet the applicable requirements of the Mine Safety Health Administration. Mining
Type 11 Protection against the corrosive effects of liquids and gases by oil immersion. Indoor
Type 12, 12K Protection against circulating dust, falling dirt, and dripping non-corrosive liquids. Indoor
Type 13 Protection against dust, splashing water, oil, and non-corrosive liquids. Indoor
6.4 Degrees of Protection according to NEMA Standards
43

IEC 60079 Part 0 to 31
Explosive atmospheres
www.iec.de/webstore
IEC 61241 Part 0 to 18
Electrical apparatus for use in the presence of
combustible dust
www.iec.ch/webstore
EN 60079 Part 0 to 31
Explosive atmospheres
www.cenelec.eu
EN 61241 Part 0 to 18
Electrical apparatus for use in the presence of
combustible dust
www.iec.ch/wekstore
EN 60529
Degrees of protection provided by enclosures
(IP code)
www.iec.ch/webstore
EN 13463 Part 1 to 8
Non-electrical equipment for potentially explosive
atmosphere
www.cen.eu
44
7. Literature
Directive 94/9/EU of the European Parliament and
the council of 23 March 1994 on the approximation
of the laws of the member states concerning
equipment and protective systems intended for
use in potentially explosive atmospheres.
Official Journal of the European Communities,
No. L 100/1
The Equipment and Protective Systems for Use
in Potentially Explosive Atmospheres Regulations,
1996 (EPS), ATEX 95/(UK).
Directive 99/92/EC on the »Minimum requirements
for improving the health and safety protection
of the worker at risk from explosive atmospheres«
16/12/1999, Official Journal of the European
Communities, L23/57–64
The Dangerous Substances and Explosive Atmos-
pheres Regulations 2002, Statutory Instrument
2002 No. 2776 (UK).
7.literature
31,967 mm

II2GExdb[ia]IICT6ATEX-marking
hazardousplacesZone0Zone20Zone1Zone21Zone2Zone22mines
Dangerousexplosive
atmosphere
continouslyorlong-
termorfrequently
likelytooccurnotlikelytooccur
orforshortperiod
equipmentcategory1G1D2G2D3G3DM1orM2
EPL*(IEC/EN60079-0)GaDaGbDbGcDcMaorMb
equipment-groupI:mines;equipment-groupII:otherplaces
mines
GroupIMethane
explosivegasatmosphere
GroupIIIIAPropane
IIBEthylene
IICHydrogene
explosivedustatmosphere
GroupIIIIIIAcombustibleflyings
IIIBnon-conductivedust
IIICconductivedust
Group
max.surfacetemperature
explosivegasatmosphere:temperatureclasses
450°CT1
300°CT2
200°CT3
135°CT4
100°CT5
85°CT6
explosivedustatmosphere:surfacetemperature
T...°C(e.g.:T80°C)
Typeofprotectionstandard
symbol
alternate
symbol
ZoneMainapplicationStandard
increasedsafetyeeb1terminalandjunctionboxes,
cageinductionmotors,lightfittings
IEC60079-7
EN60079-7
flameproofenclosuresddb1switchgear,controlstations,mo-
tors,
IEC60079-1
EN60079-1
pressurized
enclosures
px
py
pz
p
pxb
pyb
pzc
pb
pc
1
1
2
21
22
switchgearandcontrolcabinets,
analysers,largemotors
IEC60079-2/IEC61241-4
EN60079-2/EN61241-4
intrinsicsafetyia
ib
ic
ia
ib
ic
0,20
1,21
2
instrumentationtechnology,field-
bustechnology,sensors,actuators
IEC60079-11/IEC61241-11
EN60079-11/EN61241-11
oilimmersionoob1transformers,startingresistorsIEC60079-6
EN60079-6
powderfillingqqb1sensors,electronicballasts,elec-
tronicdevices
IEC60079-5
EN60079-5
encapsulationma
mb
mc
ma
mb
mc
0,20
1,21
2,22
displayunits,sensors,electronic
devices
IEC60079-18/IEC61241-18
EN60079-18/EN61241-18
typeofprotection„n“n_n_c2electricalapparatusforZone2IEC60079-15
EN60079-15
protectionbyenclo-
sures
ta
tb
tc
ta
tb
tc
20
21
22
switchgearandcontrolstation,
terminalandconnectionboxes,
controlboxes,motors,lightfittings
IEC60079-31/IEC61241-1
EN60079-31/EN61241-1
Marking
ofelectricalequipment
*whennotusingthealternatesymbolstheEPLshallbespecified::e.g.Exd[iaGa]IICT6Gb
Typeofprotection
m
45

II2GcIICT6ATEX-marking
hazardousplacesZone0Zone20Zone1Zone21Zone2Zone22mines
Dangerousexplosive
atmosphere
continouslyorlong-
termorfrequently
likelytooccurnotlikelytooccur
orforshortperiod
equipmentcategory1G1D2G2D3G3DM1oderM2
equipment-groupI:mines;equipment-groupII:otherplaces
Mines
GroupIMethane
explosivegasatmosphere
GroupIIIIAPropane
IIBEthylene
IICHydrogene
Group
max.surfacetemperature
explosivegasatmosphere:temperatureclasses
450°CT1
300°CT2
200°CT3
135°CT4
100°CT5
85°CT6
explosivedustatmosphere:surfacetemperature
T...°C(e.g.:T80°C)
TypeofprotectionsymbolsZoneMainapplicationStandard
constructionalsafetyc0,1,2
20,21,22
couplings,pumps,geardrives,
chaindrives,beltdrives
EN13463-5
ﬂameproofenclosuresd1,2
21,22
brakes,couplingsEN13463-3
pressurisationp1,2
21,22
pumpsEN60079-2
controlofignitionsourcesk0,1,2
20,21,22
pumps,belddrivesEN13463-8
liquidimmersionb0,1,2
20,21,22
submergedpumps,gearsEN13463-6
ﬂowrestrictingenclosurefr2
22
equipmentonlyforZone2or
Zone22
EN13463-2
Markingof
non-electrical
equipment
Typeofprotection
Grundlagen
31,967 mm
46

m

ID 102912
S-PB-ExBasic protection-04-en-08/2011 · Printed in Germany
R. STAHL
Am Bahnhof 30, 74638 Waldenburg
Telefon +49 7942 943-0
Telefax +49 7942 943-4333
www.stahl.de

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