IEC 60079-26:2014

IEC 60079-26 ®
Edition 3.0 2014-10
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Explosive atmospheres –
Part 26: Equipment with Equipment Protection Level (EPL) Ga

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IEC 60079-26 ®
Edition 3.0 2014-10
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Explosive atmospheres –
Part 26: Equipment with Equipment Protection Level (EPL) Ga

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.260.20 ISBN 978-2-8322-1912-6

– 2 – IEC 60079-26:2014 RLV © IEC 2014

CONTENTS
FOREWORD . 4

1 Scope . 7

2 Normative references . 8

3 Terms and definitions . 8

4 Requirements for design and construction . 8
4.1 General .
4.1 Protection measures against ignition hazards of the electrical circuits. 8
4.1.1 General . 8
4.2.2 Intrinsic safety as a sole means of protection.
4.2.3 Encapsulation as a sole means of protection .
4.1.2 Application of two independent Types of Protection providing EPL Gb . 9
4.1.3 Application of a Type of Protection providing EPL Gb and a separation
element . 10
4.2 Equipment with moving parts . 14
4.2.1 Frictional heating . 14
4.2.2 Damage arising from failure of moving parts . 14
4.2.3 Light metals . 15
4.4 Isolated conductive components .
4.5 Non-conductive enclosures and accessible non-conductive components .
4.5.1 General .
4.5.2 Limitation of the size of chargeable non-conductive surfaces .
4.5.3 Limitation of the thickness of chargeable non-conductive layers .
4.5.4 Provision of a conductive coating.
4.3 Process connection . 16
5 Type tests . 16
5.1 Standardized types of protection . 16
5.2 Separation elements . 17
5.3 Temperature evaluation . 17
6 Marking . 17
6.1 General . 17

6.2 Examples of marking . 17
7 Information for use .
7 Instructions . 18
7.1 Separation elements: . 18
7.2 Process connection: . 18
7.3 EPL allocation . 18

Annex A (informative) Introduction of an alternative risk assessment method
encompassing “equipment protection levels” for Ex equipment .

Bibliography . 23

Figure 1 – Example of a partition wall with a conductor bushing considered as gas

diffusion tight . 11

Figure 2 – Example of a separation element with a cylindrical shaft joint and

naturalventilation . 14

Table 1 – Separation elements . 13

– 4 – IEC 60079-26:2014 RLV © IEC 2014

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
EXPLOSIVE ATMOSPHERES –
Part 26: Equipment with Equipment Protection Level

(EPL) Ga
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

International Standard IEC 60079-26 has been prepared by IEC technical committee 31:

Equipment for explosive atmospheres.

This third edition cancels and replaces the second edition published in 2006 and constitutes a

technical revision.
This edition includes the following significant changes with respect to the previous edition:

Type
Changes Clause Minor and Extension Major

editorial technical
changes changes
Notes deleted 1 X
Reference to associated apparatus deleted 1 X
Additional normative references included 3 X
Requirements against mechanical and
electrostatic ignition hazards deleted (now 4.1 X
covered in IEC 60079-0)
Requirement for separation element detailed
4.1.3.2 X
regarding external influences
Intrinsic safety Ex ia as single type of protection
4.2.2
including associated apparatus deleted (now X
(ed.2)
covered by EPL)
Encapsulation Ex ma as single type of protection 4.2.3
X
deleted (now covered by EPL) (ed.2)
Conditions a) and b) linked with an “and” ,
therefore requirement of “flameproof joint” deleted
in following clause. Both requirements already 4.3 X
covered by separation elements and standardised
process connections.
Process connection requires a sufficiently tight
4.3 X
joint: IP66 added alternatively to IP67
Requirement for isolated conductive components 4.4
X
deleted (now covered in IEC 60079-0) (ed.2)
Requirements for non-conductive enclosures 4.5
X
deleted (now covered in IEC 60079-0) (ed.2)
Test of partition walls according to 4.1.3.2 b) is
5.2  C1
specified in more detail
Marking example for associated apparatus deleted 6.2 b) X
Note 3 with an additional example added 6.2 X
Specification of material of partition wall required

7 X
in instructions (also required in 4.1.3.2)
Alternative risk assessment method deleted (is AnnexA
X
now generally introduced) (ed.2)
NOTE The technical changes referred to include the significance of technical changes in the revised IEC
Standard, but they do not form an exhaustive list of all modifications from the previous version.
Explanation of the types of changes:
A) Definitions
1) Minor and editorial changes:
• Clarification
• Decrease of technical requirements
• Minor technical change
• Editorial corrections
– 6 – IEC 60079-26:2014 RLV © IEC 2014

These are changes which modify requirements in an editorial or a minor technical way.

They include changes of the wording to clarify technical requirements without any

technical change, or a reduction in level of existing requirement.

2) Extension: Addition of technical options

These are changes which add new or modify existing technical requirements, in a way
that new options are given, but without increasing requirements for equipment that was

fully compliant with the previous standard.Therefore, these will not have to be

considered for products in conformity with the preceding edition.

3) Major technical changes:
• addition of technical requirements

• increase of technical requirements
These are changes to technical requirements (addition, increase of the level or
removal) made in a way that a product in conformity with the preceding edition will not
always be able to fulfil the requirements given in the later edition. These changes have
to be considered for products in conformity with the preceding edition. For these
changes additional information is provided in Clause B below.
NOTE These changes represent current technological knowledge. However, these changes should not
normally have an influence on equipment already placed on the market.
B) Information about the background of ‘Major technical changes’
C1: Introduction of type tests for separation elements according to “4.1.3.2 b)”
The text of this standard is based on the following documents:
FDIS Report on voting
31/1146/FDIS 31/1155/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60079 series, published under the general title Explosive
atmospheres, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be

• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
EXPLOSIVE ATMOSPHERES –
Part 26: Equipment with Equipment Protection Level

(EPL) Ga
1 Scope
This part of IEC 60079 specifies the particular alternative requirements for construction, test
and marking for electrical equipment that provides Equipment Protection Level (EPL) Ga
when single standardised Types of Protection (e.g. Ex “ia” , Ex “ma”, Ex “da”) cannot be
applied. This standard also applies to equipment mounted across a boundary where different
Equipment Protection Levels may be required.
EXAMPLE: Equipment installed in the wall of a storage vessel containing Zone 0 (requiring EPL Ga) inside an
area defined as Zone 1 (requiring EPL Gb).
This electrical equipment, within the operational parameters specified by the manufacturer,
ensures a very high Level of Protection that includes rare faults malfunctions related to the
equipment or two faults malfunctions occurring independently of each other.
NOTE A malfunction may result from a failure of the component parts of the electrical equipment or from
anticipated externally applied influences. Two independent malfunctions which may occur more frequently and
which, separately, would not create an ignition hazard but which, in combination, could create a potential ignition
hazard, should be are regarded as occurring together to form a rare fault malfunction.
NOTE 2 This electrical equipment is intended for use in zone 0 hazardous areas, in which explosive gas
atmospheres caused by mixtures of air and gases, vapours or mists under normal atmospheric conditions are
present continuously, for long periods or frequently.
This standard also applies to equipment mounted across a boundary where different
protection levels may be required.
EXAMPLE: In the wall of a storage vessel containing zone 0 with an ambient defined as zone 1.
This standard also applies to equipment installed in an area requiring a lower protection level,
but electrically connected to equipment with equipment protection level (EPL) Ga (associated
apparatus).
This standard supplements and modifies the general requirements of IEC 60079-0. Where a
requirement of this standard conflicts with a requirement of IEC 60079-0, the requirement of
this standard takes precedence. and the requirements of the standardized types of protection,

in accordance with the IEC 60079 series, to adapt the level of safety provided by those
standards in order to provide EPL Ga.
NOTE 3 In designing equipment for operation in explosive gas atmospheres under conditions other than the
atmospheric conditions given in IEC 60079-0, this standard may be used as a guide. However, additional testing is
recommended related specifically to the intended conditions of use. This is particularly important when the types of
protection ‘Flameproof enclosures’ (IEC 60079-1) and ‘Intrinsic safety’ (IEC 60079-11) are applied.
NOTE 4 The classification of hazardous areas in zones is defined in IEC 60079-10.
NOTE 5 There may be other non-electrical sources of ignition (for example ultrasonic, optical or ionizing radiation)
that are not addressed by this standard; these should also be taken into consideration (see, for example, EN 1127-1).
NOTE 6 This concept provides equipment protection level (EPL) Ga. For further information, see Annex A.

– 8 – IEC 60079-26:2014 RLV © IEC 2014

2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any

amendments) applies.
IEC 60079-0:2004, Explosive atmospheres − Part 0: Equipment − General requirements

IEC 60079-1, Explosive atmospheres − Part 1: Equipment protection by flameproof enclosures

"d"
IEC 60079-10, Electrical apparatus for explosive gas atmospheres – Part 10: Classification of
hazardous areas
IEC 60079-11, Explosive atmospheres − Part 11: Equipment protection by intrinsic safety "i"
IEC 60079-18, Electrical apparatus for explosive gas atmospheres – Part 18: Construction,
test and marking of type of protection encapsulation "m" electrical apparatus
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60695-11-10, Fire hazard testing − Part 11-10: Test flames − 50 W horizontal and vertical
flame test methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60079-0 and the
following apply.
NOTE Additional definitions applicable to explosive atmospheres can be found in IEC 60050-426.
3.1
EPL
abbreviation of equipment protection level as defined in Annex A
3.1
separation element
mechanical element inside the equipment, which separates different parts of the equipment
with different EPLs
Note 1 to entry: A separation element consists of a mechanical partition wall, which may be combined with a
flameproof joint or a natural ventilation
4 Requirements for design and construction
4.1 General
The equipment shall comply with the requirements of 4.2 for the electrical circuits and with the
requirements of 4.3 to 4.6 for mechanical and electrostatic ignition hazards.
4.1 Protection measures against ignition hazards of the electrical circuits
4.1.1 General
The equipment shall comply with the requirements of either

a) 4.2.2 or 4.2.3 in the event of two faults occurring independently of each other in a single

equipment means of protection; or

b) 4.2.4 or 4.2.5 4.1.2 or 4.1.3 in the event of a failure of one equipment means of protection,

by the provision of a second independent means of protection.

NOTE 1 Types of Protection according to EPL Ga do not require a second independant means of protection, e.g.
Ex “ia” (IEC 60079-11), Ex “ma” (IEC 60079-18), Ex “da” (IEC 60079-1).

Electrical connections and permanently connected cables of the equipment sited within an

area requiring EPL Ga equipment shall comply with the same Level of Protection required by

this standard, for example an Ex “e” a cable suitable for EPL Gb containing non-Ex “ia”

circuits additionally protected by a flameproof conduit or an Ex “e” a cable suitable for EPL Gb

provided with earth leakage protection.
NOTE 2 Detailed cable and installation requirements for non Types of Protection accepted as achieving EPL Ga
beyond intrinsically safe circuits providing EPL Ga are under consideration in IEC 60079-14.
NOTE 3 Because of ignition hazards which can arise from faults and/or transient circulating currents in the
potential equalization system, galvanic isolation in the power and signal connections to the equipment according to
4.1.2 and 4.1.3 4.2.2, 4.2.3 and 4.2.4 is preferred. Consideration should also be given to minimize is commonly
applied along with minimizing the effect of transient fault currents in the potential equalization network by the use
of electrical protection equipment such as sensitive earth leakage monitors.
4.2.2 Intrinsic safety as a sole means of protection
Intrinsically safe electrical equipment providing EPL Ga and intrinsically safe electrical circuits
of associated apparatus entering an area requiring EPL Ga shall comply with the
requirements of IEC 60079-11, intrinsic safety “ia”.
NOTE Intrinsic safety “ib” in accordance with IEC 60079-11 may be considered as one of two independent means
of protection according to 4.2.4.
4.2.3 Encapsulation as a sole means of protection
Electrical equipment which is protected by encapsulation providing EPL Ga shall comply with
the requirements of IEC 60079-18, encapsulation “ma”.
NOTE Encapsulation “mb” in accordance with IEC 60079-18 may be considered as one of two independent means
of protection according to 4.2.4.
4.1.2 Application of two independent Types of Protection providing EPL Gb
Electrical equipment shall comply with the requirements of two independent Types of
Protection that provide EPL Gb. If one Type of Protection fails, the other Type of Protection
shall continue to function. The independent Types of Protection shall not have a common

mode of failure, except as specified in this clause. Combined types of protection providing
EPL Gb shall depend on different physical protection principles.
NOTE 1 An example of a common mode of failure is if an Ex “d” enclosure containing arcing contacts
components is used installed inside an Ex “e” enclosure. Should the Ex “d” enclosure be compromised, then
arcing inside the enclosure will it would also compromise the Ex “e” enclosure.
NOTE 2 Combined types of protection providing EPL Gb should depend on different physical protection principles.
For example The combination of Ex “d” and Ex “q” both depend on the avoidance of flame propagation (same
physical protection principle) and may not be useful in combination. In practice, some combinations may not be
useful, for example the combination of oil immersion “o” and powder filling “q”.
Where combined types of protection are used, it shall be possible for each Type of Protection
to be tested individually (see 5.1).
Both Types of Protection shall be assessed using the most arduous fault condition of the
other Type of Protection. When combining intrinsic safety, Type of Protection “ib”, with other
Types of Protection, the second Type of Protection shall be assessed, with the most arduous

– 10 – IEC 60079-26:2014 RLV © IEC 2014

fault condition applied to the intrinsically safe circuit. Thermal dissipation shall be considered

in case of a fault of one Type of protection.

When using two Types of Protection, which both rely on the same parameter (for example, the

creepage distance combining Ex “ib” with Ex “e”), the most stringent requirement of both

Types of Protection shall be applied.

If two Types of Protection are combined which both rely on the enclosure, one of the following

shall be met:
a) if two enclosures are used (one totally enclosed within the other), each enclosure shall

comply with the requirements of the respective Type of Protection; or
b) if only one enclosure is used, the enclosure and the cable glands shall meet the impact
test requirements of 26.4.2 of IEC 60079-0, using the Group I values.
Examples of relevant combinations of two independent Types of Protection are as follows:
– inductive transmitters (for example proximity switches, electrical position sensors) with
intrinsic safety “ib” enclosed by encapsulation “mb”. The connections to intrinsically safe
“ib” circuits can be protected by the increased safety “e”;
– a lamp with the bulb luminaire designed as increased safety “e”, the lamp circuit with the
switch as intrinsic safety “ib”. These components may be incorporated included in a
flameproof enclosure “d”;
– measuring transducers with intrinsic safety “ib” and a flameproof enclosure “d”;
– equipment with electrical circuits of intrinsic safety “ib”, additionally protected by powder
filling “q”;
– electromagnetic valves with encapsulation “mb”, enclosed by a flameproof enclosure “d”;
– increased safety “e”, with pressurized equipment “pxb”.
4.1.3 Application of a Type of Protection providing EPL Gb and a separation element
4.1.3.1 General
Equipment which is mounted through or forms part of the boundary wall to an area requiring
EPL Ga and contains electrical circuits which do not comply with protection level EPL Ga shall
comply with at least one of the Types of Protection providing EPL Gb. Additionally, it shall
contain a mechanical separation element as part of the equipment to seal off separate the
electrical circuits of the equipment from the area requiring EPL Ga.
If the Type of Protection fails, the separation element shall:
a) prevent flame propagation through the equipment into the area requiring EPL Ga,
b) maintain its safety characteristics,
c) not be heated above exceed the maximum surface temperature of the specified
temperature class of the equipment (see 5.3).
Separation elements consist of a partition wall, possibly combined with a flameproof joint or
an air gap with natural ventilation.
4.1.3.2 Partition walls
Partition walls shall be constructed of either:
a) corrosion-resistant metals, glass or ceramics, which are specified in the manufacturer’s
documentation; or
b) other materials which can be verified to provide the same level of safety. In this case, X-
marking or an advisory marking in accordance with 29.2 of IEC 60079-0 shall be applied

and the certificate shall clearly specify the material and its thermal and mechanical

properties to enable the user to confirm the suitability for the particular application the

certificate number shall include the "X" suffix in accordance with the marking requirements

of IEC 60079-0.
If the wall thickness is less than 1 mm, the equipment shall be marked with an “X” or an
advisory marking according to 29.2 of IEC 60079-0 with a special condition for safe use the

certificate number shall include the "X" suffix in accordance with the marking requirements of

IEC 60079-0 and the Specific Conditions of Use listed on the certificate shall indicate that the

material shall not be subject to environmental conditions which might adversely affect the

partition wall.
If the partition wall is under constant vibrational stress (for example vibrating membranes), the
minimum endurance limit at maximum amplitude shall be defined in the documentation (see
Clause 7). Due to specified process pressure, loads or temperature, the separation element
shall not impair the Type of Protection.
NOTE 1 A wall thickness less than 1 mm is only permitted in combination with intrinsic safety
“ib”, or a flameproof joint or natural ventilation (see 4.1.3.3).
NOTE 2 For glass or ceramics, a minimum thickness of 1/10 of the diameter/maximum
dimension but not less than 1 mm is recommended required.
In addition to the requirements of 4.1.3.1 to 4.1.3.3, metallic partition walls with a thickness
≥ 1 mm may be provided with suitable conductor bushings (see Figure 1).
To avoid a critical concentration of explosive gas atmosphere diffusing from the area requiring
EPL Ga into the enclosure containing the electrical circuits, the leakage rate through the
bushing shall be low compared to the leakage rate from the enclosure into the free
atmosphere.
NOTE 3 For example this could be done using a standard enclosure with an IP67 rating
according to IEC 60529, a bushing with a leakage rate equivalent to a helium-leakage rate
-2 –4 5
less than 10 Pa×l/s (10 mbar × l/s) at a pressure difference of 10 Pa (1 bar) is sufficient.
This can be achieved, for example, by using a glass or ceramic bushing as shown in Figure 1.
Metallic sleeve, corrosion
resistant (wall thickness ≥ 1 mm)
Bushing insulator (e.g. melted
≥ 10 mm glass, brazed ceramics)

Less hazardous
area
“ia” circuit
Area
Ex “ia” circuit
requiring
Non-“ia”
EPL Ga
Non-“ia” supply circuit
circuit
(e.g. Ex “e”)
Partition wall
Welded
(t ≥1 mm)
(joint ≥ 1 mm)
Electrical equipment
IEC
Figure 1 – Example of a partition wall with a conductor bushing
considered as gas diffusion tight

– 12 – IEC 60079-26:2014 RLV © IEC 2014

4.1.3.3 Requirements depending on the thickness of the partition wall

The combinations of separation elements and additional protective measures depend on the

wall thickness, t, of the partition wall as described below and shown in Table 1:

i) For homogeneous partition walls with a thickness ≥3 mm, no additional protection
measures are required.
ii) For homogeneous partition walls with a thickness of 3 mm > t ≥ 1 mm, one EPL Gb type of

protection is required (see example a) of Table 1). A homogeneous part of the enclosure

of an equipment with a EPL Gb type of protection may form the partition wall, even for
types of protection which rely on the enclosure, provided the equipment does not contain
an ignition capable source, for example exposed contacts (see example a) of Table 1). If

the equipment contains a source of ignition in normal operation, either a flameproof joint
(example b) of Table 1) or a ventilated air gap (example c) of Table 1) is also required.
iii) Behind partition walls of 1 mm > t ≥ 0,2 mm, one of the following protective measures is
required:
– Type of Protection intrinsic safety “ib” according to IEC 60079-11 (example a) of Table
1); or
– one EPL Gb Type of Protection in combination with a flameproof joint (example b) of
Table 1); or
– one EPL Gb Type of Protection in combination with a ventilated air-gap and a
flameproof joint (example c) of Table 1).
iv) For a partition wall with t < 0.2 mm (for example membranes), a flameproof joint and one
EPL Gb Type of Protection are required (example b) of Table 1). If the equipment contains
a source of ignition in normal operation (for example by exposed contacts), a ventilated air
gap is also required (example type c) of Table 1).
NOTE In the context of this clause, ‘homogeneous’ means a membrane constructed of a single piece of material
without any insertions such as feed-throughs, bushings.

Table 1 – Separation elements
Requirements depending on the thickness, t, of the partition wall

i) t ≥ 3 mm: no additional requirements

ii) iii) iv)
Type of construction
3 mm > t ≥ 1 mm 1 mm > t ≥ 0.2 mm t < 0.2 mm

(“X” marking required) (“X” marking

required)
a) Partition wall
Less hazardous
area Area
requiring a
EPL Gb Type of
Area
lower EPL than
Protection
requiring
Ga
EPL Ga and
Type of Protection
Not permissible
intrinsic safety’ “ib”
no ignition source
Electrical
under normal operation
Partition
equipment
(for example no exposed
wall
contacts)
b) Partition wall + joint
Less hazardous
area Area
Area
requiring a
EPL Gb Type of
requiring
lower EPL than
Protection
EPL Ga
Ga
and
EPL Gb Type of Protection
Partition
Electrical
no ignition source
a
wall
equipment
under normal operation
(for example no
exposed contacts)
a
Joint
c) Partition wall + ventilation
Less hazardous
area Area
requiring a
Area lower EPL than
requiring Ga
EPL Gb Type of Protection
a
EPL Ga
(Joint )
EPL Gb Type of
and
Protection
Electrical
Partition
flameproof joint (dashed)
a
equipment
wall
Natural
ventilation
a
Flameproof joint and partition wall are exchangeable in sequence of order.
4.1.3.4 Partition wall combined with a flameproof joint
Joints supplementing partition walls shall comply with either:
a) the requirements in IEC 60079-1;
NOTE 1 to determine the joint characteristics, the free volume of the enclosure containing
the electrical circuits should shall be considered; or
b) a construction, where the same level of safety as for a) can be demonstrated.

– 14 – IEC 60079-26:2014 RLV © IEC 2014

NOTE For example, a cylindrical PTFE-bushing pressed form-fit into a metallic enclosure at a length

≥ 40 mm. A permanently compressed joint with a length of at least 17 mm is also suitable (for example using a
conical PTFE-bushing compressed by a spring).

Non-metallic components in separation elements shall meet the requirements of IEC 60695-

11-10, flammability category V-0 and have a chemical resistivity equivalent, for example to

that of glass, ceramics, non-regenerated PTFE or epoxy resin for petrol petrochemical

applications. The materials of the separation element and its mechanical and thermal stress

limits shall be clearly defined in the documentation to enable the user to confirm their

suitability for the particular application.

4.1.3.5 Partition wall combined with an airgap with natural ventilation

The ventilation shall ensure that under the most onerous arduous process conditions specified
by the manufacturer and the anticipated leakages, an accumulation of flammable materials in
the equipment is prevented. Under atmospheric process conditions, the ventilation is valid
sufficient for all gases, vapours and mists, if the length of the air-gap is ≥10 mm and the
effective perforation in the circumference is at least 50 %. In addition to the requirements of
4.1.3.1 to 4.1.3.3, metallic partition walls with a thickness ≥1 mm and a suitable air-gap may
be provided, for example with a cylindrical flameproof shaft joint according to IEC 60079-1
(see Figure 2). In this case, the ventilation air gap shall have a minimum length of 10 mm or a
length equal to the diameter of the shaft, whichever is greater.

a
≥ 10 mm
Perforation > 50 %
Less hazardous
area
Natural
ventilation
Shaft
Area e.g. electric motor
requiring
Ex “d”
Non-“ia” supply circuit
EPL Ga
Partition wall
(≥1 mm)
Cylindrical shaft joint flameproof
according to IEC 60079-1
IEC
a
Required for sufficient ventilation.
NOTE The cylindrical shaft joint inside the partition wall as shown in Figure 2 is not a supplementing joint as
referred to in 4.1.3.4.
NOTE 2 The electrical equipment should be selected in accordance with the appropriate gas group.

Figure 2 – Example of a separation element
with a cylindrical shaft joint and natural ventilation
4.2 Equipment with moving parts
4.2.1 Frictional heating
If the equipment contains moving parts, temperature rise due to frictional heating may occur
under normal operation or fault condition. It shall be taken into consideration when
determining the maximum surface temperature.
4.2.2 Damage arising from failure of moving parts
In case of a failure of moving parts, the Types of Protection shall not be adversely affected.

4.2.3 Light metals
Operational friction or impact between equipment parts made of light metals or their alloys

(with concentrations above the limits given in IEC 60079-0) with equipment parts made of

iron/steel is not permitted. Operational friction or impact between two light metals is

permitted.
NOTE Light metals include for example aluminium, magnesium, titanium or zirconium.

4.4 Isolated conductive components

Isolated conductive components on the surface of the equipment shall be bonded to ground,

except where they cannot be charged to an ignition capable level as demonstrated by the
charging test procedure of IEC 60079-0.
4.5 Non-conductive enclosures and accessible non-conductive components
4.5.1 General
Precautions shall be taken to ensure that the risk of ignition from electrostatic discharge is
reduced to a negligible level, particularly since equipment providing EPL Ga may be applied
directly in the process and non-conductive surfaces may be charged by the flow of non-
conductive media (for example in stirring vessels or pipes).
Therefore, the accessible chargeable surfaces of the equipment shall comply with the
requirements of 7.3 of IEC 60079-0 or one of the following:
a) limitation of the size of chargeable non-conductive surfaces – see 4.5.2;
b) limitation of the thickness of chargeable non-conductive layers – see 4.5.3;
c) provision of a conductive coating – see 4.5.4.
If none of these requirements can be complied with, X-marking or an advisory marking in
accordance with 29.2 of IEC 60079-0 shall be applied and the certificate shall contain special
conditions for safe use to enable the user to decide on the suitability of the equipment for the
particular application.
4.5.2 Limitation of the size of chargeable non-conductive surfaces
The projection of the chargeable non-conductive surface shall be limited to the values given in
in Table 4 of IEC 60079-0 for zone 0 (EPL Ga). In the case of long parts with non-conductive
surfaces, such as tubes, bars, cables or ropes, independent of their length, the diameters or
widths shall not exceed
a) 3 mm for equipment of groups IIA and IIB;

b) 1 mm for equipment of group IIC.
4.5.3 Limitation of the thickness of chargeable non-conductive layers
Where a non-conductive layer covers a bonded conductive surface, the thickness of that layer
shall not exceed
a) 2 mm for equipment of group IIA, IIB;
b) 0,2 mm for equipment of group IIC.
The bonded conductive surface may be formed by a wire mesh with a mesh area as defined
in IEC 60079-0, Table 4 for zone 0 (EPL Ga).
NOTE 1 Cables with a protective covering over a screen may comply.
NOTE 2 It should, however, be noted that in the presence of a very efficient charge generating mechanism
propagating brush discharges could occur.

– 16 – IEC 60079-26:2014 RLV © IEC 2014

4.5.4 Provision of a conductive coating

Non-conductive surfaces may be covered with a bonded durable conductive coating. The

resistance between coating and the point of bond shall not exceed 1 GΩ.

The resistance shall be measured in accordance with 26.13 of IEC 60079-0 using a 1 cm

electrode at the worst case position of the surface and the point of bond.

X-marking or an advisory marking in accordance with 29.2 of IEC 60079-0 shall be applied

and the certificate shall advise on the use of the bonding connection (if separately accessible

to the user and not an integral part of the equipment) and provide information to enable the

user to decide on the durability of the coating material with respect to the environmental
conditions (see Clause 7).
NOTE The requirements of 4.5 will be deleted after incorporation in IEC 60079-0.
4.3 Process connection
If the equipment is mounted across the boundary wall between an area requiring EPL Ga and
a less hazardous area, the construction shall ensure that either under normal operation
conditions:
a) explosive gas atmospheres cannot be released from an area requiring EPL Ga creating an
explosive atmosphere in the surrounding area; and
b) that in case of an ignition of an explosive gas atmosphere in the surrounding area there is
no flame propagation into the area requiring EPL Ga.
The equipment shall be designed to allow installation in a manner that will result in a
sufficiently tight joint (IP 66 or IP 67) or a flameproof joint according to IEC 60079-1 (joints
specified for a volume ≤ 100 cm )
...