IEC 60079-29-1:2007

IEC 60079-29-1
Edition 1.0 2007-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 29-1: Gas detectors – Performance requirements of detectors for flammable
gases
Atmosphères explosives –
Partie 29-1: Détecteurs de gaz – Exigences d’aptitude à la fonction des
détecteurs de gaz inflammables

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IEC 60079-29-1
Edition 1.0 2007-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 29-1: Gas detectors – Performance requirements of detectors for flammable
gases
Atmosphères explosives –
Partie 29-1: Détecteurs de gaz – Exigences d’aptitude à la fonction des
détecteurs de gaz inflammables

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 29.260.20 ISBN 2-8318-9249-X

TC 31/Publication 60079-29-1 (2007), First edition/I-SH 01

EXPLOSIVE ATMOSPHERES –
Part 29-1: Gas detectors – Performance requirements
of detectors for flammable gases

INTERPRETATION SHEET 1
This interpretation sheet has been prepared by IEC technical committee 31: Equipment
for explosive atmospheres.
The text of this interpretation sheet is based on the following documents:
ISH Report on voting
31/809/ISH 31/817/RVD
Full information on the voting for the approval of this interpretation sheet can be found in
the report on voting indicated in the above table.
___________
There has been a request for formal interpretation of the drop test fail criterion in the
performance standard IEC 60079-29-1 (2007), Subclause 5.4.14.

The fail criterion is:
“The apparatus shall be considered to have failed this test if there is a loss of function
(e.g. alarm, pump function, controls, display) after the test”.

Question:
Is the interpretation of this text, that the loss of function, even in a short period during the
interruption and until restart of the equipment will fail the test? Or is a permanent loss of
function needed to fail the equipment, e.g. a broken display or a pump, which cannot
restart?
Bouncing of a battery spring in the moment of impact can cause the drop out of power in
battery supplied equipment, and make it shut down. Is this considered as sufficient to fail
the test? Or would it be sufficient safe situation for the user if the equipment could restart
and show the correct measurement?

Interpretation:
Any loss of function after the test including any change of state is considered a failure
since there is continued dependency on the life safety device even under adverse affects
such as an accidental drop of the device during use. Automatic or manual re-starting is
not acceptable.
– 2 – 60079-29-1 © IEC:2007
CONTENTS
FOREWORD.5
INTRODUCTION.8

1 Scope.9
2 Normative references .10
3 Definitions .10
3.1 Gas properties.10
3.2 Types of instruments .12
3.3 Sensors.13
3.4 Supply of gas to instrument .13
3.5 Signals and alarms.13
3.6 Times .14
3.7 Miscellaneous .14
4 General requirements .15
4.1 Introduction .15
4.2 Construction.16
4.2.1 General .16
4.2.2 Indicating devices.16
4.2.3 Alarm or output functions.17
4.2.4 Fault signals .18
4.2.5 Adjustments .18
4.2.6 Battery-powered apparatus.18
4.2.7 Stand-alone gas detection apparatus for use with separate control
units .18
4.2.8 Separate control units for use with stand-alone gas detection
apparatus .19
4.2.9 Software-controlled apparatus .19
4.3 Labelling and marking .21
4.4 Instruction manual.21
5 Test methods .22
5.1 Introduction .22
5.2 General requirements for tests .22
5.2.1 Samples and sequence of tests .22
5.2.2 Preparation of apparatus before testing .23
5.2.3 Mask for calibration and tests .24
5.3 Normal conditions for test.24
5.3.1 General .24
5.3.2 Test gas(es) .24
5.3.3 Standard test gas .25
5.3.4 Flow rate for test gases .25
5.3.5 Voltage.25
5.3.6 Temperature.25
5.3.7 Pressure.25
5.3.8 Humidity .25
5.3.9 Stabilization time .26
5.3.10 Orientation .26
5.3.11 Communications options.26

60079-29-1 © IEC:2007 – 3 –
5.3.12 Gas detection apparatus as part of systems .26
5.4 Test methods .26
5.4.1 General .26
5.4.2 Unpowered storage .26
5.4.3 Calibration and adjustment .26
5.4.4 Stability (continuous duty apparatus only).27
5.4.5 Stability (spot-reading apparatus only).28
5.4.6 Alarm set point(s) .28
5.4.7 Temperature.29
5.4.8 Pressure.29
5.4.9 Humidity .29
5.4.10 Air velocity .29
5.4.11 Flow rate for aspirated apparatus .30
5.4.12 Orientation .30
5.4.13 Vibration.30
5.4.14 Drop test for portable and transportable apparatus .31
5.4.15 Warm-up time.31
5.4.16 Time of response (not applicable to spot-reading apparatus) .32
5.4.17 Minimum time to operate (spot-reading apparatus) .32
5.4.18 High gas concentration operation above the measuring range .32
5.4.19 Battery capacity.33
5.4.20 Power supply variations.33
5.4.21 Power supply interruptions, voltage transients and step changes of
voltage .34
5.4.22 Addition of sampling probe .34
5.4.23 Dust (for apparatus where the air is sampled by natural diffusion
only) .34
5.4.24 Poisons and other gases .34
5.4.25 Electromagnetic immunity.35
5.4.26 Field calibration kit .36
5.4.27 Software verification .36

Annex A (normative) Performance requirements .37
Annex B (informative) Determination of time of response .42

Bibliography.49

Figure 1 – Warm-up time in clean air (typical) .15
Figure 2 – Warm-up time in standard test gas (typical) .15
Figure B.1 – Schematic example of equipment for use with aspirated apparatus.44
Figure B.2 – Schematic example of equipment during application of clean air or test gas .45
Figure B.3 – Schematic example of equipment showing change-over from clean air to
test gas to begin the time of response measurement (arrows indicate movement of
applicators).45

– 4 – 60079-29-1 © IEC:2007
Figure B.4 – Schematic example of applicator and sensor inlet during application of
test gas or clean air .46
Figure B.5 – Example of automated test chamber .47
Figure B.6 – Apparatus for step change and flooding tests.48

Table A.1 – Performance requirements .37

60079-29-1 © IEC:2007 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 29-1: Gas detectors –
Performance requirements of detectors for flammable gases

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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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.
International Standard IEC 60079-29-1 has been prepared by IEC technical committee 31:
Equipment for explosive atmospheres.
This first edition of IEC 60079-29-1 cancels and replaces the first edition of IEC 61779-1 to
IEC 61779-5:1998 series and constitutes a technical revision.
The main changes with respect to the previous edition are listed below:
– Subclause 4.2.3 (Alarm or output functions) was modified to ensure alarm devices can not
be adjustable outside their measuring range and to include requirements for de-activation
of alarm devices.
– Subclause 4.2.7 (Stand-alone gas detection apparatus for use with separate control units)
was added to allow separate evaluation of detection apparatus providing an industry
recognized output signal.
– 6 – 60079-29-1 © IEC:2007
– Subclause 4.2.8 (Separate control units for use with stand-alone gas detection apparatus)
was added to allow separate evaluation of control unit apparatus using an industry
recognized input signal.
– Subclause 4.2.9 (Software-controlled apparatus) was added to the document for improved
evaluation of software. The added text is based upon the guiding principles and
requirements of EN 50271.
– Subclause 4.5 (Diffusion sensors) was removed from the document based upon the
redundant protection allowance for equipment used in Zone 0 areas, such as Ex d ia rated
equipment.
– Subclause 5.2.1.1 was modified to require the center wavelength of the optical filters of
two apparatus at the minimum and maximum limit of this standard.
– Subclause 5.2.1.2 was modified to allow the order of testing within each block to be
conducted at the discretion of the test laboratory.
– Subclause 5.3.11 (Communications options) was added to ensure maximum transaction
rates are applied during testing.
– Subclause 5.3.12 (Gas detection apparatus as part of systems) was added to ensure
maximum transaction rates are applied during testing.
– Subclause 5.4.6 (Alarm set point(s)) was modified to include text related to alarms that are
activated at decreasing concentrations.
– Subclause 5.4.10 (Air velocity) was modified to include testing at 3 m/s and 6 m/s.
– Subclause 5.4.16 (Time of response) was modified to exclude recovery time test
requirements for Group II apparatus with a volume fraction up to 100 % LFL indication.
– Subclause 5.4.18 (High gas concentration operation above the measuring range) was
modified to define the sequence of tests.
– Annex A (Performance requirements) has undergone major modifications by eliminating
the gas/vapour table and replacing the annex with the performance requirements of Parts
2 to 5 of the former edition. Additionally, performance requirements of Parts 2 to 5 were
adjusted for consistency as appropriate. The intent of this change is to condense Parts 1
to 5 within a single standard.
This part of IEC 60079-29 is to be used in conjunction with the following standards:
– IEC 60079-0, Electrical apparatus for explosive gas atmospheres – Part 0: General
requirements
– IEC 60079-29-2, Explosive atmospheres – Part 29-2: Gas detectors – Selection,
installation, use and maintenance of detectors for flammable gases and oxygen.
The text of this standard is based on the following documents:
FDIS Report on voting
31/695/FDIS 31/711/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.

60079-29-1 © IEC:2007 – 7 –
A list of all parts of the IEC 60079 series, 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 maintenance result 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.
The contents of the interpretation sheet of July 2009 have been included in this copy.

– 8 – 60079-29-1 © IEC:2007
INTRODUCTION
Guidance for the selection, installation, use and maintenance of gas detecting apparatus are
set out in IEC 60079-29-2: Explosive atmospheres – Part 29-2: Gas detectors – Selection,
installation, use and maintenance of detectors for flammable gases and oxygen.

60079-29-1 © IEC:2007 – 9 –
EXPLOSIVE ATMOSPHERES –
Part 29-1: Gas detectors –
Performance requirements of detectors for flammable gases

1 Scope
This part of IEC 60079-29 specifies general requirements for construction, testing and
performance, and describes the test methods that apply to portable, transportable and fixed
apparatus for the detection and measurement of flammable gas or vapour concentrations with
air. The apparatus, or parts thereof, are intended for use in potentially explosive atmospheres
(see 3.1.8) and in mines susceptible to firedamp.
This standard is also applicable when an apparatus manufacturer makes any claims regarding
any special features of construction or superior performance that exceed these minimum
requirements. In these cases, all such claims should be verified and the test procedures
should be extended or supplemented, where necessary, to verify the performance claimed by
the manufacturer. When verifying the superior performance of one criterion, other
performance criteria are not required to meet the standards minimum requirements, however,
these reduced claimed performance criteria (as confirmed in the manufactures Installation
Manual) should also be verified. (e.g. temperature range of 0 °C to 60 °C; 0 °C to 40 °C at
±10 % accuracy and 40 °C to 60 °C at ±15 % (manufacturers claimed accuracy). The
additional tests should be agreed between the manufacturer and test laboratory and identified
and described in the test report.
This standard is applicable to flammable gas detection apparatus intended to provide an
indication, alarm or other output function; the purpose of which is to give a warning of a
potential explosion hazard and in some cases, to initiate automatic or manual protective
action(s).
This standard is applicable to apparatus, including the integral sampling systems of aspirated
apparatus, intended to be used for commercial, industrial and non-residential safety
applications.
This standard does not apply to external sampling systems, or to apparatus of laboratory or
scientific type, or to apparatus used only for process control purposes. It also does not apply
to open path (line of sight) area monitors. For apparatus used for sensing the presence of
multiple gases, this standard applies only to the detection of flammable gas or vapour.
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
IEC 60079-29-1 will take precedence.
NOTE 1 IEC 60079-29-1 is intended to provide for the supply of apparatus giving a level of safety and
performance suitable for general purpose applications. However, for specific applications, a prospective purchaser
(or an appropriate authority) may additionally require the apparatus to be submitted to particular tests or approval.
For example, group I apparatus (i.e. apparatus to be used in mines susceptible to firedamp) may not be permitted
to be used without the additional, prior approval of the relevant authority in mines under its jurisdiction. Such
particular tests/approval are to be regarded as additional to and separate from the provisions of the standards
referred to above and do not preclude certification to or compliance with these standards.

– 10 – 60079-29-1 © IEC:2007
NOTE 2 All apparatus calibrated on specific gases or vapours can not be expected to correctly indicate on other
gases or vapours.
NOTE 3 For the purposes of this standard, the terms "lower flammable limit (LFL)" and "lower explosive limit
(LEL)" are deemed to be synonymous, and likewise the terms "upper flammable limit (UFL)" and "upper explosive
limit (UEL)" are deemed to be synonymous. For ease of reference, the two abbreviations LFL and UFL may be
used hereinafter to denote these two sets of terms. It should be recognized that particular authorities having
jurisdiction may have overriding requirements that dictate the use of one of these sets of terms and not the other.
NOTE 4 For the purposes of this standard, the term “indicating up to a volume fraction of X %” includes apparatus
with an upper limit of the measuring range equal to or less than X %.
2 Normative references
The following referenced documents are indispensable for the application of this document.
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: Electrical apparatus for explosive gas atmospheres – Part 0: General
requirements
IEC 60079-20: Electrical apparatus for explosive gas atmospheres – Part 20: Data for
flammable gases and vapours, relating to the use of electrical apparatus
IEC 60079-29-2, Explosive atmospheres – Part 29-2: Gas detectors – Selection, installation,
use and maintenance of detectors for flammable gases and oxygen
IEC 61000-4-1: Electromagnetic compatibility (EMC) – Part 4-1: Testing and measurement
techniques – Overview of IEC 61000-4 series. Basic EMC publication
IEC 61000-4-3: Electromagnetic compatibility (EMC) – Part 4-3: Testing and measurement
techniques – Radiated, radio-frequency, electromagnetic field immunity test. Basic EMC
publication
IEC 61000-4-4: Electromagnetic compatibility (EMC) – Part 4-4: Testing and measurement
techniques – Electrical fast transient/burst immunity test – Basic EMC publication
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 Chapter 426 of the International
Electrotechnical Vocabulary (IEV) IEC 60050 (426).
3.1 Gas properties
3.1.1
ambient air
normal atmosphere surrounding the apparatus
3.1.2
clean air
air that is free of flammable gases and interfering or contaminating substances

60079-29-1 © IEC:2007 – 11 –
3.1.3
explosive gas atmosphere
mixture with air, under normal atmospheric conditions, of flammable substances in the form of
gas or vapour, in which, after ignition, self-sustaining flame propagation
NOTE 1 This definition specifically excludes dusts and fibres in suspension in air. Mists are not covered by this
standard.
NOTE 2 Although a mixture that has a concentration above the upper flammable limit (see 3.1.9) is not an
explosive atmosphere, in certain cases for area classification purposes, it is advisable to consider it as an
explosive gas atmosphere.
NOTE 3 Normal atmospheric conditions include variations above and below the reference levels of 101,3 kPa and
20 °C provided the variations have a negligible effect on the explosive properties of the flammable materials.
3.1.4
firedamp
flammable gas, consisting mainly of methane, found naturally in mines
3.1.5
flammable gas
gas or vapour which, when mixed with air in a certain proportion, will form an explosive
atmosphere
NOTE For the purposes of this standard, the term "flammable gas" includes flammable vapours.
3.1.6
lower flammable limit
LFL
volume fraction of flammable gas or vapour in air below, which an explosive gas atmosphere
does not form, expressed as a percentage (see IEC 60079-20)
NOTE This is also known as lower explosive limit (LEL).
3.1.7
poisons (for sensors)
substances, which lead to temporary or permanent loss of sensitivity of the sensors
3.1.8
potentially explosive atmosphere
atmosphere that could become explosive (the danger is a potential one)
NOTE This would include an atmosphere with gas concentration currently above UFL, where dilution with air
would render it explosive.
3.1.9
upper flammable limit
UFL
volume fraction of flammable gas or vapour in air above, which an explosive gas atmosphere
does not form, expressed as a percentage (see IEC 60079-20)
NOTE This is also known as upper explosive limit (UEL).
3.1.10
volume fraction (v/v)
quotient of the volume of a specified component and the sum of the volumes of all
components of a gas mixture before mixing, all volumes referring to the pressure and the
temperature of the gas mixture

– 12 – 60079-29-1 © IEC:2007
NOTE The volume fraction and volume concentration take the same value if, at the same state conditions, the
sum of the component volumes before mixing and the volume of the mixture are equal. However, because the
mixing of two or more gases at the same state conditions is usually accompanied by a slight contraction or, less
frequently, a slight expansion, this is not generally the case.
3.1.11
zero gas
gas recommended by the manufacturer, which is free of flammable gases, and interfering and
contaminating substances, the purpose of which is calibration/adjustment of the apparatus
zero
3.2 Types of instruments
3.2.1
alarm-only apparatus
apparatus having an alarm but not having a meter or other indicating device
3.2.2
aspirated apparatus
apparatus that samples the gas by drawing it to the gas sensor – for example, by means of a
hand-operated or electric pump
3.2.3
continuous duty apparatus
apparatus that is powered for long periods of time, but may have either continuous or
intermittent sensing
3.2.4
diffusion apparatus
apparatus in which the transfer of gas from the atmosphere to the gas sensor takes place by
random molecular movement, i.e. under conditions in which there is no aspirated flow
3.2.5
fixed apparatus
apparatus that is intended to have all parts permanently installed
3.2.6
group I apparatus
apparatus for mines susceptible to firedamp
3.2.7
group II apparatus
apparatus for places with a potentially explosive atmosphere, other than mines susceptible to
firedamp
3.2.8
portable apparatus
spot-reading or continuous duty apparatus that has been designed to be readily carried from
place to place and to be used while it is being carried. A portable apparatus is battery
powered and includes, but is not limited to
a) a hand-held apparatus, typically less than 1 kg, which requires use of only one hand to
operate,
b) personal monitors, similar in size and mass to the hand-held apparatus, that are
continuously operating (but not necessarily continuously sensing) while they are attached
to the user, and
60079-29-1 © IEC:2007 – 13 –
c) larger apparatus that can be operated by the user while it is carried either by hand, by a
shoulder strap or carrying harness and which may or may not have a hand directed probe.
3.2.9
spot-reading apparatus
apparatus intended to be used for short, intermittent or irregular periods of time as required
(typically 5 min or less)
3.2.10
transportable apparatus
apparatus not intended to be portable but which can be readily moved from one place to
another
3.2.11
stand-alone gas detection apparatus
fixed gas detection apparatus that provide a conditioned electronic signal or output indication
to a generally accepted industry standard (such as 4-20 mA or 3-15 psi), intended to be
utilized with stand-alone control units or signal processing data acquisition, central monitoring
and similar systems, which typically process information from various locations and sources
including, but not limited to gas detection apparatus
3.2.12
stand-alone control unit
fixed gas detection control units intended to provide meter indication, alarm functions, output
contacts and/or alarm signal outputs when utilized with stand-alone gas detection apparatus
3.3 Sensors
3.3.1
remote sensor
sensor that is not integral to the main body of the apparatus
3.3.2
sensor
assembly in which the sensing element is housed and that may also contain associated circuit
components
3.4 Supply of gas to instrument
3.4.1
sample line
a means by which the gas being sampled is conveyed to the sensor including accessories,
e.g. filter, water trap
3.4.2
sampling probe
separate sample line, which is attached to the apparatus as required, that may or may not be
supplied with the apparatus. It is usually short (e.g. in the order of 1 m) and rigid (although it
may be telescopic), but it may be connected by a flexible tube to the apparatus
3.5 Signals and alarms
3.5.1
alarm set point
fixed or adjustable setting of the apparatus that is intended to preset the level of
concentration at which the apparatus will automatically initiate an indication, alarm or other
output function
– 14 – 60079-29-1 © IEC:2007
3.5.2
fault signal
audible, visible or other type of output, different from the alarm signal, permitting, directly or
indirectly, a warning or indication that the apparatus is not working satisfactorily
3.5.3
latching alarm
alarm that, once activated, requires deliberate action to be deactivated
3.5.4
special state
all states of the apparatus other than those in which monitoring of gas concentration takes
place, for example warm-up, calibration mode or fault condition
3.6 Times
3.6.1
drift
variation in the apparatus indication with time at any fixed gas volume fraction (including
clean air) under constant ambient conditions
3.6.2
final indication
indication given by the apparatus after stabilisation
3.6.3
minimum time of operation (spot-reading apparatus)
time interval between the initiation of a measurement procedure and the time when the
apparatus indication reaches a stated percentage of the final indication
3.6.4
stabilisation
state when three successive readings of an apparatus, taken at 2 min intervals, indicates no
changes greater than ±1 % of the measuring range
3.6.5
time of response t(x) (not applicable to spot-reading apparatus)
time interval, with the apparatus in a warmed-up condition, between the time when an
instantaneous change between clean air and the standard test gas, or vice versa, is produced
at the apparatus inlet, and the time when the response reaches a stated percentage (x) of the
stabilised signal on the standard test gas
3.6.6
warm-up time (not applicable to spot-reading apparatus)
time interval, with the apparatus in a stated atmosphere, between the time when the
apparatus is switched on and the time when the indication reaches and remains within the
stated tolerances (see Figures 1 and 2)
3.7 Miscellaneous
3.7.1
nominal supply voltage
voltage that is given by manufacturers as the recommended operating voltage of their gas
detection apparatus
3.7.2
special tool
tool required to gain access to, or to adjust, controls. The design of the tool is intended to
discourage unauthorised interference with the apparatus

60079-29-1 © IEC:2007 – 15 –
3.7.3
type of protection
measures applied in the construction of electrical equipment to prevent ignition of the
surrounding explosive atmosphere by such apparatus (see 4.1.2)

Indication
Power off in Power on in
clean air clean air
Specified
Apparatus
0 tolerance band
}
zero
on zero indication
Time
0 Warm-up time
(see 3.6.6)
IEC  1293/07
Figure 1 – Warm-up time in clean air (typical)

Indication
Power off Power on
in standard in standard
test gas test gas
Specified
Volume ratio
tolerances of
of standard }
the indication
test gas
Zero in
0 Time
clean air
Warm-up time
(see 3.6.6)
IEC  1294/07
Figure 2 – Warm-up time in standard test gas (typical)
4 General requirements
4.1 Introduction
4.1.1 The apparatus shall comply with the requirements of this standard and Annex A
criteria.
Where an apparatus manufacturer makes any claims regarding any special features of
construction or superior performance that exceed these minimum requirements, all such
claims shall be verified and the test procedures shall be extended or supplemented, where
necessary, to verify the claimed performance.

– 16 – 60079-29-1 © IEC:2007
4.1.2 Electrical assemblies and components shall comply with the construction and test
requirements of 4.2 and Clause 5, where applicable. In addition, parts of the flammable gas
detection apparatus intended for use in hazardous areas shall employ materials, and comply
with the construction and explosion protection as specified in the other relevant parts of
IEC 60079 series.
The operation and storage temperature limits of this standard could exceed the required
temperature limits of these other parts of IEC 60079 for certain types of equipment.
Therefore, the certification of the protection technique(s) used for the apparatus shall cover
this extended temperature range. Conversely, where the certification is required outside the
normal temperature limits appropriate to the protection technique(s) used, the test
temperature exceeding the required ranges within this standard shall be changed
appropriately.
4.1.3 For group I apparatus any electrical circuits to be installed in the same area as the
sensor, including those within the sensor, shall be intrinsically safe ("ia"); the sensing
elements shall be intrinsically safe, or their enclosures shall comply with the safety
requirements specified in 4.1.2.
4.2 Construction
4.2.1 General
Gas detection apparatus or parts thereof (e.g. remote sensors) specifically intended for use in
the presence of corrosive vapours or gases, or which may produce corrosive by-products as a
result of the detection process (e.g. catalytic oxidation or other chemical process) shall be
constructed of materials known to be resistant to corrosion by such substances.
All apparatus shall be constructed to facilitate regular accuracy checks.
All materials and components used in the construction of the apparatus shall be used within
the manufacturer's ratings or limitations, unless otherwise specified by appropriate safety
standards.
NOTE Apparatus using absorption principles where the gas is sampled by diffusion would typically be expected to
have an optical chamber length of up to 30 cm. However, for special applications a longer fixed optical chamber
length may be employed for point detection purposes.
4.2.2 Indicating devices
4.2.2.1 General
An indication shall be provided to show that the apparatus is energized.
NOTE For fixed apparatus the indication may be shown at the control unit.
4.2.2.2 Resolution
For alarm-only apparatus or apparatus where the resolution of the read-out device is
inadequate to demonstrate compliance with this standard, the manufacturer shall identify
suitable points for connecting indi
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