SIST EN 60079-29-4:2010

SLOVENSKI STANDARD
01-junij-2010
Eksplozivne atmosfere - 29-4. del: Javljalniki plina - Zahteve za delovanje
javljalnikov vnetljivih plinov z odprto merilno potjo (IEC 60079-29-4:2009)
Explosive atmospheres - Part 29-4: Gas detectors - Performance requirements of open
path detectors for flammable gases n(IEC 60079-29-4:2009)
Explosionsfähige Atmosphäre - Teil 29-4: Gasmessgeräte - Anforderungen an das
Betriebsverhalten von Geräten mit offener Messstrecke für die Messung brennbarer
Gase (IEC 60079-29-4:2009)
Atmosphères explosives - Partie 29-4: Détecteurs de gaz - Exigences d'aptitude à la
fonction des détecteurs de gaz inflammables à chermin ouvert (CEI 60079-29-4:2009)
Ta slovenski standard je istoveten z: EN 60079-29-4:2010
ICS:
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60079-29-4
NORME EUROPÉENNE
April 2010
EUROPÄISCHE NORM
ICS 29.260.20 Supersedes EN 50241-1:1999 + A1:2004, EN 50241-2:1999

English version
Explosive atmospheres -
Part 29-4: Gas detectors -
Performance requirements of open path detectors for flammable gases
(IEC 60079-29-4:2009)
Atmosphères explosives -  Explosionsfähige Atmosphäre -
Partie 29-4: Détecteurs de gaz - Teil 29-4: Gasmessgeräte -
Exigences d'aptitude à la fonction Anforderungen an das Betriebsverhalten
des détecteurs de gaz inflammables von Geräten mit offener Messstrecke
à chemin ouvert für die Messung brennbarer Gase
(CEI 60079-29-4:2009) (IEC 60079-29-4:2009)

This European Standard was approved by CENELEC on 2010-04-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: Avenue Marnix 17, B - 1000 Brussels

© 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60079-29-4:2010 E
Foreword
The text of document 31/819/FDIS, future edition 1 of IEC 60079-29-4, prepared by IEC Technical
Committee 31, Equipment for explosive atmospheres, was submitted to the IEC-CENELEC parallel vote.
A draft amendment, prepared by the CENELEC SC 31-9, Electrical apparatus for the detection and
measurement of combustible gases to be used in industrial and commercial potentially explosive
atmospheres, of Technical Committee CENELEC TC 31, Electrical apparatus for potentially explosive
atmospheres, was submitted to the formal vote.
The combined texts were approved by CENELEC as EN 60079-29-4 on 2010-04-01.
requirement of this standard conflicts with a requirement of EN 60079-0, the requirement of this standard
shall take precedence.
This European Standard supersedes EN 50241-1:1999 + A1:2004 and EN 50241-2:1999.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
The following dates were fixed:
– latest date by which the amendment has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2011-01-01
– latest date by which the national standards conflicting
with the amendment have to be withdrawn (dow) 2013-04-01
Annexes ZA, ZZ and ZY have been added by CENELEC.
__________
– 3 – EN 60079-29-4:2010
Endorsement notice
The text of the International Standard IEC 60079-29-4:2009 was approved by CENELEC as a European
Standard with agreed common modifications as given below.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
ISO 6142 NOTE  Harmonized as EN ISO 6142
ISO 6144 NOTE  Harmonized as EN ISO 6144
ISO 6145 NOTE  Harmonized as EN ISO 6145
__________
COMMON MODIFICATIONS
1 Scope
Replace “IEC 60079-29” with “EN 60079-29” in paragraph 1.
Replace “IEC 60079-29-1” with “EN 60079-29-1” in Note 1.
Delete note 3.
2 Normative references
Replace “IEC 60079 (all parts)” with “EN 60079 (all parts)” in paragraph 2.
Replace “IEC 60079-0” with “EN 60079-0” in paragraph 3.
Replace “IEC 60079-29-1” with “EN 60079-29-1” in paragraph 4.

Delete references to IEC 61000-4-1 and IEC 61000-4-3 in paragraphs 6 and 7.

Add the following undated references:

EN 50270, Electromagnetic compatibility - Electrical apparatus for the detection and measurement of
combustible gases, toxic gases or oxygen

EN 50271, Electrical apparatus for the detection and measurement of combustible gases, toxic gases or
oxygen - Requirements and tests for apparatus using software and/or digital technologies

3 Terms and definitions
st
In the 1 paragraph:
Replace “IEC 60079-0” with “EN 60079-0”.
Replace “IEC 60079-29-1” with “EN 60079-29-1”.

4 General requirements
4.1.1
nd
In the 2 paragraph, line 2, replace “… of these other parts of IEC 60079” with “… of the appropriate
regulations for explosion protection”.

4.3
Add “The apparatus shall fulfil the requirements of EN 50271.”
Delete subclauses 4.3.1 to 4.3.5.

5 Test methods
5.2.4.2
In the second paragraph, replace reference to test 5.4.16 by 5.4.20.

5.4.12
rd
In the 3 paragraph, replace “A 90% of the change.” with “90% of the change.”.

5.4.15 Power supply interruptions and transients
Replace 5.4.15.1, 5.4.15.2 and 5.4.15.3 with “Text deleted”.

5.4.17
Replace this subclause by:
5.4.17 Electromagnetic compatibility
The apparatus shall be set up under normal conditions, in accordance with 5.3, and then shall be
subjected to the tests specified in EN 50270.

NOTE For this test the operating distance may be relaxed to suit the requirements of the EMC test facility.”

7.1 Labelling and marking
Delete the text and replace with:

“The equipment shall comply with the marking requirements of EN 60079-0.

In addition, the equipment shall also be marked:
a) “EN 60079-29-4” (to represent conformance with this performance standard);
b) year of construction (may be encoded within the serial number).”

7.2 Instruction manual
Add “EN” before “60079-0” in paragraph 1, line 2.

– 5 – EN 60079-29-4:2010
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

- - Electromagnetic compatibility - Electrical EN 50270 -
apparatus for the detection and measurement
of combustible gases, toxic gases or oxygen

- - Electrical apparatus for the detection and EN 50271 -
measurement of combustible gases, toxic
gases or oxygen - Requirements and tests
for apparatus using software and/or digital
technologies
IEC 60079 Series Explosive atmospheres EN 60079 Series

IEC 60079-0 - Explosive atmospheres - EN 60079-0 -
Part 0: Equipment - General requirements

IEC 60079-29-1 - Explosive atmospheres - EN 60079-29-1 -
(mod) Part 29-1: Gas detectors - Performance
requirements of detectors for flammable
gases
IEC 60825-1 - Safety of laser products - EN 60825-1 -
Part 1: Equipment classification and
requirements
Annex ZY
(informative)
Significant changes between this European Standard and EN 50241-1:1999
and EN 50241-2:1999
This European Standard supersedes EN 50241-1:1999 and EN 50241-2:1999.
The significant changes with respect to EN 50241-1:1999 and EN 50241-2:1999 are as listed below.
Type
Minor and Extension Substantial
editorial change
changes regarding
a
ESR´s
Normative references: EN 60068-2-6 (vibration), removed,
X
EN 50271 (software) added
Definitions: 3 modified, 3 added, 2 removed X
General requirements 4.1 and 4.1.1 modified, 4.1.5 replaced
by 4.3 (Software-controlled equipment, new), 4.2.2.4 (low X
battery indications) replaced within 4.2.4 (Fault signals, new)
General requirements and normal conditions for tests
modified and extended (clauses 5.1, 5.2.4.1, 5.2.4.2, 5.3.2, X
5.3.3, 5.3.7, 5.3.8, 5.3.11, 5.3.12)
Test method 5.4.2 (Unpowered storage) modified X
Test method 5.4.3 (Calibration curve) modified
X X
Test method 5.4.4.1, ‘Short term drift’ test removed, replaced
with ‘Slow increase of gas volume ratio’ for equipment with X X
automatic drift compensation
Test method 5.4.4.2 (Long term stability) modified X
Test method 5.4.4.3, Long term stability (continuous duty,
X X
battery powered) test added
Test method 5.4.4.4, Stability (spot reading equipment only)
X X
test added
Test method 5.4.6 (Temperature variation) modified X
Requirements for test 5.4.6 modified X
Test method 5.4.7 removed (Pressure variation) X
Test method 5.4.7 (Water vapour interference) modified X
Requirements for test 5.4.7 modified X
Test method 5.4.8 (Vibration) modified X
Requirements for test 5.4.8 modified X
Test method 5.4.9, Drop test for portable and transportable
X X
equipment added
– 7 – EN 60079-29-4:2010
Type
Minor and Extension Substantial
editorial change
changes regarding
a
ESR´s
Test method 5.4.12, Minimum time to operate (spot reading
X X
equipment) test added
Test method 5.4.13 removed (Power supply interruptions etc,
X
now part of EMC requirement of EN 50270)
Test method 5.4.13, Battery capacity test added X X
Test method 5.4.14 (Power supply variations) modified X
Test method 5.4.16 removed (Attenuation of radiation, now
X
part of 5.4.20, Long range operation)
Requirements for test 5.4.16 (now Recovery from power
X
supply interruption) modified
Test method 5.4.19, Partial obscuration test added X X
Requirements for test 5.4.20 (Long range operation) modified X
Labelling and marking requirements modified X
Annex A removed (atmospheric visibility) X
New Annex A added (water vapour test apparatus) X
Bibliography much reduced X
The requirements of EN 50241-2 have been incorporated
into the test methods of the new standard, thus combining X
the two previous standards into one
a
ESR = Essential Health and Safety Requirements (Annex II of Directive 94/9/EC)

General conclusion on the change of the State of the Art by this standard
CENELEC/TC 31 as the responsible committee has concluded that this new edition contains substantial
changes regarding the ESRs.
Annex ZZ
(informative)
Coverage of Essential Requirements of EC Directives
This European Standard has been prepared under a mandate given to CENELEC by the European
Commission and the European free Trade Association and within its scope the Standard covers only the
following essential requirements given in Annex II, Clauses 1.5.5 to 1.5.8 of the EC Directive 94/9/EC:
– ER 1.5.5 to 1.5.7 – the essential safety requirements for devices with a measuring function for
explosion protection
– 1.5.5 is covered by 5.4 of this standard
– 1.5.6 is covered by 4.2.1, 4.2.2, and 4.2.4
– 1.5.7 is covered by 4.2.3 and 5.4
– ER 1.5.8 – the risks arising from software
– 1.5.8 is covered by 4.3
Compliance with this standard provides one means of conformity with the specified essential
requirements of the Directive concerned.
WARNING: Other requirements and other EC Directives can be applied to the products falling within the
scope of this standard.
IEC 60079-29-4 ®
Edition 1.0 2009-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Explosive atmospheres –
Part 29-4: Gas detectors – Performance requirements of open path detectors for
flammable gases
Atmosphères explosives –
Partie 29-4: Détecteurs de gaz – Exigences d’aptitude à la fonction des
détecteurs de gaz inflammables à chemin ouvert

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
V
CODE PRIX
ICS 29.260.20 ISBN 2-8318-1067-6
– 2 – 60079-29-4 © IEC:2009
CONTENTS
FOREWORD.4
1 Scope.6
2 Normative references .7
3 Terms and definitions .7
3.1 Equipment.7
3.2 Alarms.8
3.3 Signals and indications.8
3.4 Gaseous atmospheres.8
3.5 Optical equipment .9
3.6 Performance characteristics .10
4 General requirements .11
4.1 Detection equipment .11
4.1.1 Components .11
4.1.2 Electrical assemblies and components .11
4.1.3 Optical radiation .11
4.2 Construction.11
4.2.1 General .11
4.2.2 Indicating devices.11
4.2.3 Alarm or output functions.12
4.2.4 Fault signals .12
4.2.5 Adjustments .12
4.3 Software-controlled equipment .12
4.3.1 Conversion errors.13
4.3.2 Software.13
4.3.3 Data transmission.13
4.3.4 Self-test routines .13
4.3.5 Functional concept .14
5 Test requirements .14
5.1 Introduction .14
5.2 General requirements for tests .15
5.2.1 Samples and sequence of tests .15
5.2.2 Constructional checks .15
5.2.3 Preparation of samples.15
5.2.4 Equipment for calibration and test .16
5.3 Normal conditions for test.18
5.3.1 General .18
5.3.2 Operating distance for laboratory tests .18
5.3.3 Test gases.18
5.3.4 Test gas integral concentrations .18
5.3.5 Voltage.19
5.3.6 Ambient temperature .19
5.3.7 Ambient humidity.19
5.3.8 Ambient atmosphere.19
5.3.9 Preparation of equipment .19
5.3.10 Stabilization.19
5.3.11 Communications options.20

60079-29-4 © IEC:2009 – 3 –
5.3.12 Gas detection equipment as part of systems.20
5.4 Test methods .20
5.4.1 Initial preparation and procedure .20
5.4.2 Unpowered storage .20
5.4.3 Calibration curve (not applicable to alarm only equipment with fixed
settings) .20
5.4.4 Stability .21
5.4.5 Alarm reliability.21
5.4.6 Temperature variation .22
5.4.7 Water vapour interference .23
5.4.8 Vibration.23
5.4.9 Drop test for portable and transportable equipment .24
5.4.10 Alignment .24
5.4.11 Time of response.25
5.4.12 Minimum time to operate (spot-reading equipment) .25
5.4.13 Battery capacity.25
5.4.14 Power supply variations (externally powered equipment) .26
5.4.15 Power supply interruptions and transients .27
5.4.16 Recovery from power supply interruption .27
5.4.17 Electromagnetic compatibility (EMC) .27
5.4.18 Beam block fault.28
5.4.19 Partial obscuration.28
5.4.20 Long range operation .29
5.4.21 Direct solar radiation (applicable for equipment intended for outdoor
use).29
6 Field verification equipment.30
7 Information for use .30
7.1 Labelling and marking .30
7.2 Instruction manual.30
Annex A (informative) Water vapour test apparatus .32
Bibliography.33

Figure 1 – Equipment for gas calibration and speed of response test.17
Figure A.1 – Water vapour test apparatus.32

– 4 – 60079-29-4 © IEC:2009
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 29-4: Gas detectors –
Performance requirements of open path
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
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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 60079-29-4 has been prepared by IEC technical committee 31:
Equipment for explosive atmospheres.
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 shall take precedence.
The text of this standard is based on the following documents:
FDIS Report on voting
31/819/FDIS 31/841/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.

60079-29-4 © IEC:2009 – 5 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60079 series, under the general title: Explosives 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.
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.

– 6 – 60079-29-4 © IEC:2009
EXPLOSIVE ATMOSPHERES –
Part 29-4: Gas detectors –
Performance requirements of open path
detectors for flammable gases
1 Scope
This part of IEC 60079-29 specifies performance requirements of equipment for the detection
and measuring of flammable gases or vapours in ambient air by measuring the spectral
absorption by the gases or vapours over extended optical paths, ranging typically from one
metre to a few kilometres.
Such equipment measures the integral concentration of the absorbing gas over the optical
path in units such as LFL metre for flammable gases.
NOTE 1 Actual values of concentration can be deduced only where it can be established that the concentration is
uniform over the optical path, for example in very short optical paths (<100 mm). In such cases, the equipment is
within the scope of IEC 60079-29-1.
NOTE 2 This standard is based upon present absorption techniques using infrared radiation. Other techniques
and applications may require additional test considerations (e.g. pressure test).
Equipment falling within the scope of this standard is classified by the following types:
Type 1: an optical transmitter and receiver, located at either end of a path through the
atmosphere to be monitored.
Type 2: an optical transceiver (i.e. combined transmitter and receiver) and a suitable
reflector, which may be a topographic feature or a retroreflector, located at either end of a
path through the atmosphere to be monitored.
This standard is also applicable when an equipment manufacturer makes any claims
regarding any special features of construction or superior performance that exceed the
minimum requirements of this standard. All such claims shall be verified and the test
procedures should be extended or supplemented, where necessary, to verify the claimed
performance. The additional tests shall be agreed between the manufacturer and the test
laboratory and identified and described in the test report.
This standard does not apply to any of following:
a) equipment intended to provide range resolution of gas concentration (e.g. Light direction
and ranging (LIDAR));
b) equipment consisting of a passive optical receiver without a dedicated optical source;
c) equipment intended to measure the local volumetric concentration of gas (point sensors);
d) equipment intended for the detection of dusts or mists in air;
e) equipment for cross stack monitoring;
f) equipment intended for the detection of explosives; and
g) equipment intended only for the identification of individual gas or vapour components,
(e.g. Fourier transform infrared spectroscopy (FTIR)).
This standard is applicable to equipment which is intended for use in hazardous or non-
hazardous areas, or both. Equipment for use in hazardous areas is also required to have
explosion protection (see 4.1.1).

60079-29-4 © IEC:2009 – 7 –
This standard applies to portable, transportable and fixed equipment intended for commercial
and industrial applications.
NOTE 3 This standard is intended to provide for the supply of equipment giving a level of performance suitable for
general purpose applications. However, for specific applications a prospective purchaser or an appropriate
authority may additionally require equipment to be submitted for particular tests or approval. Such tests or approval
are regarded as additional to and separate from the provisions of the standards referred to above.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60079 (all parts), Explosive atmospheres
IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements
IEC 60079-29-1, Explosive atmospheres – Part 29-1: Gas detectors – Performance
requirements of detectors for flammable gases
IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 61000-4-1, Electromagnetic compatibility (EMC) – Part 4-1: Testing and measurement
techniques – Overview of IEC 61000-4 series
IEC 61000-4-3, Electromagnetic compatibility (EMC) – Part 4-3: Testing and measurement
techniques – Radiated, radio-frequency, electromagnetic field immunity test
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60079-0 as well as
IEC 60079-29-1 and the following apply.
NOTE Additional definitions applicable to explosive atmospheres can be found in IEC 60050-426.
3.1 Equipment
3.1.1
alarm only equipment
equipment which generates an alarm signal but does not have a meter or output giving a
measure of the integral concentration
3.1.2
fixed equipment
equipment fastened to a support, or otherwise secured in a specific location
3.1.3
transportable equipment
equipment not intended to be carried by a person nor intended for fixed installation
3.1.4
portable equipment
equipment intended to be carried by a person
NOTE Typically portable equipment will be used as a spot-reading equipment.

– 8 – 60079-29-4 © IEC:2009
3.2 Alarms
3.2.1
alarm set point
fixed or adjustable setting of the equipment that is intended to pre-set the value of integral
concentration at which the equipment will automatically initiate an indication, alarm, or other
output function
3.2.2
alarm signal
audible, visual, electronic or other signal generated by the equipment when an integral
concentration of gas in excess of a preset value is detected
3.2.3
latching alarm
alarm which, once activated, requires a deliberate action to deactivate it
3.3 Signals and indications
3.3.1
fault signal
audible, visual, or other type of output which provides, directly or indirectly, a warning or
indication that the equipment is defective
3.3.2
beam blocked signal
audible, visual or other type of output which provides, directly or indirectly, a warning or
indication that the optical path is obscured or that the signal detected is too weak to enable
the equipment to function normally
3.3.3
inhibition signal
audible, visual, or other type of output which provides, directly or indirectly, a warning or
indication that normal operation has been suspended
3.3.4
indicating devices
means for displaying values or states in analogue or digital form
3.3.5
special state
state of the equipment other than those in which monitoring of gas concentration takes place
NOTE  For example warm-up, calibration mode or fault condition
3.4 Gaseous atmospheres
3.4.1
ambient air
atmosphere in the area being monitored by the equipment
3.4.2
clean air
air which is free from gases or vapours (flammable, toxic or environmentally harmful gases) to
which the equipment is sensitive or which influence the performance of the equipment

60079-29-4 © IEC:2009 – 9 –
3.4.3
flammable atmosphere
mixture with air, under normal atmospheric conditions, of flammable materials in the form of
gas, vapour or mist, in which, after ignition, combustion spreads throughout the unconsumed
mixture
NOTE 1 This definition specifically excludes dusts and fibres in suspension in air. Mists, though included in the
definition, are not covered by this standard.
NOTE 2 Although a mixture which has a concentration above the upper explosive limit is not a flammable
atmosphere, there is a risk of creating a flammable atmosphere by dilution.
NOTE 3 Normal atmospheric conditions include variations above and below reference levels of 101,3 kPa (1013
mbar) and 20 °C provided the variations have negligible effect on the explosion properties of the flammable
materials.
NOTE 4 For the purposes of this standard, the terms "explosive", "combustible" and "flammable" are regarded as
synonymous.
3.4.4
flammable gas
gas which, when mixed with air in certain volumetric ratios, forms a flammable atmosphere
3.4.5
integral concentration
mathematical integral of the gas concentration along the optical path.
NOTE 1  It is expressed in units of concentration multiplied by distance, e.g. LFL.metre for flammable gases or
ppm.metre for toxic gases
NOTE 2 100 % LFL x 1 metre = 1 LFL.metre;
10 % LFL × 10 metre = 1 LFL.metre.
3.4.6
lower flammable limit
LFL
volume ratio of flammable gas or vapour in air below which a flammable gas atmosphere will
not be formed
3.4.7
upper flammable limit
UFL
volume ratio of flammable gas or vapour in air above which an explosive gas atmosphere will
not be formed
3.4.8
explosion protection
measures applied in the construction of electrical equipment to prevent ignition of a
surrounding explosive gas atmosphere by the equipment
3.4.9
toxic gas
gas that may be harmful to human health and/or the performance of persons due to its
physical or physico-chemical properties
3.5 Optical equipment
3.5.1
open path
distance in space which traverses the area (or part of the area) in which the atmosphere is
being monitored and through which gases in the atmosphere are free to move

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3.5.2
optical axis
median line of the optical path
3.5.3
optical path
path traversed by optical radiation from an optical transmitter to an optical receiver.
NOTE  The radiation may traverse the open path once, twice or many times depending on the form taken by the
instrument
3.5.4
optical radiation
ultra-violet, visible or infra-red regions of the electromagnetic spectrum
3.5.5
albedo
proportion of incident light scattered back from a surface
3.5.6
transmitter
assembly in which the optical transmitting element(s) are housed and which may contain
associated optical and electrical components
3.5.7
transceiver
assembly in which the optical detecting element(s) and optical transmitting element(s) are
housed and which may contain associated optical and electrical components
3.5.8
receiver
assembly in which the optical detecting element(s) are housed and which may contain
associated optical and electrical components
3.5.9
retroreflector
individual or multiple arrangement of reflecting corners of cubes arrayed so that light is
reflected back parallel to its incident path
3.5.10
gas cell
sealed enclosure (capable of being filled with test gases) and having transparent ends
3.6 Performance characteristics
3.6.1
drift
variation with time of the indication produced by the equipment under normal conditions when
monitoring a fixed distribution of gas concentration in the optical path
3.6.2
time of response
t
x
time interval, with the equipment stabilised, between the time when an instantaneous variation
in the integral concentration is produced in the optical path and the time when the indication
reaches a stated percentage (x) of its final value

60079-29-4 © IEC:2009 – 11 –
4 General requirements
4.1 Detection equipment
4.1.1 Components
All parts of the open path gas detection equipment intended for use in explosive gas
atmospheres shall comply with the appropriate requirements for explosion protection.
The operation and storage temperature limits of this standard could exceed the required
temperature limits of these other parts of IEC 60079 series for certain types of equipment. In
this case, the examination and testing of the protection technique(s) used for the equipment
shall be extended to cover the temperature range. If this extension is not possible due to
requirements of the protection techniques used, then the temperature range of this standard
shall be reduced to the range specified for the protection technique(s).
4.1.2 Electrical assemblies and components
Electrical assemblies and components shall comply with the appropriate construction and test
requirements of 4.2 and of Clause 5 respectively.
4.1.3 Optical radiation
Optical radiation produced by the equipment shall conform to the requirements given in
IEC 60825-1.
4.2 Construction
4.2.1 General
The gas detection equipment shall be so designed and manufactured as to avoid physical
injury or other harm which might be caused by direct or indirect contact.
All parts of the equipment shall be suitable for its intended use. It shall be capable of
withstanding, without damage or impairment of performance, the effects of vibration, dust,
corrosive media and climatic conditions to be expected during operational use in
environments in which the equipment is intended to be used.
Fine adjustment of the optical beam direction shall be possible and an indication shall be
provided to confirm that satisfactory alignment of the optical beam has been achieved. Such
equipment need not form a permanent part of the equipment.
All equipment shall be constructed to facilitate, where applicable, regular functional, service,
and calibration checks.
4.2.2 Indicating devices
4.2.2.1 Indications and output signals
An indication or output signal shall be provided to show that the equipment is switched on.
The indication or output signal shall be a measure of the actual integral concentration over
the open path.
NOTE The open path is independent of the number of times the optical radiation traverses it.
If the equipment enters a special state (eg. inhibition, beam blockage or a fault), a signal shall
be provided. For fixed equipment, this shall include a contact or other transmittable output
signal. If these conditions are separately indicated, they shall be clearly identified.

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Indicating or controlling devices, where provided, need not be an integral part of the
equipment.
When the equipment is intended for alarm only, the manufacturers shall provide or identify
suitable points for connecting an indicating or recording device for testing the compliance of
the equipment with this standard.
4.2.2.2 Individual indicator lights
When individual indicator lights are incorporated in the equipment they shall be coloured as
follows:
a) alarm indicators shall be coloured RED;
b) fault, inhibition and beam blockage indicators shall be coloured YELLOW;
c) power supply indicators and normal operation indicators shall be coloured GREEN.
4.2.2.3 Indicator light marking
In addition to the colour requirements, the indicator lights shall be adequately labelled to show
their functions.
4.2.3 Alarm or output functions
When non-latching alarm devices, output contacts, or signal outputs are provided to indicate
detection of an integral gas concentration in excess of a pre-set alarm level, the fact shall be
indicated clearly and prominently in the instruction manual.
The operation of any other output functions shall be clearly stated in the manual.
4.2.4 Fault signals
Equipment shall provide a fault signal if any of the following conditions (as a minimum) occur:
a) under range indication (below the zero point) between zero and -10 % full scale
equivalent;
b) beam blockage;
c) low battery indication, if applicable;
d) a short-circuit or open-circuit in connections to any remote sensor, if applicable.
Such signals shall be differentiated from any alarms.
4.2.5 Adjustments
All means of adjustment shall be designed so as to discourage unauthorised interference with
the equipment.
Fixed explosion-protected equipment housed in explosion-protected enclosures shall be
designed s
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