Explosive atmospheres - Part 42: Electrical safety devices for the control of potential ignition sources for Ex-Equipment

IEC TS 60079-42:2019 provides guidance for equipment manufacturers where electrical safety devices are used to reduce the likelihood of potential ignition sources becoming effective in Ex Equipment located in Explosive Atmospheres. Electrical safety devices perform a safety function to control potential ignition sources from both, electrical or non-electrical Ex Equipment in explosive atmospheres.
This Technical Specification may also be applied to a combination of elements performing a safety function. For example: Sensor, Logic system, Final element. This Technical Specification can also be used for assessing the safety device independently, without being designed for a specific Ex Equipment. A safety device can be a measure to achieve a required EPL of the Ex Equipment with respect to a potential ignition source. The combination of the safety device and the Ex Equipment could then comply with the relevant standards of the IEC 60079 series and the ISO 80079 series with respect to the Equipment Protection Level. However, increasing the EPL of Ex Equipment by the simple addition of a safety device is not within the scope of this Technical Specification.
This Technical Specification does not apply to:
• mechanical control equipment such as pressure relief valves, mechanical governors and other mechanical safety devices
• the use of gas detection
• control equipment to prevent the occurrence of explosive atmospheres, e.g. inerting systems and ventilation systems
• mitigation of an explosion

Atmosphères explosive - Partie 42: Dispositifs électriques de sécurité pour la commande des sources potentielles d’inflammation des appareils Ex

IEC TS 60079-41:2019 fournit des recommandations pour les constructeurs d’appareils lorsque des dispositifs électriques de sécurité sont utilisés pour réduire la probabilité que les sources potentielles d’inflammation deviennent effectives dans les appareils Ex situés en atmosphères explosives. Les dispositifs électriques de sécurité exécutent une fonction de sécurité pour contrôler les sources potentielles d’inflammation, provenant d’appareils Ex électriques ou non électriques, en atmosphères explosives.
La présente Spécification technique peut également s’appliquer à une combinaison d’éléments exécutant une fonction de sécurité. Par exemple: Capteur, Système logique, Élément terminal. La présente Spécification technique peut également être utilisée pour évaluer le dispositif de sécurité de manière indépendante, sans qu’il soit conçu pour un appareil Ex spécifique.
Un dispositif de sécurité peut être une mesure permettant d’atteindre un niveau de protection du matériel (EPL - equipment protection level) exigé de l’appareil Ex contre une source potentielle d’inflammation. La combinaison du dispositif de sécurité et de l’appareil Ex peut alors être conforme aux normes pertinentes des séries de normes IEC 60079 et ISO 80079 eu égard à l’EPL. Cependant, l’augmentation de l’EPL d’un appareil Ex par le simple ajout d’un dispositif de sécurité ne relève pas du domaine d’application de la présente Spécification technique.
La présente Spécification technique ne s’applique pas:
• aux appareils mécaniques de commande tels que les soupapes de surpression, les régulateurs mécaniques et autres dispositifs mécaniques de sécurité
• à l’utilisation de détection de gaz
• aux appareils de commande visant à éviter la formation d’atmosphères explosives, par exemple, systèmes d'inertage et systèmes de ventilation
• à l’atténuation d’une explosion

General Information

Status
Published
Publication Date
16-Apr-2019
Current Stage
PPUB - Publication issued
Completion Date
17-Apr-2019
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IEC TS 60079-42
Edition 1.0 2019-04
TECHNICAL
SPECIFICATION
SPECIFICATION
TECHNIQUE
colour
inside
Explosive atmospheres
Part 42: Electrical Safety Devices for the control of potential ignition sources
from Ex-Equipment
Atmospheres explosive
Partie 42: Dispositifs électriques de sécurité pour la commande des sources
potentielles d’inflammation des appareils Ex
IEC TS 60079-42:2019-04(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TS 60079-42
Edition 1.0 2019-04
TECHNICAL
SPECIFICATION
SPECIFICATION
TECHNIQUE
colour
inside
Explosive atmospheres
Part 42: Electrical Safety Devices for the control of potential ignition sources
from Ex-Equipment
Atmospheres explosive
Partie 42: Dispositifs électriques de sécurité pour la commande des sources
potentielles d’inflammation des appareils Ex
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.260.20 ISBN 978-2-8322-6807-0

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC TS 60079-42:2019 © IEC 2019
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 8

3 Terms and definitions ...................................................................................................... 8

4 Basic requirements .......................................................................................................... 8

5 Ignition prevention by safety devices ............................................................................... 9

5.1 General concept of ignition risk reduction ............................................................... 9

5.2 Safety characteristics of a safety device ................................................................. 9

5.3 Associated safety device ....................................................................................... 10

6 Functional requirements for a safety device ................................................................... 10

6.1 General requirements ........................................................................................... 10

6.2 Specification of the safety function ........................................................................ 10

6.3 Requirements for achieving the safety integrity ..................................................... 10

6.3.1 Simple safety devices .................................................................................... 10

6.3.2 Complex safety device ................................................................................... 11

7 Testing and Verification ................................................................................................. 11

7.1 Type tests ............................................................................................................. 11

7.2 Proof tests ............................................................................................................ 11

8 Marking ......................................................................................................................... 11

9 Instructions .................................................................................................................... 11

Annex A (informative) Guidance for assessment of a simple safety device ........................... 13

Annex B (informative) Examples for the application of safety devices .................................. 14

B.1 General ................................................................................................................. 14

B.2 Ex Equipment with a temperature controlled surface ............................................. 14

B.2.1 Problem: ........................................................................................................ 14

B.2.2 Consequence: ............................................................................................... 14

B.2.3 Solution: ........................................................................................................ 14

B.3 Current-dependent safety device for thermal protection of motors with type

of protection Ex eb ................................................................................................ 15

B.3.1 Problem: ........................................................................................................ 15

B.3.2 Consequence: ............................................................................................... 15

B.3.3 Solution: ........................................................................................................ 15

B.4 Risk reduction by ignition control and mitigation, bucket elevator example ............ 16

B.4.1 Problem ......................................................................................................... 16

B.4.2 Ignition Hazard Assessment .......................................................................... 17

B.4.3 Safety controls to prevent ignition .................................................................. 17

B.4.4 Safety Controls with explosion mitigation ....................................................... 18

B.5 Control of high temperatures ................................................................................. 19

B.5.1 Problem ......................................................................................................... 19

B.5.2 Ignition hazard assessment ........................................................................... 19

B.5.3 Safety controls............................................................................................... 20

Annex C (informative) Use of the Safe Motor Temperature (SMT) sub-function with

converter-fed motors ............................................................................................................. 21

C.1 General ................................................................................................................. 21

C.2 Reliability of the safety motor temperature control function. .................................. 22

---------------------- Page: 4 ----------------------
IEC TS 60079-42:2019 © IEC 2019 – 3 –

C.3 Control without temperature sensors ..................................................................... 22

C.4 Control with temperature sensors .......................................................................... 22

Bibliography .......................................................................................................................... 24

Figure B.1 –Safety Device to limit the temperature rise ......................................................... 15

Figure B.2 – Overload protection device to limit the temperature rise of a motor under

stall and overload conditions ................................................................................................. 16

Figure B.3 – Bucket elevator principle ................................................................................... 17

Figure B.4 – Bucket elevator sensors for ignition hazard detection........................................ 18

Figure B.5 – Controls with explosion mitigation ..................................................................... 19

Figure C.1 – Overview .......................................................................................................... 21

Figure C.2 – Control without temperature sensors ................................................................ 22

Figure C.3 – Control with temperature sensors ..................................................................... 23

Table 1 – Minimum RRF for a safety device for ignition risk reduction ..................................... 9

Table A.1 – Relationship between λ and RRF ...................................................................... 13

Table C 1– SMT safety sub function Risk Reduction Factors (RRF) ...................................... 22

---------------------- Page: 5 ----------------------
– 4 – IEC TS 60079-42:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES
Part 42: Electrical Safety Devices for the control of potential ignition
sources from Ex-Equipment
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 Technical Specification IEC 60079-42 has been prepared by IEC technical

committee 31: Equipment for explosive atmospheres.
The text of this Technical Specification is based on the following documents:
FDIS Report on voting
31/1418/DTS 31/1441/RVDTS

Full information on the voting for the approval of this Technical Specification 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.

---------------------- Page: 6 ----------------------
IEC TS 60079-42:2019 © IEC 2019 – 5 –

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.

This International Technical Specification is to be read in conjunction with the International

Standards for the specific types of protection listed in the ISO 80079-37 and the IEC 60079

series.

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.
---------------------- Page: 7 ----------------------
– 6 – IEC TS 60079-42:2019 © IEC 2019
INTRODUCTION

Generally, the probability of potential ignition sources becoming effective is mitigated by

applying the protection measures according to the IEC 60079 and the ISO 80079 series. If the

probability of an ignition source becoming effective cannot be mitigated by these measures, it

could be controlled by using a suitable safety device. The combination of the safety device

and the Ex Equipment may then comply with the relevant standards of the IEC 60079 series

and the ISO 80079 series with respect to the Equipment Protection Level.

Safety devices, which are used as part of the protection of equipment for explosive

atmospheres for control of potential ignition sources, should consider reliability for the

intended purpose to recognise the principles for the classification of hazardous areas and

explosion protection techniques. This document provides guidance for the application of

safety functions to provide a reduction of ignition risk for equipment as part of the IEC 60079

series and ISO 80079 series. It relies on relevant IEC and ISO standards for safety related

control systems.
---------------------- Page: 8 ----------------------
IEC TS 60079-42:2019 © IEC 2019 – 7 –
EXPLOSIVE ATMOSPHERES
Part 42: Electrical Safety Devices for the control of potential ignition
sources from Ex-Equipment
1 Scope

This part of IEC 60079, which is a Technical Specification, provides guidance for equipment

manufacturers where electrical safety devices are used to reduce the likelihood of potential

ignition sources becoming effective in Ex Equipment located in Explosive Atmospheres.

Electrical safety devices perform a safety function to control potential ignition sources from

both, electrical or non-electrical Ex Equipment in explosive atmospheres.

This document may also be applied to a combination of elements performing a safety function.

For example:
• Sensor
• Logic system
• Final element

This Technical Specification can also be used for assessing the safety device independently,

without being designed for a specific Ex Equipment.

A safety device can be a measure to achieve a required EPL of the Ex Equipment with

respect to a potential ignition source. The combination of the safety device and the Ex

Equipment could then comply with the relevant standards of the IEC 60079 series and the

ISO 80079 series with respect to the Equipment Protection Level. However, increasing the

EPL of Ex Equipment by the simple addition of a safety device is not within the scope of this

document.
This document does not apply to:

• mechanical control equipment such as pressure relief valves, mechanical governors and

other mechanical safety devices
• the use of gas detection

• control equipment to prevent the occurrence of explosive atmospheres, e.g. inerting

systems and ventilation systems
• mitigation of an explosion

NOTE Some potential ignition sources might not be practicably controlled by safety devices.

Electrical safety devices, where the level of safety integrity is identified under other parts of

the IEC 60079 series, this document can be used as a reference for the realization of the

level of safety integrity.

Electrical safety devices may be installed either as part of or separate to the Ex Equipment

under control (EEUC) and may be located inside or outside the hazardous area.
---------------------- Page: 9 ----------------------
– 8 – IEC TS 60079-42:2019 © IEC 2019
2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements 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, Explosive atmospheres - Part 0: Equipment - General requirements

IEC 61508 (all parts), Functional safety of electrical/electronic/programmable electronic

safety-related systems

IEC 61508-4, Functional safety of electrical/electronic/programmable electronic safety-related

systems – Part 4: Definitions and abbreviations (see http://www.iec.ch/functionalsafety)

IEC 61511-1, Functional safety - Safety instrumented systems for the process industry sector

- Part 1: Framework, definitions, system, hardware and application programming requirements

ISO 80079-37, Non Electrical Equipment for Explosive Atmospheres – Non electrical Type of

Protection constructional safety ‘c’, control of ignition Source ‘b’, liquid immersion ‘k’

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60079-0,

IEC 61508-4, IEC 61511-1, ISO 80079-37 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
safety device

device intended for use inside or outside explosive atmospheres but required for or

contributing to the safe functioning of Ex Equipment and protective systems with respect to

the risks of explosion

Note 1 to entry: Safety devices differ from the term devices used in the IEC 61508 and IEC 61511 series. Safety

devices can be compared to the terms like “safety-related system (IEC 61508)” or “safety instrumented system

(IEC 61511)”.
3.2
Ex Equipment under control
EEUC

Ex Equipment which contains a potential ignition source which is controlled by a safety device

3.3
risk reduction factor
RRF

factor by which the probability of the occurrence of an ignition source in the EEUC is reduced

by the safety device
4 Basic requirements

Safety functions shall respond before a potential ignition source of the EEUC becomes

effective. Safety functions shall therefore be considered as operating in low demand mode.

---------------------- Page: 10 ----------------------
IEC TS 60079-42:2019 © IEC 2019 – 9 –

The detection of a dangerous failure in a safety device (by diagnostic tests, proof tests or by

any other means) shall result in a specified action to achieve or maintain a safe state of

the EEUC.

The safety device and the Ex Equipment shall be assessed for use as a combination

according to the relevant standards of the IEC 60079 series and the ISO 80079 series and

shall be marked accordingly.

NOTE If safety devices are located in a hazardous area, they are selected and installed in accordance with

IEC 60079-14.
5 Ignition prevention by safety devices
5.1 General concept of ignition risk reduction

To comply with a defined EPL, Ex Equipment shall first be protected against potential ignition

sources by applying the measures according to the IEC 60079 and the ISO 80079 series. If an

ignition source cannot be prevented by these measures, it may be controlled by using a

suitable safety device.

The ignition hazard assessment of Ex Equipment starts with the evaluation of potential

ignition sources including the assessment of malfunctions related to the Ex Equipment. The

Ex Equipment to be controlled and the safety devices shall first be assessed as a combination

relevant to the EPL. The minimum risk reduction factor of the safety devices shall meet the

requirements of 5.2.

NOTE Equipment may have also been assessed without the control of a safety device, but with a lower EPL rating.

If Ex Equipment contains several potential ignition sources, for each ignition source the same

procedure shall be performed and the ignition risk mitigated by appropriate measures.

5.2 Safety characteristics of a safety device

A safety device shall provide a safety integrity suitable for the required ignition risk reduction

for the Ex Equipment. Safety devices shall provide a minimum risk reduction factor for the Ex

Equipment according to Table 1.
Table 1 – Minimum RRF for a safety device for ignition risk reduction
Target EEUC Safety device
Ex Equipment with a residual ignition source
EPL RRF
Gc, Dc ≥10
which is not a source of ignition in normal
operation and could become active as an ignition
Gb, Db ≥100
source in the case of regular expected
occurrences
Ga, Da Not permitted
Gc, Dc Not required
which could become a source of ignition only
Gb, Db ≥10
during expected malfunctions
Ga, Da ≥100
Gc, Dc Not required
which could become a source of ignition only
Gb, Db Not required
during rare malfunctions
Ga, Da ≥10

NOTE 1 Regular expected occurrences include anticipated conditions such as high temperatures on a brake,

failure of a lamp or opening of a fuse. Such devices cannot be controlled by a safety device to achieve EPL

Ga or Da.
---------------------- Page: 11 ----------------------
– 10 – IEC TS 60079-42:2019 © IEC 2019

NOTE 2 For EPL Gc/Dc the risk reduction factor provides for additional protection to ensure an ignition source

remains inactive in the case of regular expected occurrences. For EPL Gb/Db the definition from IEC 60079-0 does

not identify the case of regular expected occurrences but these still have to be considered. Thus the higher RRF

provides additional integrity for control of such ignition sources.

NOTE 3 Regular expected occurrences do not include ignition sources during normal operation. Additional

measures are provided to avoid that those regular expected occurrences would become effective ignition sources

(see IEC 60079-0, definition EPL Gc).

Ignition sources during normal operation (e.g. sparking contacts or sparking relays) shall not

be controlled by safety devices as they are considered as unacceptable risk.. Such ignition

sources cannot be controlled by safety devices.

Where an additional risk reduction measure is applied in the event of an ignition e.g. a dust

explosion suppression system, the RRF shown in Table 1 may be reduced. In this case the

additional RRF has to be verified.
Examples of the use of Table 1 are provided in Annex B and C.
5.3 Associated safety device

A safety device not designed for specific equipment to be controlled may be assessed

independently. The safety integrity and other technical parameters of this associated safety

device as well as the interface to the Ex Equipment shall be specified in the instructions of the

Ex Equipment.

The combination of the equipment to be controlled and the associated safety device is to be

considered as Ex Equipment (EEUC) and shall be assessed according to Table 1.
See example in B.2.
6 Functional requirements for a safety device
6.1 General requirements

A safety device shall be specified taking into account the potential ignition source to be

controlled. The safety function for the safety device shall be determined.

The safety device shall be designed to provide the safety function reliably under the specified

range of operating conditions. For example, during commissioning, the number of accessible

parameters shall be minimized and locked after parameterisation, e.g. by password, jumper,

or switch. Cyber security risks and protection against external interference e.g. EMC, shall be

considered.
6.2 Specification of the safety function
On demand the safety f
...

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