General requirements for Home and Building Electronic Systems (HBES) and Building Automation and Control Systems (BACS) - Part 4: General functional safety requirements for products intended to be integrated in Building Electronic Systems (HBES) and Building Automation and Control Systems (BACS)

IEC 63044-4:2021 provides the functional safety requirements for HBES/BACS. In addition, it defines functional safety requirements for the interface of equipment intended to be connected to an HBES/BACS network. It does not apply to interfaces to other networks. This document does not provide functional safety requirements for safety-related systems. This document does not provide requirements on data protection and security.

Allgemeine Anforderungen an die Elektrische Systemtechnik für Heim und Gebäude (ESHG) und an Systeme der Gebäudeautomation (GA) - Teil 4: Anforderungen an die funktionale Sicherheit für Produkte, die für den Einbau in ESHG/GA vorgesehen sind

Systèmes électroniques pour les foyers domestiques et les bâtiments (HBED) et systèmes de gestion technique du bâtiment (SGTB) - Partie 4: Exigences générales de sécurité fonctionnelle pour les produits destinés à être intégrés dans les HBES et SGTB

L'IEC 63044-4:2021 spécifie les exigences de sécurité fonctionnelle pour HBES/SGTB. De plus, elle spécifie des exigences de sécurité fonctionnelle relatives à l'interface des équipements destinés à être connectés à un réseau HBES/SGTB. Elle ne s'applique pas aux interfaces avec d'autres réseaux. Le présent document ne spécifie pas d’exigences de sécurité fonctionnelle des systèmes relatifs à la sécurité. Le présent document ne spécifie pas d’exigences relatives à la protection et la sécurité des données.

Splošne zahteve za stanovanjske in stavbne elektronske sisteme (HBES) in sisteme za avtomatizacijo in krmiljenje stavb (BACS) - 4. del: Varnostne zahteve za splošno funkcionalnost proizvodov, namenjenih za integracijo v stavbne elektronske sisteme (HBES) in sisteme za avtomatizacijo in krmiljenje stavb (BACS)

General Information

Status
Published
Publication Date
11-Oct-2021
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
05-Oct-2021
Due Date
10-Dec-2021
Completion Date
12-Oct-2021

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SLOVENSKI STANDARD
SIST EN IEC 63044-4:2021
01-november-2021
Splošne zahteve za stanovanjske in stavbne elektronske sisteme (HBES) in

sisteme za avtomatizacijo in krmiljenje stavb (BACS) - 4. del: Varnostne zahteve za

splošno funkcionalnost proizvodov, namenjenih za integracijo v stavbne
elektronske sisteme (HBES) in sisteme za avtomatizacijo in krmiljenje stavb
(BACS)

General requirements for Home and Building Electronic Systems (HBES) and Building

Automation and Control Systems (BACS) - Part 4: General functional safety

requirements for products intended to be integrated in Building Electronic Systems

(HBES) and Building Automation and Control Systems (BACS)
Ta slovenski standard je istoveten z: EN IEC 63044-4:2021
ICS:
35.240.67 Uporabniške rešitve IT v IT applications in building
gradbeništvu and construction industry
97.120 Avtomatske krmilne naprave Automatic controls for
za dom household use
SIST EN IEC 63044-4:2021 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN IEC 63044-4:2021
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SIST EN IEC 63044-4:2021
EUROPEAN STANDARD EN IEC 63044-4
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2021
ICS 29.120.01; 29.120.99
English Version
Home and building electronic systems (HBES) and building
automation and control systems (BACS) - Part 4: General
functional safety requirements for products intended to be
integrated in HBES and BACS
(IEC 63044-4:2021)

Systèmes électroniques pour les foyers domestiques et les Allgemeine Anforderungen an die Elektrische

bâtiments (HBED) et systèmes de gestion technique du Systemtechnik für Heim und Gebäude (ESHG) und an

bâtiment (SGTB) - Partie 4: Exigences générales de Systeme der Gebäudeautomation (GA) - Teil 4:

sécurité fonctionnelle pour les produits destinés à être Anforderungen an die funktionale Sicherheit für Produkte,

intégrés dans les HBES et SGTB die für den Einbau in ESHG/GA vorgesehen sind
(IEC 63044-4:2021) (IEC 63044-4:2021)

This European Standard was approved by CENELEC on 2021-08-03. 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 CEN-CENELEC

Management Centre 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 CEN-CENELEC Management Centre 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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN IEC 63044-4:2021 E
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SIST EN IEC 63044-4:2021
EN IEC 63044-4:2021 (E)
European foreword

The text of document 23/973/FDIS, future edition 1 of IEC 63044-4, prepared by IEC/TC 23 “Electrical

accessories” was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as

EN IEC 63044-4:2021.
The following dates are fixed:

• latest date by which the document has to be implemented at national (dop) 2022–05–03

level by publication of an identical national standard or by endorsement

• latest date by which the national standards conflicting with the (dow) 2024–08–03

document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Any feedback and questions on this document should be directed to the users’ national committee. A

complete listing of these bodies can be found on the CENELEC website.
Endorsement notice

The text of the International Standard IEC 63044-4:2021 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards

indicated:
IEC 60364 (series) NOTE Harmonized as HD 60364 (series)
IEC 60664-1:2020 NOTE Harmonized as EN IEC 60664-1:2020 (not modified)
IEC 61000-1-2 NOTE Harmonized as EN 61000-1-2
IEC 61000-6-1 NOTE Harmonized as EN IEC 61000-6-1
IEC 61000-6-2 NOTE Harmonized as EN IEC 61000-6-2
IEC 61000-6-3 NOTE Harmonized as EN IEC 61000-6-3
IEC 61000-6-4 NOTE Harmonized as EN IEC 61000-6-4
IEC 61508-1 NOTE Harmonized as EN 61508-1
IEC 61508-2 NOTE Harmonized as EN 61508-2
IEC 61508-3 NOTE Harmonized as EN 61508-3
ISO 9000 NOTE Harmonized as EN ISO 9000
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SIST EN IEC 63044-4:2021
EN IEC 63044-4:2021 (E)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the

relevant EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available

here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60364 series Low-voltage electrical installations HD 60364 series
IEC 61508 series Functional safety of EN 61508 series
electrical/electronic/programmable
electronic safety-related systems
IEC 61709 2017 Electric components - Reliability EN 61709 2017
Reference conditions for failure rates and
stress models for conversion
IEC 63044-3 2017 Home and Building Electronic Systems EN IEC 63044-3 2018
(HBES) and Building Automation and
Control Systems (BACS) - Part 3: Electrical
safety requirements
IEC 63044-5 series Home and Building Electronic Systems EN IEC 63044-5 series
(HBES) and Building Automation and
Control Systems (BACS) - Part 5: EMC
requirements
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SIST EN IEC 63044-4:2021
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SIST EN IEC 63044-4:2021
IEC 63044-4
Edition 1.0 2021-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Home and building electronic systems (HBES) and building automation and
control systems (BACS) –
Part 4: General functional safety requirements for products intended to be
integrated in HBES and BACS
Systèmes électroniques pour les foyers domestiques et les bâtiments (HBES) et
systèmes de gestion technique du bâtiment (SGTB) –
Partie 4: Exigences générales de sécurité fonctionnelle pour les produits
destinés à être intégrés dans les HBES et SGTB
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.120.01; 29.120.99 ISBN 978-2-8322-9898-5

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
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SIST EN IEC 63044-4:2021
– 2 – IEC 63044-4:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 3

INTRODUCTION ..................................................................................................................... 5

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 6

4 General requirements .................................................................................................... 10

4.1 General ................................................................................................................. 10

4.2 Method of establishment of the requirements ........................................................ 10

4.2.1 General ......................................................................................................... 10

4.2.2 HBES/BACS application environment ............................................................ 11

4.2.3 Sources of hazards ........................................................................................ 11

4.2.4 Hazardous events .......................................................................................... 11

4.2.5 Derivation of requirements ............................................................................. 11

5 Requirements for functional safety ................................................................................. 12

5.1 General ................................................................................................................. 12

5.2 Power feeding ....................................................................................................... 12

5.3 Life time ................................................................................................................ 13

5.4 Reasonably foreseeable misuse ............................................................................ 13

5.5 Software and communication ................................................................................ 13

5.6 Remote operations ................................................................................................ 15

5.6.1 General recommendations ............................................................................. 15

5.6.2 Within a single building or in its immediate vicinity ......................................... 15

5.6.3 From outside the building .............................................................................. 15

5.6.4 Management .................................................................................................. 16

Annex A (informative) Example of a method for the determination of safety integrity

levels .................................................................................................................................... 17

A.1 General ................................................................................................................. 17

A.2 As low as reasonably practicable (ALARP) and tolerable risk concepts ................. 17

Annex B (informative) Hazards and development of necessary functional safety

requirements ......................................................................................................................... 19

Annex C (informative) Some examples of non-safety-related HBES/BACS applications ....... 27

C.1 General ................................................................................................................. 27

C.2 Examples of non-safety-related HBES/BACS applications ..................................... 27

C.2.1 Example 1: Oven ........................................................................................... 27

C.2.2 Example 2: Devices presenting a high potential risk of hazard ....................... 27

C.2.3 Example 3: Mains plugs, socket outlets and circuits ....................................... 28

C.2.4 Example 4: Water temperature adjustment .................................................... 28

Bibliography .......................................................................................................................... 29

Figure A.1 – Risk reduction – General concept ..................................................................... 17

Table 1 – Requirements for avoiding inadvertent operations and possible ways to

achieve them ........................................................................................................................ 16

Table A.1 – Example of risk classification of accidents.......................................................... 18

Table A.2 – Interpretation of risk classes .............................................................................. 18

Table B.1 – Requirements and/or risk reduction measures .................................................... 19

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SIST EN IEC 63044-4:2021
IEC 63044-4:2021 © IEC 2021 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HOME AND BUILDING ELECTRONIC SYSTEMS (HBES) AND
BUILDING AUTOMATION AND CONTROL SYSTEMS (BACS) –
Part 4: General functional safety requirements for
products intended to be integrated in HBES and BACS
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.

IEC 63044-4 has been prepared by IEC technical committee 23: Electrical accessories. It is an

International Standard.
The text of this International Standard is based on the following documents:
FDIS Report on voting
23/973/FDIS 23/975/RVD

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this International Standard is English.
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SIST EN IEC 63044-4:2021
– 4 – IEC 63044-4:2021 © IEC 2021

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.

A list of all parts in the IEC 63044 series, published under the general title Home and Building

Electronic Systems (HBES) and Building Automation and Control Systems (BACS), can be

found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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SIST EN IEC 63044-4:2021
IEC 63044-4:2021 © IEC 2021 – 5 –
INTRODUCTION

Functional safety includes the safe operation of devices and appliances ("products") when

installed into and operating on a communications network in a home or building ("premises").

This document specifies installation, control, operating, and failure mode procedures to

enhance the functional safety of devices installed in homes and buildings. A device functions

safely if it causes no harm while operating and performing an intended task. Such devices might

not operate safely due to installation or control problems.

The growing use of home and building networks to interconnect devices introduces additional

challenges to maintaining functional safety because of possible device interactions. Therefore,

this document addresses the risks of connecting devices to a home or building network, which

enables data exchanges and remote control from within the home or building.

Furthermore, if the home or building network is connected to a public network, control from

remote locations may be possible. Such control messages might originate from a smart phone

app, be sent through a mobile telephone network, routed to a building gateway, and sent via a

home or building network to a device communications interface. Thus, there are many

opportunities for such messages to be compromised. Remote access poses additional threats

to functional safety that are addressed in this document.

This document is part of IEC 63044 series and applies to home and building electronic systems

(HBES/BACS).

This document applies to home and building electronic systems (HBES) in general and

specifically to systems conforming to the home electronic system (HES) family of ISO/IEC

standards.
HBES/BACS products in this document are for non-safety-related systems.

The intention of this document is to specify, as far as possible, all safety requirements for

HBES/BACS products in their life cycle.

This document specifies the general functional safety requirements for devices connected to a

home or building network following the principles of the basic standard for functional safety,

IEC 61508 (all parts). It covers functional safety issues related to device and device

installations. The requirements are based on a risk analysis in accordance with IEC 61508.

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SIST EN IEC 63044-4:2021
– 6 – IEC 63044-4:2021 © IEC 2021
HOME AND BUILDING ELECTRONIC SYSTEMS (HBES) AND
BUILDING AUTOMATION AND CONTROL SYSTEMS (BACS) –
Part 4: General functional safety requirements for
products intended to be integrated in HBES and BACS
1 Scope

This part of IEC 63044 provides the functional safety requirements for HBES/BACS.

In addition, it defines functional safety requirements for the interface of equipment intended to

be connected to an HBES/BACS network. It does not apply to interfaces to other networks.

NOTE 1 An example of another network is a dedicated ICT network covered by IEC 62949.

This document does not provide functional safety requirements for safety-related systems.

NOTE 2 Examples of non-safety-related HBES/BACS applications are given in Annex C.

This document does not provide requirements on data protection and security.
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 60364 (all parts), Low-voltage electrical installations

IEC 63044-3:2017, Home and Building Electronic Systems (HBES) and Building Automation

and Control Systems (BACS) – Part 3: Electrical safety requirements

IEC 63044-5 (all parts), Home and Building Electronic Systems (HBES) and Building

Automation and Control Systems (BACS)

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

related systems

IEC 61709:2017, Electric components – Reliability – Reference conditions for failure rates and

stress models for conversion
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
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SIST EN IEC 63044-4:2021
IEC 63044-4:2021 © IEC 2021 – 7 –
3.1
authentication

means for certifying that the entity sending a message is what or who it purports to be and

confirmation that the message is identical to that which was sent
3.2
authorisation

mechanism to ensure that the entity or person accessing information, functions or services has

the authority to do so
3.3
disturbed communication

communication in which for any reason a message being communicated is incomplete,

truncated, contains errors or has the correct format but delivers information which is outside

the range of expected parameters for such a message
3.4
functional safety

freedom from unacceptable risk of harm due to the operation of an HBES/BACS, including that

resulting from:
1) normal operation,
2) reasonably foreseeable misuse,
3) failure,
4) temporary disturbances,

and forming part of the overall safety relating to the EUC (equipment under control, see 3.17)

and the EUC control system that depends on the correct functioning of the E/E/PE

(electrical/electronic/programmable electronic) safety-related systems and other risk reduction

measures

Note 1 to entry: The definitions of "functional safety" given in IEC/TR 61000-2-1 and IEC 61000-1-2 are taken into

account.

[SOURCE: IEC 61508-4:2010, 3.1.12, modified – Addition of introduction and items 1 to 4 of

list, text in brackets, and note.]
3.5
Hamming distance
number of bits in which two binary codes differ
3.6
harm

physical injury or damage to the health of people either directly or indirectly as a result of

damage to property or the environment

[SOURCE: IEC 61508-4:2010, 3.1.1, modified – Addition of "either directly or indirectly as a

result of".]
3.7
hazard
potential source of harm

Note 1 to entry: The term includes danger to persons arising within a short time scale (for example, fire and

explosion) and also those that have a long-term effect on a person's health (for example, release of a toxic

substance).
[SOURCE: IEC 61508-4:2010, 3.1.2]
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SIST EN IEC 63044-4:2021
– 8 – IEC 63044-4:2021 © IEC 2021
3.8
hazardous event
situation which results in harm on normal operation or abnormal condition

Note 1 to entry: Whether or not a hazardous event results in harm depends on whether people, property or the

environment are exposed to the consequence of the hazardous event and, in the case of harm to people, whether

any such exposed people can escape the consequences of the event after it has occurred.

Note 2 to entry: Adapted from IEC 61508-4:2010, 3.1.4.
3.9
product

device in the form of hardware or firmware, and its associated software and configuration tools

3.10
product documentation

manufacturer's installation and operations literature, such as manufacturer's catalogue, leaflet

and other printed or electronic product information
3.11
safety-related system
designated system that both

– implements the required safety functions necessary to achieve or maintain a safe state for

the EUC, and

– is intended to achieve, on its own or with other E/E/PE safety-related systems and other

technology risk reduction measures, the necessary safety integrity for the required safety

functions

Note 1 to entry: The term refers to those systems, designated as safety-related systems, that are intended to

achieve, together with the other risk reduction measures, the necessary risk reduction in order to meet the required

tolerable risk. See also Annex A of IEC 61508-5.

Note 2 to entry: Safety-related systems are designed to prevent the EUC from going into a dangerous state by

taking appropriate action on detection of a condition which may lead to a hazardous event. The failure of a safety-

related system would be included in the events leading to the determined hazard or hazards. Although there may be

other systems having safety functions, it is the safety-related systems that have been designated to achieve, in their

own right, the required tolerable risk. Safety-related systems can broadly be divided into safety-related control

systems and safety-related protection systems.

Note 3 to entry: Safety-related systems may be an integral part of the EUC control system or may interface with the

EUC by sensors and/or actuators. That is, the required safety integrity level may be achieved by implementing the

safety functions in the EUC control system (and possibly by additional separate and independent systems as well)

or the safety functions may be implemented by separate and independent systems dedicated to safety.

Note 4 to entry: A safety-related system may

a) be designed to prevent the hazardous event (i.e. if the safety-related systems perform their safety functions then

no harmful event arises);

b) be designed to mitigate the effects of the harmful event, thereby reducing the risk by reducing the consequences;

c) be designed to achieve a combination of a) and b).

Note 5 to entry: A person can be part of a safety-related system. For example, a person could receive information

from a programmable electronic device and perform a safety action based on this information, or perform a safety

action through a programmable electronic device.

Note 6 to entry: A safety-related system includes all the hardware, software and supporting services (for example,

power supplies) necessary to carry out the specified safety function (sensors, other input devices, final elements

(actuators) and other output devices are therefore included in the safety-related system).

Note 7 to entry: A safety-related system may be based on a wide range of technologies including electrical,

electronic, programmable electronic, hydraulic and pneumatic.

[SOURCE: IEC 61508-4:2010, 3.4.1, modified – The word "technology" has been added to the

definition.]
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SIST EN IEC 63044-4:2021
IEC 63044-4:2021 © IEC 2021 – 9 –
3.12
safety integrity

probability of a safety-related system satisfactorily maintaining the required safety functions

under all the stated conditions within a stated period of time

Note 1 to entry: The higher the level of safety integrity, the lower the probability that the safety-related system will

fail to carry out the specified safety functions or will fail to adopt a specified state when required.

Note 2 to entry: There are four levels of safety integrity (see 3.5.8 of IEC 61508-4:2010).

Note 3 to entry: In determining safety integrity, all causes o
...

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