EN ISO 13849-1:2006

SLOVENSKI STANDARD
01-marec-2007
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Safety of machinery - Safety-related parts of control systems - Part 1: General principles
for design (ISO 13849-1:2006)
Sicherheit von Maschinen - Sicherheitsbezogene Teile von Steuerungen - Teil 1:
Allgemeine Gestaltungsleitsätze (ISO 13849-1:2006)
Sécurité des machines - Parties des systemes de commande relatives a la sécurité -
Partie 1: Principes généraux de conception (ISO 13849-1:2006)
Ta slovenski standard je istoveten z: EN ISO 13849-1:2006
ICS:
13.110 Varnost strojev Safety of machinery
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 13849-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2006
ICS 13.110 Supersedes EN 954-1:1996
English Version
Safety of machinery - Safety-related parts of control systems -
Part 1: General principles for design (ISO 13849-1:2006)
Sécurité des machines - Parties des systèmes de Sicherheit von Maschinen - Sicherheitsbezogene Teile von
commande relatives à la sécurité - Partie 1: Principes Steuerungen - Teil 1: Allgemeine Gestaltungsleitsätze (ISO
généraux de conception (ISO 13849-1:2006) 13849-1:2006)
This European Standard was approved by CEN on 2 October 2006.
CEN 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 CEN 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 CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 13849-1:2006: E
worldwide for CEN national Members.

Foreword
This document (EN ISO 13849-1:2006) has been prepared by Technical Committee CEN/TC 114
"Safety of machinery", the secretariat of which is held by DIN, in collaboration with Technical
Committee ISO/TC 199 "Safety of machinery".

This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by May 2007, and conflicting national standards shall
be withdrawn at the latest by November 2009.

This document supersedes EN 954-1:1996.

This document has been prepared under a mandate given to CEN by the European Commission
and the European Free Trade Association, and supports essential requirements of EU Directive(s).

For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this
document.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Cyprus,
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Annex ZA
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 98/37/EC, amended by Directive 98/79/EC

This European Standard has been prepared under a mandate given to CEN by the European
Commission and the European Free Trade Association to provide a means of conforming to
Essential Requirements of the New Approach Directive 98/37/EC, amended by Directive 98/79/EC.

Once this standard is cited in the Official Journal of the European Communities under that Directive
and has been implemented as a national standard in at least one Member State, compliance with
the normative clauses of this standard confers, within the limits of the scope of this standard, a
presumption of conformity with Essential Requirements 1.2.1 and 1.2.7 of Annex I of that Directive
and associated EFTA regulations.

WARNING: Other requirements and other EU Directives may be applicable to the products falling
within the scope of this standard.
INTERNATIONAL ISO
STANDARD 13849-1
Second edition
2006-11-01
Safety of machinery — Safety-related
parts of control systems —
Part 1:
General principles for design
Sécurité des machines — Parties des systèmes de commande relatives
à la sécurité —
Partie 1: Principes généraux de conception

Reference number
ISO 13849-1:2006(E)
©
ISO 2006
ISO 13849-1:2006(E)
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ii © ISO 2006 – All rights reserved

ISO 13849-1:2006(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms. 2
3.1 Terms and definitions. 2
3.2 Symbols and abbreviated terms . 8
4 Design considerations . 9
4.1 Safety objectives in design. 9
4.2 Strategy for risk reduction. 11
4.2.1 General. 11
4.2.2 Contribution to the risk reduction by the control system . 11
4.3 Determination of required performance level (PL ). 14
r
4.4 Design of SRP/CS . 14
4.5 Evaluation of the achieved performance level PL and relationship with SIL. 15
4.5.1 Performance level PL . 15
4.5.2 Mean time to dangerous failure of each channel (MTTF ) . 17
d
4.5.3 Diagnostic coverage (DC) . 18
4.5.4 Simplified procedure for estimating PL. 18
4.6 Software safety requirements . 21
4.6.1 General. 21
4.6.2 Safety-related embedded software (SRESW) . 21
4.6.3 Safety-related application software (SRASW) . 22
4.6.4 Software-based parameterization . 25
4.7 Verification that achieved PL meets PL . 26
r
4.8 Ergonomic aspects of design. 26
5 Safety functions . 26
5.1 Specification of safety functions . 26
5.2 Details of safety functions . 28
5.2.1 Safety-related stop function . 28
5.2.2 Manual reset function. 29
5.2.3 Start/restart function . 29
5.2.4 Local control function . 30
5.2.5 Muting function. 30
5.2.6 Response time . 30
5.2.7 Safety–related parameters. 30
5.2.8 Fluctuations, loss and restoration of power sources. 31
6 Categories and their relation to MTTF of each channel, DC and CCF. 31
d avg
6.1 General. 31
6.2 Specifications of categories . 32
6.2.1 General. 32
6.2.2 Designated architectures. 32
6.2.3 Category B. 32
6.2.4 Category 1 . 33
6.2.5 Category 2 . 34
6.2.6 Category 3 . 35
6.2.7 Category 4 . 36
6.3 Combination of SRP/CS to achieve overall PL . 39
ISO 13849-1:2006(E)
7 Fault consideration, fault exclusion. 40
7.1 General . 40
7.2 Fault consideration . 40
7.3 Fault exclusion . 41
8 Validation . 41
9 Maintenance. 41
10 Technical documentation. 41
11 Information for use . 42
Annex A (informative) Determination of required performance level (PL ) . 44
r
Annex B (informative) Block method and safety-related block diagram . 47
Annex C (informative) Calculating or evaluating MTTF values for single components. 49
d
Annex D (informative) Simplified method for estimating MTTF for each channel . 57
d
Annex E (informative) Estimates for diagnostic coverage (DC) for functions and modules. 59
Annex F (informative) Estimates for common cause failure (CCF). 62
Annex G (informative) Systematic failure . 64
Annex H (informative) Example of combination of several safety-related parts of the control
system . 67
Annex I (informative) Examples . 70
Annex J (informative) Software.77
Annex K (informative) Numerical representation of Figure 5 . 80
Bibliography . 83

iv © ISO 2006 – All rights reserved

ISO 13849-1:2006(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 13849-1 was prepared by the European Committee for Standardization (CEN) Technical Committee
CEN/TC 114, Safety of machinery, in collaboration with Technical Committee ISO/TC 199, Safety of
machinery, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This second edition cancels and replaces the first edition (ISO ISO 13849-1:1999), which has been technically
revised.
ISO 13849 consists of the following parts, under the general title Safety of machinery — Safety-related parts
of control systems:
⎯ Part 1: General principles for design
⎯ Part 2: Validation
⎯ Part 100: Guidelines for the use and application of ISO 13849-1 [Technical Report]
ISO 13849-1:2006(E)
Introduction
The structure of safety standards in the field of machinery is as follows.
a) Type-A standards (basis standards) give basic concepts, principles for design and general aspects that
can be applied to machinery.
b) Type-B standards (generic safety standards) deal with one or more safety aspect(s), or one or more
type(s) of safeguards that can be used across a wide range of machinery:
⎯ type-B1 standards on particular safety aspects (e.g. safety distances, surface temperature, noise);
⎯ type-B2 standards on safeguards (e.g. two-hands controls, interlocking devices, pressure sensitive
devices, guards).
c) Type-C standards (machinery safety standards) deal with detailed safety requirements for a particular
machine or group of machines.
This part of ISO 13849 is a type-B-1 standard as stated in ISO 12100-1.
When provisions of a type-C standard are different from those which are stated in type-A or type-B standards,
the provisions of the type-C standard take precedence over the provisions of the other standards for machines
that have been designed and built according to the provisions of the type-C standard.
This part of ISO 13849 is intended to give guidance to those involved in the design and assessment of control
systems, and to Technical Committees preparing Type-B2 or Type-C standards which are presumed to
comply with the Essential Safety Requirements of Annex I of the Council Directive 98/37/EC, The Machinery
Directive. It does not give specific guidance for compliance with other EC directives.
As part of the overall risk reduction strategy at a machine, a designer will often choose to achieve some
measure of risk reduction through the application of safeguards employing one or more safety functions.
Parts of machinery control systems that are assigned to provide safety functions are called safety-related
parts of control systems (SRP/CS) and these can consist of hardware and software and can either be
separate from the machine control system or an integral part of it. In addition to providing safety functions,
SRP/CS can also provide operational functions (e.g. two-handed controls as a means of process initiation).
The ability of safety-related parts of control systems to perform a safety function under foreseeable conditions
is allocated one of five levels, called performance levels (PL). These performance levels are defined in terms
of probability of dangerous failure per hour (see Table 3).
The probability of dangerous failure of the safety function depends on several factors, including hardware and
software structure, the extent of fault detection mechanisms [diagnostic coverage (DC)], reliability of
components [mean time to dangerous failure (MTTF ), common cause failure (CCF)], design process,
d
operating stress, environmental conditions and operation procedures.
In order to assist the designer and help facilitate the assessment of achieved PL, this document employs a
methodology based on the categorization of structures according to specific design criteria and specified
behaviours under fault conditions. These categories are allocated one of five levels, termed Categories B, 1, 2,
3 and 4.
vi © ISO 2006 – All rights reserved

ISO 13849-1:2006(E)
The performance levels and categories can be applied to safety-related parts of control systems, such as
⎯ protective devices (e.g. two-hand control devices, interlocking devices), electro-sensitive protective
devices (e.g. photoelectric barriers), pressure sensitive devices,
⎯ control units (e.g. a logic unit for control functions, data processing, monitoring, etc.), and
⎯ power control elements (e.g. relays, valves, etc),
as well as to control systems carrying out safety functions at all kinds of machinery — from simple (e.g. small
kitchen machines, or automatic doors and gates) to manufacturing installations (e.g. packaging machines,
printing machines, presses).
This part of ISO 13849 is intended to provide a clear basis upon which the design and performance of any
application of the SRP/CS (and the machine) can be assessed, for example, by a third party, in-house or by
an independent test house.
Information on the recommended application of IEC 62061 and this part of ISO 13849
IEC 62061 and this part of ISO 13849 specify requirements for the design and implementation of safety-
related control systems of machinery. The use of either of these International Standards, in accordance with
their scopes, can be presumed to fulfil the relevant essential safety requirements. The following table
summarizes the scopes of IEC 62061 and this part of ISO 13849.
Table 1 — Recommended application of IEC 62061 and ISO 13849-1
Technology implementing the
ISO 13849-1 IEC 62061
safety-related control function(s)
A Non-electrical, e.g. hydraulics X Not covered
B Electromechanical, e.g. relays, Restricted to designated All architectures and up to SIL 3
a
and/or non complex electronics
architectures and up to PL = e
C Complex electronics, e.g. Restricted to designated All architectures and up to SIL 3
a
programmable
architectures and up to PL = d
D A combined with B Restricted to designated
c
X
a
architectures and up to PL = e
E C combined with B Restricted to designated All architectures and up to SIL 3
architectures (see Note 1) and up to
PL = d
F C combined with A, or C
b c
X X
combined with A and B
X indicates that this item is dealt with by the International Standard shown in the column heading.
a
Designated architectures are defined in 6.2 in order to give a simplified approach for quantification of performance level.
b
For complex electronics: use designated architectures according to this part of ISO 13849 up to PL = d or any architecture
according to IEC 62061.
c
For non-electrical technology, use parts in accordance with this part of ISO 13849 as subsystems.

INTERNATIONAL STANDARD ISO 13849-1:2006(E)

Safety of machinery — Safety-related parts of control
systems —
Part 1:
General principles for design
1 Scope
This part of ISO 13849 provides safety requirements and guidance on the principles for the design and
integration of safety-related parts of control systems (SRP/CS), including the design of software. For these
parts of SRP/CS, it specifies characteristics that include the performance level required for carrying out safety
functions. It applies to SRP/CS, regardless of the type of technology and energy used (electrical, hydraulic,
pneumatic, mechanical, etc.), for all kinds of machinery.
It does not specify the safety functions or performance levels that are to be used in a particular case.
This part of ISO 13849 provides specific requirements for SRP/CS using programmable electronic system(s).
It does not give specific requirements for the design of products which are parts of SRP/CS. Nevertheless, the
principles given, such as categories or performance levels, can be used.
NOTE 1 Examples of products which are parts of SRP/CS: relays, solenoid valves, position switches, PLCs, motor
control units, two-hand control devices, pressure sensitive equipment. For the design of such products, it is important to
refer to the specifically applicable International Standards, e.g. ISO 13851, ISO 13856-1 and ISO 13856-2.
NOTE 2 For the definition of required performance level, see 3.1.24.
NOTE 3 The requirements provided in this part of ISO 13849 for programmable electronic systems are compatible with
the methodology for the design and development of safety-related electrical, electronic and programmable electronic
control systems for machinery given in IEC 62061.
NOTE 4 For safety-related embedded software for components with PL = e see IEC 61508-3:1998, Clause 7.
r
NOTE 5 See also Table 1.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 12100-1:2003, Safety of machinery — Basic concepts, general principles for design — Part 1: Basic
terminology, methodology
ISO 12100-2:2003, Safety of machinery — Basic concepts, general principles for design — Part 2: Technical
principles
ISO 13849-2:2003, Safety of machinery — Safety-related parts of control systems — Part 2: Validation
ISO 13849-1:2006(E)
1)
ISO 14121 , Safety of machinery — Principles of risk assessment
IEC 60050-191:1990, International electrotechnical vocabulary — Chapter 191: Dependability and quality of
service, and IEC 60050-191-am1:1999 and IEC 60050-191-am2:2002:1999, Amendment 1 and Amendment 2,
International Electrotechnical Vocabulary. Chapter 191: Dependability and quality of service
IEC 61508-3:1998, Functional safety of electrical/electronic/programmable electronic safety-related systems -
Part 3: Software requirements, and IEC 61508-3 Corr.1:1999, Corrigendum 1 — Functional safety of
electrical/electronic/programmable electronic safety-related systems — Part 3: Software requirements
IEC 61508-4:1998, Functional safety of electrical/electronic/programmable electronic safety-related
systems — Part 4: Definitions and abbreviations, and IEC 61508-4 Corr.1:1999, Corrigendum 1 — Functional
safety of electrical/electronic/programmable electronic safety-related systems — Part 4: Definitions and
abbreviations
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12100-1 and IEC 60050-191 and
the following apply.
3.1.1
safety–related part of a control system
SRP/CS
part of a control system that responds to safety-related input signals and generates safety-related output
signals
NOTE 1 The combined safety-related parts of a control system start at the point where the safety-related input signals
are initiated (including, for example, the actuating cam and the roller of the position switch) and end at the output of the
power control elements (including, for example, the main contacts of a contactor).
NOTE 2 If monitoring systems are used for diagnostics, they are also considered as SRP/CS.
3.1.2
category
classification of the safety-related parts of a control system in respect of their resistance to faults and their
subsequent behaviour in the fault condition, and which is achieved by the structural arrangement of the parts,
fault detection and/or by their reliability
3.1.3
fault
state of an item characterized by the inability to perform a required function, excluding the inability during
preventive maintenance or other planned actions, or due to lack of external resources
NOTE 1 A fault is often the result of a failure of the item itself, but may exist without prior failure.
[IEC 60050-191:1990, 05-01]
NOTE 2 In this part of ISO 13849, “fault” means random fault.

1) To be published. (Revision of ISO 14121:1999)
2 © ISO 2006 – All rights reserved

ISO 13849-1:2006(E)
3.1.4
failure
termination of the ability of an item to perform a required function
NOTE 1 After a failure, the item has a fault.
NOTE 2 “Failure” is an event, as distinguished from “fault”, which is a state.
NOTE 3 The concept as defined does not apply to items consisting of software only.
[IEC 60050–191:1990, 04-01]
NOTE 4 Failures which only affect the availability of the process under control are outside of the scope of this part of
ISO 13849.
3.1.5
dangerous failure
failure which has the potential to put the SRP/CS in a hazardous or fail-to-function state
NOTE 1 Whether or not the potential is realized can depend on the channel architecture of the system; in redundant
systems a dangerous hardware failure is less likely to lead to the overall dangerous or fail-to-function state.
NOTE 2 Adapted from IEC 61508-4:1998, definition 3.6.7.
3.1.6
common cause failure
CCF
failures of different items, resulting from a single event, where these failures are not consequences of each
other
[IEC 60050-191-am1:1999, 04-23]
NOTE Common cause failures should not be confused with common mode failures (see ISO 12100-1:2003, 3.34).
3.1.7
systematic failure
failure related in a deterministic way to a certain cause, which can only be eliminated by a modification of the
design or of the manufacturing process, operational procedures, documentation or other relevant factors
NOTE 1 Corrective maintenance without modification will usually not eliminate the failure cause.
NOTE 2 A systematic failure can be induced by simulating the failure cause.
[IEC 60050-191:1990, 04-19]
NOTE 3 Examples of causes of systematic failures include human error in
⎯ the safety requirements specification,
⎯ the design, manufacture, installation, operation of the hardware, and
⎯ the design, implementation, etc., of the software.
3.1.8
muting
temporary automatic suspension of a safety function(s) by the SRP/CS
ISO 13849-1:2006(E)
3.1.9
manual reset
function within the SRP/CS used to restore manually one or more safety functions before re-starting a
machine
3.1.10
harm
physical injury or damage to health
[ISO 12100-1:2003, 3.5]
3.1.11
hazard
potential source of harm
NOTE 1 A hazard can be qualified in order to define its origin (e.g. mechanical hazard, electrical hazard) or the nature
of the potential harm (e.g. electric shock hazard, cutting hazard, toxic hazard, fire hazard).
NOTE 2 The hazard envisaged in this definition:
⎯ either is permanently present during the intended use of the machine (e.g. motion of hazardous moving elements,
electric arc during a welding phase, unhealthy posture, noise emission, high temperature);
⎯ or may appear unexpectedly (e.g. explosion, crushing hazard as a consequence of an unintended/unexpected start-
up, ejection as a consequence of a breakage, fall as a consequence of acceleration/deceleration).
[ISO 12100-1:2003, 3.6]
3.1.12
hazardous situation
circumstance in which a person is exposed to at least one hazard, the exposure having immediately or over a
long period of time the potential to result in harm
[ISO 12100-1:2003, 3.9]
3.1.13
risk
combination of the probability of occurrence of harm and the severity of that harm
[ISO 12100-1:2003, 3.11]
3.1.14
residual risk
risk remaining after protective measures have been taken
See Figure 2.
NOTE Adapted from ISO 12100-1:2003, definition 3.12.
3.1.15
risk assessment
overall process comprising risk analysis and risk evaluation
[ISO 12100-1:2003, 3.13]
3.1.16
risk analysis
combination of the specification of the limits of the machine, hazard identification and risk estimation
[ISO 12100-1:2003, 3.14]
4 © ISO 2006 – All rights reserved

ISO 13849-1:2006(E)
3.1.17
risk evaluation
judgement, on the basis of risk analysis, of whether risk reduction objectives have been achieved
[ISO 12100-1:2003, 3.16]
3.1.18
intended use of a machine
use of the machine in accordance with the information provided in the instructions for use
[ISO 12100-1:2003, 3.22]
3.1.19
reasonably foreseeable misuse
use of a machine in a way not intended by the designer, but which may result from readily predictable human
behaviour
[ISO 12100-1:2003, 3.23]
3.1.20
safety function
function of the machine whose failure can result in an immediate increase of the risk(s)
[ISO 12100-1:2003, 3.28]
3.1.21
monitoring
safety function which ensures that a protective measure is initiated if the ability of a component or an element
to perform its function is diminished or if the process conditions are changed in such a way that a decrease of
the amount of risk reduction is generated
3.1.22
programmable electronic system
PES
system for control, protection or monitoring dependent for its operation on one or more programmable
electronic devices, including all elements of the system such as power supplies, sensors and other input
devices, contactors and other output devices
NOTE Adapted from IEC 61508-4:1998, definition 3.3.2.
3.1.23
performance level
PL
discrete level used to specify the ability of safety-related parts of control systems to perform a safety function
under foreseeable conditions
NOTE See 4.5.1.
3.1.24
required performance level
PL
r
performance level (PL) applied in order to achieve the required risk reduction for each safety function
See Figures 2 and A.1.
3.1.25
mean time to dangerous failure
MTTF
d
expectation of the mean time to dangerous failure
NOTE Adapted from IEC 62061:2005, definition 3.2.34.
ISO 13849-1:2006(E)
3.1.26
diagnostic coverage
DC
measure of the effectiveness of diagnostics, which may be determined as the ratio between the failure rate of
detected dangerous failures and the failure rate of total dangerous failures
NOTE 1 Diagnostic coverage can exist for the whole or parts of a safety-related system. For example, diagnostic
coverage could exist for sensors and/or logic system and/or final elements.
NOTE 2 Adapted from IEC 61508-4:1998, definition 3.8.6.
3.1.27
protective measure
measure intended to achieve risk reduction
EXAMPLE 1 Implemented by the designer: inherent design, safeguarding and complementary protective measures,
information for use.
EXAMPLE 2 Implemented by the user: organization (safe working procedures, supervision, permit-to-work systems),
provision and use of additional safeguards, personal protective equipment, training.
NOTE Adapted from ISO 12100-1:2003, definition 3.18.
3.1.28
mission time
T
M
period of time covering the intended use of an SRP/CS
3.1.29
test rate
r
t
frequency of automatic tests to detect faults in a SRP/CS, reciprocal value of diagnostic test interval
3.1.30
demand rate
r
d
frequency of demands for a safety-related action of the SRP/CS
3.1.31
repair rate
r
r
reciprocal value of the period of time between detection of a dangerous failure by either an online test or
obvious malfunction of the system and the restart of operation after repair or system/component replacement
NOTE The repair time does not include the span of time needed for failure-detection.
3.1.32
machine control system
system which responds to input signals from parts of machine elements, operators, external control equipment
or any combination of these and generates output signals causing the machine to behave in the intended
manner
NOTE The machine control system can use any technology or any combination of different technologies (e.g.
electrical/electronic, hydraulic, pneumatic, mechanical).
6 © ISO 2006 – All rights reserved

ISO 13849-1:2006(E)
3.1.33
safety integrity level
SIL
discrete level (one out of a possible four) for specifying the safety integrity requirements of the safety functions
to be allocated to the E/E/PE safety-related systems, where safety integrity level 4 has the highest level of
safety integrity and safety integrity level 1 has the lowest
[IEC 61508-4:1998, 3.5.6]
3.1.34
limited variability language
LVL
type of language that provides the capability of combining predefined, application-specific library functions to
implement the safety requirements specifications
NOTE 1 Adapted from IEC 61511-1:2003, definition 3.2.80.1.2.
NOTE 2 Typical examples of LVL (ladder logic, function block diagram) are given in IEC 61131-3.
NOTE 3 A typical example of a system using LVL: PLC.
3.1.35
full variability language
FVL
type of language that provides the capability of implementing a wide variety of functions and applications
EXAMPLE C, C++, Assembler.
NOTE 1 Adapted from IEC 61511-1:2003, definition 3.2.80.1.3.
NOTE 2 A typical example of systems using FVL: embedded systems.
NOTE 3 In the field of machinery, FVL is found in embedded software and rarely in application software.
3.1.36
application software
software specific to the application, implemented by the machine manufacturer, and generally containing logic
sequences, limits and expressions that control the appropriate inputs, outputs, calculations and decisions
necessary to meet the SRP/CS requirements
3.1.37
embedded software
firmware
system software
software that is part of the system supplied by the control manufacturer and which is not accessible for
modification by the user of the machinery.
NOTE Embedded software is usually written in FVL.
ISO 13849-1:2006(E)
3.2 Symbols and abbreviated terms
See Table 2.
Table 2 — Symbols and abbreviated terms
Symbol or Definition or
Description
abbreviation occurrence
a, b, c, d, e Denotation of performance levels Table 3
AOPD Active optoelectronic protective device (e.g. light barrier) Annex H
B, 1, 2, 3, 4 Denotation of categories Table 7
B
Number of cycles until 10 % of the components fail dangerously (for Annex C
10d
pneumatic and electromechanical components)
Cat. Category 3.1.2
CC Current converter Annex I
CCF Common cause failure 3.1.6
DC Diagnostic coverage 3.1.26
DC Average diagnostic coverage E.2
avg
F, F1, F2 Frequency and/or time of exposure to the hazard A.2.2
FB Function block 4.6.3
FVL Full variability language 3.1.35
FMEA Failure modes and effects analysis 7.2
I, I1, I2 Input device, e.g. sensor 6.2
i, j Index for counting Annex D
I/O Inputs/outputs Table E.1
i , i Interconnecting means Figure 4
ab bc
K1A, K1B Contactors Annex I
L, L1, L2 Logic 6.2
LVL Limited variability language 3.1.34
M Motor Annex I
MTTF Mean time to failure Annex C
MTTF
Mean time to dangerous failure 3.1.25
d
 Number of items 6.3, D.1
n, N, N
N Number of SRP/CS with PL in a combination of SRP/CS 6.3
low low
O, O1, O2, OTE Output device, e.g. actuator 6.2
P, P1, P2 Possibility of avoiding the hazard A.2.3
PES Programmable electronic system 3.1.22
PL Performance level 3.1.23
8 © ISO 2006 – All rights reserved

ISO 13849-1:2006(E)
Table 2 (continued)
Definition or
Abbreviation Description
occurrence
PLC Programmable logic controller Annex I
PL Lowest performance level of a SRP/CS in a combination of SRP/CS 6.3
low
PL Required performance level 3.1.24
r
r
Demand rate 3.1.30
d
RS Rotation sensor Annex I
S, S1, S2 Severity of injury A.2.1
SW1A, SW1B, SW2 Position switches Annex I
SIL Safety integrity level Table 4
SRASW Safety-related application software 4.6.3
SRESW Safety-related embedded software 4.6.2
SRP Safety-related part General
SRP/CS Safety-related part of a control system 3.1.1
TE Test equipment 6.2
T Mission time 3.1.28
M
4 Design considerations
4.1 Safety objectives in design
The SRP/CS shall be designed and constructed so that the principles of ISO 12100 and ISO 14121 are fully
taken into account (see Figures 1 and 3). All intended use and reasonable foreseeable misuse shall be
considered.
ISO 13849-1:2006(E)
a
Refers to ISO 12100-1:2003.
b
Refers to this part of ISO 13849.
Figure 1 — Overview of risk assessment/risk reduction
10 © ISO 2006 – All rights reserved

ISO 13849-1:2006(E)
4.2 Strategy for risk reduction
4.2.1 General
The strategy for risk reduction at the machine is given in ISO 12100-1:2003, Clause 5, and further guidance is
given in ISO 12100-2:2003, Clauses 4 (inherent design measures) and 5 (safeguarding and complementary
protective measures). This strategy covers the whole life cycle of the machine.
The hazard analysis and risk reduction process for a machine requires that hazards are eliminated or reduced
through a hierarchy of measures:
⎯ hazard elimination or risk reduction by design (see ISO 12100-2:2003, Clause 4);
⎯ risk reduction by safeguarding and possibly complementary protective measures (see ISO 12100-2:2003,
Clause 5);
⎯ risk reduction by the provision of information for use about the residual risk (see ISO 12100-2:2003,
Clause 6).
4.2.2 Contribution to the risk reduction by the control system
The purpose in following the overall design procedure for the machine is to achieve the safety objectives
(see 4.1). The design of the SRP/CS to provide the required risk reduction is an integral subset of the overall
design procedure for the machine. The SRP/CS provides safety function(s) at a PL which achieves the
required risk reduction. In providing safety function(s), either as an inherently safe part of the design or as a
control for
...