ISO 26262-4:2011

Road vehicles - Functional safety - Part 4: Product development at the system level

ISO 26262 is intended to be applied to safety-related systems that include one or more electrical and/or electronic (E/E) systems and that are installed in series production passenger cars with a maximum gross vehicle mass up to 3 500 kg. ISO 26262 does not address unique E/E systems in special purpose vehicles such as vehicles designed for drivers with disabilities. Systems and their components released for production, or systems and their components already under development prior to the publication date of ISO 26262, are exempted from the scope. For further development or alterations based on systems and their components released for production prior to the publication of ISO 26262, only the modifications will be developed in accordance with ISO 26262. ISO 26262 addresses possible hazards caused by malfunctioning behaviour of E/E safety-related systems, including interaction of these systems. It does not address hazards related to electric shock, fire, smoke, heat, radiation, toxicity, flammability, reactivity, corrosion, release of energy and similar hazards, unless directly caused by malfunctioning behaviour of E/E safety-related systems. ISO 26262 does not address the nominal performance of E/E systems, even if dedicated functional performance standards exist for these systems (e.g. active and passive safety systems, brake systems, Adaptive Cruise Control). ISO 26262-4:2011 specifies the requirements for product development at the system level for automotive applications, including the following: requirements for the initiation of product development at the system level, specification of the technical safety requirements, the technical safety concept, system design, item integration and testing, safety validation, functional safety assessment, and product release.

Véhicules routiers — Sécurité fonctionnelle — Partie 4: Développement du produit au niveau du système

General Information

• Status: Withdrawn
• Publication Date: 13-Nov-2011
• Withdrawal Date: 13-Nov-2011
• ICS: 43.040.10 - Electrical and electronic equipment
• Technical Committee: ISO/TC 22/SC 32 - Electrical and electronic components and general system aspects
• Drafting Committee: ISO/TC 22/SC 32/WG 8 - Functional safety
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 17-Dec-2018
• Completion Date: 13-Dec-2025

Relations

• Revised: ISO 26262-4:2018 - Road vehicles - Functional safety - Part 4: Product development at the system level
• Effective Date: 05-Nov-2015

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 26262-4
First edition
2011-11-15
Road vehicles — Functional safety —
Part 4:
Product development at the system level
Véhicules routiers — Sécurité fonctionnelle —
Partie 4: Développement du produit au niveau du système

Reference number
©
ISO 2011
©  ISO 2011
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
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ii © ISO 2011 – All rights reserved

Contents Page
Foreword . v
Introduction . vi
1  Scope . 1
2  Normative references . 2
3  Terms, definitions and abbreviated terms . 2
4  Requirements for compliance . 2
4.1  General requirements . 2
4.2  Interpretations of tables . 3
4.3  ASIL-dependent requirements and recommendations . 3
5  Initiation of product development at the system level . 3
5.1  Objectives . 3
5.2  General . 4
5.3  Inputs to this clause . 6
5.4  Requirements and recommendations . 6
5.5  Work products . 6
6  Specification of the technical safety requirements . 7
6.1  Objectives . 7
6.2  General . 7
6.3  Inputs to this clause . 7
6.4  Requirements and recommendations . 7
6.5  Work products . 10
7  System design . 10
7.1  Objectives . 10
7.2  General . 11
7.3  Inputs to this clause . 11
7.4  Requirements and recommendation . 11
7.5  Work products . 16
8  Item integration and testing . 16
8.1  Objectives . 16
8.2  General . 16
8.3  Inputs to this clause . 16
8.4  Requirements and recommendation . 17
8.5  Work products . 25
9  Safety validation . 25
9.1  Objectives . 25
9.2  General . 25
9.3  Inputs to this clause . 26
9.4  Requirements and recommendation . 26
9.5  Work products . 27
10  Functional safety assessment . 28
10.1  Objectives . 28
10.2  General . 28
10.3  Inputs to this clause . 28
10.4  Requirements and recommendation . 28
10.5  Work products . 28
11  Release for production . 28
11.1  Objectives .28
11.2  General .29
11.3  Inputs to this clause .29
11.4  Requirements and recommendations .29
11.5  Work products .30
Annex A (informative) Overview and document flow of product development at the system level .31
Annex B (informative) Example contents of hardware-software interface .33
Bibliography .36

iv © ISO 2011 – All rights reserved

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 26262-4 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 3,
Electrical and electronic equipment.
ISO 26262 consists of the following parts, under the general title Road vehicles — Functional safety:
 Part 1: Vocabulary
 Part 2: Management of functional safety
 Part 3: Concept phase
 Part 4: Product development at the system level
 Part 5: Product development at the hardware level
 Part 6: Product development at the software level
 Part 7: Production and operation
 Part 8: Supporting processes
 Part 9: Automotive Safety Integrity Level (ASIL)-oriented and safety-oriented analyses
 Part 10: Guideline on ISO 26262
Introduction
ISO 26262 is the adaptation of IEC 61508 to comply with needs specific to the application sector of electrical
and/or electronic (E/E) systems within road vehicles.
This adaptation applies to all activities during the safety lifecycle of safety-related systems comprised of
electrical, electronic and software components.
Safety is one of the key issues of future automobile development. New functionalities not only in areas such
as driver assistance, propulsion, in vehicle dynamics control and active and passive safety systems
increasingly touch the domain of system safety engineering. Development and integration of these
functionalities will strengthen the need for safe system development processes and the need to provide
evidence that all reasonable system safety objectives are satisfied.
With the trend of increasing technological complexity, software content and mechatronic implementation, there
are increasing risks from systematic failures and random hardware failures. ISO 26262 includes guidance to
avoid these risks by providing appropriate requirements and processes.
System safety is achieved through a number of safety measures, which are implemented in a variety of
technologies (e.g. mechanical, hydraulic, pneumatic, electrical, electronic, programmable electronic) and
applied at the various levels of the development process. Although ISO 26262 is concerned with functional
safety of E/E systems, it provides a framework within which safety-related systems based on other
technologies can be considered. ISO 26262:
a) provides an automotive safety lifecycle (management, development, production, operation, service,
decommissioning) and supports tailoring the necessary activities during these lifecycle phases;
b) provides an automotive-specific risk-based approach to determine integrity levels [Automotive Safety
Integrity Levels (ASIL)];
c) uses ASILs to specify applicable requirements of ISO 26262 so as to avoid unreasonable residual risk;
d) provides requirements for validation and confirmation measures to ensure a sufficient and acceptable
level of safety being achieved;
e) provides requirements for relations with suppliers.
Functional safety is influenced by the development process (including such activities as requirements
specification, design, implementation, integration, verification, validation and configuration), the production
and service processes and by the management processes.
Safety issues are intertwined with common function-oriented and quality-oriented development activities and
work products. ISO 26262 addresses the safety-related aspects of development activities and work products.
Figure 1 shows the overall structure of this edition of ISO 26262. ISO 26262 is based upon a V-model as a
reference process model for the different phases of product development. Within the figure:
 the shaded “V”s represent the interconnection between ISO 26262-3, ISO 26262-4, ISO 26262-5,
ISO 26262-6 and ISO 26262-7;
 the specific clauses are indicated in the following manner: “m-n”, where “m” represents the number of the
particular part and “n” indicates the number of the clause within that part.
EXAMPLE “2-6” represents Clause 6 of ISO 26262-2.
vi © ISO 2011 – All rights reserved

Figure 1 — Overview of ISO 26262

1. Vocabulary
2. Management of functional safety
2-6 Safety management during the concept phase 2-7 Safety management after the item´s release
2-5 Overall safety management
and the product development for production
4. Product development at the system level
3. Concept phase 7. Production and operation
4-5 Initiation of product
4-11 Release for production
3-5 Item definition 7-5 Production
development at the system level
4-10 Functional safety assessment
7-6 Operation, service
3-6 Initiation of the safety lifecycle
4-6 Specification of the technical
(maintenance and repair), and
safety requirements
decommissioning
4-9 Safety validation
3-7 Hazard analysis and risk
assessment
4-7 System design 4-8 Item integration and testing
3-8 Functional safety
concept
5. Product development at the 6. Product development at the
hardware level software level
5-5 Initiation of product 6-5 Initiation of product
development at the hardware level
development at the software level
5-6 Specification of hardware
safety requirements
5-7 Hardware design 6-7 Software architectural design
5-8 Evaluation of the hardware 6-8 Software unit design and
architectural metrics implementation
5-9 Evaluation of the safety goal
6-9 Software unit testing
violations due to random hardware
failures
6-10 Software integration and
5-10 Hardware integration and
testing
testing
6-11 Verification of software safety
requirements
8. Supporting processes
8-5 Interfaces within distributed developments 8-10 Documentation
8-6 Specification and management of safety requirements 8-11 Confidence in the use of software tools
8-7 Configuration management 8-12 Qualification of software components
8-8 Change management 8-13 Qualification of hardware components
8-9 Verification 8-14 Proven in use argument
9. ASIL-oriented and safety-oriented analyses
9-5 Requirements decomposition with respect to ASIL tailoring 9-7 Analysis of dependent failures
9-6 Criteria for coexistence of elements 9-8 Safety analyses
10. Guideline on ISO 26262
INTERNATIONAL STANDARD ISO 26262-4:2011(E)

Road vehicles — Functional safety —
Part 4:
Product development at the system level
1 Scope
ISO 26262 is intended to be applied to safety-related systems that include one or more electrical and/or
electronic (E/E) systems and that are installed in series production passenger cars with a maximum gross
vehicle mass up to 3 500 kg. ISO 26262 does not address unique E/E systems in special purpose vehicles
such as vehicles designed for drivers with disabilities.
Systems and their components released for production, or systems and their components already under
development prior to the publication date of ISO 26262, are exempted from the scope. For further
development or alterations based on systems and their components released for production prior to the
publication of ISO 26262, only the modifications will be developed in accordance with ISO 26262.
ISO 26262 addresses possible hazards caused by malfunctioning behaviour of E/E safety-related systems,
including interaction of these systems. It does not address hazards related to electric shock, fire, smoke, heat,
radiation, toxicity, flammability, reactivity, corrosion, release of energy and similar hazards, unless directly
caused by malfunctioning behaviour of E/E safety-related systems.
ISO 26262 does not address the nominal performance of E/E systems, even if dedicated functional
performance standards exist for these systems (e.g. active and passive safety systems, brake systems,
Adaptive Cruise Control).
This part of ISO 26262 specifies the requirements for product development at the system level for automotive
applications, including the following:
 requirements for the initiation of product development at the system level,
 specification of the technical safety requirements,
 the technical safety concept,
 system design,
 item integration and testing,
 safety validation,
 functional safety assessment, and
 product release.
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 26262-1:2011, Road vehicles — Functional safety — Part 1: Vocabulary
ISO 26262-2:2011, Road vehicles — Functional safety — Part 2: Management of functional safety
ISO 26262-3:2011, Road vehicles — Functional safety — Part 3: Concept phase
ISO 26262-5:2011, Road vehicles — Functional safety — Part 5: Product development at the hardware level
ISO 26262-6:2011, Road vehicles — Functional safety — Part 6: Product development at the software level
ISO 26262-7:2011, Road vehicles — Functional safety — Part 7: Production and operation
ISO 26262-8:2011, Road vehicles — Functional safety — Part 8: Supporting processes
ISO 26262-9:2011, Road vehicles — Functional safety — Part 9: Automotive Safety Integrity Level (ASIL)-
oriented and safety-oriented analyses
3 Terms, definitions and abbreviated terms
For the purposes of this document, the terms, definitions and abbreviated terms given in ISO 26262-1:2011
apply.
4 Requirements for compliance
4.1 General requirements
When claiming compliance with ISO 26262, each requirement shall be complied with, unless one of the
following applies:
a) tailoring of the safety activities in accordance with ISO 26262-2 has been planned and shows that the
requirement does not apply, or
b) a rationale is available that the non-compliance is acceptable and the rationale has been assessed in
accordance with ISO 26262-2.
Information marked as a “NOTE” or “EXAMPLE” is only for guidance in understanding, or for clarification of
the associated requirement, and shall not be interpreted as a requirement itself or as complete or exhaustive.
The results of safety activities are given as work products. “Prerequisites” are information which shall be
available as work products of a previous phase. Given that certain requirements of a clause are
ASIL-dependent or may be tailored, certain work products may not be needed as prerequisites.
“Further supporting information” is information that can be considered, but which in some cases is not required
by ISO 26262 as a work product of a previous phase and which may be made available by external sources
that are different from the persons or organizations responsible for the functional safety activities.
2 © ISO 2011 – All rights reserved

4.2 Interpretations of tables
Tables are normative or informative depending on their context. The different methods listed in a table
contribute to the level of confidence in achieving compliance with the corresponding requirement. Each
method in a table is either
a) a consecutive entry (marked by a sequence number in the leftmost column, e.g. 1, 2, 3), or
b) an alternative entry (marked by a number followed by a letter in the leftmost column, e.g. 2a, 2b, 2c).
For consecutive entries, all methods shall be applied as recommended in accordance with the ASIL. If
methods other than those listed are to be applied, a rationale shall be given that these fulfil the corresponding
requirement.
For alternative entries, an appropriate combination of methods shall be applied in accordance with the ASIL
indicated, independent of whether they are listed in the table or not. If methods are listed with different
degrees of recommendation for an ASIL, the methods with the higher recommendation should be preferred. A
rationale shall be given that the selected combination of methods complies with the corresponding
requirement.
NOTE A rationale based on the methods listed in the table is sufficient. However, this does not imply a bias for or
against methods not listed in the table.
For each method, the degree of recommendation to use the corresponding method depends on the ASIL and
is categorized as follows:
 “++” indicates that the method is highly recommended for the identified ASIL;
 “+” indicates that the method is recommended for the identified ASIL;
 “o” indicates that the method has no recommendation for or against its usage for the identified ASIL.
4.3 ASIL-dependent requirements and recommendations
The requirements or recommendations of each subclause shall be complied with for ASIL A, B, C and D, if not
stated otherwise. These requirements and recommendations refer to the ASIL of the safety goal. If ASIL
decomposition has been performed at an earlier stage of development, in accordance with ISO 26262-9:2011,
Clause 5, the ASIL resulting from the decomposition shall be complied with.
If an ASIL is given in parentheses in ISO 26262, the corresponding subclause shall be considered as a
recommendation rather than a requirement for this ASIL. This has no link with the parenthesis notation related
to ASIL decomposition.
5 Initiation of product development at the system level
5.1 Objectives
The objective of the initiation of the product development at the system level is to determine and plan the
functional safety activities during the individual subphases of system development. This also includes the
necessary supporting processes described in ISO 26262-8.
This planning of system-level safety activities will be included in the safety plan.
5.2 15BGeneral
The necessary activities during the development of a system are given in Figure 2. After the initiation of
product development and the specification of the technical safety requirements, the system design is
performed. During system design the system architecture is established, the technical safety requirements are
allocated to hardware and software, and, if applicable, on other technologies. In addition, the technical safety
requirements are refined and requirements arising from the system architecture are added, including the
hardware-software interface (HSI). Depending on the complexity of the architecture, the requirements for
subsystems can be derived iteratively. After their development, the hardware and software elements are
integrated and tested to form an item that is then integrated into a vehicle. Once integrated at the vehicle level,
safety validation is performed to provide evidence of functional safety with respect to the safety goals.
ISO 26262-5 and ISO 26262-6 describe the development requirements for hardware and software. This part
of ISO 26262 applies to both the development of systems and subsystems. Figure 3 is an example of a
system with multiple levels of integration, illustrating the application of this part of ISO 26262, ISO 26262-5
and ISO 26262-6.
NOTE 1 Table A.1 provides an overview of objectives, prerequisites and work products of the particular subphases of
product development at the system level.
Part 4: Product development: system level
Initiation of product development
4-5
at the system level
Specification of the technical safety
4-6
requirements
System design
4-7
Part 5: Product development: hardware level Part 6: Product development: software level
Item integration and testing
4-8
Safety validation
4-9
Functional safety assessment
4-10
Release for production
4-11
NOTE 2 Within the figure, the specific clauses of each part of ISO 26262 are indicated in the following manner: “m-n”,
where “m” represents the number of the part and “n” indicates the number of the clause, e.g. “4-5” represents Clause 5 of
ISO 26262-4.
Figure 2 — Reference phase model for the development of a safety-related item
4 © ISO 2011 – All rights reserved

NOTE Within the figure, the specific clauses of each part of ISO 26262 are indicated in the following manner: “m-n”,
where “m” represents the number of the part and “n” indicates the number of the clause, e.g. “4-5” represents Clause 5 of
ISO 26262-4.
Figure 3 — Example of a product development at the system level
System
Initiation of product
4-5
development at the system level
Specification of the technical
4-6
safety requirements
4-7 System design
Sub-system A Sub-system B
Specification of the technical
4-6
safety requirements
4-7 System design
Specification of the technical
4-6
safety requirements
4-7 System design
Sub-system B1 Sub-system B2
Specification of the technical Specification of the technical
4-6 4-6
safety requirements safety requirements
4-7 System design 4-7 System design
Part 5: Product Part 6: Product Part 5: Product Part 6: Product Part 5: Product Part 6: Product
development: development: software development at the development at the development: development:
hardware level level hardware level software level hardware level software level
4-8.4.2 Hardw are - softw are integration and testing 4-8.4.2 Hardw are – softw are integration and testing 4-8.4.2 Hardw are – softw are integration and testing
4-8.4.3 System integration and testing
4-8.4.3 System integration and testing
4-8.4.4 Vehicle integration and testing

5.3 Inputs to this clause
5.3.1 Prerequisites
The following information shall be available:
 project plan (refined) in accordance with ISO 26262-2:2011, 6.5.2;
 safety plan in accordance with ISO 26262-3:2011, 6.5.2;
 functional safety assessment plan in accordance with ISO 26262-2:2011, 6.5.4; and
 functional safety concept in accordance with ISO 26262-3:2011, 8.5.1.
5.3.2 Further supporting information
The following information can be considered:
 preliminary architectural assumptions (from external source); and
 item definition (see ISO 26262-3:2011, 5.5).
5.4 Requirements and recommendations
5.4.1 The safety activities for the product development at the system level shall be planned including
determination of appropriate methods and measures during design and integration.
NOTE The results of planning of the verification activities during design in accordance with 6.4.6 (Verification and
validation) and 7.4.8 (Verification of system design) are part of the safety plan while the planning of item integration and
testing in accordance with 8.4.2 (hardware/software), 8.4.3 (element integration) and 8.4.4 (item integration) is
represented in a separate item integration and testing plan in accordance with requirement 8.4.1.3.
5.4.2 The validation activities shall be planned.
5.4.3 The functional safety assessment activities for the product development at the system level shall be
planned (see also ISO 26262-2).
NOTE An example of a functional safety assessment agenda is provided in ISO 26262-2:2011, Annex E.
5.4.4 The tailoring of the lifecycle for product development at system level shall be performed in accordance
with ISO 26262-2, and based on the reference phase model given in Figure 2.
NOTE The project plan can be used to provide the relationship between the individual subphases of product
development at the system level and the hardware and software development phases. This can include the integration
steps at each level.
5.5 Work products
5.5.1 Project plan (refined) resulting from requirement 5.4.4.
5.5.2 Safety plan (refined) resulting from requirement 5.4.1 to 5.4.4.
5.5.3 Item integration and testing plan resulting from requirement 5.4.1.
5.5.4 Validation plan resulting from requirement 5.4.2.
5.5.5 Functional safety assessment plan (refined) resulting from requirement 5.4.3.
6 © ISO 2011 – All rights reserved

6 Specification of the technical safety requirements
6.1 Objectives
The first objective of this subphase is to specify the technical safety requirements. The technical safety
requirements specification refines the functional safety concept, considering both the functional concept and
the preliminary architectural assumptions (see ISO 26262-3).
The second objective is to verify through analysis that the technical safety requirements comply with the
functional safety requirements.
6.2 General
Within the overall development lifecycle, the technical safety requirements are the technical requirements
necessary to implement the functional safety concept, with the intention being to detail the item-level
functional safety requirements into the system-level technical safety requirements.
NOTE Regarding the avoidance of latent faults, requirements elicitation can be performed after a first iteration of the
system design subphase.
6.3 Inputs to this clause
6.3.1 Prerequisites
The following information shall be available:
 functional safety concept in accordance with ISO 26262-3:2011, 8.5.1; and
 validation plan in accordance with 5.5.4.
6.3.2 Further supporting information
The following information can be considered:
 safety goals (see ISO 26262-3:2011, 7.5.2);
 functional concept (from external source, see ISO 26262-3:2011, 5.4.1); and
 preliminary architectural assumptions (from external source, see ISO 26262-3:2011, 8.3.2).
6.4 Requirements and recommendations
6.4.1 Specification of the technical safety requirements
6.4.1.1 The technical safety requirements shall be specified in accordance with the functional safety
concept, the preliminary architectural assumptions of the item and the following system properties:
a) the external interfaces, such as communication and user interfaces, if applicable;
b) the constraints, e.g. environmental conditions or functional constraints; and
c) the system configuration requirements.
NOTE The ability to reconfigure a system for alternative applications is a strategy to reuse existing systems.
EXAMPLE Calibration data (see ISO 26262-6:2011, Annex C) is frequently used to customise electronic engine
control units for alternate vehicles.
6.4.1.2 The consistency of the preliminary architectural assumptions in ISO 26262-3:2011, 8.3.2 and the
preliminary architecture assumptions in this subphase shall be ensured.
6.4.1.3 If other functions or requirements are implemented by the system or its elements, in addition to
those functions for which technical safety requirements are specified in accordance with 6.4.1 (Specification of
the technical safety requirements), then these functions or requirements shall be specified or references made
to their specification.
EXAMPLE Other requirements are coming from Economic Commission for Europe (ECE) rules, Federal Motor
Vehicle Safety Standard (FMVSS) or company platform strategies.
6.4.1.4 The technical safety requirements shall specify safety-related dependencies between systems or
item elements and between the item and other systems.
6.4.2 Safety mechanisms
6.4.2.1 The technical safety requirements shall specify the response of the system or elements to stimuli
that affect the achievement of safety goals. This includes failures and relevant combinations of stimuli in
combination with each relevant operating mode and defined system state.
EXAMPLE The Adaptive Cruise Control (ACC) ECU disables the ACC functionality if informed by the brake system
ECU that the Vehicle Stability Control functionality is unavailable.
6.4.2.2 The technical safety requirements shall specify the necessary safety mechanisms (see
ISO 26262-8:2011, Clause 6) including:
a) the measures relating to the detection, indication and control of faults in the system itself;
NOTE 1 This includes the self-monitoring of the system or elements to detect random hardware faults and, if
appropriate, to detect systematic failures.
NOTE 2 This includes measures for the detection and control of failure modes of the communication channels (e.g.
data interfaces, communication buses, wireless radio link).
b) the measures relating to the detection, indication and control of faults in external devices that interact with
the system;
EXAMPLE External devices include other electronic control units, power supply or communication devices.
c) the measures that enable the system to achieve or maintain a safe state;
NOTE 3 This includes prioritization and arbitration logic in the case of conflicting safety mechanisms.
d) the measures to detail and implement the warning and degradation concept; and
e) the measures which prevent faults from being latent [see 6.4.4 (Avoidance of latent faults)].
NOTE 4 These measures are usually related to tests that take place during power up (pre-drive checks), as in the
case of measures a) to d), during operation, during power-down (post-drive checks), and as part of maintenance.
6.4.2.3 For each safety mechanism that enables an item to achieve or maintain a safe state the following
shall be specified:
a) the transition to the safe state;
NOTE 1 This includes the requirements to control the actuators.
b) the fault tolerant time interval;
NOTE 2 In-vehicle testing and experimentation can be used to determine the fault tolerant time interval.
8 © ISO 2011 – All rights reserved

c) the emergency operation interval, if the safe state cannot be reached immediately; and
NOTE 3 In-vehicle testing and experimentation can be used to determine the emergency operation interval.
EXAMPLE 1 Switching off can be an emergency operation.
d) the measures to maintain the safe state.
EXAMPLE 2 A safety mechanism for a brake-by-wire application, which depends on the power supply, can include
the specification of a secondary power supply or storage device (capacity, time to activate and operate, etc.).
6.4.3 ASIL Decomposition
6.4.3.1 If ASIL decomposition is applied during the specification of the technical safety requirements it
shall be applied in accordance with ISO 26262-9:2011, Clause 5 (Requirements decomposition with respect to
ASIL tailoring).
6.4.4 Avoidance of latent faults
6.4.4.1 This requirement applies to ASILs (A), (B), C, and D, in accordance with 4.3: if applicable, safety
mechanisms shall be specified to prevent faults from being latent.
NOTE 1 Concerning random faults, only multiple-point faults have the potential to include latent faults.
EXAMPLE On-board tests are safety mechanisms which verify the status of components during the different
operation modes such as power-up, power-down, at runtime or in an additional test mode to detect latent faults. Valve,
relay or lamp function tests that take place during power up routines are examples of such on-board tests.
NOTE 2 Evaluation criteria that identify the need for safety measures preventing faults from being latent are derived in
accordance with good engineering practice. The latent fault metric, given in ISO 26262-5:2011, Clause 8, provides
evaluation criteria.
6.4.4.2 This requirement applies to ASILs (A), (B), C, and D, in accordance with 4.3: to avoid
multiple-point failures, the multiple-point fault detection interval shall be specified for each safety mechanism
implemented in accordance with 6.4.4 (Avoidance of latent faults).
6.4.4.3 This requirement applies to ASILs (A), (B), C, and D, in accordance with 4.3: to determine the
multiple-point fault detection interval, the following parameters should be considered:
a) the reliability of the hardware component with consideration given to its role in the architecture;
b) the probability of exposure of the corresponding hazardous event(s);
c) the specified quantitative target values for the maximum probability of violation of each safety goal due to
hardware random failures (see requirement 7.4.4.3); and
d) the assigned ASIL of the related safety goal.
NOTE The use of the following measures depends on the time constraints:
 periodic testing of the system or elements during operation;
 on board tests of elements during power-up or power-down; and
 testing the system or elements during maintenance.
6.4.4.4 This requirement applies to ASILs (A), (B), C, and D, in accordance with 4.3: the development of
safety mechanisms that prevent dual point faults from being latent shall comply with:
a) ASIL B for technical safety requirements assigned ASIL D;
b) ASIL A for technical safety requirements assigned ASIL B and ASIL C; and
c) engineering judgement for technical safety requirements assigned ASIL A.
6.4.5 Production, operation, maintenance and decommissioning
6.4.5.1 The technical safety requirements concerning functional safety of the item or its elements during
production, operation, maintenance, repair and decommissioning, addressed in ISO 26262-7, shall be
specified.
NOTE There are two aspects that assure safety during production, operation, maintenance, repair and
decommissioning. The first aspect relates to those activities performed during the development phase which are given in
requirement 6.4.5.1 and 7.4.7 (Requirements for production, operation, service and decommissioning), while the second
aspect relates to those activities performed during the production and operation phase, which are addressed in
ISO 26262-7.
6.4.6 Verification and validation
6.4.6.1 The technical safety requirements shall be verified in accordance with ISO 26262-8:2011,
Clause 9, to provide evidence for their:
a) compliance and consistency with the functional safety concept; and
b) compliance with the preliminary architectural design assumptions.
6.4.6.2 The criteria for safety validation of the item shall be refined based on the technical safety
requirements.
NOTE The system validation planning and the system validation specifications are developed in parallel with the
technical safety requirements (see Clause 9).
6.5 Work products
6.5.1 Technical safety requirements specification resulting from requirements 6.4.1 to 6.4.5.
6.5.2 System verification report resulting from requirement 6.4.6.
6.5.3 Validation plan (refined) resulting from requirement 6.4.6.2.
7 System design
7.1 Objectives
The first objective of this subphase is to develop the system design and the technical safety concept that
comply with the functional requirements and the technical safety requirements specification of the item.
The second objective of this subphase is to verify that the system design and the technical safety concept
comply with the technical safety requirements specification.
10 © ISO 2011 – All rights reserved

7.2 General
The development of the system design and the technical safety concept is based on the technical safety
requirements specification derived from the functional safety concept. This subphase can be applied iteratively,
if the system is comprised of subsystems.
In order to develop a system architectural design, functional safety requirements, technical safety
requirements and non-safety-related requirements are implemented. Hence in this subphase safety-related
and non-safety-related requirements are handled within one development process.
7.3 Inputs to this clause
7.3.1 Prerequisites
The following information shall be available:
 item integration and testing plan in accordance with 5.5.3; and
 technical safety requirements specification in accordance with 6.5.1.
7.3.2 Further supporting information
The following information can be considered:
 preliminary architectural assumptions (from external source, see ISO 26262-3:2011, 8.3.2);
 functional concept (from external source); and
 functional safety concept (see ISO 26262-3:2011, 8.5.1).
7.4 Requirements and recommendation
7.4.1 System design specification and technical safety concept
7.4.1.1 The system design shall be based on the functional concept, the preliminary architectural
assumptions and the technical safety requirements. The consistency of the preliminary architectural
assumptions in ISO 26262-3:2011, 8.3.2 and the preliminary architectural assumptions in this subphase shall
be ensured.
7.4.1.2 The technical safety requirements shall be allocated to the system design elements.
7.4.1.3 The system design shall implement the technical safety requirements.
7.4.1.4 With regard to the implementation of the technical safety requirements the following shall be
considered in the system design:
a) the ability to verify the system design;
b) the technical capability of the intended hardware and software design with regard to the achievement of
functional safety; and
c) the ability to execute tests during system integration.
7.4.2 System architectural design constraints
7.4.2.1 The system and subsystem architecture shall comply with the technical safety requirements at
their respective ASILs.
7.4.2.2 Each element shall inherit the highest ASIL from the technical safety requirements that it
implements.
7.4.2.3 If an element is comprised of sub-elements with different ASILs assigned, or of non-safety-related
sub-elements and safety-related sub-elements, then each of these shall be treated in accordance with the
highest ASIL, unless the criteria for coexistence, in accordance with ISO 26262-9:2011, Clause 6, are met.
7.4.2.4 Internal and external interfaces of safety-related elements shall be defined, in order to avoid other
elemen
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