Conformity Assessment of Safety-related Systems

CASS is an open and transparent methodology for assessing compliance to IEC 61508 and related standards.

CASS methodology

At the heart of the CASS methodology, there are a number of tables (assessment templates) that can be used to map evidence of compliance (the assessee’s documentation) to the relevant clauses from IEC 61508 and record the assessor’s evaluation of that evidence. The methodology guides the assessor through the various evaluations to be performed. Each template lists a number of ‘targets of evaluation’ (TOEs) relevant to a particular type of assessment.

The assessment templates are free of charge and are available from the Downloads page. There are a number of supplementary documents that, together with the templates, form the methodology. It can be used in-house to prepare evidence of conformity supporting a Self-declaration, used by external auditors or even for Accredited Certification.


Advantages of using CASS

The CASS methodology has been designed by industry for industry to demonstrate functional safety compliance. It offers the following advantages:

  • Open to all and free of charge
  • Transparency in the assessment method – when complete, the templates show clear links between the evidence of conformity, the requirements from the standard used and the assessor’s evaluation
  • The methodology can be used to support a (self-) declaration of conformity
  • Can be used by certification bodies and is recognised by national accreditation bodies
  • Evidence can be prepared by the duty holder in advance of an external audit
  • Compatibility with industry guidance standards such as IEC 61511

Being able to demonstrate compliance with IEC 61508 (or related standard) is important to many organisations because it:

  • Is required by regulatory authorities for many plant owner/operators
  • Provides assurance to business stakeholders of operating companies managing high risks
  • Enables competitive advantage for equipment and service providers
  • Provides increased confidence in procurement of safety-related equipment and services
Safety requirements specification

Who owns and manages CASS

The CASS methodology is owned and managed by The CASS Scheme Association, a group of organisations active in developing, using and promoting the CASS methodology for conformity assessments to IEC 61508 and related functional safety standards, for the benefit of industry at large.

New assessment templates or guidance documents can be created by technical working groups set up within The 61508 Association under the mutual Memorandum of Understanding signed by the two parties. The 61508 Association and The CASS Scheme Association therefore work together in providing a wide base of technical expertise for the CASS methodology.

61508 safety documentation

The Members of The CASS Scheme Association are:

  • Actemium Automation
  • CSA Group
  • DEKRA UK Ltd
  • DNV
  • ERM
  • Fichtner Consulting Engineers
  • Mutech
  • P & I Design
  • ProSalus
  • ROAK Engineering
  • Sensia UK Ltd
  • UL Solutions

New members to The CASS Scheme Association are welcomed and those interested should contact the T6A Convenor in the first instance via the contact us page.


The CASS Scheme Association now also offers a registered assessor scheme to support organisations looking for an experienced assessor to perform functional safety audits and assessments. Please see the: Assessors page.
61508 safety documentation

History of CASS

CASS was formed soon after publication of the first edition of IEC 61508 in 1998. Sponsored as a UK government-funded initiative, it was intended to provide an industry-wide approach and interpretation to IEC 61508 assessment and certification.

The scheme had the involvement and “buy-in” from many safety-related system stakeholders: regulators, plant owner/operators, engineering companies, systems integrators, instrumentation suppliers, certification and accreditation bodies. One of the original objectives of CASS was that the assessment criteria, scope, guidance and approach should be open to all and the scheme documents have always been freely available in the public domain.

For traceability to its origins, further details about CASS are contained in the ‘CASS Guide to Functional Safety’ which, although is now out of date, may be of interest to some and can be found in our downloads section.