Functional Safety: 

General Principles for Designing Safety-Related Parts of Control Systems for Machinery

This American National Standard provides requirements and guidance for the implementation of safety-related control functions (also known as “functional safety”) as they relate to electrical, electronic, pneumatic, hydraulic, and mechanical components of control systems.

Informative Note 1:  This document includes a large number of detailed schematic circuit diagrams that are provided as EXAMPLE circuits only, representing common solutions in use at the time of creating this document.  It is important to understand that there are many ways to fulfil a given engineering requirement and the examples only present one option.  These examples are not normative, nor intended to limit innovation or the advancement of technology.
Informative Note 2:  This document references ISO 13849-2 – Validation as part of an annex.
Informative Note 3:  See also, clause 4 on “How to use this standard.”