This document describes a safety communication layer (services and a protocol) for the exchange of safety data using IEC 62541 mechanisms. It identifies the principles for functional safety communications defined in IEC 61784-3 that are relevant for this safety communication layer. This safety communication layer is intended for implementation in safety devices only. NOTE 1 This document targets controller-to-controller communication. However, easy expandability to other usecases (e.g. OPC UA field level communication) has already been considered in the design of this document. NOTE 2 This document does not cover electrical safety and intrinsic safety aspects. Electrical safety relates to hazards such as electrical shock. Intrinsic safety relates to hazards associated with potentially explosive atmospheres. This document defines mechanisms for the transmission of safety-relevant messages among participants within a network using OPC UA technology in accordance with the requirements of IEC 61508 series and IEC 61784-3 for functional safety. These mechanisms may be used in various industrial applications such as process control, manufacturing, automation, andmachinery. This document provides guidelines for both developers and assessors of compliant devices and systems. NOTE 3 The resulting SIL claim of a system depends on the implementation of this document within the system implementation of this document in a standard device is not sufficient to qualify it as a safety device.