The paper gives an overview of draft international standard IEC 1508: Functional Safety: Safety-Related Systems. The objective of this standard is to provide a basis for safely automating process plant machinery, medical devices and other industrial equipment. The standard is concerned with preventing two basic types of unsafe incident. Firstly, failures of control systems that have the potential to trigger other events which in turn could lead to danger eg. fire, release of toxic materials, repeat stroke of machine, etc. Secondly, covert failures in protection systems that make them unavailable when needed for a safety action e.g. an emergency shutdown system. The paper describes how the standard treats random hardware faults, common cause faults and systematic faults (eg. design errors) in both hardware and software. Examples of incidents involving control system failure are also described.