System configurations [safety systems]

A discussion is given on hardware aspects of the system configuration of safety systems. When considering the configuration it is essential to include everything that is related to the safety system and not just the programmable part. The total configuration of safety related systems may include other electrical or electronic systems, mechanical or pneumatic equipment or possibly actions of the operator. The system approach presented, identifies every part of the configuration and considers the safety aspects of each one. The Health and Safety Executive Guidelines PES 2 suggests the three elements which could be used to evaluate each part: configuration, reliability and overall quality. The author addresses the first 2 elements. Having identified all the parts of the total configuration then the criteria for the programmable part can be established in order to achieve a specific level of reliability. Three areas must then be considered: what configuration to use; does it meet the criteria; and effect of the configuration on total equipment reliability