The conceptual design is based on selecting the correct transmitters, logic solver and final elements and the most suitable architecture to ensure the risk assessment SIL targets are achieved. Significant cost savings can be achieved over the lifetime of the project (Often 25 Years or greater) by selecting the correct SIS equipment.

​

Equipment can be selected on the basis of IEC61508 and will have a Safety Manual and SIL Certification or based on Prior Use. The use of certified devices to IEC61508 is preferred as the systematic capability SC will have been assessed. To satisfy Prior Use the end user will need to prove a device has been used in a similar application and environment, in either a safety or non-safety related application, for a sufficient time period without any dangerous failures. In many cases a FMEDA or FMEA will need to be undertaken to satisfy the systematic requirements.