Segregated integration the paradox

BS EN IEC 61511 provides the guidance to Control and Safety Integration and it states: ´.....Wherever practicable, the safety instrumented functions should be separated from the non-safety instrumented functions.´ ´.... the basic process control system shall be designed to be separate and independent to the extent that the functional integrity of the safety instrumented system is not compromised.´ ´.... Adequate independence means that neither the failure of any non-safety functions nor the programming access to the non-safety software functions is capable of causing a dangerous failure of the safety instrumented function´ If we want to share common items between the safety system and the basic process control system then can we? For new installations can we design for this? For existing installations (called ´Legacy´ installations) this requirement has often neither been present nor covered properly. Since 61511 is seen by Health & Safety legislators as providing internationally recognised good practice they see its publication as an opportunity for companies to review their legacy installations against the standard. This will entail, amongst other requirements, a review to determine what is common mode between Control & Measurement and Safety systems and more importantly what aspects of the common elements would lead to failure of control and a demand on the Safety Function which inhibits the Safety Function from achieving its design intent. The presentation will investigate the requirements of 61511 and will also consider those requirements in relation to Legacy instrumentation systems.