Where Did that IEC 61511 SIF Go! Allocating Safety Functions Can Be a Messy Affair

  • Conference Program
  • Safety
  • April 10, 2019
  • 9:15 am - 10:00 am

International Function safety standards IEC 61511/ 61508 provide the framework for the entire safety lifecycle of a safety system. With this standard in hand, a safety design engineer may feel that any project can be easily managed. However, the execution of the project varies considerably on other factors rather than the safety system. As the project evolves from conception design and the safety design engineer has to go through many interfaces in order to formulate a good safety requirements specification. Tackling the issues early in a project can make the best out of the situation. Thereby, tough designs can be better handled.

Process licensors come in a variety of forms for Chemical plants (e.g., Propylene, Methanol, Sulphuric Acid, Gasification) to Refinery Processes (e.g., LNG, Hydrocrackers, LC Finers). The plant throughput, product quality, risk profile, energy efficiency and so on define the performance guarantees, and are the requirements for engineering design. Instrument technology, architectures, proof testing requirements, configuration of basic control and safety system interface, and risk tolerance criteria affect the safety system design from process licensors. The sooner the identification of potential conflicts between the licensor and project design are identified , the better will be the path for a successful safety systems design.

The objective of this presentation/paper is to explore the importance of early involvement by safety design engineer on the process licensors design to get the best out of the situation for safety system. Gasifier reactor from one of the licensor is analysed for the difficulty arising from use of inferred measurement for the condition of the reactor. Also, a simple trip function is analysed which is not doing one thing but led to sequence of trips.