Development of Process Safety System by Using LOPA with Applying Conditional Modifiers.


M.H.Hawash, Process Engineer
Engineering for Petroleum and Process Industries (ENNPI), Egypt.
W.M.Shehata, F.K.Gad, Faculty of Petroleum and Mining Engineering
Department of Refining and Petrochemical Engineering, Suez University, Egypt.


This paper presents systematic approach of reducing the total Safety Integrity Level “SIL” rating for the Safety Instrument System “SIS” of Vacuum Distillate Unit “VDU”. The method is applying the applicable conditional modifiers such as Ignition Probability and occupancy factor during developing Layer of Protection Analysis Method “LOPA”. The results of this approach that the SIL rating of VDU feed Node is reduced from SIL 3 to SIL 2 by using the applicable condition modifiers. Such Reduction in SIL rating without reducing the required safety measures has a great impact for the total cost reduction of the unit and reduce design and installation, operation and maintenance complexity and cost.