Abstract
Passive fire protection (PFP) has been used in the Oil & Gas industry for many years as a method to avoid/delay global collapse of offshore installations. However location of PFP has normally been based on simplistic assumptions, standards, guidance and methods that do not always consider the real response of the structure to fire. The resulting PFP schemes can be conservative leading to unnecessary cost to the Operator in terms of application and maintenance costs. More importantly, there is the potential for the PFP scheme to be insufficient for the actual fire hazards which will increase the level of risk for the personnel on board.
Fire induced progressive collapse is a function of the level of redundancy of a structure, it is for this reason that redundancy analyses have sometimes been used as a simplistic method to calculate the level of PFP required. However this method does not take into account the size of the fire threat against which the PFP is designed and could lead to less than conservative results as it only considers removing one member of the structure at a time, without considering reduction in the strength of the surrounding members as they are also being heated by the fire.
Performance based fire collapse analysis provides an understanding of the response of the individual members as well as the entire structural system to fire. Understanding the failure mechanisms, susceptibility to progressive collapse of the structure, and key members that must remain in place during an accident situation allows for the optimisation of the PFP scheme, protecting only the required members while allowing for local failure of redundant members.
The present paper provides a comparison between the different methods, and provides case studies that have resulted in optimum PFP schemes linked to design fires based on acceptable risk levels.
