Fire Risk Assessment in FPSO: A Discussion on Risk-Based Approaches
Authors: Paruolo N. , Braga E. , Teixeira P. , Pereira R. 
Published: October 2023

In the context of offshore structures acting on production and storage of flammable liquids and gas, Fire Risk Assessment (FRA) is an important asset to ensure the safe operation. This analysis allows the identification of possible hydrocarbon accidental release scenarios and structural elements susceptible to be heated as it combines a risk and structural assessments. Based on the identification of the possible leak scenarios and their probability of occurrence and consequence (risk assessment), a detailed structural analysis is carried out for the relevant scenarios with the purpose of indicate Passive Fire Protection (PFP) to be applied on critical structural members that fail the survivability criterium.

In the case of a process plant on a FPSO (Floating, Production, Storage and Offloading) unit, where one may find different liquid and gas process lines, the possibilities of accidental flammable liquid or gas releases leading to fire scenarios are significant. The risk assessment identifies the relevant scenarios, i.e., the scenarios associated to relevant frequency of occurrence and considerable inventory.

Currently, in the industry, different approaches are considered to determine which scenarios are relevant. In this paper, two approaches will be covered. The first will be called "Express Probabilistic Approach" as it is made through a probabilistic tool that summarizes the contribution of process devices that reinforce or mitigate the fire scenario. The weather conditions probabilities, ventilation conditions, operating pressure and temperature and other relevant important variables are also accounted. This approach considers process devices application as an important input for structural assessment.

The second approach will be called "Scenario Based Approach". Through this approach the mapped fire scenarios are ranked from the most to the less frequent in an impairment curve. The relevant scenarios are selected in a structural assessment by applying a screening analysis which identifies the structure's temperature when heated by the fire scenario and the need for PFP application, i.e., the plastic strain level after fire is compared to the allowable plastic strain. Differently from the abovementioned approach, this one considers the fire scenario consequence as an important input for structural assessment.

It is noted that consider the process devices application in the risk assessment provides robustness to the analyses as by doing so the fire scenarios are restricted to the ones with highest probability of occurrence.

The main objective of this paper is to bring to discussion both approaches presenting examples of application of each one. Since the application of PFP is the practical result of this assessment, a comparison between PFP indication based on each risk approach is also presented. This may be of interest since PFP application represents an additional cost and potentially also operational issues during the asset lifecycle for most operators and offshore units’ owners.