Elsevier

Ocean Engineering

Volume 167, 1 November 2018, Pages 293-309
Ocean Engineering

Efficient water deluge nozzles arrangement on offshore installations for the suppression of pool fires

https://doi.org/10.1016/j.oceaneng.2018.08.038Get rights and content

Highlights

  • Modified water deluge nozzle arrangement framework for jet and pool fires.

  • Provided the water deluge location index of pool fire.

  • Provided a demonstration and validation of the proposed method through CFD.

Abstract

Offshore installations that handle hydrocarbons are in serious danger of fires and/or explosions. Pool fires are a significant risk related to major fire accidents, and active protection systems such as water deluge systems are used to reduce the consequences of high temperature and radiation resulting from pool fires. Thus, it is important to decide on the locations of water deluge nozzles for effective fire suppression, and the aim of this study is to introduce an efficient methodology for selecting the locations of water deluge nozzles. The locations of water deluge nozzles are selected using a proposed water deluge location index based on the characteristics of pool fires. The methodology is based on probabilistic approaches associated with credible scenarios representing possible events on offshore topside structures. This methodology, applied to examples, is used to determine the efficient arrangement of water deluge nozzles on a hypothetical FLNG topside structure. The effectiveness of the new methodology is verified through comparison with uniformly distributed nozzles using a computational fluid dynamics simulation.

Introduction

Onshore and offshore platforms have the potential for various hazardous risks. In particular, fires with high temperatures may result in catastrophic consequences such as significant human casualties, economic losses and serious environmental pollution. The fire risk assessment and management, which includes presented rules and recommended practices, have been identified for reducing the risk of fire accidents (Czujko and Paik, 2012a, 2012b; Spouge, 1999; NORSOK, 2010; ABS, 2014; LR, 2014). In addition, design guidelines have been established to detail the methods of fire risk assessment and management (Nolan, 1996; Walker et al., 2003; Vinnem, 2007; Paik and Czujko, 2009, 2010; 2011, 2012; Paik et al., 2011).

Risk control options are effective means of minimising the probability of an event and its associated risk (UKOOA/HSE, 2006). Generally, active protection devices such as gas detectors and water spray systems are used as preventive and/or mitigating safety systems against fire accidents. Most installations have a two-tier alert system for preventing spurious shutdowns and unnecessary alerts. System failures generally occur when a detector fails to detect the specified information such as flammable gas, flame, smoke, heat, toxic gas and oil mist, or when the alarm or signal transmission systems fail to alert operators or activate emergency mitigation systems (DeFriend et al., 2008).

Water deluge systems are designed to cool equipment and control the growth of a fire by providing a simultaneous application of water over the entire fire hazard (ISO, 1999). For the efficient application of such water deluge systems, the location of the water deluge nozzles is important for ensuring their performance. The locations of the water deluge nozzles are usually selected through engineering judgments based on the deterministic approach (Dembele et al., 2007). However, the conventional method has an element of uncertainty in light of human error and accidental fires. To reduce the risk of such uncertainty, a probabilistic approach, based on credible fire scenarios, becomes necessary to select the locations of water deluge nozzles.

Numerous studies of fire-fighting systems have been performed (Svensson, 2002; Himoto and Tanaka, 2012; Jee et al., 2013; Alarifi et al., 2014). McCaffrey (1984) investigated the effect of water deluge on jet fires, and Prasad et al. (1999) conducted an experimental test for the suppression of pool fires with water deluge systems. Gosse and Hankinson (2001) and Hankinson and Lowesmith (2004) carried out large-scale studies to investigate the mitigation effect of water deluge systems on jet and pool fires.

Regarding active protection systems, some research has contributed to the application of the probabilistic approach. Seo et al. (2013) introduced a method for determining efficient gas detector locations using a quantitative approach. Recently, Kim et al. (2016) stressed water deluge location in the control of jet fires, and successfully implemented the approximate optimisation method to calculate the efficient nozzle locations for offshore platforms. They suggested the use of a water deluge index, based on the characteristics of jet fires, to determine the efficient locations of water deluge nozzles. The present paper is a sequel to the previous paper (Kim et al., 2016). In contrast to the previous paper, which concerned jet fires, this paper focuses on pool fires. Pool fires have different characteristics than jet fires, and thus a proper method should be developed to reflect those characteristics. The aims of this study are to use the water deluge location index for pool fires (WLIP) to suggest an efficient method of arrangement based on a probabilistic approach, and to verify the effectiveness of the proposed methodology for the arrangement of water deluge nozzles. Finally, this study compares its results with current industrial practices.

Section snippets

Jet fires

The location of water deluge nozzles has traditionally been determined based on engineering judgment and deterministic procedures. To reduce the risk of uncertainty in the conventional method, it is necessary to take a probabilistic approach based on engineering technology. Kim et al. (2016) successfully implemented a procedure for selecting efficient water deluge system locations to prevent, and reduce the consequences of, jet fire accidents on offshore installations. The WLI (water deluge

Target structure

Part of a hypothetical FLNG topside structure, is used as the target structure in the applied example. It consists of one deck, called the process deck (Fig. 3).

Selection of fire scenarios

The selection of a credible pool fire scenario is important for the determination of water spray positions. The Latin hypercube samplings (LHSs) technique (Ye, 1998) is used in this applied example for selecting the fire scenarios. The LHSs technique partitions each input distribution into N intervals of equal probability and selects

Concluding remarks

The aim of this study is to suggest a new method for the selection of water deluge nozzles to efficiently prevent and reduce the risk of pool fire accidents. The water deluge index for pool fires (WLIP) is calculated using the pool area and the frequency of fire scenarios. As the pool area is calculated with a simple equation, oil spill CFD analysis can be used to yield more precise results. The reliability of the WLIP is validated using risk-based comparison, which shows that the WLIP is more

Acknowledgements

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2017R1A2B4004891).

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