Elsevier

Marine Structures

Volume 24, Issue 2, June 2011, Pages 73-96
Marine Structures

Quantitative assessment of hydrocarbon explosion and fire risks in offshore installations

https://doi.org/10.1016/j.marstruc.2011.02.002Get rights and content

Abstract

A risk-based design framework should involve both risk assessment and risk management. This article introduces and describes a number of procedures for the quantitative assessment and management of fire and gas explosion risks in offshore installations. These procedures were developed in a joint industry project on the explosion and fire engineering of floating, production, storage and off-loading units (the EFEF JIP), which was led by the authors. The present article reports partial results, focussing on defining the frequency of fires and explosions in offshore installations. Examples of the aforementioned procedures’ application to a hypothetical floating, production, storage, and off-loading unit (FPSO) are presented. A framework for the quantitative risk assessment of fires and explosions requires the definition of both the frequency and consequences of such events. These procedures can be efficiently applied in offshore development projects, and the application includes the assessment of design explosion and fire loads as well as the quantification of effects of risk control options (RCO) such as platform layout, location and number of gas detectors, isolation of ignition sources etc.

Introduction

More than 70% of the accidents that occur in offshore installations stem from hydrocarbon explosions and fires, which are extremely hazardous, involving blasts and heat [1], and have serious consequences for human health, structural safety and the surrounding environment.

Recent decades have seen a number of explosion and fire accidents in offshore installations, well documented in statistical data [2]. Fig. 1 presents a photo of the Piper Alpha accident, which occurred on 6 July 1988, and Fig. 2 a photo of the more recent Deepwater Horizon accident, which occurred on 20 April 2010 in the Gulf of Mexico.

Since the Piper Alpha accident, a substantial amount of effort has been directed towards the management of explosions and fire in offshore installations. Risk-based approaches have begun to replace traditional prescriptive approaches in offshore design, and 26 joint industry projects have been undertaken since 1990 [3]. In spite of these efforts, however, accidents continue to occur, as evidenced by the recent Deepwater Horizon incident.

The authors are leaders of the ongoing 27th Joint Industry Project on the Explosion and Fire Engineering of Floating, Production, Storage and Off-loading Units (FPSOs) (EFEF JIP hereafter) [3], [4], [5]. The aim of the EFEF JIP is to develop state-of-the-art technologies for the quantitative assessment and management of the risk of hydrocarbon explosions and fires in offshore installations, a review of which is presented in Refs. [6], [7].

A framework for the quantitative assessment and management of the risks associated with fires and gas explosions, Refs. [8], [9], [10], [11], requires the identification of both the frequency and consequences of these incidents. This paper describes methods of defining the frequency of fires and gas explosions, and presents examples of these methods’ application to a hypothetical FPSO. The EFEF JIP also involves definition of fire and explosion design loads and the damaging structural consequences of the incidents, and the results of these investigations will be presented in future, separate papers.

Section snippets

EFEF JIP procedure for fire risk assessment and management

Although hydrocarbon explosions and fires often accompany each other in offshore installations, they are by nature different phenomena [12], [13]. Fire is a combustible vapour or gas that combines with an oxidiser in a combustion process that is manifested by the evolution of light, heat and flame. The impact of overpressure from explosions and that of elevated temperature from fire are the primary concerns in terms of the actions that result from hazards within the risk assessment and

EFEF JIP procedure for explosion risk assessment and management

Hydrocarbons can explode through ignition when combined with an oxidiser (usually air). Thus, when the temperature rises to the point at which hydrocarbon molecules react spontaneously to an oxidiser, combustion takes place. This hydrocarbon explosion causes a blast and a rapid increase in overpressure.

Fig. 4 presents the EFEF JIP procedure for the explosion risk assessment and management of offshore installations [4]. Similar to that employed for fire risk assessment and management, a set of

Frequency analysis of explosions or fires

Fire and gas explosions cannot occur without ignition even in the event of a flammable gas or oil leak. Fire or gas explosion frequency is expressed as the frequency per offshore platform per year, and can be calculated as follows.Explosion/firefrequency=leakfrequency×ignitionprobability.

In current maritime industry practice, the following approaches are usually applied to analyse the frequency of fires and explosions [8].

  • -

    Historical accident frequency data

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    Fault tree analysis

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    Theoretical modelling

Topside of hypothetical FPSO

The topside of a hypothetical very large crude oil carrier class FPSO is now considered as an applied example. Fig. 6 depicts the layout of this topside [14]. The accommodation is located in the bow or stern area, as it is necessary to maximise the separation between the accommodation (including the principal evacuation systems) and the major hydrocarbon hazards. The topside modules are divided into a process area and a utility area. The former includes space for hydrocarbon-containing

Concluding remarks

This paper presents the procedures for the quantitative assessment and management of fire and hydrocarbon explosion risks in offshore installations developed during the EFEF led by the authors. As discussed herein, the use of simulation-based methods, such as CFD simulations and nonlinear finite element methods, is essential in such quantitative risk assessment and management [16], [17]. This paper focuses on the frequency analysis of fires and explosions, whilst other of the EFEF JIP’s results

Acknowledgements

The present study is part of the EFEF JIP (Phase I). The authors are pleased to acknowledge the support of their partners in this project: the American Bureau of Shipping, ComputIT AS, Daewoo Shipbuilding and Marine Engineering, Gexcon AS, Hyundai Heavy Industries, and the UK Health and Safety Executive. This work was also supported for two years by Pusan National University Research Grant.

References (24)

  • D. Bjerketvedt et al.

    Gas explosion handbook

    Journal of Hazardous Materials

    (1997)
  • B.J. Kim et al.

    Load characteristics of steel and concrete tubular members under jet fire: an experimental and numerical study

    Ocean Engineering

    (2010)
  • Accident statistics for floating offshore units on the UK continental shelf (1980–2003)

    (2005)
  • J.E. Vinnem

    Offshore risk assessment: principles, modelling and applications of QRA studies

    (2007)
  • Paik JK, Czujko J, Explosion and fire engineering and gas explosion of FPSOs (phase I): hydrocarbon releases on FPSOs –...
  • Paik JK, Czujko J, Explosion and fire engineering of FPSOs (phase II): definition of fire and gas explosion design...
  • Czujko J, Paik JK, Explosion and fire engineering of FPSOs (phase II): definition of gas explosion design loads. Final...
  • HSE, Review of analysis of explosion response. Report No. OTO 98174. London: Health and Safety Executive;...
  • Paik JK, Czujko J, Assessment of hydrocarbon explosion and fire risks in offshore installations. The IES Journal Part...
  • J. Spouge

    A guide to quantitative risk assessment for offshore installations

    (1999)
  • Guidelines for the application of formal safety assessment (FSA) for use in the IMO rule-making process

    (2002)
  • Risk management vocabulary, guidelines for use in standards

    (2002)
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