La’o Hamutuk

Bulletin  |  Surat Popular  |  Topic index  |  Reports & Announcements  |  Updates
Reference  |   Presentations  |  Mission Statement  |  LH Blog  |  Search  |  Home

Sunrise LNG in Timor-Leste: Dreams, Realities and Challenges

A Report by La’o Hamutuk
Timor-Leste Institute for Reconstruction Monitoring and Analysis

February 2008

Appendix 5. Risk Analysis

Link to Index and Table of Contents

Risk is defined in the Sandia National Laboratories LNG Spill on Water Risk Assessment as “the potential for suffering harm or loss and [it] is often quantified as the product of the probability of occurrence of a threatening event times the system vulnerability to that event and the consequences of that event.” [31] Mathematically, it is typically expressed as:

Risk = Pt · Ps · C

where Pt stands for the probability of the specific threat occurring, Ps is the probability of the system failing under that threat – or vulnerability – and C represents the consequences expressed in terms of loss of life or money.

Here, we follow the study for one type of accident – LNG spills on water – by Sandia National Laboratories [31] to point out how risk is taken into account and what conclusions were reached in that report. The steps in LNG spill risk assessment are summarized as follows:

  1. Evaluate the potential for a breach or loss of LNG from a ship

  2. Establish the potential damage to a cargo tank or other system from these events and the potential spills that could occur

  3. Estimate the volume and rate of a potential LNG spill based on the dimensions and location of the breach, properties, and characteristics of the LNG, ship construction and design, and environmental conditions (e.g. wind, waves, currents, etc.)

  4. Estimate the dispersion, volatilization, and potential hazards of a spill based on physical and environmental conditions; and

When necessary, identify prevention and mitigation strategies to meet risk management goals.

Figure 29, from the Sandia report, shows the event tree of LNG spills at sea that can lead to threatening situations.

Figure 29. Potential sequences of events following a breach of an LNG cargo tank. [31]

According to the Sandia study, six main damaging events can occur as a consequence of an LNG spill, namely injuries from asphyxiation, cryogenic burns and structural damage, combustion and thermal damage, LNG fireballs, LNG and air explosions, and Rapid Phase Transitions (RPT). The four existing models of spill dispersion and ignition analyzed by the Sandia report ([47], [21], [68] and [111]) yield substantial differences in their estimates of thermal damage and there are some disparities in the treatment of meteorological conditions. There is, therefore, high uncertainty in the results. Moreover, no probabilities of occurrence of triggering events are assumed. Indeed, the existing models assume that the event has a 1.0 probability of occurrence. These studies are not probabilistic but analyze a “worse case” scenario or a consequence-based scenario. In order to accurately carry out economically-conscious risk mitigation procedures, these probabilities need to be taken into account. There is very limited experience with large-scale LNG spills, and it is basically impossible to estimate realistic probabilities of occurrence for many of the steps involved in the event tree.

The problem of the uncertainty of hazards estimates is addressed by the independent analysis presented in the Sandia report [31] which uses state-of-the-art modeling tools to calculate the damage potential from LNG spills on water in order to arrive at the classification of hazard depending on the distance to the potential spill:

Pool sizes can range from 150 m in diameter for small, accidental spills to several hundred meters for large, intentional spills. High thermal hazards from fire are expected to occur within approximately 250-500 m from the origin of the spill. Major injuries and significant structural damage are possible in this zone. The extent of damage will depend on the spill size, and the dispersion from wind, waves and currents. People, major commercial and industrial areas or other critical infrastructure elements, such as chemical plants, refineries, bridges or tunnels, or national icons located within portions of this zone could be seriously affected.

Hazards and thermal impacts transitions to lower levels with increasing distance from the origin of the spill. Some potential for injuries and property damage can still occur in portions of this zone, but this will vary based on the spill size, distance from the spill, and site-specific conditions. For small spills, the hazards transition quickly to lower hazards levels.

Beyond approximately 750 m for small accidental spills and 1,600 m for large spills, the impacts on public safety should generally be low for most of the potential spills. Hazards will vary but minor injuries and minor property damage are most likely at these distances. Increased injury and property damage would be possible if vapor dispersion occurred and a vapor cloud was not ignited until after reaching this distance. Distances of dispersion as high as 2,500 m are possible.

 

Figure 30. Different areas of thermal radiation threat predicted by the four different models. [30]

Given the technical descriptions of the hazards obtained through the modeling of the spill event, three zones of security are proposed in the Sandia report [31] with varying degrees of risk mitigation intensity, as discussed in Chapter 6.3.

In order to carry out the necessary risk management process, the Sandia report lists the following critical steps:

Characterize assets: The context of the LNG facility including location, site-specific conditions, and nominal operations need to be identified. These must collect information on the type and proximity of neighbors, the environmental conditions, and the nominal operation conditions.

Identify potential threats: Accidental and intentional events need to be considered.

Determine risk management goals and consequence levels: Set goals with regard to property damage and injury, loss of service, and economic loss.

Define safeguards and risk management system elements: Prevention and mitigation considerations and protective designs.

Analyze system and assess risks: The risk management goals need to be compared to the consequence levels. An event tree needs to be identified for the site-specific conditions and its consequences evaluated.

Assess risk prevention and mitigation techniques: If the potential hazards exceed the consequence and mitigation goals, then an enhanced risk mitigation strategy needs to be developed.

Table 17 lists several prevention and mitigation techniques that could be necessary or recommended depending on the threat level. Some are easier to implement than others, and Timor-Leste should develop a specific study to select some of these procedures, or variations thereof, to reduce risk with the available resources.

Table 17. Prevention and mitigation measures identified by the Sandia report. [31]

PREVENTION

MITIGATION

ISOLATION

RECOVERY OPERATIONS

  • physical separation (distance)

  • physical barriers

  • keep-out or exclusion zones (buffers)

  • interrupted operations (aircraft, bridge traffic)

  • plans in place & current

  • equipment & people in place & ready

  • drills

  • evacuation plans

VOID SPACES WITH INERT GAS

MAINTAIN MOBILITY (tanker + towing)

INERTING OF VOID SPACES

LIMIT SPILL AMOUNTS & RATES

VARIED TIMES OF OPERATIONS

SECURITY EMERGENCY RESPONSE FORCES

INTELLIGENCE

FIRE-FIGHTING CAPABILITIES

  • communication links in place & ready

  • timely updates

  • interagency communication links

  • leak detectors

  • deluge systems

  • radiant barriers ( high-pressure high-density foam systems)

  • backup fire fighting capabilities

INCREASED MOBILITY (tugs)

REDUNDANT MOORING & OFFLOADING CAPABILITIES

ARMED SECURITY ESCORT (boat, aircraft or on-board)

OFFSHORE MOORING & OFFLOADING CAPABILITIES

SWEEPS (divers, sonar, U.S.C.G. boarding)

SPEED LIMITS

SURVEILLANCE (on-ship, on-land, underwater & aerial)

CRYOGENICALLY-HARDENED VESSEL

EMPLOYEE BACKGROUND CHECKS

SHIP ARMOR, ENERGY-ABSORBING BLANKETS

TANKER ACCESS CONTROL PROGRAM

MISSILE DEFENSE SYSTEM

STORM PREDICTION & AVOIDANCE PLANS

REDUNDANT CONTROL SYSTEMS

SAFETY INTERLOCKS

BACKUP FUEL SOURCE (oil)

 

Continue to Appendix 6. Field visit report

Go back to Appendix 4. History of accidents in the LNG industry

Return to Table of Contents

 

The Timor-Leste Institute for Development Monitoring and Analysis (La’o Hamutuk)
Institutu Timor-Leste ba Analiza no Monitor ba Dezenvolvimentu
Rua D. Alberto Ricardo, Bebora, Dili, Timor-Leste
P.O. Box 340, Dili, Timor-Leste
Tel: +670-3321040 or +670-77234330
email: 
info@laohamutuk.org    Web: http://www.laohamutuk.org    Blog: laohamutuk.blogspot.com