DNV Port toolkit risk profile LNG bunkering

DET NORSKE VERITAS

Report

Port toolkit risk profile

LNG bunkering

Port of Rotterdam, Ministry of Infrastructure &

Environment, Port of Antwerp, Port of Amsterdam and

Zeeland Seaport

Report No./DNV Reg No.: PP035192-R2

Rev. 2, 28 August 2012

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Port toolkit risk profile LNG bunkering

DNV Reg. No.: PP035192-R2 Revision No.: 2

Date : 2012-08-28 Page ii of iii

Table of Contents

CONCLUSIVE SUMMARY ................................................................................................... 1

1 INTRODUCTION ............................................................................................................. 3

2 LNG BUNKERING SYSTEM DEFINITION ............................................................... 5

2.1 LNG Bunkering at a glance ........................................................................................ 5

2.2 Bunker configurations ................................................................................................ 7

2.3 Location .................................................................................................................... 10

2.4 Characterization of bunker parameters .................................................................... 11

3 WHAT IS LNG? .............................................................................................................. 13

4 METHODOLGY AND SCENARIO DEFINITION .................................................... 14

4.1 Scenario’s and parameters related to safety distances for passing ships .................. 14

4.1.1 Hazard identification and Loss of containment scenarios ................................. 14

4.1.2 Selection of representative scenario .................................................................. 16

4.1.3 Calculation of effect of representative scenario ................................................ 16

4.2 Risk distances to vulnerable objects ......................................................................... 16

4.2.1 What can go wrong: Loss of containment scenarios ......................................... 17

4.2.2 How bad? Consequence Modelling ................................................................... 17

4.2.3 How often? Failure frequencies ......................................................................... 18

4.2.4 So What? Risk Assessment ............................................................................... 20

4.2.5 What do I do? Risk Management ...................................................................... 20

5 ASSESSMENTS RESULTS ........................................................................................... 21

5.1 Safety distances for passing ships ............................................................................ 21

5.1.1 Discussion .......................................................................................................... 22

5.2 Risk distances to vulnerable objects ......................................................................... 24

5.2.1 Category 1 - LNG bunkering with a small bunker vessel ................................. 24

5.2.2 Category 2 - LNG bunkering with a large bunker vessel .................................. 27

5.2.3 Category 3 - LNG bunkering with a tank truck ................................................. 30

5.2.4 Category 4 - LNG bunkering from a bunker pontoon ....................................... 32

5.2.5 Category 5 - LNG STS transfer ......................................................................... 34

5.2.6 Discussion .......................................................................................................... 36

RISK MITIGATION AND FURTHER RESEARCH ........................................................ 39

5.3 General risk mitigation measures ............................................................................. 39

5.4 Study specific ........................................................................................................... 40

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Port toolkit risk profile LNG bunkering

DNV Reg. No.: PP035192-R2 Revision No.: 2

Date : 2012-08-28 Page iii of iii

6 CONCLUSIONS .............................................................................................................. 42

7 REFERENCES ................................................................................................................ 43

Appendix 1 Scenarios

Appendix 2 Nautical risk assessment of moored LNG bunker vessels

Appendix 3 Background parameters for risk calculation

Appendix 4 Results distances to 10-6

per year risk contour

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Port toolkit safety distances LNG bunkering

DNV Reg. No.: PP035192-R2

Revision No.: 2 Date : 2012-08-28 Page 1

CONCLUSIVE SUMMARY

The Port of Rotterdam, the Port of Antwerp, the Port of Amsterdam and Zeeland Seaports are

preparing for the arrival of LNG as a fuel. Large scale bunkering of LNG is novel and differs

on several aspects from the bunkering of conventional marine fuels. LNG is stored at low

temperatures and the development of a gas cloud in case of a potential release to the

atmosphere requires insight into the risks which have to be translated into procedures for safe

and practical operation during For successful incorporation of these activities into their

current safety systems (e.g. guidelines, operational procedures) and operations they DNV has

been asked to develop a “harbour toolkit safety distances LNG bunkering” to help identify (a)

the safety distances for passing ships and (b) the risk distance to vulnerable objects such as

residential housing, offices, hospitals etc. The toolkit will help get insight what safety/risk

distance should be taken into account given a specified bunker configuration and as function

of the number of bunkers. As such it can be used as a (first) screening tool for suitability of

bunker locations in the port area.

The Port of Rotterdam identified various LNG bunker activities in a port area. Those activities

can be grouped in five different categories:

1) LNG bunkering from small inland bunker vessel to small vessels

2) LNG bunkering from large bunker vessel to seagoing vessels

3) LNG bunkering from trucks to small vessels

4) LNG bunkering from bunker pontoons to small vessels

5) LNG transfer from ship to ship

The determination of the safety distances for passing ships is determined by a consequence

based methodology, where a representative risk scenario and consequence are selected. The

selection of the representative scenarios is based on a (desktop) hazard identification.

DNV found that the calculated safety distance for categories 1, 3 and 4 are in line with the

nautical safety distances that are prescribed in the existing Dutch shipping regulation BPR.

The calculated safety distances for the categories 2 and 5 are significantly larger than the

nautical safety distances that are currently prescribed in the existing Dutch shipping

regulation BPR. The relatively large safety distances that are found for those categories could

enforce additional rules for the LNG bunkering of large vessels in area with intensive nautical

traffic. It may not give restriction on LNG bunkering activities in area where lower nautical

activities take place and collision scenarios are less credible / likely.

The risk distances to vulnerable objects are calculated using a Quantitative Risk Assessment

(QRA) methodology which includes both frequency and consequences calculations of

possible Loss of Containment (LOC) scenarios (e.g. hose leakage). DNV have calculated the

risk distances to vulnerable objects towards the Dutch risk criteria for vulnerable objects, i.e.

10-6

/year.

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The risk distances that are found for the different categories vary from 10 to 510 meter,

depending on the category, bunker parameters, ignition method and number of bunker

activities. The risk distances for the categories 1, 2 and 5 are mainly caused by the scenario

where ship collision results in a loss of containment of the LNG cargo (bunker) tank on the

LNG bunkering vessel. It is found that lowering of the nautical activities in the bunkering area

may reduce the risk distance. For areas where (very) low nautical activities take place the risk

distance is driven by the rupture of the bunkering hose and leakage through a 25 mm hole.

It is found that the risk distance of category 3 and 4 is independent of the nautical activities

because the distance is driven by the scenario ‘rupture of the bunkering hose’ and leakage

through a 25 mm hole.

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1 INTRODUCTION

Liquid Natural Gas (LNG) is becoming more and more interesting as fuel for shipping. One

of the main reasons is the upcoming stringent requirements for emissions from ship engines

following the adoption of Emission Control Area’s as of 2015. A ship engine running on LNG

is emitting significant lower amounts of NOx, SOx and particulate matter as well as reduces

the output of CO2 than a ships engines running on conventional fuels. Next to that costs

saving may be achieved.

In order to use LNG as a shipping fuel there is a need to develop a LNG bunkering

infrastructure. Several bunkering configurations are possible to deliver the LNG to the vessel.

An example of a LNG bunkering configuration already used today can be seen on the DNV

LNG blog [1].

Figure 1: Screenshots bunkering film

Large scale bunkering of LNG is novel and differs on several aspects from the bunkering of

conventional marine fuels. LNG is stored at low temperatures and the development of a gas

cloud in case of a potential release to the atmosphere requires insight into the risks which

have to be translated into procedures for safe and practical operation during LNG bunkering

activities.

Different ports are preparing for the arrival of LNG as a fuel. For successful incorporation of

these activities into their current safety systems (e.g. guidelines, operational procedures), the

Port of Rotterdam, Ministry of Infrastructure & Environment, Port of Antwerp, the Port of

Amsterdam and Zeeland Seaports asked Det Norske Veritas (DNV) to determine the

following:

Safety distances for the determination of exclusion zones related to passing vessels during

LNG bunkering activities, i.e. what is a safe passing distance for other traffic related to an

ongoing LNG bunkering activity?

Risk distances to vulnerable objects, i.e. what should be the minimum distance between an

LNG bunker location and (fixed) vulnerable objects such as residential housing, offices,

hospitals etc. based on the quantified risk. The purpose is to develop a risk-based toolkit,

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with which suitable locations for LNG bunkering activities can be identified in the port at

any given time.

Concerning the bunkering of LNG a significant amount of uncertainties still exist, e.g. related

to ship designs (both for bunker vessel and recipient vessel), vessel types, bunkering

equipment, process parameters etc. as there is only a limited number of LNG bunker stations

operational to date In this study considerable effort has been made to make defendable

assumptions but in case choices needed to be made the conservative option have been chosen

in an attempt not to underestimate the risks related to LNG bunkering.

And although in this study a lot of effort has been put in making the assessment as detailed

and realistic as possible, future real life bunker configurations might have different parameters

and characteristics. As such the results presented should be interpreted with care and as a

minimum real life situations should be verified in detail to see whether their parameters are in

line with the assumptions made in this study before conclusions are drawn based on this

study.

The report outline is as follows: Chapter 2 gives an overview of the LNG bunkering system

definition. This chapter include a brief overview of the history of LNG and a description of

the categorised LNG bunkering activities considered in this study. Next, a brief overview of

the (safety) characteristics of LNG is presented in Chapter 3. Chapter 4 describes the applied

methodology and scenario definition to determine the safety and risk distances. A detailed

assessment of the results is provided in Chapter 5. Chapter 6 provided general and specific

mitigation measures to reduce the risk that is found in Chapter 5. The report ends with

Chapter 7 in which the main findings are summarised and conclusions are drawn.

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2 LNG BUNKERING SYSTEM DEFINITION

In order to correctly assess and quantify the risks of LNG bunkering definition of the

following key aspects are important:

The configuration of bunkering: several bunkering configurations are feasible and each

configuration has specific risks;

The location of bunkering: the vicinity and number of passing vessels, presence of

ignition sources, distance to vulnerable objects and such all can have a significant

influence on the risk level;

Bunker parameters: the number of bunker operations, the volume of the LNG flow, and

the characteristics of safety equipment, e.g. time needed to close Emergency Shut Down

(ESD) valves and other also have a significant impact on the risk level.

In the paragraphs below a more detailed description of these various aspects is given. A short

description of the LNG bunker process is also presented.

2.1 LNG Bunkering at a glance

The typical main steps in a bunkering process are:

Approach of the bunker vessel

Setting up mooring arrangement

Grounding and connecting of the bunker hoses;

Inerting and purging of the filling lines;

The bunker transfer;

Stripping, purging and inerting of filling lines;

Disconnecting of grounding and bunker hoses.

The figure below is an illustration of the different elements in a LNG bunkering transfer

chain. Focus is on the different equipment and the systems involved.

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Figure 2: Different elements in a LNG bunkering transfer chain

LNG fuelled ships have bunkered successfully for ten years, since the first LNG fuelled ship –

a car and passenger ferry named Glutra – was put into operation in 2000. Currently, a total of

26 LNG fuelled ships are in operation, and ~30 more new-builds have been ordered. In

addition, some conversions are planned for convention fuelled ships.

The bunkering operations currently in use for LNG fuelled ships in Norway are bunkering

from trucks or from a land based tank via a fixed installation on pier or jetty. Trucks are

common due to small scale supply, long distances between LNG production sites and

bunkering sites, as well as between locations where the LNG fuelled vessels operate.

Last year a LNG bunkering JIP in the Netherlands (LESAS project) started to investigate the

possibility of LNG ship bunkering. Recently, the same initiative is launched in Singapore.

The LNG bunkering JIP in Singapore identified the (manual) bolted connection of LNG

hoses, as used in Norway at the moment, to be disputable. They prefer breakaway couplings

which can be equipped with ESD2 option for rapid disconnection of the transfer hose / from

the ship.

Next to that the loading and unloading of cryogenic substances has been around for decades.

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2.2 Bunker configurations

The Port of Rotterdam has identified various LNG bunker configurations in a port area and

created a virtual port to visualise those bunker configurations. This virtual port is known as

the Beanport after its creator Cees Boon. An overview of the Beanport is found in Figure 3.

Some of these bunker configurations are classed as land base, e.g. bunkering from an onshore

storage facility. These configurations are not part of the scope of this study. Instead this study

focuses on the water based configurations with one addition: the bunkering of small vessels

by truck. The water based configurations can be divided in five different groups:

1) LNG bunkering from small inland bunker vessel to small vessels

2) LNG bunkering from large bunker vessel to seagoing vessels




Each group is discussed in more detail and represented in figure 3 below.

Figure 3: Overview of the LNG bunkering configurations in “Beanport”

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1) Bunkering of LNG from a small inland bunker vessel

Small inland bunker vessels will load LNG from large scale or intermediate LNG terminals

and transport it to bunker locations. At the bunker location the LNG is bunkered to small

(inland) vessels through a flexible hose. The size of the bunker barge is strongly depending on

the number of bunker operations and the bunker volume of the recipient vessel to be

bunkered. Bunkering of short sea vessels and short sea Ro/Ro ferries does require more LNG

bunker volume than inland vessels. The bunkering of LNG from a small inland bunker vessel

will take between 1 or 2 hours depending on the LNG demand of the bunkered vessel and the

bunkering flow rate. Bunkering flow rates vary from 80 to 500 m3/h.

The volume of LNG per cargo tank is limited for small inland bunker vessel. The ADN [1]

limit the volume of cargo tanks for standard inland vessel to 380 m3, which means that cargo

tanks of bunker vessels cannot be constructed above this threshold value. Bunker barges

which will transport more LNG must be equipped with multiple cargo tanks.

After special permission the ADN [1] allows cargo tanks with a volume up to 1000 m3. To

comparison; The Pioneer Knutsen, which is at the moment the only LNG small bunker vessel

in operation, contains two spherical stainless steel 550 m3 cargo tanks. This bunker vessel

operates at 3 bar(a) [4].

2) Bunkering of LNG with use of a large LNG bunker vessel

Large LNG bunker vessels will load LNG from large scale or intermediate LNG terminals

and transport it to the bunker locations. At the bunker location the LNG is bunkered to small

vessels which could vary from tankers to large container ships. The size and main dimensions

of small scale LNG carriers can vary significantly, depending on different market demands,

draught and other physical limitations of the ports and bunker sites to be used. Typical

cargo capacity for small scale LNG carriers may be approximately 7.000 to 21.000 m3, but

smaller and bigger vessels exist. According to the information received by the Port of

Rotterdam the large container ships require a maximum bunker volume of 21.000 m3, which

means that the entire volume of a large LNG bunker vessel is needed to bunker one container

vessel.

The LNG bunkering time of vessels in this study is limited to 7 hours. To meet the required

bunkering volume in 7 hours LNG is bunkered by 3 flexible hoses. Bunkering flow rates per

hose vary from 500 to 1000 m3/h.

3) Bunkering of LNG with use of LNG tank truck

Regional land-based distribution of LNG can be carried out by heavy duty trucks, for example

to serve nearby industries, other ports in the region and transportation within the port. LNG

trucks are also used for transporting LNG from small scale liquefactions plants to customers

who are not connected to the gas network. Examples of countries where LNG is distributed by

trucks are Norway, Sweden, Finland, Belgium, Germany, the Netherlands, Poland, Spain,

Turkey, China and Russia. LNG terminals with regional distribution of LNG by trucks are

equipped with facilities for loading and unloading of trucks. Flexible hoses are used for the

transfer of LNG between the terminal and the truck. The size of the truck is in Europe limited

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by the Accord européen relatif au transport international de marchandises Dangereuses par

Route ADR to 40 m3 [3]. A normal bunkering operation from a semi-trailer takes up to two

hours including signing of documents and safety procedures. The actual pumping / transfer

time is approximately one hour.

According to the information received by the Port of Rotterdam short sea Ro/Ro vessels

require a maximum bunker volume of 200 m3, which means that multiple trucks are required

to bunker a single Ro/Ro vessel. Inland vessel require less bunkering volume. The first LNG

fuelled inland vessel, Argonon, requires 40 m3 of LNG. This inland vessel is bunkered with a

single LNG truck.

4) Bunkering of LNG with use of a fixed land based tank/installation (bunker pontoon)

Bunker pontoons and other small scale land based LNG installation will load LNG from LNG

feeder vessels. Small scale land based LNG installation in port area could be as large as

100000 m3. The volume of land based installations such as bunker pontoons, is much lower.

Here, typical volumes up to 1000 m3 can be expected. The smaller land based installations are

likely to be used for the bunkering of inland vessels, harbour tugs or fishing vessels or even

trucks. The bunkering of LNG from small scale installations to inland vessel will take

approximately 1 hour depending on the LNG demand of the bunkered vessel and the

bunkering flow rate. Bunkering flow rates vary from 30 to 80 m3/h.

5) LNG transhipment on the buoys or dolphins (ship to ship transfer)

Most of the cargo operations normally take place between the large or small bunker vessels

and intermediate LNG storage terminals. Nevertheless, it is possible to transfer LNG from a

LNG feeder to a bunker vessel. During this ship-to-ship (STS) transfer the LNG bunker

vessel will moor alongside the LNG feeder to transfer LNG. The advantage of the transfer

method is the absence of an immediately land based terminal to transfer LNG to bunker

vessels. The flow at which the LNG is transported is highly depending on the size of the

receiving bunker vessel. LNG STS transfer can be applied to both large and small bunker

vessels.

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2.3 Location

Although the outcome of this study will be used to assess the suitability of proposed bunker

locations, a definition of representative locations is needed in order to reach this outcome.

Together with the port of Rotterdam it was decided two simulate three situations:

1. An area with intensive nautical activity: The intensive nautical traffic area is defined as a

location where large ships with high velocity will pass the moored LNG bunker vessel.

The potential impact energy of this scenario is high due to the combination of large ships

with high velocities. In the Port of Rotterdam area, de Oude Maas could be seen as a

representative case for an intensive nautical traffic area.

The average traffic density on the Oude Maas is estimated at approx. 108,000 ships per

year. The majority of the ships are less than 140 meter and have a speed around 8 knots.

This combination of length (mass) and velocity results in a high potential impact energy

on the waterway.

2. An area with low nautical activity: The low nautical traffic area is defined as a location

where the traffic density is less than the intense nautical traffic area. At this location the

average velocity of the ships is low and large vessels are supported by tugs which limits

the probability of collision. The potential impact energy at this location is low.

Representative locations for this scenario could be found in the Caland canal area.

The average traffic density on the Caland canal is estimated at approx. 48,500 ships per

year. The majority of the ships is less than 140 meter and have a speed around 8 knots. At

this location the combination of length (mass) and velocity also results in high potential

impact energy on the waterway. However the number of ships is significantly smaller than

the Oude Maas, which significantly reduces the probability of collision.

3. An area with very low nautical activity: The very low nautical traffic area is defined as a

location where ships are going to be berthed. At this location the average velocity of the

ships is low (<5 knots) and large vessels are supported by tugs which limits the

probability of collision. The potential impact energy at this location is low. Representative

locations for this scenario could be found in a dock in the Amazonehaven area.

The average traffic density on the Amazonehaven area is estimated at approx. 4,200 ships

per year. At this location the average velocity of the ships is low and large vessels are

supported by tugs. The potential impact energy at this location is low.

All three areas will be used for the simulation of the risk associated with LNG bunker

activities. For each of the locations the width of the waterway is estimate on 300 meter. The

locations are displayed in Figure 4.

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Figure 4: Overview of the location of nautical traffic areas.

2.4 Characterization of bunker parameters

A final key aspect that influences the overall risk levels is the characteristics of the bunkering

process itself: e.g. the volume of the LNG flow or the number of bunker activities has a

significant impact to the overall risk levels. To account for this some assumptions had to be

made. These assumptions are described below.

Number of bunker activities

Since the number of bunkering activities will increase over time (as more gas fuelled ships

will become available) three levels of bunker activity have been defined per bunker

configuration: an upper bound, mean and lower bound level. The number of bunker activities

per level is an indication for the visualisation of the risk. They do not represent the expected

number of bunker activities in the Port of Rotterdam.

The upper bound level of bunker activities for the categories 1, 3 and 4 are 10 per day. The

mean and lower bound level for these categories equal 5 bunker activities per day and 1

bunker activity per week.

For the category 2 the upper bound level of bunker activities is 1 per day. The mean and lower

bound level for category 2 equal 1 bunker activities per 2 days and 1 bunker activity per

month.

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For the last category, category 5, the upper bound level of bunker activities is 3 per week. The

mean and lower bound level for category 5 equal 7 bunker activities per month and 1 bunker

activity per month.

Process characteristics

Since the actual bunkering infrastructure is not yet available there is uncertainty in what the

bunkering process parameters such as flow and pressure will be. To solve this situation two

sets of process parameters have been used based on current comparable processes as well as

known designs. Per bunkering configuration a minimal and maximal process parameter set

has been defined. The variations in parameters include flow, diameter, bunker time, number

of hoses and ignition method. Quantification of these parameters is given in appendix I and

the addendum [13]. It must be note that the risk calculation with the maximum parameter set

is based on the conservative ignition method where the flammable cloud is ignited at its

largest volume. The minimum parameter set is based on the less conservative ignition method

where the actual ignition sources like passing ships are taken into account. More information

regarding ignition sources is found in Appendix III.

Based on the above the following simulation scenarios are possible for each of the five bunker

configurations. This leads to a total of 90 simulation scenarios.

Figure 5: Overview of various simulation scenarios per bunker category

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3 WHAT IS LNG?

LNG is Liquefied Natural Gas and as such is the same gas (mostly consisting of methane) that

is used for cooking in many homes. In its liquid state, LNG is not flammable, nor explosive.

When LNG is heated and becomes a gas, the gas is not explosive if it is unconfined. Natural

gas is only flammable within a narrow range of concentrations in the air (5% to 15%). Less

air does not contain enough oxygen to sustain a flame, while more air dilutes the gas too

much for it to ignite. Ignition without ignition source (auto ignition) is not possible in normal

conditions. The temperature at which auto ignition may occur is above 500°C (in an air-fuel

mixture of about 10% methane in air, the auto ignition temperature is approximately 540°C,

while the auto ignition temperature for diesel oil is in the range of 260°C to 371°C).

In the event of a spill, LNG vapours will disperse with the prevailing wind. Cold LNG vapour

will appear as a white cloud. Parts of that cloud contain flammable concentrations of gas. The

flammable concentrations of gas could be ignited, which can results in a jet fire, flash fire or

explosion (if confined). The probability of explosion could be limited by a good design of the

facility or vessel which is fuelled by LNG. This means that facilities or vessels should have an

open design where confinement is limited, so no significant overpressures can be built up

after ignition.

Localized jet or flash fires would burn with intense heat. To keep the public at a safe distance,

thermal exclusion zones are established for installation that handle LNG. When LNG is

released the liquid droplets rain out and may form a pool of LNG. The LNG pool cannot be

ignited but the flammable concentration above can. Ignition of the flammable concentration

above the pool will result in a pool fire. For pool fires also thermal exclusion zones are

established to keep the public safe.

When skin touches an extremely cold body or LNG, heat is transferred from the skin and

organs to the cold body or LNG. This will cause damage to the skin and underlying tissues.

The normal functioning of the body may be disturbed by the cooling of internal organs, which

will lead to a critical condition called hypothermia. The cooling of the brain or heart is very

dangerous. Proper procedures and the use of protective clothing and equipment to prevent any

contact with the LNG are hence imperative. Large scale exposure to LNG will cause a

fatality.

However, the extremely low temperatures are not only hazardous to people. While stainless

steel will remain ductile, carbon steel and low alloy steel will become brittle and fractures are

likely if they are exposed to such low temperatures. Standard ship steel must therefore be

protected and insulated from any possible exposure to LNG (e.g. using stainless steel drip tray

etc.).

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4 METHODOLGY AND SCENARIO DEFINITION

This chapter will discuss the methodology that is used for the determination of the safety

distance to passing ships and the methodology that is used for the determination of risk

distances to vulnerable objects.

4.1 Scenario’s and parameters related to safety distances for passing ships

The determination of the safety distances for passing ships is determined by a consequence

base methodology, where a representative scenario and consequence are selected. The

methodology is illustrated in Figure 6.

Figure 6: Methodology of determination of safety distance

4.1.1 Hazard identification and Loss of containment scenarios

The selection of the representative scenarios is based on a (desktop) hazard identification

which is focussed on hazards that can results in a loss of containment of LNG. During the

hazard identification the cause, consequences and credibility of each of the hazards were

identified. It is reasonable to assume to the overfilling of the fuel tank and improper boil of

gas control do not occur if proper measures are in place. Hazards that arise from the

intermediate LNG storage and/or fuel tank are not considered within the scope of this study.

The other identified hazards that could occur are grouped in two different categories:

Coupling failure

Damage to the hose

These two categories will be discussed below in more detail:

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Coupling failure

Before the bunkering operation the hose is connected to the ship’s manifold. The connection

should be established by operators which could make an operational error while connection

the hose. It is assumed that the system is tested (purged) prior to each bunkering operation,

using nitrogen as inert gas. After the bunkering of LNG is finished the LNG hose is purged to

prevent possible releases of LNG when disconnecting the hose.

Nevertheless, a leak could occur at the flange face, resulting in an initial slow release, with

little impact and growing to a wire cut across the flange face. The operator, which is present

during the loading operation, would detect the leak and will shut down the installation. The

shutdown action of the operator would isolate the leak and further release of LNG is

prevented. A conservative estimate of the wire cut diameter/hole size that could occur during

this incident would be between 5 – 10 mm.

Hose Failure

There are various failure mechanisms for (flexible) hoses. For the LNG bunkering purpose the

following failure mechanisms where identified:

Fatigue due to high pressure or low temperature;

Ship securing/ mooring line failure;

Collision of ships;

Extreme weather conditions

External impact due to lifting activities or maintenance

The flexible hoses that are used for the bunkering of LNG are in European countries subjected

to the Pressure Equipment Directive (PED). The PED prescribes periodic inspection of

flexible hose if a certain threshold value of pressure and diameter is exceeded. European

design standard EN1472-2 [7] states that he maximum allowable working pressure in a hose

should not be less than 10 bar(g). For pressures of 10 bar(g) and higher the PED prescribes a

periodic inspection for hoses with a diameter above 2.5 inch. To ensure the technical integrity

of the hose, the periodic inspection should be performed by an independent party.

In industry it is also common to perform a visual inspection before the hose is connected. It is

likely to assume that the inspection by bunkering company and independent party will secure

the technical integrity of the bunker hose and failure or rupture of the hose is therefore not

selected as credible scenario.

During the bunker operation the receiving and bunker vessel are connected with mooring lines

to prevent drifting. For all bunkering operations the receiving vessel is fixed to the shore as

well. In case of collision the mooring lines will (partly) absorb the first impact energy.

Colliding vessels with low amount of impact energy (e.g. low mass and/or velocity) will not

have sufficient energy to rupture the mooring lines and loss of containment is not expected.

For higher impact energies the mooring lines can fail and the tensile strength of the bunker

hose could be the limiting factor for loss of containment. However coupling of flexible hose

for gas transfer are equipped with a breakaway coupling to limit the spilled volume.

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The traffic density on the waterways around the Port of Rotterdam is high. Therefore collision

scenarios are not negligible and collision of passing vessels could be seen as a credible

hazardous scenario.

4.1.2 Selection of representative scenario

In the above analyses two representative scenarios are identified as credible scenarios;

leakage at the flange face with a hole diameter between 5 – 10 mm and disconnection of the

breakaway coupling in case of a collision scenario.

For bunker locations where the traffic density is relatively high the safety distance could be

best determined with the disconnection of the breakaway coupling scenario. This selected

scenario would be applicable for the Rotterdam port area where the traffic density is high.

4.1.3 Calculation of effect of representative scenario

The results of the effects of representative scenarios are presented in the results chapter. Here

the maximum effect of the representative scenario is used to determine the safety distance.

4.2 Risk distances to vulnerable objects

The risk distances to vulnerable objects are calculated with using a Quantitative Risk

Assessment (QRA) methodology. The QRA methodology is a well-known and widely

accepted approach to determining risk levels associated with Loss of Containments (e.g.

spills). The modeling practice is described in the Dutch Reference Manual Risk Assessments

[4].

A QRA gives insight into the risks to human life of a certain activity by calculating the

potential effects of a variety of scenarios as well as considering the probability of occurrence

of these scenarios.

A QRA tries to answer five simple questions. Beside each question, the technical term is

listed for that activity in the risk assessment process:

What can go wrong? Hazard Identification

How bad? Consequence Modelling

How often? Frequency Estimation

So What? Risk Assessment

What do I do? Risk Management

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4.2.1 What can go wrong: Loss of containment scenarios

The individual risk contours will be calculated for all the 60 individual bunkering scenarios

which are defined in Figure 5. A detailed scenario definition is provided in appendix I. Note

that for each simulation scenario separate loss of containment scenarios are defined, which are

reported in the next paragraph.

During bunkering activities loss of containment (LOC) might occur due to various reasons

(e.g. external ship collision, failure of hoses) and at several locations. As mentioned earlier,

only potential LOC scenarios are taken into account during bunkering activities (i.e. failure of

hoses or tanks on bunkering vessels due to external ship collision). LOC scenarios related to

failures of storage tanks on bunkering vessels or inland bunker pontoons/tank trucks are

outside the scope of this study and therefore not considered.

The loss of containment scenarios used for the risk calculations per bunkering operation are

specified in Table 1.

Table 1: Loss of containment scenarios

Scenario Description Hole size

(mm)

1 Hose leakage 5

2 Hose leakage 25

3 Hose rupture Full bore

4 Tank leakage (only cat 1,2,5) 250

5 Disconnection of hose due to

ship collision

Full bore

The hose failure scenarios are representative for failure of hoses taken from the ARF

document [6], which gives a suggestion for typical hole size diameters of leakages that could

be taken into account when considering loss of containment during liquefied gas transfer in

hoses or arms. The full bore rupture hole size varies for each bunkering activity/scenario setup

depending on the typical hose diameter used (appendix I). For ship collisions between passing

ships and bunkering or receiving vessels additional rupture scenarios are defined. The tank

leakage scenario is only applicable in case ship collisions between passing ships and

bunkering ship are possible. For a complete definition regarding potential loss of containment

caused by ship collisions, a reference is made to Appendix II.

4.2.2 How bad? Consequence Modelling

In parallel with the frequency analysis, consequence modeling evaluates the resulting effects

if the accidents occur, and their impact on personnel, equipment and structures, the

environment or business. In chapter 3 it is commented that natural gas is flammable in a

narrow range of concentrations (5% to 15% in air). When ignited it can results in, jet,-, pool, -

or flash fire depending on the time of ignition and place of ignition. Explosions could only

occur when ignited flammable concentrations of gas are enclosed. The consequences of the

fire are mostly dependent on the loss of containment parameters and the process conditions

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during the release. The loss of containment scenarios are discussed above. The process

conditions are discussed below.

Process conditions

European design standard EN1472-2 [7] states that he maximum allowable working pressure

in a hose should not be less than 10 bar(g). According to internal sources within DNV a

typical pressure in a bunker hose is around 5-6 bar(g). For this study a generic bunkering hose

pressure of 5 bar(g) (stagnant, absolute pressure) is assumed, which is independent of type of

bunkering activity.

Pressure in the storage tank of the bunker vessel/pontoon or tank truck is estimated at 2

bar(g). The Swedish Marine Technology Forum (together with other organizations in a joint

industry project) has developed a LNG bunkering Ship to Ship procedure, which is in

principle accepted and approved by DNV [8]. The procedure states that a LNG bunker ship

may be equipped with an insulated storage tank type C for liquefied natural gas, which could

contain around 1000 m3 at 3 bar(g) and -163°C. However, internal sources within DNV state

that a typical operating pressure of LNG tanks in vessels would be closer to 2 bar(g). The

latter pressure is used for the risk calculations for any type of bunkering vessel or LNG tank

truck for that matter. A recent QRA study carried out by DNV confirms that storage pressure

of LNG in tank trucks is typically equal to 2 bar(g). Based on the above mentioned pressures,

it is reasonable to assume that the pump head is sufficient to realize the flows for each

bunkering scenario provided by the Port of Rotterdam (ranging from 30 m3/hour for category

4, minimal transfer parameters and 1500 m3/hour for category 5, maximal transfer

parameters).

A typical LNG storage and transfer temperature of -162°C is used, under the assumption that

bunkering vessels/installations have the ability to maintain the temperature constant by

handling/escaping the boil-off vapors to, for instance, a compressor and subsequently a re-

condenser for liquefaction. Tank trucks are usually equipped with double-walled tanks with

vacuum and insulation between the outer (carbon steel) and inner (aluminum) tank in order to

maintain the low temperature.

4.2.3 How often? Failure frequencies

The frequencies given in ARF are based on road or rail tanker transfer accident data and are

therefore not suitable to use for this study. The technical notes of DNV for process failure

frequencies [9], proposes a base frequency of 6.77 x 10-5

/visit for failure of loading arms

(resulting in leakages). It is the best available data and is taken from the ACDS document

from 1991 [10]. This frequency is based on liquefied gas transfers using articulated arms

(rather than transfer hoses). Furthermore, incidents reported in the ACDS document are

dominated by LPG spills rather than LNG spills. Nonetheless, the frequency is considered to

be “conservative best-estimate”, if not ‘upper bound’ for LNG transfers. The base frequency

of articulated arms is factored with the following aspects to obtain the frequency that is used

for transfer hoses:

The base frequency is per visit and must be converted into failure frequency per hour per

hose

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The base frequency is based on failure of articulated arms rather than hoses. Therefore a

factor is applied to the base frequency.

A reference is made to the Addendum [13] for the assumptions made to factor the base

frequency. The frequency distribution between of respective loss of containment scenarios is

based on the Dutch guideline for risk calculations (HARI) [4], which states that 10% of all

leaks consist of rupture scenarios. The ARF document states that 10% of all small leaks are

ruptures, which is more or less in the same order of magnitude. The frequencies of the smaller

leaks (5, 25mm) are equally distributed, which is in agreement with the ARF document.

Table 2: Loss of containment scenarios and likelihood

Scenario Description Hole size

(mm)

Frequency

(1/hour/hose)

Frequency

distribution (%)

1 Hose leakage 5 1.5 x10-6

45%

2 Hose leakage 25 1.5 x 10-6

45%

3 Hose rupture Full bore 3.4 x 10-7

10%

4 Tank leakage (only cat 1,2,5)* 250 - -

5 Disconnection of hose due to ship

collision*

Full bore - -

* Failure frequency is dependent on the level of nautical activity in the bunkering area (a

reference is made to Appendix II for a specification of these frequencies)

Intervention times of operators and EMS/ESD systems in place

Measures such as the presence the operators, emergency shutdown systems (ESD/EMS)

during transfer might mitigate discharge effects by tripping pumps or closing valves in case of

a LOC. Small intervention times, which usually vary for each mitigation measure, are

essential to significantly limit the amount of material being discharged during loss of

containment.

For operators, the intervention time is taken from HARI [4] and is equal to 120 seconds. The

following conditions have to be met to ensure an intervention time of 120 seconds by an

operator is achievable:

The operator has the possibility to visual monitor the hose during the entire transfer.

The presence of an operator is ensured by either a dead man’s switch or a procedure in the

safety management system. These measures should be inspected on a regular basis.

Manual activation of an emergency shutdown during loss of containment by an operator

should be well-documented in a procedure.

The operator should be well-trained and is also familiarized with the procedures

applicable.

The emergency shutdown button should be positioned according to applicable rules and

standards, which ensures fast, manual activation independent of release direction in case

of loss of containment.

The probability of failure on demand (PFD) of an operator is 0.1 and is also taken from HARI

[4].

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A fully automatic emergency shutdown system can detect leakages (gas detection, flow

measurements) and are able to trip pumps/close valves automatically. Operation intervention

is not necessary in case the EMS/ESD system is working properly. The PFD of automated

shutdown systems is equal to 0.001 (source: HARI). In the event that an automated shutdown

system fails, an operator is still able to initiate the shutdown manually. Intervention time is

assumed to be equal to 20 seconds for the 25mm hole and full bore rupture scenarios based on

data provided by the Port of Rotterdam. It must be noted that the exact duration of

intervention would be highly dependent on the design of the intervention system in place. It is

reasonable to assume that a small leak will take longer to detect automatically and as such, the

intervention time for the 5 mm hole size scenarios is set to 120 seconds.

An EMS/ESD system and operator with each a response time of 20 and 120 s, respectively, is

present at all bunkering vessels and installations (bunkering categories 1, 2, 4 and 5). Note

that ESD systems might not be available for tank trucks (cat 3). For category 3, LNG

bunkering with a LNG tank truck, only intervention of an operator is deemed possible.

All flexible bunkering hose are equipped with a safety breakaway coupling. The breakaway

coupling is a passive device that is located between the bunker hose and the receiving vessel.

For external impact scenarios, like ship collision, the breakaway coupling will disconnect the

bunker hose and immediately close the outflow area. The closure of the outflow area will be

mechanical driven and last for less than a second. It is reasonable to assume that the closure of

the breakaway coupling will be less than 5 seconds. Based on breakaway manufacturers’

information, the shut-off valves inside the breakaway coupling close immediately in the event

of sudden disconnection (i.e. less than 1 second). As such, 5 seconds reaction time can be

considered as a conservative estimate.

4.2.4 So What? Risk Assessment

Up to this point, the process has been purely technical, and is known as risk analysis. The next

stage is to introduce criteria which are yardsticks to indicate whether the risks are

“intolerable” or “negligible” or to make some other value-judgment about their significance.

This step begins to introduce non-technical issues of risk acceptability and decision making,

and the process is then known as risk assessment.

The Dutch risk criteria are implemented in the Decree External Safety Establishments 2011.

For this study the Individual risk criteria is used to assess the calculated risk related to LNG

bunkering activities. The Dutch Individual risk criteria states for vulnerable objects, a risk

limit value of 10-6

per year must not be exceeded. For objects with limited vulnerability, the

same value applies as an orientation norm and may be exceeded under certain conditions.

4.2.5 What do I do? Risk Management

In order to make the risks acceptable, risk reduction measures may be necessary. The benefits

from these measures can be evaluated by repeating the QRA with them in place, thus

introducing an iterative loop into the process. Detailed investigation of risk mitigation

measures and their impact of the risk calculation is not part of the scope of this study.

However chapter 0 of this rapport gives a summation of risk mitigating measures that could

be used to lower the risk related to LNG bunkering.

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5 ASSESSMENTS RESULTS

This chapter will give an indication of the safety distance for passing ships as well as the risk

distance to vulnerable objects. Both distances are given for the categories defined in chapter

2. The calculation of the distances is based on the scenarios defined in chapter 4. The

background information, e.g. weather data, ignition sources and general risk parameters, that

are used for the risk calculation are enclosed in Appendix III.

5.1 Safety distances for passing ships

This section determines the indicative safety distance for all bunkering scenarios. Thereafter

the determined safety distances are compared with the safety distances that are currently in

place in the Rotterdam port area. The section is closed with a sensitivity analysis of two key

parameters.

As stated earlier the safety distance can best be determined based on the disconnection of the

breakaway coupling scenario. The released volume and corresponding consequence is

strongly depending on the flow rate and closure time of the breakaway coupling. For the

determination of the safety distance the maximum bunker parameters are used. For the closure

time of the breakaway coupling a value of 5 seconds is considered.

The safety distance is based on the maximum effect of the selected scenario. The maximal

effect for the disconnection of the breakaway coupling is a flash fire. A flash fire could occur

when the released flammable cloud is ignited. This ignition could occur till the Lower

Flammable Limit (LFL) concentration. The weather type wherefore the flash fire contour is

calculated is stability class D and a wind speed of 5 m/s.

The safety distance is determined as the LFL distance corresponding to the released volume

of a disconnected breakaway coupling. The determined safety distances are summarised in

Table 3.

Table 3: Safety distances for the different bunker categories

Bunker category Safety distance [m] (based on LFL)

1 LNG bunkering with a small bunker vessel 61

2 LNG bunkering with a large bunker vessel 218*

3 LNG bunkering with a tank truck 49

4 LNG bunkering from a bunker pontoon 45

5 LNG STS transfer 235*

*the calculated safety distance for category 2 is based on the simultaneous disconnection of three hoses. For category 5 the safety distance is based on the simultaneous disconnection of two hoses.

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5.1.1 Discussion

This section will compare the calculated safety distances for passing ships with the current

nautical safety distances that are applicable in the Port of Rotterdam area. Hereafter the

sensitivity of the closure time of breakaway coupling is discussed. The discussion section will

be closed with a discussion about the applicability of the calculated safety distances for

“very” low nautical risk areas. The term “very” low nautical risk areas must be seen in the

context of the traffic density in the Port of Rotterdam. It may be possible that “very” low

nautical risk areas in the Port of Rotterdam are seen as normal traffic densities in smaller

ports.

Current nautical safety distances

Currently, the Rotterdam Port Management Bye-Laws (version: June 2011) [11] state that

open ignition sources, like flames or areas where the temperature equal to or higher than the

minimum ignition temperature of the substance in the cargo tank of the ship, are prohibited

within a distance of 25 metres of the ship, with some exception cases. However, it is also

suggested that this distance may have to be extended for ship of a specialized nature such as

gas tankers. Furthermore, article 4.8 of the Port Bye-Laws states that activities related to the

operation of the ship or objects on the ship have to be performed at least 25 metres away from

dangerous substances or combustible material.

Existing shipping regulations BPR [12] enforce a minimum passing distance of 50 metres

between ships carrying specific explosive substances and other ships, unless ships are passing

each other in opposite directions.

A Swedish bunkering procedure [8] states that bunkering areas on both ships (bunkering

vessel and receiving vessel) should be EX-classified and restricted area during bunkering. The

size of the EX-zone shall be according to class rules for gas-dangerous space and 10 m

horizontally on each side of the receiving ship bunker station plus the whole shipside

vertically.

The calculated safety distance for categories 1, 3 and 4 are in line with the nautical safety

distances that are prescribed in the existing Dutch shipping regulation BPR and the Belgian

shipping regulations. However, the safety distances are roughly a factor two higher than the

distances in the Rotterdam Port Management Bye-Laws. The calculated safety distances for

the categories 2 and 5 are significantly larger than the nautical safety distances that are

prescribed in the existing Dutch inland shipping regulation and the distances in the Rotterdam

Port Management Bye-Laws. The relatively large safety distances that are found for those

categories restrict the LNG bunkering of large vessels in area with intensive nautical traffic. It

may not give restriction on LNG bunkering activities in area where lower nautical activities

take place and collision scenario are less credible. The sensitivity of the nautical activities is

investigated in the following section.

Sensitivity to Nautical activities

For “very” low nautical risk area the collision of passing ships into the bunker operation may

not be a credible scenario. In this case it would be better to selected the leakage at the flange

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face with a hole diameter between 5 – 10 mm. The driving force of this scenario is the

pressure during the bunker operation. In section 4.2.2 a pressure of 5 bar(g) is considered

during the bunkering activity. For area where the nautical risk is not significant the

determined safety distance for each category is 20 meter. From the assessment of the nautical

activities is found that the safety distances could theoretically be reduced to 20 meter in case

collision scenarios are not significant. However the safety distances cannot be less than the

safety distances that is prescribed in the Dutch shipping regulations.

Sensitivity of breakaway coupling closure time

The closure of the outflow area of the breakaway coupling will be mechanically driven and

will be accomplished in less than a second. However for the determination of the safety

distances the closure time is conservative estimated on 5 seconds. The effect of the closure

time of the breakaway coupling on the safety distance is investigated for the category 1 and 2.

The results of this investigation are shown in Figure 7, where the left figure represents

category 1 and the right figure category 2. The results of the sensitivity analysis show that the

closure time of the breakaway coupling do not have a major effect within the investigated

time range. The conservative time of 5 seconds to close to breakaway coupling does not have

a significant influence on the safety distance, which means that the determined safety distance

cannot be significantly reduced by quicker closure of the breakaway coupling.

Figure 7: Safety distances for different closure time of the breakaway coupling; category

1 (left), category 2 (right)

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5.2 Risk distances to vulnerable objects

The distances to the 10-6

/year individual risk (IR) contours for all bunkering scenarios defined

in paragraph 4.2.1 are visually displayed in the figures in this section. The distance to the 10-

6/year individual risk (IR) contours for the three levels of bunker activities per year (upper

bound, mean and lower bound) are visualised with a dot. For practical reasons the dots are

interconnected with a fitted line. The line between the calculated results does not give the

exact distance to the 10-6

/year risk contour and should be used with care. More accurate

results could be obtained in case more bunker activities per category are calculated. However

this is not part of the scope of this project.

It is important to mention that the results are based on the maximum and minimum parameter

set as discussed earlier in section 2.4. The maximum parameter set is a summation of

conservative assumptions (e.g. maximum flow, maximum diameter, maximum bunker time,

maximum number of hoses and the most conservative ignition methodology). This means that

the maximum parameter set gives an upper bound of expected risk level. The minimum

parameter set is based on more average parameters and does not necessary represent the

minimum / lower bound risk level. A detailed overview of all maximum and minimum

parameters per bunker category is found in appendix I.

5.2.1 Category 1 - LNG bunkering with a small bunker vessel


risk level for the different simulation scenarios from category 1 are

given in Figure 8.

From Figure 8 can be observed that for the maximum parameter set the distance to the 10-6

/year risk level differs for the intense and the less dense nautical traffic areas. The intense

nautical traffic area does results in a higher distance to the 10-6

/year risk level. In the lower

range of the nautical activities, there is no significant difference in distance. This means that

the differences in distance to the 10-6

/year risk level for the low and very low nautical traffic

area negligible. For the same figure could be seen that for minimum parameter set there is a

difference in distance to the 10-6

/year risk level for each of the different nautical traffic area.

In this parameter set a reduction of the nautical activities decreases the distances to the 10-

6/year risk level with 50 -60 %.

The individual risk contours for maximum parameters are shown in Figure 9 where the orange

line represents the 10-6

/year risk contour. The purple and light blue lines in Figure 9 represent

the 10-5

/year and 10-4

/year risk contours. It is seen that there is only a small difference in

distance between the 10-6

/year and 10-5

/year risk contour. The individual risk contours for

minimal parameters are shown in Figure 10, where the same colours represent the different

risk levels.

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Figure 8: LNG bunkering toolkit for category 1

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Figure 9: IR contour for 5 bunker activities per day in cat 1, maximal parameters in intensive nautical risk traffic areas (left), low

nautical traffic areas (middle) and very low nautical traffic areas (left). The orange line represents the 10-6

/year risk contour.

Figure 10: IR contour for 5 bunker activities per day in cat 1, minimal parameters in intensive nautical risk traffic (left), low nautical

traffic (middle) and very low nautical traffic (left). The orange line represents the 10-6/year risk contour.

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5.2.2 Category 2 - LNG bunkering with a large bunker vessel


/year risk level for the different nautical scenarios from category 2 are

shown in Figure 11. From the figure can be observed that for the maximum parameter set the

10-6

risk level do not significantly changes over the nautical scenarios. From this observation

it can be concluded that the nautical activities does not have a significantly contribution the

individual risk level of 10-6

/year. However for the minimum parameter set, changes in

distance could be observed. In this parameter set a reduction of the nautical activities

decreases the distances to the 10-6

/year risk level with 37%.

In the intense nautical traffic scenario with minimum parameters the individual risk level of

10-6

/year is dominated by the collision scenario where a 250 mm hole is formed in hull of the

large bunker vessel. The remaining risk is not related to collision scenarios and caused by full

bore rupture of the bunkering hose. For low nautical traffic areas the collision scenarios are

less contributing to the individual risk level of 10-6

/year, but still have a significant

contribution. For the very low nautical traffic areas the collision scenarios are negligible.

The individual risk contours for maximum parameters are shown in Figure 12 where the

orange line represents the 10-6

/year risk contour. The purple and light blue lines in Figure 12

represent the 10-5

/year and 10-4

/year risk contours. It is seen that there is only a small

difference in distance between the 10-6

/year and 10-5

/year risk contour. The individual risk

contours for minimal parameters are shown in Figure 13, where the same colours represent

the different risk levels.

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Figure 12: IR contour for 1 bunker activities per 2 days in category 2, maximal parameters in intensive nautical traffic areas (left), low

nautical traffic areas (middle) and very low nautical traffic areas (left). The orange line represents the 10-6

/year risk contour.

Figure 13: IR contour for 1 bunker activities per 2 days in cat 2, minimal parameters in intensive nautical traffic areas (left), low

nautical traffic areas (middle) and very low nautical traffic areas (left). The orange line represents the 10-6/year risk contour.

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5.2.3 Category 3 - LNG bunkering with a tank truck



given in Figure 15

The difference in the distances to the 10-6

/year risk contour for intensive, low and very low

nautical traffic areas that could be observed from Figure 15 is negligible. In this category

there is no scenario where a possible LOC from the bunker vessel could occur. Bunkering

operation is performed from a truck. The collision scenarios in this category could only results

in rupture of the bunker hose. The LOC scenarios from the truck are not considered within the

scope of this study.

For most of the scenarios the 10-6

/year risk level is mainly caused by a combination of rupture

and leakages through a 25 mm hole in the bunker hose. The risk caused by the rupture of the

bunker hose during collision is negligible to the risk caused by rupture and leakage of the

bunker hose during bunkering. With other words, the nautical activities in the surrounding of

the bunker location do not have a significant influence on the 10-6

risk contour.

Figure 14 shows the individual risk contours for maximum and minimum parameters at an

intensive nautical traffic area.

Figure 14: : IR contour for 1826 bunker activities in cat 3, intensive nautical traffic area

, maximal parameters in (left), minimum parameters intensive nautical traffic area

(right)

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5.2.4 Category 4 - LNG bunkering from a bunker pontoon



given in Figure 16.

The risk drivers of category 4 do show a huge similarity to category 3. For most of the

scenarios the 10-6

/year risk level is mainly caused by a combination of rupture and leakages

through a 25 mm hole in the bunker hose. The LOC scenarios from equipment on the bunker

pontoon are not considered within the scope of this study. It is expected that a separate risk

assessment is performed for the permit application of the bunker pontoon and its equipment.

Therefore collision scenarios that resulted in LOCs of the storage tank of the bunker pontoon

are not considered.

The risk caused by the rupture of the bunker hose during collision is negligible to the risk

caused by rupture and leakage of the bunker hose during bunkering. This results in a limited

difference between the distances to the 10-6

/year risk contour for the different nautical traffic

areas. With other words, the nautical activities in the surrounding of the bunker location do

not have a significant influence on the 10-6

risk contour.

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5.2.5 Category 5 - LNG STS transfer



given in Figure 17.

The risk that is observed for the maximum parameter set seems to be independent of the

nautical traffic area. For the minimum parameter set there is a significant difference between

the three nautical areas. In general it can be concluded that the risk drivers of category 5 do

show a huge similarity to risk driver in category 1 and 2. For most of the scenarios the 10-

6/year risk level is mainly caused by the collision scenario where a 250 mm hole is formed in

hull of the large bunker vessel.

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5.2.6 Discussion

From the previous sections it could be concluded that for the maximum parameter set the

distance to the 10-6

risk level do not significantly changes over the nautical scenarios. The

bunkering of LNG with small bunker vessel, category 1, is an exception where the intense

nautical traffic area differs from the low and very low nautical traffic areas. Despite the small

difference in distance between the low and very low nautical traffic areas, the 10-6

risk level

of the low nautical risk area is dominated by the collision scenario where a 250 mm hole is

formed in hull of the small bunker vessel.

For the maximum parameter set of category 1 and 2 it is found that the difference in distance

between the 10-6

and 10-5

risk level is small. A detailed analysis of the risk drives reveals that

the 10-5

risk level is dominated by the hose rupture scenario where the ESD system works

probably. This result clarifies why the distances of the low and very low nautical traffic areas

do not significantly differ despite that they do not share the same risk driver.

The maximum parameter set is based on the free field method which means that flammable

clouds ignite when the lower flammable limit is reached. Table 4 shows the effect distances

(Lower Flammable Limit (LFL)) of the different LOC scenarios from category 1. The largest

effect distances are found for the collision scenario where a 250 mm hole is formed in hull of

the small bunker vessel.

Table 4: Effect distances LOC scenarios category 1 (likelihood is not taken into account)

Scenario Effect distance [m]

F 1.5m/s D 5m/s

Full bore rupture ESD works 416 179

Full bore rupture due to collision 226 136

25 mm hole ESD works 93 67

250 mm hole in bunker vessel 595 205

The minimal parameter set is based on specific ignition sources that are present in the

surrounding of the bunkering activity. In most of the cases the cloud is ignited before it

reaches is LFL distance. Figure 18 shows the risk distribution for 5 bunker activities per day

in category 1. The figure shows that for the minimal parameters the 10-6

/year risk level for

intense and low nautical traffic areas is dominated by the collision scenario where a 250 mm

hole is formed in hull of the small bunker vessel. In the very low nautical traffic area the 10-

6/year risk level is dominated by the scenario where the hose is ruptures and the ESD system

works properly. The same trends can be seen for bunker activities in category 2.

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Figure 18: Risk distribution of 5 bunker activities per day in cat 1 for three different

risk levels; left, intense nautical traffic; middle low nautical traffic, right; very low

nautical traffic

For the bunker categories 3 and 4 is observed that the distance to the 10-6

risk level do not

significantly changes over the nautical scenarios. For the maximum parameter set of category

3 and 4 it is found that the distance to the 10-6

risk level is mainly caused by the hose rupture

scenarios. An increase of the number of bunker activities shifts the risk driver to scenarios

that are less likely to occur. For instance; for the lower bound activities the 10-6

/year risk level

is mainly caused by the hose rupture scenario where the ESD system works probably, while

for the higher bound activities the 10-6

/year risk level is mainly caused by the hose rupture

scenario where the ESD system fails to work.

The maximum parameter set is based on the free field method which means that flammable

clouds ignite when the lower flammable limit is reached. Table 5 shows the effect distances

(Lower Flammable Limit (LFL)) of the different LOC scenarios from category 3. The largest

effect distances are found in case of rupture of the bunker hose.

Table 5: Effect distances LOC scenarios category 3 (likelihood not taken into account)

Scenario Effect distance [m]

F 1.5m/s D 5m/s

Full bore rupture ESD works 92 63

Full bore rupture due to collision 59 49

25 mm hole ESD works 87 61

The minimal parameter set is based on specific ignition sources that are present in the

surrounding of the bunkering activity. In most of the cases the cloud is ignited before it

reaches is LFL distance. The left side of Figure 19 shows the risk distribution for 1 bunker

activities per week in category 3. The right side shows the risk distribution for 10 bunker

activities per day.

The figure shows that for the minimal parameters and 1 bunker activity per week the 10-6

/year

risk level is dominated by leakage through a 25 mm hole. For the lower risk levels, (10-8

/year)

the dominant scenarios are shifted to the hose rupture scenarios. The figure also shows that

for an increase in bunker activities (10 bunker activities per day) the dominant scenarios that

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contribute to the 10-6

/year risk level are shifted to the hose rupture scenarios. The same trends

can be seen for bunker activities in category 4.

Figure 19: Risk distribution in cat 3 for two different bounds; left, lower bound (1

bunkeractivity a week); right upper bound (10 bunkeractivities a day)

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RISK MITIGATION AND FURTHER RESEARCH

This chapter gives an overview of risk mitigation measures that can improve the safety

performance of the LNG bunker operations. Two set of measures are given:

General mitigation measures that will ensure safe bunker operations,

More study specific mitigation measures and topics for further research will be given to

ensure safe LNG bunkering in the future.

5.3 General risk mitigation measures

Risk levels could be reduced by two different sets of mitigation measures; mitigated measures

that reduce the consequence of the loss of containment and mitigated measures that reduce the

likelihood that loss of containment can occur.

Mitigated measures should be focused on the prevention of loss of containment (LOC).

Prevention of LOC scenario is often accomplished by technical and procedural measures. For

bunkering of LNG the technical measures that could reduce the risk are:

The technical integrity of the bunkering hose is secured by inspection. It is recommended

that the bunker hose is visually inspected before each bunkering operation;

Purging of bunker hose with for instance nitrogen before bunkering operations. Purging of

transfer hose in common practice in industry for transferring large amounts of LPG.

Leakages and coupling errors could be noticed when purging operations are performed;

Specify rules sets for the distance between the hull of the bunker vessel and the LNG

cargo tank for inland vessels. From the risk analysis of bunkering with inland vessels is

concluded that the LOC of the cargo tank caused by collision is the main contributor the

10-6

risk level.

Additional collision protection of hull on LNG bunker vessels

More procedural measures that could reduce the risk are:

Training of bunker operators. The safety aspects of bunkering of LNG can be compared

with the bunkering of convention diesel. Bunkering personnel must be aware of the risks

associated with LNG operations;

Another procedural measure to prevent LOC scenarios is the bunker procedure which

should be followed during the preparation and bunkering operation itself. At this moment

most of the ports do not have a bunker procedure for bunkering of LNG. Before bunkering

activities can be realised a bunkering procedure must be in place;

Nevertheless, loss of containment could occur. If LOC occurs the consequences of the release

must be kept as minimal as possible. Technical measures are often in place to minimise the

release volume or/and consequence of the release:

The release volume can be minimised by a proper ESD system that quickly detects the

leak and shutdown the pumps and valves to prevent further outflow. The detection time of

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leakage is often depending on the amount of gas detectors and or/sensitivity of the excess

flow valve. For LNG bunkering operations it could be recommended to install a ESD1

and ESD2 system where:

- ESD 1 stop transfer pumps and compressors, hence providing a quick and safe

means of stopping the transfer and isolating bunker vessel and recipient vessel

systems

- ESD 2 gives an additional level of protection by providing for a rapid

disconnection of the transfer hose / loading arms from the ship. ESD 2 could, for

example, be used if there is a fire on one of the ships (bunker vessel or recipient

vessel).

The domino effect to the bunker vessel and receiving ship can be minimised by equipping

with a water spray or curtain. The water curtain sprays the affected area with water to

prevent the deck steel from cracking. Another advantage is that the water curtain will

dilute the released LNG cloud and lower the concentration of gas in the air. This measure

reduces the distances at which the cloud is flammable.

5.4 Study specific

The risk drivers for the different bunker categories are identified in chapter 5. Roughly two

different risk drivers are identified:

Category 1, 2 and 5; ship collision results in a loss of containment of the LNG cargo

(bunker) tank.

Category 3 and 4; rupture of the bunkering hose and leakage through a 25 mm hole

For each of the risk drivers suggestions for mitigating measures or suggestions for further

research will be given below:

Nautical risk

The individual risk level of 10-6

/year is for the category 1 and 2 activities mainly caused by

the scenario where ship collision results in a loss of containment of the LNG cargo (bunker)

tank. This conclusion is application for both intensive and low nautical traffic areas.

The nautical risk calculations are based on a model that predicts the collision frequency. The

predicted collision frequency is used as a starting point for the assessment of loss of

containment frequency. The model predicts for the intensive nautical traffic area a collision

frequency around 1.4 x 10-2

per year. For the low nautical traffic area the collision frequency

is estimated at 3.8 x 10-3

per year. For a more detailed representation of the nautical risk these

collision frequencies must be compared with the actual collision frequency in the Port of

Rotterdam area.

The calculated loss of containment frequency from LNG cargo tanks is strongly influenced by

the layout of the bunker vessel. The key design parameters are the strength of the hull and the

distance between the cargo tank and the hull of the bunker vessel. At this moment no inland

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bunker vessels do exist and estimation of the detailed technical layout of the vessel is

difficult. For estimation of a more accurate loss of containment frequency, detailed

investigation between the impact energy and the hole formation in cargo tanks of inland

bunker vessels is necessary. The conclusion of this detailed investigation could lower the

nautical risk significantly.

Another option is to prescribe a minimum distance between the LNG cargo tank and the hull

of the bunker vessel. For seagoing vessel this prescription is already in place: a minimum

distance between the cargo tank and the hull is prescribed in the class rules of the

classification societies. As most of the bunker vessels will be inland vessels class rules do not

apply.

A fourth option could be to lower the nautical risk by procedural measures. Although speed

limitation of passing vessels and other procedural measures are not practical, they do lower

the nautical risk significantly.

Bunkering risk

The individual risk level of 10-6

/year for the category 3 and 4 activities is mainly caused by

rupture of the bunkering hose and leakage through a 25 mm hole. Risk reduction measures

must be applied to the bunker activity itself since collision risk is negligible. The measures

should be focused on limiting the amount of outflow or limiting the frequency at which the

loss of containment can occur.

The frequency at which rupture of the bunkering hose by external impact occur can for

example be lowered by mitigation measures such as the application of a safety net above the

bunker operation to mitigate the risk of falling objects (e.g. container couplings) or by

limiting the number of maintenance and/or lifting activities in the surrounding of the bunker

activity.

The consequences of a release could be lowered by quick closure of valves and pumps in case

of a loss of containment. Quick detection of the loss of containment is a key parameter in

reduction of the possible consequences. For most of the categories in this study is assumed

that an EMS/ESD system does have a response time of 20. For category 3, LNG bunkering with a

LNG tank truck, it is assumed that only intervention measures of an operator are possible. In this

case a response time of 120 seconds is taken into account. This response time could be

significantly lowered if an automatic system is in place.

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6 CONCLUSIONS

The Port of Rotterdam has identified various LNG bunker activities in a port area. Those

activities can be grouped in five different categories:

1) LNG bunkering from bunker barges to small vessels

2) LNG bunkering from small scale LNG carriers to seagoing vessels




DNV has calculated the indicative safety distances for the determination of exclusion zones

related to passing vessels during LNG bunkering activities. It is found that the calculated

safety distance for categories 1, 3 and 4 are line with the nautical safety distances that are

prescribed in the existing Dutch shipping regulation BPR. The calculated safety distances for

the categories 2 and 5 are significantly larger than the nautical safety distances that are

prescribed. The relatively large safety distances that are found for those categories could

enforce additional rules to the LNG bunkering of large vessels in area with intensive nautical

traffic. It may not give restriction on LNG bunkering activities in area where lower nautical

activities take place and collision scenario are less credible.

DNV calculates the risk distances to vulnerable objects for the Dutch risk criteria of 10-6

/year.

The risk distances that are found for the different categories vary from 10 to 510 meter,

depending on the category, bunker parameters, ignition method and number of bunker

activities. The risk distance for the categories 1, 2 and 5 is mainly caused by the scenario

where ship collision results in a loss of containment of the LNG cargo (bunker) tank. It is

found that lowering of the nautical activities in the bunkering area may reduce the risk

distance. For areas were (very) low nautical activities take place the risk distance is driven by

the rupture of the bunkering hose and leakage through a 25 mm hole. It is found that the risk

distance of category 3 and 4 is independent of the nautical activities because the distance is

driven by the rupture of the bunkering hose and leakage through a 25 mm hole.

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7 REFERENCES

[1] DNV LNG Blog; http://blogs.dnv.com/lng/2011/10/lng-bunkering-operation-

caught-on-tape/

[2] European Argeement concerning the International Carriage of Dangerous Goods by

Inland Waterways (ADN), United Nations Economic Commission for Europe

(UNECE) and the Central Commission for the Navigation of the Rhine (CCNR),

Geneva ,2008

[3] Accord européen relatif au transport international de marchandises Dangereuses par

Route (ADR), United Nations Economic Commission for Europe (UNECE),

Geneva, 1968

[4] Pioneer Knutsen, website Vuyk Engineering Rotterdam B.V.

[5] Reference Manual Bevi Risk Assessments version 3.2, National Institute of Public

Health and the Environment (RIVM), Bilthoven, 2009.

[6] ARF document T14 rev 1; Process equipment failure frequencies for transfer

equipment , Det Norske Veritas, Høvik, 1999.

[7] EN1472-2: Installation and equipment for liquefied natural gas – Design and testing

of marine transfer systems – Part 2: Design and testing of transfer hoses, European

Committee for standardization (CEN), Brussels, 2008

[8] LNG ship to ship bunkering procedure, Swedish Marine Technology forum | Linde

Cryo AB | FKAB Marine Design | Det Norske Veritas AS | LNG GOT | White

Smoke AB , Sweden,

[9] DNV process failure frequencies, standardized offshore leak frequencies, technical

note 14, D.23 loading arms, rev0, Det Norske Veritas, Høvik, 2011

[10] ACDS; Major Hazard Aspects of the Transport of Dangerous Substances, Advisory

Committee on Dangerous Substances, Health & Safety Commission, HMSO Major

hazard aspects of the transport of dangerous substances, 1991.

[11] Rotterdam Port Management Bye-Laws (version juni 2011), ‘Part A – Bulk Liquids

– General – Physical checks-ups, section 37: naked light regulations are observed,

Port of Rotterdam, Rotterdam, 2011

[12] Inland shipping police regulations (‘Binnenvaartpolitieregelement’), article 6.18,

subsection 2, Ministry of infrastructure and environment, the Hague, 2012.

[13] Addendum; Input assumptions for risk calculations bunkering study Port of

Rotterdam, Det Norske Veritas, Rotterdam, 1999.

http://blogs.dnv.com/lng/2011/10/lng-bunkering-operation-caught-on-tape/

http://blogs.dnv.com/lng/2011/10/lng-bunkering-operation-caught-on-tape/

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APPENDIX I SCENARIOS

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A high-level overview of all calculated scenarios is given in Figure 5, section 2.4. This

appendix provides more detailed specifications on the applied LNG transfer parameters used

for each scenario. Some transfer parameters vary per bunkering category and are divided into

two extremes: minimal and maximal. Only the transfer parameters that vary per scenario are

given in Table 6 (e.g. hose diameter, pump rate, number of hoses used per transfer, bunkering

duration per transfer). For a complete overview of all used transfer parameters a reference is

made to the addendum [13].

Table 6: Detailed bunkering scenario definition – transfer parameters

Scena

rio

Nautical

activities

Transfer

parameters

Ignition

method

Hose

diameter

(inch)

Single

pump

rate

(m3/hou

r)

Number

of hoses

used

Duration

per

transfer

(hours)

Category 1 – LNG bunkering with a small inland LNG bunker vessel

1.1 Intensive Maximal Free field 5 500 1 2



1.4 Intensive Minimal Ignition

sources

3 80 1 1


sources

3 80 1 1


sources

3 80 1 1

1.7 Low Maximal Free field 5 500 1 2



1.10 Low Minimal Ignition

sources

3 80 1 1


sources

3 80 1 1


sources

3 80 1 1

1.13 Very Low Maximal Free field 5 500 1 2



1.16 Very Low Minimal Ignition

sources

3 80 1 1


sources

3 80 1 1


sources

3 80 1 1

Category 2 – LNG bunkering with a large LNG bunker vessel



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Scena

rio

Nautical

activities

Transfer

parameters

Ignition

method

Hose

diameter

(inch)

Single

pump

rate

(m3/hou

r)

Number

of hoses

used

Duration

per

transfer

(hours)



sources 5

500 3 6.7


sources 5

500 3 6.7


sources 5

500 3 6.7





sources 5

500 3 6.7


sources 5

500 3 6.7


sources 5

500 3 6.7





sources 5

500 3 6.7


sources 5

500 3 6.7


sources 5

500 3 6.7

Category 3 – LNG bunkering with a LNG tank truck

3.1 Intensive Maximal Free field 3 80 1 2.5



3.4 Intensive Minimal

Ignition

sources

3 40 1 1


Ignition

sources

3 40 1 1


Ignition

sources

3 40 1 1

3.7 Low Maximal Free field 3 80 1 2.5



3.10 Low Minimal

Ignition

sources

3 40 1 1

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Scena

rio

Nautical

activities

Transfer

parameters

Ignition

method

Hose

diameter

(inch)

Single

pump

rate

(m3/hou

r)

Number

of hoses

used

Duration

per

transfer

(hours)

3.11 Low Minimal

Ignition

sources

3 40 1 1

3.12 Low Minimal

Ignition

sources

3 40 1 1

3.13 Very Low Maximal Free field 3 80 1 2.5



3.16 Very Low Minimal

Ignition

sources

3 40 1 1


Ignition

sources

3 40 1 1


Ignition

sources

3 40 1 1

Category 4 – LNG bunkering from a bunkerpontoon





sources

3 30 1 1


sources

3 30 1 1


sources

3 30 1 1





sources

3 30 1 1


sources

3 30 1 1


sources

3 30 1 1




4.16 Very Low

Minimal Ignition

sources

3 30 1 1

4.17 Very Low

Minimal Ignition

sources

3 30 1 1

4.18 Very Low Minimal Ignition 3 30 1 1

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Scena

rio

Nautical

activities

Transfer

parameters

Ignition

method

Hose

diameter

(inch)

Single

pump

rate

(m3/hou

r)

Number

of hoses

used

Duration

per

transfer

(hours)

sources

Category 5 – Ship to ship LNG transfer





sources

5 1500 1 2.7


sources

5 1500 1 2.7


sources

5 1500 1 2.7





sources

5 1500 1 2.7


sources

5 1500 1 2.7


sources

5 1500 1 2.7




5.16 Very Low

Minimal Ignition

sources

5 1500 1 2.7

5.17 Very Low

Minimal Ignition

sources

5 1500 1 2.7

5.18 Very Low

Minimal Ignition

sources

5 1500 1 2.7

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APPENDIX II NAUTICAL RISK ASSESMENT OF MOORED LNG BUNKERVESSEL

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NAUTICAL RISK ASSESMENT OF THE MOORED LNG

BUNKERVESSEL

When the small inland or large LNG bunker vessel is moored and bunkering activities are

ongoing, various accidental scenarios can be identified. For the scenario that a passing vessel

collides with the docked LNG bunker vessel a detailed and quantitative assessment is

performed using a DNV Energy Model. Bunkering activities do always take place in port

areas where ship velocities are still relatively small. To enable a LNG bunker infrastructure

LNG bunkering along waterways could be a possibility as well. Along the (inland) waterways

velocities could be high.

To assess the nautical risk an intensive, low and very low nautical traffic area is considered.

All three scenarios are based on estimations of maritime traffic on three representative

scenarios. This appendix will determine the loss of containment frequency of three identified

nautical traffic areas (intensive, low and very low nautical traffic). Figure 20 shows the three

different nautical traffic areas.

Figure 20: Nautical traffic areas

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Methodology

The risk analysis of the moored LNG bunker vessel is performed using DNV`s methodology

for probabilistic hole assessment in moored LNG Carrier cargo tanks due to ship collisions.

The methodology has been based on a DNV research program where the damage extents have

been estimated for different ship sizes as a function of striking angles and bow types. This

DNV energy model approach is developed to analyse only the risk of a moored LNG Carrier,

since this activity is expected to be most relevant with regards to potential external risk

exposure on land.

The methodology is divided into a frequency and a collision part. In the frequency assessment

“average maximum impact energy” is estimated with corresponding frequency. In the

collision assessment experience data from previous studies is used to transform the “average

maximum impact energy” to probability distribution for size impact damages.

This applied probabilistic approach for collision risk assessment is visualized in the figure

below.

Figure 21: Probabilistic approach for collision risk assessment

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Frequency Assessment

Estimation of maximum impact energy

In the frequency assessment the vessel traffic passing a bunkering LNG vessel is dived into

six classes of vessels, given by the properties of the passing vessels. These six classes are:

Bulb bow vessels with length below 120 meters

Raked bow vessels with length below 120 meters

Bulb bow vessels with length between 120 and 180 meters

Raked bow vessels with length between 120 and 180 meters

Bulb bow vessels with length above 180 meters

Raked bow vessels with length above 180 meters

For each of the classes the vessels are grouped according to their type and displacement. The

impact energy is estimated for each group and then summarised to weighted “average impact”

energy for the vessel class, which is used as input in the collision assessment.

Probability of collision

The methodology assumes there are two dominant failure modes leading to collision:

Steering gear failure

Black out

The probabilities for steering gear failure have been found from DNV`s internal database

RiskNet.

From this reference the following basis figures are applied:

Steering gear failure : 8.3 x10-7

per nautical mile

Black-out : 4.8 x10-6

per nautical mile

The probability for one of these failure modes leading to an actual impact with an LNG

Carrier dock at a berth is assumed to be a function of the geometric probability of hitting the

docked carrier and the time available to implement mitigating actions.

Geometric probability of hitting a passing carrier

The geometric probabilities are a function of the length of the potentially stroked LNG

Carrier, the distance to passing shipping lanes and physical obstacles such as breakwaters or

shallows.

Time to implement mitigating actions

It is assumed that the probability of having time to implement mitigating action has a

“Weibull” distribution. This means that the probability for implementing actions is very low

up to a given time, where the probability increases sharply, to a time where very high

probability that preventive action is implemented successfully. The typical actions that are

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implemented to mitigate striking incidents are assessed to be emergency anchoring, running

engine full astern and re-powering of the vessel.

In the methodology it is assumed that the probability of implementing mitigating actions starts

to rise sharply around an average one minute. This is represented by a “Weibull” distributing

with mean value of 60 seconds and a standard deviation of 31 seconds.

The time available to implement mitigating actions are a function of the vessels speed and the

distance from the shipping lanes and the potentially stroked vessel.

Output from the frequency assessment is a probability for striking impact in to the LNG

bunker vessel per vessel category with corresponding “average maximum impact energy”.

Collision Assessment The relationship between the striking angles, the ship speeds and the absorbed deformation

energy of the colliding ships is determined by,

In the above formula the effect of striking location against the LNG vessel, x2, is taken into

account. A mean value of x2 = 0.225*LLNG is assumed.

For each of the selected striking ship sizes of L = 90 m, L = 140 m and L = 230 m the

absorbed deformation energy has been calculated for a series of impact cases where the

apparent striking angles and the ship speeds have been varied.

The speed distribution of impacting vessels is adjusted relatively to the impact speed, based

on the speed distribution found from the HARDER study, for impact at the time of collision.

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Hence, the energy is distributed, with the “average max impact energy” from the frequency

assessment as the maximum impact energy and the downwards. Further, effect of the impact

angle is included, where impact angels of 0 to 22,5 degrees and 167 to 180 degrees are

assumed only to give glancing impacts, with no potential for cargo containment penetration.

The remaining impact angels are grouped and represented in the structural model with impact

angels of 45 degrees and 90 degrees.

Results An estimation of vessel movements in the intensive, low and very low nautical traffic area

was provided by the Port of Rotterdam. The DNV energy model however also needs

additional input which is summed in the nautical part of appendix I.

The collision frequency per category is calculated in the frequency assessment. For the

intensive nautical traffic area it is found that the total collision frequency is around 1.4 x 10-2

per year. The total collision frequency for the low and very low nautical risk area is around

3.8 x 10-3

per year and 6.8 x 10-5

per year. Details about the segmentation of collision

frequencies per category are given in Table 7 till Table 9.

Table 7: Collision frequency of different types of vessels at intensive nautical traffic location

Vessel type Collision

frequency

[/year]

Average

maximum impact

energy [MJ]

Bulb bow vessels with length below 120 meters 8.0 x 10-3

59

Raked bow vessels with length below 120 meters 5.3 x 10-3

59

Bulb bow vessels with length between 120 - 180

meters

7.2 x 10-3

567

Raked bow vessels with length between 120 - 180

meters

4.8 x 10-3

567

Bulb bow vessels with length above 180 meters 1

1

Raked bow vessels with length above 180 meters 1

1

Table 8: Collision frequency of different types of vessels at low nautical traffic location


frequency

[/year]

Average

maximum impact

energy [MJ]


41


41


meters

6.9 x 10-6

91


meters

4.6 x 10-6

91

Bulb bow vessels with length above 180 meters 3.4 x 10-6

227

Raked bow vessels with length above 180 meters 2.3 x 10-6

227

1 On this representative waterway no vessel longer than 180 meters are recorded

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Table 9: Collision frequency of different types of vessels at very low nautical traffic location


frequency

[/year]

Average

maximum impact

energy [MJ]


23


23


meters

6.9 x 10-7

91


meters

4.6 x 10-7

91

Bulb bow vessels with length above 180 meters 5.2 x 10-7

227

Raked bow vessels with length above 180 meters 3.4 x 10-7

227

It must be noted that the collision frequencies are highly theoretically and may not represent

the actual collision frequency in the Port of Rotterdam area. The collision frequency also

represents all theoretical collision and not only the collisions which will results in a loss of

Containment of LNG. The probability of Loss of containment is made in the collision

assessment.

The frequency assessment is followed up by the collision assessment where the probabilities

of certain indentation depths into a moored LNG Bunker vessel are calculated. Graphical

representations of indentation depths for the three nautical traffic areas are given in Figure 22.

More details regarding the indentation depths for the nautical traffic areas are found in Table

10 till Table 12.

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Figure 22: Probability of indentation for intensive,

low and very low nautical traffic areas

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Table 10: Probability of indentation for intensive nautical traffic areas

Representative

length [m]

Bow

type

Type

ID

Indentation depth [m]

0.5-1.0 1.0-1.5 1.5-2.0 2.0-3.0 3.0-4.0 4.0-5.0

90 Bulb 1.1 9.2x10-4

2.3x10-4

1.5x10-4

1.5x10-4

3.8x10-5

3.8x10-5

90 Raked 1.2 7.4x10-4

1.1x10-4

5.3x10-5

1.3x10-4

2.7x10-5

0

150 Bulb 2.1 7.2x10-5

0 1.4x10-5

0 1.4x10-5

0

150 Raked 2.2 4.8x10-5

0 9.5x10-6

0 9.5x10-6

4.8x10-6

240 Bulb 3.1 2

2 2 2 2 2

240 Raked 3.2 2

2 2 2 2 2

Total 1.8x10-3

3.4x10-4

2.3x10-4

2.9x10-4

8.9x10-5

4.3x10-5

Table 11: Probability of indentation for low nautical traffic areas

Representative

length [m]

Bow

type

Type

ID


0.5-1.0 1.0-1.5 1.5-2.0 2.0-3.0 3.0-4.0 4.0-5.0

90 Bulb 1.1 2.7x10-4

9.1x10-5

4.6x10-5

3.4x10-5

1.1x10-5

0

90 Raked 1.2 2.3x10-4

3.0x10-5

3.0x10-5

1.5x10-5

0 0

150 Bulb 2.1 1.4x10-7

6.9x10-8

6.9x10-8

6.9x10-8

1.4x10-7

3.4x10-8

150 Raked 2.2 5.5x10-7

1.4x10-7

4.6x10-8

9.2x10-8

4.6x10-8

4.6x10-8

240 Bulb 3.1 6.9x10-8

6.9x10-8

0 6.9x10-8

0 3.4x10-8

240 Raked 3.2 4.6x10-8

4.6x10-8

2.3x10-8

2.3x10-8

4.6x10-8

4.6x10-8

Total 5.0x10-4

1.2x10-4

7.6x10-5

5.0x10-5

1.2x10-5

1.6x10-7

Table 12: Probability of indentation for very low nautical traffic areas

Representative

length [m]

Bow

type

Type

ID


0.5-1.0 1.0-1.5 1.5-2.0 2.0-3.0 3.0-4.0 4.0-5.0

90 Bulb 1.1 5.6x10-6

1.6x10-6

6.0x10-7

3.4x10-5

1.1x10-5

0

90 Raked 1.2 4.3x10-6

8.0x10-7

2.7x10-7

1.5x10-5

0 0

150 Bulb 2.1 1.4x10-8

6.9x10-9

6.9x10-9

6.9x10-8

1.4x10-7

3.4x10-8

150 Raked 2.2 5.5x10-8

1.4x10-8

4.6x10-9

9.2x10-8

4.6x10-8

4.6x10-8

240 Bulb 3.1 1.0x10-8

1.0x10-8

0 6.9x10-8

0 3.4x10-8

240 Raked 3.2 6.9x10-9

6.9x10-9

3.4x10-9

2.3x10-8

4.6x10-8

4.6x10-8

Total 9.9x10-6

2.4x10-6

8.8x10-7

2.3x10-7

2.5x10-8

2.0x10-8

For inland LNG barges an indentation depth of 2 meter or more is expected to cause a 250

mm LNG leak. In the case of small scale LNG vessels an indentation depth of 3 meter or

more is expected to cause a 250 mm LNG leak.

2 On this representative waterway no vessel longer than 180 meters are recorded

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Table 13 gives a summary of the LOC frequencies for the leakage of the cargo tank in case of

collision. It must be noticed that all frequencies in Table 13 are based on the assumption that

the bunker vessel and/or receiving vessel are continuously present (100% of the time) at the

bunker location. For the actual LOC frequency per category and parameter set (maximum or

minimum) the frequency of Table 13 should be multiplied with the presence factor of the

bunker vessel and/or receiving vessel.

Table 13: Summary of the LOC frequencies of the bunker cargo tank

Category LOC frequency [/year]

of intensive nautical

traffic area

LOC frequency [/year]

of low nautical traffic

area

LOC frequency

[/year] of very low

nautical traffic area

Cat 1 2.9 x 10-4

5.0 x 10-5

2.3 x 10-7

Cat 2 8.9 x 10-5

1.2 x 10-5

2.5 x 10-8

Cat 5 Max parameters 8.9 x 10-5

Min parameters 2.9 x 10-4

Max parameters 1.2 x 10-5

Min parameters 5.0 x 10-5

Min parameters 2.5 x

10-8

Min parameters 2.3 x

10-7

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NAUTICAL RISK ASSESSMENT OF THE LOADING OPERATION

In the previous chapter the collision of ships to the moored bunker vessel resulted in a loss of

containment of the cargo tanks of the bunker vessel. This chapter will focus on the impact that

the collision can have on the bunker operation. The impact of a colliding ship can results in

rupture of the bunker hose depending on the impact energy of the colliding vessel.

Methodology

The methodology is divided into a frequency and a collision part. The frequency of the ship

collision on the bunker operation is based on the same collision frequency model that is used

for the risk analysis of the moored bunker vessel. The collision frequency in both case is

same, the difference is found in the loss of containment frequency. In the collision assessment

the collision frequency is transformed to a LOC frequency of the bunker operation.

Results

The risk analysis of bunker operation is based on the overall collision frequency and does not

make any distinction between the different shipping classes. The total collision frequency for

the intensive nautical traffic area is around 1.4 x 10-2

per year. For the low and very low

nautical traffic area the total collision frequency is reduced to around 3.8 x 10-3

and 6.8 x 10-5

per year. During the bunker operation the receiving and bunker vessel are connected with

mooring lines to prevent drift away. For all bunkering operations the receiving vessel is

fixed/moored to the shore as well. In case of collision the mooring lines will absorb the first

impact energy. Colliding vessels with low amount of impact energy (e.g. low mass and/or

velocity) will not have sufficient energy to rupture the mooring lines and loss of containment

could not occur. For higher impact energies the mooring lines could fail and the tensile

strength of the bunker hose is the limited factor for loss of containment.

It is common practice in the industry to equip bunker hoses for gas purpose with a breakaway

coupling. For this bunker hose configuration the weak point of the confirmation is shifted to

the breakaway coupling because the tensile strength of the bunker hose will exceed the

strength at which the breakaway coupling will be activated.

In case the colliding vessel contains enough impact energy to release the breakaway coupling

the coupling will close in less than a second because of the mechanical closing system. The

quick closure of the breakaway coupling limits the release volume. The probability that the

colliding vessel contains enough impact energy to release the breakaway coupling is estimate

on 0.1. This expert judgment is based on the average energy on the waterway, strength of the

mooring line and set pressure of the breakaway coupling.

Table 14 gives a summary of the LOC frequencies for the rupture of bunker hoses due to

collision. It must be noticed that all frequencies in Table 14 are based on the assumption that

the bunker vessel and/or receiving vessel are continuously present (100% of the time) at the

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bunker location. For the actual LOC frequency per category and parameter set (maximum or

minimum) the frequency of Table 14 should be multiplied with the presence factor of the

bunker vessel and/or receiving vessel.

Table 14: Summary of the LOC frequencies for the rupture of bunker hoses due to collision

Category LOC frequency

[/year] of intensive


LOC frequency

[/year] of low


LOC frequency

[/year] of very low


Cat 1,2,3,4 and 5 1.5 x 10-3

3.8 x 10-4

6.8 x 10-6

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APPENDIX III BACKGROUND

PARAMETERS FOR RISK

CALCULATION

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MODEL PARAMETERS

Together with the scenarios defined in the chapter 4, model parameters represent the basis

input of the model. For many of the general model parameters default values in Phast Risk 6.7

are taken. However, for some parameters a deviation of the default values was needed. The

most important and influential (with respect on the output) general model parameters used to

calculate the individual risk are described below. Specific model parameters, such as weather

data and ignition sources, are also discussed in this chapter. A reference is made to addendum

[13] for a complete overview of all model parameters, which includes a justification of the

chosen value/method.

General parameters

The following general parameters are discussed below:

General risk/model parameters

Ignition parameters (for immediate and delayed explosions)

Explosion parameters

General risk/model parameters

In the event that all effect mitigating measures fail (e.g. ESD, operator), the maximum release

duration of each loss of containment scenario is limited by 1800s (based on the Dutch

guideline risk calculations). Note that this limit also applies for the failure scenario of a LNG

storage tank on a bunkering vessel caused by external collision where effective mitigation is

not deemed possible.

Fractions between day and night are set to 0.44 for day and 0.56 for night and are specifically

applicable for the Netherlands [5]. This also implies that bunkering activities are equally

distributed over a 24 hour period. The Port of Rotterdam assumes/expects no difference in

amount of bunkering activities between day and night.

Ignition and explosion parameters

Two types of ignition events can be distinguished in case of release of a flammable material:

immediate ignition and delayed ignition. Immediate ignition can lead to flammable effects

such as jet fires and pool fires in the event of a continuous discharge. Delayed ignition could

result in residual pool fires, flash fires and explosions.

Explosions

Related to explosion there are two possibilities:

When a vapor cloud enters an area of congestion, a confined explosion is possible that

could lead to potentially high overpressures depending on the level of confinement.

If there is no confinement, a potential unconfined vapor explosion could occur, which

is essentially a flash fire with accompanying explosion that usually generates relative

low overpressures.

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In case of continuous LNG releases during bunkering activities or LNG ship to ship transfers,

it is reasonable to assume that unconfined vapor explosions could occur in the event of

delayed ignition due to the low level of confinement in the immediate area. As such, vapor

explosions are modeled with the Multi-Energy (ME) explosion model (rather than the TNT

equivalent default explosion model, which is unrealistic and over-conservative) setting the

unconfined explosion strength to 1 (lowest ME strength curve).

Immediate ignition

Materials have different probabilities of immediate ignition depending on the flash point and

reactivity. Class 0 materials, materials having a flash point under 0 ºC and a boiling point

under 35 ºC, are divided in two categories: average to high reactivity and low reactivity. LNG

is a class 0 material with low reactivity. The immediate ignition probabilities for LNG that are

used are taken from the Dutch guideline on risk calculations and vary per type of

installation/transport asset and are highly dependent on the initial continuous discharge rate or

amount of material releases in case of instantaneous release. Note, instantaneous release

scenarios (e.g. a BLEVE domino scenario of tank truck) are not considered in this study due

to scope limitations. Immediate ignition probabilities for LNG bunkering/transfer activities

are based on those of applicable for stationary installations. This approach is in agreement

with the Dutch guidelines. Immediate ignition probabilities associated with bunkering tank

failure scenarios resulting from ship collisions are based on the probabilities applicable for

ships in the event of a continuous discharge.

An overview of all used immediate ignition probabilities in the model is given below:

Table 15: Overview of used immediate ignition probabilities for class 0 materials with

low reactivity (e.g. methane) (adopted and modified from the Dutch guideline risk

calculations)

Installation/transport asset Discharge for continuous

releases

Immediate ignition

probability

Stationary

installations/transfers >100 kg/s

0.02

Stationary

installations/transfers 10-100 kg/s

0.04

Stationary

installations/transfers >100 kg/s

0.09

Ship – gas tanker >180 m3

0.7

Delayed ignition

The delayed ignition of gas clouds is modeled using the following two approaches:

Free field method: the cloud ignites when the maximum ground footprint area to the

LFL fraction to finish is reached.

No free field (ignition sources): cloud ignition is dependent on the presence of ignition

sources in the area and their probability of causing an ignition. A specification of all

ignition sources considered in this study is given later in this appendix.

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Both the free field and no free field method are used in the risk calculations for the

‘maximum’ and ‘minimum’ bunkering parameters scenarios, respectively (see also Figure

23). The advantage of the free-field method is that the individual risk results are location

independent (i.e. independent of potential ignition sources present at a particular location).

However, this method generally results in higher calculated individual risk and can therefore

be considered as conservative. Note, the free field method of delayed ignition is the default

method in Safeti-NL, the mandatory QRA modeling package for Dutch QRA’s.

Weather data

The consequences of releases of flammable and toxic materials into the atmosphere are

strongly dependent upon the rate at which the released material is diluted and dispersed to

safe concentrations. The rate of dispersion is dependent on the meteorological conditions

prevailing at the time of release, particularly the wind speed and the degree of turbulence in

the atmosphere. The wind direction is also of importance as it determines the direction in

which the cloud of material will travel.

Meteorological parameters (e.g. wind speeds and directions, environmental temperatures,

atmospheric pressure, humidity) are based on Dutch weather statistics measured during a time

period of 29 years by the KNMI. The used wind data are specifically applicable for the

Rotterdam region.

Ignition sources In order to address delayed ignition without using the earlier mentioned free-field method, the

model requires information about the distribution of ignition sources in the vicinity the

bunkering activity. Several different types of ignition source could be present, such as ships,

other transport vehicles and people.

The following two sources of ignition are considered in the model (also graphically visualized

in Figure 23):

Ships passing a bunkering/ LNG ship to ship transfer location where, concurrently, a

specific bunkering activity is taking place.

The LNG receiving vessel, which is not entirely EX-zoned (only the area around the

LNG fuel tank and bunkering point / station) and could therefore be a potential

ignition source.

Ignition sources not considered in the model:

The bunkering ship is assumed to be EX-zoned, meaning that all deck equipment is

explosion-proof. As such, no ignition can occur at the bunkering ship and is not

considered to be a potential ignition source.

Electrical installations, industrial equipment, people or transport vehicles in the

immediate vicinity. The assumption is that an (inland) area in the immediate vicinity

of the activity will be EX-zoned.

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In the event of a ship collision, the colliding ship strikes the bunkering vessel or a

receiving ship. It is common practice in nautical QRA’s not to include the colliding

ship as additional ignition source in case the collision results in loss of containment of

flammable materials. The immediate ignition probability with respect to the latter loss

of containment scenarios on bunkering vessels (i.e. LNG tank failure) is higher in the

event of a ship collision, which accounts to some extend that the presence of a

colliding ship is essentially an additional ignition source.

Figure 23: Overview of ignition sources considered (location Oude Maas)

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APPENDIX IV RESULTS -

DISTANCES TO 10-6

/YEAR

CONTOUR

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Table 16: Distance to 10-6

/year contour for each bunkering scenario

Scenari

o

Transfer

parameters

Delayed

ignition

Transfer

activities

(/year)

Nautical

activity

Distance to 10-6

/year

contour (m)

Category 1 – LNG bunkering with a small inland LNG bunker vessel

1.1 Maximal Free field 52 Intensive 273



1.4 Minimal Ignition

sources

52 Intensive 70


sources

1826 Intensive 174


sources

3652 Intensive 185

1.7 Maximal Free field 52 Low 215




sources

52 Low 28


sources

1826 Low 146


sources

3652 Low 171

1.13 Maximal Free field 52 Very low 210




sources

52 Very low 28


sources

1826 Very low 88


sources

3652 Very low 95

Category 2 – LNG bunkering with a large LNG bunker vessel





sources

12 Intensive 111


sources

183 Intensive 215


sources

365 Intensive 237



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Scenari

o

Transfer

parameters

Delayed

ignition

Transfer

activities

(/year)

Nautical

activity

Distance to 10-6

/year

contour (m)



sources

12 Low 105


sources

183 Low 170


sources

365 Low 192





sources

12 Very low 85


sources

183 Very low 135


sources

365 Very low 150

Category 3 – LNG bunkering with a LNG tank truck




3.4 Minimal

Ignition

sources

52 Intensive 80

3.5 Minimal

Ignition

sources

1826 Intensive 144

3.6 Minimal

Ignition

sources

3652 Intensive 151




3.10 Minimal

Ignition

sources

52 Low 85

3.11 Minimal

Ignition

sources

1826 Low 146

3.12 Minimal

Ignition

sources

3652 Low 152




3.16 Minimal

Ignition

sources

52 Very low 85

3.17 Minimal

Ignition

sources

1826 Very low 146

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Scenari

o

Transfer

parameters

Delayed

ignition

Transfer

activities

(/year)

Nautical

activity

Distance to 10-6

/year

contour (m)

3.18 Minimal

Ignition

sources

3652 Very low 152

Category 4 – LNG bunkering from a bunkerpontoon





sources

52 Intensive 8


sources

1826 Intensive 85


sources

3652 Intensive 94





sources

52 Low 8


sources

1826 Low 82


sources

3652 Low 91





sources

52 Very low 8


sources

1826 Very low 82


sources

3652 Very low 91

Category 5 – Ship to ship LNG transfer





sources

12 Intensive 115


sources

84 Intensive 250


sources

156 Intensive 270



DET NORSKE VERITAS

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Scenari

o

Transfer

parameters

Delayed

ignition

Transfer

activities

(/year)

Nautical

activity

Distance to 10-6

/year

contour (m)



sources

12 Low 68


sources

84 Low 152


sources

156 Low 175





sources

12 Low 68


sources

84 Low 145


sources

156 Low 165

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DNV Port toolkit risk profile LNG bunkering

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