ship or installation collisions 434-16

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Risk Assessment Data Directory

Report No. 434 16

March 2010

I n t e r n a t i o n a l A s s o c i a t i o n o f O i l & G a s P r o d u c e r s

Ship/installationcollisions


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RADD Ship/installation collisions

OGP

contents

1.0 Scope and Definitions ........................................................... 1 1.1 Scope ............................................................................................................... 11.2 Definitions ....................................................................................................... 11.2.1 Collisions .................................................................................................................... 11.2.2 Damage ....................................................................................................................... 2

2.0 Summary of Recommended Data............................................ 3 2.1 Basics of ship collision risk modelling......................................................... 32.1.1 Collision Frequency ................................................................................................... 32.1.2 Collision consequences ............................................................................................ 4

2.2 Overview of historical ship/installation collision information.................... 72.3 Passing vessel collisions............................................................................... 9

2.3.1 Shipping traffic patterns and vessel behaviour ...................................................... 92.3.2 Best practice collision risk modelling for passing vessels ................................. 112.4 Field related vessel collisions ..................................................................... 122.4.1 Frequencies of field related vessel collisions....................................................... 122.4.2 Consequences of vessel related field collisions................................................... 162.4.3 Collisions of mobile units........................................................................................ 17

2.5 Collision risk management .......................................................................... 18

3.0 Guidance on use of data ...................................................... 183.1 General validity ............................................................................................. 183.2 Uncertainties ................................................................................................. 183.3 Example .........................................................................................................18

4.0 Review of data sources ....................................................... 195.0 Recommended data sources for further information ............ 206.0 References .......................................................................... 206.1 References for Sections 2.0 to 4.0 ..............................................................206.2 References for other data sources.............................................................. 21


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Abbreviations:

AIS Automatic Identification System

ARPA Automatic Radar Plotting AidBHN Bombay High North

DP Dynamic PositioningDSV Diving Support Vessel

ERRV Emergency Response and Rescue VesselFPSO Floating Production, Storage and Offloading unitFPU Floating Production UnitFSU Floating Storage UnitH2S Hydrogen sulphide

HC HydrocarbonHSE Health and Safety Executive

MODU Mobile Offshore Drilling Unit

MSV Multipurpose Support VesselQRA Quantitative Risk AssessmentREWS Radar Early Warning SystemROV Remotely Operated Vehicle

TEMPSC Totally Enclosed Motor Propelled Survival CraftTLP Tension Leg Platform

TR Temporary RefugeUK United KingdomUKCS United Kingdom Continental Shelf


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1.0 Scope and Definitions1.1 Scope

This datasheet provides data on ship/installation collision risks in relation to activities

within the offshore oil & gas Exploration and Production industry, for use inQuantitative Risk Assessment (QRA). The risks related to icebergs are not considered.

Ship traffic may be divided into two groups:

Passing vessels: Ship traffic which is not related to the installation beingconsidered, including merchant vessels, fishing vessels, naval vessels and alsooffshore related traffic going to and from other installations than that beingconsidered.

Field related: Offshore related traffic which is there to serve the installation beingconsidered, e.g. supply vessels, oil tankers, work vessels.

For passing vessels, collision risk is highly location dependent due to variation in shiptraffic from one location to another. The ship traffic volume and pattern at the specific

location should hence be considered with considerable care. This dependency onlocation also means that use of historical data which are averaged over a large numberof different locations, is not possible. For passing vessels, the datasheet thereforepresents best current practice in modelling collisions of passing vessels with offshoreinstallations rather than recommended frequencies.

Field related offshore traffic refers to those vessels which are specifically visiting theinstallation, and is therefore considered to be less dependent of the location of theinstallation. The frequency of infield vessel impacts will depend on the durations thatvessels are alongside, the installation layout, environmental conditions, and

procedures, so care is required to ensure these factors are considered appropriately.

In addition, the datasheet presents an overview of historical data on ship collisions that

have occurred, with an emphasis on the circumstances and consequences of thecollisions.

1.2 Definitions

1.2.1 Collisions

Collisions can be divided into two groups:

Powered collisions (vessel moving under power towards the installation)

Drifting collisions (vessel drifting towards the installation)

Powered collisions include navigational/manoeuvring errors (human/technical failures),watch keeping failure, and bad visibility/ineffective radar use. A drifting vessel is a

vessel that has lost its propulsion or steerage, or has experienced a progressive failureof anchor lines or towline and is drifting only under the influence of environmentalforces.

Table 1.1 sets out the different types of vessels that may collide with an offshoreinstallation.


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Table 1.1 Categories of Colliding VesselsType OfTraffic TrafficCategory VesselCategory Remarks

Merchant Merchant ships:cargo, ferries

etc.

Commercial traffic passing the area

Surface vessels Both war ships and submarinesNaval traffic

Submergedvessels

Submerged submarines

Fishing

vessels

Fishing vessels Sub-categorised into vessels in

transit and vessels operating in thearea

Pleasure Pleasure vessels Traffic passing the area

Standby boats Vessels going to and from otherfields

Supply vessels Vessels going to and from otherfields

Offshore tankers Vessels going to and from otherfields

Passing

Offshoretraffic

Tow Towing of drilling rigs, flotels, etc.

Standby vessels Dedicated standby vessels

Supply vessels Visiting supply vessels

Working vessels Special services/support such asdiving vessels, flotels, pipe lay

barges, intervention vessels and

crane barges

Offshoretraffic

Offshore tankers Shuttle tankers visiting the field

Field related

Drilling rigs MODUs May collide with fixed installation

either on approach or as a result ofmooring failure

1.2.2 Damage

Sections 2.2 and 2.4.2 present data for the following damage levels as defined in WOAD[1]:

Total loss Total loss of the unit including constructive total loss froman insurance point of view. However, the unit may berepaired and put into operation again.

Severe damage Severe damage to one or more modules of the unit;large/medium damage to loadbearing structures; major

damage to essential equipment.

Significant damage Significant/serious damage to module and local area of theunit; minor damage to loadbearing structures; significant

damage to single essential equipment; damage to moreessential equipment.

Minor damage Minor damage to single essential equipment; damage tomore none-essential equipment; damage to non-loadbearingstructures.


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Insignificant damage Insignificant or no damage; damage to part(s) oressential equipment; damage to towline, thrusters,generators and drives.

2.0 Summary of Recommended DataThe data presented in this section are set out as follows:

Basics of ship collision risk modelling (Section 2.1) Overview of historical ship/installation collision information (Section 2.2)

Passing vessel collisions (Section 2.3) Field related vessel collisions (Section 2.4)

Collision risk reduction (Section 2.5)

2.1 Basics of ship collision risk modelling

The risk arising from collision of a ship with an offshore installation is considered in twoparts: collision frequency and collision consequences.

2.1.1 Collision Frequency

The collision frequency is calculated as:

Collision frequency = Frequency of ship being on collision course

Probability that collision is not avoided

For powered collisions, the frequency of a ship being on a collision course can beestimated from knowledge of shipping traffic in the vicinity of the installation. This isdiscussed, for passing vessels, in Section 2.3.2.1.

For drifting collisions, the frequency of a ship being on a collision course depends on

where the ship loses power or steerage, and the direction and strength of the currentand wind.

For a passing vessel, not suffering from propulsion or steerage problems, to collidewith an offshore installation, the following three conditions must occur:

1. The ship needs to be on a collision course with the installation;

2. The navigator/watchkeeper must be unaware of the collision course sufficiently long

for the ship to reach the installation (watchkeeping failure);

3. The installation/standby vessel crews must be either be unaware of the developingsituation or be unable to warn the vessel to normalise the situation.

Watchkeeping failure is discussed further in Section 2.3.2.1. Measures available to theoperator to prevent a collision can be divided into two categories:

Standby vessel (or ERRV) intervention: Detection of the errant vessel by radar / AIS /

visual sighting; intervention in the form of VHF communication, or approaching thevessel and attracting its attention using light and sound signals, such aspyrotechnics.

Installation intervention: This is normally limited to VHF communication, assuming

there is a means to detect the errant vessel on the installation, such as radar and/orAIS.

Standby vessel intervention is normally more effective as the bridge crew consists ofdedicated watch-keepers with maritime training and experience.


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These scenarios can be addressed by using appropriate collision risk models. Careshould be taken that the model used is calibrated against historical data1.

2.1.2 Collision consequences

If a collision occurs, consequences can range from superficial damage to complete loss

of the installation. The damage to the installation depends on:

Size of vessel (M, te)

Speed of vessel(V, m/s)

The Impact Energy, E (kJ), is related to these by E = 0.5kMV2

where k is the hydrodynamic added mass constant: k = 1.1for end-on (powered) impact, k = 1.4 for broadside (drifting)

impact.

Point of impact, e.g. legs, conductors, risers, bracings

Whether angle of impact is head-on, glancing, or sideways-on (broadside)

Partitioning of impact energy between installation and vessel

Fatalities on the installation as a result of a collision will depend first and foremost onwhether the impending collision has been detected, e.g. by radar or AIS, and whether aprecautionary alarm, evacuation or down-manning has then been carried out. If a vesselunder power is observed on a collision course, the time available for precautionary

evacuation/down-manning will be limited (e.g. typically 30 minutes if observed by radardown to zero if visual observation only in conditions of poor or night visibility). A

decision may have to be made whether to carry out a precautionary evacuation/down-manning, which would have to be by TEMPSC or escape direct to sea (see datasheetEvacuation, Escape and Rescue), or for personnel to remain on the installation. Each ofthese carries attendant risks. If a drifting vessel is observed on a collision course, thetime available for response is likely to be much longer and it may be possible to initiate

precautionary evacuation/down-manning by helicopter, or to manoeuvre the vessel /

barge clear of the installation by a security or field support vessel.Figure 2.1 and Figure 2.2 give example flow charts to determine possible outcomes

given potential collisions by powered and drifting vessels respectively. These figuresare more typical of a fixed production installation than a MODU but illustrate issues that

may need to be considered when analysing ship collisions for any type of installation.The appropriate flow chart for a specific analysis will depend on the means provided todetect vessels on a collision course, their availability, and the procedures to decide onmustering and precautionary evacuation/down-manning. Any or all of these may bedependent on the weather conditions at the time (e.g. visibility may affect observation,

sea state affects the risks in evacuation by TEMPSC).

Note: Figure 2.1 and Figure 2.2 refer to the TR (Temporary Refuge), defined as [14]: [a] place

provided where personnel can take refuge for a predetermined period whilst investigations,emergency response and evacuation preparations are undertaken. Depending on thejurisdiction, impending ship collision is not necessarily considered to require a TR; however, themuster location in this scenario is conveniently identified with the TR.

1Lack of such calibration is often a shortfall of simple models.


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Figure 2.1 Example Flow Chart for Powered Vessel on Coll ision Coursewith Installation

Note: No specific time value is given to Early or Late observation of a vessel on a collision

course. Early can be considered to be sufficient to muster personnel, make a decisionwhether or not to evacuate, and if to evacuate then for TEMPSCs to be sufficiently far away at thetime of collision. Late can be considered to give some time to muster at least some personnelin the TR but insufficient for TEMPSC evacuation; on a bridge linked complex, some personnelare considered in this example to have insufficient time to reach the TR and therefore to attemptescape to sea.


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Figure 2.2 Example Flow Chart for Drift ing Vessel on Coll ision Course withInstallation

Note: No specific time value is given to Early or Late observation of a vessel on a collision

course. Early can be considered to be sufficient to initiate helicopter evacuation (consideringthe time required to mobilise sufficient helicopters) if this is possible (e.g. sufficient visibility), orelse to muster personnel, and make a decision whether or not to evacuate. Late can beconsidered to give some time to muster at least some personnel in the TR but insufficient forTEMPSC evacuation; on a bridge linked complex, some personnel are considered in thisexample to have insufficient time to reach the TR and therefore to attempt escape to sea. Adrifting vessel typically moves at 1 to 2 kn so, in this example, it is assumed that the driftingvessel is observed sufficiently early for at least partial mustering to take place.

The likelihood of receiving an Early or Late warning will be dependent on the procedures inplace at the field and the detection system that is used. Information on the performance of somedetection systems is available in [13].


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2.2 Overview of historical ship/installation collision information

WOAD [1] provides details of 465 collision incidents worldwide during 1970-2002, ofwhich 326 have occurred since 1980. As the collision frequency is strongly location

specific, it is not useful to use these records to estimate absolute collision frequencies.However, other useful information can be derived.

57 of the 1980-2002 incidents in WOAD can be identified with passing vesselsunconnected with field activity. 189 of the remaining incidents in WOAD occurred

during drilling, production or workover, including 10 during shuttle tanker operations(loading of liquids). Many of these involved supply vessels, standby vessels or crew

boats. Table 2.1 presents statistics for different levels of damage resulting fromcollisions.

Table 2.1 Collisions with Offshore Installations (Worldwide)Passing Vessels Infield Vesselsamage*

Number Percent Number PercentTotal Loss 3 5% 1 0.5%

Severe 19 33% 16 8%

Significant 8 14% 55 29%

Minor 10 18% 65 34%

Insign./No 17 30% 52 28%

All 57 100% 189 100%

* See Section 1.2.2 for definitions of damage categories.

These records do not include the most serious ship-installation collision, that at

Bombay High North (BHN) on 27 July 2005, when an MSV (Multipurpose Support Vessel)approaching the installation lost control, drifted and collided with the installation. Thisresulted in serious oil leakage and a major fire, resulting in the loss, within two hours, ofboth the BHN platform and a jackup rig working alongside. A total of 22 fatalitiesresulted, on the installation, jackup and MSV; 362 personnel were rescued, some afterspending more than 12 hours in the water [15]. The collision occurred despite the MSVbeing DP (Dynamic Positioning) equipped.

Other types of incident in the WOAD database include:

Collision during towing or mobilizing/demobilizing of MODUs (involving vesselsassociated with the activity such as tugs, supply vessels, and anchor handling

vessels).

Collision during construction/repair (involving vessels involved with the activitysuch as crane barges, pipeline barges and tugs).

Moorings broken when MODU was idle/stacked.

In only one incident did fatalities occur, when a jackup punched through the seabed,resulting in collapse of two legs; subsequently the jackup drifted into an adjacent unit.In this incident, there were 2 fatalities and 43 personnel were successfully evacuated.

In 7 incidents, of which 3 were during loading, there was a release of oil from the struckinstallation, a pipeline or a loading hose. In one incident, the colliding vessel wasdamaged and oil leaked from its fuel and lube oil tanks. In a further 2 incidents, gas

including H2S was released.


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Table 2.5 UKCS Coll ision Event Categories 1990-2005Passing Vessels Visiting VesselsventCategory1 Number Percent Number Percent

Accident 13 31% 11 4%

Incident 4 10% 54 22%Near Miss 23 55% 77 31%

Unsignificant2 2 5% 103 42%

All 42 100% 245 100%

Notes

1. The event categories in this table are not equivalent to those used in Table2.1.

2. This can be read as Insignificant (Unsignificant is used for consistencywith the original data source: see Table 4.1).

Of the 31 passing vessel collision events listed for fixed installations, 14 (46%) involved

fishing vessels, and of these 3 involved fishing gear becoming entangled with subseawellhead equipment rather than vessel impact with the surface installation. 7 (23%) of

these 31 collision events are known to have involved either infield vessels visiting otherinstallations or shuttle tankers, i.e. 7 of the events are known to have involved fieldrelated vessels.

Visiting vessel collisions are examined in more detail in Section 2.4.

2.3 Passing vessel collisions

2.3.1 Shipping traffic patterns and vessel behaviour

Each of the passing vessel traffic types listed in Table 1.1 behaves in one of severaldistinct ways in relation to a installation. This must be considered both when reviewing

traffic data and when estimating collision frequency. Each type is discussed in thefollowing sub-sections, with an evaluation of relevant traffic patterns and vessel

behaviour in the vicinity of offshore installations.

2.3.1.1 Merchant Vessels

Merchant vessels are frequently found to represent the greatest installation collisionhazard, since:

Merchant vessels are often large and may thus represent considerable impact

energy. Traffic may be very dense in some areas.

Oil and gas operators have no prevailing influence.

In addition there is a problem with the uncertainties in the risk estimates, which arehigher than for many of the other vessel groups as merchant vessel operating

standards vary.


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2.3.1.2 Naval Traffic

Estimating risk associated with naval vessels is difficult because information aboutmovements and volume is restricted and hence difficult to obtain. Estimation very often

has to be based on surveys or subjective evaluation. Further, the naval traffic volume isdifficult to assess since possible routes and areas where naval vessels operate/exercisecan vary from year to year. The variation in traffic routes and density can also be

dependent on the political situation.

Naval traffic may be divided into two main categories, surface traffic (submarinesincluded) and submerged traffic.

2.3.1.2.1 Surface TrafficAs for merchant vessels, collisions are either due to drifting of the vessel or may occur

while the vessel is under power (errant vessels).

As regards collisions under power, it may be acceptable to disregard this scenario asthese vessels have a large crew compared to merchant vessels. They will always haveat least two persons on the bridge (large vessels such as frigates, destroyers andaircraft carriers will have more personnel on the bridge). Normally the operations roomis also manned. Considering the number of personnel on watch it seems very unlikely,

compared to a merchant vessel, that a naval surface vessel should not know of ordetect the installation, and avoid it. In addition, naval vessels are more likely to operatein groups, which also will reduce the collision probability. Submarines operating on thesurface are not considered to represent any higher threat to the installation than anyother surface vessel.

Overall, it is considered that the contribution to overall collision risk from such vesselsis in general likely to be very low.

2.3.1.2.2 Submerged Submarine TrafficAs for naval surface vessels, due to a reduced probability of drifting combined with arelatively low number of vessels, the contribution from drifting submarines to the

overall collision risk is negligible.

Submerged submarines are in a special situation because they do not have a look-out.Navigation is therefore completely dependent on electronic navigational aids and sonar.

In principle submarines are officially restricted from operating in the immediate vicinityof offshore installation in times of peace. Nevertheless a 1988 incident when asubmarine collided with Norsk Hydros Oseberg B platform shows a deviation from thisprinciple. In connection with this accident, it was stated that it was often very difficult

for submarines to detect platforms, which do not emit much sound in the water.

Some data on submarine traffic have been collected [2]. At the time of publication(1995), an appropriate number of submarines active in the entire North Sea, at all times,

seems to have been in the region of 15 to 25. It is not known if this has changedappreciably since then.

2.3.1.3 Fishing Vessels

Fishing vessels are divided into two groups, depending on the operational pattern:

Fishing vessels in transit from the coast to and from different fishing areas.

Vessels may be fishing in an area. The vessels operation and behaviour during

fishing (primarily trawling) will be complex and varied, but usually at low speed andwith no preferred heading.


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Fishing vessels vary in size from large factory/freezer ships to smaller vessels operatingnear the coast. Typically, a large fishing vessel will have a displacement around1000 tonnes. This implies that the collision energy will be less than 20 MJ. For a typicalNorth Sea installation neither drifting vessels nor vessels under power will normally be

able to threaten the installations integrity.

However, risers and other relevant equipment have considerably less impact resistance;

being typically much smaller than merchant vessels, it is also more likely that a fishingvessel may pass between the legs of an installation and reach risers or conductors.

Collisions of both powered and drifting fishing vessels should therefore be considered,taking this into account.

2.3.1.4 External Offshore Traffic

Passing offshore vessels and tankers as well as supply, standby and work vessels arein many respects similar to passing merchant vessels, except that such vessel

operations tend to be more aware of the offshore installations and also may benefit fromoperator influence (procedure, training competency, communication etc.).

Vessels or installations under tow pose particular problems which are consideredseparately (Section 2.4.3).

2.3.2 Best practice collision risk modelling for passing vessels

2.3.2.1 Collision frequency estimation

As set out in Section 2.1.1, there are two parts to this:

1. Estimating the frequency of a ship being on a collision course

2. Estimating the probability that collision is not avoided

The first of these is strongly dependent on the installations location with respect toshipping traffic, and also on the installations size (although, in a bridge linked complex,for some approach directions one platform may be shielded by another).

Shipping databases are available to assist in this task such as ShipRoutes. Wherepossible, other methods of logging vessel tracks in and around a field can beimplemented such as Automatic Identification Systems (AIS). This can be achieved

using systems such as AISTracker and will provide an enhanced understanding of thebehaviour of shipping around the field. This offers considerable benefit to collision risk

assessment work in relation to passing and infield vessel risk assessment. Details areprovided on ship type, size, speed, navigation status, etc.

Fishing vessel activity can be assessed by processing satellite tracking data on fishing

vessel movements: this has already been done, for example, for part of the North Sea(Anatec unpublished).

Based on the work undertaken within the HSEs OTO 1999 052 study [9], the followingcauses of ineffective watchkeeping were identified:

Watch-keeper present on bridge but:

o Busy/preoccupied with other tasks

o Asleep

o Incapacitated due to sickness, accident or substance abuse

Watch-keeper absent from the bridge

Poor visibility combined with undetected radar fault.

Further discussion on each of these causation factors is provided in the OTO report [9].


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The probability of radar failure can be estimated from reliability data for the systemconcerned (considering all parts: radar, processor, power supply, display).

One widely used model which takes account of these factors when assessing passing

ship collision is COLLRISK [12]. Based on analysis of collision data for the region ofinterest (e.g., North Sea), as well as traffic data and installation operating experience,the model has been back-tested to ensure it provides results in line with experience. As

well as the calibration factor, the main influences on the collision risk are trafficvolumes in proximity to the installation, ship characteristics (e.g. type, size and speed),

installation dimensions/orientation, and metocean data, in particular visibility. Themodel can also take into account the benefits of various risk reducing measures.

2.3.2.2 Collision consequences

As shown in Table 2.1, collisions of passing vessels can result in damage ranging frominsignificant to total loss. Table 2.1 shows that almost 40% of such collisions resulted

in severe damage or total loss, although none of these resulted in fatalities toinstallation personnel.

Initially, the damage breakdown in Table 2.1 could be used directly in a QRA togetherwith suitable assumptions about warning, mustering and precautionary evacuation

(using a flow chart such as the examples in Figure 2.1 and Figure 2.2). Although nofatalities have occurred to date as a result of a passing vessel collision, the Bombay

High North incident summarised in Section 2.2 demonstrates that a major accidentinvolving fatalities is credible, especially if escalation to a hydrocarbon fire or explosionoccurs.

If this relatively simple approach indicates high ship collision risks, then more detailedanalysis may be required in order to demonstrate that the simple approach isconservative. This could involve structural analysis of the effect of a vessel collisionwith the installation2.

2.4 Field related vessel collisions

2.4.1 Frequencies of field related vessel collisions

Unlike passing vessel collisions, the dependency of field related vessel collisions ongeographical location is largely limited to metocean conditions and allowable weathercriteria; conversely, field related vessel collisions are strongly dependent on the fieldactivities (drilling or production) and on the associated support requirements (e.g.provision of supplies, anchor handling, diving support).

Table 2.6 presents worldwide field related vessel collision statistics based on WOAD [1]

and corresponding exposure data3

[8]. This shows much lower collision frequencies forfixed platforms compared with FPSOs and FPUs, and wide variation between thecollision frequencies for the different types of FPU. There are also variations betweendifferent types of MODU but these are not so great.

2Such a project was undertaken in 2008 for a variety of jacket types; it is intended to publish the

outcome of this work.3

Note that exposure data is here measured by unit-years in service. It should be noted thatcollision frequencies for a particular unit will be strongly dependent on the number of visits peryear and on the types of vessel visiting. Such data are not readily available. However, if the unit

being studied can be considered to have a typical number of visits per year, then thefrequencies given in Table 2.6 can be used. If field related collision frequencies prove to be anissue, then a more detailed analysis should be undertaken, using actual data combined withcollision risk modelling.


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Figure 2.3 shows worldwide collision frequencies for production installations, Figure 2.4collision frequencies for MODUs; both show error bars corresponding to 90%confidence limits. From these figures it is concluded:

The collision frequency for fixed production units is significantly different fromthose for FPSOs and FPUs.

TLPs appear to be subject to a significantly higher collision frequency than jackupsand semi-submersibles.

Table 2.6 Field Related Vessel Collision Statistics (Worldwide)Unit Type Collisions Exposure

(unit-years)Collision

Frequency(per unit-year)

Production UnitsFixed 77 135122 5.7 10 -4FPSO 4 445 9.0 10 -3 TLP 3 88 3.4 10 -2 Jackup 1 89 1.1 10-2

Semi-submersible 4 363 1.1 10-2

All FPU (not FPSOs) 8 540 1.5 10-2

Jackups + Semi-subs 5 452 1.1 10 -2 Loading Buoy 6 Not available -

Dri l l ing Units (MODUs)Jackup 41 10743 3.8 10-3

Semi-submersible 45 4837 9.3

10

-3

Drill ship/barge/tender 14 2183 6.4 10

-3

All MODUs 100 17763 5.6 10-3

Figure 2.3 Production Unit Vessel Coll ision Frequencies (Worldwide)

Error bars indicate 90% confidence limits.


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Figure 2.4 MODU Vessel Coll ision Frequencies (Worldwide)

Error bars indicate 90% confidence limits.

Table 2.7 shows the proportions of collisions by vessel type.

Table 2.7 Collisions by Vessel Type (Worldwide)Vessel Type ProductionUnits MODUsSupply Vessel 34% 60%

Standby Vessel 19% 11%

Working Vessel 34% 16%

Rig 7% 6%

Shuttle Tanker 3% 1%

Other 3% 5%

Unknown 0% 1%

Generally, collisions with any sort of offshore-related traffic can be more easily

controlled because many of these vessels are operated by the oil companiesthemselves, and they can impose restrictions on vessel operations if it is deemednecessary.

Figure 2.5 shows infield vessel collision frequencies by geographical region.

Comparing this with Table 2.2, it is clear that infield vessel collision frequencies varysignificantly from region to region, even considering only the regions with largenumbers of offshore installations and MODUs operating. Of these areas, the frequencyis highest by far in the North Sea (see also Table 2.9) and has only reduced by 19% over

the two time periods presented. On the UKCS the frequency is even higher relative tothe worldwide average. It is not clear from the data whether these high frequencies aredue to better reporting, especially of minor collisions, the more severe weather

conditions in the North Sea compared with other regions, or better control of infieldvessel movements in other regions. There has been no collision resulting in significantor severe damage or total loss in the North Sea since 1994.

Table 2.8 gives a detailed breakdown of collisions between visiting vessels andinstallations on the UKCS for 1990-2005. This shows considerably higher frequencies.

Table 2.10 shows the distribution of damage levels for the main regions: it shows amuch higher proportion of collisions in the North Sea resulting in insignificant or no

damage than any other region. Nevertheless, even excluding these, or counting those


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resulting in significant or severe damage or total loss, the North Sea frequency issignificantly higher than any other region.

Table 2.8 UKCS Field Related Vessel Collision Statistics 1990-2005Unit Type Collisions Exposure

(unit-years)Collision

Frequency(per unit-year)

Production UnitsFixed 90 3383 2.7 10 -2FPSO & FSU 14 265 5.3 10 -2 Dri l l ing Units (MODUs)All MODUs 109 982 1.1 10 -1

Figure 2.5 Geographical Variation of Infield Vessel Collision Frequencies

Table 2.9 Geographical Variation of Infield Vessel Collision FrequenciesCompared to Worldwide Average

Region Fraction of 1990-2002 WorldwideAverageAfrica 0.36

Asia 0.17

Central & S. America 0.59

Europe: North Sea 9.55

Middle East 0.11

US: Gulf of Mexico 0.24

UKCS* 49.35

* Fraction is based on UKCS 1990-2005 frequency as given in Table 2.4.


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Table 2.10 Infield Vessel Collision Damage Levels by Region: AllInstallationsDamage Level (see Section 1.2.2 for definit ions)eographicalArea TotalLoss Severe Significant Minor Insignif. /No

Africa 0% 0% 14% 86% 0%

Asia 0% 0% 44% 33% 22%

Central & S America 0% 17% 33% 33% 17%

Europe: N Sea 0% 5% 16% 31% 48%

Middle East 0% 20% 10% 60% 10%

US-GoM 2% 13% 48% 33% 4%

2.4.2 Consequences of vessel related field collisions

Worldwide average collision damage levels are tabulated for different vessel types and

overall as follows: Fixed installations: Table 2.11 FPSOs: Table 2.12

FPUs: Table 2.13

MODUs: Table 2.14

Table 2.11 Collision Damage Levels by Vessel Type: Fixed InstallationsDamage Level (see Section 1.2.2 for definit ions)essel Type

TotalLoss Severe Significant Minor Insignif. /NoSupply 0% 11% 15% 52% 22%

Standby 0% 0% 20% 13% 67%

Barge/Tug 0% 30% 11% 48% 11%

Rig 0% 0% 0% 80% 20%

Shuttle Tanker 0% 0% 33% 33% 33%

Other n/a n/a n/a n/a n/a

Unknown n/a n/a n/a n/a n/a

ALL 0% 14% 14% 44% 27%

Table 2.12 Collision Damage Levels by Vessel Type: FPSOsDamage Level (see Section 1.2.2 for definit ions)essel Type

Total Loss Severe Significant Minor Insignif. /NoSupply 0% 0% 0% 0% 100%

Standby n/a n/a n/a n/a n/a

Barge/Tug n/a n/a n/a n/a n/a

Rig n/a n/a n/a n/a n/a

Shuttle Tanker n/a n/a n/a n/a n/a


Unknown 0% 0% 33% 33% 33%

ALL 0% 0% 25% 25% 50%


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Table 2.13 Collision Damage Levels by Vessel Type: FPUsDamage Level (see Section 1.2.2 for definit ions)essel Type


Standby 0% 0% 0% 0% 100%

Barge/Tug 0% 33% 0% 33% 33%

Rig 0% 0% 0% 0% 100%

Shuttle Tanker n/a n/a n/a n/a n/a


Unknown n/a n/a n/a n/a n/a

ALL 0% 13% 13% 25% 50%

Table 2.14 Collision Damage Levels by Vessel Type: MODUsDamage Level (see Section 1.2.2 for definit ions)essel Type


Standby 0% 9% 18% 27% 45%

Barge/Tug 0% 0% 56% 25% 19%

Rig 17% 0% 50% 0% 33%

Shuttle Tanker 0% 0% 40% 20% 40%

Other 0% 0% 0% 0% 100%

Unknown 0% 0% 0% 0% 100%

ALL 1% 4% 42% 28% 25%

Note however that, for example, the Norwegian and the UK criteria for design against

vessel impacts have been derived from a probabilistic evaluation of supply vesselimpacts [6], [7]. These collisions are therefore to a large degree minimized by platformdesign. Hence the distribution of damage levels to be expected from field related vesselcollisions in different geographical areas may vary from those tabulated aboveaccording to the installation design criteria. They may also vary according tooperational procedures: for example, an arriving supply vessel may be required to stopon arrival at the installation exclusion zone (500 m radius) and then proceed at low

speed to the installation. Hence, where more specific information is available on designcriteria and operational procedures, these should be taken into account if the risk levelsare sufficiently high to occasion concern. The trend towards the use of larger,multipurpose vessels, which may exceed the size the installation was originallydesigned for, should also be considered where appropriate.

2.4.3 Collisions of mobile units

9 separate incidents of collisions between installations have been identified in WOAD[1]. Of these, 1 occurred during hurricane Juan (27/10/1985) and 3 during hurricaneAndrew (27/08/1992). 3 further weather related incidents occurred. Of the remaining 2incidents, one appears to have been an operational error; in the other case, the

description refers to a drifting rig but does not indicate the cause.

The HSE report [4] and database identifies 5 collision incidents during towing of mobileunits. One involved a collision during preparation for tow-out from the construction

yard; no details are given for the remaining 4 but, based on WOAD information, it is


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possible these involved the towing tugs contacting the unit rather than the unit itselfcontacting another unit.

2.5 Collision risk management

Collision risk management is examined in the UK HSE OTO 1999 052 report [9], to which

reference should in the first place be made, in particular to Chapter 7. This commenceswith the HSEs general Safety Management System model as set out in HS(G)65 [10] andshows how this can be applied specifically to managing ship collision risks. [9] thenpresents specific measures for managing in-field and passing vessel collision risks. Italso includes as Appendix B an overview of ship collision detecting and alerting

(hardware) systems. This includes normal setups such as standby vessel with standardmarine radar or ARPA, and more sophisticated systems such as REWS (Radar Early

Warning System using installation-mounted scanners to increase detection range andprovide early warning of vessels on a possible collision course with the installation,allowing an early decision and response such as precautionary partial or fullevacuation).Although still cited by the HSE [11], this report is already outdated in some

respects in that the general introduction of AIS post-date it. AIS enables tracking andidentification of vessels in the vicinity of an offshore installation with improved rangeand accuracy over radar.

Models (e.g. COLLRISK [12]) allow the benefits of such measures to be taken intoaccount within the risk modelling.

3.0 Guidance on use of data3.1 General validity

As stressed in Section 2.3.2.1, the frequency of passing vessel collisions with offshore

installations is highly location specific and therefore it is not appropriate to present inthis datasheet any statistical passing vessel collision frequencies. The frequenciesrequired should be estimated as described in Section 2.3.2.1.

The data selected for presentation in Section 1.2.2 are those which can be consideredvalid for use in QRA, at least to determine whether ship collision risks are significant. Ifthey are, then more detailed analysis of frequencies (for infield vessel collisions) and/or

of consequences may be required.

3.2 Uncertainties

As in all analyses of incident data, the completeness of incident reporting in particular

is open to question, especially as regards potential under-reporting of minor incidents.However, for a QRA it is those collisions with the potential to result in fatalities,significant damage or pollution that need to be considered, and reporting of suchincidents is more likely to be complete.

The exposure data (i.e. unit-years) can be considered reliable, although for MODUs theydo not appear to distinguish between units in operation offshore and units laid-up; also,prior to 1983, geographical data are only available for some regions.

3.3 Example

The frequency of supply vessel collisions causing significant or severe damage or total

loss to a fixed installation in the North Sea is required for a QRA. It is assumed that thesupply vessel visit frequency is typical of such installations.


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Worldwide average infield vessel collision frequency = 9.3 10-4

per year (Table 2.2, 1990-

2002)

North Sea weighting = 9.55 (Table 2.9)

Fraction of collisions due to supply vessels = 0.34 (Table 2.7, production units)

Fraction of significant damage + severe damage + total loss = 0.26 (Table 2.11, supply

vessels4

)

Hence the overall frequency of significant supply vessel collisions with the installationis estimated as:

(9.3 10-4) 9.55 0.34 0.26 = 7.9 10

-4

Further, installation specific analysis would be required to determine the consequences(e.g. damage to conductors, escalation) of such a collision. If the overall risk wereconsidered high, then more detailed analysis taking into account existing collision risk

management (e.g. supply vessel approach procedures) could be carried out.

4.0 Review of data sourcesThe analysis presented in Section 1.2.2 is derived from two sources:

Worldwide: WOAD incident data [1] for the period 1980-2002 combined with DNVsanalysis of offshore unit exposure [8] for the same period. The WOAD database hasbeen used for the detailed information available in it as regards damage levels andgeographical region.

UKCS: HSE reports [3][4] and associated accident databases for the period 1980-2005. The reports include exposure data as well as summaries of accident statistics.The databases give the year, type of unit involved, operation mode and event

category (see below) as well as an event description.Incidents involving collision recorded in the WOAD database include incidents that haveoccurred during transfer of mobile units, to units that were idle, to units underconstruction, or to units under repair in port or in a yard. These were eliminated fromconsideration, as have units of other types, i.e. not involved in drilling or production.However, accommodation units are included. The analysis in Section 1.2.2 is therefore

for fixed units offshore and for mobile units operating (drilling or production) offshore.

The UKCS databases distinguish between collision events involving passing vessels(event code CL) and collision events involving visiting vessels (event code CN), The

accident descriptions have been reviewed to identify those that resulted in an actualcollision as well as the type of vessel involved (for passing vessel collisions). Event

categories do not specifically indicate damage levels; they are defined in Table 4.1.

4The last of these could also have been selected from Table 2.10, taking the North Sea value.

Table 2.11 has been used as the data are specific to a fixed installation and to a supply vessel.The value is also higher than would have been obtained from Table 2.10 (0.21), hence the resultwill be more conservative and hence will accentuate any requirement for more detailed analysisand/or improved collision risk management.


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Table 4.1 Event Categories in UKCS Database [3][4]Category DescriptionA Accident Hazardous situation which have developed into an accidental situation. In

addition, for all situations/events causing fatalities and severe injuriesthis code should be used

I Incident Hazardous situation not developed into an accidental situation. Lowdegree of damage, but repairs/replacements are required. This codeshould also be used for events causing minor injuries to personnel orhealth injuries.

N Near-Miss Events that might have or could have developed into an accidentalsituation. No damage and no repairs required

U Unsignificant Hazardous situation, but consequences very minor. No damage, norepairs required. Small spills of crude oil and chemicals are alsoincluded. To be included are also very minor personnel injuries, i.e. "losttime incidents".

5.0 Recommended data sources for further informationThe analysis derived from the WOAD database [1] has used only some of theinformation available in the database. Each incident record contains a description (ofvarying quality) and (besides the information used in the analysis presented here) alsothe following information that could be used for more detailed investigation:

Accident date Unit name Human and equipment causes

Geographical area, shelf and field block Numbers of crew and 3rd party fatalities and injuries Fluid spilt (if any)

Repairs required

Evacuation

The WOAD database also includes collisions that have occurred in situations other than

drilling and production offshore: units that were under transfer, idle, under constructionor under repair in a port or yard. It can therefore be used to obtain information aboutcollision incidents in these circumstances if required.

The UK HSE has published accident statistics for fixed and floating offshore units on

the UK Continental Shelf 1980-2005 ([3], [4] respectively). These include collisions butdo not give details in the reports; more detailed information is available in theaccompanying databases (available as Excel spreadsheets)

The Petroleum Safety Authority Norway publishes annual reports on risk levels in thepetroleum industry and an annual report including a Facts Section that includes someinformation on accidents including collisions.

The US Minerals Management Service publishes numbers of incidents including

collisions by year and provides links to more detailed descriptions of each incident,however it has not proved possible to obtain the corresponding annual exposure data.

6.0 References6.1 References for Sections 2.0 to 4.0

[1] DNV. WOAD -Worldwide Offshore Accident Databank, v5.0.1.[2] Dovre Safetec AS, 1995. SAFETOW Reference Manual Risk Assessment of Towing

Operations, Draft Report No. ST-95-CR-015-00.


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[3] DNV, 2007a. Accident statistics for fixed offshore units on the UK Continental Shelf 1980-2005, HSE Research Report RR566, Sudbury, Suffolk: HSE Books.http://www.hse.gov.uk/research/rrhtm/rr566.htm

[4] DNV, 2007b. Accident statistics for floating offshore units on the UK Continental Shelf

1980-2005, HSE Research Report RR567, Sudbury, Suffolk: HSE Books.http://www.hse.gov.uk/research/rrhtm/rr567.htm

[5] J. P. Kenny, 1988. Protection of Offshore Installations Against Impact, Report No. OTI 88535, Sudbury, Suffolk: HSE Books.

[6] NPD, 1984. Regulation of Structured Design of Loadbearing Structures.[7] Department of Energy, 1990. Offshore Installations, Guidance on Design, Construction

and Certification, 4th. ed.

[8] DNV, 2004. Exposure Data for Offshore Installations 1980-2002, Technical Note 22(unpublished internal document).

[9] HSE, 2000. Effective Collision Risk Management for Offshore Installations, Offshore

Technology Report OTO 1992 052, Sudbury, Suffolk: HSE Books.http://www.hse.gov.uk/research/otopdf/1999/oto99052.pdf

[10] HSE, 1997. Successful health and safety management, ISBN 0717612767, HS(G)65,Sudbury, Suffolk: HSE Books.

[11] HSE, 2008. Collision risk management guidance on enforcement, HSE SemiPermanent Circular SPC/ENFORCEMENT/24.http://www.hse.gov.uk/foi/internalops/hid/spc/spcenf24.htm

[12] Anatec. COLLRISK. www.anatec.com/collrisk.htm[13] Anatec, 2007. Assessment of the benefits to the offshore industry from new

technology and operating practices used in the shipping industry for managingcollision risk, HSE RR592.

[14] ISO, 2000. Petroleum and natural gas industries Offshore production installations Requirements and guidelines for emergency response, International Organization for

Standardization, ISO 15544:2000.[15] ONGC, 2006. Annual Report 2005-06, p33.

http://www.ongcindia.com/download/AnnualReports/annual_reports05-06.htm

6.2 References for other data sources

NorwayPetroleum Safety Authority Norway.

Annual Report 2007 Facts Sectionhttp://www.ptil.no/getfile.php/PDF/FACTS%202008.pdf

Risk Levels in the Petroleum Industry, Trends 2007

http://www.ptil.no/getfile.php/PDF/Summary_rep_2008.pdf

Similar reports available for previous and subsequent years from the above.

USA Minerals Management Service, OCS Related Incidents, Incident Statistics andSummaries 1996-2010 http://www.mms.gov/incidents/IncidentStatisticsSummaries.htm tabulates numbers of incidents including collisions by year and provides links to moredetailed descriptions of each incident.


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