Ship Collision

Risk Assessment Data Directory

Report No. 434 16March 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/ installation collisions

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RADD Ship/installation collisions

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contents

1.0 Scope and Definitions ........................................................... 1 1.1 Scope ............................................................................................................... 1 1.2 Definitions ....................................................................................................... 1 1.2.1 Collisions .................................................................................................................... 1 1.2.2 Damage ....................................................................................................................... 2 2.0 Summary of Recommended Data ............................................ 3 2.1 Basics of ship collision risk modelling......................................................... 3 2.1.1 Collision Frequency ................................................................................................... 3 2.1.2 Collision consequences ............................................................................................ 4 2.2 Overview of historical ship/installation collision information.................... 7 2.3 Passing vessel collisions............................................................................... 9 2.3.1 Shipping traffic patterns and vessel behaviour ...................................................... 9 2.3.2 Best practice collision risk modelling for passing vessels ................................. 11 2.4 Field related vessel collisions ..................................................................... 12 2.4.1 Frequencies of field related vessel collisions ....................................................... 12 2.4.2 Consequences of vessel related field collisions................................................... 16 2.4.3 Collisions of mobile units........................................................................................ 17 2.5 Collision risk management .......................................................................... 18 3.0 Guidance on use of data ...................................................... 18 3.1 General validity ............................................................................................. 18 3.2 Uncertainties ................................................................................................. 18 3.3 Example ......................................................................................................... 18 4.0 Review of data sources ....................................................... 19 5.0 Recommended data sources for further information ............ 20 6.0 References .......................................................................... 20 6.1 References for Sections 2.0 to 4.0 .............................................................. 20 6.2 References for other data sources.............................................................. 21


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Abbreviations: AIS Automatic Identification System ARPA Automatic Radar Plotting Aid BHN Bombay High North DP Dynamic Positioning DSV Diving Support Vessel ERRV Emergency Response and Rescue Vessel FPSO Floating Production, Storage and Offloading unit FPU Floating Production Unit FSU Floating Storage Unit H2S Hydrogen sulphide HC Hydrocarbon HSE Health and Safety Executive MODU Mobile Offshore Drilling Unit MSV Multipurpose Support Vessel QRA Quantitative Risk Assessment REWS Radar Early Warning System ROV Remotely Operated Vehicle TEMPSC Totally Enclosed Motor Propelled Survival Craft TLP Tension Leg Platform TR Temporary Refuge UK United Kingdom UKCS United Kingdom Continental Shelf


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1.0 Scope and Definitions 1.1 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 in Quantitative 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 being

considered, including merchant vessels, fishing vessels, naval vessels and also offshore related traffic going to and from other installations than that being considered.

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

For passing vessels, collision risk is highly location dependent due to variation in ship traffic from one location to another. The ship traffic volume and pattern at the specific location should hence be considered with considerable care. This dependency on location also means that use of historical data which are averaged over a large number of different locations, is not possible. For passing vessels, the datasheet therefore presents best current practice in modelling collisions of passing vessels with offshore installations rather than recommended frequencies. Field related offshore traffic refers to those vessels which are specifically visiting the installation, and is therefore considered to be less dependent of the location of the installation. The frequency of infield vessel impacts will depend on the durations that vessels 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 the collisions.

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 failure of anchor lines or towline and is drifting only under the influence of environmental forces. Table 1.1 sets out the different types of vessels that may collide with an offshore installation.


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Table 1.1 Categories of Colliding Vessels

Type Of Traffic

Traffic Category

Vessel Category

Remarks

Merchant Merchant ships: cargo, ferries etc.

Commercial traffic passing the area

Surface vessels Both war ships and submarines Naval traffic Submerged vessels

Submerged submarines

Fishing vessels

Fishing vessels Sub-categorised into vessels in transit and vessels operating in the area

Pleasure Pleasure vessels Traffic passing the area Standby boats Vessels going to and from other

fields Supply vessels Vessels going to and from other

fields Offshore tankers Vessels going to and from other

fields

Passing

Offshore traffic

Tow Towing of drilling rigs, flotels, etc. Standby vessels Dedicated standby vessels Supply vessels Visiting supply vessels Working vessels Special services/support such as

diving vessels, flotels, pipe lay barges, intervention vessels and crane barges

Offshore traffic

Offshore tankers Shuttle tankers visiting the field

Field related

Drilling rigs MODUs May collide with fixed installation either on approach or as a result of mooring 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 from

an insurance point of view. However, the unit may be repaired 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 the unit; minor damage to loadbearing structures; significant damage to single essential equipment; damage to more essential equipment.

Minor damage Minor damage to single essential equipment; damage to more none-essential equipment; damage to non-loadbearing structures.


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

2.0 Summary of Recommended Data The 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 two parts: 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 be estimated from knowledge of shipping traffic in the vicinity of the installation. This is discussed, 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 current and wind. For a passing vessel, not suffering from propulsion or steerage problems, to collide with 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 developing

situation 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 the operator 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 the vessel and attracting its attention using light and sound signals, such as pyrotechnics.

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/or AIS.

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


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These scenarios can be addressed by using appropriate collision risk models. Care should 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 = 0.5 kMV2 where k is the hydrodynamic added mass constant: k = 1.1 for 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 on whether the impending collision has been detected, e.g. by radar or AIS, and whether a precautionary alarm, evacuation or down-manning has then been carried out. If a vessel under 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 radar down 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 datasheet Evacuation, Escape and Rescue), or for personnel to remain on the installation. Each of these carries attendant risks. If a drifting vessel is observed on a collision course, the time 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 figures are 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 to detect vessels on a collision course, their availability, and the procedures to decide on mustering and precautionary evacuation/down-manning. Any or all of these may be dependent 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 the jurisdiction, impending ship collision is not necessarily considered to require a TR; however, the muster location in this scenario is conveniently identified with the TR.

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


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Figure 2.1 Example Flow Chart for Powered Vessel on Collision Course with 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 decision whether or not to evacuate, and if to evacuate then for TEMPSCs to be sufficiently far away at the time of collision. Late can be considered to give some time to muster at least some personnel in the TR but insufficient for TEMPSC evacuation; on a bridge linked complex, some personnel are considered in this example to have insufficient time to reach the TR and therefore to attempt escape to sea.


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Figure 2.2 Example Flow Chart for Drifting Vessel on Collision Course with 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 initiate helicopter evacuation (considering the time required to mobilise sufficient helicopters) if this is possible (e.g. sufficient visibility), or else to muster personnel, and make a decision whether or not to evacuate. Late can be considered to give some time to muster at least some personnel in the TR but insufficient for TEMPSC evacuation; on a bridge linked complex, some personnel are considered in this example to have insufficient time to reach the TR and therefore to attempt escape to sea. A drifting vessel typically moves at 1 to 2 kn so, in this example, it is assumed that the drifting vessel 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 in place at the field and the detection system that is used. Information on the performance of some detection 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, of which 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 vessels unconnected 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 from collisions.

Table 2.1 Collisions with Offshore Installations (Worldwide)

Passing Vessels Infield Vessels Damage*

Number Percent Number Percent Total 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. This resulted in serious oil leakage and a major fire, resulting in the loss, within two hours, of both the BHN platform and a jackup rig working alongside. A total of 22 fatalities resulted, on the installation, jackup and MSV; 362 personnel were rescued, some after spending more than 12 hours in the water [15]. The collision occurred despite the MSV being DP (Dynamic Positioning) equipped. Other types of incident in the WOAD database include: Collision during towing or mobilizing/demobilizing of MODUs (involving vessels

associated with the activity such as tugs, supply vessels, and anchor handling vessels).

Collision during construction/repair (involving vessels involved with the activity such 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 struck installation, a pipeline or a loading hose. In one incident, the colliding vessel was damaged and oil leaked from its fuel and lube oil tanks. In a further 2 incidents, gas including H2S was released.


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Worldwide passing vessel collision frequencies for the periods 1980-1989 and 1990-2002 have been estimated separately as shown in Table 2.2. Both passing vessel and infield vessel collisions have considerably reduced from the earlier to the later period, by almost 60% for passing vessels and 50% for infield vessels.

Table 2.2 Worldwide Collision Data during 1980-1989 and 1990-2002

Collisions Exposure (installation-years)

Collision Frequency (per installation-year)

Vessel Type

1980-1989 1990-2002 1980-1989 1990-2002 1980-1989 1990-2002 Passing 33 24 5.9 10-4 2.5 10-4 Infield 103 86

56243 97627 1.8 10-3 8.8 10-4

Note: figures for Infield vessels exclude loading buoy incidents, for which exposure data is not available.

DNV has prepared research reports [3], [4] and associated incident databases for the UK HSE covering accident statistics for offshore installations on the UKCS 1980-2005. These include 432 events described as Collision, although not all of these resulted in actual impact. Table 2.3 summarises the statistics for all recorded collision related events, including near misses; Table 2.4 presents summary statistics for those events that resulted in actual impact, however minor. Clearly visiting vessels dominate the statistics even more completely than they do worldwide. However, as Table 2.5 shows, only 5% of collision events are classified as Accidents, as compared with 31% of passing vessel events; most visiting vessel events involve minor scrapes. The number of collision related events involving passing powered vessels appears to have increased significantly from 1980-1989 to 1990-2005, possibly due to better reporting of near misses; however, the frequency of actual collisions has fallen by 30% to 40%, for both passing and visiting vessels. This may be attributable to improved communication systems, electronic charting, and navigational techniques, systems and procedures. Introduction of ARPA and DP systems may also have played a role.

Table 2.3 UKCS Collision Event Data during 1980-1989 and 1990-2005

Events Exposure (installation-years)

Event Frequency (per installation-year)

Vessel Type

1980-1989 1990-2005 1980-1989 1990-2005 1980-1989 1990-2005 Passing 5 42 3.0 10-3 9.1 10-3 Visiting 140 245

1685 4630 8.3 10-2 5.3 10-2

Table 2.4 UKCS Collision Data during 1980-1989 and 1990-2005

Collisions Exposure (installation-years)

Collision Frequency (per installation-year)

Vessel Type

1980-1989 1990-2005 1980-1989 1990-2005 1980-1989 1990-2005 Passing 5 10 3.0 10-3 2.2 10-3 Visiting 132 213

1685 4630 7.8 10-2 4.6 10-2


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Table 2.5 UKCS Collision Event Categories 1990-2005

Passing Vessels Visiting Vessels Event Category1 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 Table 2.1.

2. This can be read as Insignificant (Unsignificant is used for consistency with 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 subsea wellhead 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 other installations or shuttle tankers, i.e. 7 of the events are known to have involved field related 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 several distinct 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 the following 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 collision hazard, 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 are higher 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 about movements 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 is difficult to assess since possible routes and areas where naval vessels operate/exercise can 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 (submarines included) and submerged traffic. 2.3.1.2.1 Surface Traffic

As 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 as these vessels have a large crew compared to merchant vessels. They will always have at least two persons on the bridge (large vessels such as frigates, destroyers and aircraft carriers will have more personnel on the bridge). Normally the operations room is 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 or detect the installation, and avoid it. In addition, naval vessels are more likely to operate in groups, which also will reduce the collision probability. Submarines operating on the surface are not considered to represent any higher threat to the installation than any other surface vessel. Overall, it is considered that the contribution to overall collision risk from such vessels is in general likely to be very low. 2.3.1.2.2 Submerged Submarine Traffic

As for naval surface vessels, due to a reduced probability of drifting combined with a relatively 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 vicinity of offshore installation in times of peace. Nevertheless a 1988 incident when a submarine collided with Norsk Hydros Oseberg B platform shows a deviation from this principle. 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 changed appreciably 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 and with no preferred heading.


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Fishing vessels vary in size from large factory/freezer ships to smaller vessels operating near the coast. Typically, a large fishing vessel will have a displacement around 1000 tonnes. This implies that the collision energy will be less than 20 MJ. For a typical North 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 fishing vessel 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 are in 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 from operator influence (procedure, training competency, communication etc.). Vessels or installations under tow pose particular problems which are considered separately (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 to shipping 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. Where possible, other methods of logging vessel tracks in and around a field can be implemented such as Automatic Identification Systems (AIS). This can be achieved using systems such as AISTracker and will provide an enhanced understanding of the behaviour of shipping around the field. This offers considerable benefit to collision risk assessment work in relation to passing and infield vessel risk assessment. Details are provided 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 following causes 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 system concerned (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 of interest (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 traffic volumes in proximity to the installation, ship characteristics (e.g. type, size and speed), installation dimensions/orientation, and metocean data, in particular visibility. The model 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 from insignificant 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 to installation personnel. Initially, the damage breakdown in Table 2.1 could be used directly in a QRA together with 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 no fatalities 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 accident involving fatalities is credible, especially if escalation to a hydrocarbon fire or explosion occurs. If this relatively simple approach indicates high ship collision risks, then more detailed analysis may be required in order to demonstrate that the simple approach is conservative. This could involve structural analysis of the effect of a vessel collision with 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 on geographical location is largely limited to metocean conditions and allowable weather criteria; conversely, field related vessel collisions are strongly dependent on the field activities (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 for fixed platforms compared with FPSOs and FPUs, and wide variation between the collision frequencies for the different types of FPU. There are also variations between different types of MODU but these are not so great.

2 Such 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 that collision frequencies for a particular unit will be strongly dependent on the number of visits per year 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 the frequencies given in Table 2.6 can be used. If field related collision frequencies prove to be an issue, then a more detailed analysis should be undertaken, using actual data combined with collision risk modelling.


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Figure 2.3 shows worldwide collision frequencies for production installations, Figure 2.4 collision 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 from

those for FPSOs and FPUs. TLPs appear to be subject to a significantly higher collision frequency than jackups

and semi-submersibles.

Table 2.6 Field Related Vessel Collision Statistics (Worldwide)

Unit Type Collisions Exposure (unit-years)

Collision Frequency

(per unit-year) Production Units Fixed 77 135122 5.7 10-4

FPSO 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 Collision Frequencies (Worldwide)

Error bars indicate 90% confidence limits.


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Figure 2.4 MODU Vessel Collision 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 Production Units

MODUs

Supply 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 companies themselves, and they can impose restrictions on vessel operations if it is deemed necessary. 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 vary significantly from region to region, even considering only the regions with large numbers of offshore installations and MODUs operating. Of these areas, the frequency is 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 to the worldwide average. It is not clear from the data whether these high frequencies are due to better reporting, especially of minor collisions, the more severe weather conditions in the North Sea compared with other regions, or better control of infield vessel movements in other regions. There has been no collision resulting in significant or severe damage or total loss in the North Sea since 1994. Table 2.8 gives a detailed breakdown of collisions between visiting vessels and installations 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 a much 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 is significantly higher than any other region.

Table 2.8 UKCS Field Related Vessel Collision Statistics 1990-2005

Unit Type Collisions Exposure (unit-years)

Collision Frequency

(per unit-year) Production Units Fixed 90 3383 2.7 10-2

FPSO & 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 Frequencies Compared to Worldwide Average

Region Fraction of 1990-2002 Worldwide

Average Africa 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: All Installations

Damage Level (see Section 1.2.2 for definitions) Geographical Area Total

Loss 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 Installations

Damage Level (see Section 1.2.2 for definitions) Vessel Type Total Loss Severe Significant Minor Insignif./No

Supply 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: FPSOs


Supply 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 Other 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: FPUs


Supply 0% 0% 50% 50% 0% 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 Other 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: MODUs


Supply 0% 5% 43% 33% 18% 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 vessel impacts [6], [7]. These collisions are therefore to a large degree minimized by platform design. Hence the distribution of damage levels to be expected from field related vessel collisions in different geographical areas may vary from those tabulated above according to the installation design criteria. They may also vary according to operational procedures: for example, an arriving supply vessel may be required to stop on 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 design criteria and operational procedures, these should be taken into account if the risk levels are sufficiently high to occasion concern. The trend towards the use of larger, multipurpose vessels, which may exceed the size the installation was originally designed 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 hurricane Andrew (27/08/1992). 3 further weather related incidents occurred. Of the remaining 2 incidents, 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 mobile units. 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 itself contacting 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 commences with the HSEs general Safety Management System model as set out in HS(G)65 [10] and shows how this can be applied specifically to managing ship collision risks. [9] then presents specific measures for managing in-field and passing vessel collision risks. It also includes as Appendix B an overview of ship collision detecting and alerting (hardware) systems. This includes normal setups such as standby vessel with standard marine radar or ARPA, and more sophisticated systems such as REWS (Radar Early Warning System using installation-mounted scanners to increase detection range and provide early warning of vessels on a possible collision course with the installation, allowing an early decision and response such as precautionary partial or full evacuation).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 and identification of vessels in the vicinity of an offshore installation with improved range and accuracy over radar. Models (e.g. COLLRISK [12]) allow the benefits of such measures to be taken into account within the risk modelling.

3.0 Guidance on use of data 3.1 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 in this datasheet any statistical passing vessel collision frequencies. The frequencies required 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 considered valid for use in QRA, at least to determine whether ship collision risks are significant. If they 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 such incidents is more likely to be complete. The exposure data (i.e. unit-years) can be considered reliable, although for MODUs they do 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 the supply 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 installation is 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 were considered 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 sources The analysis presented in Section 1.2.2 is derived from two sources: Worldwide: WOAD incident data [1] for the period 1980-2002 combined with DNVs

analysis of offshore unit exposure [8] for the same period. The WOAD database has been used for the detailed information available in it as regards damage levels and geographical 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 have occurred during transfer of mobile units, to units that were idle, to units under construction, or to units under repair in port or in a yard. These were eliminated from consideration, 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 actual collision 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.

4 The 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 result will be more conservative and hence will accentuate any requirement for more detailed analysis and/or improved collision risk management.


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Table 4.1 Event Categories in UKCS Database [3][4]

Category Description A Accident Hazardous situation which have developed into an accidental situation. In

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

I Incident Hazardous situation not developed into an accidental situation. Low degree of damage, but repairs/replacements are required. This code should also be used for events causing minor injuries to personnel or health injuries.

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

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

5.0 Recommended data sources for further information The analysis derived from the WOAD database [1] has used only some of the information available in the database. Each incident record contains a description (of varying quality) and (besides the information used in the analysis presented here) also the 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 construction or under repair in a port or yard. It can therefore be used to obtain information about collision 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 but do not give details in the reports; more detailed information is available in the accompanying databases (available as Excel spreadsheets) The Petroleum Safety Authority Norway publishes annual reports on risk levels in the petroleum industry and an annual report including a Facts Section that includes some information 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 References 6.1 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 88 535, 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 Semi Permanent 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 managing collision 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 Norway Petroleum Safety Authority Norway. Annual Report 2007 Facts Section http://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 and Summaries 1996-2010 http://www.mms.gov/incidents/IncidentStatisticsSummaries.htm tabulates numbers of incidents including collisions by year and provides links to more detailed descriptions of each incident.

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