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Environment guidelines for EER systems in ice-covered waters
Cold Regions Science and Technology 42 (2005) 201 – 214 www.elsevier.com/locate/coldregions
Environment guidelines for EER systems in ice-covered waters G.W. Timcoa,T, D.F. Dickinsb a
Canadian Hydraulics Centre, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6 b DF Dickins Associates Ltd., 9463 Poole Street, La Jolla, CA 92037, USA Received 8 November 2004; accepted 17 January 2005
Abstract The effects of ice and cold water environments on escape, evacuation, and rescue (EER) systems for offshore structures in ice-covered waters are discussed. The cold region environment influences all aspects of EER system design. Guidance is provided, for a wide range of ice and environmental conditions, on the factors that should be considered in developing an EER system for a structure that is to be operated in ice-covered waters. There is no one EER system that can reliably accommodate all of the requirements for safe evacuation from Arctic structures and several different systems may be required for year-round operation. Furthermore, the most suitable evacuation system will be different for different environmental conditions. Careful design, planning, training, and ongoing maintenance of the EER system are required for these harsh environmental conditions. D 2005 Elsevier B.V. All rights reserved. Keywords: Arctic structures; Environment guidelines; EER systems; Ice-covered waters
1. Introduction Oil and gas activity in terms of exploration, production, and transportation is increasing in icecovered waters worldwide. At the present time, there is year-round production in ice-covered waters in Canada, Alaska, and China, and seasonal production in the Sakhalin region of Russia. Exploration activity is, or will be, undertaken in the ice-covered portions of the Caspian Sea, Canada’s east coast and Beaufort Sea frontiers, the Barents Sea, and the Kara Seas. T Corresponding author. E-mail addresses: [email protected] (G.W. Timco)8 [email protected] (D.F. Dickins). 0165-232X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.coldregions.2005.01.005
Year-round production in ice-covered waters of the North Caspian and off the Northeast Coast of Sakhalin Island will become a reality within the next 3 years. Platforms in ice-covered waters face many unique challenges in terms of providing reliable escape, evacuation, and rescue (EER) systems. In cold climates, there are several complicating factors that can influence the selection of appropriate EER systems. Often, one type of system cannot be used throughout the year due to the changing ice and other environmental conditions at the site. There have been a number of papers published on evacuation procedures from offshore structures in icecovered waters. Zahn and Kotras (1987) did a study of the evacuation procedures from offshore drilling and
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production units in the Bering, Chukchi, and Beaufort seas. Poplin et al. (1998a,b) provided an excellent overview of the issues related to evacuation in icecovered waters. Polomoshnov (1998) discussed aspects of evacuation from a platform in the Sakhalin offshore region. Bercha (2004) and Bercha et al. (2001, 2004) have discussed various aspects of the reliability of Arctic EER systems. Barker et al. (2001) and Barker and Timco (2003) presented the results of a numerical modelling approach that provides information on the range of safe zones around the Arctic structures for different ice conditions. Cremers et al. (2001) discussed the current status and development of emergency evacuation from ships and offshore structures in icecovered waters. Wright et al. (2003a,b) presented an overview of evacuation systems for ice-covered waters. Chin et al. (2003) discussed the EER system developed for the Sakhalin II Phase 2 platform. Poplin and Timco (2003) discussed the size of the ice damage zone around conical structures. Simo˜es Re´ and Veitch (2003), Simo˜es Re´ et al. (2002, 2003), and Barker et al. (2004) presented information on the performance limits of survival craft in different wave/ice conditions. Most of the previous works have dealt with evacuation systems and their reliability, but, to date, there has been little detailed discussion on the implications of environmental conditions on different EER systems. The Arctic environment can influence all aspects of EER system design, specifications, and maintenance. Relevant environmental conditions must also be considered in the development and implementation of an EER plan or system. This paper provides guidance on the factors that should be considered in developing an EER system for an offshore production structure in icecovered waters. The paper does not consider any particular EER system; rather, it focuses on the impact of different ice environments on the whole EER system. It should be mentioned that the authors are members of ISO TC67/SC7/Technical Panel 8 developing the EER standards for offshore structures designed for use in ice-covered waters. This paper is an outgrowth of work conducted on behalf of this panel.
2. Low temperatures
of
Temperatures in the Arctic routinely reach values 40 8C and colder, and affect both hardware and
people in a significant manner. Machinery and any device with moving parts can become immobile. Materials become brittle at low temperatures and this effect must be considered in the selection of components and materials to be used in all elements of the EER systems. Lubricants, fuels, and hydraulic fluids need to be selected to suit the expected minimum temperature. Engines must be able to handle the additional demands of cold temperature starting (preheaters, high-capacity batteries, etc.). Cooling systems (radiator and/or seawater) need to be designed to prevent ice blockage from freezing inlets. Low temperatures also dictate that personnel must wear suitable warm clothing and footwear. This makes movement more difficult. Face and head protection can impair communications. Operating machinery with heavy gloves can be difficult and sometimes impossible if the controls are not designed properly. All of these factors must be considered in the yearround design, operation, and maintenance of the EER system. The IMO Circular on Guidelines for Ships Operating in Arctic Ice-Covered Waters (IMO, 2002) gives valuable guidance on selecting, designing, and maintaining marine equipment for Arctic operations.
3. Limited daylight There can be a large variation in daylight hours at platforms located in ice-covered regions (particularly at high latitude locations). In early winter, a true Arctic structure may experience only a few hours of twilight in a day. Therefore all designated outdoor escape routes must be sufficiently lit. The choice of lighting systems must also be able to deal with the full range of expected temperatures.
4. Strong winds and blowing snow The combination of cold temperatures and even moderate winds can create dangerous levels of wind chill. Strong winds, often encountered in winter storms with large ocean fetches, can make outside survival extremely challenging without suitable shelter and personal protection. Severe frostbite can occur on unprotected skin in a matter of minutes. Blowing snow often associated with storm events can lead to a
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disorienting condition known as a bwhite out,Q with essentially zero visibility. Low visibility, combined with the need to wear heavy winter clothing and footwear, will lead to seriously impaired mobility and dexterity. All of these issues need to be taken into account in the detailed design of EER systems.
5. Sea spray and atmospheric icing The combination of low temperatures and strong winds can often lead to icing on a platform, standby vessel, or exposed evacuation system (chutes, capsules, etc.). In many instances, this icing can be extremely severe (see Fig. 1). Outdoor escape routes must be designed to prevent or minimize icing on walkways and handrails, and indoor escape routes are preferred. Methods for removing icing must be in place and used as soon as icing occurs. Hardware and mechanical systems (winches, davits, shackles, nets, etc.) can become covered with ice, which may prevent or impair their operation. Systems must be continuously monitored for dangerous ice accumulation on a regular basis and steps taken to remove the ice as it builds.
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6. Open water conditions In all ice-covered regions, the platform will likely be in open water conditions for a part of the year. Suitable evacuation and rescue systems, not necessarily the same systems that work in ice, need to be in place to deal with these cold open water periods. Laboratory tests that can provide guidance on the clearing of survival craft in various wave conditions (Simo˜es Re´ et al., 2002), broken ice (Simo˜es Re´ et al., 2003), and wave/ice conditions (Barker et al., 2004) have been performed. Fig. 2 shows a photograph of a model survival craft in waves and high ice concentration (after Barker et al., 2004). These test programs have shown that in calm water, there is a threshold of ice concentration of approximately six-tenths above which survival craft designed for open water has difficulty traversing (Simo˜es Re´ et al., 2003). With waves and ice, the craft can travel further in similar ice concentration, but only in the wave direction. Travelling into the waves with broken ice proved to be quite difficult (Barker et al., 2004). Cold water drastically affects the personnel survival time (Brooks, 2001). An approved Class A immersion suit is required to achieve a desirable
Fig. 1. Photograph showing spray icing covering the deck and an evacuation lifeboat. This presents a very dangerous condition if quick escape is required.
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Fig. 2. Photograph showing a laboratory test of a model of a survival craft in high waves and high ice concentrations. The tests provide information on the ability of the craft to move in different wave/ice conditions (after Barker et al., 2004).
survival time of 6 h in water temperatures less than 2 8C, characteristic of offshore areas where ice is present (ISO 15027, 2002). For cases of escape onto the ice surface, existing survival/immersion suits can degrade survivability by restricting mobility and manual dexterity, and offering inadequate protection to the extremities from risk of frostbite (hands, feet, and face). In addition, many existing survival suits can be extremely difficult to don in cold temperatures due to stiffening of the suit materials. Selection of effective immersion suits for an offshore installation needs to account for issues of survivability in a high wind chill environment on the ice surface, the possible need to move away from the hazard zone on foot through rough ice, and the immersion suit survivability in an ice/water mixture.
7. Currents Currents in the presence of ice will influence the validity and accuracy of trajectory models used to estimate position of survivor locations over time. The relative effects of residual currents, currents at depth, cyclical tidal streams, and wind-driven surface currents all need to be accounted for in the trajectory
model(s) used to support the search and rescue operations. Trajectory models may need to be run for survivors that may be in the water, or for those on the surface of drifting ice. For example, thick ice features with significant draft can often move in a direction different from the prevailing surface water motion. Also, ice with a rough surface (high drag coefficient), or isolated ice floes in areas of low concentration can move at much higher velocities than ice confined in an area of higher (over 6/10) concentrations (Vaudrey and Dickins, 1996).
8. Ice conditions Evacuation systems in ice-covered waters must be designed and developed to cope with a wide variety of different ice conditions or ice regimes. This section provides information on the types of ice regimes that might be encountered by a structure in Arctic or subArctic waters. It also provides guidance on how various ice conditions can affect the performance of the EER systems. It should be noted that any given structure may not encounter all of these different regimes. A detailed analysis should be done to define the ice regimes at a specific location.
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Several ice characteristics can influence the type of evacuation and rescue system that could be used in ice-covered waters. Detailed information on ice properties and environments can be obtained from various sources and will not be discussed here. From an EER standpoint, the following ice characteristics are especially important: Ice concentration The total ice coverage on the water is expressed as a concentration in tenths. The impact of the ice concentration is very much dependent on the evacuation system used. Some systems may benefit from low, medium, or higher concentrations and may perform better in one ice concentration than another. Ice speed The speed of the ice is an important factor and highly dynamic ice conditions are typically the most challenging. For example, rapidly moving floes may interfere with launching and successful clearing of survival crafts. On the other hand, high drift speeds can aid in the rapid movement of survivors away from the platform. Ice thickness The ice thickness can influence the evacuation in many ways. New, thin ice generally presents fewer problems but precludes any consideration of direct evacuation onto the ice surface. Thick ice generally presents many challenging issues for survival craft designed for use in open water as well as consideration of standby vessels needs. On the other hand, thick ice can support an evacuation craft or potentially provide a temporary refuge (TR) if appropriate survival gear is available. Ice type Some regions will have only first-year ice present while others may have a mix of first-year ice, second-year ice, and multi-year ice, and glacial. Old ice floes can be considerably stronger and thicker than first-year ice, and can threaten the integrity of survival crafts and stationkeeping of icebreaking vessels. On the other hand, such floes can also be used as a stable platform for survivors. Floe size The sizes of the ice floes are important. Large floes (hundreds of metres) with appropriate thickness can offer places of refuge, while dynamic small floes in combination with high sea states and swell could threaten the stability and structural integrity of small survival craft. Small floes/ice pieces could affect the ability of a survival craft to clear a platform after launch by blocking propellers and water intakes.
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Ice roughness/deformation The surface roughness or deformation of the ice can create problems with over-ice mobility. This could be critical if survivors have to evacuate through ice rubble to reach a TR or a standby rescue vessel. Thick deformed ice may also prevent a standby vessel from approaching a platform for direct survivor recovery. Heavily deformed pack ice can provide additional problems for stationkeeping of standby vessels. Ice pressure Internal pressure in the ice sheet can significantly affect the ability of survival craft to move away from the platform or make any headway. Severe pressure could result in bnippingQ and potential destruction of a small survival craft through crushing and/or overturning. Ice wave conditions In low ice concentrations, waves or swell can cause complications in launching a survival craft or survival craft into the sea. If there are small floes present, they could also compromise the integrity and stability of survival craft (wave energy combined with small ice fragments can create potentially high local impact loads). Spring melt This situation can introduce a number of evacuation issues depending upon the type of evacuation system chosen. Mobility on the ice is severely curtailed by melt pools and open holes, and the ice surface may become too dangerous to consider direct evacuation as an option. The following sections discuss the key ice parameters and relative difficulty of evacuation and rescue for a wide range of ice regimes. 8.1. New Ice (high ice concentrations) Fig. 3 shows a photograph of a structure in New Ice conditions. This ice is quite thin (less than 0.1 m) and flexible. In these conditions, waves and/or swell could hamper evacuation and rescue, and direct evacuation to the ice surface is not an option. In such light ice conditions, stationkeeping of a supply (rescue) vessel is not usually difficult. As shown in the figure, vessels close alongside in light ice can facilitate direct evacuation and rescue. A survival craft lowered onto this type of ice would immediately break through. However, movement and maneuverability of the survival craft could be hampered by the
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Fig. 3. The Sunkar structure in the Caspian Sea in New Ice conditions.
ice if the craft has insufficient power or a bluff hull shape. In the worst case, New Ice could limit the ability to move quickly out of the danger zone of the facility.
needs to be paid to the possibility of ice piling up around the survival craft and overriding the relatively light superstructure or canopy. Young Ice cannot be
8.2. Young Ice (high ice concentrations) Fig. 4 shows a photograph of a structure in Young Ice conditions in which the ice is 0.1–0.3 m thick. This ice condition presents greater challenges to stationkeeping vessels but should not present a major problem for moderately powered icebreaking support vessels. Survival craft lowered onto this ice may break through depending upon the loaded weight of the craft. Survival craft designed primarily for open water will not be able to make progress through high concentrations of Young Ice.It should be kept in mind that this ice can also be dynamic with a variety of active deformation processes (ridge building, rubbling, and rafting). Rafting or ridging under pressure could threaten the stability of a small craft and potentially lead to nipping and overturning in the worst case. Pressured ice conditions can put high stresses on water-borne survival crafts, even though the ice is relatively thin. The stresses on the hull will depend on the shape of the craft. Particular attention
Fig. 4. Overhead view of the Tarsiut structure in the Canadian Beaufort Sea with Young Ice forming around it. Note the icebreaking supply vessels breaking ice to create a route for offloading supplies.
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used as a safe haven for personnel as floes of this thickness are subject to unpredictable fracturing. 8.3. Very light pack ice (1/10 to 2/10 concentration) Fig. 5 shows a photograph of very light pack ice conditions. In this case, there is a low concentration of ice floes, covering 1/10 to 2/10 of the water’s surface. This ice regime can be complicated for EER if there is either wave activity or swell. Ice in very low concentrations has a limited effect on damping the local sea state. The option of evacuating directly to an ice floe in these low concentrations is not feasible. The launch system for survival crafts should be designed with sufficient control so that the survival craft does not impact an ice floe during launching. Moreover, survival craft should have adequate visibility and maneuverability to avoid collisions with ice floes. 8.4. Light pack ice (3/10 to 4/10 concentration) Fig. 6 shows a photograph of light pack ice conditions with ice concentrations of 3/10 to 4/10. Similar to the lighter ice concentration case, the evacuation system must take into account that there could be either wave activity and/or swell associated with this ice regime. Wave damping effects will be
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evident with light pack ice in the area, but a substantial ocean swell can still penetrate a significant distance into the pack. There is increasing potential in this ice condition for ice floes to interfere with the launching of survival craft into the sea. To try to minimize the risk, the launch system for survival crafts should be designed with sufficient control so that the survival craft does not impact an ice floe during launching. Survival crafts should have adequate visibility and maneuverability to ensure that they do not collide with an ice floe. Navigating through a pack ice field becomes progressively more challenging as the concentration increases as shown in ice tank tests by Simo˜es Re´ et al. (2003) and Barker et al. (2004). Ice strengthening of the hull of the survival craft may be required to maintain structural integrity during unavoidable contact with ice floes. 8.5. Moderate pack ice (5/10 to 6/10 concentration) Fig. 7 shows a photograph of a structure surrounded by moderate pack ice conditions. In this case, the ice is relatively thick (say 0.3–0.8 m) with ice concentrations of 5/10 to 6/10. This type of ice regime presents many challenges, especially when the ice speed is high. Launching and maneuvering a survival craft directly onto an ice floe could become an unavoidable option at these concentrations.
Fig. 5. Photograph showing the Gulf Beaufort in very light pack ice with 1/10 to 2/10 ice concentration.
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Fig. 6. Photograph showing light pack ice with 3/10 to 4/10 ice conditions.
Launching a water-borne survival craft will almost certainly result in it impacting with the ice. Higher impact forces will be experienced with large, thick floes moving through the drop zone. Stationkeeping of supply or rescue vessels can be difficult in these conditions, especially if the ice is thick, deformed, and moving at high speed. Dynamic ice conditions
can produce ridge building and rubbling, and floes can readily split through interfloe collisions. Ice floes under these conditions cannot provide a safe basis for a primary or secondary evacuation system. However, large thick floes in moderate pack ice could be considered as a preferred alternative to wet evacuation.
Fig. 7. Photograph showing the Molikpaq in the Canadian Beaufort Sea surrounded by moderate pack ice with 5/10 to 6/10 ice concentration. Note the ice crushing along the edge of the structure. Launching a survival craft in these conditions could be very dangerous.
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8.6. Heavy pack ice (7/10 to 8/10 concentration) Fig. 8 shows a photograph of a floating structure in heavy pack ice conditions. In this case, the surface is mostly covered with ice floes having wide range of sizes. High ice concentrations of thick ice will jeopardize the ability of many vessels to maintain station. Launching evacuation craft directly into open water under these conditions is difficult; high ice speeds further complicate the situation. The option of launching a survival craft directly onto the ice surface is easier to achieve. The loads on a survival craft will be greatly influenced by the floe size and ice thickness. Navigating through heavy pack ice of a craft designed to travel in open water will involve frequent, possibly damaging collisions, depending on the distribution of floe sizes and ice thickness. Large floes will lead to considerable meandering of the survival craft and increased potential for the craft to be nipped (trapped) as the larger floes come together. Small floes may require course changes that are too frequent and sharp to be practical. Self-propelled survival craft travelling in the water may not be able to make any substantial progress in these ice conditions. Wind shifts can rapidly lead to convergence of the ice and potentially dangerous pressure situations. The movement of the survival craft may be
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at the mercy of the ice for much of the time. Survival craft optimized for on-ice operations would be more suited for this condition. In some circumstances, large thick floes in heavy pack ice may provide a safer place of refuge than dedicated survival craft. However, this option should only be considered as a last method for evacuation. 8.7. Very heavy pack ice (9/10 to 10/10 concentration) Fig. 9 shows a photograph of a structure in very heavy pack ice conditions. In this case, the ice sheet is essentially continuous. Ice movement will create a wake behind the structure, which is filled with broken ice of various sizes. Depending upon the ice thickness and ice speed, stationkeeping of support vessels can be very difficult and, in some cases, impossible. Higher ice speeds will generally make evacuation more difficult. It is almost certain that the craft will land on the ice (except for a possible deliberate launch into the wake). Consequently, there is a need for quick-disconnect systems that can operate under significant offsets and line tensions to produce careful, controlled timing of the launch. A high-speed impact with the ice cover would almost certainly damage the craft.A band of floating and, in some cases, grounded ice rubbles of variable extents (typically a few metres
Fig. 8. Photograph showing the floating structure Kulluk in heavy pack ice with 8/10 to 9/10 ice concentration. Note that the icebreaker is breaking the floes to help minimize the ice loads. The small ice floes cannot be used as a temporary refuge except as a last resort.
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is a function of the ice speed, ice thickness, slope of the structure, and failure mode of the ice (see Barker et al., 2001; Barker and Timco, 2003; Poplin and Timco, 2003).Survival craft launched into the wake region will still encounter pieces of broken ice, often several meters in size. If the ice floes are relatively small, the ice is similar to a slurry and the wake will quickly fill with broken ice. The length of the downdrift wake will vary with the ice drift speed and direction, while its width will narrow as a function of pressure (or convergence) in the ice cover. In-plane pressure in the ice greatly complicates the evacuation procedures. Pressure makes it more difficult for a support vessel to maneuver or stationkeep, and, in severe cases, could render it immobile. Pressure will also cause the wake to close more quickly behind the structure. In high ice pressure situations, the wake behind the structure is often very short and, in low speed ice, it may be virtually nonexistent. Large thick floes in heavy pack ice may provide a safer place of refuge than the dedicated survival craft. 8.8. Fast ice with no rubble field
Fig. 9. Photograph showing the wake behind the Molikpaq in thick moving pack ice. Note the slurry of ice pieces in the wake and the wide range of ice piece sizes. In-plane pressure can quickly close this wake.
to many tens or hundreds of metres where the ice action and ice forces are usually extreme) will normally be seen across the platform’s updrift width in the perpendicular ice drift case (see Fig. 10). In diagonal ice drift situations, ice rubble will span its larger diagonal width, but will taper off in extent towards the structure’s corners. The resultant rubble orientation relative to the predominant ice drift will prevent launching of survival craft from all sides of the structure and limit safe launches to its downdrift sides, where active ice failure and rubbling are not underway. The oncoming ice cover will always fail against the updrift side(s) of a platform, with some failures and fractures often seen in a broken ice zone along the structure’s sides (alongside direction). Fig. 11 illustrates these zones. The size of the failure zones
Fig. 12 shows a photograph of a structure in fast ice with no rubble field surrounding the structure. This stable ice regime is less problematic than a heavy or a very heavy pack ice situation. Survival craft that operates on the ice surface offers the best means of enabling personnel to reach a safety zone. Waterborne survival craft would be completely immobile in this ice condition, and does not present a viable means of moving away from the hazard zone. Evacuation off the structure onto the ice to a temporary refuge can be a viable approach, depending on the condition of the ice surface and the thickness of the sheet. The main issue is how to get people onto the ice, their protection and safety while there, and how best to pick them up. Guidance can be found in the publication bCold Weather Marine Survival GuideQ (Transport Canada, 1997), and the Arctic Shipping Guidelines (IMO, 2002). The Transport Canada report is especially useful since it collates the results of the research into a readable manual that provides good guidance on the key issues and approaches that can be used for survival in the Arctic.Although a well-designed temporary refuge can be a viable evacuation option
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Fig. 10. Photograph showing the ice failing and piling up along the front of the Molikpaq structure from a moving ice cover. Deployment of a survival craft in this region would lead to catastrophic consequences.
in these ice conditions, on-ice evacuation can psychologically affect some personnel who are not comfortable with being on a floating ice cover. Also, on-ice evacuation to a temporary refuge must consider the likelihood of natural predators (bears and wolves). Spring melt can create unique problems, since the ice cover becomes less able to support travel or shelter. While thick, decaying ice may still have sufficient bearing capacity for personnel; it can appear very unsafe (with associated psychological affects on some personnel).
Alongside Direction
Downdrift (Wake) Direction
Updrift Direction NOT SAFE
USUALLY SAFE
Ice Movement Direction
PERIODICALLY SAFE
Fig. 11. Schematic illustration in plan view showing a structure in a moving ice cover. The regions around the structure are identified in terms of the safety of evacuation.
Fig. 12. Photograph of the SSDC in fast ice with no rubble field surrounding it.
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Fig. 13. Photograph showing the Tarsiut caisson structure with a grounded rubble field surrounding it. The rubble field is surrounded by thick sheet ice. This ice could be used to house a temporary refuge.
8.9. Fast ice with a rubble field Fig. 13 shows an overhead view of a structure surrounding by a large rubble field in fast ice. The presence of the rubble field can significantly complicate evacuation. Traversing a rubble field either on
foot or in a vehicle will appreciably slow down the evacuation process. Rubble also introduces a serious risk of physical injury to individuals on foot. These complications can be reduced if a suitable pathway through the grounded rubble is constructed and maintained during the winter. Spring melt can create unique problems. Fig. 14 shows a photograph of the edge of the rubble field during the early part of the spring melt. The rubble field is very difficult to traverse and the deteriorating fast ice surrounding it may or may not be reliably used as a safe haven. The rubble field often remains around all or part of a structure well into the spring (see Fig. 15) and this would complicate the evacuation and rescue. Rubble fields late in the season cannot be used as a temporary refuge, but they still prevent icebreakers and supply boats from getting near the structure.
9. Summary and conclusions This paper summarizes many of the environmental issues that need to be addressed for safe and reliable EER systems in ice-covered regions. The paper illustrates that a wide range of factors needs to be considered in designing evacuation systems to cope with different ice conditions, including an
Fig. 14. Photograph showing the edge of a grounded rubble field during the spring break-up. Evacuation across this ice would be difficult at this time of year.
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Fig. 15. Photograph showing the remains of the grounded rubble field in the spring around the Tarsiut structure. This ice is thick and grounded on the seabed.
analysis of the full range of ice regimes expected throughout the operating season. There is no single EER system that can reliably meet the requirements of all Arctic structures (or even a single structure subjected to variable conditions in time and space). Furthermore, the most suitable (primary) evacuation system may change throughout the year as the environmental conditions change. Careful design, planning, training, and ongoing maintenance of the EER system are required to deal with the harsh environmental conditions associated with the presence of sea ice.
Acknowledgements The authors would like to acknowledge the comments and interest provided by the ISO EER Technical Panel chaired by J. Poplin and including V. SantosPedro, C. Brummelkamp, S. Knight, F. Bercha, A. Simo˜ es Re´ , D. Kjekstad, M. Morland, and Y. Mansurov. The photographs in this paper were drawn from a variety of sources including Gulf Canada Resources, National Research Council of Canada, Dome Petroleum, Government of the Northwest Territories, Hamburg Ship Model Basin, and the Canadian Ice Service. G. Timco would like to
acknowledge support of this work by the Program of Energy Research and Development (PERD) through the Marine Transportation and Safety POL and the Northern POL.
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Arctic Conditions, POAC’01, vol. 1. Canadian Hydraulics Centre, National Research Council of Canada, Ottawa, Ont., Canada, pp. 495 – 504. Bercha, F.G., Cerovsek, M., Abel, W., 2004. Reliability assessment of arctic EER systems. Proceedings of the 17th IAHR Symposium on Ice, vol. 2. All-Russian Research Institute of Hydraulic Engineering (VNIIG), St. Petersburg, Russia, pp. 232 – 240. Brooks, C.J., 2001. Survival in Cold Waters. Transport Canada report TP-13822E, Ottawa, Ont., Canada. Chin, N., Brummelkamp, C., Dyer, M., Watt, G., 2003. Sakhalin II, Phase 2 offshore EER systems. Proceedings of the 17th International Conference on Port and Ocean Engineering Under Arctic Conditions, POAC’03, vol. 2. Norwegian University of Science and Technology, Trondheim, Norway, pp. 775 – 786. Cremers, J., Morris, S., Stepanov, I., Bercha, F., 2001. Emergency evacuation from ships and offshore structures and survivability in ice-covered waters: current status and development. Proceedings of the 16th International Conference on Port and Ocean Engineering Under Arctic Conditions, POAC’01, vol. 1. Canadian Hydraulics Centre, National Research Council of Canada, Ottawa, Ont., Canada, pp. 517 – 526. IMO MSC/MEPC circular on guidelines for ships operating in Arctic ice covered waters. 2002. Annex 10 of the Forty-fifth Session of the Sub-Committee (DE 45/27)—reference Chapter 11 of the Circular. Draft guidelines submitted to MSC76 , December 2002. London, UK. ISO 15027, 2002. ISO 15027 (1st Edition 03/15/02) consists of three parts under the general title: immersion suit: Part 2 Abandonment suits, and Part 3 Test methods. Prepared on their behalf by the European Committee for Standardization (CEN), Geneva, Switzerland. National Standard of Canada, Canadian General Standards Board, CAN/CGSB-65.16. Marine Abandonment Immersion Suit Systems, Ottawa, Ont., Canada. Polomoshnov, A., 1998. Scenario of personnel evacuation from platform on Sakhalin offshore in winter season. Proceedings of the International Conference on Marine Disasters: Forecast and Reduction. State Oceanic Administration China, Beijing, China, pp. 351 – 355. Poplin, J.P., Timco, G.W., 2003. Ice damage zone around conical structures: implications for evacuation. Proceedings of the 17th International Conference on Port and Ocean Engineering Under Arctic Conditions, POAC’03, vol. 2. Norwegian University of Science and Technology, Trondheim, Norway, pp. 797 – 806.
Poplin, J.P., Wang, A.T., St. Lawrence, W., 1998a. Consideration for the escape, evacuation and rescue from offshore platforms in ice-covered waters. Proceedings of the International Conference on Marine Disasters: Forecast and Reduction. State Oceanic Administration China, Beijing, China, pp. 329 – 337. Poplin, J.P., Wang, A.T., St. Lawrence, W., 1998b. Escape, evacuation and rescue systems for offshore installations in icecovered waters. Proceedings of the International Conference on Marine Disasters: Forecast and Reduction. State Oceanic Administration China, Beijing, China, pp. 338 – 350. Simo˜es Re´, A.S., Veitch, B., 2003. Performance limits for evacuation systems in ice. Proceedings of the 17th International Conference on Port and Ocean Engineering Under Arctic Conditions, POAC’03, vol. 2. Norwegian University of Science and Technology, Trondheim, Norway, pp. 807 – 818. Simo˜es Re´, A.S., Veitch, B., Sullivan, M., Pelley, D., Colbourne, B., 2002. Systematic experimental evaluation of lifeboat evacuation performance in a range of environmental conditions—Phase I. IMD/NRC report TR-2002-02, St. John’s, Nfld., Canada. Simo˜es Re´, A.S., Veitch, B., Elliot, B., Mulroney, S., 2003. Model testing of an evacuation system in ice-covered water. IMD/NRC report TR-2003-03, St. John’s, Nfld., Canada. Transport Canada, Prairie and Northern Region Marine, 1997. Cold weather marine survival guide. Transport Canada report TP11690E, Ottawa, Ont., Canada. Vaudrey, K., Dickins, D., 1996. Oil spill tracking at the Northstar development during break-up and freeze-up using satellite tracking buoys. Report prepared for BP Exploration (Alaska), Anchorage, AK, USA. Wright, B.D., Timco, G.W., Dunderdale, P., Smith, M., 2003a. Evaluation of emergency evacuation systems in ice-covered waters. PERD/CHC Report 11-39, Ottawa, Ont., Canada. Wright, B.D., Timco, G.W., Dunderdale, P., Smith, M., 2003b. An overview of evacuation systems in ice-covered waters. Proceedings of the 17th International Conference on Port and Ocean Engineering Under Arctic Conditions, POAC’03, vol. 2. Norwegian University of Science and Technology, Trondheim, Norway, pp. 765 – 774. Zahn, P.B., Kotras, T.V., 1987. Evacuation and survival from offshore drilling and production units in the Bering, Chukchi, and Beaufort seas. Arctic Engineering Incorporated Report 1040C. Maritime Administration, U.S. Department of Transportation, Columbia, Maryland, USA.
Environment guidelines for EER systems in ice-covered waters G.W. Timcoa,T, D.F. Dickinsb a
Canadian Hydraulics Centre, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6 b DF Dickins Associates Ltd., 9463 Poole Street, La Jolla, CA 92037, USA Received 8 November 2004; accepted 17 January 2005
Abstract The effects of ice and cold water environments on escape, evacuation, and rescue (EER) systems for offshore structures in ice-covered waters are discussed. The cold region environment influences all aspects of EER system design. Guidance is provided, for a wide range of ice and environmental conditions, on the factors that should be considered in developing an EER system for a structure that is to be operated in ice-covered waters. There is no one EER system that can reliably accommodate all of the requirements for safe evacuation from Arctic structures and several different systems may be required for year-round operation. Furthermore, the most suitable evacuation system will be different for different environmental conditions. Careful design, planning, training, and ongoing maintenance of the EER system are required for these harsh environmental conditions. D 2005 Elsevier B.V. All rights reserved. Keywords: Arctic structures; Environment guidelines; EER systems; Ice-covered waters
1. Introduction Oil and gas activity in terms of exploration, production, and transportation is increasing in icecovered waters worldwide. At the present time, there is year-round production in ice-covered waters in Canada, Alaska, and China, and seasonal production in the Sakhalin region of Russia. Exploration activity is, or will be, undertaken in the ice-covered portions of the Caspian Sea, Canada’s east coast and Beaufort Sea frontiers, the Barents Sea, and the Kara Seas. T Corresponding author. E-mail addresses: [email protected] (G.W. Timco)8 [email protected] (D.F. Dickins). 0165-232X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.coldregions.2005.01.005
Year-round production in ice-covered waters of the North Caspian and off the Northeast Coast of Sakhalin Island will become a reality within the next 3 years. Platforms in ice-covered waters face many unique challenges in terms of providing reliable escape, evacuation, and rescue (EER) systems. In cold climates, there are several complicating factors that can influence the selection of appropriate EER systems. Often, one type of system cannot be used throughout the year due to the changing ice and other environmental conditions at the site. There have been a number of papers published on evacuation procedures from offshore structures in icecovered waters. Zahn and Kotras (1987) did a study of the evacuation procedures from offshore drilling and
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production units in the Bering, Chukchi, and Beaufort seas. Poplin et al. (1998a,b) provided an excellent overview of the issues related to evacuation in icecovered waters. Polomoshnov (1998) discussed aspects of evacuation from a platform in the Sakhalin offshore region. Bercha (2004) and Bercha et al. (2001, 2004) have discussed various aspects of the reliability of Arctic EER systems. Barker et al. (2001) and Barker and Timco (2003) presented the results of a numerical modelling approach that provides information on the range of safe zones around the Arctic structures for different ice conditions. Cremers et al. (2001) discussed the current status and development of emergency evacuation from ships and offshore structures in icecovered waters. Wright et al. (2003a,b) presented an overview of evacuation systems for ice-covered waters. Chin et al. (2003) discussed the EER system developed for the Sakhalin II Phase 2 platform. Poplin and Timco (2003) discussed the size of the ice damage zone around conical structures. Simo˜es Re´ and Veitch (2003), Simo˜es Re´ et al. (2002, 2003), and Barker et al. (2004) presented information on the performance limits of survival craft in different wave/ice conditions. Most of the previous works have dealt with evacuation systems and their reliability, but, to date, there has been little detailed discussion on the implications of environmental conditions on different EER systems. The Arctic environment can influence all aspects of EER system design, specifications, and maintenance. Relevant environmental conditions must also be considered in the development and implementation of an EER plan or system. This paper provides guidance on the factors that should be considered in developing an EER system for an offshore production structure in icecovered waters. The paper does not consider any particular EER system; rather, it focuses on the impact of different ice environments on the whole EER system. It should be mentioned that the authors are members of ISO TC67/SC7/Technical Panel 8 developing the EER standards for offshore structures designed for use in ice-covered waters. This paper is an outgrowth of work conducted on behalf of this panel.
2. Low temperatures
of
Temperatures in the Arctic routinely reach values 40 8C and colder, and affect both hardware and
people in a significant manner. Machinery and any device with moving parts can become immobile. Materials become brittle at low temperatures and this effect must be considered in the selection of components and materials to be used in all elements of the EER systems. Lubricants, fuels, and hydraulic fluids need to be selected to suit the expected minimum temperature. Engines must be able to handle the additional demands of cold temperature starting (preheaters, high-capacity batteries, etc.). Cooling systems (radiator and/or seawater) need to be designed to prevent ice blockage from freezing inlets. Low temperatures also dictate that personnel must wear suitable warm clothing and footwear. This makes movement more difficult. Face and head protection can impair communications. Operating machinery with heavy gloves can be difficult and sometimes impossible if the controls are not designed properly. All of these factors must be considered in the yearround design, operation, and maintenance of the EER system. The IMO Circular on Guidelines for Ships Operating in Arctic Ice-Covered Waters (IMO, 2002) gives valuable guidance on selecting, designing, and maintaining marine equipment for Arctic operations.
3. Limited daylight There can be a large variation in daylight hours at platforms located in ice-covered regions (particularly at high latitude locations). In early winter, a true Arctic structure may experience only a few hours of twilight in a day. Therefore all designated outdoor escape routes must be sufficiently lit. The choice of lighting systems must also be able to deal with the full range of expected temperatures.
4. Strong winds and blowing snow The combination of cold temperatures and even moderate winds can create dangerous levels of wind chill. Strong winds, often encountered in winter storms with large ocean fetches, can make outside survival extremely challenging without suitable shelter and personal protection. Severe frostbite can occur on unprotected skin in a matter of minutes. Blowing snow often associated with storm events can lead to a
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disorienting condition known as a bwhite out,Q with essentially zero visibility. Low visibility, combined with the need to wear heavy winter clothing and footwear, will lead to seriously impaired mobility and dexterity. All of these issues need to be taken into account in the detailed design of EER systems.
5. Sea spray and atmospheric icing The combination of low temperatures and strong winds can often lead to icing on a platform, standby vessel, or exposed evacuation system (chutes, capsules, etc.). In many instances, this icing can be extremely severe (see Fig. 1). Outdoor escape routes must be designed to prevent or minimize icing on walkways and handrails, and indoor escape routes are preferred. Methods for removing icing must be in place and used as soon as icing occurs. Hardware and mechanical systems (winches, davits, shackles, nets, etc.) can become covered with ice, which may prevent or impair their operation. Systems must be continuously monitored for dangerous ice accumulation on a regular basis and steps taken to remove the ice as it builds.
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6. Open water conditions In all ice-covered regions, the platform will likely be in open water conditions for a part of the year. Suitable evacuation and rescue systems, not necessarily the same systems that work in ice, need to be in place to deal with these cold open water periods. Laboratory tests that can provide guidance on the clearing of survival craft in various wave conditions (Simo˜es Re´ et al., 2002), broken ice (Simo˜es Re´ et al., 2003), and wave/ice conditions (Barker et al., 2004) have been performed. Fig. 2 shows a photograph of a model survival craft in waves and high ice concentration (after Barker et al., 2004). These test programs have shown that in calm water, there is a threshold of ice concentration of approximately six-tenths above which survival craft designed for open water has difficulty traversing (Simo˜es Re´ et al., 2003). With waves and ice, the craft can travel further in similar ice concentration, but only in the wave direction. Travelling into the waves with broken ice proved to be quite difficult (Barker et al., 2004). Cold water drastically affects the personnel survival time (Brooks, 2001). An approved Class A immersion suit is required to achieve a desirable
Fig. 1. Photograph showing spray icing covering the deck and an evacuation lifeboat. This presents a very dangerous condition if quick escape is required.
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Fig. 2. Photograph showing a laboratory test of a model of a survival craft in high waves and high ice concentrations. The tests provide information on the ability of the craft to move in different wave/ice conditions (after Barker et al., 2004).
survival time of 6 h in water temperatures less than 2 8C, characteristic of offshore areas where ice is present (ISO 15027, 2002). For cases of escape onto the ice surface, existing survival/immersion suits can degrade survivability by restricting mobility and manual dexterity, and offering inadequate protection to the extremities from risk of frostbite (hands, feet, and face). In addition, many existing survival suits can be extremely difficult to don in cold temperatures due to stiffening of the suit materials. Selection of effective immersion suits for an offshore installation needs to account for issues of survivability in a high wind chill environment on the ice surface, the possible need to move away from the hazard zone on foot through rough ice, and the immersion suit survivability in an ice/water mixture.
7. Currents Currents in the presence of ice will influence the validity and accuracy of trajectory models used to estimate position of survivor locations over time. The relative effects of residual currents, currents at depth, cyclical tidal streams, and wind-driven surface currents all need to be accounted for in the trajectory
model(s) used to support the search and rescue operations. Trajectory models may need to be run for survivors that may be in the water, or for those on the surface of drifting ice. For example, thick ice features with significant draft can often move in a direction different from the prevailing surface water motion. Also, ice with a rough surface (high drag coefficient), or isolated ice floes in areas of low concentration can move at much higher velocities than ice confined in an area of higher (over 6/10) concentrations (Vaudrey and Dickins, 1996).
8. Ice conditions Evacuation systems in ice-covered waters must be designed and developed to cope with a wide variety of different ice conditions or ice regimes. This section provides information on the types of ice regimes that might be encountered by a structure in Arctic or subArctic waters. It also provides guidance on how various ice conditions can affect the performance of the EER systems. It should be noted that any given structure may not encounter all of these different regimes. A detailed analysis should be done to define the ice regimes at a specific location.
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Several ice characteristics can influence the type of evacuation and rescue system that could be used in ice-covered waters. Detailed information on ice properties and environments can be obtained from various sources and will not be discussed here. From an EER standpoint, the following ice characteristics are especially important: Ice concentration The total ice coverage on the water is expressed as a concentration in tenths. The impact of the ice concentration is very much dependent on the evacuation system used. Some systems may benefit from low, medium, or higher concentrations and may perform better in one ice concentration than another. Ice speed The speed of the ice is an important factor and highly dynamic ice conditions are typically the most challenging. For example, rapidly moving floes may interfere with launching and successful clearing of survival crafts. On the other hand, high drift speeds can aid in the rapid movement of survivors away from the platform. Ice thickness The ice thickness can influence the evacuation in many ways. New, thin ice generally presents fewer problems but precludes any consideration of direct evacuation onto the ice surface. Thick ice generally presents many challenging issues for survival craft designed for use in open water as well as consideration of standby vessels needs. On the other hand, thick ice can support an evacuation craft or potentially provide a temporary refuge (TR) if appropriate survival gear is available. Ice type Some regions will have only first-year ice present while others may have a mix of first-year ice, second-year ice, and multi-year ice, and glacial. Old ice floes can be considerably stronger and thicker than first-year ice, and can threaten the integrity of survival crafts and stationkeeping of icebreaking vessels. On the other hand, such floes can also be used as a stable platform for survivors. Floe size The sizes of the ice floes are important. Large floes (hundreds of metres) with appropriate thickness can offer places of refuge, while dynamic small floes in combination with high sea states and swell could threaten the stability and structural integrity of small survival craft. Small floes/ice pieces could affect the ability of a survival craft to clear a platform after launch by blocking propellers and water intakes.
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Ice roughness/deformation The surface roughness or deformation of the ice can create problems with over-ice mobility. This could be critical if survivors have to evacuate through ice rubble to reach a TR or a standby rescue vessel. Thick deformed ice may also prevent a standby vessel from approaching a platform for direct survivor recovery. Heavily deformed pack ice can provide additional problems for stationkeeping of standby vessels. Ice pressure Internal pressure in the ice sheet can significantly affect the ability of survival craft to move away from the platform or make any headway. Severe pressure could result in bnippingQ and potential destruction of a small survival craft through crushing and/or overturning. Ice wave conditions In low ice concentrations, waves or swell can cause complications in launching a survival craft or survival craft into the sea. If there are small floes present, they could also compromise the integrity and stability of survival craft (wave energy combined with small ice fragments can create potentially high local impact loads). Spring melt This situation can introduce a number of evacuation issues depending upon the type of evacuation system chosen. Mobility on the ice is severely curtailed by melt pools and open holes, and the ice surface may become too dangerous to consider direct evacuation as an option. The following sections discuss the key ice parameters and relative difficulty of evacuation and rescue for a wide range of ice regimes. 8.1. New Ice (high ice concentrations) Fig. 3 shows a photograph of a structure in New Ice conditions. This ice is quite thin (less than 0.1 m) and flexible. In these conditions, waves and/or swell could hamper evacuation and rescue, and direct evacuation to the ice surface is not an option. In such light ice conditions, stationkeeping of a supply (rescue) vessel is not usually difficult. As shown in the figure, vessels close alongside in light ice can facilitate direct evacuation and rescue. A survival craft lowered onto this type of ice would immediately break through. However, movement and maneuverability of the survival craft could be hampered by the
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Fig. 3. The Sunkar structure in the Caspian Sea in New Ice conditions.
ice if the craft has insufficient power or a bluff hull shape. In the worst case, New Ice could limit the ability to move quickly out of the danger zone of the facility.
needs to be paid to the possibility of ice piling up around the survival craft and overriding the relatively light superstructure or canopy. Young Ice cannot be
8.2. Young Ice (high ice concentrations) Fig. 4 shows a photograph of a structure in Young Ice conditions in which the ice is 0.1–0.3 m thick. This ice condition presents greater challenges to stationkeeping vessels but should not present a major problem for moderately powered icebreaking support vessels. Survival craft lowered onto this ice may break through depending upon the loaded weight of the craft. Survival craft designed primarily for open water will not be able to make progress through high concentrations of Young Ice.It should be kept in mind that this ice can also be dynamic with a variety of active deformation processes (ridge building, rubbling, and rafting). Rafting or ridging under pressure could threaten the stability of a small craft and potentially lead to nipping and overturning in the worst case. Pressured ice conditions can put high stresses on water-borne survival crafts, even though the ice is relatively thin. The stresses on the hull will depend on the shape of the craft. Particular attention
Fig. 4. Overhead view of the Tarsiut structure in the Canadian Beaufort Sea with Young Ice forming around it. Note the icebreaking supply vessels breaking ice to create a route for offloading supplies.
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used as a safe haven for personnel as floes of this thickness are subject to unpredictable fracturing. 8.3. Very light pack ice (1/10 to 2/10 concentration) Fig. 5 shows a photograph of very light pack ice conditions. In this case, there is a low concentration of ice floes, covering 1/10 to 2/10 of the water’s surface. This ice regime can be complicated for EER if there is either wave activity or swell. Ice in very low concentrations has a limited effect on damping the local sea state. The option of evacuating directly to an ice floe in these low concentrations is not feasible. The launch system for survival crafts should be designed with sufficient control so that the survival craft does not impact an ice floe during launching. Moreover, survival craft should have adequate visibility and maneuverability to avoid collisions with ice floes. 8.4. Light pack ice (3/10 to 4/10 concentration) Fig. 6 shows a photograph of light pack ice conditions with ice concentrations of 3/10 to 4/10. Similar to the lighter ice concentration case, the evacuation system must take into account that there could be either wave activity and/or swell associated with this ice regime. Wave damping effects will be
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evident with light pack ice in the area, but a substantial ocean swell can still penetrate a significant distance into the pack. There is increasing potential in this ice condition for ice floes to interfere with the launching of survival craft into the sea. To try to minimize the risk, the launch system for survival crafts should be designed with sufficient control so that the survival craft does not impact an ice floe during launching. Survival crafts should have adequate visibility and maneuverability to ensure that they do not collide with an ice floe. Navigating through a pack ice field becomes progressively more challenging as the concentration increases as shown in ice tank tests by Simo˜es Re´ et al. (2003) and Barker et al. (2004). Ice strengthening of the hull of the survival craft may be required to maintain structural integrity during unavoidable contact with ice floes. 8.5. Moderate pack ice (5/10 to 6/10 concentration) Fig. 7 shows a photograph of a structure surrounded by moderate pack ice conditions. In this case, the ice is relatively thick (say 0.3–0.8 m) with ice concentrations of 5/10 to 6/10. This type of ice regime presents many challenges, especially when the ice speed is high. Launching and maneuvering a survival craft directly onto an ice floe could become an unavoidable option at these concentrations.
Fig. 5. Photograph showing the Gulf Beaufort in very light pack ice with 1/10 to 2/10 ice concentration.
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Fig. 6. Photograph showing light pack ice with 3/10 to 4/10 ice conditions.
Launching a water-borne survival craft will almost certainly result in it impacting with the ice. Higher impact forces will be experienced with large, thick floes moving through the drop zone. Stationkeeping of supply or rescue vessels can be difficult in these conditions, especially if the ice is thick, deformed, and moving at high speed. Dynamic ice conditions
can produce ridge building and rubbling, and floes can readily split through interfloe collisions. Ice floes under these conditions cannot provide a safe basis for a primary or secondary evacuation system. However, large thick floes in moderate pack ice could be considered as a preferred alternative to wet evacuation.
Fig. 7. Photograph showing the Molikpaq in the Canadian Beaufort Sea surrounded by moderate pack ice with 5/10 to 6/10 ice concentration. Note the ice crushing along the edge of the structure. Launching a survival craft in these conditions could be very dangerous.
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8.6. Heavy pack ice (7/10 to 8/10 concentration) Fig. 8 shows a photograph of a floating structure in heavy pack ice conditions. In this case, the surface is mostly covered with ice floes having wide range of sizes. High ice concentrations of thick ice will jeopardize the ability of many vessels to maintain station. Launching evacuation craft directly into open water under these conditions is difficult; high ice speeds further complicate the situation. The option of launching a survival craft directly onto the ice surface is easier to achieve. The loads on a survival craft will be greatly influenced by the floe size and ice thickness. Navigating through heavy pack ice of a craft designed to travel in open water will involve frequent, possibly damaging collisions, depending on the distribution of floe sizes and ice thickness. Large floes will lead to considerable meandering of the survival craft and increased potential for the craft to be nipped (trapped) as the larger floes come together. Small floes may require course changes that are too frequent and sharp to be practical. Self-propelled survival craft travelling in the water may not be able to make any substantial progress in these ice conditions. Wind shifts can rapidly lead to convergence of the ice and potentially dangerous pressure situations. The movement of the survival craft may be
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at the mercy of the ice for much of the time. Survival craft optimized for on-ice operations would be more suited for this condition. In some circumstances, large thick floes in heavy pack ice may provide a safer place of refuge than dedicated survival craft. However, this option should only be considered as a last method for evacuation. 8.7. Very heavy pack ice (9/10 to 10/10 concentration) Fig. 9 shows a photograph of a structure in very heavy pack ice conditions. In this case, the ice sheet is essentially continuous. Ice movement will create a wake behind the structure, which is filled with broken ice of various sizes. Depending upon the ice thickness and ice speed, stationkeeping of support vessels can be very difficult and, in some cases, impossible. Higher ice speeds will generally make evacuation more difficult. It is almost certain that the craft will land on the ice (except for a possible deliberate launch into the wake). Consequently, there is a need for quick-disconnect systems that can operate under significant offsets and line tensions to produce careful, controlled timing of the launch. A high-speed impact with the ice cover would almost certainly damage the craft.A band of floating and, in some cases, grounded ice rubbles of variable extents (typically a few metres
Fig. 8. Photograph showing the floating structure Kulluk in heavy pack ice with 8/10 to 9/10 ice concentration. Note that the icebreaker is breaking the floes to help minimize the ice loads. The small ice floes cannot be used as a temporary refuge except as a last resort.
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is a function of the ice speed, ice thickness, slope of the structure, and failure mode of the ice (see Barker et al., 2001; Barker and Timco, 2003; Poplin and Timco, 2003).Survival craft launched into the wake region will still encounter pieces of broken ice, often several meters in size. If the ice floes are relatively small, the ice is similar to a slurry and the wake will quickly fill with broken ice. The length of the downdrift wake will vary with the ice drift speed and direction, while its width will narrow as a function of pressure (or convergence) in the ice cover. In-plane pressure in the ice greatly complicates the evacuation procedures. Pressure makes it more difficult for a support vessel to maneuver or stationkeep, and, in severe cases, could render it immobile. Pressure will also cause the wake to close more quickly behind the structure. In high ice pressure situations, the wake behind the structure is often very short and, in low speed ice, it may be virtually nonexistent. Large thick floes in heavy pack ice may provide a safer place of refuge than the dedicated survival craft. 8.8. Fast ice with no rubble field
Fig. 9. Photograph showing the wake behind the Molikpaq in thick moving pack ice. Note the slurry of ice pieces in the wake and the wide range of ice piece sizes. In-plane pressure can quickly close this wake.
to many tens or hundreds of metres where the ice action and ice forces are usually extreme) will normally be seen across the platform’s updrift width in the perpendicular ice drift case (see Fig. 10). In diagonal ice drift situations, ice rubble will span its larger diagonal width, but will taper off in extent towards the structure’s corners. The resultant rubble orientation relative to the predominant ice drift will prevent launching of survival craft from all sides of the structure and limit safe launches to its downdrift sides, where active ice failure and rubbling are not underway. The oncoming ice cover will always fail against the updrift side(s) of a platform, with some failures and fractures often seen in a broken ice zone along the structure’s sides (alongside direction). Fig. 11 illustrates these zones. The size of the failure zones
Fig. 12 shows a photograph of a structure in fast ice with no rubble field surrounding the structure. This stable ice regime is less problematic than a heavy or a very heavy pack ice situation. Survival craft that operates on the ice surface offers the best means of enabling personnel to reach a safety zone. Waterborne survival craft would be completely immobile in this ice condition, and does not present a viable means of moving away from the hazard zone. Evacuation off the structure onto the ice to a temporary refuge can be a viable approach, depending on the condition of the ice surface and the thickness of the sheet. The main issue is how to get people onto the ice, their protection and safety while there, and how best to pick them up. Guidance can be found in the publication bCold Weather Marine Survival GuideQ (Transport Canada, 1997), and the Arctic Shipping Guidelines (IMO, 2002). The Transport Canada report is especially useful since it collates the results of the research into a readable manual that provides good guidance on the key issues and approaches that can be used for survival in the Arctic.Although a well-designed temporary refuge can be a viable evacuation option
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Fig. 10. Photograph showing the ice failing and piling up along the front of the Molikpaq structure from a moving ice cover. Deployment of a survival craft in this region would lead to catastrophic consequences.
in these ice conditions, on-ice evacuation can psychologically affect some personnel who are not comfortable with being on a floating ice cover. Also, on-ice evacuation to a temporary refuge must consider the likelihood of natural predators (bears and wolves). Spring melt can create unique problems, since the ice cover becomes less able to support travel or shelter. While thick, decaying ice may still have sufficient bearing capacity for personnel; it can appear very unsafe (with associated psychological affects on some personnel).
Alongside Direction
Downdrift (Wake) Direction
Updrift Direction NOT SAFE
USUALLY SAFE
Ice Movement Direction
PERIODICALLY SAFE
Fig. 11. Schematic illustration in plan view showing a structure in a moving ice cover. The regions around the structure are identified in terms of the safety of evacuation.
Fig. 12. Photograph of the SSDC in fast ice with no rubble field surrounding it.
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Fig. 13. Photograph showing the Tarsiut caisson structure with a grounded rubble field surrounding it. The rubble field is surrounded by thick sheet ice. This ice could be used to house a temporary refuge.
8.9. Fast ice with a rubble field Fig. 13 shows an overhead view of a structure surrounding by a large rubble field in fast ice. The presence of the rubble field can significantly complicate evacuation. Traversing a rubble field either on
foot or in a vehicle will appreciably slow down the evacuation process. Rubble also introduces a serious risk of physical injury to individuals on foot. These complications can be reduced if a suitable pathway through the grounded rubble is constructed and maintained during the winter. Spring melt can create unique problems. Fig. 14 shows a photograph of the edge of the rubble field during the early part of the spring melt. The rubble field is very difficult to traverse and the deteriorating fast ice surrounding it may or may not be reliably used as a safe haven. The rubble field often remains around all or part of a structure well into the spring (see Fig. 15) and this would complicate the evacuation and rescue. Rubble fields late in the season cannot be used as a temporary refuge, but they still prevent icebreakers and supply boats from getting near the structure.
9. Summary and conclusions This paper summarizes many of the environmental issues that need to be addressed for safe and reliable EER systems in ice-covered regions. The paper illustrates that a wide range of factors needs to be considered in designing evacuation systems to cope with different ice conditions, including an
Fig. 14. Photograph showing the edge of a grounded rubble field during the spring break-up. Evacuation across this ice would be difficult at this time of year.
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Fig. 15. Photograph showing the remains of the grounded rubble field in the spring around the Tarsiut structure. This ice is thick and grounded on the seabed.
analysis of the full range of ice regimes expected throughout the operating season. There is no single EER system that can reliably meet the requirements of all Arctic structures (or even a single structure subjected to variable conditions in time and space). Furthermore, the most suitable (primary) evacuation system may change throughout the year as the environmental conditions change. Careful design, planning, training, and ongoing maintenance of the EER system are required to deal with the harsh environmental conditions associated with the presence of sea ice.
Acknowledgements The authors would like to acknowledge the comments and interest provided by the ISO EER Technical Panel chaired by J. Poplin and including V. SantosPedro, C. Brummelkamp, S. Knight, F. Bercha, A. Simo˜ es Re´ , D. Kjekstad, M. Morland, and Y. Mansurov. The photographs in this paper were drawn from a variety of sources including Gulf Canada Resources, National Research Council of Canada, Dome Petroleum, Government of the Northwest Territories, Hamburg Ship Model Basin, and the Canadian Ice Service. G. Timco would like to
acknowledge support of this work by the Program of Energy Research and Development (PERD) through the Marine Transportation and Safety POL and the Northern POL.
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