Marine evacuation systems: slides and chutes

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DOCUMENTATION PAGE

REPORT NUMBER SR-2006-31

NRC REPORT NUMBER DATE

December, 2006 REPORT SECURITY CLASSIFICATION

Unclassified

DISTRIBUTION Unlimited TITLE

MARINE EVACUATION SYSTEMS: SLIDES AND CHUTES

AUTHOR(S)

Johnathan Barrington

CORPORATE AUTHOR(S)/PERFORMING AGENCY(S)

Institute for Ocean Technology, National Research Council, St. John’s, NL PUBLICATION

SPONSORING AGENCY(S)

Institute for Ocean Technology, National Research Council, St. John’s IMD PROJECT NUMBER

PJ 2066

NRC FILE NUMBER KEY WORDS

Evacuation Slides, Chutes

PAGES 18, App. A-F FIGS. 4 TABLES SUMMARY

The following report presents an overview of the design and testing of Marine Evacuation Systems, with an emphasis on Marine Evacuation Slides and Chutes. International regulations and descriptions of various Marine Evacuation Systems are discussed in the subsequent sections. A severe lack regulations and available modeling programs have lead to questions concerning the safety of the design and performance of these systems. The scope of this report is to outline the information available today concerning the design of the various systems, the regulations in place and discuss the methods and programs that can be used to create an accurate numerical model of an evacuation slide.

ADDRESS National Research Council Institute for Ocean Technology Arctic Avenue, P. O. Box 12093 St. John's, NL A1B 3T5

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National Research Council Conseil national de recherches Canada Canada Institute for Ocean Institut des technologies Technology océaniques

MARINE EVACUATION SYSTEMS: SLIDES AND CHUTES

SR-2006-31

Johnathan Barrington

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Marine Evacuation Systems: Slides and Chutes

Institute for Ocean Technology National Research Council of Canada

i

Summary

The following report presents an overview of the design and testing of Marine Evacuation Systems, with an emphasis on Marine Evacuation Slides and Chutes. International regulations and descriptions of various Marine Evacuation Systems are discussed in the subsequent sections. A severe lack of regulations and available modeling programs have lead to questions concerning the safety of the design and performance of these systems. The scope of this report is to outline the information available today concerning the design of the various systems, the regulations in place and discuss the methods and programs that can be used to create an accurate numerical model of an evacuation slide.

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ii

1.0 Introduction

1.1 Background

Due to the increasing activities in the offshore petroleum and marine transportation industries, there has been continuing importance on designing safe evacuation procedures. One safe evacuation procedure is the marine slide, which combines the benefits of a speedy evacuation and easy deployment.

Based on gravity deployment, the slide is capable of being deployed by one person. The slide also incorporates the use of a liferaft to escape an unsafe vessel. Slides provide evacuation from heights up to fifteen metres and are operable in trimmed positions of up to 10 degrees, a list position of up to 20 degrees and any combination of these conditions. Slides exit either onto a platform or directly into a life raft and are designed to self-inflate within minutes.

1.2 Purpose

The implementation of policies and regulations governing the design, construction and performance of evacuation slides, as well as the development of accurate computer modelling software, are dependent on model and full scale testing of the systems.

After reviewing the literature available on slides and chutes, it was determined that there is limited technical information available concerning these systems. Presently, there are only a few companies manufacturing and distributing these evacuation systems around the world, and the regulations governing their design and performance are limited. There are no

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2 comprehensive computer models available and results from previous model or full scale testing are limited or unavailable to the public.

1.3 Scope

This report contains information pertaining to Marine Evacuation Systems and some of the regulations and modelling software that exists relevant to their construction and performance expectations and requirements. A short outline of a key regulation governing marine evacuation systems is presented, followed by a description of several systems currently being manufactured worldwide. A brief account of a few mathematical principles used to formulate a numerical model for a marine evacuation slide will then be discussed, as well the computer software used to create the numerical model. Conclusions and recommendations on the best path to proceed with creating an accurate numerical model are also examined.

2.0 Marine

Evacuation

Systems

2.1 International Life Saving Appliance Code

To date, few policies and regulations have been set forth to the marine and offshore industry governing the design, construction and performance of Marine Evacuation Systems (MES). The International Life-Saving Appliance (LSA) Code composed by the International Maritime Organization (IMO) has some basic regulations that apply to MES.

The LSA Code guidelines deal with the construction as well as the performance of the chutes or slides. Construction of the MES including the slide or chute and associated platform must provide a satisfactorily level of strength

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3 that meets with the approval of the administration of the IMO. Marine evacuation systems must also be designed and built to allow for the evacuation of evacuees that are of various ages and sizes as well as persons of varying degrees of physical capability. For either a slide or chute, the construction of the system must compensate for the wearing of approved lifejackets by the evacuees. In summary, the different physical and environmental conditions must be considered while designing systems that provide a safe descent for evacuees.

Subsequent to evacuating the vessel/installation, if the slide or chute provides direct access to a liferaft without means of a boarding platform, a quick release mechanism must be included to the system so as to detach the liferaft from the MES. If a boarding platform is included, then the platform is required to provide sufficient buoyancy and stability to safely transfer passengers and crew to liferafts. This level of buoyancy must be provided when the platform is loaded to working capacity. The platform should be subdivided to ensure that it remains operational in case one compartment becomes damaged and no longer efficient. The design of the platform should include a stabilizing system, so as to provide a safe means of transfer and a stable working area for operators. It must be constructed to provide sufficient strength to secure liferafts that are associated with the slide or chute.

The LSA Code also has performance requirements for the MES. Timed trials and heavy weather sea trails determine the performance level of the system. Performance requirements are also associated with the deployment and evacuation capacity of the system. The system must be able to be deployed by

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4 one person, either a passenger or a crewmember. The capacity of the system is evaluated from a timed harbour trial. The system must be capable of evacuating the number of evacuees for which it is designed within 30 minutes from the time that the abandon ship signal is given. Therefore, for a system designed with the ability to evacuate 300 people, all 300 people must be transferred from the vessel to the liferafts in 30 minutes. No reference is made as to what sea state this regulation falls under and it is unclear how the capacity of a system is determined. The system must be deployable even under unfavourable conditions of list and trim, and must remain effective, to a practical extent, under icing conditions. Heavy weather sea trails must show that the system is capable of evacuating passengers in a satisfactorily manner in a sea state that is associated with Beaufort six wind forces, including average wave heights of 6.4 to 9.6 meters, with a wind velocity of 22 to 27 knots. A description of Beaufort 6 wind force conditions is as follows; large waves begin to foam, the white foam crests are more extensive everywhere, strong breeze.

After construction has occurred, testing of the slide or chute materials and the container must be completed. Weather and watertight tests, as well as dry deployments must be carried out to verify the effectiveness of the system. Static loads should be applied to sections of the equipment to illustrate its resistance to deformation and other damage.

For the slide system, there are requirements as to what angle the slide creates with the still waterline. This angle is required to be between 30 and 35

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5 degrees when the vessel is at even keel and at its lightship displacement. This angle may increase to a maximum of 55 degrees in the case of flooding.

2.2 Marine Evacuation Slides and Chutes

The Marine Evacuation System has been designed for a safe, efficient method of evacuation while providing ease of deployment and operability in changing vessel and installation conditions. There are only a few companies around the world that manufacture and sell MES for use on marine and offshore installations and vessels. These companies are located in Australia, Canada, Denmark and Northern Ireland. The products produced by these companies are detailed below.

Viking Life-Saving Equipment is located in Denmark and manufactures both ‘Slide’ and ‘Chute’ evacuation systems. An external power supply is not required with the Viking systems and a platform is used for transferring evacuated passengers and crew to liferafts.

The Viking Evacuation Slide is a dual-track slide consisting of eight separate compartments. These compartments contain twelve main longitudinal tubes, which are individually inflated by means of nitrogen and air aspirators. The bottom end of the slide is connected to the self-draining platform. The slide and platform system is contained within a steel or aluminium stowage box, which requires a deck area of 1.0 m deep and 2.3 to 2.4 m in length, dependant on the stowage box material. A thirty-degree angle between the slide and ship’s side is maintained with a bowsing line. This angle can be adjusted between zero and thirty degrees to compensate for sea and ship movements. There was no

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6 reference found as to how this angle is measured or who is responsible for the adjustment of the bowsing line. The slide itself is at an angle of thirty to thirty-five degrees to the waterline when the ship is upright under calm water conditions. Slides range in length from 12 to 25.5 metres for the system. A single lane mini slide is also manufactured for installation heights of 1.5 to 3 metres.

Figure 1: Viking Marine Evacuation Slide System

The Viking Evacuation Chute is also designed for use in offshore and marine evacuation. The offshore chute is ideal for floating and fixed platforms with installation heights up to 35 metres. The chute is divided into cells each with a speed-retarding slide. Each slide runs at an opposing angle to the previous one so as to create a zigzag pattern. Situated five to ten metres below the water surface is a stabilizing weight attached to the bottom of the boarding platform. This weight aids in reducing side motions in the chute and keeps the chute stable

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7 in rough wind and sea conditions. Through an opening in the platform, several tension lines connect the stabilizing weight to the bottom of the chute. This allows the platform to rise and fall with the waves while avoiding submersion. The stabilizing weight is deployed as part of the chute system. As in the slide system, the platform is self-inflating. The platform is composed of natural rubber while the chute is made of Kevlar stainless steel rings. Stowage for the offshore evacuation system is in a carbon steel box that can be in-deck mounted or cantilevered out from the platform.

In the marine vessel case, the chute can be used at stowage heights of 5 to 20 metres above the waterline. The marine chute consists of a Kevlar-nylon net for the lining, with a water and fire resistant nylon protective covering. The design of this system allows for launching from passenger and marine vessels without need of a boarding platform. Elimination of the boarding platform allow passengers to be evacuated directly from the vessel to the inflated life raft, providing a dry-shod evacuation as stated by the manufacturer. The size of the stowage box ranges from 2.73 m x 2.93 m x 3.0 m to 2.75 m x 2.93 m x 3.5 m.

Further details on the Viking Slide and Chute can be found in Appendices A and B, respectively.

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Figure 2: Viking Marine Evacuation Chute System

DBC Marine Systems, a Canadian company located in British Columbia, manufactures both marine evacuation slides and chutes. The ‘Slide’ system is designed for freeboard heights of 3 to 3.65 metres, and incorporates the use of an open platform for evacuation. The slide deploys and inflates through the release of a safety pin. It is made of a butyl fabric (a material made of nylon cloth and butyl rubber) and inflated by carbon dioxide stored in cylinders. The slide and platform, as well as all other components, are stored within an aluminium housing that is powder coated to provide additional corrosion prevention. Additional platforms or liferafts can be deployed from a separate launch point on the vessel and bowsed into place alongside the vessel. An area of 380 mm deep and 1380 or 1665 mm wide (dependant on capacity of platform) is required to accommodate this housing.

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Figure 3: DBC Marine Systems Deployed Slide and Platform

DBC’s ‘Chute’ is also stored in a compact housing with an inflatable platform. The housing may be located at either the embarkation deck or on the deck above. The embarkation deck installation, the ‘O’ type chute, requires an area of 1.6 square metres (1.5 m wide by 1.3 m deep) for the housing. The chute pack is deployed when the release arm is activated. For the evacuation deck installation, the ‘I’ type chute, an area of 2.4 square metres (1.5 m wide by 1.65 m deep) is needed. Both the ‘O’ and ‘I’ type systems are composed of an inner slideway, constructed of a translucent fabric, which is contained inside a protective nylon covering. The inner slideway is sewn with a zigzag pattern at an angle of eighteen degrees to control the descent speed of the evacuee.

To protect passengers and crew as well as the chute from interference with rub rails or protruding hull appendages, there is a fender available. The fender is composed of a butyl fabric and self-inflatable as well. The chute system is functional in positive and negative list conditions of 20 degrees, trim conditions

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10 of 10 degrees and all combinations of list and trim up to these values. There are three available models of chutes with varying lengths up to 24.9 metres.

Figure 4: DBC Marine Systems Marine Evacuation Chute System

RFD Marine, located in Northern Ireland, base the design of their marine evacuation system on the elimination of a boarding platform enabling passengers and crew to be transferred directly into the life raft. With the use of a telescopically designed chute, which compensates for sea and ship motions, evacuees can make use of the chute in all weather conditions as stated by the manufacturer. The system can be installed from heights ranging from 8.0 to 23.5 metres. The self-contained stowage unit encloses the chute and liferafts all in one and can be mounted on an open deck or in between decks. According to the manufacturer, the system is operational within 90 seconds of being deployed by

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11 a single release mechanism. The system includes two side-by-side chutes, each equipped with a liferaft. More information can be found in Appendix C

The last company discussed in this report is Liferaft Systems Australia, which is located in Tasmania. Their slide system is designed to eliminate the use of a boarding platform. Available on a single or dual lane path, the slide can be installed up to a height of 12.5 metres. Netting runs the length of the slide path to reduce descent speeds and a contour at the bottom of the slide decreases the evacuee’s speed immediately before entering the life raft. The system is stowed on a marine grade aluminium stowage cradle.

A numerical model can be created for each of the slides based on its construction and material properties. NRC created a generic engineering drawing of a slide system in the event that no further information from the manufacturer becomes available. This drawing is located in Appendix D.

3.0 Testing

Overview

The following sections give a brief overview into some of the methods and programs that can be utilized to formulate a numerical model. Combining these tools with accurate slide properties and specifications can produce an accurate numerical model of an evacuation slide. A validated numerical slide model could eliminate the need for full scale model testing in dangerous conditions.

3.1 Wrinkling

Criterion

For the aforementioned Marine Evacuation Slides, the wrinkling criterion is the point at which a beam wrinkles and begins to fail. In the case of a simply

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12 supported horizontal inflated beam of circular cross-section under a uniform load

q per unit length and a point load F at the midspan, the following equation can be

derived:

Where σ0 = Tensile stress on the top part of inflated beam p = Internal pressure

R = External radius

t = Thickness

L = Length of beam

s = Distance from applied load

Wrinkling occurs when the internal pressure balances the tensile stress of the top inflated beam fabric and σ0 = 0. We assume that this occurs at the midspan where s= L/2. The wrinkling criterion at the midspan can then be found by substituting these values into the above equation to form

If the beam does not wrinkle or fail under extreme conditions, it is then possible to proceed with a numerical model of the beam system to view how it reacts under different conditions. Two approaches for creating a numerical model of the slide are through lumped-mass multibody dynamics and the Finite Element Method.

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3.2 Lumped-Mass

Multibody

Dynamics

One approach to defining a numerical model for a slide is to base it on lumped-mass multibody dynamics formulation of beam dynamics. W. Raman-Nair and R. E. Baddour in the 2003 technical paper, “Three-Dimensional Dynamics of a Flexible Marine Riser Undergoing Large Elastic Deformations” first described this method.

Applying the lumped-mass multibody dynamics method to the slide requires dividing each hollow circular supporting beam on the slide into n segments by designated points. With the motion of the ends specified, the beam is free to experience axial forces, gravity, wind loads, bending and the effect of sliding masses. The mass of each segment is then equally divided at the ends. This setup enables the system to behave with spring-like tendencies and, thus, spring stiffness, elasticity and damping coefficient must all be accounted for. Each point can then be modeled to show each one reacts to various loads. More details of lumped-mass multibody dynamics can be found in W. Raman-Nair’s 2006 technical paper, “Numerical Model of a Marine Evacuation Slide.”

The numerical model of a Marine Evacuation Slide using this method was created in Matlab. The slide was modeled using the above principle by modifying the code of an existing program used to model a marine riser. Inputting the values of mass and wind spend and stiffness, Matlab was able to compute results such as bending moment, tensile strength and displacement

3.3 Finite

Element

Method

The basis behind the finite element method is to find the solution to a complex problem by replacing it with a simpler one. Since the actual problem is

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14 being substituted with a simpler one, the resultant solution will be an approximation. In most practical problems, the existing mathematical tools are not sufficient to find an exact solution. Some typical applications for the finite element method are stress analysis, buckling, vibration analysis, heat transfer, fluid flow and distribution of electric or magnetic potential. Two programs computer programs used to create a numerical model using the FEM are Finite Element Personal Computer and ANSYS.

C.E. Knight at the Virginia Polytechnic Institute and State University Blacksburg, Virginia developed the Finite Element Personal Computer (FEPC) program in 1992. It is a DOS based program that allows the user to input the type of element (beam, truss, etc,), material properties, the number of nodes and elements, the restraints on the nodes and the loads, either force or pressure, that are applied to the system. Once all this information is entered, the program outputs a text file detailing the forces and stresses acting on each node and how they are affected in each plane.

ANSYS is a general-purpose finite element modeling software package that can be used to numerically solve a wide range of mechanical problems. A graphical user interface is used to contain analysis tools incorporating pre-processing (geometry creation, meshing) solver and post pre-processing modules. Creating a numerical model of the slide using ANSYS follows the same steps as with the FEPC but is more graphically intensive. The results are displayed in a separate window within the ANSYS program.

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4.0 Conclusions

Analysis for the numerical slide model was calculated with all three programs listed in the previous sections. Although each program has the ability to create a numerical model for a slide, they each have their advantages and disadvantages and the choice of which one to use would depend on the information required and how much time one has to learn the software.

The multibody dynamics model in Matlab worked well for certain stiffness values and calculated all significant forces and stresses. However, when the value of Young’s Modulus lies within a certain range, the program stalls and does not calculate the unknown forces and stresses. This may be due to the fact that the program is designed for large motions of very flexible structures. Sample results of a slide with a Young’s Modulus of 3.0 GPa can be found in Appendix E.

The FEPC also performed well. It was much faster than the multibody dynamics code and it still displayed the calculated forces and stresses acting on the slide. Despite its simplicity and poor graphics, FEPC proved to be a better solution for the numerical slide problem than Matlab because of its speed, ease of use and there were no problems experienced while it was used. Sample results from FEPC for a 9-metre slide model are located in Appendix F.

Unlike Matlab and FEPC, ANSYS has a steeper learning curve and the development of an equivalent beam to represent the slide proved to be difficult. ANSYS is more powerful tool than FEPC and would be the best program to calculate a numerical slide model if one has the time to master it.

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5.0 Recommendations

As of now, the numerical model of a Marine Evacuation Slide is based on educated guesses of the material properties and slide dimensions. Without knowing if these inputs are reasonable, there is no way of knowing if the numerical model is reacting accurately. To produce accurate results from a numerical model of an evacuation slide, the following should be done:

• Obtain the material properties and slide dimensions from the manufacturer and base the numerical model on these values

• Perform testing on a full scale model of the slide and compare results to those calculated from the numerical model

• Use a program that specializes in finite element analysis instead of multibody dynamics and model the slide as one equivalent beam

6.0 References

DBC Marine Systems. www.dbcmarine.com

IMO. 1997. International Life-Saving Appliance Code (LSA Code) Resolution MSC. 48 (66), Chapter IV: Survival craft. International Maritime Organization.

IMO. 1998. Testing of LSA. Marine Evacuation Unit Resolution MSC.81 (70) Revised Recommendations on the Testing of Life Saving Appliances Part

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1-Marine Evacuation Systems: Slides and Chutes

17 Prototype Test for Life-Saving Appliances, Chapter 12: Marine Evacuation Systems. International Maritime Organization.

Liferaft Systems Australia. www.liferaftsystems.com.au

Raman-Nair, W. 2006. Numerical Model of a Marine Evacuation Slide. Institute

for Ocean Technology.

RFD. www.rfd.co.uk

Simoes Re, A., Veitch, B., Newbury, S. 1999. Workshop on Escape, Evacuation and Rescue in the Offshore Industry, Section 2.5. Institute for Marine Dynamics.

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