ShippingWorld & Shipbuilder October 2010 31

as the hunger for far flung cruises and remote offshore exploration has intensified, administrations at IMO have recognised that Search and Rescue alone will be unlikely to meet all possible accident scenarios.

For this reason, July 2010 saw the entry into force of new regulations, amending SOLAS and demanding more emphasis on the prevention of a casualty from occurring in the first place. They demand that future ships should be designed for improved survivability so that, in the event of a casualty, persons can stay safely onboard as the ship proceeds to port.

The rules incorporate criteria for a casualty threshold, defined as the amount of damage a ship can sustain according to its design and still safely return to port. Catching the eye is the provision for alternative designs for fire safety and evacuation arrangements so long as they can be shown to meet the same safety standard as prescriptive rules, and similar provisions for alternative designs for escape routes. Less widely acknowledged are new overall assessments for

essential systems’ availability for safe return to port (SRTP).

In detail, the amendments include: alterna-tive designs and arrangements; safe areas and the essential systems to be maintained while a ship proceeds to port after a casualty. This will require redundancy of propulsion and other essential systems; onboard safety centres, from where safety systems can be controlled, operated and monitored; fixed fire detection and alarm systems, including requirements for fire detectors and manually operated call points to be capable of being remotely and individually identified; fire prevention, including amendments aimed at enhancing the fire safety of atriums, the means of escape in case of fire and ventilation systems; and time for orderly evacuation and abandonment, including requirements for the essential systems that must remain operational in case any one main vertical zone is unserviceable due to fire.

Initially driving the IMO’s Maritime Safety Committee was concern over larger passenger ships, working on the principle that ‘a ship is its own best lifeboat’. This approach envisages that passengers and crew should normally be able to evacuate to a safe haven on board and stay there. In addition, this envisages that a ship should always be able to proceed to port at a minimum safe speed.

OffShOrE EquivaLEncEHowever, as the number of large accommoda-tion vessels set to work in increasingly remote locations for offshore construction has increased, so too has impetus grown for the rule changes to be transposed for use within the IMO’s guideline Code of Safety for Special Purpose Ships. The Code, revised in 2008, applies to vessels of more than 500gt and carrying more than 12 special per-sonnel. It entered into force in May 2010. Under SOLAS provisions, any vessel carrying more than 12 personnel not crew or special personnel auto-

neW Safety at Sea SOftWare OfferS

SyStematic apprOach tO Safe

return tO pOrt ruleS

Large accommodation vessels like Dan Swift,

pictured, fall under SOLaS Safe return

to Port rules

a screen shot of Safety at Sea’s software

Staying alive

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32 October 2010 ShippingWorld & Shipbuilder

Safe

ty matically becomes a passenger ship. To understand how the general aspira-

tions of IMO thinking have been translated into specific ship design guidelines, it is necessary to turn to the detailed contribu-tory work undertaken as part of the EU-funded SAFEDOR project, and the devel-opment of system availability software codes to develop a methodology to define and assess safe return to port require-ments. Participants included Safety at Sea (SaS) and the Ship Stability Research Centre (University of Strathclyde). Subse-quently, SaS continued the development of the code as the SRTP requirements were being developed at IMO resulting in the software sold today as I-SYS

firE & fLOOdThe software identifies essential systems as all systems and those sections of systems in spaces not directly affected by the casualty that need to remain opera-tional after a fire or flooding casualty. Critical systems, meanwhile, are essential systems identified in the overall assess-ment of essential systems to have a pos-sibility to fail to operate adequately as a consequence of one or more fire casualty case, each not exceeding the fire casualty threshold, or as a consequence of one or more flooding case, each not exceeding a single watertight compartment.

The resulting package has already been used in a number of projects in the passenger ship sector, forming the basis for fire and flooding protection assessments of systems’ of safe return to port capabilities on behalf of Daewoo Shipbuilding and Marine Engineering and Samsung Heavy Industries. Also proceeding has been initial work in the offshore sector, where SaS has worked on requirements as they relate to fire protection, vessel subdivisions and systems redundancy.

Luis Guarin, director, safety engi-neering, Safety at Sea, said that the new software code offered key opportunities in relation to offshore construction, field development support vessels and other offshore craft.

’We have carried out two initial jobs for Samsung Heavy Industries,’ he said. ‘One of these focused on the risk assess-ment of fire protection arrangements in some areas below the main deck for a field development support vessel under construction for Saipem. This included advanced fire engineering calculations and escape route analysis (by simula-tions). Alternative design evaluations were also made of fire protection arrange-ments in machinery spaces.

’In the second project, which focused on an offshore construction vessel, we carried out evacuation analyses/escape

route analyses on behalf of ULSTEIN Sea of Solutions (whose client is Heerema), as part of analyses required by Norwegian Maritime Directorate (NMD) regulations.’

I-SYS uses a set of logical (Boolean) expressions to define physical systems’ dependencies, including equipment, piping, pumps, switchboards, cabling and tanks, and a set of Binary Decision Diagrams to solve input equations. A fire or flooding casualty occurring within a space or group of spaces affects directly or indirectly the systems and functions embedded within ship environment.

Essential functions include water tight compartments and their casualty thresh-old, fire zones, considered discretely per compartment (in line with ship’s General Arrangement).’

Results of the overall assessment are given in a form of listings of systems affected by analysed damage scenarios. Additionally, for each damage scenario (or set of scenarios) a list of unique ‘restoring solutions’ can be generated. These solutions provide guidance for eliminating system vulnerabilities.

Where casualty scenarios included flooding to single watertight compart-ments, fire casualty threshold and the loss of single main vertical fire zones due to fire, Dr Guarin said the assessment of ship systems’ capabilities covered the fol-lowing scenarios: y Availability of essential systems after

a flooding casualty, according to SOLAS regulation II-1/8-1;

y Availability of essential systems to support a ship’s safe return to port after a fire casualty, according to SOLAS regulation II-2/21; and

y Availability of essential systems to support a ship’s evacuation and aban-donment after a fire casualty, accord-ing to SOLAS regulation II-2/22.

He said that work was rapidly developing to extend the use of the I-SYS package. ’So far, in general, the assess-ment has been focused on evaluating the design of safety systems. Watertight subdivision is optimised separately but it is our intention in the short term future to modify and use the software to evaluate the impact of subdivision on the SRTP capabilities. This requires an interface linking automatically the systems’ compo-nents and the watertight subdivision.’

Already, however, the use of I-SYS had proved far reaching for ship design-ers. ‘Changes have been made to electric distribution/piping systems topology. So far, we have been able to identify mainly gaps in the electric distribution system and piping systems (e.g. lack of redundancy in piping or cabling – various systems, lack of bypass and/or isolation valves for technical water).

‘We have also already extended the package’s use to other systems in the cruise ship context. Working with Royal Caribbean International, for example, we have used the same modelling principles and analysis approach in the “I-Stand” decision support system software to verify the operability of bilge and ballast systems and service tanks. A prototype of the software is being tested onboard Oasis of the Seas. I-Stand is being developed by RCI, SaS and SSRC.

’In future, a major part of develop-ment work will be to enhance the user interface. Modelling of systems and post-processing of results is currently rather time consuming but, based on the experience so far, we are writing the specification requirements for a graphi-cal user interface that will allow import-ing watertight subdivision and A-class bulkheads geometric information into the systems’ definition environment. The new GUI will also allow more efficient post-processing of results.’ SW&S

a schematic showing SrTP redundancy requirements

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