The Application of High Pressure Water Mist as Part of a Holistic Fire Fighting System

8/10/2019 The Application of High Pressure Water Mist as Part of a Holistic Fire Fighting System

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The application of highpressure water mist aspart of a holistic firefighting systemAbstract

Current accommodation standards consume significant space on boardships. The development of a holistic approach to fire fighting wouldenable a reduction in the requirement for trained ships crew and inturn in accommodation. This will drive savings in a reduced hull size,propulsion requirements, and reduce the number of people exposed torisk in the event of a fire.

This study aims to explore the use of High Pressure Water Mist (HPWM)to provide ship wide reactive fire fighting by considering its applicationto a generic area of the Type 26 Frigate in peacetime and battlescenarios. This study also offers a brief discussion of the surroundingissues associated with implementing such a system, including estimatedtechnology readiness levels.

The cost of a ship relates directly to itssize, both in the concept phase and inservice. Being able to reduce the size ofa ship enables savings to be made overan otherwise larger vessel. However, oneof the most significant drivers for thesize of a ship is the manpower neededto crew it. Current crew living standardsconsume significant space due toaccommodation, stores, black and greywater requirements etc.

Where advancements in technology,particularly navigation and combatmanagement systems, have enabledthe number of crew needed to sail theship to be reduced, these savings areoften not realised. The sticking pointis the manpower required to fight fireson board, especially in damage andthreat situations. Current fire fightingtechniques and systems require a certainamount of manpower in order tofunction. This underlying factor preventsships crews from being reduced below aminimum level.

The development of a fully automatedand holistic approach to fire fighting

onboard Royal Navy (RN) ships wouldenable a reduction in the requirementfor trained ships crew. With fewer crewto support this would allow ships to bedesigned with a smaller hull size whilststill delivering the same capability. Thiswill see savings in;

The cost of building the ship;

Reduced propulsion requirements;

Reduced ships services requirements;

Lower ships emissions;

The number of personnel exposed torisk in the event of a fire;

Ultimately, investment in a modernfire fighting solution will bring savingsin the through life cost of a platform.

Ships fire fighting principlesThe following section outlines the basicprinciples for optimised fire prevention,fighting and protection. The FPA report1discusses a progressive and scaledapproach to fire protection, beginning withprevention in the first instance and leadingthrough to fire fighting as a last resort. Thisapproach is summarised in Figure 1.

Prevention and protection

In any fire management policy, theavoidance of fire should play as great arole as fire protection. The first step of fire

prevention encompasses removing andreducing fire hazards and risks to avoid anyincident. Techniques for doing so mightinclude changing process to reduce failurepaths that may lead to fire, or changingthe design of equipment to remove firehazards altogether.

Introduction

102

SimonE RatcliffeGraduate Engineer

Defence

Atkins

Acronyms

BD Battle DamageBGCV Branch Group Control ValveCMS Combat Management SystemDNV Det Norske VeritasFAR Firefighters Assistance RobotFN Frame NumberFPA Fire Protection AssociationFSC Future Surface CombatantGB Glass BulbHPWM High Pressure Water MistIMO International Maritime OrganisationIR InfraredNDP Naval Design Partnering TeamO OpenPD Positive DisplacementPT Peace TimeRN Royal Navy

TRL Technology Readiness LevelUS United States (of America)

Figure 1. Reducing through life costs by anincrease in automation


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Fire prevention also includes the detectionand prediction of fire scenarios longbefore the outbreak of fire. Fires andexplosions are generally preceded by aseries of events that lead step by stepto the fire situation. Depending on thenature of these events, there may beopportunities to intervene and detect afire scenario early. Detecting these eventsleading up to a fire is often outside theboundary of traditional fire detectionsystems. For example, monitoring anengines vibration, fuel consumption andpressure may provide clues as to whetheror not mechanical failure which couldlead to fire is imminent.

Damage limitation and response

The damage and consequence resultingfrom a fire can be characterisedinto two areas; the primary damageresulting directly from the fire and itsby-products, and the secondary damageand consequences of the implementedfire suppression strategy. The extentof the damage resulting from a fireand its suppression is a function of thescale of the fire and hence the scale ofthe response. The earlier that fires aredetected, prevented and suppressed,the greater the benefits are for reducingboth primary and secondary damage.Early detection also allows a betterbalance between a rapid but highimpact response against a measured andproportionate (directed) response causingless overall damage.

Traditionally, ships fire fighting methodsare not predictive by nature and,following the failure of first aid firefighting, accept large amounts ofdamage as alternative means are readied.The modernising of fire fighting responserequires the replacement of the man

with an extinguisher with automated onthe spot alternatives such as equipmentcontrol, local suppression and aimedsystems designed to reduce the impact ofsecondary damage.

Redundency and integrityof systems

Fire safety systems and the supportinginfrastructure generally embody safetyfactors to ensure availability andeffectiveness when required. Thesefactors may include;

System duplication;

System over-specification;

System protection(resource guarantee);

Manual backup;

Assigning worst case thresholdand designing infrastructure to copewith it.

High pressure watermist systems

General description

In suppressing a fire, traditional low-pressure sprinkler and deluge systemsoften cause significant water damagethat can be greater than the damagecaused by the fire itself.

HPWM offers equivalent or better firesuppression than traditional systems withminimal water discharge, minimisingdamage to property and reducing thetime and cost of clean-up.

High pressure water is dispersed by fixednozzles which create an ultra fine mistover the protected area. The mist fightsfires in three main ways;

Cooling Millions of tiny waterdroplets produce a very large heatcollecting surface and rapidlyreduces the temperature of the air inthe space;

Smothering The vapour displacesthe oxygen volume in the fire itself,rather than in the entire space. Thismeans that it does not present anasphyxiation hazard to personnel;

Attenuation The mist absorbsradiant heat.

Ultra fine mist has the advantage that itrequires very little water and consequentlydoes minimal damage to equipment. Ifde-ionised water is used HPWM systemscan also be applied to live electrical fires.In machinery spaces the major benefit of

water mist is that since it is harmless topeople, the system can be activated thesecond a fire is detected, without anyneed to first evacuate. Nor is there anyneed to shut off vents or close openingsbefore evacuation, as the water mist willnot escape the space, as gases would.This possibility for immediate activationmeans that the fire damage is kept ata minimum.

Once the fire has been extinguished, thewater mist will quickly cool down thespace and thus prevent re-ignition.

Flash suppression

A fire protection system designedto provide flashover suppressionaims to keep air/gas temperatures incompartments too low for materialsand fuel sources to ignite. One of theadvantages of flashover suppression isthat it can be achieved with less water

with a high pressure mist system thana traditional sprinkler extinguishingsystem. Live fire tests conducted by theUS Navy on the ex-USS Shadwell havedemonstrated that flashover suppressioncan be achieved using fewer water mistnozzles in each compartment than wouldbe needed using a conventional marinesprinkler system2.

Pre-emptive action

A networked system of HPWM sprinklerscould be used to pre-emptively coolcertain spaces. This might be a reaction todeveloping fire conditions, ie equipment

telemetry reporting increased risk, or asa precautionary measure during a firescenario. For example, water mist couldbe used to cool an established escaperoute reducing the chance of it beingblocked by fire.

Blast mitigation

The use of water mist has been shown tohave benefits for mitigating the effectsof blasts on Navy ships. Navier-Stokessimulations performed by Ananth et al3and the experimental results found byThomas et al4suggest that latent heatabsorption is the primary mechanism

behind water mist explosion suppressionin a confined space. The shock frontthat propagates ahead of the thermalfront immediately following a detonationcauses the water mist droplets to breakup; this increases the heat absorbingsurface area and results in an increase inthe droplet vaporisation rate. This coolsthe gasses in the region between theshock and thermal fronts.

The second mechanism by which watermist mitigates blast energy is throughmomentum absorption. Simulations bySchwer and Kailasanath5concluded that

quasi-static pressures produced by smallexplosions were suppressed by watermist. The droplets interact with the frontas it is reflected multiple times absorbingenergy and changes of momentum.

In 2009 the US Naval Research Laboratoryconducted a series of detonationexperiments designed to establish a linkbetween the mist density conditionsof a sprinkler system and its ability toreduce blast impulse in a confined space6.The results of these experiments showthat the higher mist density conditionsoutperformed lower mist concentrations

in suppressing blast effects. This shows asignificant opportunity for building watermist into a ships defensive suite.

System configuration

Water mist systems can be configured invarious ways;


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Thermally activated (Wet pipe) -Wet pipe systems are typically used inaccommodation and similar areas wheresolid materials are the combustiblemedia. When ambient temperatureexceeds a given limit, the activation bulbof the sprinkler bursts and water mist isdischarged from that particular sprinkler.

Deluge - A deluge system normallyhas open spray heads with water flowcontrolled by closed valves. When a valveis opened, water mist is discharged by allspray heads in the section controlled bythat valve. Deluge systems are typically

used in spaces where fuel fires could occur.

Class A fires

Class A, or ordinary combustible fires arethose started from solid organic material,such as wood, paper, cloth etc. Typically,spaces containing Class A fire hazards areprotected by thermally activated sprinklers,ie localised heat sources cause the sprinklerin the immediate vicinity to activate. ClassA fires typically spread outwards from asingle point, so initially only the closestsprinklers will open, tackling the firedirectly. As the fire spreads, more nozzleswill open and the water demand from the

system will increase.

Class B fires

Class B, or flammable liquid fires, arethose started from liquid fuels, oils,chemicals etc. Machinery spaces presentnumerous Class B hazards. Since highlyflammable liquids like petroleum canspread quickly and set alight almostinstantaneously, it is necessary to coverthe entire area with water mist from theoffset. In such spaces open nozzle delugesystems are used.

System designand application

Subject area T26 baseline 2v0

For the purpose of this study, an area ofT26 Frigate concept design was selectedto provide a framework on which todemonstrate the use of HPWM, seeFigure 2. The deck area was split intofour Fire Zones separated by watertight bulkheads.

One fire zone across two decks wasisolated for use as a representative areafor the application of HPWM.

Frame 71 to Frame 103 on 2 Deck T26Baseline 2v0 was chosen to act as asingle Fire Zone. This zone representsa typical area on a Surface Combatant.It houses common functions and utilityspaces that represent a range of potentialfire conditions.

102 The application of high pressure water mist aspart of a holistic fire fighting system

Figure 2. Type 26 Frigate concept. Source: http://www.defenseindustrydaily.com/Britains-Future-Frigates-06268/

Figure 3. Fire zone 2, 2 deck arrangement and sprinkler layout

Figure 4. Fire zone 2, 3 deck arrangement and sprinkler layout


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Commercial water mistsystem selection

In order to design for and demonstratethe application of a HPWM system in thisstudy, it was necessary for a commerciallyavailable HPWM system to be selected forinclusion in the design. In this case the HI-FOG Marine System by Marioff, Finlandwas chosen on the basis of its pedigree asa marine fire fighting system.

Nozzle layout

Nozzle layouts have been mapped for 2and 3 Decks between Frame Numbers103 and 71. See Figure 3and Figure 4.

The spacing rules are shown in Table 1.These were derived from the TypeApproval Certificates for the HI-FOGSystem issued by Det Norske Veritas(DNV)7,8.

The HI-FOG system meets the fire testprotocols for Accommodation areas,public spaces and service areas oncivilian ships. The International MaritimeOrganisation (IMO) terminology of

Accommodation Areas, Corridors,Public Spaces and Service Areascorrespond in RN terminology to Smallspaces, Passageways, Large spacesand Storage areas respectively.

IMOCompartment

Cabins, 16m2

Public spaces,2 deck height

Corridors andstairways

Storageareas

Machineryspaces

Navalequivalent

Cabins/Smallcompartments

Largecompartments

Largecompartments,2 deck height

Passage andstairways

Storageareas

Machinery space

Max deckheight

2.5m 2.5m 5.0m 2.5m 2.5mVertical distancefrom object 1.5m 5.5m

Nozzle type a 1B 1MB 6MB 1B 1MB 6MB 1B 1MC 6MC 1B 1MB 6MB1B 1MC6MC

4S 1MC 8MB

Symbol

Glass Bulb b)(GB) or Open(O)

GB GB GB GB GB O

K-factor [lpm/bar]

1.45 1.45 2.5 1.45 2.5 1.9

Flow rate at 120bar [lpm] c)

15.9 15.9 27.4 15.9 27.4 20.8

Max spacing One per room 3.5m d) 3.5m3.75 m,centred

2.65m 4.0me)

Max distance tobulkhead

2.850m 1.750m 1.750m 1.875m 1.325m -

Max coveragearea

16m2 12.3m2 12.3m2 14.1m2 7m2 16 m2

Nominal waterdensity [lpm/m2]

1.0 1.3 2.2 1.1 3.9 1.3

Notes on Tablea) Nozzle designation code: 1B 1MB 6MB or 4S 1MC 8MB

6MB or 8MB 6 or 8 mist orifices surrounding the centre jet, 1MB or 1MC 1 mist orifice on centre axis, B = 0.7mm diameter, C = 1.0mm diameter 1B or 4S 1 = 120 degree cone angle, thermally activated; 4 = 90 degree come angle, open nozzle; B = Brass; S = Stainless Steel

b) 2mm, Job 57oC (orange code) bulbs

c) Maximum system working pressure is 140 bar, while minimum initial working pressure at the sprinkler heads is 120 bar. A minimum of 100 m2is to be covered at 120 bar pressure, whereas 280 m2should be covered at minimum 60 bar (measured at the nozzle).

d). This sprinkler head may also be used at ceiling height of 3.0m and 3.5m. The sprinkler head spacing should then be reduced to 3.30m and3.05m respectively.

e) Spray heads should be installed outside of the protected area a distance of at least 1/4 of the maximum nozzle spacing, in this case 1.0 moutside at the periphery of the protected object (see IMO MSC/Circ.913, annex 3.4.2.1).

Table 1. Sprinkler spacing and layout requirements


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For the purposes of this paper, both opendeluge and closed thermally activatednozzle types are used. It has beenassumed that Branch Group ControlValves (BGCV) will control the flow toeach branch pipe. This will allow nozzlesto be activated remotely without theneed for the local temperature beinghigh enough to thermally trigger thebulb. Thus, the system will still maintainthe reactive nature of thermally activatedbulbs but also allow a central controlsystem to pre-emptively open branchgroups to protect spaces in advance offire or blast situation.

Distribution architecture options

In this section, different possible HighPressure Water Main distributionarchitectures will be discussed. Inparticular, the way in which they mightcontribute to enabling a holistic andsurvivable water mist system capable ofintelligent self diagnosis and damagecontrol will be considered. Key factorsare the degree of redundancy in pumpsources, the number of routes availablefor water to reach any portion of thepiping network, the degree of separationbetween redundant components andthe arrangement of control valves andsprinklers. Other factors that effectsurvivability are the integrity of thepower supply to pumps and valves,communications and logic systems,location, mounting and armouring ofrisers and valves etc all of which areexcluded from this discussion

Three distribution architectures willbe considered;

Centre main distribution;

Dual main distribution;

Sectional loop architecture.Centre main

Centre main architectures consist of asingle main running down the centreline on each deck of the ship. Sectionalcontrol valves are located at the zoneboundaries and at riser connections,which are spaced so to bring water fromthe pumps on the lower decks to eachlevel. Sprinkler heads are connectedin branch groups which in turn areconnected to the centre main via a BGCV.If a pipe was to be ruptured betweenrisers on one deck, valves on the mains

would close to isolate that length of pipe.Water would still be able to flow to theintact portions of the main on that deckthrough the adjacent risers. The centremain in this case must be large enough toaccommodate the combined flow of allthe branch groups.

The level of redundancy in the centremain design is low; the options forre-routing the water around isolatedsections is limited and as a result thenumber of branch groups that can be

kept active in the event of damage is low.Dual main

A step further from the centre mainconcept is the use of a dual main. Thisfeatures mains running down both theport and starboard side of each deckwith vertical risers spaced at intervalsalong the length of the ship supplyingthe mains on each side. Branch grouplines are connected to either the port orstarboard main via BGCVs. Zonal valvesare placed at intervals along the twomains so that damaged sections can beisolated. Any undamaged branch lines

within a compartment that are fed fromthe undamaged side of the ship will stillbe functional. This architecture can bemodified to include crossover mains andvalves to create offset loops.

Sectional loop

Sectional loop architectures are similarto dual main arrangements in that ahigh pressure main runs along the portand starboard side of each deck of theship, with vertical risers placed at regularintervals along the length of the ship,see Figure 5. The network of pipes isseparated into loops by valves and

crossover mains. Each loop is served byits own riser, which can supply that loopwith water or any of the loops adjacentto it. Risers alternate between port andstarboard sides along the length of theship in order to minimise vulnerability.Unlike the dual main architecture,

however, crossover mains connectport and starboard mains on the samelevel, one on either side of each watertight bulkhead.

The advantage of sectional looparchitecture is the ability it has torecover from damage with minimal lossof functionality. Valves are placed sothat each loop can be supplied in twoindependent ways;

With all the supply coming up theriser serving that particular loop;

The riser can be closed off so thatthe supply must come from anadjacent loop.

Sectional loop architectures allow forthe subdivision of the main networkinto small cells that can be individually

isolated. The greater the number of cellsthe better the ability to recover fromdamage while leaving as much of thenetwork operational as possible.

Sectional loop architectures also offerhydraulic advantages in that the numberof pathways for water to flow to anyone demand point is maximised. Alarge demand at a particular point willdistribute across multiple mains andrisers, thus allowing for lower flow ratesthrough the mains, requiring smallerdiameter piping9.

It is for these reasons that using asectional loop architecture offers thegreatest potential for providing a flexibleand survivable HPWM system. Sectionalloop architecture will be considered fromhere on.


Figure 5. Sectional loop architecture


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Branch group layoutFigure 6and Figure 7show the nozzlesand branch lines connected to the mainon each deck. Typically a branch groupconnects four nozzles to the mainand is controlled by a branch groupcontrol valve.

Where possible, branch lines are arrangedso that nozzles can provide a curtain ofwater across the beam of the ship. Eachnozzle would be connected to the branchline by a branch vein (not shown), sizedto only need to carry the flow for oneindividual sprinkler, regardless of where

it is in the system ie regardless of howmany sprinklers are in front of it.

Water flow demands

A system configured to provide flashoversuppression cover across an entireplatform has the advantage that its flowdemand grows progressively to match thespread and intensity of the fire. As the firespreads through the ship, more branchgroups can be brought online as needed.For the purpose of this study, the waterflow demands will be calculated for twodamage scenarios; peace time and battledamage scenarios.

Table 3compiles the nozzle count andestimated water flow demands for theHPWM system based on the layoutsshown in Figure 4 and Figure 5. Forsimplicity, it has been assumed that eachbranch group holds four sprinkler headswith a K-factor of 1.45 lpm / bar,except for the machinery space where aK-factor of 1.9 lpm / baris used.

Pumping strategy

There are several possible approaches forproviding the pumping capacity for theHPWM system. Some high level options

are discussed in Table 2.

Option B

Option B affords 100% redundancywhile also separating the two pumpingassets. The sizing of both pumps toprovide the total design flow rate guardsagainst the loss of a single pump throughroutine mechanical breakdown and theseparation of the units ensures that therisk of losing both through battle damageis greatly reduced.

However, option B may not offer thescalability or design flexibility requiredwhen considering much larger or muchsmaller ships. As the number and sizeof fire zones increases the demand flowrate will also increase. Sizing a singlepump unit to provide 100% of the designflow rate in all circumstances may notbe sensible.

Option C

Option C maintains a reasonable level ofredundancy in four pumps each providinga third of the design flow rate. The useof one pump per fire zone ensures thatpump units are adequately separated anddistributed throughout the ship. OptionsC offers advantages over Option B inthe size and the scalability of the pumpsrequired. Running several smaller pumpunits rather than relying on large pumpssized to meet the entire demand should

enable savings to be made in runningcosts and enable a more flexible design.The remainder of this study assumesOption C.

Pump type

Selecting a pump to supply a highpressure water mist system presentsa challenging problem. Such a systemdemands a very high pressure, but alsorequires the flexibility to vary the flow rateas the demand changes. Potentially, the

Option High level pumping strategy Comments

A

One large pump unit sized to meetthe full design flow rate, connectedto a distribution main supplyingmultiple risers

Option A has no redundancy and isnot discussed further

B

Two pump units in parallel, oneaft of midships, and one forwardserving a common distributionmain and multiple risers; eachpump unit sized to meet full designflow, so that one unit is redundant.

Provides for 100% redundancyand can assume at a reasonablecost for connections, powerand filtration. Pump units areadequately separated so that atleast one should be functional atall times

C

Four pump units in parallel, one for

each fire zone; each pump unit sizedfor 1/3 of the full design flow, so thatthree units will meet full design flowwith the largest out of service

Provides for redundancy in a waythat permits each pump unit to be

smaller than arrangement C, suchthat redundancy can be achievedwith three of the four pumps. Canassume that smaller pump unitswill be cheaper to run

Table 2.High level pumping strategy

Figure 6. General arrangement of 2 deck showing sprinklers, branch groups and water main


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pumping system could need to go fromproviding high pressure fluid at a lowflow rate in a single compartment to veryhigh pressure high flow rate fluid acrossseveral fire zones.

The high pressures required of the watermist system (up to 150bar) mean thatthe pumps selected need to be of highquality and high capability. Traditionally,centrifugal pumps are used with sprinklersystems because they allow a constantlyvarying flow rate to be delivered at withrelatively simple equipment. However, athigh pressures, multi-stage centrifugal

pumps are required. These have thepotential to be more complex and requiresignificant maintenance.

More reliable high pressure pumpscome in the form of piston type positivedisplacement (PD) pumps. PD pumps,by nature of their design, deliver a fixedvolume of fluid and as such are notbest suited to variable demand sprinklersystems. However, PD pumps can becoupled with special design features tomatch the fixed volume output of the PDpump to a system of variable demand.

PD pumps applied to water

mist systemsTo design for the BD3 scenario (Table 3)each pumping unit would need to besized to provide a flow rate of 381.6litres/minute.

The use of PD pumps to drive HPWMsystems has been demonstrated onthe ex-USS Shadwell by the US NavalResearch Laboratory9. Their approach issummarised here.

We can assume that in basic terms, eachpump unit consists of two smaller pumps,a primary and a secondary pump, driven

by a single motor. The two pumps mightbe connected by a check valve, heldclosed by the high pressure form theprimary pump and preventing flow fromthe secondary pump entering the system.This excess flow from the secondarypump flow might be bypassed by asuction line via a flow bypass valve andre-circulated to the reservoirs. As long asthe system demand is less than or equalto the capacity of the primary pump, thesystem pressure remains high. Thus thefirst nozzles to operate at the early stageof a fire deliver water mist with maximumvelocity and flow rate.


Scenario

Branch

groups Nozzles

Flow rate

(120bar,K=1.45)

Average branch group 1 4 63.6 Lpm

PT1 3 branch groups active inimmediate fire area.

3 12 190.8 Lpm

PT2 3 branch groups active plus 1branch group in corridor

4 16 254.4 Lpm

BD1 Branch groups in adjacent spacesincluding 4 branch groups immediatelyabove the damage area.

7 28 445.2 Lpm

BD2 As BD1 but increasing to a further

2 branch groups on the same deck and 4branch groups above damage area.

13 48 763.2 Lpm

BD3 As BD2 but including further 2 ondeck and 3 above

18 72 1144.8 Lpm

MS1 machinery space drench systemactivated (Nozzle type 4S 1MC 8MB,K-factor 1.9)

2 8 166.4 Lpm

BP1 nozzles in the outer mostcompartments of the ship open inthe vicinity of an expected weaponsstrike. This may be on one or moredecks depending on the accuracy of the

prediction.

6 24 381.6

Table 3. Water flow demands

Figure 7. General arrangement of 3 deck showing sprinklers, branch groups and water main


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As more nozzles open and the volumetricdemand of the sprinkler system exceedsthe capacity of the first pump, the systempressure will drop. Once it drops to thesetting of the secondary pump flowbypass valve, this will allow flow fromthe secondary pump to enter the system,albeit at a lower pressure. A schematic ofthis arrangement is shown in Figure 8.

For a large HPWM system, several pumppairs could be assembled in a skid to form

one pump unit. The minimum demandfor the system, for example one or twonozzles operating in peacetime conditionscould be met with one pump operating.As more nozzles open, the systempressure will drop until it falls below thesetting of the next flow bypass valve. Thatvalve then closes and the flow from thatpump then enters the system to make upthe demand. In this way the pump unitself adjusts to match the demand fromthe sprinkler system. Figure 9shows anassembly of pump pairs to form one offour pump units sized to meet one thirdof the maximum expected demand.

Sensors and control

Being able to detect fires quickly andaccurately is key to ensuring a shipssurvivability and protecting life at sea.Early detection allows the ships systems

and crew to deal with the fire and limitits damage. Generally, on most surfaceships there is poor integration betweensensors and suppression systems, limiteduse of multiple sensor types and astrong reliance on human input, leadingto slow detection and numerous falsealarms10. The principle fire detectionsystem on ships is still routine humanwatch keeping; arguably simple, butslow and potentially dangerous for thepersonnel involved.

The aim of a fire detection system shouldbe to provide comprehensive, fullyintegrated, multi criteria fire detectioncover across the entire ship, intelligentlyinterfacing with fire suppression systems,fluid control systems and ships crew.Without this advanced functionality, pre-emptively reacting to fire conditions usingHPWM systems will be limited. A novelway of thinking about this is to emulatethe sensory functions that humans use todetect fire (Table 4).

The basis of an intelligent sensor networkwould be the employment of multiplesensor types and analysis to diagnosewhether there is a fire rather than merelydetect one of the symptoms. Multiplesensors working together can providemore accurate clues as to whether a firehas started or not and more importantlyif a fire is likely to start. Like the human

crew, the system should be able tomake a reasoned judgement as to thefire situation based on all its data. Theadvantage over the human crew is thatthe ship can be monitored in all places,24 hours a day.

In order for the system to correctlymatch sensor readings to fire scenarios,a database of fire signatures and sensorpatterns would need to be establishedfor different types of fire and typical

false alarms. The more sensor patternsand fire signatures the system has accessto, increased accuracy of diagnosis isachieved. However, given that no twofires are identical, the system would needto include the capacity to learn.

Network integration

A holistic system will rely on multiplesystems talking to each other in orderto co ordinate the response to a fire ordamage situation. The key elementsthat might be involved are shown inFigure 10. It shows the breakdownof the Fire Control system into two

main components; the Sensors andthe HPWM system, ie sensing andreacting. Crossovers exist where GBsprinklers both sense and react to fireevents. It also shows how the combatmanagement system might feed into thefire and damage control system. Threat

Human faculty System

Optical detection Eyes

IR cameras

Machinery monitoring

Casualty location

Real-time situational feedback

Electronic Nose

Ionising and photoelectric smoke detectors

CO and CO2detectors

Heat sensors

Acoustic monitoring Ears

Machinery monitoring

Shock/blast detection

Brain power

Micro processors

Intelligent control

Pattern recognition

Neural networks

Voice!

Alarms

Situational feedback

Personal address

Table 4. Fire fighting systems approximated to human sensory faculties.

Figure 8. Diagram of a PD pump pair consistingof two PD pumps driven by a single motor

Figure 9. Diagram of an assembly of pump pairsconnected in parallel to provide a range of flows


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information can be used to coordinateblast suppression response using watermist. A key challenge is the design ofa coordinating management suite thatcan effectively interface with other

ships systems and coordinate action.The position of the human operatorin the management system will alsopresent interesting questions regardingaccountability and autonomy.

The control system will need to digestinformation regarding the fire itself, thesuppression response, the location andmovement of personnel, any damagecontrol efforts and the health of the firefighting infrastructure. An ideal systemwill be able to react instantly to a firesituation by activating relevant branchgroups and then continuing to monitorthe progress of that fire and watch fornew events. New fire situations mightcome in the form of further sensorreadings from multiple sources, a manualactivation at an alarm call point or thebursting of a glass bulb sprinkler.

Supporting technologies

The following section discusses some ofthe novel technologies that would benecessary to enable a fully integratedHPWM system that provides a pre-emptive fire fighting capability

Smart valvesValves that can autonomously open orclose depending on the flow conditionsthat they see are essential to providinga fire fighting system that removes theneed for human input and decisionmaking. Positioned at critical points inthe distribution main, these motorised

valves incorporate pressure sensors andflow meters to monitor the conditions inthe main.

A balance must be achieved betweenthe benefits and the cost of installingsmart valves in the distribution mains. Thespacing between the valves determinesthe size of the area that will be non-functional if valves must be closed toisolate a rupture. When considering thesectional loop architecture, the maximumlevel of control for isolating damagedpiping and rerouting flows could beachieved by installing a valve on each endof every pipe connecting two separatedgrid points. So for a T-intersection thiswould mean having a valve on all threebranches. This strategy would result ina high valve count and, depending onthe type of valve used, be prohibitivelyexpensive. An alternative might be to usevalve nodes at each T-intersection; ieconsolidating actuators and logic circuitsinto one housing capable of operatingeach valve individually. This would takeadvantage of the proximity of the valvesat each intersecting node in the pipenetwork and achieve some economiesof design.

Heat sensors

Heat sensors will form a key part of anadvanced fire detection system. Risingtemperature conditions indicate the

increased likelihood of a fire. Whencoupled with other sensor types suchas smoke or visual recognition, heatsensors can provide an accurate pictureof a developing fire and how it isspreading. This information can be usedto coordinate and prioritise the responseto the fire. Heat sensing also has the

potential to provide feedback to thecontrol system on the effectiveness of thefire suppression being applied.

Use of infra-red cameras

Infra-red (IR) cameras can also be used tospot and identify fires. In particular, theyare able to spot fires in hot environments,where heat sensors may give false alarms.IR cameras measure the intensity ofthe IR radiation emitted from objectsand surfaces. Using image recognitionsoftware the difference between aflame flare can be distinguished sayfrom the hot casing of an engine. This

sort of image processing and softwarerecognition is not completely foolproof,flares and reflexions might give rise forfalse alarms. IR cameras can, however,provide clear unambiguous informationon the situation as it develops by feedinglive pictures back to an operator. Thisallows them to question whether thecause of alarm is false or a real fire anddirect actions accordingly.

Technology readiness levels

This section offers a brief discussion on

the maturity of the technology requiredto implement a holistic fire fightingsystem. It does not seek to providea definitive answer with respect totechnology readiness levels, but more so afood for thought and provides estimatesof the technology readiness levels of eachsolution on a scale of 1 to 10.

HPWM system

HPWM technology is well established.It forms a natural progression fromtraditional low pressure sprinklersystems. HPWM systems are made bya variety of specialist manufacturers

and can be found currently in useacross a wide range of civilian vesselsand increasingly land installations.Military Naval use is known, the US navyinvestigating its application as early asthe year 20009. HPWM systems can befound in small fixed system set ups egmachinery spaces, and also protectinglarger spaces providing the primarymeans of fire fighting. Class SocietyCertification for passenger and cruiseship applications exists for most systems,including the Marioff products. Estimateat a technology readiness level of 8-9.

Sensors and control

The sensor technology required todrive a holistic system should be widelyavailable and in use. Smoke detectors,heat detectors, IR cameras etc are allrelatively mature technologies. Theoil and gas industry are often at theforefront of innovation in this area, using

Fire signaturedatabase

Combatmanagement

system

Cameranetworks

Smart valvefeedback

Smoke / heatsensor networks

Telemetryreporting

Pumpcontroller

Valvecontroller

Reservoirmonitoring

Fire anddamage controlmanagement

system

User interfaceand command

input

Sensor controlsystem

HPWM controlsystem

Alarmsystem

Figure 10. Fire and damage control system hierarchy



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fuel mist detection to spot fire situationsearly and IR cameras to identify fires andfalse alarms. The processing of the datathey gather is where the key technologyquestions lie. Creating a managementsystem that can learn the differencebetween characteristics of a real fire anda false alarm is not beyond the realmsof modern computing power but mayrequire investment in specific examplesand programmes to drive forward.Technology readiness level 4 7.

Smart valves

Smart valves in various forms are common

across the energy and process industries.The drive for greater efficienciesfrom deep sea drilling operations hasdemanded large investment from thesubsea sector. Schemes have beendesigned and implemented for use off-shore, for example Unocal, now part ofChevron, installed intelligent pump andvalve systems to boost the efficiency ofits Monopod platform in the Cook InletBasin, Alaska11. The controller technologythat powers such valves is where the keydevelopment lies the logic behind theactuated valves. Since their use in highpressure mains to provide automateddamage repair and optimisation responseis less well documented, valve solutionswill be custom built to meet the specificneeds of their applications. Technologyreadiness level 7.

Whole system

The key to creating a holistic systemis linking the different technologiestogether. Sensor suites combiningwith suppression systems to fight fires;potential blasts being detected andmitigated against; intelligent controllersspotting false alarms and reroutingaround damage will require the system tobe greater than the sum of its parts. Thiswill present the greatest challenge. Formanpower savings to be realised it willrequire a change of doctrine, process andattitude, away from current techniquesand further towards pre-emptive andinstant response. Technology readinesslevel 4.

Conclusions

This report raises the issue that currentships fire fighting techniques are oldfashioned and slow to act failing initialfirst aid fire fighting efforts. If shipscrews are to be reduced on futurevessels, attention will need to be paid todeveloping a holistic and intelligent firefighting system that can remove the manwith an extinguisher as far as possible.

This report sees that HPWM is anexcellent solution for providingcomprehensive cover across a surface

ship. It allows for an instant response to afire situation, in that it is non-toxic, doesnot require spaces to be sealed and canbe deployed in HV and machinery spaces.The mist acts in several ways to fight firebut can also be used to prevent flashoversand pre-emptively cool compartments.Water mist has also been found to offerblast mitigation. Mist systems in outlayingcompartments could be activated aheadof a weapon strikes to reduce thepotential damage of internal explosions.

In order to provide comprehensive coverhowever, the entire ship needs to be

covered by high pressure sprinkler nozzlesthat can either be triggered locally byrising temperatures or on commandfrom a control system. It is this totalcoverage element that means personnelare not required in the large numbersthat currently operate in fire fightingonboard surface ships. Installing andsupplying such a large system presents itsown complexities. Possible savings couldbe made if certain areas of a platformwere prioritised for HPWM cover. Thiscould be limited to high risk areas orpriority escape routes and passagewaysfor personnel.

A sectional loop architecture was foundto provide the most scope for enablingan effective HPWM system, both in termsof hydraulic efficiency and protectionagainst ruptures. The three dimensionalgrid with multiple flow paths provideshydraulic advantage in that it enables areduced pumping energy requirement ora reduction in the distribution pipe size.

The use of sectional valves at crossoverpoints either side of each bulkhead offersprotection and flexibility in the event ofblast damage to any particular section.The subdivision of the network into smallcells that can be individually isolated, orsupplied from alternate routes, offers theadvantage for developing a fast recoveryfrom blast damage.

The disadvantage of such a system lies inthe expected extra cost in labour, designspace and material needed to installthe necessary crossover mains, and thenumber of nozzle heads needed. Therequirement of smart valves at each pipenode may also present a significant cost.

PD pumping technology was highlightedas an appropriate means to supplythe network. PD pump pairs could bearranged in parallel in a skid to achievea range of flow demands. Each fire zoneshould contain its own pump unit andeach should be sized to meet a third of

the demand. Water would need to beprovided from a fresh, de-ionised sourceand could not be supplemented from theSea Water Main.

A truly holistic system will requireadvanced control and management. Theintegration of smart sensors, a controlsystem and human operators will be vitalto ensuring the full implementation of anintelligent fire fighting system. A range oftelemetry and joined up sensing processesneed to be combined with a sophisticatedcontrol system that can diagnose fire aswell as detect its symptoms. The more

automated this detection and diagnosisprocess is, the greater the potentialfor saving time taken to respond toa fire and the scale of the responserequired to control it. Integration withCombat Management System (CMS)offers potential for building in reactiveprotection.

Aside from the technical challengesthis presents, it will also requirecomprehensive rethinking of how firesand damage control are managedpresently and how they are pictured inthe future. A full analysis of the costs ofsuch a system would need to be assessed

against the savings made in manpowerand ships size, also taking into accountthe reduction in risk to personnel as aresult of the system being implemented.Provisionally however, the use of HPWMis recommended for meeting the reducedmanning objectives set out by thisreport. Coupled with smart sensor andcontrol technology it enables a swift andintelligent response to fire across theentire ship with little or no need for theman with an extinguisher.


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Defence


References

1. FIRE PROTECTION AGENCY, NA-FS Firefighting Improvement Initiatives as part of the Future Surface Combatant (FSC) Fire Policy,Final Report (Revision 2), Ref. FPA/001020, 17 March 2009.

2. Mawhinney, J.R., DiNenno, P.J., and Williams, F.W., Water Mist Flashover Suppression and Boundary Cooling System forIntegration with DC-ARM: Summary of Testing, NRL Memorandum Report 8400, September 30 1999.

3. R.Ananth, H.D.Ladouceur, H.D.Willauer, J.P.Farley, F.W.Williams, Effect of Water Mist on a Confined Blast, Presented beforethe Suppression and Detection Research and Applications A Technical Working Conference (SUPDET 2008), March 2008Orlando Florida.

4. G.O.Thomas, A.Jones, M.J.Edwards, Influence of Water Sprays on Explosion Development in Fuel-Air Mixtures, CombustionScience and Technology, 1991, 80, Pages 47-61

5. D. SCHWER, K. KAILASANATH, Blast Mitigation by Water Mist (3) Mitigation of Confined and Unconfined Blasts, Center for

Reactive Flow and Dynamical Systems, Laboratory for Computational Physics and Fluid Dynamics, NRL/MR/6410--06-8976, July14, 2006

6. Heather D. Willauer, Ramagopal Ananth, John P. Farley, Gerald G. Back, Victor M. Gameiro, Matthew C. Kennedy, John OConnorFrederick W. Williams, Blast Mitigation Using Water Mist: Test Series II, Navy Technology Center for Safety and Survivability,Chemistry Division, NRL/MR/6180--09-9182, 12 March 2009.

7. Det Norske Veritas Type Approval Certificate, Certificate number F-18732, 7 August 2008.

8. Det Norske Veritas Type Approval Certificate, Certificate number F-18536, 16 November 2007.

9. JR Mawhinney PJ DiNenno, New Concepts for Design of an Automated Hydraulic Piping Network for a Water mist FireSuppression System on Navy Ships, Naval Research Laboratory, Ref NRL/MR/6180-01-8580, September 2001

10. Michelle Peatross and Dr Fred Williams An Overview of Advances in Shipboard Fire Protection, Hughs Associates Inc

11. Jim Banks Take Control: Smart valves Step Forward, offshore-technology.com, dated 18 June 2008, viewed

The Application of High Pressure Water Mist as Part of a Holistic Fire Fighting System

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