DEVELOPMENT OF A LOW-PRESSURE FINE WATER SPRAY FIRE SUPPRESSION 

SYSTEM FOR THE ROYAL NAW: INTERMEDIATE-SCALE TESTING 

James L.D. Glockling 

BRE, FRS, CF&ST 

Mike Edwards and Steve Watkins 

Warship Support Agency 

INTRODUCTION 

The United Kingdom Ministry of Defence Warship Support Agency (MoD/WSA) is the engineering 

support authority for the Royal Navy (RN). Under the Directorate of Operations Equipment, one of 

MFFMS’s responsibilities is the research and development of halon alternatives for the RN. The fire 

protection design policy for Royal Navy surface ships has in the past relied heavily upon halon drench 

systems, fixed sprinkler systems and extensive manual attack ability. Halon is not permitted on future 

ships and with the envisaged reductions in ships complement there may not be the manpower available to 

immediately tackle a fire manually, particularly during action. Extinguishment of all fires by a halon 

replacement system is therefore of primary importance. Other gaseous alternative systems have been 

considered. Currently the preferred alternative is carbon dioxide, although its inherent dangers make this 

far from an ideal solution. For this reason, water-based replacement technologies are being investigated 

that will be able to operate within these and many other constraints that have a profound impact upon the 

selection and implementation ofthe system. It is also hoped that the derived system will be suitable for 

retrospective installation into existing vessels. 

This paper details results of the “intermediate-scale test phase” of an ongoing project funded by the Warship Support Agency and conducted by the Special Projects Group of the Building Research Establishment (BRE), formerly the Loss Prevention Council (LPC). The selection of a water-based system was 

made after a review of RN fire protection requirements and an assessment of a wide range of halon alternatives. When conducting the assessment, two points became clear: first, that the constraints placed on 

the system by a war time role were very challenging (see below), and second, that any gaseous system, 

including halon, was unlikely to satisfy all of these requirements. In particular the ability to extinguish a 

fire in a battle damaged and therefore ventilated compartment, whilst creating an acceptable environment 

suitable for immediate re-entry and recovery, was a key requirement. Examination of the potential benefits of improved spray systems led to an initial project conducted in 1997 comparing typical commercially 

available water mist systems. 

Likely fire scenarios: (a) Pool fires of marine diesel, aviation fuel, lubricating & hydraulic oils 

(b) Spray fires of diesel, aviation fuel, and oils 

(c) Combination fires of all fuels soaked into sound and thermal mineral 

(d) Electric cable fires 

insulation materials 

Fire configuration: 

Enclosure configuration: 

High degree of clutter in machinery spaces, fires may be obscured 

Sealing of the enclosure cannot be guaranteed (Le., missile strike), therefore 

(a) Degree of ventilation is unknown 

(b) Number of ventilation paths is unknown 

(c) Location of ventilation paths is unknown 

Enclosure temperatures: 

Water supply pressures: 

Enclosures are usually metal constructions capable of achieving and storing 

much heat. 

Present sprinkler systems have a nominal design pressure of 7 bar. 

Depending on fire main system configuration and demand, supply pressure 

may be as low as 3.5 bar. 

Water source & quality: (a) Seawater preferred option 

(b) Capability to tolerate low water quality (some solids content) 

(c) Capability to use additives 

414 Halon Options Technical Working Conference 24-26 April 2001 
Enclosure occupancy: 

Manual attack ability: 

System ability: 

Machinery spaces are likely to be unmanned, but not unattended 

Reduced crew sizes mean manual attack may not be possible 

All fire sizes and types must be extinguished 

PROGRESS 

Starting in 1997, the project has been undertaken in a number of logical research phases, the results of 

which are briefly outlined below. 

LABORATORY-BASED RESEARCH PROGRAMME 

These preliminary tests compared typical high and low pressure water mist systems in a variety of scaled, 

ventilated, obscured and unobscured scenarios with a range of Class A and B fuels. The results showed 

the potential for a low-pressure system to work at existing navy seawater main pressures of 7 bar and to 

provide better performance in ventilated conditions than high-pressure systems. Considering the system 

goals it was determined that this approach should be pursued via a phased development programme. All 

research has been conducted by the UK Building Research Establishment (formerly the LPC). 

Phase 1 and 2 -Baseline Tests and Literature Studies: All tests at laboratory scale were conducted in 

a carefully controlled 96m’ 8m x 4m x 3m high test compartment. Phase 1 tested existing FW systems 

(Halon 1301, CO,, and traditional sprinklers) as a baseline to compare with water mist systems. Phase 2 

conducted a literature study on commercially available low-pressure mist nozzles and potential additives. 

A range of promising nozzles and additives were then selected for assessment in the next phase. 

Phase 3 and 4 -Nozzle Screening and WatedAdditive Tests: Phase 3 developed specialised calorimetry and distribution tests to enable initial comparison of nozzle performance without the expense of 

live fire testing. The selected nozzles were then screened using these techniques; four were assessed as 

having the performance characteristics required. These would be taken forward to full fire performance 

testing later in Phase 5; however, Phase 4 deviated to assess water source and additive performance using 

one of the new nozzles as well as an existing ship-fitted sprinkler for comparison. The results showed 

little significant difference between sea and fresh water in extinguishing terms. The best additives improved knock down and gave varying degrees of post fire security (burn back) performance. The best all 

round were AFFF and FFFP; the foams claiming to be more environmentally friendly did not perform as 

well. At this stage the additives were used at the manufacturers’ normal recommended concentrations. 

Phase 5A and 5B - Small-Scale Fire Testing and Nozzle Characterization: Phase 5A returned to the 

main theme by fully fire testing the four best low-pressure mist nozzles. Small difficult fires of diesel, 

avtur, heptane, wood cribs, cable and fuel soaked insulation were used to stretch the systems abilities. 

These small fires reduced the effect of global oxygen depletion, demonstrating each systems true capability. A GW Low Flow K15-C nozzle with a K factor of 15 gave the best all-round performance with 

impressive extinguishing performance particularly using additive. Phase 5B progressed to analyse the 

droplet characteristics of this nozzle using laser phase Doppler anemometry. It was shown that the nozzle 

produced a range of droplet sizes from 100 to 400 microns with a Dv,, of 322 microns. This indicated 

that the nozzle was able to provide larger droplets capable of delivering additive to the fire whilst maintaining a floating mist fraction. With the majority of droplets in the fine spray range as opposed to true 

water mist, the term Fine Water Spray (FWS) was used for the system from then on. The nominal flow 

rate of 39 Vmin at 7 bar, while higher than many true mist nozzles, still allows significant water consumption savings compared to existing RN sprinklers, which typically have a K factor of 59. It had also been 

hoped to size droplets doped with additive, but the high rejection rate as a result of the droplets losing 

their spherical shape when doped made this technique inaccurate. Other techniques were also tried, 

which indicated that the lower the additive concentration the better the quality of mist. More surprisingly, 

when further fire testing was conducted varying the ratio of water/AFFF from the normal 9416 down to 

9930.5 (using 6% AFFF concentrate), the system extinguishing performance improved and the burn 

back protection suffered only slightly. It was observed that the optimum ratio of 1 part AFFF to 99 parts 

seawater gave the best balance between these aspects of performance. 

Halon Options Technical Working Conference 24-26 April 2001 4 15 
Phase 6 -Spray Fire Tests: Phase 6 followed with an examination of the performance of the system 

against diesel spray fires impinging on to a simulated array of pipes. This deliberately created a reignition source. Phase 6 testing was again conducted in the LPC test compartment but with varying 

degrees of free ventilation that proved to be a particularly significant factor with this type of fire. While 

the system could tackle larger spray fires successfully regardless of ventilation state, the smaller fires 

proved difficult to extinguish until the ventilation was limited. The use of an additive, while not detrimental to the results, did not enhance knock down as with the pool fires; however, it did help tackle fuel 

that pooled having hit the pipe array. These results proved the most challenging and would be duplicated 

to some extent in the intermediate-scale test programme undertaken as Phase 7. 

INTERMEDIATE-SCALE TESTS 

Having developed a system and operating philosophy at the laboratory scale there was a need to evaluate 

its performance on a larger scale with some hitherto untested scenario parameters prior to conducting a 

full-scale test. In particular, the tests were to appraise system performance: 

On larger fires On obstructed fires 

In an enclosure with heat retaining surfaces In an enclosure with greater 

In an enclosure with a more complex internal geometry deckhead height 

The tests were conducted using one of MFFM's existing facilities at the Naval Fire Training School on 

Horsea Island, Portsmouth. A schematic of the rig of 140 m' volume and 4.9 m height is shown in Figure 1. The rig was modified to allow different levels of symmetrical free ventilation or sealing to be 

achieved (with inlets and outlets high and low) (Figure 2). 

The rig contained a false bilge, a walkway at half height, a ladder, pipe obstructions, and several pieces of 

machinery at deck level. Tests were conducted initially using four Low Flow KI 5 nozzles on 3 m spacing at the overhead, then later adding another four nozzles at mid height. A wide range of fire types were 

tested including Class A cribs and insulation material, Class B diesel pan fires of around 800 kW, and 

two sizes of diesel spray fire, 1.5 and 3.0 MW impinging on an engine block. All fires were operated in 

open and obstructed locations. 

. earn - 5lDm 

$ I - 

. 1 

. mm 

*% 

I I 

4- \ a a li)m - 

R 6 edn 

Ca(....Sb.N;M ""I 

EIo 

PUTi 

DrndC**IQ.hdm 

416 Halon Options Technical Working Conference 24-26 April 2001 

.~ __ 
WEST WALL 

*Not to scale 

Figure 2. Ventilation panel positions in test rig (each panel 0.5 m high x 1 .O m wide), 

RESULTS 

Issues pertaining to extinguishing fires with Fine Water Spray systems with respect to performance and 

installation criteria are discussed below. 

PERFORMANCE 

Implications of Enclosure Conditions Prior to Extinguishing System Operation 

Much has been written regarding the relationships that exist between the performance of fine water spray/ 

water mist systems and, the enclosure size; amount of ventilation; fire size; and fire preburn times (detection). With respect to extinguishing performance, the key parameters that are changed by any combination of these variables are the following: the mean oxygen content of the enclosure prior to system operation; the mean atmospheric temperature of the enclosure prior to system operation; and the temperature of 

surfaces within the enclosure prior to system operation. If atmospheric and surface temperatures are high, 

then steam generation and therefore oxygen displacement are more prolific; if oxygen content is already 

low, then the extinguishing process is improved still further. 

Favourable conditions for operation might be a large fire in a small enclosure with zero, or little ventilation, and an unfavourable condition might be a small fire in a large ventilated enclosure. The ability to 

tackle fires between these limits depends upon the rates at which heat is generated and oxygen is depleted 

by the fire, against the rate at which heat escapes and oxygen is replaced through ventilation. Each of the 

parameters that influences the starting conditions tested in this study is discussed in turn below. 

Fire Preburn Times: Table 1 shows the difference in starting conditions for fire preburn times of 3 and 

7 1/2 min, respectively (all other experimental parameters identical). 

TABLE 1. 1NFLUENCE OF PREBURN TIMES ON EXTINGUISHMENT OF THE LARGE 

AND SMALL SPRAY FIRES. 

Mean Enclosure Oxygen Concentrations Prior to Preburn Time System Operation (%) Extinguishing 

Time (sec) .~ ~~ 

Run No. Temperature Prior to (min) System Operation ("C) High Low 

Large spray fire 

2 7% 295 8.34 15.19 IO 

10 3 258 10.04 17.23 45 

1 IO 202 14.58 16.48 22 

II ~ 

3 131 -- 17.83 19.88 Not extinguished 

Small spray tire 

Halon Oplions Technical Working Conference 24-26 April 2001 4 17 
The benefits of an extended preburn time are clearly shown. During the extended preburn period, the 

mean temperature of the enclosure is increased by an additional 37 OC and the oxygen lowered by a mean 

of 1.87%. The result is an extinguishing time difference of 35 sec. The results are more pronounced 

when data from the small spray fire are compared. Here the difference in pre-burn times is the difference 

between satisfactory extinguishment and failure. 

Ventilation: In this example, the small fire fails to produce the conditions for its own extinguishment, 

whilst the larger spray fire does. Table 2 shows the difference in starting conditions for ventilation conditions of 2, 4, and 8 panels removed from the rig (all other experimental parameters identical). For ventilated enclosures the benefits of reduced ventilation on extinguishing performance are clearly shown. 

Operating with only 2 panels removed as opposed to 8, the enclosure temperatures at the time of system 

operation are 91 "C higher and the mean oxygen concentration is 5% lower. 

TABLE 2. INFLUENCE OF VENTILATION ON EXTINGUISHMENT OF THE LARGE 

AND SMALL SPRAY FIRES. 

Mean Enclosure Oxygen Concentrations Prior to Extinguishing Vent Panels 

.-. Time (sec) Temperature Prior to System Operation _- (%) 

System Operation ("C) High Low Run No. Removed 

Large spray fire 

25 2 238 11.64 17.08 14 

39 4 175 15.75 20.81 21 

47 8 I65 11.65 20.84 35 

24 8 I47 18.06 20.83 Not extinguished 

31 2 170 16.53 19.34 16 

38 4 129 17.82 20.45 Not extinguished 

20 8 112 19.08 20.82 I95 

Small spray fire 

Fire Size: The influence of fire size on the atmospheric conditions prior to extinguishing system operation where data from the large and small spray fires operated under identical conditions are compared 

(Table 3). In this example, the small fire fails to produce the conditions for its own extinguishment, 

whilst the larger spray fire does. 

TABLE 3. INFLUENCE OF FIRE SIZE UPON EXTINGUISHMENT BY FINE WATER SPRAY. 

M~~ ~~~l~~~~~ T~~~- 

Run No. Fire Size erature Prior to system to System Operation (%) 

Oxygen Concentrations Prior 

Extinguishing 

- Time(sec) Operation (T) High Low 

38 Smallspray 129 17.82 20.45 Not extinguished 

39 Largespray 175 15.75 20.81 31 

Atmospheric Cooling Ability 

A primary attribute of fine water spray is its ability to remove heat from its surroundings efficiently. The 

rapidity with which it can do this is a function of the thermodynamic properties of water, the temperature 

and vapour concentration gradients existing between droplet and atmosphere, and the surface area over 

which heat and mass transfer can take place (heat absorption by the droplets and steam generation from 

the droplet). The finer the mist, the more efficiently and rapidly this can take place. 

Even in the event ofthe fine water spray system not extinguishing the fire, the environment may be cooled sufficiently to make re-entry possible for manual tackling of the fire. Table 4 shows mean enclosure 

temperatures measured during successful and unsuccessful extinguishment of all fires. 

41 8 Halon Options Technical Working Conference 24-26 April 2001 
TABLE 4. INFLUENCE OF FWS ON ATMOSPHERIC TEMPERATURES 

Run Mean Enclosure Temperature Mean Enclosure Temperature 

No. Ext. Fire Type Prior to System Operation FC) 3 min after System Operation CC) 

24 Largespray 147 59 No 

39 Large spray 175 31 Yes 

38 Small spray 129 43 No 

31 Small spray 170 21 Yes 

7 Single pool 109 49 No 

6 Single pool 89 22 Yes ~ 

Generally the fine water spray system is capable of maintaining atmospheric temperatures to within 40 "C 

of the ambient value. This has far reaching considerations for rapid entry into the enclosure (with suitable breathing apparatus) and for bulkhead cooling (see Bulkhead Cooling Ability). 

Bulkhead Cooling Ability 

Bulkhead cooling external to the fire enclosure is required to preserve the structural integrity of the vessel 

and prevent damage and spread to other areas. The use of fine water spray has the potential to replace the 

need for bulkhead cooling by: 

rapidly reducing enclosure temperatures 

putting limited amounts of water directly onto the internal bulkhead surfaces 

attenuating thermal radiation to the bulkhead 

producing all the above benefits regardless of whether the fire is extinguished or not 

The rate at which cooling occurs will be a function of the enclosure temperature, amount of water impacting upon the bulkheads, aerosol properties, and the thermal inertia possessed by the structure. The use of 

wetting agents will also influence the efficiency with which water coating of surfaces occurs. Table 5 

shows the bulkhead cooling during tackling ofthe large spray, and double-pool fires. Two large spray 

tests describe bulkhead cooling performance when the fire is extinguished successfully, and when it is not 

TABLE 5. BULKHEAD COOLING BY FINE WATER SPRAY. 

i Mean Temperature Prior to System Operation and Cooling Rate Shortly After I 1 ~~. ~ ~~ ~~ ~ ~ ~~ ..... ~..-~ . .: 

~ i --~; 

Run j Unobscured i Obscured ! 

No. bulkhead i bulkhead ~ 

FireType ~ Enclosure ~ Deckhead ~ Ext. 

9 Large spray 1 251 418 106 45 1 130 12 i -- __ j Yes 

24 Largespray 1 147 500 i 71 10.5 1 86 27' ~ 56 -5.8 ~ No 

27 Doublepool ~ 183 418 1 50 10 ~ 45 4.4' 1 63 1.4 I YesMo 

* Bulkhead location not actually obscured from direct water impingement when 8 nozzles are used instead 

of 4, as in Runs 24 and 27 

Run 9 demonstrates clearly the difference in cooling rates of the 5 mm thick bulkhead resulting from 

atmospheric cooling with and without direct surface water impingement. Unobscured surfaces (where 

direct drop impingement is possible) are seen to cool at the faster rate of 45 "Chin as opposed to 

12 "Urnin on obscured surfaces. Even when the fire is not extinguished significant bulkhead cooling is 

induced. 

Halon Options Technical Working Conference 24-26 April 2001 41 9 
Egress Smoke Temperatures 

In a fire scenario, there is often scope for extensive consequential damage as a result of hot gases 

escaping from the fire zone to sensitive areas. This damage may take the form of: 

0 

0 

e 

heat damage to other areas and possible fire spread 

toxicity hazard as combustion products escape to manned areas 

chemical hazard to personnel and systems in adjoining spaces by corrosive/imtant gases 

As with the measured cooling of the fire enclosure, escaping fire products are likewise cooled and most 

likely scrubbed of soluble corrosive and irritant gases, such as hydrogen chloride, hydrogen cyanide, and 

hydrogen fluoride that may be produced by the burning of plastic products (e+, cable sheathing and 

insulation). Table 6 shows egress smoke temperatures measured for the large and small spray fires. 

Regardless of whether the fire is extinguished or not, it is highly likely that consequential damage resulting from leakage of hot and corrosive gases to other areas of the ship may be significantly reduced by the 

use of a Fine Water Spray. 

TABLE 6. EGRESS SMOKE COOLING BY FINE WATER SPRAY. 

24 Large spray 148 60 

39 Largespray 175 37 

38 Small spray 129 45 

31 Small spray 170 31 

7 Singlepool 110 49 

6 Singlepool 89 24 

23 1 66 No 

265 42 Yes 

201 63 No 

155 43 Yes 

34 28 No 

48 22 Yes 

Additive Inclusion 

Although under sealed enclosure conditions (or circumstances that promote FWS function [see Implications of Enclosure Conditions Prior to Extinguishing System Operation]), FWS performance may be 

perfectly satisfactory without the use of an additive, it is likely that conditions will not be ideal or possible 

to guarantee. In determining the need for an additive, it is important to appreciate the differences in fire 

types and fuels, as its use is not always beneficial. 

It is clear that an additive enhanceshakes possible the tackling ofthe unobscured Class A wood crib, 

Class A PVC cable, and Class B liquid fuel fires. It is obviously also beneficial in tackling floor burning 

fuel from the spray fires (a very important part in their extinguishing process). It has been demonstrated 

previously that an additive increases the drop size distribution of the FWS. To this end it is likely that it 

will have a negative impact upon the tackling of obscured fires (larger drops are less mobile and less 

likely to ‘flow’ to fill volume). The increased drop size has already been demonstrated to have a negative 

effect upon the tackling of spray fires as the extinguishing process is a surface area-based issue (as 

opposed to putting a layer of additive onto of the top of a liquid pool). However, normal procedures in 

tackling spray fires would be to isolate the source of fuel. 

In summary, the following is probably true and this will be a factor in determining the installation criteria 

of the system (Table 7). Installation guidelines for the envisaged system must ensure that the likelihood 

of significantly obscured fires occurring is zero. 

420 Halon Options Technical Working Conference 24-26 April 2001 

__ ___ 
TABLE 7. SUMMARY DIFFERENCES FOR TACKLING OF DIFFERENT FIRE TYPES. 

FireType Access Class of AFFF Benefit Ideal Extinguishing Means 

Fuel 

Wood crib Unobscured A Good AFFF 

Wood crib Ohscurcd A No benefit unless capable of AFFF and nozzle mounted under 

ultimately ‘flowing’ onto fuel under 

gravity resulting in ‘Good’ benefit’ 

Cable Unohscured A Good AFFF 

Cable Obscured A No benefit unless capable of AFFF and nozzle mounted under 

ultimately ‘flowing’ onto fuel under 

obstruction 

.... ~~~~~.~ ~ ~~~~ .......... ~~~~ ~ ~~~~~~~~ ............ ~~~ ~~-~ ~ .......... .~~~ 

obstruction 

gravity resulting in ‘Good’ benefit . ~~~~ ~ ~~~ ~ .~ ~ ~~ 

1.iouid nod llnobscured B Good ~~ AFFF 1~~ 3 ~~ ~~~~ 

~~~ 

Liquid pool Obscured B No benefit unless capable of AFFF and no7zle mounted under 

ultimately ‘flowing’ onto fuel under 

gravity resulting in ‘Good’ benefit 

ultimately ‘flowing’ onto resulting 

pool fires under gravity 

ultimately ‘flowing’ onto resulting 

pool fires under gravity 

obstruction 

.......... ~ .~~ ~~ ............. ~~~~~ .......... ~~~~~ .. ...... ~~.~ ........ ~~ ~~ ..... ~.. Spray Unobscured B Detrimental unless capable of Increased aerosol density and/or fuel 

isolation (AFFF to tackle spilled fuel) 

Spray Obscured B Detrimental unless capable of Nozzle mounted under obstruction and 

increased aerosol density andlor fuel 

isolation (AFFF to tackle spilled fuel) 

INSTALLATION 

Ultimately a design manual for the derived system must be developed. The design manual must ensure 

that for each probable scenario the system is installed in a manner that optimises its performance in terms 

of extinguishing ability and reliability. Circumstances will arise where a degree of compromise in terms 

of over-design is evident, but this is offset against negating the need for a real-scale evaluation of all 

installations and the implementation of simple rules that are robust and easy to use. The installation rules 

for the envisaged system will be appropriate for areas with a certain level of risk. Where specific risks 

are identified as presenting a special hazard in terms of likelihood or scale of potential damage, a separate 

system or different rules may apply. From these tests, the importance of a number of installation criteria 

necessary to complete this study has been demonstrated, namely, nozzle numberslspacings and nozzle 

locations/obstructions. 

Nozzle Numbers 

Pressure is a variable that influences the amount of water entering the enclosure, as is the number of 

nozzels. Extra nozzles may be introduced to a volume by either decreasing the spacing or introducing 

more nozzles at various heights within the enclosure on the same spacing. Unlike modifying the operating pressure, changing the number of nozzle does not influence the drop size of the FWS. Table 8 shows 

the mean temperature and oxygen values measured whilst tackling small and large spray fires with 4 and 

6 deckhead mounted nozzles, (all other parameters remain the same). 

TABLE 8. SUMMARY DATA OF TESTS USING DIFFERENT NUMBERS OF NOZZLES. 

Oxygen Concentrations Prior 

to System Operation (??) 

High Low 

Run Nozzle Mean Enclosure Temperature Extinguishing 

No. S Prior to System Operation (“C) ~ ~~~~ Time (set) Fire Size 

II 4 Small spray 131 17.83 19.88 Not 

extinguished 

14 6 Small spray 125 18.00 19.53 52 

IO 4 Largespray 258 10.04 17.23 45 

15 6 Largespray 24 1 11.33 17.72 17 ~ 

Halon Options Technical Working Conference 24-26 April 2001 421 
By increasing the amount of water supplied to the enclosure in this way, the extinguishing time of the 

large spray fire is reduced and the small fire is extinguished where previously it was not. We have 

already seen in the Additive Inclusion section that spray fires differ significantly from pool or Class A 

fires in the way a system tackles them. For a given spray fire, an air aerosol loading will exist that will 

extinguish a fire by local oxygen depletion and cooling. As smaller fires are attempted, greater efficiency 

of heat removalkteam generation is required, which would generally require higher operating pressure or 

decreased nozzle spacings to achieve. Fuel isolation remains the best form of tackling spray fires, and it 

should be a key requirement when possible to do so. 

Nozzle Locations/Obstructions 

In all but a few isolated cases (generally where ventilation was minimal) Class A and Class B pool fires 

were not tackled by the system when obscured from the direct line-of-fire of the FWS nozzle. Relying so 

heavily on its good performance on these small fires (from the additive in the water supply) means that 

where the water does not go, fires are not extinguished. High-pressure systems attempt to do this by producing high momentum systems that force aerosol into all parts of the enclosure although again they can 

be easily defeated (as is a gas system) by even limited ventilation. The additive in water does “flow” 

after impacting the surface and to this end it was essential in the extinguishment of the pool burning portion of spray fires and of even heavily obstructed bilge fires under the diesel generator. 

Consequently, the key to the design of such systems is that significant obstructions like walkways are not 

tolerated and extra nozzles are installed to tackle the obstacle. 

The most appropriate installation philosophy for these tests involved the allocation of each nozzle to 

protect a given volume with a few basic rules, for example: 

Nozzle to nozzle spacing 3 m Nominal operating pressure 7 bar 

Max. nozzle operating height 3 ms Maximum additive supply 1% 

Nozzle to wall spacing 1.5 m Minimum additive supply 0.5% 

Using these rules explains why for an enclosure height in excess of 5 m two nozzle arrays were required 

--one suspended from the deckhead, the other at a lower deck height. Further investigation on a larger 

scale will establish whether other nozzles, probably with a larger K-factor, could be used where greater 

unobstructed deckhead heights exist to avoid the inconvenience of intermediate level nozzles. What has 

been demonstrated is that with these few simple rules, a very promising level of protection has been 

established in this sizeable (136 m’ volume) test enclosure, on a range of likely fuels and fire sizes, using 

conservative amounts of water. Further testing will establish (I) if even greater economies of water 

usage are achievable without compromising the level of protection and (2) whether performance may be 

increased in the light of renewed information concerning future ship pumping capacities. 

CONCLUSIONS 

This series of tests has enabled the performance of the derived Fine Water Spray system to be evaluated 

under some previously untested circumstances, namely, on larger fires, in a larger enclosure, and with 

realistic obstructions, and to evaluate other parameters, such as bulkhead cooling. The results presented 

herein will aid in the definition of the envisaged large-scale test rig, and ultimately the system design and 

associated installation manual. A brief summary of key factors studied in this work programme follows. 

The ability of water mist to tackle fires has been demonstrated to be closely linked to environmental conditions prior to operation. Due to the operational requirements of a fighting ship, potentially beneficial 

environmental conditions cannot be guaranteed, so an additive is required to tackle problematic fire scenarios. Although an additive is beneficial for tackling unobscured surface burning fires such as wood crib 

and diesel pool fires, it is detrimental to the extinguishment of sprayed liquid fires and hidden surface 

fires (except where the fuel is located at low level where the additive will ultimately reach by gravity, 

422 Halon Options Technical Working Conference 24-26 April 2001 
such as a bilge). Spray fires can be tackled by increasing local aerosol densities, which may be achieved 

by increasing water supply pressure, reducing nozzle spacings, or selecting specialist nozzles, but are best 

handled by isolation of the fuel supply. Robust management of severely obscured fires with this lowpressure system can only be achieved by placement of nozzles to tackle the risk directly. 

In adopting this approach, nozzle selection and additive usage must be considered together if optimum 

performance is to be achieved. In an attempt to preserve key attributes ofwater mist and sprinkler systems, low concentrations of additive have proven most favourable and the ability to dose such quantities 

accurately will be paramount. Testing to date has only considered water supply pressures up to 7 bar. It 

is possible that future ship designs will allow for operational pressures above this, which may offer significant performance enhancements to the FWS system. Similarly, operation at lower pressures has been 

shown to be detrimental to system performance unless the nozzles are optimised at the lower pressure. 

This study has demonstrated how the FWS quickly induces very rapid and extensive environmental 

cooling that should accelerate re-entry and subsequent re-commissioning of the enclosure. The level of 

cooling and personnel protection is such that re-entry may well be possible with the fire still burning 

enabling manual attack to be considered where previously it might have been impossible. Cooling of the 

atmosphere and attenuation of thermal radiation additionally offers the potential of replacing/ reducing 

the need for bulkhead cooling. Smoke escaping from the enclosure is similarly cooled and potentially 

scrubbed of soluble toxidirritant gases such as hydrogen chloride, hydrogen fluoride, and hydrogen 

cyanide, which will limit consequential damage and aid evacuation. 

With respect to the enclosure in which these tests were conducted, a nozzle spacing of 3 m was appropriate for tackling most unobscured fires (aside from spray fires) from a deckhead mounting point. With 

the introduction of obstructions, an alternative installation criterion was successfully used whereby each 

nozzle protected a volume of size 3 x 3 x 3 m, which required a secondary water main mounted at a lower 

level. The water consumption for this installation (320 I mid) represents a significant saving of resources when considering that it must replace (partially or wholly) three existing systems, namely, (I) fixed 

sprinkler system, (2) fixed 2-shot gas system, and (3) manual firetighting, and be capable of functioning 

in sealed and ventilated conditions. A fair comparison can only be made by consideration of the abilities 

of the established and ‘hew” system on each fire type in each condition. Table 9 compares the performance of these systems and includes high-pressure water mist for further information. 

TABLE 9. COMPARISON OF ALTERNATIVE SYSTEM ABILITIES ON A RANGE OF FIRE 

FOR EACH ENCLOSURE CONDITION. 

“IDEAL” Enclosure 1 “NON-IDEAL” Enclosure 

Condition, Sealed/Small ~ Condition, VentilateULarge 

Pool Spray ClassA ~ Pool Spray ClassA 

High 0, Low TC System Low 0, High ~ T “C ~ ~ ~ ~ ~ 

Established Fixed sprinkler J - J’J - J 

Established Fixed gas J J J - - - 

Established Manual attack J J* J:J J* J 

Alternative High pressure water mist J J J; - - - 

Envisaged FWS with - AFFF J J JiJ ?+ J - 

* - by shutting off the fuel supply 

+ - should be possible without having to shut off the fuel supply 

Overall, the envisaged system continues to offer the prospect of satisfying economic replacement of 

existing onboard extinguishing systems for the total volume protection of open areas, e.g., machinery 

spaces. Fundamental to its development is its robustness of operation to function under a range of scenarios without some of the detrimental aspects of other systems, such as fire re-flash, excessive water 

usage, the need for bulkhead cooling, and the need for relatively sealed enclosures. 

Halon Options Technical Working Conference 24-26 April 2001 423 
The next stage in this development programme is a full-scale, real geometry fire test programme, which 

will demonstrate the effectiveness of the design in larger volumes with more realistic clutter and enable 

the development of an understanding of the implications of nozzle placement and spray pattern requirement to achieve the degrees of surface covering and volume filling desired. Design and installation rules 

will be derived for future implementation of the system. 

SUMMARY OF THE DERIVED METHODOLOGY 

FOR MACHINERY SPACE PROTECTION OF ROYAL NAVY SURFACE SHIPS 

A summary of the conclusions drawn from the work to date is given below. Ongoing and future work 

may impact upon these at a later date. 

A FWS system may be best suited to fulfill the design criteria for naval surface vessels. 

AFFF (Mil. Spec.) additive shall be used to enhance the ability of the system to extinguish small 

fires and inert liquid fuels thereafter. 

Location of nozzles will reflect the need to project water and additive onto surfaces, and fill 

volumes with floating mist. 

A range of nozzles will probably be required to enable correct implementation of the system 

suitable for horizontal and vertical mounting with a selection of spray angles, patterns, and drop 

distributions. 

Hidden fires will be tackled by “design”; no 3-dimensional performance is inferred especially on 

small fires. 

Where possible, enclosures shall maintain their integrity, preventing ingress of oxygen and leakage 

of oxygen-depleted fire products and aerosol. 

ACKNOWLEDGMENTS 

Recognition is given to Kelvin Annable, Building Research Establishment, and WOMEA Paul Winton 

for their extensive input into the experimental content of this work. (British Crown Copyright 2001 / 

MOD; Published with the permission of the Controller of Her Britannic Majesty’s Stationary Office) 

NOTE 

Further information may be found in the following reports, most of which are on file with the author. 

C. Buckley, and D. Rush, “Development of Water Mist for the Royal Navy,” published MOD paper 1996. 

M. Edwards, and S. Watkins, “Further Development of Water Mist for the Royal Navy,” published MOD 

J.L.D. Glockling, M. Edwards, and S. Watkins, “Development of a Water Based Fire Suppression System 

Unpublished MOD reports: 

paper, 1997 

for Naval Fighting Ships,” published MOD paper, 1999 

J.L.D. Glockling, K. Annable, “Comparative Performance Testing of Water Mist Systems,” 1997. 

J.L.D. Glockling, K. Annable, “Water Mist Development Phase 1 ResuIts,”1998. 

J.L.D. Glockling, K. Annable, “Water Mist Development Phase 2 Results,” 1998. 

J.L.D. Glockling, K. Annable, “Water Mist Development Phase 3 Results,” 1998. 

J.L.D. Glockling, K. Annable, “Water Mist Development Phase 4 Results,” 1999. 

J.L.D. Glockling, K. Annable, “Water Mist Development Phase 5 Results,” 1999. 

J.L.D. Glockling, K. Annable, “Fine Water Spray Development Phase 6 Results,” 1999. 

J.L.D. Glockling, K. Annable, “Fine Water Spray Development Phase 7 Results,” 2000. 

424 Halon options Technical Working Conference 24-26 April 2001