the use portable water mist on high altitude

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Journal of Fire Sciences

DOI: 10.1177/0734904107069675 2007; 25; 217 Journal of Fire Sciences

Xin Huang, Xishi Wang, Xiang Jin, Guangxuan Liao and Jun Qin System under High-altitude Conditions

Fire Protection of Heritage Structures: Use of a Portable Water Mist

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Fire Protection of HeritageStructures: Use of a PortableWater Mist System underHigh-altitude ConditionsXIN HUANG, XISHI WANG,* XIANG JIN, GUANGXUAN LIAO

AND JUN QIN

State Key Laboratory of Fire Science, University of Science and Technologyof China, Hefei, Anhui, 230026, PR China

(Received April 30, 2006)

ABSTRACT: In order to verify the application of water mist on fire protectionof the Potala Palace in Tibet and deepen the knowledge of its suppressionmechanisms under high-altitude conditions, a series of experiments areperformed with a portable water mist fire protection system and with dieseloil, gasoline and, in Lhasa, ghee as fuels. All of the experimental tests areconducted with and without multicomposition (MC) additives. The experimentalresults show that the MC additive can evidently improve the extinguishingefficiency of water mist for a diesel fire, but the gasoline fire is a little difficultto extinguish. The effects of high-altitude conditions on fire suppression arediscussed.

KEY WORDS: water mist, heritage structures, additive, fire extinguish,fire suppression mechanism.

INTRODUCTION

IT IS WELL known that the use of water mist for fire suppression wasfirst studied in the 1950s, and there has been a renewed interest in this

*Author to whom correspondence should be addressed. E-mail: [email protected] 1, 2, 4 and 5–14 appear in color online: http://jfs.sagepub.com

JOURNAL OF FIRE SCIENCES, VOL. 25 – MAY 2007 217

0734-9041/07/03 0217–23 $10.00/0 DOI: 10.1177/0734904107069675� 2007 SAGE Publications



old technology since the first version of the Montreal Protocol wasintroduced in 1987 [1,2]. This international commitment to protectingthe Earth’s ozone layer from further damage by chlorinated fluoro-carbons (CFCs) has driven about 20 years of testing to developalternative fire suppression technologies to replace the chlorine- orbromine-based gaseous fire suppressants known as halons. In addition,some traditional and chemical agents were found to be a danger topersonnel due to toxicity and asphyxiation. Water mist is not associatedwith such dangers to people in occupied areas, and has receivedconsiderable attention as one of the potential methods for replacementof Halon 1301 and 1211 [3–9]. Many studies on water mist suppressionmechanisms and its application in practical fires, such as aircraft cabins,military radar, computer rooms, communication equipment cabinets,have been performed [10–16]. However, little work has been carried outon fire suppression with water mist under high-altitude conditions,such as in Lhasa, the provincial city of Chinese Tibet, at an altitudehigher than 3600m.

China has a considerable number of historical buildings, which are notonly valuable to Chinese culture but also an important constituentof international cultural heritage. Based on incomplete statistics, thereare 3000 historic buildings (excluding historic civilian buildings) inChina, including 1000 towers and 2000 palaces and temples [17].Therefore, research on protecting historic buildings is very important inChina [18]. As one of the well-known world cultural heritages, PotalaPalace (Figure 1) is a key fire protection object in China.

Located on the Red Hill in Lhasa, the stone-and-wood-structuredPotala Palace covers an area of over 360,000m2 and is 119m high with 13floors. It houses a large number of priceless cultural relics, as well as silksand satins, including prayer banners, thangkas, and hadas. The woolenrugs, wooden cabinets, and religious books in the Palace also make thefire load very high. Moreover, nearby structures of the Palace areconnected by corridors and no fire compartmentation exists. Combustiblecurtains and canopies made of cloth are placed above the corridors or inthe windows. Therefore, fire can spread quickly between nearbystructures and floors. Ghee-fueled lamps, burning incense, electricalequipment, and lightning are potential ignition sources. In summer,visitors to the Potala Palace number more than 1000 daily. With windingand narrow passageways, only two steep and narrow stairways exit. Ifa fire were to occur, the loss of life and property could be great.

It should be noted that there are special requirements for fireprotection in the Potala Palace, since it is not only a famous travel scenicspot, but also a Holy Land of Buddhism. For instance, a pipe system

218 H. XIN ET AL.



cannot be installed inside the Palace because of its unsightly appearanceand potential damage to the building structure. In addition, a pipesystem might place too much burden on the weight capacity of thePalace. In order to avoid damage to the cultural relic, massive amountsof released water and corrosive fire suppression agents are also rejectedby the Buddhists of the Zang nationality. In addition to the PotalaPalace, the fire protection of some other historical temples in Tibetface the difficulties of remote location and lack of readily availablewater resources. Therefore, selection of appropriate fire suppressionmethodology is essential for heritage structures in Tibet.

A portable water mist fire protection system could be regarded asa suitable means for fire protection of the Potala Palace because of itssmall and unobtrusive presence, cleanliness, etc. These merits can makethe system avoid negative effects on the appearance of the Palacebecause it can be placed in a corner, a convert, or other appropriatelocations, and it can reduce the potential for cultural relic corrosion,breakage, and adverse environmental effects. But no research or testinghad been done on fire extinguishing with a portable water mist in Tibet.

The purpose of this study was to verify the application of water mistfire protection in the Potala Palace and deepen the knowledge ofits suppression mechanisms under high-altitude conditions.

Figure 1. The Potala Palace in Tibet province (The altitude is about 3700m).

Fire Protection of Heritage Structures 219



The experiments were performed in a 4� 2� 4m confined compartment,using a 300mm� 300m� 50mm standard stainless steel fuel pan.Although heptane, diesel, or crude oil pool fires are usually used in firesuppression testing [11,19], diesel oil, gasoline, and ghee, a typicalpotential ignition source inside the Potala Palace, were used as fuelsin our work. A multi-composition (MC) additive [16], newly developedby our research group, was also used. The experimental results showedthat the MC additive can evidently improve the water mist extinguishingefficiency for a diesel fire, but the gasoline fire was still a little difficultto extinguish.

EXPERIMENTAL APPARATUS

As shown in Figure 2, the experiments were conducted in a4� 2� 4m confined compartment in Tibet at 3658m altitude and66 kPa atmospheric pressure. A 300� 300� 50mm3 standard stainlesssteel pan was placed on the floor. Water mist was produced by a portablesystem, which worked with a single fluid nozzle and a 3L water tank(containing 1.5L water and 1.5 L 3.2MPa nitrogen). The nozzle wasconnected to the tank with a 300mm long stainless steel pipe anda 400mm long flexible tube so that the water mist injecting directionand its working distance can be varied easily. The droplet size andvelocity distribution were measured previously by a phase Doppleranemometry (PDA) system [13,20] at Hefei, where the atmosphericpressure is about 101 kPa and the altitude is about 23m. In addition,some K-type thermocouples were located along the pool centerline tomeasure the temperature. A CCD camera was used to visualize the firesuppression. An in situ gas analyzer (produced by MSK Co.) was located

Figure 2. Schematic of the experimental apparatus.

220 H. XIN ET AL.



1.5m from the fire source and 2m above the ground to measure theconcentrations of CO, CO2, and O2. An electric balance was used tomeasure the fuel mass loss. In order to compare the experimental resultsbetween Tibet and Hefei, some cases were repeated in Hefei with thesame conditions, both at room temperature of about 12�C.The concentration of the MC additive was 0.2%, which is the optimizedvalue as stated elsewhere [16].

All of the systems began to work after ignition, and the firewas allowed to burn for about 50–90 s before the water mist injection.All the raw data were saved and processed automatically by a computer.

EXPERIMENTAL RESULTS AND DISCUSSION

Water Mist Characteristics

As shown in Figure 2, water mist is discharged from a single fluidnozzle. The droplet size and velocity were measured by a PDA systemat the cross section 1.0m away from the nozzle exit. The workingpressure of the system is about 3.0MPa, and the discharge coefficient(K-factor) is about 0.66. Figure 3 gives the measured results of Sauter

0 50 100 150 200 250 300 350 400

80

90

100

110

120

130

140

3.0MPa

1.0m away from the nozzle exit

SM

D (

mm)

Distance from exit centerline (mm)

Figure 3. Radial distribution of the Sauter mean diameter (SMD) measured by PDA.




mean diameter (SMD) and Figure 4 gives the droplet velocitydistribution both axially and radially. It shows that the system hasa radially uniform droplet size distribution. The value of axial velocitynear the center of the spray cone is about two times higher than the onenear the envelop edge.

Tests on Diesel Fire Suppression

The tests of suppressing diesel fire with portable water mist systemwere conducted in Tibet and Hefei. For each test, 300 g diesel oil and10 g ethanol, which was used to ignite diesel oil, were poured into thepan. During the ejection of water mist, the distance between the poolfire and the fire fighter was fixed, but the injecting direction can beadjusted a little according to the scene of the suppressing fire behavior.After the fire was extinguished, the fan was turned on to exhaust smoke.Table 1 gives the extinguishing time of the diesel fire tests underdifferent conditions. The temperature history of diesel fire beforeand after the application of water mist at Tibet and Hefei are shown

0 50 100 150 200 250 300 350 400

0.0

0.5

1.0

1.5

2.0

2.5

3.0M

ean

vel

oci

ty (

ms−1

)

Distance from exit centerline (mm)

Axial mean velocity (U) Radial mean velocity (V) Radial mean velocity (W)

Injection pressure: 3.0MPa1.0m away from the nozzle exit

Figure 4. Radial distribution of the droplet’s three-dimensional velocity measuredby PDA.

222 H. XIN ET AL.



in Figures 5 and 6 for different distances and agents. The variationof the CO concentration in the test room is shown in Figure 7.

Tests on Gasoline Fire Suppression

The tests of suppressing gasoline fire were also conducted in bothTibet and Hefei. In each test, 250 g gasoline oil was poured into the pan.Table 2 gives the extinguishing time of the gasoline fire suppressiontests under different conditions. The temperature history of gasolinefire before and after the application of water mist in tests at Tibetand Hefei are shown in Figures 8 and 9 for different agents.The variation of the CO concentration in the test room is shown inFigures 10 and 11. Table 3 gives the minimum concentration of O2 andmaximum concentration of CO2 measured in each case.

Discussion

In order to analyze the experimental results measured in Tibet andHefei, the fuel mass loss without water mist discharging was measuredby an electric balance. As presented in Figure 12, the fuel mass lossrate in Tibet is much slower than in Hefei because of the lack of oxygen:300 g diesel oil and 250 g gasoline were burned out within 600 s and300 s, respectively, in Tibet but in only 330 and 160 s in Hefei, and thehighest flame temperature measured in Tibet is about 100–200�Cless than in that in Hefei. Therefore, using pure water the fire can beextinguished easily in Tibet. For a diesel fire, the fire-extinguishingefficiency has little difference between the test in Tibet and Hefei.

Table 1. Extinguishing time of the tests on diesel fire suppression.

Case number Locality Fire suppression agent Distance (m) Extinguishing time (s)

1 Tibet Pure water 2 102 Tibet Pure water 3 203 Tibet Pure water 4 Failure4 Tibet 0.2% MC additive 4 45 Tibet 0.2% MC additive 5 46 Tibet 0.2% MC additive 6 Failure7 Hefei Pure water 2 128 Hefei 0.2% MC additive 4 49 Hefei 0.2% MC additive 5 410 Hefei 0.2% MC additive 6 Failure




Both in Tibet and in Hefei, it was more difficult to extinguish a gasolinefire than a diesel fire because of the low ignition point, good volatility,and quick fire spreading. Upon discharging water mist, the temperaturenear the pool surface decreased immediately as the water mist wasejected to the fire root. In the tests, one part of pool fire was

0

100

200

300

400

500

600

700T

emp

erat

ure

(°C

)T

emp

erat

ure

(°C

)

Time (s)

Time (s)

Water mistactivated

(a)

0 40 80 120 160 200

Near the pool surface

Near the pool surface

5cm above the pool surface

10cm above the pool surface15cm above the pool surface20cm above the pool surface25cm above the pool surface30cm above the pool surface35cm above the pool surface

Extinguishing time: 4s

Water mistactivated 5cm above the pool surface

10cm above the pool surface15cm above the pool surface20cm above the pool surface25cm above the pool surface30cm above the pool surface35cm above the pool surface

Extinguishing time: 4s

(b)

0 40 80 120 160 200

0

100

200

300

400

500

600

700

800

Figure 5. Temperature history of diesel fire before and after the application of watermist for tests in (a)Tibet and (b) Hefei (distance: 4m, agent: 0.2% MC additive).

224 H. XIN ET AL.



extinguished first, and then the fire fighter changed the direction of thenozzle to extinguish the rest of the fire. In the case of a diesel fire,the fire was extinguished quickly. However, in a gasoline fire, when thenozzle direction was changed, the first extinguished fire was reignited bythe rest of the fire. Therefore, the extinguishing time was prolonged.

0

0 40 80 120 160 200

100

200

300

400

500

600

700T

emp

erat

ure

(°C

)

Time (s)

Water mistactivated

5 cm above the pool surface

10 cm above the pool surface15 cm above the pool surface20 cm above the pool surface25 cm above the pool surface30 cm above the pool surface35 cm above the pool surface

5 cm above the pool surface10 cm above the pool surface15 cm above the pool surface20 cm above the pool surface25 cm above the pool surface30 cm above the pool surface35 cm above the pool surface

Extinguishing time: 10 s

(a)

0 20 40 60 80 100 120 140 160

0

100

200

300

400

500

600

700

800

Tem

per

atu

re (

°C)

Time (s)

Water mistactivated


(b)

Figure 6. Temperature history of diesel fire before and after the application of watermist for tests in (a) Tibet and (b) Hefei (Distance: 2m, agent: pure water).




The results also show that the MC additive has different effects onfire suppression in different fuels and places. On using a 0.2% MCadditive, the diesel fire-extinguishing efficiency was greatly improvedboth in Tibet and Hefei. The extinguishing time reduced and theeffective fire suppression distance increased. But in a gasoline fire,

20 40 60 80 100 120 140

0

20

40

60

80

100

120C

O C

on

cen

trat

ion

(p

pm

)

Time (s)

Tibet (extinguishing time: 10 s)

Hefei (extinguishing time: 11 s)Diesel fire

Water mistactivated

Figure 7. CO concentration history in the test room before and after the applicationof water mist (distance: 2m, agent: pure water).

Table 2. Extinguishing time of the gasoline fire tests.

Case number Locality Fire suppression agent Distance (m) Extinguishing time (s)

11 Tibet Pure water 2 2012 Tibet Pure water 4 Failure13 Tibet 0.2% MC additive 2 2114 Tibet 0.2% MC additive 3 Failure15 Hefei Pure water 2 2516 Hefei Pure water 4 Failure17 Hefei 0.2% MC additive 2 1718 Hefei 0.2% MC additive 4 19

226 H. XIN ET AL.



0 20 40 60 80 100 120 140 160

0

100

200

300

400

500

600

700 5 cm above the pool surface




25 cm above the pool surface30 cm above the pool surface




Water mistactivated

Tem

per

atu

re (

°C)

Time (s)

(a)

(b) 5 cm above the pool surface








Water mistactivated

0

100

200

300

400

500

600

700

800

900

Tem

per

atu

re (

°C)

0 20 40 60 80 100 120 140

Time (s)Figure 8. Temperature history of gasoline fire before and after the applicationof water mist in tests at (a) Tibet and (b) Hefei (distance: 2m, agent: 0.2%MC additive).




the MC additive has almost no effect on fire suppression in Tibet,although the fire-extinguishing efficiency improved, the extinguishingtime reduced, and the effective fire suppression distance increasedin Hefei. These results can be attributed to by the composition of the

0

100

200

300

400

500

600

700Water mistactivated

Water mistactivated

0 20 40 60 80 100 120 140

0 20 40 60 80 100 120 140 160 180 200

Time (s)

Time (s)

Tem

per

atu

re (

°C)

0

100

200

300

400

500

600

700

800

900

Tem

per

atu

re (

°C)







(a)

(b)

Figure 9. Temperature history of gasoline fire before and after the application ofwater mist in tests at (a) Tibet and (b) Hefei (distance: 2m, agent: pure water).

228 H. XIN ET AL.



0 10 20 30 40 50 60 70 80 90 100

0

50

100

150

200

250

Tibet (extinguishing time: 20 s)Hefei (extinguishing time: 25 s)

Gasoline fire

CO

Co

nce

ntr

atio

n (

pp

m)

Time (s)

Water mistactivated

Figure 10. CO concentration history in the test room before and after the applicationof water mist (distance: 2m, agent: pure water).

0 10 20 30 40 50 60 70 80 90−20

0

20

40

60

80

100

120

140

160

180 Tibet (extinguishing time: 21 s)

Hefei (extinguishing time: 17 s)Gasoline fire

CO

Co

nce

ntr

atio

n (

pp

m)

Time (s)

Water mistactivated

Figure 11. CO concentration history in the test room before and after the applicationof water mist (distance: 2m, agent: 0.2% MC additive).




MC additive, which is made from mixing five different components. Thefirst component is a fluorocarbon surfactant, which forms a thin layer offilm on the liquid surface after being sprayed out from the nozzle. Thesecond component is a viscosity modifier, which improves the blanketing

0 100 200 300 400 500 600

0

50

100

150

200

250

300

350

Fu

el m

ass

(g)

Time (s)

Diesel fire (Tibet)

Diesel fire (Hefei)

Gasoline fire (Tibet)

Gasoline fire (Hefei)

Figure 12. Fuel mass loss of the diesel and gasoline fire without applicationof water mist.

Table 3. O2 minimum and CO2 maximum concentration measuredduring each test.

Test in Tibet Test in Hefei

Fuel

Fire

suppression

agent

Distance

(m)

O2 Minimum

concentration

(%)

CO2 Maximum

concentration

(%)

O2 Minimum

concentration

(%)

CO2 Maximum

concentration

(%)

Diesel Pure water 2 20.0 0.4 19.8 0.5

Diesel MC additive 4 20.5 0.2 20.4 0.4

Gasoline Pure water 2 19.8 0.5 19.8 0.9




Gasoline MC additive 2 19.9 0.4 20.0 0.7



230 H. XIN ET AL.



and runoff of water mist. The third component is an organic metalliccompound, which produces active radicals in the course of extinguishingthe fires. The fourth component is carbamide, which absorbs energyfrom flame and generates a great amount of inert gases by decomposi-tion. The fifth component is an N,N-dimethyl-formamide, which acts asan antifreeze and dissolves all the components. The combined influenceof these components improved the fire-extinguishing efficiency. Exceptfor these positive effects, the organic solution, organic metal compound,and decomposable material also have adverse effects on the water mistfire-extinguishing efficiency. The organic metal compound anddecomposable material not only increase the surface tension of thewater but also make it more difficult for the water mist to evaporateby increasing the boiling point [16]. Improved the fire-extinguishingefficiency is to be expected mainly because of the formation of the filmthat mitigates the radiative feedback from the fire to the burning fuelsurface and obstructs the evaporation of the fuel. The molecular weightof the diesel is large, and diesel is not so easy to vaporize. Therefore, onlya very thin layer of film can help extinguish the fire except when thefire is obstructed by the pan side, which is a little more difficult toextinguish. Gasoline vaporizes easily, and the ignition point is low, andso the effect of the film is not as good as that of a diesel fire. Thickerfilms are needed to prevent the evaporation of gasoline. In addition, theboiling point of the fuel is lower in Tibet than in Hefei and the gasoline iseasier to vaporize under high-altitude conditions. Therefore, the filmcover on the gasoline surface cannot prevent the fuel evaporationeffectively.

In addition, the fire temperature is lower in Tibet than in Hefei, so thedroplet is more difficult to vaporize and the effects of the organicmetallic compound and carbamide are difficult to present. However,on the other hand, the boiling point of the droplet is also lowerin Tibet, so the evaporation is relatively easier. We use the followingequations to compare the two effects. The changes in droplet diameterover time in the flame zone can be written as [21]

D20 �D2 ¼ � � t ð1Þ

where D0 and D are initial and instantaneous diameters of thedroplet, respectively, and � is the evaporation coefficient, which can bedescribed as

� ¼8 � k ��T

Hv � �ð2Þ




where k is the thermal conductivity of fire gas, �T is the temperaturedifference between the flame and the droplet, Hv is the evaporatingheat of the water, and � is the water density. Based on Equations (1) and(2), the droplet lifetime can be determined. For the pure water dropletwith 120 mmdiameter, its lifetime is about 60.8ms inHefei and 90.3ms inTibet, while the temperature of the gasoline fire is 800�C in Hefeiand 650�C in Tibet. Obviously, the droplet is more difficult to evaporatein Tibet.

As shown in Figures 10 and 11 and Table 3, the measured resultsof CO, CO2, and O2 concentration are also different between Tibet andHefei. These can be explained as, the combustion of unit mass fuelproduces more CO in Tibet due to the incomplete reaction underconditions of less oxygen. On the other hand, the fire size is larger andmore fuel is combusted in unit time at normal atmospheric pressure.Therefore, either in a diesel fire or a gasoline fire, the increasing rates ofCO concentration in the test room of two different locations were almostthe same before the application of water mist as shown in Figures 7, 10,and 11. After the water mist discharged, the flame structure wasdestroyed and the air became turbulent by the impulse of the water mist.Then the smoke that moved upwards formerly was blown around.It made the concentration of CO and CO2 at the measuring pointincrease promptly and the O2 concentration decrease, and withdischarging water mist, the water droplets vaporized in the flamezone. The vapor diluted the O2 concentration and the combustionreaction became more incomplete, which promoted the productionof CO. The phenomenon was more prominent under high-altitudeconditions. Therefore, the increasing rate of CO concentration is largerin Tibet after the application of water mist. For a gasoline fire, the ratein Tibet is about two times faster than in Hefei. The descent of thesmoke layer and the high CO concentration would make fire fightingmore dangerous, especially in Tibet. Table 3 shows that more CO2 wasproduced in Hefei when consuming the same quantity of O2, whichalso confirms that the combustion reaction is more complete at normalatmospheric pressure.

Tests on Ghee Fire

Ghee is a dairy product used in Tibet. It is a kind of white and strawyellow solid fat made from creamy milk, used for lighting lamps andas food. It is widely used in Buddhist temples, such as the PotalaPalace, and may very likely be a typical fire ignition source in Tibet.

232 H. XIN ET AL.



So, a set of experimental tests on ghee fire suppression with water mistwere performed in Tibet.

To the cases without MC additive, 250 g of ghee was placed in a roundstainless steel pan 200mm in diameter, and the pan was located200mm above the ground. Because the ignition point of ghee is veryhigh, a 400� 160� 80mm rectangular pan with 300 g of gasoline wasplaced under the round pan to heat the ghee. After the ignition ofgasoline, the ghee melted gradually with the rise of temperature. About320 s later, a small blue fire was observed above the ghee pool surface andthe ghee started to combust. When the gasoline was exhausted at 490 s,the water mist without MC additive was activated 3m away from the firesource, and the fire was extinguished within 12 s. Figure 13 shows thevariation of ghee flame temperature measured before and after theinjection of water mist in Tibet. At first, the temperature measuredby the thermocouples above the ghee pool surface was the temperature ofthe gasoline fire. After the ghee was ignited, the flame temperatureincreased, and with the decrease of the gasoline temperature due to itsbeing exhausted, the temperature above the ghee pool surface decreased.The temperature near the ghee pool surface decreased to about440�C, and then there were no changes until the water mistwas injected. It means that the boiling point of ghee is about 440�C.

0 200 400 600 800 1000

0

200

400

600

800

1000 10 cm above the gasoline pool surface

Near the ghee pool surface5 cm above the ghee pool surface15 cm above the ghee pool surface25 cm above the ghee pool surface30 cm above the ghee pool surface

Tem

per

atu

re (

°C)

Time (s)

Ghee was ignited

Water mistactivated

Figure 13. Temperature history of ghee fire before and after the application of watermist (distance: 3m, agent: pure water).




0 200 400 600 800 1000

0

50

100

150

200

250

300

In Tibet

CO

Co

nce

ntr

atio

n (

pp

m)

Water mist activated

(a)

Time (s)

20.5

20.0

19.5

19.0

18.5

18.0

21.0

21.5

In Tibet

O2

Co

nce

ntr

atio

n (

%)


(b)

0 200 400 600 800 1000

Time (s)

Figure 14. (a) CO, (b) O2, and (c) CO2 concentration histories in the test room beforeand after the application of water mist (distance: 3m, agent: pure water).

234 H. XIN ET AL.



Figure 14 gives the variation of gas (CO, O2, CO2) concentration beforeand after the application of water mist. The concentrations of CO andCO2 decreased and that of O2 increased with the diminishing gasolinefire, and after the water mist was discharged, the concentrations of COand CO2 increased and that of O2 decreased. The test on ghee firesuppression with MC additive was also performed in Tibet with anapparatus similar to that in a diesel fire and gasoline fire tests, and thefire was extinguished within 13 s when the water mist was injected 2maway from the fire source. It was more easily extinguished thana gasoline fire but was more difficult to extinguish than a diesel fire.

CONCLUSION

The fire-extinguishing efficiency of portable water mist fireprotection systems under high-altitude conditions was studied inTibet. The contrastive experiments at normal atmospheric pressureswere performed in Hefei. In order to improve the fire-extinguishingefficiency, a newly developed MC additive was used in the tests.The results show that the fire was easier to extinguish in Tibet withpure water owing to lower oxygen levels, and the MC additive did not

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.6

1.8

In TibetC

O2

Co

nce

ntr

atio

n (

%)


(c)

0 200 400 600 800 1000

Time (s)

Figure 14. Continued.




show an evident effect on suppression of a gasoline fire in Tibet. The testresults also showed that extinguishing a ghee fire was easier thana gasoline fire, but more difficult than a diesel fire.

At the lower layer of the test room, the concentration of CO and CO2

increased while that of O2 decreased quicker after the water mist wasactivated, and the rising rate of CO concentration was more evidentin Tibet owing to incomplete combustion. It should be noted thatthis situation may be more dangerous to people in densely populatedareas. Future work will be focused on: (1) detailed suppression tests onother typical combustible materials in Tibet, such as prayer flags,thangka, hada, and wood and (2) a selection of appropriate nozzles andadditives to improve the fire-extinguishing efficiency of the water mistsystem.

ACKNOWLEDGMENTS

The authors appreciate the support of the Natural Science Foundationof China (NSFC) (Grant No. 50536030) and the China NKBRSF project(No. 2001CB409600).

REFERENCES

1. Ndubizu, C.C., Ananth, R., Tatem, P.A., et al. (1998). On Water Mist FireSuppression Mechanisms in a Gaseous Diffusion Flame, Fire Safety Journal,31(3): 253–276.

2. Prasad, K., Li, C. and Kailasanath, K. (1998). Optimizing Water-mistInjection Characteristics for Suppression of Coflow Diffusion Flames, In:27th Symposium (Int.) on Combustion, pp. 2847–2855, The CombustionInstitute.

3. Mawhinney, J.R. (March 1993). Engineering Criteria for Water Mist FireSuppression Systems, NISTIR 5207, pp. 37–73.

4. Alpert, R.L. (1993). Incentive for Use of Misting Spray as a Fire SuppressionFlooding Agent, In: Proceedings of Water Mist Fire Suppression Workshop,pp. 31–36.

5. Jones, A. and Nolan, P.F. (1995). Discussions on the Use of Fine WaterSprays or Mists for Fire Suppression, Journal of Loss Prevention in theProcess Industries, 8(1): 17–22.

6. Mawhinney, J.R. (1996). The Role of Fire Dynamics in Design of Water MistFire Suppression Systems, In: Proc. the Seventh International Fire Scienceand Engineering Conference, pp. 415–424, Cambridge, England.

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BIOGRAPHIES

Xin Huang

Mr Huang was born in 1981. He is currently a PhD candidate, andreceived his Bachelor’s degree from the University of Science andTechnology of China (USTC) in 2002. His research interests aremodeling and experimental study on water mist fire suppression.

Xishi Wang

Dr Wang was born in 1969. He received his Bachelor’s degree in physicsfrom the North-West Normal University in 1994, his Master’s degreefrom the Anhui Inst. of Optics and Fine Mechanics of the ChineseAcademy of Science in 1997, and his Doctor degree from the Departmentof Mechanics & Mechanical Engineering of USTC in 2002. He worked inthe Tokyo University as a visiting scholar for three months at the end of2003, and then worked in the Hong Kong University of Science andTechnology as a post doctor for two years. He is currently associateProfessor of the State Key Lab of Fire Science. His research interests arefocused on optical diagnostics (such as DPIV, PDA and PLIF, etc.) fortwo/multi phase flows, dynamics and heat transfer of micro bubbles/droplets, and fire suppression technologies.

Xiang Jin

Mr Jin was born in 1982. He is currently a PhD candidate, and receivedhis Bachelor’s degree from the University of Science and Technology ofChina (USTC) in 2003. His research interests are experimental study ongas fire suppression technique.

Guangxuan Liao

Mr Liao was born in 1948. He is currently professor and executivedirector of the State Key Lab of Fire Science (SKLFS). His researchinterests include fire safety science and technology, simulation of fireprocess, fire suppression and extinction mechanisms by water mist anddiagnostics of combustion flows.

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Jun Qin

Mr Qin was born in 1953. He is currently senior engineer of the StateKey Lab of Fire Science (SKLFS). His research interest is focused ondiagnostic technique for spray field measurement.




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