flame propagation in a tent camp

*Correspondence to: Abdulghani A. Al-Farayedhi, Mechanical Engineering Department, King Fahd University ofPetroleum and Minerals, Dhahran 31261, Saudi Arabia.

�E-mail: [email protected]

Received 13 September 1999Copyright � 2001 John Wiley & Sons, Ltd. Accepted 25 October 1999

INTERNATIONAL JOURNAL OF ENERGY RESEARCHInt. J. Energy Res. 2001; 25:555}561 (DOI: 10.1002/er.636)

Flame propagation in a tent camp

Abdulghani A. Al-Farayedhi*��

Mechanical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

SUMMARY

This paper presents an experimental study leading to the understanding and modelling of the e!ect of airspeed and its direction on #ame propagation in tent fabrics in addition to "re propagation in a tent camp.The study was conducted on burning fabrics of di!erent densities subjected to wind speeds ranging betweenzero (stagnant) and 1.4 m s��. Moreover, several air directions with respect to the #ame were considered inthe study to cover the cases of vertically upward, downward, horizontally aiding and opposing, and inclineddirections. These cases were used in simulating actual #ame propagation in a tent. It is found that there isa logarithmic relation between the time of burning a tent and air speed and the density of tent fabrics. Twodi!erent types of fabric are considered; waterproof and non-waterproof. It is also observed that the surface#ame temperature is invariant with air speed or fabric density and it reaches about 6503C. The results showthat denser fabrics require more time for burning. The maximum #ame propagation speed is observed forvertically upward #ame concurrent with air direction. On the other hand, minimum #ame propagation isobserved for vertically downward #ames opposing the air direction. A model is derived for predicting thetime required for #ame propagation in a known camp area. Copyright � 2001 John Wiley & Sons, Ltd.

KEY WORDS: tent; #ame; "re; fabrics; camp

1. INTRODUCTION

Fire accidents in buildings, warehouses, forests or tent camps are considered among the mostcatastrophic events that hit societies because of the adverse consequences such as the loss of livesand destruction of properties. The "re spread is in#uenced by di!erent factors such as wind speed,distribution of buildings and their structure materials. The extent of "re damage is extremelyin#uenced by the location of the source of the "re. Fire can be initiated by di!erent means. It wasobserved statistically that 75 per cent of the #ames are caused by man because of neglecting theappropriate measures of safety (Kutbi, 1990). In Saudi Arabia, the incidence of "re accidents hasbeen steadily increasing as a result of the continuous development in industries and growth inpopulation. Approximately, the number of "re accidents doubles every decade. Annually, abouttwo million pilgrims use tent camps for two weeks. These tents are generally made of fabrics whichare vulnerable to catch "re accidentally which may lead to "re spread throughout the camp.

Table I. Density of fabrics.

Fabric number, i Density (�) kg m��

1 5922 374.63 3274 2855 264.66 624.57 309.38 506

The major reasons for increasing "re spreads include high population per square meter,increasing camp area, use of #ammable/in#ammable tent fabrics, use of electric appliances and thelack of compliance with the proper safety measures. The "re spread and its propagation in tentcamps are not the same as in concrete buildings. This is attributed to the horizontal distribution ofthe tents, and the fast propagation of "re due to the absence of obstacles or concrete walls.Moreover, the fabrics contribute to the "re as fuel. Furthermore, the wind speed and its directionhave a major role in the rate of "re spread in the camps. The ambient temperature has an importantrole in the number of incidents of "re per year. The number of incidents of "re in summer are morethan those in the winter season due to the increase in ambient temperature.

Many research projects have been conducted to have a comprehensive understanding of "repropagation and control. All factors involved in "re spread such as wind speed and direction andfabric density are considered. Williams (1976) explained various mechanisms of "re spread. Hecategorized and described theoretical aspects and di!erent models of "re spread such as heattransfer, #uid #ow and chemical rate kinetics. Fernandez-Pello (1979) pointed out that the #amespread in concurrent #ow is enhanced in the proximity of the hot gases to the combustible gasesfavouring the transfer of heat. Modelling #ame spread over fuel elements was carried out bya number of researchers: Frey and Tien (1979), Fernandez-Pello (1984), Backer (1976) and Wol!et al. (1991). A model of discrete fuel elements which was supported by experimental investigationwas developed by Wol! et al. (1991). They concluded that the rate of wind-assisted "re spreadthrough a fuel bed is predicted according to v

�&(;/m)�� where; is the wind speed and m is the

fuel bed mass per unit platform area. Hirano and Tazawa (1976) observed that the #ame spreadrate is primarily dependent on the surface temperature of the solid prior to the #ame arrival.Al-Farayedhi and Antar (1999) studied experimentally the burning rates of tent fabrics inconvective environment.

This study aims at predicting the time required for a "re spread in a speci"ed tent camp areabased on the experimental data obtained previously (Al-Farayedhi and Antar, 1999). Fabrics withdi!erent densities (265}625 kg m��) were used in this study as listed in Table I.

2. RESULTS AND DISCUSSION

2.1. Burning a single tent

Fire spread in tent fabrics is governed by a number of factors. The major dominating factors arethe wind speed and the direction of the #ame. The time needed to burn a complete tent can be

556 A. A. AL-FARAYEDHI

Copyright � 2001 John Wiley & Sons, Ltd. Int. J. Energy Res. 2001; 25:555}561

Figure 1. A typical tent.

predicted by knowing the time required to burn each individual side of the tent. The time forburning each side depends on the wind speed, its direction and the e!ect of buoyancy component.In addition, the point of "re initiation plays an important role in determining that time. In thisstudy, a square tent of 5�5 m, 2 m high with 453 inclined roof as shown in Figure 1 is consideredfor the analysis. The time required for burning a tent is predicted based upon the followingassumptions:

1. The e!ects of openings: windows and doors are neglected.2. The e!ects of internal supports are neglected.3. The tent is empty.4. The tent burns out in its location.5. The e!ect of radiation is neglected.

Five di!erent cases were considered based on the origin of "re as shown in Figure 2.Case 1 represents a tent catching "re at the bottom of a vertical wall while the wind is directed

horizontally onto it.Case 2 represents a burning tent catching "re from its top.Case 3 represents a burning tent catching "re from the rear wall which is protected from the

horizontal wind.Case 4 represents a burning tent catching "re from the top of the front wall facing the

horizontal wind.Case 5 represents a burning tent catching "re from the rear wall.The time required to burn a tent completely can be determined by summing up the times

required to burn the principal walls. For example, the time required to burn the tent in case 1 isfound to be 27 min for a fabric having a density of 506 kg m�� at a wind speed of 1.14 m s��. Thistime is determined from the time needed to burn the vertical wall (wall A in Figure 2) which is13 min in addition to 13.7 min required to burn completely wall B. Both walls A and B areconsidered the principal walls in this case since the other walls C and D are subjected to extremelyhot gases and the #ame emitted from walls A and B. The burning time for C and D is smallcompared to the time required to burn the whole tent. Therefore, the time required for burningthe whole tent is determined by the time (t

�#t

) required to burn walls A and B. A similar

procedure is carried out for di!erent speeds and fabric densities. In cases 2 and 5, the walls C and

FLAME PROPAGATION IN A TENT CAMP 557


Figure 2. Di!erent cases for "re initiation in the tent.

D are burned in stagnant air since they are protected from air current and not a!ected by thewind. In case 4, the principal walls are the side walls parallel to the wind current. The e!ect ofwind speed on the time required for burning the tent as a function of fabric density for case 1 isshown in Figure 3. This case represents the minimum time for burning a tent compared with other



Figure 3. E!ect of wind speed on the time of burning a tent as a function of fabric density (case 1).

Table II. Duration of burning a tent, min [v (m s��)].

Case i 1 2 3 4 5 6 7 8v

1 0.63 44 40.2 32 58.3 33 30.6 36.3 33.81 1.14 24.8 22.8 22.4 21.1 20.2 17 14.6 271 1.32 21.4 27.6 26 19 15.6 22.4 22.9 141 1.4 40.5 33 32.1 19.7 21.8 26.2 24.8 282 0.63 124 100 48.5 171 152 188 55.8 78.52 1.14 Extinguished 76.5 40 Extinguished Extinguished 112 28 433 All speeds 65 47 38 63 47.7 32 44.6 284 0.63 18.4 8.2 13.7 20.6 22 16.5 19.6 21.64 1.14 12.5 12.2 11.8 10.6 11 7.45 7.85 13.74 1.32 14.1 12.6 11.8 11 9.4 8.6 12.9 7.54 1.4 17 16.5 15.5 13.5 14.2 12.6 14.4 11.55 All speeds 30 23 19 28 23 15 22.6 14

cases since air direction favours the burning of the tent. It was found from Figure 3 that the time forburning a tent is related to the wind speed and fabric density according to the following relations.

a. For waterproof fabrics:

t/�"4.45 [log(v�#5.62)]!7.66 log(v�#5.62)#3.36 with R"0.984.

b. For non-waterproof fabrics:

t/�"5.29 [log(v�#6.25)]!9.54 log(v�#6.25)#4.35 with R"0.976.

The time required for burning a tent for di!erent densities and wind speeds for the "ve cases,respectively, are summarized in Table II. In case 2, for some conditions, the #ame was



Figure 4. Fire spread in a tent camp: case X: "re propagating in the same wind direction; case Y: "repropagating against the wind direction.

extinguished because of high speed of the wind and the direction of the #ame propagation withrespect to the wind. For speeds higher than 1.14 m s��, the #ame did not propagate and "nallyextinguished.

2.2. Burning a camp

The time required for burning a camp of a given area can be predicted as a function of the timerequired for burning a single tent. Figure 4 illustrates the distribution of a camp composed ofM rows �N columns of tents. Two cases were considered. In the "rst case, the camp is assumedto catch "re at tent (x) when the wind is in the same direction of "re propagation. The second caserepresents "re initiation at the tent (y) where the #ame propagates in the opposite direction ofwind direction. In this model, the tents are assumed to be 2 m apart which is a su$cient distanceto transfer "re from one tent to another as a result of the collapse of the walls of the burning tenton the adjacent unburning tents.

In order to determine the time required to burn all the tents (¹ ) in the camp, it is assumed thatthe "re will propagate from one tent to all the neighbouring tents in all directions after it iscompletely burned as shown in Figure 4. Therefore, ¹ can be predicted according to the followingrelation:

¹"t(M#0.5N!2)

For example, for the "rst case (case X), the time required to burn a camp consisting of "ve rowsand "ve columns of tents of fabric density 264.6 kg m�� is 62.4 min when the wind speed is1.32 m s��. The time required for burning a single tent (t"15.6 min) is obtained from Table II.On the other hand, for the same condition, the time required for burning the camp is 191 minfor the second case (case Y). It is worth mentioning that the percentage error in the results is$15 per cent as determined from the experimental analysis.

3. CONCLUSION

This study presents an experimental analysis leading to the understanding and modelling of theburning of a tent and "re propagation in a camp as a function of air speed, its direction and fabricdensity. Two di!erent types of fabric are considered, waterproof and non-waterproof. A logarith-mic relation between the time for burning a tent and the air speed as a function of the fabric



density is obtained for waterproof and non-waterproof fabrics. More time is required to burncompletely a waterproof tent fabric as compared with a non-waterproof tent fabric. The timerequired to burn a typical tent (5�5�2 m) ranges between 12 and 188 min depending upon thewind speed, the point of "re initiation and the fabric density. As the wind speed increases, the timefor burning a tent decreases and reaches a minimum value at about 1.2 m s��, then it starts toincrease. Fire propagation in a tent camp reaches a maximum value when the wind is in the samedirection of the "re spread and the minimum value occurs when the wind is in the oppositedirection of the "re spread. Generally, the burning time is proportional to the density of thefabrics. The time required to burn a tent camp of M rows in the direction of the wind andN columns normal to the direction of the wind is given by this relation: ¹"t(M#0.5N!2)where t is the time required to burn a single tent.

ACKNOWLEDGEMENT

The support of King Fahd University of Petroleum and Minerals to carry out this work is gratefullyacknowledged.

NOMENCLATURE

M "number of tent rows in the direction of the windN "number of tent rows normal to the direction of the windR "correlation coe$cientt "time required for burning a tent, min¹ "total time required for burning a camp of a given area, minv "air speed, m s��

Greek letters

� "tent fabric density, kg m��

REFERENCES

Al-Farayedhi AA, Antar MA. 1999. Burning rates of tent's fabric in a convective environment. Proceedings of the FifthSaudi Engineering Conference, Umm Al-Qura University, 1}4 March, 493}503.

Backer S. 1976. ¹extile Fabric Flammability. The MIT Press: Cambridge, MA.Fernandez Pello AC. 1979. Flame spread in forward forced #ow. Combustion and Flame 36:63}78.Fernandez Pello AC. 1984. Flame spread modelling. Combustion Science and ¹echnology 39:110}134.Frey AE, Tien JS. 1979. A theory of #ame spread over a solid fuel including "nite rate kinetics. Combustion and Flame

36:263}289.Hirano T, Tazawa K. 1976. E!ect of thickness on downward #ame spread over paper. Bulletin of Japanese Association ofFire Science and Engineering 26:191.

Kutbi Z. 1990. Civil defence services in Makkah city*an applied study in site theory. Civil Defense Report (in Arabic).Williams FA. 1976. Mechanisms of "re spread. Proceedings of the 16th Symposium on Combustion, The Combustion

Institute, 1281}1294.Wol!MF, Carrier GF, Fendell FE. 1991. Wind aided "respread across arrays of discrete fuel elements. II. Experiment.Combustion Science and ¹echnology 77:261}289.



flame propagation in a tent camp

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