火灾科学
第1 1 卷第3 期V ol . 1 1 , N o . 3 2 0 0 2 年7 月FIRE SAFETY SCIENCE J u l . 2 0 0 2 文章编号:100425309 (2002) 0320125207
Study of Prevention of Forest Fire
by H el i copters
Prop agation
———E ffect of W ater Applied to F allen Leaves to Protect
from I gnition by Fire brands
K ohyu S atoh1 , Chuji . K onishi2 , Liu Naian3
(1 . N ational Rearch I nstitute of Fire and Disaster , Ja pan ; 2 . Ohita N ational C ollege of Technology , Ja pan)
(3 . University of Science and Technology of China , SK LFS , China)
Abstract : E very year m any forest fires have occurred in the w orld. H owever , fire protecti on m easures of fires are not sufficient yet , although forest fires cau heavy dam2 ages to the preci ous natural environment . A large green area in m ountains often disappears due to the spread of fires under such ri ous weather conditi ons as strong dried winds. There have been m any cas taking l ong hours to repress large2scale forest fires , although helicopters and aircrafts of fire departments are often ud. Firebrands can easily jum p over valleys in the ridges from leeward ridges of forests and are widely scattered by the strong winds. Therefore , it is very im portant to ex amine m ethods to prevent the rapid fire propagati on due to the spread of firebrands. G enerally , fires at the early stage just when a firebrand ignites at a new spot are still com paratively weak and sm all in siz e . Therefore , it m ay be possible to attack the fires in a still early stage , by applying water from he2 licopters and aircrafts. The objective of this study is fo2 cud on the m ethod to apply water in the leeward area where firebrands reach , using helicopters and aircrafts and ex amined are the effective m ethods to prevent the fire spread due to firebrands from a ridge to a leeward ridge , by laboratory ex periments and com puter sim ulati on.
K ey w or d s : forest fire ; water ; helicopter 1 .I ntroduct ion
In the w orld , many forest fires have occurred year by year . F or exam ple , approxim ately 3000 , 7
000 and 90000 forest fires are counted every year in J apan , in C hina and in US A , respectively. H owever , fire protecti on m easures are not sufficient yet , although forest fires cau the heavy dam ages to the preci ous natural environm ent . A large green area in forests often disappears due to the rapid spread of fires under such ri ous weather conditi ons as the strong dried wind.
路由器怎么设置wifi密码There have been m any cas taking l ong hours to re2 press large2scale forest fires , although helicopters and air2 crafts of fire departm ents are ud. H owever , fire depart2 m ent helicopters generally attack the burning area directly in the forests , but the water to drop is usually too limited and firebrands can easily jum p over valleys in the ridges from the ridges of forests and are widely scattered by the strong winds. Therefore , it is very im portant to ex amine m ethods to prevent the rapid fire propagati on due to the spread of firebrands in forests.
Fires at the early stage just when a firebrand ignites at a new spot on the fuel in forests are still com paratively weak and sm all in siz e . Naturally , it needs too m uch wa2
收稿日期:2002205230 ；修改日期:2002207201
作者简介: K ohyu S atoh ，日本国立消防研究所研究员。
火灾科学FIRE S A FE TY SCIE NCE 第11 卷第3 期126
ter to repress large grown2up fires. Therefore , it m ay be possible to attack the fires still in early stages , by apply2 ing water from helicopters and aircrafts. The objective of this study is focud on the effective m ethod to apply wa2 ter in advance in the leeward area where firebrands reach due to winds , using helicopters and aircrafts. Many stud2 ies on forest fires1 ～4 already exist , but esntially no studies on the fire repress by applying water in advance in the leeward area by helicopters and aircrafts are ex istent . In this study , we ex amined the effective m ethods t o pre2 vent the fire spread due to firebrands from a ridge to a leeward ridge , by ex periments and com puter sim ulati ons.
(3) Altitude of a helicopter is 30 to 50 m and then the height of bucket outlet is 20 to 40 m
(4) Flying speed of a helicopter is 10 to 20 m/ s.
Then the oval form area of dropped water on the ground is from 400 to 600 m2 . Thus , the corresponding water density dropped on the ground is from 0 . 5 to 1 . 5 litters per square m eters , respectively. T able 1 shows the water density range dropped from sm aller helicopters and larger helicopters , where the product of the water sprayed area and the water density is not al ways the total am ount of water dropped , since the water density is not distribut2 ed uni formly and nearly hal f of the dropped water changed into m ist and disappears in the air .
T a b. 1 Water d ensity f o r the smaller helicopters
and larg er helicopters
工地顺口溜大全2 E xperim ents
2. 1 E stim ation of w ater d ensity dropp e d from a
S maller helicopters Larg er helicopters f i re2f i ghting helicopter
G enerally the am ount of water to drop is too limited , com pared with the vi olently growing forest fires. The vol2 um e of water bucket ud for sm aller fire2fighting heli2 copters and larger helicopters is either about 1 ton or 5 tons , respectively. As generally well known , the water density sprayed on the ground from a helicopter depends on the flight speed and the altitude of flying helicopter . The water density on the ground has been estim ated , us2 ing the video pictures of dropping water relead from a helicopter in the air .
F or the estim ati on of effectiveness of fire repress , one of the author has ex amined the conditi ons of water dropped from larger helicopters are given5 as , relating to fires of w ooden hous ,
(1) V olume of water dropped is 5 . 6 tons
(2) Wind speed is 1 to 6 m/ s
毕竟英语(3) Altitude of a helicopter is 40 to 60 m and then the height of bucket outlet is 20 to 40 m
(4) Flying speed of a helicopter is 10 to 20 m/ s.
Then the oval form area of water sprayed on the ground is from 700 to 1300 m2 . Thus , the corresponding water density dropped on the ground is from 4 to 8 litters per square m eters , respectively.
Water dro pped ( k g)
Main sprayed area
(m2 ) w here the w a2
ter d ensity is m ore
than 0. 5 litter/ m2
Water d ensity (liter/
m2 ) in main sprayed
area
1200 5600
400 to 600 700 to 1300
0. 5 to 1. 5 4 to 8
2. 2 E xp erim ents to p revent f i re ignition due to f i re2 bran ds
C orresponding to the presum ed conditi ons that fire2 brands fly over the valleys , reaching leeward m ountains from windward m ountains , the foll owing ex perim ental t2 up is m ade in a laboratory with a wind fan , as shown in Figure 1 .
(1) The ex perim ents were m ade on the testing bench (width 5 . 4 m , length 7 . 2m and height 1 . 3m) placed in发烧了怎么快速退烧
a large2scale wind laboratory.
(2) The area of fuel leaves was 2 . 4 square m eters of either W = 2 . 2 m by L = 1 . 1 m or W = 2 . 4 m by L = 1 .
0 m , naturally m ounted in the height of 0 . 3 m , where the dim ensi ons of L and W of leaves are defined as in Figure 1 .
(3) The distance (D) between both leaves was ei2 ther 2 . 1 m or 2 . 4 m.保安英文
(4) The fuel was the fallen leaves of J apane oak , dried for m ore than 1 year in a laboratory of 20 m x 20 m x 20 m in height .E ach oval leaf dim ensi ons were roughly
Sim ilarly , the conditi ons of water dropped
sm aller helicopters are given as ,
(1) V olume of water dropped is 1 . 2 tons
(2) Wind speed is 0 to 3 m/ s
from
V ol . 11 N o . 3
127
9 cm l ong and 3 cm wide . The m oisture content of the leaves was m easured by a m oisture m eter of was about 10 to 13 % in weight . The ignition of the windward leaves
was started , using a little am ount (50 ml ) of n 2heptane to initially ignite . Figure 2 shows the burning leaves of windward leaves for C a 1 .
am ount of fuel and weak fire , is ranging from 3 . 5 to 8 . 5 kg and from 7 . 9 to 11 . 5 kg , respectively. The C L AS S B , middle am ount of fuel and middle strong fire , is rang 2 ing from 11 . 5 to 15 . 0 kg and from 14 . 2 to 15 . 0 kg , re 2 spectively. The C LASS C , much am ount of fuel and strong fire , is 25 . 0 kg and 15 . 0 kg , respectively.
(A ) Without water applicati on to the leeward leaves In the ex perim ents of 5 cas where no water was ap 2 plied in advance to the leeward leaves and firebrands were flying toward the leeward , there was only one ca ( C as 1) where the leeward leaves did not burn by the fire 2 brands. In the other 4 cas the leeward leaves burnt within the tim e ranging from 183 to 897 conds due t o the firebrands.
(B ) Water applied to the leeward leaves in advance and during fires.
F ig. 1 E xperimental tup in a la b oratory with a w ind fan
F ig. 3 T he f i re sprea d to lee w ard lea v es
due to f i rebrands in C a 5
F ig. 2 B urning lea v es of w indw ard lea v es
f o r Ca 1 ( N o f i re sprea d )
(5) The wind speed (U o ) due to a large 2scale wind
fan , with a diam eter of 4 m , is t at 3 m / s at the igni 2 ti on of the windward leaves and at 1 minute later from the igniti on the wind speed was incread at 4 m / s.
( 6 ) T otally 14 cas of ex periments were m ade , varying the water am ount applied on the lee
ward leaves in advance and the am ount of windward leaves and leeward leaves. T w o ways of water applicati on were em pl oyed , (a ) all for once and ( b ) parated in three times. Details are shown in T able 2 . 2. 3 E xp erim ental R esults
Ex perim ental results of fire spread from the windward leaves to the leeward leaves due to firebrands are shown in T able 2 . The com binati on of the upwind fuel and the downwind fuel to ex amine the fire propagati on due to the di fference of fire strengths is classi fied into three class to ex amine the effect of fire strength. The C LASS A , few
F ig. 4 F ire sprea d from w indw ard lea v es to lee w ard lea v es with a p p lied w ater in Ca 7
The water applicati on toward the downwind fuel was very effective to prevent the fire spread to the leeward leaves due to firebrands. Within totally 9 cas of water applied , 4 cas showed that the fire did not spread in the downwind within 1200 conds. In the other 5 cas , the fire spreads t o the leeward leaves due to the firebrands , but the igniti on tim es of the fire spread at the leeward
火灾科学 FIRE S A FE TY SCIE NCE 第 11 卷第 3 期
128
leaves where the water was applied were m uch l onger , com pared with tho cas without water applicati on , ranging from 311 to 957 conds. When the water density
applied to the leeward leaves are too few , the surface of the leeward leaves could dry due to the heated air from the windward and easily ignite due to the firebrands.
Figure 3 shows the fire spread t o leeward leaves due to firebrands in C a 5 and also Figure 4 shows the in 2 frared picture of fire spread to leeward leaves due to fire 2 brands in C a 7 .
T a b . 2 Conditio ns o f experiments Distance
Weig ht of dry leaves
T otal w ater applied
Sustaining time自行车用英语怎么说>如何去角质
C LASS A (Weak fire )
C a 1 (A )
6. 8 kg (B )
7. 9 kg 2. 4 m
None m ore than 1200 s
C a 2 2. 4 m 8. 5 kg 11. 7 kg None 307 s C a 3
C a 4
C a 5
2. 1 m
2. 1 m
2. 4 m
3. 5 kg
7. 9 kg
6. 8 kg
10. 5 kg
10. 5 kg
7. 9 kg
None
1. 0 liter x 1
2. 5 liter x 3
183 s
897 s
m ore than 1200 s
C LASS B (Midd le fire )
C a 6 2. 4 m 15. 0 kg 15. 0 kg None 426 s C a 7
2. 1 m 11. 5 kg 14. 2 kg 5. 0 liter x 1 663 s C a 8
C LASS C ( S trong fire )
2. 1 m
15. 0 kg
15. 0 kg
1. 5 liter x 3
m ore than 1200 s
C a 9 2. 4 m 25. 0 kg 15. 0 kg none 311 s C a 10 2. 4 m 25. 0 kg 15. 0 kg 0. 5 liter x 3 407 s C a 11 2. 4 m 25. 0 kg 15. 0 kg 0. 8 liter x 3 775 s C a 12 2. 4 m 25. 0 kg 15. 0 kg 1. 3 liter x 3 957 s C a 13
2. 4 m 25. 0 kg 15. 0 kg 2. 0 liter x 3 m ore than 1200 s C a 14
2. 4 m
25. 0 kg
15. 0 kg
生日祝福的话语2. 8 liter x 3
m ore than 1200 s
F ig. 5 R elationship b et w een a p p lied w ater d ensities and ig nition time due to f i rebrands
Although the fire siz e in the ex perim ents varied ship between the tim e of fire spread and the water density applied to the leeward leaves in advance . When the water is applied at the density of m ore than 3 litters per m 2
to the leeward leaves , the fire spread was prevented until the
widely as shown in Table 2 , the igniti on tim e was pl otted in one figure changing the sym bols for each class to show the water applicati on effect . Figure 5 shows the relati on 2
V ol . 11 N o . 3
129
burn out of the windward leaves , nam ely 20 minutes. Much effective applicati on of water is not t o drop once , but to drop parating in three times. Naturally , the water
drop from sm aller helicopters was less effective , but could delay the fire 2spread tim e , effectively. The water densi 2 ties well correspond to tho of water , about 4 litters per m 2 , dropped from the larger helicopters shown in T able 1 , where the fuel density was m uch larger than tho in forest fires.
analyz ed to com pare with the com puter sim ulati on on the water applicati on to prevent the fire spread to leeward m ountains , using helicopters. Figure 6 shows the vel ocity vectors of water drop from a sm aller fire 2fighting heli 2 copter . The software to analyz e the video pictures was a comm ercial one , nam ed FLOW 2VEC 32 bad on a pat 2 tern tracking analysis. The conditi on of water drop is
(1) Bucket height is 15 m (2) Am ount of water is 0 . 6 tons. (3) Wind speed is 5 m / s.
(4) Flight speed of helicopter is 10 m / s.
In the video pictures , particularly focud behavi or of the dropping water in the air is the water splitting into the teeth of a saw from a larger bl ock.
3 Simulat ion
3. 1 Analysis of vid eo pictures of w ater drop from
helicop ters
Video pictures of water drop from helicopters were
F ig. 6 Analy zed v elocity v ectors o f w ater drop from a smaller f i re 2f i ghting helicopter
F ig. 7 Numerical simulations of w ater dropped from a smaller helicopter
3. 2 Computer simulation of w ater d rop from a heli 2 copter
It qualitatively coped with the m odel ex periment and a 32D num erical sim ulati on on the preventi on of the fire spread due to the water applicati on. The calculated condi 2 ti ons em pl oyed correspond to the ones for the ca of video analysis m enti oned above . The num ber of grids was 128 (flight directi on ) x 64 x 64 . Instead of flight speed , the wind directing to the body of the helicopter was given as
10 m / s and also the downward wind from the blades of the helicopter was gives as 10 m / s.
rotating A dropped water range spreads very widely as shown in Figure 7 when it is com pared with a result of an analy 2 sis of the video im age of the ex perim ents. The num erical m odel is considerably di fferent from the ex perim ental schem e. One particular difference between both the re 2 sults of num erical simulati ons and video analysis is the scattering behavi or of the dropping water in the air . This
