外文翻译油罐火灾中的泡沫使用效率

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1、油罐火灾中的泡沫使用效率 D. 海德 , A. .罗德里格斯, D. 斯密斯摘要：在用于储存易燃液体的浮顶罐上，防火用的移动式泡沫灭火器有替代固定式灭火器的趋势，而且这一趋势正在增强。作者研究了使用泡沫方式对泡沫效率的影响，同时比较了：两种普通蛋白泡沫、普通轻水泡沫和大家熟知的F.P. 70.氟蛋白泡沫的使用效率。流散火灾对蛋白泡沫的灭火性能的影响已经在多篇论文中论述解释了。所有的情况都是：泡沫平缓地被施放到燃烧物的表面。Tuve 和 Peterson在他们自己写的论文中很方便的得出一些结论，他们总结出了一下几点结论： 泡沫的膨胀性和密度可以承受一定的效率变化，只要它超过最小临界值。 泡沫的黏

2、度和它的水吸出率是密切相关的。 在泡沫的应用中，需要0.02美制加仑每平方英尺的泡沫含水量用以平衡后大火中产生的热量。 协同救火研究组织从French等人所著的论文中也总结出了相似的结论。 所有的这些工作是从模拟将泡沫易平缓的方式通过分布在油罐顶部的喷头施放到燃烧的油料表面这一应用中得出的。关键词：油罐；火灾；泡沫；研究影响 现代储存技术的影响 近十年，用于储存A类易燃液体的油罐正朝着没有固定式泡沫灭火器的大直径浮顶罐的趋势发展。固定泡沫灭火器的使用经验表明，在严重的大火中灭火器是极易损坏的，同时，现在又有这样一个趋向，既趋向于使用大容量的泡沫灭火器来保护油罐。它们有能力投送超过600美制加仑

3、的泡沫与水的混合物。 从灭火器或其它移动灭火设备中产生的泡沫显然不能缓和地被施放到储罐中的的燃料表面，尽管还没有获取到定量的信息以致使我们还不理解为什么在这种条件下灭火效率会被削弱。实验室测试一个火域面积只有0.78平方英尺的小型实验室测试被建立，测试中，泡沫由实验室的泡沫产生器产生，并被直接喷射到燃烧着的90号汽油表面。调整喷射孔以便产生一个8.2米/秒流速的恒定流量，这与正常的设备可获得的流量是相似的。泡沫以不同的速率试验，临界应用率将从一张把要求的灭火时间与泡沫液的使用率进行对照的图中得到（图一）。 我们发现临界应用率会受到燃料温度的巨大影响，为了测试这一点，测试是在超过了所允许的15分

4、钟预烧后实施的。图2中显示燃料的温度曲线在不同的预烧时间下是不同的。试验使用了4%的泡沫溶液，这种泡沫溶液由两种可获得的已商业化的水解蛋白和一种最新发展的F.P. 70氟蛋白组成。表一给出了泡沫的性能数据。在图3中绘制了三种泡沫的临界应用率与预烧时间的对照情况，通过对照下面这些观点是显而易见的：三种泡沫的临界应用率都是随预烧时间的增加而增加的。 即使是在短的预烧时间下，以直接喷射到燃料表面的方式使用的蛋白A泡沫和蛋白B泡沫的临界应用率也比以缓和方式释放到燃料表面时得到的临界应用率高。 F.P. 70氟蛋白泡沫比水解蛋白泡沫表现更优越。燃料温度测量 由于使用的是小尺寸的容器，在实验室获得的温度曲

5、线不被认为是与在大型容器中获得的曲线非常接近的。这使得人们决定进行户外的更大型的火灾，并在没有进行泡沫测试前测量它温度曲线图。 一份由Burgoyne 和 Katan编写的论文提供了有用的信息，这信息就是一个装有低标号汽油的22英尺直径的油罐的表面温度曲线。结果显示，一个大约90摄氏度（194华氏度）的热油层或说“热区”会在燃烧的油品下面形成。蒸馏试验表明，在该温度下会蒸馏出19%的燃料。热区以每小时24到36英寸的速率形成，并且在热区和冷油之间存在剧烈地温度变化。TABLE 1.测试中使用的泡沫的属性- 临界剪切应力 析出25%水份的时间 泡沫类型 膨胀系数 (dynes/cm2) (分)

6、-水解蛋白A 8 250 3-5 水解蛋白B 8 370 2-5 F.P.70氟蛋白 8 250 2-4 - 在22英寸直径的罐中第一次使用常规90号汽油进行了测试。绝热石棉是用来减少火焰的热量通过罐壁传递的。同时在最小干扰的前提下一个固定流量的设备被允许使用，从而使燃烧的燃料上保持一个恒定的空距。大火持续了30分钟，在液面以下每隔1英寸检测燃料的温度。也对直径4.8英尺的罐进行了试验，但因为这个原因，在燃烧过程中燃料的液面没有被保持在不变的位置。在大型罐中，当罐壁对传热的影响不那么明显时，绝热材料就不再使用。在两组罐中的实验结果在表4中以图表的形式显示。小罐中 70摄氏度（158华氏度）的热

7、区和大罐中80摄氏度（176华氏度）的热区都被记录了下来。实验中使用了两个不同批次的燃料，蒸馏实验显示了热区在每种情况下所对应的20%的蒸馏温度。这些很好的应证了Burgoyne 和 Katan所获得的结果。在两个罐之间存在一些可以忽略不记的差别，这结果还说明，一个12英寸深的热区在燃烧30分钟后以1/2英寸/分钟的最终速率形成。18平方英尺火灾的测试设计这一系列的测试是为了大规模的考证在很深的燃料大火中强力使用泡沫的影响，测试是在下列情况下进行的： 短预烧时间（2分钟）并且在燃料低温的情况下； 长预烧时间（30分钟）并且燃料温度处于70到80摄氏度的情况下。在这些测试中，泡沫具有表1所示范围

8、的理化特性，测试时这些泡沫被直接喷射到含有150加仑（18英深）90号汽油的直径18平方英尺的有关火灾中。临界应用率从表2中得出并被显示出来。TABLE 2. 18平方英尺火灾中的临界应用率- 临界应用率 (gpm/ft2) -泡沫种类 2分钟的预烧时间 30分钟的预烧时间-水解蛋白A 0.07 0.17水解蛋白B 0.07 0.17F.P.70氟蛋白 0.03 0.06-人们将看到,观测到的实验数据表明了一个相似的趋势,就像从长时间预烧中获得的临界速率的显著增加一样。然而。这个从实验室火灾中获得的值，说明了规模效应的重要性。再者，A类和B类之间的显著差异在大型火灾测试中基本消失了。据说这种规

9、模效应部分原因是油罐壁影响了泡沫流的路径从而影响了泡沫层的形成。在实验室小直径的火盘中，泡沫流迅速顺着容器壁扩散并在其上面形成一个泡沫层，并且构成一个明显深度。在大型火灾中，形成一个泡沫层非常的不容易，即便是当泡沫覆盖在了燃料的表面时也很难构建起一个不透气的泡沫层。这种应用方式的迹象显示，自从油罐实际保护的问题受到关注后，规模效应的现象变得重要了。因此在更大的火灾面积中（400平方英尺）进行了一小部分的测试，以进一步关注并检验规模效应。 400英尺火灾面积的测试因为会导致测试区的烟雾污染问题,所以不可能开展大型火灾长时间预烧的测试。实验中,因此,限制在应用泡沫从一个标准的泡沫产生器喷嘴喷到40

10、0加仑常规汽油产生的400平方英尺火灾中去(大约2英寸深)。在试验中的预烧时间是2分钟。喷嘴提供了一个不断排放40美制加仑/分钟密度0.10美制加仑/平方英尺的泡沫,泡沫尽量直接喷向测试火中心。所得结果见表3。表3. 18平方英寸测试火的测试结果泡沫类型和性质防火性能水解蛋白A 膨胀，7；临界剪应力，180dynes/cm2；失25%水时间，2分30秒。水解蛋白B 膨胀，7.3；临界剪应力，340 dynes/cm2；失25%水时间，3分20秒。不控制火灾。使用泡沫4-6分钟后，一些火焰强度降低了。没有进一步减少。泡沫使用的12分钟后停止。停用后2分钟内火焰重新达到全亮度。F.P. 70氟蛋白

11、 膨胀，7；临界剪应力，90 dynes/cm2；失25%水时间，2分25秒。火势在45秒内得到控制。泡沫在使用1分15秒后停止使用。1分30秒后火被扑灭。从实验室的实验的结果和18平方英尺火灾来看，可以预见的一点是：在测试条件下，使用两个流量为0.10gpm/平方英尺的喷嘴，400平方英尺的火灾是容易控制的。其中的一个不同点是，400平方英尺面积的测试火灾只有2英寸。燃料深度常用来与火势更小但油层更深的火灾的做比较。它可以是被认为可以解释实验室小型测试火与18平方英寸测试火结果的不同点的规模效应的延伸。轻水美国海军研究实验室调查了新的发泡剂促进了轻水复合泡沫的发展。有许多报告是关于它在飞机坠

12、毁引起的浅层油品火灾中的应用表现的。不过没有关于深层油品火灾的测试结果报告。因此，在测试程序中进行了一项测试：在一个经过了30分钟预烧的18平方英尺的测试大火中使用F.P. 70氟蛋白，以一个接近临界流量的流量进行。结果在表4中与在测试程序中的另一项测试发泡剂的结果一起给出。表4.18平方一尺17英寸深的常规90号汽油预烧时间30分钟的实验结果（泡沫以0.07gpm/平方英尺的速率直接喷射到着火区域的中心位置）。泡沫灭火剂防火性能轻水泡沫，6%的F.P.70氟蛋白，6%的水解蛋白A6%的水解蛋白B1分钟后90%得到控制，5分钟后火灾熄灭2分钟后90%得到控制，5分钟后火灾熄灭使用泡沫15分钟后

13、火势仍没有得到控制使用泡沫15分钟后火势仍没有得到控制*虽然轻水泡沫比F.P. 70泡沫能更迅速的控制火灾，但在这两种情况下，时间长的灭火时间都是由于火焰持续性的靠近高温罐壁。结 论从这篇论文的描述中我们可以得到一下结论： 与缓和地将常规泡沫覆盖到A类易燃油品表面相比，用泡沫强行灭火的效率极大的降低的。 在汽油罐发生大火的过程中，可能形成一个70C到80 C的高温油层区。这情况下普通的蛋白基泡沫的效率是比较低的，除非能缓和的将泡沫覆盖到油品表面，同时如果按目前建议的泡沫量（0.1gpm/平方英尺）使用，将不会对火灾起到任何作用。 400平方英尺试验结果表明，即使在短时间的预烧下，泡沫的使用形式

14、和较高值的临界应用率都存在规模效应。此外，还需要进行在该规模和更大规模下的更深层次油品在长时间预烧的试验。 用F.P.70氟蛋白和轻水制造的泡沫，适合于目前建议的低速率、快速熄灭试验火甚至深层次的高温油层区已经形成的条件下。参考文献1 Tuve，RL和彼得森.一些机械泡沫灭火的研究，他们对石油火灾.3725报告.1950年8月23日，美国海军研究实验室2法国，RJ，欣克利，特等.的泡沫表面用汽油火灾应用.火灾研究注意第21号，1952年，Scientiiic和工业研究和消防局的联合研究组织消防处。3弗莱，樱和法语的RJ.使用的机械泡沫发生器.应用化学研究所硕士论文. 1（1951）.425-4

15、29页 4伯戈因，JH和咯痰.火灾在石油产品开放坦克：一些基本方面.石油学院学报. 33（1947），第158页5 Tuve，RL等.一种新型气体和易燃液体火灾安全灭火剂.6057报告.1964年3月13日.美国海军研究实验室.6 Tuve，RL等. 全尺寸火灾模拟试验研究评价者和蛋白型泡沫.6573报告.1967年8月15日.美国海军研究.7 Fittes，DW和纳什.光水.第170-171.Foam - - - Its Efficiency In Tank Fires D. H I R D , A. RODRIGUEZ, and D. S M I T H Abstract： The inc

16、reasing use of floating roof tanks for the storage of flammable liquids has given rise to a tendency toward using foam monitors for fire protection instead of fixed applicators.The authors studied the effect of application methods on foam efficiency and compared the effectiveness of two protein-base

17、d foams, Light Water, and a fluoroprotein foam known as F.P. 70. The effect of foam properties on the fire fighting ability of protein foam on bulk fuel storage fires has been examined in a number of reports. In all cases, foam was applied gently onto the fuel surface. The results obtained are conve

18、niently summarized in a report by Tuve and Peterson. 1 They concluded the following: That the expansion or density of a foam has little bearing on its efficiency as long as it exceeds a critical minimum value; That foam viscosity and its rate of water precipitation are closely related; and That a su

19、rface application density of 0.02 gpm/ft2. of water-in-foam is needed to equilibrate the heat produced by the test fire. Simila results were obtained by the Joint Fire Research Organization and are summarized in a paper by French et al.2 All this work, carried out by applying foam gently to the surf

20、ace of the burning fuel, simulated the type of application obtained with the fixed, top applicators prevalent at the time. Keywords：tanks；fire；foam ；studied the effectEFFECT OF MODERN STORAGE METHODS Recent trends in the storage of Class A flammable liquids have been towards much larger diameter flo

21、ating roof tanks without provision for fixed, foam application. Experience shows that fixed foam applicators are *Imperial gallons are used throughout this paper . A British Institute of Petroleum classification for flammable liquids having closed cup flash points below 73 F (22.8 C), which is compa

22、rable to Class IA and Class IB materials as defined in the Flammable Liquids Code (NFPA No. 30). highly vulnerable to damage in the event of a serious outbreak of fire, and there is now a tendency towards the use of high-capacity foam monitors for the protection of storage tanks. These are capable o

23、f delivering more than 600 gpm of water-in-foam. Foam produced from monitors or from other types of mobile equipment obviously cannot be applied gently to the fuel surface in a storage tank, and although there has been an understanding that there would be some loss in efficiency under these conditio

24、ns, no quantitative information is available .The work described in this paper was undertaken in an attempt to provide such quantitative information . LABORATORY TESTS A small-scale laboratory test having a fire area of 0.78 ft2 was set up in which foam produced in a laboratory foam generator3 was a

25、pplied as a straight stream onto burning 90 octane gasoline. The size of the orifice was adjusted with changes in application rate to give a constant stream velocity of 8.2 m/sec ,which is similar to that obtained with conventional equipment. Foam was applied at a series of rates, and critical appli

26、cation rates were determined by plotting the time required for extinguishment against the rate of application of foam liquid (Figure i). It was found that the critical application rates were greatly affected by changes in the temperature of the fuel, and to examine this, tests were performed in whic

27、h pre burn times of up to 15 min were allowed, The temperature profile in the fuel at different preburn times is shown in Figure 2. The tests were made using 4 per cent solutions of two commercially available hydrolyzed protein foams and a recently developed fluoroprotein foam (F.P. 70). Table 1 giv

28、es the foam properties obtained . In Figure 3, the critical application rates for the three foams are plotted against fire preburn times, and several observations are evident . The critical application rate for all three foams increased as the preburn time increased. Even with short preburn times, t

29、he critical application rates for foams A and B, applied as a straight stream to the fuel surface,were appreciably higher than the results obtained from gentle application to the fuel surface. 1.2 The fluoroprotein foam, F.P. 70, appeared to have a performance superior to the hydrolyzed protein foam

30、s. Preburn times Because of the small size of vessel used,the fuel temperature gradient obtained with the laboratory fires was not thought to relate cIosely to the temperatures obtained with fires in larger tanks. It was decided to measure the subsurface temperature profile on larger outdoor fires b

31、efore carrying out tests with foam. A report by Burgoyne and Katan4gives useful information on the subsurface temperatures obtained with fires in a 22-in. diameter tank containing low grade gasoline . Their results showed that a layer of hot fuel or a hot zone was formed under the burning surface wi

32、th a temperature of about 90 C (194 F). Distillation tests showed that this temperature would give a 19 per cent distillation of the fuel used.The rate at which the depth of the hot zone increased was between 24 and 36 in./hr , and a sharp temperature gradient existed between the hot zone and the co

33、ol fuel beneath . TABLE 1. Properties o/the Foams Used in the Fire Tests- Critical shear 25 per cent drainage stress time Type of foam Expansion (dynes/cm2) (min) -Hydrolyzed protein A 8 250 3-5 Hydrolyzed protein B 8 370 2-5 Fluoroprotein foam F.P. 70 8 250 2-4 - O Hydrolizod protein A 3 Hydrolized

34、 protein B A Fluoroprotein foom FP-70 Tests with regular grade 90 octane gasoline were irst made using a 22-in. diameter tank. Asbestos insulation was used to reduce heat transfer from the flames to the fuel via the sidewalls, and a constant head device allowed the addition of fuel to the base of th

35、e tank with minimum disturbance so that constant ullage could be maintained during burning. Fires of 30-min duration were used, and fuel temperatures were measured at 1-in. intervals below the surface. Experiments were also carried out using a 4.8-ft diameter tank; but in this case, the fuel level w

36、as not maintained during burning; and since wall effects are less significant on larger tanks, no insulation was used. The results of experiments with both tanks are shown graphically in Figure 4. Hot zone temperatures of 70 C (158 F) in the small tank and 80 C (176 F) in the larger tank were record

37、ed. Two separate batches of fuel were used in the experiments, and distillation tests showed that in each case the hot zone temperature corresponded to the 20 per cent distillation temperature. This correlates well with the results obtained by Burgoyne and Katan4.There were negligible differences in

38、 the rates of hot zone formation in the two tanks, and the results indicate a hot zone depth of 12 in. after 30 min of burning wiTAa a final rate of formation of )4 in./min.TESTS ON 18-FT 2 FIRE This series of tests was designed to investigate, on a larger scale, the effects of forceful foam applica

39、tion on a deep fuel fire under the following conditions: Short preburn times (2 min) and low fuel temperatures, and Long preburn times (30 rain) and fuel temperatures in the range of 70C to 80 C. In these tests, foam having properties in the range shown in Table 1 was applied as a straight stream to

40、 the center of the fire in an 18-ft tank containing 150 gal (17 in. deep) of 90 octane gasoline. The critical rates of application were determined and are shown in Table 2. It will be seen that trends similar to those indicated by the laboratory results were observed, as significant increases in the

41、 critical rates of application were obtained for the longer preburn times. However, the values obtained for the critical rates were greater than the corresponding values obtained from the laboratory fires, indicating the importance of some scale effect. Furthermore, the apparent large differences sh

42、own between types A and B in the laboratory tests largely disappear in the larger fire tests. It is thought that this effect of scale is due in part to the way in which the wall of the tank affects the flow of foam in forming a foam blanket. With the small diameter laboratory fire tray, the foam qui

43、ckly spread to the walls of the vessel forming a foam blanket upon which a significant depth of foam could be built. For the larger scale fires, a foam blanket appeared to be formed far less readily, and even when foam covered the surface of the fuel, it was more difficult to build up an impervious

44、foam layer. The indications of a scale effect for this method of application are important since the practical problem of storage tank protection is concerned with fires many orders greater than those so far discussed. A small number of tests, therefore, were carried out on a much larger fire, 400 f

45、t2, in a concrete dike to examine further the effects of scale.TESTS ON 400 FT2 Free Because of smoke pollution problems in the area where the tests weremade, it was not possible to carry out tests with long preburn times on the larger fires. The tests, therefore, were limited to applying foam from

46、a standard foam-making nozzle to a 400-ft2fire of 400 gal of regular grade gasoline (approximately 2 in. deep). A 2-min preburn time was used in these tests. The nozzle provided a constant discharge of 40 gpm, an application density of 0.10 gpm/ft2, which was directed as far as possible to the cente

47、r of the test fire. The results obtained are shown in Table 3. TASLE 3. Results of the 18-ft2Fire Test Foam type and propertiesFire performanceHydrolyzed protein A expansion, 7; critical shear stress, 180dynes/cm2; 25 per cent drainage time,2 min 30 sec. Hydrolyzed protein B expanmon, 7.3; critical

48、shear stress,340 dynes/cm2; 25 per cent drainagetime, 3 rain 20 sec. No fire control. After 4-6 rnin of foam application, some reduction in flame intensity. No further reduction. Foam application stopped after 12 min. Fire reached full intensity again within an additional 2 min.Fluoroprotein F.P. 70

49、 expansion, 7; critical shear stress, 90 dynes/cm2; 25 per cent drainage time, 2 rain 25 sec.Fire controlled in 45 sec. Foam application stopped after min 15 sec. Fire out after 1 rain 30 sec.From the results of the laboratory tests and the 18-ft2 fire, one might have expected that the 400-ft 2 test

50、 fire would have been controlled readilyunder test conditions by the two hydrolyzed protein foam compounds applied at an application density of 0.10 gpm/ft 2. One difference in the400-ft2 test fire was that only a 2-in. fuel depth was used as compared with deeper fuel layers on the smaller fires. It

51、 could, however, be an extension of the scale effect that was thought to explain the differences obtained between the small laboratory test fires and the 18-ft 2 test fire results. LIGHT WATER Investigations of new foaming agents at the U.S. Naval Research Laboratory led to the development of Light

52、Water foam compound. There are a number of reports 5-7 relating its performance on shallow fuel layers associated with its use on aircraft crash fires. There are no test results reported on its performance on deep fuel layers; therefore, a test was made on the 18-ft2 test fire with a 30-min preburn

53、time at an application rate near the critical rate for the fluoroprotein foam F.P. 70 used in the test program. The results are given in Table 4 together with the results for the other foaming agents used in the test program.TABLE 4. Results of 18 ft2 Fire Test of Regular Grade 90 Octane Gasoline, 1

54、7 in. Deep, after 30 rain Preburn Time (Foam Applied in Straight Stream to Center of Fire Area at a Rate of 0.07 gpm/ft2)Foaming agentFire performanceLight Water, 6 per cent solution Fluoroprotein F.P. 70, 6 per cent solution Hydrolyzed protein A Hydrolyzed protein B90 per cent control in 1 rain. Ex

55、tinction in 5 rain* 90 per cent control in 2 rain. Extinction in 5 rain * No control after 15-rain foam application No control after 15-rain foam application*Although Light Water had a more rapid control time than F.P. 70, the long extinction times in both cases were due to persistence of flames nea

56、r the hot tank wall.CONCLUSIONSThe following conclusions were drawn from the work described in this paper. Where normal protein-based foams are applied forcibly to fires in Class A flammable liquids, their efficiency is greatly reduced compared with gentle application to the surface. Under operation

57、al conditions in the event of fire in a fuel storage tank containing gasoline, a hot zone at 70C to 80 C is likely to form. Under these conditions, normal protein-based foams are even less efficient, unless applied gently, and foam application at the present recommended rates (0.1 gpm/ft 2) would ha

58、ve no effect on the fire. Results on the 400-ft2 test fire suggest that there could be scale effects for this type of foam application and point to higher values of the critical rate of application even for short preburn times. Further work is required at this and larger scales on fires in deep fuel

59、 layers with long preburn times in metal tanks. Foams made from the fluoroprotein foam F.P.70 and Light Water, applied at rates below the present recommended rates of application, extinguished the test fires rapidly, even when a deep hot zone had been formed.REFERENCES1 Tuve, R. L. and Peterson, H. B., A Study of Some Mechanical Foa