R-20F method: An approach for measuring the isolation effect of foams used fighting forest fires

Transcription

1 AARMS Vol. 11, No. 2 (2012) TECHNOLOGY R-20F metod: An approac for measuring te isolation effect of foams used figting forest fires ÁGOSTON RESTÁS* National University of Public Service, Budapest, Hungary Aerial fire figting is a very expensive solution; owever bombing just pure water not always enoug for suppressing fires. In many cases special agent is added to water for wetting it or creating foam. Tis foam covers te surface and aving some special extinguising effects suc as separate, cool, wetting and isolation. Isolation effect is come from te canged feature of te structure. Hanging on te expansion rate many air bulbs are inside te foam structure raising te isolation effect. No doubt tis effect is very notable owever tere is no official metod for measuring tis value. R-20F metod gives a simple solution for measuring te isolation effect of foam and determining its value in water equivalent. During te process 3% foam solution was used and different foams caracterized wit expansion ratio of were made. Wooden plate samples were covered by mm tick foam blanket and te ignition time was measured in a special electric oven. Water equivalent was calculated from te different ignition times. Results sow tat te maximum rate of isolation effect, expressed by water equivalent is more tan 2.3. Introduction Up to now tere was no objective metod known for measuring te complex effect of increasing te efficiency of foams wile suppressing fires. Te suppression potential of foams suc as Class A foams specially used for structure or forest fires is measured by a special way; bonfires classified by international standards are extinguised by te foams and te potential is evaluated by te size of te bonfires. Tis metod, measuring te active impact of foams is appropriate and accepted as international standards for structure fires. Te standard metods are not measuring te isolation effect of foams, owever tere were more initiatives regarding tis topic. 1,2. But eac manufacturer caracterizes teir agent wit te good isolation effect. Te isolation effect is not an active action against * Associate professor, National University of Public Service, Institute of Disaster Management, Department of Fire Figting and Tecnical Rescue, Budapest, Hungary; Pone: , arestas@r-fire.u Received: February 28, 2012 Address for correspondence: ÁGOSTON RESTÁS arestas@r-fire.u

2 te flame but passive influence of te ignition caused by te blanket covering te surface. 3,4 Since tere is no accepted metod for measuring te isolation effect of foams, and eac producer caracterizes its own foam as aving good isolation effect, it is required to develop a process wic is objective, practical and ready to demonstrate te different isolation effects of te different type foams. For te first we ave to declare te reference base to wic te effect is evaluated and expressed in equivalent. Pure water as te most frequently used material for fire suppression tat is wy it was taken as base and te scale of equivalent. As usual foam is featured as aving passive isolation effect but not as aving te active extinguising potential; tis feature also can be very important during intervention, especially in case of forest fires using aerials. Te added value of using foam for te fire suppression is not only isolation of te combustible material against eat radiation but it also plays an active role in suppression. If te quality or quantity of foam blanket is not suited for stopping te spread of fire means tat te consumed resources were ineffective, costs for aerials used elpless. R-20F metod Te metod was developed in order to measure te extinguising potential of foam blanket. As usual foam featured as aving passive isolation effect but not as aving te active extinguis potential; owever tis feature also can be very important during intervention. Means for te process Below is decelerated te main important tings for preparing te test, and some basic process for being ready to measure te ignition time of samples. Means required for te process: 1. Radiant eater: KAL VK1 i wit 35 kwm 2 eating flux; ii 2. Samples wit metal rings 0.06 m 0.0 6m 0.01 m dried pine wood samples; 3. Foams, made from type EVAM iii agent, 3% mixed rate solution, expenditure rate in series ; 4. Pure water, temperature 293 K. i KAL VK1 radiant eater: produced by KALÓRIA HKtecnikai Kft., H-1071 Budapest, Betlen út 43 Hungary ii Certificated by Szent Istvan University, Ybl Miklos Department, Budapest iii EVAM: foam agent for universal applications, made by EVM Rt., H-1172 Budapest, Cinkotai út 26. Hungary 234 AARMS 11(2) (2012)

3 Preparation of te samples Special metal ring stacked to eac sample in order to ensure te same tickness of foam blanket covering te samples. Ring is made of steel, wit 0.06 m diameter and m seet tickness, in series of mm ring eigt. Rings are fixed by eat resistant stove glue, purcased from te market. Ignition time of differently treated samples Tree different ignition times were measured. 1. it is necessary to measure te natural sample for getting te net ignition time; 2. te measurement of te water treated sample gives te reference base; and 3. te foam treated sample is measured for te purposes of te test metod. Ignition time of natural sample Natural sample wit metal ring but witout any surface treatment is needed to put in to te radiant eater and measured te ignition time. As usual, te space between te foam blanket and te eater is fix and ave to ensure tat te radiant eat fluxes is 35 kwm 2 continuously. At least 3 or more samples are needed for measuring te ignition times. Ignition time of water treated sample Te effect of water s ignition delay relates to te ability of eat abstraction; it is used for base to similar te effect of foam s ignition delay. Ring on sample is needed to fill wit 293 K temperature pure water by te volume of rings depending on te series. Sample is needed to put in to te radiant eater and measured te ignition time. As usual, te space between te rim of ring and te eater is fix and ave to ensure tat te radiant eat fluxes is 35 kwm 2 continuously. At least 3 or more samples are needed for measuring te ignition times, in series wit mm deep water column. Ignition time of foam covered sample From pure water and foam agent ave to prepare a solution wit 3% mix rate. From te solution different expansion rated foam is prepared in series Ring on sample is needed to fill wit foam by te volume of rings depending on te series. Sample is needed to put in to te radiant eater and measured te ignition time. Te space between AARMS 11(2) (2012) 235

4 te rim of ring and te eater is fix and ave to ensure tat te radiant eat fluxes is 35 kwm 2 continuously. At least 3 or more samples are needed for measuring te ignition times, in series wit mm tick foam blanket. Te effect of foam is obviously influenced bot te structure made by air bulbs and te solution itself foam contains (water and agent). Since te R-20F metod focuses to measuring typically te isolation effect of foam, influence of te solution is needed to exclude. Te effect of solution is taken away from te complex effect; it depends on te different quantity in series of te solution foam contains. Since te extract rate is very low (3%) te effect of pure water and solution is taken equal. Matematical formulas for calculations Based on te measured data, it is required to calculate different parameters. For calculations and evaluating te measured value, notations and different matematical formulas were used. 1. Heigt of te metal ring [mm]; (F.1) 2. t Ignition time [sec]; (F.2) 3. Upper index, eigt of water column or tick of foam blanket (eigt of te metal ring) [mm]; (F.3) 4. nature Lower index, untreated sample; (F.4) 5. B Lower index, gross ignition time [sec]; (F.5) 6. N Lower index, net ignition time (measured ignition time reduced by te ignition time of te untreated sample) [sec]; (F.6) 7. W Lower index, ignition time of water treated sample [sec]; (F.7) 8. F Lower index, ignition time of foam treated sample [sec]; (F.8) 9. y Lower index, expansion rate of te foam [ ]; (F.9) 10. W Water content of te foam/water expressed by water column eigt [mm]; (F.10) 11. Y Effect of ignition delay regarding water content [ ]; (F.11) 12. Z Effect of ignition delay expressed by water equivalent [ ]; (F.12) 13. tnature Ignition time, nature sample [sec]; (F.13) 14. tbw Gross ignition time, sample covered wit mm eigt water column [sec]; (F.14) 15. tnw Net ignition time, gross ignition time reduced by t nature, sample covered wit mm eigt water column [sec]; tnw = tbw tnature (F.15) 236 AARMS 11(2) (2012)

5 tbfy Gross ignition time, sample covered by mm tick and y expansion rated foam [sec]; (F.16) tnfy Net ignition time, gross ignition time reduced by t nature, sample covered wit mm tick and y expansion rated foam [sec]; tnfy = tbfy tnature (F.17) WW Water content of mm eigt water column [mm]; (F.18) WFy Water content of mm tick and y expansion rated foam, expressed by water column eigt [mm]; WFy = y (F.19) t W / W Ignition time measured (2 mm) or linear calculated (3 4 5 mm), sample covered wit mm eigt water column [sec]; t W / W = tnw (F.20) t W / Fy Ignition time calculated wit water quantity of foam contains, sample covered by mm tick and y t W / W WFy expansion rated foam [sec]; t W / Fy = (F.21) WW YW Coefficient, meaning te effect of water s ignition delay, sample covered wit mm eigt water column, evaluated by water equivalent. Rate = 1 [ ]; Y W = 1 (F.22) YFy Coefficient, meaning te extra effect of foam s ignition ZEquW delay correlate to its own water content, sample covered wit mm tick and y expansion rated foam [ ]; YFy tnfy t W / Fy = (F.23) Water equivalent of water s ignition delay, expressed EquW by mm ig water column [mm]; Z = W (F.24) W AARMS 11(2) (2012) 237

6 25. ZEquFy Water equivalent of foam s ignition delay, evaluated by mm eigt water column equivalent, foam blanket x mm tick and y expansion rated foam [mm]; Z EquFy = YFyWFy (F.25) Te above formulas marked in brackets signed in many places (text and tables) make process following easier. Study for ignition times Tis study contains only te extracted data meaning usually te average value of measured ignition time but in explanation deviations also mentioned. Te wole study located in te arcives of R-Fire Ltd. iv Measured ignition times of differently treated samples Te first test results used for tis study appened in 21 st January 2010, at te Szent István University, Ybl Miklós Department, Budapest. Te Table 1 contains te average value of measured ignition time. Table 1. Measured data of ignition time Legend: Nature: samples witout treatment R exp6/9/12: Expansion rate of foam used for series Calculations Based on te measured data and matematical formulas different calculations were made. Te series of tis calculation can be following in Table 2, Table 3 and Table 4. iv R-Fire Ltd.: frounded by Ágoston Restás, PD, located H-3752 SzendrK, Nagyállomás út 1/k. 238 AARMS 11(2) (2012)

7 Net time of ignition delay For evaluating te results different calculations were made. Firstly te ignition delays of differently treated sample were measured; in case of no treatment (nature) F.13, water F.14 and foam F.16 figures meaning. Tese results can be evaluated as net effect of ignition delay of extinguising material covering te samples. For te calculations F.15 (water) and F.17 (foam) formulas were used (Table 2). Table 2. Net time of ignition delay Foam s efficiency and expression by water equivalent Secondly te water content of te foam, expressed by water column appens (F.19). Logically water covered samples also belongs to tis series (F.18). Tereafter te ignition delay of water, foam contains is calculated (F.21). Water covered samples belongs again to tis series (F.20). Based on te F.17 and F.21 a coefficient created (F.23) expressed te relation between te ignition delay in case of same water quantity but different features (water-foam). As before, water covered samples also belongs to tis series (F.15 and F.20) meaning te base to tis calculation (F.22) and logically ratio always results 1 (Table 3). AARMS 11(2) (2012) 239

8 Table 3. Coefficient of ignition delay Table 4. Foam s extra ignition delay and its expression by water equivalent Based on te coefficient (F.23) and water content (F.19) of te foam can be calculated te ignition delay expressed by te equivalent of water column (F.25). Tis equivalent means tat water as extra ignition delay effect in case of foam formulas (Table 4). 240 AARMS 11(2) (2012)

9 Evaluation As a first momentum, te ignition time of samples witout treatment (nature) was measured. For te correct base nature samples were measured also during series. Precision of measuring ignition time was below 1 second. Based on 6 samples te average ignition time is 19 seconds wit minimal deviation (+3/ 2 seconds). In te series, te water covered samples were measured firstly. For aving more precisions measure te 2 mm ig ring samples were filled wit water up using ypodermic syringe, to be precise te volume. d V = A = = (60 10 m 3 m) = m 3 = 5.65cm Based on five measures te average ignition time was 108 seconds, wit +15/ 18 seconds maximal deviation; te rate of deviation is not bigger tan at nature samples. Te speciality of water series was tat no more precisions measure could be appen wit iger ring on samples. Unfortunately te rings divorced from te sample surface (3 mm) and causing some water leakage during tests defeated te genuine process. Te problem was identified as a minimal deformation of samples surface caused by water and cement was not enoug flexible to compensate te minimal gap. Terefore in case of mm ig ring tere was no measured value only calculated in scale based on linear interpolation. Since te above some results can be taken into account wit just critics; and additional test series also required. But results were evaluated as a tendency better tan principle of eac measured data. 3 Figure 1. Time and Net time of ignition versus Dept of foam In te next series te different expansion rated foams were tested wit different dept of blanket covering te samples. Te same quantities of foam in eac sample were assured by rings. Te measured values are in te Table 1 and Figure 1 also sows AARMS 11(2) (2012) 241

10 values in te grapics. Te grapics sows not just te time of ignition but te tendency of te cange anging on te dept of foam covering samples. Te study focused to inspection ow canging te ignition delay and wat is te tendency of it anging on te own quality of te foams. Tat is wy te ignition time of no treated sample (nature) required subtracting from te ignition time of treated samples (water and foam). In tis case te data sows te net ignition time of substances anging on teirs own features (Figure 1). Based on measured data and grapics next conclusion were stated: 1. Rising te dept of foam covering samples te time of ignition delay also rise. Tendency yes, but exact data for rising caracteristic was not establised; more test needed. 2. Rising te dept of foam a special symptom, co-called foam boiling was observed. Tis symptom was more intensive during raising te dept of foam, especially in case of 5 mm foam blanket wit ig expansion rated foam (exp. rate = 12). It modified te result, obviously reduced te delay of ignition time. 3. Taking into account te symptom of foam boiling (see above) and te curve tendency of foams (expansion rate is 6 9, and dept of foam is 2 5 mm) te tendency more or less can be also linear. 4. Since te tecnical difficulties and te assumed rate for iger mistake tis study didn t measure te 1 mm ig ring samples, owever te Figure 2 generated te data by linear interpolation. Te effect of foam s ignition delay is aggregated by two different factors as below. Factor of quantity. Mecanical foam is made of special solution and air bulbs; solution consists of pure water and special foam agent. Te mixture rate angs on conditions intervention aving; ratio is required usually between 0.1 6%. During te study of R-20 metod 3% solution was used. Since te rate was relatively low and te eat capacity of te agent doesn t differ drastically from te water, te value of solution was taken equal to water. Obviously during te test radiation eat evaporated te solution meaning tat its eat capacity influenced te ignition time, delayed it similar as water usual. Factor of quality. Foam as a special effect not just aving water quantity. Te feature of foam means also isolation as an extra effect. Fire figters often use tis isolation effect even if te practice does not know exactly wat is it or wit more precisions wat te background of tis effect is. Obviously te isolation effect often means defence against radiation eat but also separation between flammable liquid and oxygen. R-20F metod focuses to study te extra effect caused by te special feature of foam. Te interest focuses not to te feature of foam but finding a common scale 242 AARMS 11(2) (2012)

11 expressing tis extra effect and measures tese wit water equivalent, understanding it by any fire figter. If te foam produces longer ignition delay tan ignition delay belongs to its own water quantity means tat tis extra effect caused by te special features wat foam as. In order to reduce te mistake during test, series started from 2 mm ig covering. Value before it was rated logically. In te Figure 2 left from te broken line sows te estimated value, rigt te measured except in case of water. Problem of water was mentioned above. Based on te own water quantity of foam (F.7) te ignition delay belonged to it was determined by linear interpolation (F.9). Dividing te time of measured ignition delay to its own water quantity results a rate. If te value of tis rate is more tan 1 means tat foam as extra delay effect (F.11). Based on te R-20F study te analysis of measured data resulted tat tis rate is significantly always more tan 1. It means tat foam as extra isolation effect tan just te effect of its own water quantity. Figure 2. Measured and interpolated value of ignition time Te efficiency of foams wit different features is represented in different functions. 1. Expansion rate on x axle and anging on dept of foam efficiency sown in Figure 3a; 2. Dept of foam on x axle and anging on expansion rate efficiency sown Figure 3b; AARMS 11(2) (2012) 243

12 3. For better demonstration bot diagram were made in 3 dimensional versions using belt diagrams Figure 4a and Figure4b. Based on experience during te test, calculations and grapics statements are te next: 1. Te efficiency of foam rises wit raising te expenditure rate. Te caracteristic of tis raise can t be surely stated; taking into account te deviations from te average, te near linear curve can t be close out. 2. Te efficiency of foam reduces wit raising te tickness. Te caracteristic of tis reduce can t be surely stated; taking into account te deviations from te average, te near linear curve ere also can t be close out. 3. Relatively tin foam blanket but ig expansion rate results ig efficiency. Figure 3. Efficiency versus rate of foam (a) and dept of foam (b) Figure 4. Efficiency versus rate of foam (a) and dept of foam (b); belt diagrams After determining te efficiency of foams, R-20F metod focuses to te expression of tis extra effect by practical metod; to be able to explain tis extra effect also to fire figters. Water equality as an easiest way can give te solution (F.25). Te water 244 AARMS 11(2) (2012)

13 equality of foam wit its own water quantity can be also demonstrated in a function sown by Figure 5. Te difference between values in vertical sows also te extra ignition delay effect of foam. Figure 5. Real and relative water content Te grapic also demonstrate tat raising te tickness of foam (2 mm 5 mm) te curves close to eac oters; consequently te delay effect reduces. Tis statement armonises to Figure 6. Wit fine analysis can be observe tat, te angel wit x axis rises in bot case (real and equivalent water quantity of foam s curve) if tickness of foam blanket also rises. Figure 6. Efficiency of foam AARMS 11(2) (2012) 245

14 Te coefficient reduces wile raising te tickness of foam blanket, parallel as te angel between curves and x axis reduces (Figure 7). Harmony is also demonstrated in te function were foams wit different features, te real and equivalent water contain of foams and coefficient is represented. Figure 7. Efficiency versus rate of foam (a) and dept of foam (b); belt diagrams Summarizing Based on te R-20F metod a common used fire figting foam was tested. Tere are many experiences after making test series. Main statements: 1. R-20F is appropriate metod for declare te extra effect of foam wic is caused by te special feature of te structure and resulted longer ignition delay tan sould by own water contain. 2. R-20F is appropriate metod drawing conclusion regarding most effective intervention, declare te quality and quantity of foam used especially in case of forest fire. 3. Results given by R-20F metod declare tat te most effective figure of foam means a relatively tin foam blanket (5 mm) but iger expenditure rate tan 6. For better and more precisions results additional test are required using different foam concentrate especially used for figting forest fires even by aerials. Based on te 246 AARMS 11(2) (2012)

15 results some traditional tactic can cange and cause more effective figting against forest fires. References 1. BOYD, C. F., MERZO, M. (1996): Fire Protection Foam Beavior in a Radiative Environment; Final Report, Mecanical Engineering Department, University of Maryland, US. 2. STP 2007 Standard Test Procedures, Evaluation of Wildland Fire Cemicals, Lateral Ignition and Flame Spread (LIFT), STP 2.2, Revised 5/30/07, Department of Agricultural, Forest Service, US, ttp:// 3. IGISHEV, V. G., PORTOLA V. A. (1993): Evaluation of foam parameters in extinction of self-ignition sources; Mine Aerodynamics, Institute of Mining, Russian Academy of Sciences, Prokopyevsk, Fiziko- Tekniceskie Problemy Razrabotki Poleznyk Iskopaemyk, No. 4, Russia 4. SALGADO, J., PAZ-ANDRADE, M. I. (2009): Te effect of Firesorb as a fire retardant on te termal properties of a eated soil; Journal of Termal Analysis and Calorimetry, Vol. 95 (2009) 3, Akadémiai Kiadó, Budapest, Hungary. AARMS 11(2) (2012) 247