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Compressed-air-foam (CAF) fire suppression system for aircraft hangar protection
http://irc.nrc-cnrc.gc.ca
C o m p r e s s e d - a i r - f o a m ( C A F ) f i r e s u p p r e s s i o n
s y s t e m f o r a i r c r a f t h a n g a r p r o t e c t i o n
N R C C - 5 0 5 6 0
K i m , A . ; C r a m p t o n , G .
A version of this document is published in / Une version de ce document se trouve dans: Proceedings of 2008 Fire Suppression and Detection Research Applications – A
Technical Working Conference (SUPDET 2008), Orlando, FL., March 11-13, 2008, pp. 1-6
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Compressed-Air-Foam (CAF) Fire Suppression System for Aircraft Hangar Protection
Andrew Kim and George Crampton Fire Research Program, National Research Council of Canada
1200 Montreal Road,
Ottawa, Ontario, Canada, K1A 0R6 Phone #: (613) 993-9555
Fax #: (613) 954-0483 E-mail: andrew.kim@nrc.gc.ca
INTRODUCTION
Fixed pipe Compressed-Air-Foam (CAF) system was developed by the National Research Council of Canada (NRC), incorporating a new and innovative air injection method and foam distribution nozzles. Previous full-scale tests [1-3] showed that CAF has superior fire suppression performance. However, the fire suppression performance of the CAF system for practical applications was not systematically evaluated.
NRC has initiated a project to investigate the feasibility of a compressed air foam (CAF) fire suppression system in providing fire protection equivalent to conventional fire suppression for aircraft hangars. A prototype CAF fire suppression system for aircraft hangar protection was developed and evaluated to determine whether it can meet the fire safety objectives.
At present, foam-water sprinkler systems with overhead application are
commonly used for aircraft hangar protection. In this project, a systematic comparison of the fire suppression performances of the CAF system and foam-water sprinkler system was carried out. The experimental procedure used in this project was similar to the test requirement listed in UL162 standard [4]. This study was carried out to determine the minimum requirements for the various parameters of the CAF system to meet the fire suppression performance of existing sprinkler systems using foam solution, and to quantify the benefits of the CAF system over sprinkler systems. This paper describes the experimental facility for the study and presents experimental results comparing the fire suppression performances of CAF and foam/sprinkler systems for aircraft hangar protection.
EXPERIMENTAL SET-UP AND PROCEDURE
A series of full-scale fire tests was carried out to compare the fire suppression performance of the CAF system with that of a foam-water sprinkler system in providing
aircraft hangar protection. The experimental procedure used in this project was based on the test requirement listed in UL162 standard [4].
Piping system and nozzles
A full-scale fire test set-up for foam-water sprinkler and CAF systems was constructed. The test set-up included a 3.74 m by 3.74 m (12 1/4 feet by 12 1/4 feet) test piping grid for the foam-water sprinkler and CAF systems. There were four sprinkler heads or four CAF nozzles installed at each corner of the piping grid. The piping grid and the sprinkler heads and CAF nozzles were installed 4.5 m (15 ft) or 7.6 m (25 ft) above the floor.
The sprinkler heads used in the tests were Viking Standard Response Model M Pendant, Standard Orifice, 15mm BSP Identification VK102 K-Factor: 5.6. Each sprinkler was designed to cover approximately a 6 m (20 feet) diameter circular area.
The small spinner CAF nozzle has a 25.4 mm (1 inch) diameter body with a 19.05 mm (3/4 inch) outlet opening piece attached to the body. The outlet opening piece spins due to the momentum of the CAF flow as it discharges CAF. This spinning action distributes CAF uniformly over a 5.27 m (17.3 feet) diameter area. This nozzle was used in the tests with a liquid flow rate of approximately 23 L/min.
Test Fire
The test fire was a heptane pool fire. Commercial grade heptane fuel in a fire test pan was placed on the floor, centered below the piping grid for the sprinkler and small rotary nozzle CAF tests. The fire test pan was square, straight-sided, with an area of 4.65
m2 (50 square feet), and made of 6.4 mm (1/4 inch) thick steel plate.
The test pan contained not less than a 25.4 mm deep water layer, with
approximately 100 to 205 litres of heptane poured over the water. The water depth was adjusted to provide a distance from the top of the pan to the surface of the heptane fuel of not less than 203 mm.
Foam Concentrates
Foam concentrates used in the tests were Class A and Class B foam concentrates. Class B foam concentrate was Aquous-Film-Forming-Foam (AFFF), manufactured by the National Foam Co. Class A foam concentrate was Silvex foam, manufactured by Ansul. Class B foam concentrate was used at 3% in the sprinkler tests and at
approximately 2% in the CAF tests. Class A foam concentrate was used only in the CAF tests, at approximately 1%.
Test Procedure
The heptane in the test pan was ignited and the resulting fire was allowed to burn freely for a 15 s pre-burn. At the end of the 15 s pre-burn, the CAF or foam water spray discharge commenced and continued for 5 minutes. During this period, the time for complete extinguishment of the heptane pool fire was measured.
After all discharge was completed, the foam blanket formed on top of the fuel was left undisturbed for 15 minutes. During this period, a lighted torch was passed at
approximately 25.4 mm above the entire foam blanket, including corners, in an attempt to re-ignite the fuel. It was to observe whether the fuel would re-ignite while the torch was passing over the fuel. This torch test was conducted twice during this period,
immediately after the end of the foam or water discharge, and 1 min prior to the burn-back test. Each torch test lasted for a period of not less than 1 minute. This procedure is as required in UL-162.
The UL-162 test procedure for foam-water sprinklers requires that, following the 5 min foam-water discharge on heptane fuel, an additional 5 min of water (alone)
discharge be allowed to occur. The water discharge is followed by a period of 10 min during which the foam is left undisturbed. Since a CAF system is not designed to flow water alone, it was decided to follow the 5 min foam discharge with a 15 min waiting period during which the foam was left undisturbed. This latter procedure of a 5 min foam discharge followed by a 15 min undisturbed period is an accepted alternative procedure in UL-162 when a polar solvent fuel is used. This same procedure (5 min discharge + 15 min undisturbed) was used for the foam-water sprinklers as well as the CAF nozzles to ensure a consistent basis of comparison.
After the re-ignition attempts, the burn-back test was conducted. A 0.3 m diameter stovepipe was placed approximately 0.76 m from each of two adjacent sides of the test pan, in the corner where the flame extinguished last, and placed in such a manner that the foam blanket was not disturbed. The portion of the foam blanket that was
enclosed by the stovepipe was removed, and the fuel inside the stovepipe was ignited and allowed to burn for 1 minute. The stovepipe was then slowly removed from the pan while the fuel continued to burn. After the stovepipe was removed, the time for the flame
to spread through the foam blanket over an area larger than 0.9 m2 (10 ft2) was measured.
RESULTS AND DISCUSSION
Table 1 shows the test conditions and fire suppression performance results of the foam-water sprinkler and CAF systems with its nozzles located at 4.5 m (15 ft) or 7.6 m (25 ft) above the floor. In Test #1, 4 sprinkler heads, located at 4.5 m height, with 3% Class B foam concentrate extinguished the heptane pool fire in 2 min 32 s. The burn-back time was 9 min. In Test #2, CAF system, with its nozzle height of 4.5 m, was successful in extinguishing the test fire in 50 s, and the burn-back time was more than 23 min. The results showed that CAF system can extinguish the large heptane fire at less
than half the extinguishing time of the foam-water sprinkler system, with much less water flow rate. Also, the burn-back time with the CAF system was more than double that of foam-water sprinkler system.
In Test #3, the CAF system using 1% Class A foam concentrate with nozzle height of 4.5 m was able to extinguish the heptane pool fire in 59 s. It shows that CAF system, using Class A foam concentrate, can extinguish a Class B (heptane pool) fire. This also shows that, using Class A foam concentrate, the fire extinguishment time of the CAF system was again less than one-half that of foam-water sprinklers.
Burn-back time of the Class A foam is, however, not as good as the Class B foam. Class B foam, with its film-forming capability, has strong burn-back resistance, but Class A foam was only able to withstand the burn-back for 10 min.
Tests #4 to #5 are repeats of Tests #2 and #3. The results show that in the repeat tests, the extinguishment and burn-back times are similar for the same operational conditions, indicating the repeatability of the CAF system performance.
Since the ceiling of actual air craft hangar is much higher than the 4.5 m high nozzle location specified in the UL162 test standard, another series of tests was carried out to study the fire suppression performances of the CAF system and foam-water sprinkler system in 7.6 m (25 ft) height application.
As shown by Tests #7 and #8 in Table 1, at the 7.6 m height, the fire
extinguishment and burn-back performance of the CAF system (using both Class B and A foams) was approximately the same as that for the 4.5 m height (Tests #2 and #3) with extinguishment at approximately one-half the time of the foam-water systems (Test #6). The CAF system with Class B foam burned back at approximately twice the time for the foam-water sprinklers and Class A foam burned back at approximately the same time. The CAF system exceeded the minimum fire extinguishment and burn-back benchmarks required by UL-162 using both the Class B and Class A foams.
CONCLUSION
NRC has developed a prototype compressed air foam (CAF) fire suppression system for aircraft hangar applications, and carried out tests to determine whether it can meet the fire safety objectives. At present, foam-water sprinkler systems with overhead application are commonly used for aircraft hangar protection, therefore, a systematic comparison of the fire suppression performances of the CAF system and foam-water sprinkler system was carried out. The experimental procedure used in this study was similar to the test requirement listed in UL162 standard [4]. A series of full-scale fire tests was conducted to measure the effectiveness of foam-water sprinkler and CAF systems in extinguishing a large heptane pool fire, using Class A and Class B foam concentrates, with nozzles located at 4.5 m or 7.6 m height.
The test results showed that the CAF system performed much better than the foam-water sprinkler system, using Class B foam concentrates. The CAF system used 40% of the sprinkler water flow rate and extinguished the fire in less than 1/2 the extinguishment time of the sprinkler. The CAF system used a concentration of only 2% foam concentrate while the sprinkler used 3%. Burn-back time of the CAF system was also much longer than the sprinkler system, typically 20 minutes for the CAF system and approximately 10 minutes for the sprinkler system.
The tests also showed that the CAF system could extinguish liquid fuel fires using Class A foam concentrate. CAF system, using Class A foam concentrate, extinguished the test fire in less than 1/2 the extinguishment time and with less than ½ the water flow rate of the foam-water sprinkler system.
The study showed that nozzle height, whether it is located at 4.5 m or 7.6 m above the test fire, did not make much difference in extinguishing the test fire, and clearly showed that the CAF system can provide as effective fire protection as the current foam-water sprinkler system in aircraft hangars.
REFERENCES
1. Kim, A.K. and Dlugogorski, B.Z., “Multipurpose Overhead Compressed-Air Foam
System and Its Fire Suppression Performance,” Journal of Fire Protection Engineering, Vol. 8, No. 3, 1997.
2. Crampton, G.P., Kim, A.K. and Richardson, J.K., “A New Fire Suppression
Technology,” NFPA Journal, July/August, 1999.
3. Kim, A.K. and Crampton, G.P., “Application of a Newly-Developed
Compressed-Air-Foam Fire Suppression System,” Proceedings of INTERFLAM 2001, Edinburgh, UK, 2001.
4. UL 162 – UL Standard for Safety for Foam Equipment and Liquid Concentrates,
seventh edition, Underwriters Laboratories Inc., Northbrook, IL, 1994. ACKNOWLEDGEMENT
Authors would like to acknowledge the assistance of Fire Flex for allowing the use of their ICAF system in the test series. Authors would also like to express deep appreciation to Mr. Jean-Pierre Asselin and Mr. Raymond Quenneville of Fire Flex Systems Inc. for their assistance. Authors acknowledge the assistance of Michael Ryan of NRC in conducting the tests.
Table 1 Summary of Test Results.
Test # 1 2 3 4 5 6 7 8
System Foam-water
sprinkler
CAF CAF CAF CAF Foam-water
sprinkler
CAF CAF Nozzle height
(m)
4.5 4.5 4.5 4.5 4.5 7.6 7.6 7.6 Water flow rate
(L/min)
227 90 90 90 90 227 90.8 90.8
Air flow rate (L/min)
N/A 905 905 905 905 N/A 939 939
Foam type Class B
(National) Class B (National) Class A (Silvex) Class B (National) Class A (Silvex) Class B Class B (National) Class A (Silvex) Foam conc. % (%) 3 2 1 2 1 3 2 1 Expansion ratio 3.5 10 10 10.9 8.62 3.5 10 10 Drainage time (min:s) - 3 : 30 10 : 00 3 : 30 10 : 00 - 3 : 30 10 : 00 Extinguishment time (min:s) 2 : 32 0 : 50 0 : 59 0 : 49 1 : 06 2 : 16 0 : 50 1 : 09 Burn-back time (min:s) 9 : 00 23 : 35 10 : 10 21 : 15 9 : 15 9 : 21 23 : 40 9 : 37
