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Gollner masters thesis presentation final jan 2010

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  • Initial funding for experiments was provided by Schirmer Engineering.
  • The goal of this study is to evaluate a method of characterizing the relative fire hazard of a grouped warehouse commodity. * Commodity classification refers to a ranking of estimated fire challenge to sprinkler protection.
  • Why are warehouse fires, and particularly upward spread problems being revisited for study? Examples of losses, where “fully-protected” facilities are still burning down despite what should be full protection. There are still glaring lacks of scientific understanding of the fire spread process, let alone suppression process for these large fires. This endangers firefighters, occupants, and local environments. Soot production and toxic runoffs from 2-day long fires are extreme.
  • Commodity classification in warehouse used to determine requirements of suppression system based on Area Density Curves. Full-scale fire tests are preferred by more than just the sprinkler industry. They give the best approximation available; however, there are several problems:By rushing to full-scale tests exclusively, we are glossing over the fundamental physics into something that is so complex that it defies clear comprehensionFull-scale testing is not always economically feasible or even physically possible (i.e. very tall rack storage arrangements)Free-burning HRR paints an incomplete picture. Several other driving and resisting influences govern combustion such as...Free-burning HRR is scale dependent. Ranking via intermediate scale measurements doesn’t necessarily translate into accurate full-scale assessment. The scale dependence may extend to multiple geometric dimensions (i.e. wood cribs).Are results repeatable? Tyco was unable to reproduce data points on the existing curves according to Golinveaux presentation at NFPA Conference 2007.Are results reproducible? Inconsistencies between NFPA and CENClassification by analogy is common industry practice. No testing performed. Analogies made in non-standard manner and generally very poorly substantiated (i.e. plastic totes in Tupperware facility in S.C.)Suppression and control are vaguely defined. The difference between them is unclear.The distinction between a fire under control and out of control is also unclear.
  • Goal is to make fire scenarios more predictable with scientifically verifiable results from testing. Distinguish & predict levels of fire control, suppression, and extinction for multiple commodities and layouts.Currently: Working on Cone Calorimeter (see other presentation) and small-scale testing on a standard commodity to determine non-dimensional parameters. Later will predict & assess accuracy of new methods with intermediate (Fire products collector) & large scale testing.
  • Our contribution is Bench-scale tests to determine nondimensional parameters, (B)Will be used to rank commodities on a fundamental scale used to design a sprinkler system.May also be useful as an input into modeling applications in the future.
  • Commodity classification in warehouse used to determine requirements of suppression system based on Area Density Curves. Full-scale fire tests are preferred by more than just the sprinkler industry. They give the best approximation available; however, there are several problems:By rushing to full-scale tests exclusively, we are glossing over the fundamental physics into something that is so complex that it defies clear comprehensionFull-scale testing is not always economically feasible or even physically possible (i.e. very tall rack storage arrangements)Free-burning HRR paints an incomplete picture. Several other driving and resisting influences govern combustion such as...Free-burning HRR is scale dependent. Ranking via intermediate scale measurements doesn’t necessarily translate into accurate full-scale assessment. The scale dependence may extend to multiple geometric dimensions (i.e. wood cribs).Are results repeatable? Tyco was unable to reproduce data points on the existing curves according to Golinveaux presentation at NFPA Conference 2007.Are results reproducible? Inconsistencies between NFPA and CENClassification by analogy is common industry practice. No testing performed. Analogies made in non-standard manner and generally very poorly substantiated (i.e. plastic totes in Tupperware facility in S.C.)
  • Laminar case is not a principal hazard but likely present in initial stages and useful for theoretical analyses.Corrugated board is ignited at the base, heats to a pyrolysis temperature where the board pyrolyzes expelling fuel vapors. Oxygen in the air diffuses towards this region and forms a thin diffusion flame at some standoff distance above the commodity. Not all of the fuel is burned directly in front of the pyrolysis region, some flows upwards beyond the pyrolysis zone into the combusting plume, where it burns above. This is called “excess pyrolyzate.” This excess pyrolyzate burning in the combusting plume heats the rest of the commodity incredibly fast as it burns in front of the surface, developing a very quickly growing upward spreading flame.
  • The same pyrolysis zone, combusting plume, and buoyant plume exist in this case. Now, the flame is larger and the combusting plume begins to extend above the height of the commodity surface, and the flame becomes very turbulent. The fire grows more rapidly. The remaining products are then propelled above into a buoyant plume.
  • In the mixed case the same processes still occur but now some leakage of the commodity (in the form of melted plastic) pool in front of the commodity. Now remaining cardboard burns as well as a small pool fire at the base of the commodity. The characteristics of the pool fire as well as the flat plate burning must be taken into account. In our tests, for safety reasons the fire was extinguished before significant commodity leakage occurred. We burnt approximately only 3/4 of the commodity. It would take upwards of 3-5 minutes for this to occur based on observations from tests, so characterizing the earlier region to involved suppression is more important for this study.
  • In the mixed case the same processes still occur but now some leakage of the commodity (in the form of melted plastic) pool in front of the commodity. Now remaining cardboard burns as well as a small pool fire at the base of the commodity. The characteristics of the pool fire as well as the flat plate burning must be taken into account. In our tests, for safety reasons the fire was extinguished before significant commodity leakage occurred. We burnt approximately only 3/4 of the commodity. It would take upwards of 3-5 minutes for this to occur based on observations from tests, so characterizing the earlier region to involved suppression is more important for this study.
  • “Universal Meaning”The B number can be thought of as a thermodynamic or mass transfer driving force. It was first introduced by Spalding in 1950 to develop an expression for the burning rate of a liquid fuel droplet in a gas stream. The uncorrected B-number is a property of pyrolyzing material, and it appears in boundary conditions of energy conservation at the fuel surface. The corrected B-number accounts for influences of additional heat-transfer processes. Physically, it relates the heat release of combustion (the numerator) to the energy required to generate fuel gasses (the denominator).In a mass-transfer sense it is the ratio of an impetus for interphase transfer to a resistance opposing that transfer.
  • Mf’’ is the mass loss rate per unit are of the material, which is related to the heat transfer component (h/Cg) times the thermodynamic component ln(B+1). Because of the log relationship of B, heat transfer plays a larger role in this process. H is assumed to be a constant in this process and is determined by a relation first relating it to the Nusselt number, and a nusselt number correlation which is a function of the cubed root of the Grashof number times Prandtl number. This approach is not exact, but for these small-scale experiments it is acceptable to ignore these small variations in h. Future work we are conducting will investigate the heat transfer coefficient numerically. The resulting formula for the average B number is an exponential function of the mass loss rate of the fuel per area over constants minus 1.
  • Deemphasize
  • Representative test
  • Shaded region denotes overlap between regions 1 & 2. Test timelines have been adjusted so transition between stage I and II lie on the same point on the time scale.
  • Shaded region denotes overlap between regions 1 & 2. Test timelines have been adjusted so transition between stage I and II lie on the same point on the time scale.
  • Shaded region denotes overlap between regions 1 & 2. Test timelines have been adjusted so transition between stage I and II lie on the same point on the time scale.
  • Time averaged mass loss rates used to calculate B-number over entire region. This B-number is an ESTIMATE in the region, it has been shown by Rangwala et al. that the B-number does change during upward spread, but deviations on average are minimal and results over this region are roughly repeatable for multiple tests.
  • Shaded region denotes overlap between regions 1 & 2. Test timelines have been adjusted so transition between stage I and II lie on the same point on the time scale.
  • Shaded region denotes overlap between regions 1 & 2. Test timelines have been adjusted so transition between stage I and II lie on the same point on the time scale.
  • Shaded region denotes overlap between regions 1 & 2. Test timelines have been adjusted so transition between stage I and II lie on the same point on the time scale.
  • Transcript

    • 1. 1
    • 2. Collaboration Prof. Ali Rangwala Fire Protection Eng. WPI Todd Hetrick MS Student, WPI Small Scale Testing Kris Overholt M.S. Student, WPI Small-Scale Testing Cecilia Florit, French Exchange Student Heat Flux Measurements Jonathan Perricone Creative FPE Solutions, Inc. Industry Consultant Opening picture from Bruce Smith, AP, 6/20/07, Charleston furniture warehouse where 9 firefighters died 2
    • 3. Outline I. Introduction to Commodity Classification II. Theory III. Experimental Setup IV. Experimental Data and Results V. Conclusion VI. Future Work 3
    • 4. I. Introduction to Commodity Classification 4
    • 5. Current Commodity Classification Plastic Group A-C Warehouse Commodity Class I -IV Warehouse commodity (Carton, packaging, plastic) Classify grouped commodity into one of seven hazard groups (Based on HRR) Use large-scale test data to design fire protection system (NFPA 13) 5
    • 6. Recent Loss Case Example  2007 – Tupperware storage warehouse fire1  15,392 m2 warehouse burned for 24 hours – a total loss  Sprinklers met state & local requirements including NFPA 13 but the fire could not be extinguished once plastic became involved  2007 – Furniture warehouse fire kills 9 firefighters in Charleston, SC.2 Warehouse fires pose significant risks to occupants, local environments, and responding fire personnel (Photo: Georgetown Country Fire Dept. Hemingway, SC) 1The Problem with Big, NFPA Journal, March/April 2009 Career Fire Fighters Die in Rapid Fire Progression at Commercial Furniture Showroom – South Carolina, Fire Fatality Investigation Report, NIOSH. 2Nine 6
    • 7. Shortcomings of Current Methodology  Current classification uses ranking scheme (Model is based on commodity classification: Class I-IV, Group A-C Plastics) according to the free-burning heat-release rate (HRR)  Full-scale fire tests are preferred, but intermediate tests are more commonly used to assess Free-burning HRR & classification  Tests are not economically feasible  Free-burning HRR is scale dependent  Fundamental physics is glossed over  Tests have not been shown to be repeatable1  Classification by analogy presents a dangerous, yet common industry practice. (i.e. plastic totes in S.C. Tupperware facility) 1Golinveaux, “What We Don’t Know about Storage,” NFPA Presentation 7
    • 8. Sprinkler Warehouse Fire Modeling Zalosh, Industrial Fire Protection Engineering, pg 159 8
    • 9. Our Approach Current Research Small Scale Testing Commodity type classification Cone Calorimeter testing Intermediate Scale Testing (Proof of concept) Large/Full Scale Modeling (Proof of concept) Engineering Approach to Commodity Classification 9
    • 10. Our Area of Contribution Computer Fire Modeling Model potential rack setups & sprinkler interactions Modeling used to test warehouse designs costeffectively, based on ranking Commodity Classification Provide input parameters Add influence of large-scale Large-Scale Testing (Verification of both) Bench-scale tests determine nondimensional parameters (B) Rank commodities on fundamental scale used to design sprinkler system
    • 11. Material Flammability  Factors controlling flammability and fire hazard  Ignition  Fire Growth  Burning Intensity  Generation of Smoke and Toxic Compounds  Extinction/Suppression 11
    • 12. Commodities Used in Testing Class II Class III Class IV/Group B Group A Plastic Commodities Used in Reality 12
    • 13. II. Theory 13
    • 14. Commodity Fire: Stage 1 – Laminar Case Boundary layer B is a function of: 1. Corrugated board Buoyant Plume Plume Radiative + Convective Heat Transfer Commodity Combusting Plume Excess Pyrolyzate Pyrolysis Zone   mF Flame Radiative + Convective Heat Transfer XF flame XP • Flame height <25 cm • Unrealistic in fire situation Corrugated board • Study important because provides physical understanding of the problem (~ 20 to 25 cm Laminar Flame Propagation) Y-axis 14
    • 15. Stage 2 – Turbulent Case Buoyant Plume Boundary layer B is a function of: 1. Corrugated board 2. Commodity pyrolysis vapor Combusting Plume Flame Radiative + Convective Heat Transfer Excess Pyrolyzate Commodity   mF Pyrolysis Zone • Flame height >25 cm • Realistic fire situation • Cardboard still intact Plume Radiative + Convective Heat Transfer XP XF (Turbulent flame height >25 cm) flame Y-axis Corrugated board 15
    • 16. Stage 3 – Mixed Case • Flame height >25 cm • Realistic fire situation • Cardboard breaks 16
    • 17. Buoyant Plume Plume Radiative + Convective Heat Transfer Stage 3 – Mixed Case Combusting Plume B is a function of: 1. Corrugated board 2. Commodity pyrolysis vapor Excess 3. Commodity Pyrolyzate flame Flame Radiative + Convective Heat Transfer (from pool and wall fire) Commodity XF Solid/Liquid Pool fire Corrugated board  m  F • Flame height >25 cm • Realistic fire situation • Polystyrene leaks and starts pool fire Boundary layer Pyrolysis Zone   mF Commodity leakage Pyrolysis Zone Y-axis 17
    • 18. The B-number B  im petuses  i.e. heat of com bustion  for bu rning  resistances  i.e. heat of vaporization  to the process “Thermodynamic Driving Force” B (1   )(  H c YO ,  ) /  s  C p ,  (Tp  T ) χ = Fraction of radiation lost [-] ∆Hc = Heat of combustion [kJ/kg] YO,∞ = Mass fraction of oxygen in ambient [-] νs = Oxygen-fuel mass stoichiometric ratio [-] Cp,∞ = Specific heat of ambient air [kJ/kg-K] Tp = Pyrolysis temperature of the fuel Hg  Q B-number T∞ = Ambient temperature [K] L = Latent heat of vaporization [kJ/kg] ∆Hc = Heat of gasification [kJ/kg] Cp,f = Specific heat of the fuel [kJ/kg-K] Q = L + Cp,f(TB-TR) [kJ/kg] [1] Kanury, A. M. An Introduction to Combustion Phenomena. s.l. : Gordon & Breach Science Publishers, Inc, 1977. 18
    • 19. Reynolds Analogy Application to Warehouse Commodity Classification   mF  1 Flow Condition hT ln(1  B ) cg Material Properties 2 B-number 19
    • 20. Experimentally-Measured B •Solving for B and using Nu correlation for the heat-transfer coefficient:  ''  mf B  exp     0.13[G r Pr]1 / 3  g g  1   •Formula for average B-number based on measured rate of mass loss •Applies in regimes dominated by convective heat transfer, as found in many small-scale experiments. •Effective B-number derived by same formula with radiation included Kanury, A. M. An Introduction to Combustion Phenomena. Gordon & Breach Science Publishers, Inc, 1977. 20
    • 21. III. Experimental Setup 21
    • 22. Experimental Setup  Standard Group-A Plastic Commodity  Polystyrene cups in compartmented cardboard carton 22
    • 23. Picture of Experimental Setup WPI, Summer 2008 TC wires Heat flux sensors Back View Front View 23
    • 24. Measurement of Heat Flux Thin-Skin Calorimeter Combined heat flux from calorimeter (accounting for losses) q i  q c  q r  q sto  q c , st qi qc qr q c , st q sto American Society of Testing and Materials, Standard ASTM E 459-97 24
    • 25. IV. Experimental Results 25
    • 26. Commodity Test Results 30 s 92 s Front Face of Cardboard Burning Stage I 100 s 132 s 150 s Plateau PS Cups & Cardboard Burning Stage II Stage III 26
    • 27. Commodity Test Results Video of test 3 27
    • 28. 3 Stages of Burning 28
    • 29. Mass Lost 29
    • 30. Mass-Loss Rate Mass- Loss Rate Front face burning Plateau Region PS Cups 30
    • 31. Commodity Test Results Time-Varying B-number B = 1.8 B = 1.4 B = 1.9 31
    • 32. Heat Flux above the Commodity 32
    • 33. Thermocouple Measurements 33
    • 34. Commodity Test Results 34
    • 35. Commodity Test Results Summary of Stages Stage I Stage II Stage III Outer layer of commodity is ignited, producing rapid upward turbulent flame spread over the front face of a commodity. B is independent of polystyrene. Front layer of corrugated cardboard has burned to top, exposing inner region, which burns and then smolders. Polystyrene does not burn because of its higher ignition temperature. B 1.8 & m 0.83 g/s X 0.51 m f ,a vg & q f" 1.2 kW/m2 B 1.4 & m X f ,a vg 1.7 g/s & q f" Polystyrene ignites and a rapid increase B in the burning rate occurs. & m X f ,a vg & q f" 0.48m 0.38 kW/m2 1.9 2.2 g/s 0.65 m 2.4 kW/m2 35
    • 36. V. Conclusions 36
    • 37. Conclusions  A new method of hazard ranking is suggested in this study based on a nondimensional parameter: B  In a warehouse setting, where the burning rate is the dominant fire hazard, the effective B-number may appropriately classify the hazard of a grouped commodity  The B-number can be calculated using small-scale tests  Commodity Upward Spread via Mass Loss Rate  Cone Calorimeter Upward Spread via Mass Loss Rate (Overholt et al.)  Flame Standoff Distance (Rangwala et al.) 1. K.J. Overholt, M.J. Gollner, and A. Rangwala, "Characterizing Flammability of Corrugated Cardboard Using a Cone Calorimeter," Proceedings of the 6th U.S. National Combustion Meeting, 2009. 2. A.S. Rangwala, S.G. Buckley, and J.L. Torero, "Analysis of the constant B-number assumption while modeling flame spread," Combustion and Flame, vol. 152, 2008, pp. 401-414. 37
    • 38. Conclusions Increasing Costs Bench Scale Tests B-number Ys Small Scale Tests Large Scale Tests 38
    • 39. Conclusions  This parameter is nondimensional and in preliminary tests predictions from this parameter show good correlations to test data  The economic advantage of predicting full-scale performance with small-scale experiments may be an impetus for a significant evolution in the field of fire protection engineering. 39
    • 40. VI. Future Work 40
    • 41. Future Work  Flame height prediction (including influence of radiation)  Study possible correlations between B-number and other relevant flammability parameters (TRP, FPI, CHF, etc.)  Variation of Fuel/Commodity Volume/Mass Ratios  Incorporate suppression – minimum suppressant (water spray) can be incorporated in B-number via loss term 41
    • 42. Experimental setup to determine the water application rate ω g/cm2-s at different external heat fluxes flame Lab air supply commodity External heat flux nozzle Pan for water collection excess water collector regulator  Pressurized water supply z (cm) water ω Water application rate g/cm2s Load cell Load cell 42
    • 43. Acknowledgements  David LeBlanc at Tyco for generous donation of standard Group A storage commodity and sharing full scale test data conducted at UL labs by Tyco.  San Diego office of Schirmer Engineering for contributing start up funding at the beginning of the project.  WPI Lab Manager Randy Harris, Research Assistants: Cecelia Florit and Todd Hetrick, and helpful discussions with Jose Torero (University of Edinburgh) 43
    • 44. Questions? 44
    • 45. Initial Flame Height Predictions Important for early-stage fire prediction, including sprinkler activation. 45
    • 46. Material Flammability 46
    • 47. Define a Baseline Curve (Class II) & make all other Curves Parallel 47
    • 48. Flame Spread Theory  Many different theories of upward-spreading flames exist  Annamalai & Sibulkin X f ~ A( B  t ) 2  Saito, Quintiere, Williams X f ~ Ae t   f (T R P, X f  ''f ) / X p,q 1. Annamalai, K. and Sibulkin, M. Flame spread over combustible surfaces for laminar flow systems. Part I & II: Excess fuel and heat flux. 1979, Combust. Sci. Tech., vol. 19, pp. 167-183. 2. Saito, J.G. Quintiere, and F.A. Williams, "Upward Turbulent Flame Spread," Fire Safety Science-Proceedings of the First International Symposium, 1985, pp. 75-86. 48
    • 49.  Sibulkin & Kim Yo , YF vs x f  0.64( r / B ) 2 / 3 xp Convection Convection + Radiation Sibulkin and Kim, Comb. Sci. Tech. vol. 17, 1977 49
    • 50. Variation of Fuel/Commodity Volume/Mass Ratios  Experimental set up allows systematic control of two important parameters at small scale:  volume fuel / volume total  commodity weight / packing material weight 50
    • 51. Proposed Experimental Setup Hood Detailed front view in next slide Quartz tube External heat flux IR lamps Extension plate Flow seeding Aluminum tube Flow straightener (honey comb mesh) O2 + N2 mixture Load cell 51
    • 52. Noncombustible board 50 cm Thinskin Calorimeter TS (b) insulation 10 cm Side view camera 50 cm Corrugated cardboard TC Insulation Corrugated cardboard Plastic/ packing material grid 5cm Ignition tray Drip tray To load cell 52
    • 53. Suppression Modeling  Experimental set up allows variation of oxygen to determine B-number at limits of burning 53
    • 54. burning rate g/cm2s Top view of experimental apparatus Plastic grid Volume fraction = Ф 50 x 10 x 5 cm commodity Corrugated cardboard (outer cover) Zero water application (free burn) 1.5ω g/cm2s Critical mass flux (control) 5 cm ω g/cm2s 2ω g/cm2s 3ω g/cm2s z (cm)  Critical mass flux (extinction) Radiant heater Increasing rate of water application Water spray nozzle ω g/cm2s 0 d c b a External heat flux, kW/m2 Burning rate vs. external heat flux for various water application rates. Curves are hypothetical, based on experimental data reported by Magee and Reitz Magee, R.S. and R.D. Reitz, Extinguishment of radiation augmented plastic fires by water sprays. Proc. Combust. Inst. 15: p. 337-347. 54