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Workshop at Indian Institute of Science 9-13 August, 2010 Bangalore India Fire Safety Engineering & Structures in Fire Organisers:CS Manohar and Ananth.

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Presentation on theme: "Workshop at Indian Institute of Science 9-13 August, 2010 Bangalore India Fire Safety Engineering & Structures in Fire Organisers:CS Manohar and Ananth."— Presentation transcript:

1 Workshop at Indian Institute of Science 9-13 August, 2010 Bangalore India Fire Safety Engineering & Structures in Fire Organisers:CS Manohar and Ananth Ramaswamy Indian Institute of Science Speakers:Jose Torero, Asif Usmani and Martin Gillie The University of Edinburgh Funding and Sponsorship: Fire Safety Engineering Methods Session JT10

2 Suppression  Water Suppression

3 Should Active Suppression be Used?  Why can the decision of not using active suppression be made?  Cost  Environmental Concerns  Damage of Property  Incompatibility with the purpose of the building  Fire is a complex problem that requires a “cost/benefit” analysis

4 The Problem

5 Fire Control and Suppression

6 Fire Prevention  Early Detection  Smoke Detectors, CO Detectors, IR Detectors, UV Detectors, Motion Detectors  Effective but not infallible  Proper Material Selection  Low Flammability Materials - not always possible to use – many times are not cost effective  Fuels – aircraft, cars, ships  Plastics – everyday use  Metals – flammable under extreme conditions – i.e. turbine engines

7 Fire Retardants  Additives used to reduce the “flammability” of a material  Halogen-based retarded materials – i.e. PVC  Inhibit gas phase combustion chemistry  Produce contaminants during a fire  Produce contaminants during recycling  Phosphorous based charring materials  Formation of chars – reduces flow of fuel to flame  Produce contaminants during fire  Contaminate suppression water  Lead to smolder fires – very difficult to detect and suppress  New environmentally friendly technologies  Based on carbon fibers and nano-composites – still under development

8 Fire Suppression  Water Sprinklers  Water Mists  Gaseous Agents  Foams  Dry Chemicals

9 Mechanisms of Flame Suppression  Thermal Sink  Reduces the Mass Transfer number  Reduces the flame temperature  Reduces the Damk ö hler Number  Oxygen Displacement  Reduces the Mass Transfer number  Reduces the flame temperature  Reduces the Damk ö hler Number  Chemical Inhibition  Affects the Chemistry  Reduces the Damk ö hler Number

10 Water Based Systems  Work on the basis of energy removal and oxygen displacement  Sprinkler Systems  Simple systems, Low Maintenance, Low Cost  Work by wetting the fuel surrounding the fire  Not a suppression technique, more a control system  Therefore: High Water discharge ~ 0.25 lt/m 2 s  Water Mists  Water Discharge ~ lt/m 2 s  High penetration due high momentum injection  Everything else is more complex due to high pressure

11 Foams  Very limited applications  liquid fuels  protection of structures  Need to produce a film that spreads across the fuel lead to complex chemical composition generally based on Fluorine and Iodide  i.e AFFF Foams

12 Dry Chemicals  Generally can only be discharged once  Reduced penetration  Act as mostly as thermal sinks – Less Efficient  Chemical suppression only present if dry chemical is “halogen” based  Generally – highly corrosive

13 Gaseous Agents  High effectiveness  Chemically active – i.e. Halons  Less effective  Chemically inactive – extinction by reduction of oxygen concentration or thermal sink  Advantages  No clean-up necessary, easy storage, low weight/volume ratio, high penetration (total flooding), electrically non-conductive, mostly non-corrosive, etc., etc., etc.

14 Mechanisms of Flame Suppression  Most effective is Chemical Inhibition  Halons are extremely effective at attacking “chain branching” reactions in combustion processes

15 Halons  Nomenclature C F Cl Br I Halon CF 3 Br Halon CH 2 ClBr Halon C 2 F 4 Br 2

16 Why is Halon so Effective? Combustion of Methane Halon Heat

17 Why is Halon an Environmental Problem?

18 Consequences  The Montreal protocol banned the manufacturing and use of Halon 1301  No other alternative has proven to be as effective as Halon 1301 Fact  Halon is present in 98% of commercial aircraft  In 2000 there where 178 Halon discharges in commercial aircraft  It has been estimated that of those 178 discharges more than 100 would have resulted in generalized fires that would have crashed- landed the aircraft

19 Conclusion  Is it justifiable to ban the use of Halon 1301 for fire applications?  Is environmental protection a sufficient “cost” to overwhelm the “benefits” of Halon 1301? Fact  The ozone depleting potential of all fire related Halon 1301 deployments in a year is equivalent to that of the emissions of 132 cars!

20 Water Suppression-Sprinkler Systems  Water suppression is the most commonly used mechanism of active fire control in structures  Among the different water suppression systems, sprinklers are by far the most commonly used  Some design considerations will be presented

21 Effect of Sprinklers (I)

22 Effect of Sprinklers (II)  Increase the time to “Flash-Over”  Decrease toxic product concentrations, CO, HCN, etc.  Decrease the room temperature  Push the hot layer down slowing fire growth Push the hot layer down slowing fire growth  Increase visibility “soot” dissolves in water

23 Effect of Sprinklers (III)  “sprinklers” are NOT designed to Extinguish the fire  “sprinklers” are designed to Increase the time available to extinguish the fire

24 Tg,ugTg,ug M, c p, A s Fire Detector Activation  A first order analysis for predicting fire detector activation based on convective heating and a lumped capacity analysis  Principles of the DETAC Model

25 Background  Alpert - “Calculation of response time of ceiling- mounted fire detectors” - quasi-steady fires  Heskestad & Smith - Development of plunge test & RTI concepts  Heskestad & Delichatsios - “Initial convective flow in fire” - t-squared fires  NFPA 72E App. C  Evans & Stroup - DETACT models  Heskestad & Bill - Conductance factor added  SFPE Task Group - Review bases of DETACT

26 Bases  Heat balance at detector  Convective heating only  Lumped capacity analysis  Negligible losses ( basic model )

27  Predictive equation for temperature rise  Definition of detector time constant  Time constant not really constant Solution

28 Response Time Index  For cylinders in cross flow  Implications  Definition of RTI  Predictive equation

29 RTI relationships  Lower RTI  Faster response  Lower m or c p  Lower RTI  Higher h c or A s  Lower RTI  In limit, as RTI  0, T d  T g

30 RTI determination (1)  Plunge test  T g = constant  u g = constant  T act = known  Analytical solution

31 Plunge test

32 DETACT formulation  Euler equation for T d  Substitute equation for dT d /dt  Evaluation requires RTI, T g (t) and u g (t)

33 Detector activation  Fixed temperature devices  Rate-of-rise devices  Typical value of dT act /dt: 8.3ºC (15 ºF) /min

34 Gas parameters - T g, u g  Alpert correlation (unconfined ceiling jet) TemperatureVelocity

35 General Information  Based on NFPA 13 – National Fire Protection Association Codes  Sprinkler selection is based on the rapidity with which the thermal sensor operates - RTI

36 Sprinkler System Design  The design of a sprinkler system consists of the following steps:  Identification of the fuel load  Identification of the use of the building  Calculation of the sprinkler density  Determination of sprinkler placement  Definition of the different components of the system  Sprinklers  Pipes  Pumps  Valves  Establishment of maintenance procedures

37 Procedures  Classification of occupancy or  Classification of the fuel load  Determination of quantity of water needed  Determination of sprinkler type  Water flow  Activation temperature and RTI

38 Occupancy  Light risk  Moderate risk  High risk  Special Occupancy:  I.e. Historic documents, film, art, nuclear power plants, airports, etc.

39 Fuel Load  Class I: Non combustible materials stocked on “wood pallets” or in single thickness cardboard boxes covered with a plastic film cover.  Class II: Non combustible materials stocked on “wood pallets” or in multiple thickness cardboard boxes covered with a plastic film cover.  Class III: Wood products, paper, natural fibers, C-Type plastics.  Class IV: A Type Plastics (between 5-15% of the weight) and plastics of types B or C for the rest.

40 Liquids  Flammable Liquid (Class I): “Flash Point” (T f ) lower than 37.8 o C  Subdivided in:  Class IA:T f <22.8 o C (ambient temperature), T e <37.8 o C  Class IB:T f 37.8 o C  Class IC: 22.8 o C 93 o C  T e =Boiling temperature

41 Plastics  Type A: ie. Polyethylene, polystyrene, polypropylene, PVC, etc.  Type B: ie. Fluoroplastics, natural rubber, nylon, silicone  Type C: ie. Melamine, fenolites, urea

42 Water Density (Q d )

43 Flow Through a Sprinkler: “K” Factor Factor-K Nominal gpm/(psi) 1/2 Factor-K Range gpm/(psi) 1/2 Factor-K Range dm 3 /min/ (kPa) 1/2 % Over Nominal Discharge with K-5.6 Thread /2 in. NPT /2 in. NPT /2 in. NPT /2 in. NPT in. NPT in. NPT

44 Sprinkler Density  Sprinklers per m 2 : “n”  Total number of sprinklers: “N” N=n.A

45 Activation Temperature  The decision is based on the fuel load/occupancy

46 Distribution and Installation  Sprinklers are distributed through the protected space homogeneously  The water pressure will be established by the code and the sprinkler density  Water pumps are many times necessary  The total flow is established on the basis of the number of sprinklers

47 Installation Details  NFPA 13 gives details on how to place sprinkler heads S T-A STST SASA S SPSP SCSC SCSC

48 Special Sprinkler Types  Regular Sprinklers: Direct 40-60% of the water towards the fire  ESFR-Early suppression fast response  Extended Coverage  Large Drop Sprinkler  Open Sprinklers (no actuator)  Quick Response (QR)  Quick Response Early Suppression (QRES)  Residential Sprinklers (fast response sprinklers rated for residential use), etc., etc., etc.,

49 Installation Types  Wet Pipe System-Standard, water filled pipes with sensor at the sprinkler head  Circulating-Closed Loop System-combined wet pipe sprinkler system with HVAC system  Dry Pipe System-Pressurized air/nitrogen, its release opens the water valve-for non-heated environments  Combined-Dry Pipe Pre-reaction System-thermal sensor + fire detection system, for fast or screened response  Deluge System-Dry pipes with a fire sensor, no thermal sensor (open sprinklers)

50 Limitations of this approach  Effectiveness of the system is base on empirical data for a reduced number of configurations  No quantitative estimate of the “probability of success” can be stated  No quantitative estimate of the potential “outcome” can be specified  This approach is being phased-out by performance design….

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