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Smoke Extraction Design
1. SMOKE EXTRACTION IN BUILDINGS Presented by VysakhManohar GATE-Chennai Tuesday, June 07, 2011 1 Smoke Extraction In Buildings
2. INTRODUCTION Effective smoke extraction in buildings has been one of the inevitable considerations in the building design as the number of buildings and the concern of people about the regular fire accidents in buildings are increasing much. This presentation includes a brief description about the different design consideration principles and methods to be taken care for the effective heat extraction in different types of buildings . Tuesday, June 07, 2011 2 Smoke Extraction In Buildings
3. What is smoke? By product of combustion or pyrolysis . Mixture of liquid , solid particulate matter and gaseous products. It is a cocktail of carbon monoxide, carbon dioxide ,HCL and HCN Tuesday, June 07, 2011 3 Smoke Extraction In Buildings
4. FIRE TIME LINE 00.00- Household is asleep 00.30- Fire ignites and grows in downstairs 1.04- Fire spreads and smoke begins to fill In the room. 1.35- Smoke layer descends rapidly and temperature exceeds 88 deg 1.50 – Smoke detector sounds an alarm. 2.30- Temperature becomes 205 deg 2.48- smoke pours into other rooms Tuesday, June 07, 2011 4 Smoke Extraction In Buildings
5. 3.03-Temperature in the room becomes more than 260 deg 3.20-upstairs,corridors,all the rooms are filled with smoke 3.41- flashover occurs , temperature becomes 760 deg 3.50 –Two minutes after the alarm sound, only the second exit will be the way out 4.33- Flames will be apparent from the outside , the first evidence of fire visible from outside. Tuesday, June 07, 2011 5 Smoke Extraction In Buildings
6. Will follow similar scenario in other location The variations will be based on 1-fire size 2-size of building 3-flammable materials in the building 4-alarm systems 5-safety measures available Tuesday, June 07, 2011 6 Smoke Extraction In Buildings
7. GETTING THE DESIGN RIGHT FROM THE BEGINNING Factors affected Design fire size Stack and wind effects Temperature effect of fire HVAC and ventilation systems Climate Expansion of ducts
8. COMMON SAFETY METHODS Use sprinklers Smoke curtains HVAC system incorporating F & S dampers. Extraction fans Alarm systems Pressurisation Tuesday, June 07, 2011 8 Smoke Extraction In Buildings
9. HAZARDS OF DANGEROUS SMOKE Impair visibility Coughing,nausea,vomiting Generation of high temperature Irritation and respiratory problems Bronchospasms and hypoxia Inflict death if it contains dangerous gases Even low concentration of CO can cause diminished coordination and increased disorientation Amount of oxygen is reduced- suffocation Exacerbate corrosive nature of HCL Tuesday, June 07, 2011 9 Smoke Extraction In Buildings
10. Smoke Pathways Air and service ducts connecting floors HVAC/ventilation systems Extract duct systems Gaps between wall and floor constructions Stairwells Lift shafts Tuesday, June 07, 2011 10 Smoke Extraction In Buildings
11. Need of smoke extraction for life safety and reducing property loss for fire fighter access To clear smoke after a fire –smoke purging Tuesday, June 07, 2011 11 Smoke Extraction In Buildings
12. Smoke extraction design objectives Effective protection of building occupants by maintaining tenable conditions on egress systems. Reliable and functional fire fighting controls used by firefighters to increase visibility and reduce heat exposure. Tuesday, June 07, 2011 12 Smoke Extraction In Buildings
13. Make up air routes External doors Louvers in wall or roof Central air plant configured to supply air From adjacent unaffected areas ->avoid mixing of smoke and make up air ->extraction points-avoid creation of “hole” Tuesday, June 07, 2011 13 Smoke Extraction In Buildings
14. Smoke Production and movement Amount of smoke produced is dependent on size of fire Path through which it goes Plume height Tuesday, June 07, 2011 14 Smoke Extraction In Buildings
15. Fundamental design factors Design fire size Smoke layer depth Identify smoke reservoirs Calculate smoke volume and temperature Minimum number of extract points Vent or fan size and fan temperature rating Inlet air Duct work Tuesday, June 07, 2011 15 Smoke Extraction In Buildings
16. Design fire size Fire starts small and becomes large Vent area=2.5 % of floor area-otherwise mechanical 6 ac/hour is used often Design fire size is greatly dependent on building contents. Based on the largest fire source Cannot surely withstand post flash over conditions Tuesday, June 07, 2011 16 Smoke Extraction In Buildings
17. Heat output of fire National bureau of standards in USA Based on time- safe escape time brigade response time Tuesday, June 07, 2011 17 Smoke Extraction In Buildings
18. Acceptable smoke layer depth Smoke layer base should be above the people 2.5 m-single storey 3 m - upper storey of 2 storey Tuesday, June 07, 2011 18 Smoke Extraction In Buildings
19. Smoke reservoirs If smoke is held in a too large reservoir-lose buoyancy 2000 m^2 - natural extraction 2600 m^2 -powered extraction Smoke curtains can be used to reduce horizontal spread Tuesday, June 07, 2011 19 Smoke Extraction In Buildings
21. Smoke- volume, mass flow rate and temperature T=Q/m cp 1/3 is gained by building structure Tuesday, June 07, 2011 21 Smoke Extraction In Buildings
22. Minimum no of extract points Mcr is not exceeded No smoke need to travel more than 30 m to extraction point Tuesday, June 07, 2011 22 Smoke Extraction In Buildings
23. Inlet air To make up the smoky gases At least 1.5m beneath smoke layer If natural inlet is given Inlets should be away from the outlets Inlet velocity should be less than 3 m/s Tuesday, June 07, 2011 23 Smoke Extraction In Buildings
25. Ductwork Must be able to withstand anticipated temp- From the formula HVCA specification DW144 For sprinkled buildings To limit fire spread -fire protection of steel ducts -construct from proprietary material - use fire and smoke dampers Tuesday, June 07, 2011 25 Smoke Extraction In Buildings
26. Fire resisting requirement of ductwork To prevent fire inside one duct to breaking out to other compartment. To prevent fire from outside enter into duct and then enter another fire compartment To prevent fire from outside enter into duct and the break out into other compartment Tuesday, June 07, 2011 26 Smoke Extraction In Buildings
29. Performance criteria for fire resisting duct work Stability Integrity Insulation Tuesday, June 07, 2011 29 Smoke Extraction In Buildings
30. Other things to be noted Duct must be able to retain at least 75% of its size after the smoke removal. Sound or thermal insulation should not be raised to ignition temperature. Fire stopping seals should be used Buckling or collapse. Tuesday, June 07, 2011 30 Smoke Extraction In Buildings
31. Construction of fire resisting smoke extract ducts a) galvanized steel duct with additional protection b) fire resisting boards(eg . calcium silicate) c)proprietary fire resistant ductwork eg: PROMATECT-H Tuesday, June 07, 2011 31 Smoke Extraction In Buildings
32. Protection of duct with fire resisting board Tuesday, June 07, 2011 32 Smoke Extraction In Buildings
38. Design guide for different building types Multi-storey office and similar buildings Warehouse Underground car parks/basement Atrium buildings Shopping malls Tuesday, June 07, 2011 38 Smoke Extraction In Buildings
39. Multi storey office and similar buildings Phased evacuation Evacuation time will be varying Smoke should not spread 1, smoke extraction 2, pressurisation The recirculation of air in normal hvac system is prevented by dampers Tuesday, June 07, 2011 39 Smoke Extraction In Buildings
41. Important design considerations The system is not for providing a smoke free layer Both supply and extract ducts should be having fire resistance equal to that of the floors /walls Exhaust fans should be able to run at the highest expected temperature Tuesday, June 07, 2011 41 Smoke Extraction In Buildings
42. The power supply to the system must be duplicated The power and instrumentation cabling should be of fire resistant type Smoke and fire dampers should be having suitable specification-UL555s class-I,II,III,IV in high storey buildings-wind pressure Tuesday, June 07, 2011 42 Smoke Extraction In Buildings
48. Enclosures are 2 types 1- fire resisting enclosure-fire resisting glazing 2- enclosure of limited combustibility but not fire resisting Tuesday, June 07, 2011 48 Smoke Extraction In Buildings
52. Extract from single shops Smoke is prevented to enter to mall area Very large fans are not required But complex and costly Shops must be sprinkled Combined duct work is used to reduce cost Tuesday, June 07, 2011 52 Smoke Extraction In Buildings
53. Extract from mall Tuesday, June 07, 2011 53 Smoke Extraction In Buildings
55. Limitations With high atriums there is a cut off point of mass flow rate of 150 to 250 kg/s-economically impractical. Temperature stratification Cooling effect Tuesday, June 07, 2011 55 Smoke Extraction In Buildings
56. Fire,smoke and building code agencies Industrial risk insurers (IRI) Southern building code congress inc(SBCCI) National fire protection association(NFPA) Underwriters Laboratories(UL) British standards(BS) National Building Standards(NBS) Tuesday, June 07, 2011 56 Smoke Extraction In Buildings
57. CONCLUSION By following discriminative approaches and methods needed for different types of buildings and constructions provided by the different approved agencies ,the threat from fire and smoke can be reduced to a considerable level. Tuesday, June 07, 2011 Smoke Extraction In Buildings 57
58. References Promat International Ltd National Fire protection Association,Guide for smoke and heat venting,NFPA-204 M BS 5839: Fire Protection and alarm systems in buildings,Part1 2002 Underwriters Laboratories,Leakage rated dampers for use in smoke in control systems,UL555 S Tuesday, June 07, 2011 58 Smoke Extraction In Buildings
59. THANKING YOU ALL…….. Tuesday, June 07, 2011 59 Smoke Extraction In Buildings
Notas del editor
Toxicity depends upon the material which is under fire.Pyrolysis- Thermochemicaldecomposition of organics without oxygen.
The given time line is for a 2 storey house –this is just a time line representing the different steps from fire commence to the fire fighter arrivalNFPA-types of firesA,-from paper, cloth etcB,-from gasoline ..C,-electrical equipmentsD,-from metalsK- kitchen containing natural oilsOther classifications are also there.Borosilicate glass-fire resistant glazing Fire resistant wall-gypsum board partitions, reinforced concrete
->not practical to design based on any fire size->smoke developed depends on room size,firesize,material combustibility->smoke extraction rate –fan size,temperature rating for fans,incoming air resistance of make up air.->extract fans are the principal mechanical means of smoke and fume removal->vent size,escapetime,sprinklers,fans,fire and smoke dampers,smoke curtains,->stack effect-movement of air due to the buoyancy,temperature effect and pressure difference-chimney effect-dP=Cah(1/T0-1/T1)-during heating season,the hot air in the room rise high,and make the cold air enter through the lower openings
- Sprinkler-each closed head sprinkler is held closed by heat sensitive glass bulb or two part metal link held together with fusible alloy -in a standard wet pipe sprinkler system,each sprinklers operate indipendantly- Sprinklers will be in to the action 1-4 minutes,for fire fighters it will requre minimum 5 minutes to reach and 10 minutes to fix the arrangemets.
-low amount of oxygen-affect fire fighting-corrosive nature of hcl-attack structural steel and rcc-weakens the construction-treatment-avail oxygen
Reduce property loss
Extreme care for avoiding mixingHole-if smoke is tried to be extracted through 1 opening only ,then a hole like shape occurs just below the extraction point and thorugh this more fresh air than the smoke will be lostMany extraction points-evenly placed
-don’t push or suck-just carry smoke from the room to outside area.
-all fire starts small and grow larger-difficult to select a smoke extraction system for all fire sizes-
-fire cant be represented by a single source-frequent strategy is to relate design fire size to sprinkler operation-normal combustibles rarely exceeds .5MW/m2-sprinklers are placed according to max fire size area(below)-
Smoke production depends on fire size and plume heightFor fire fighter access only-2 and 2.5 respectivelyProperty protectionPrevents to adjacent areasSmoke curtains
Half for the multi storey buildingPermanent smoke curtains- glazed smoke screenRetractable smoke screen-drops when alarm operatesMust extend below the base of smoke layer
300 deg is usually expectedBut will be less if sprinklers are thereSpecific heat of smoke=1kj/kg
When smoke being extracted from 2 or more interconnected storeys ,the highest smoke temperature will occur with fire on highest storey
If natural inlet is given-like doors and windows , should open automatically when extract system starts workingIf not possible to maintain below 1.5 m- use smoke curtains , horizontal shields.Curtains or shafts are used not to make mix of fresh air with the smoke
Standard galvanized steel ductwork can withstand up to 400 deg provided no aluminium rivets and combustible seals-dampers should be within the thicknes-the fsd should be operated not only with temp but also with smoke detectionHVCA-heating and ventilation contractors association
Most cases fire resistance to internal and external fire are required-but some cases its not required.Fire resistance of the duct =fire resistance of wall through which it passes. But in some cases eg: here the possibility of getting any fire in the corridor is very less ,so the duct at that place need not be fire resistant to external fire.
BS 476.part 24:1987-another requirement is that duct must be able to retain 75% of its cs area throughout the fireStabilitySaid to have violated stability criteria,if a frdw exposed to external fire (duct A) collapses in furnaceSaid to have violated s .if either length of duct A or duct B exposed to internal and external fire within furnace collapses outside the furnaceIntegrityCracks ,holes or other types of openings through which smoke leaksInsulationWhen temperature rise above initial temperature on the unexposed surface of duct exceeds 1, 140 deg as an avg value 2, 180 deg as maximum valueThen it fails to keep its insulation property
Buckling-when smoke goes –expansion occur
HangersSteel hangers with more than 2000mm of length must be insulated with fire resisting material to resisting expansion and catastrophic failure
Evacuation time is >60 minSmoke must not spreadNormal hvac system can be modified to smoke extract
Here the main function of smoke extraction system is property protection and fire fighting assistance
Design fire size is based on 1 carIf sprinkled-1.5 MwUnsprinkled-3 MwGenerally both inlets and outlets are ductedInlets should be at low level and outlet at high levelMin 10 ach If duct 500mm there is no fire chance –insulation requirement may be given with some flexibility.
Separated from all other floors except at the base
1,if it provides both integrity and insulation-no other action is needed2, if provides only integrity, fire protection systems should be designed-temp should not go beyond -300 deg, sprinklersNon combustible non fire resistant-Building should be sprinkled,300 deg or failure temperature of glass whichever is lower, negative atrium pressure can be given to avoid the movement of smoke to floors
If the people are acquaintant with the then normal single stage evacuation can be provided,If not aquaintant ,then smoke base should not come beyond the enclosure for a specific time
Sprinkler systems must be providedMust be designed in a way that no untenable should occur ,atleast for the expected evacuation timeWaiting areas-which is pressurised-can be used for other purposes when there is no fire, provided there should be having enough space for people to enter to that place when fire happens.
Mall area are the escape areas
Not effective for more than 2 stories
If area of shop greater than 3000m sq, and 1000 m sq,then independent extraction is better
Temp stratification-happens if the temp of smoke just below the ceiling is more hotter than the floor smoke –it happens in summer-due to this the smoke will not be able to reach fastly to the top where the detectors are placed. so this time lag will create a situation of spreading of smoke to more areas before the fire alarm starts.Cooling effect- is the process of mixing of smoke with more fresh air and settling down by the loss of buoyancy when the height or area of reservoir is more than that of allowed value.
-deals with life safety-design and performance standards-IRI-insures properties based on information manual deals with belt driven smoke exhaust fans-sbcci-us +other foreign countries-building codes-NFPA-3 functional categories 1-improves the methods of fire protection ,elctrical safety and other safeties 2-obtains and circulates information on these subjects 3-secures cooperation of its members and public in establishing proper safeguards against loss of life and -National building code of India(NBC)-2005-London District Surveyors Association(LDSA)