Quantitative methods in fire safety engineering 5 U01620 7' Smoke management Smoke control

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Quantitative methods in fire safety engineering 5
(U01620) 7. Smoke management(Smoke control)

• Stephen Welch
• S.Welch_at_ed.ac.uk
• School of Engineering and Electronics
• University of Edinburgh

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Smoke management (L7-10)

• In Course Guide
• L7 Smoke control
• Reservoirs, entrainment, flow through vents and
  fans, simple calculations
• Analytical calculations
• L8 Principles of CFD
• Physical and numerical models
• L9,10 Smoke management (CFD lab)
• Design calculations

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Smoke control (L7)

• Introduction
• Fundamental phenomena
• Control strategies
• Passive
• Active
• Simple calculations
• Vents
• Smoke reservoirs

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Smoke management

• Smoke transport is a life safety issue
• Stairwells
• Lifts
• Atria

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Smoke movement

• Passive control
• Compartmentation
• Smoke barriers
• Smoke vents
• Smoke shafts
• Active control
• Fan airflows
• Pressurisation
• Extraction
• Sprinklers

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Building ventilation

• Smoke flows driven by
• Stack effect
• Temperature difference with outside environment
• Buoyancy
• Temperature of products
• Expansion
• Volume of products
• Wind
• External factors
• HVAC
• Pros/cons

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Stack effect

• Pressure difference equation
• ?P pressure difference
• Ks constant (3460 NK/m3)
• h distance above neutral plane
• For example
• h 30m
• TExternal 0oC
• TInternal 20oC
• ?P 25Pa

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Buoyancy

• Pressure difference equation
• For example
• h 3m
• TSurroundings 20oC
• TFire 700oC
• ?P 25Pa

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Expansion

• Volumetric flow rates
• Q volumetric flow rate m3/s
• T absolute temperature K
• For example
• QIn 1.5 m3/s
• TIn 20oC
• TOut 700oC
• QOut 5.0 m3/s

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Wind

• Wind pressure
• Cw pressure coefficient -
• ?External air density kg/m3
• V wind velocity m/s
• For example
• V 20 m/s
• TExternal 0oC
• ?P 50Pa

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HVAC

• HVAC
• Heating
• Ventilation
• Air Conditioning
• Pros and cons
• May aid detection
• Removes smoke
• Spreads smoke
• Supplies air to fire

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Passive measures

• Barriers
• Compartmentation
• Ceiling mounted
• Smoke vents
• Sprinkler interaction
• Smoke shafts
• BRE study

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Active measures

• Airflows
• Opposing smoke
• Pressure differences
• Prevent leakage

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Barriers

• Contain smoke using
• Smoke reservoirs
• Downstands
• Smoke/draft curtains

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Smoke vents

• Natural ventilation
• Flow is a function of density differences
• Mechanical ventilation
• Calculate size of fans

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Smoke shafts

• CFD analysis
• BRE report 79204

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Airflows

• Appropriate for large areas
• Overcome buoyant flow of smoke
• Backlayering
• Critical flow velocity (Thomas)
• Not much use for leakage flows

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Pressurisation

• Vent the fire floor
• Pressurise neighbouring floors
• Fans must be able to cope
• Large volumes of smoke
• Provisios
• No use if large leakage flows!
• Careful about door opening!

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Demonstration video

• Compartmented buildings
• Subdivided spaces
• Pressurisation
• External openings
• Large undivided spaces
• Smoke reservoirs/barriers

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Video clip 1

• Introduction No smoke with fire
• Smoke control strategies
• Life safety issues
• Toxic species
• Visibility issues

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Video clip 2

• Maintanence of safe escape routes
• Multi-compartented buildings
• Office buildings
• Large undivided volumes
• Shopping malls
• Atria
• Warehouses
• Transport facilities

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Video clip 2
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Video clip 3

• Test rig
• Fire compartment Shop fire
• Corridor Mall
• Stairwell Atrium

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Video clip 4

• Smoke release
• Egress hazard

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Video clip 5

• Compartmentation
• Partitions
• Good smoke seals
• Reliable

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Video clip 6

• Pressurisation
• Partitions
• Good smoke seals
• Reliable

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Video clip 7

• Pressurisation
• Lobby door open

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Video clip 8

• Open mall
• Shop fire
• Fire operates as a pump
• Draws smokey air back in at low level!

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Video clip 9

• Mall control measures
• Smoke barriers
• Smoke reservoirs
• Access to replacement air
• Extract system
• Sprinklers

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Video clip 10

• Mall control measures OFF
• NO smoke barriers
• NO smoke reservoirs
• NO access to replacement air
• NO extract system

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Video clip 11

• Summary
• Importance of a well-designed smoke control
  system!

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Calculation examples

• Natural ventilation
• Flow is a function of density differences
• Mechanical ventilation
• Calculate size of fans
• Plume entrainment expressions
• Centre fire, wall and corner plumes

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Example applications

• Mont Blanc tunnel fire
• HVAC effects
• Naturally ventilated building
• Stack effects
• Battersea gallery fires
• Entrainment onto a long gallery

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Mont Blanc tunnel fire

• Insufficient smoke extraction
• Management issue
• Confusion about fan directions

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BRE Environmental Building

• Natural ventilation
• Stack effect

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Battersea gallery fires

• Long shopping gallery

Atriumspace
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Battersea - Numerical parameters

• Compare mass flows
• excess flow total into gallery flow into
  fire plume
• Should equal zero!

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Battersea - Numerical grid

• More uniform outflow with finer grid

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Battersea - Numerical grid

• More uniform inflow with finer grid

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Battersea Boundary conditions
OPEN

• Ideal

BLOCKED
BLOCKED
BLOCKED
OPEN
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Battersea Fire location
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Battersea Long gallery
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Battersea Long gallery
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References (1)

• Klote, J.H. (2002) Smoke control, SFPE
  Handbook, 3rd-ed., pp. 4-274 to 4-291
• Milke, J.A. (2002) Smoke management in covered
  malls and atria, SFPE Handbook, 3rd-ed., pp
  4-292 to 4-310
• Cooper, L.Y. (2002) Smoke and heat venting,
  SFPE Handbook, 3rd-ed., pp 3-219 to 3-242
• Cooper, L.Y. (2002) Compartment fire-generated
  environment and smoke filling, SFPE Handbook,
  3rd-ed., pp 3-243 to 3-267

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References (2)

• BS5588
• Fire precautions in the design, construction and
  use of buildings
• BRE reports
• Harrison, R Miles S. (2002) Smoke shafts
  protecting fire shafts their performance and
  design, BRE report 79204
• http//www.bre.co.uk/filelibrary/Smoke_Ventilation
  .pdf
• CIBSE
• CIBSE Guide E Fire engineering chapter 7
• http//www.cibse.org/