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Fire Behaviour. Ventilation. Aim. To provide students with information to give them an understanding of the behaviour of fire . Learning Outcomes At the end of the session students will be able to:.

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fire behaviour

Fire Behaviour

Ventilation

slide2
Aim

To provide students with information

to give them an understanding of the behaviour of fire.

learning outcomes at the end of the session students will be able to
Learning OutcomesAt the end of the session students will be able to:
  • Describe the effects of forced and natural ventilation on the development of a range of fires.
ventilation
Ventilation

Defined as;

The removal of heated air, smoke and other airborne contaminants from a structure, and their replacement with a supply of fresher air.

ventilation1
Ventilation
  • Self ventilation
  • Automatic ventilation
  • Tactical ventilation

Before fire control

After control but before fire extinction

After fire extinction.

smoke
Smoke
  • Mixture of fine particles, water droplets, other liquids and gases given off by the burning material
  • Usually toxic
  • Can be hot
  • Can burn.
value of ventilation
Value of ventilation
  • Assist escape
  • Aid rescue operations
  • Improve firefighters’ safety
  • Earlier entry
  • Reduce damage
  • Restrict fire spread.
slide8

The effect

of a broken

window.

when to use ventilation
When to use ventilation
  • A tactic to be used by the Officer in charge
  • Vertical ventilation
  • Horizontal ventilation
  • Defensively
  • Offensively.
slide10

Smoke layer

in an atrium.

vertical ventilation
Vertical ventilation

Advantages;

  • Minimize risk of backdraught
  • Minimize fire spread
  • Provide rapid smoke clearance

Disadvantages;

  • Need to work to make the vent from above the fire.
slide12

The stack

effect.

making vents
Making vents
  • Use any inbuilt systems
  • Use roof lights / windows
  • Lift slates or tiles
  • Work from ladder or aerial appliance
  • Work from below the vent.
slide16

Vertical ventilation(1)

Making a

roof vent.

slide17

Vertical ventilation(2)

Clearing the escape route and improving access for firefighters.

horizontal ventilation
Horizontal ventilation
  • Most used type of ventilation
  • Use where vertical not suitable
  • Open exhaust vent on downwind side
  • Inlet vent on upwind side
  • Only open any vent as part of the ventilation plan.
making vents1
Making vents
  • Open windows where possible
  • Cover exit vents with jets
  • Ensure no-one working above vent
  • Fresh air may result in backdraught, withdraw all personnel from danger area
  • Glass may travel long distances.
slide23

Inlet and outlet vents - Same window

Viewed

from

inside

the

room.

slide24

Inlet and

outlet vents

Different

windows.

slide25

Making a vent

Working from below and to the side.

forced ventilation advantages
Forced ventilation - Advantages
  • Smoke removed rapidly
  • Makes horizontal ventilation more effective
  • Reduces the need for vertical ventilation
  • Less affected by wind conditions
  • More controllable.
slide28

PPV

Wide opening

Extra air pressure needed.

forced ventilation disadvantages
Forced ventilation - Disadvantages
  • It requires mechanical device
  • Can increase the intensity of the fire
  • If large compartment - large fan or several smaller ones needed
  • Time to set up
  • When used defensively it means a room by room approach.
main techniques
Main techniques
  • Positive pressure ventilation (PPV)
  • Negative pressure ventilation (NPV)
  • Heating, ventilation and air conditioning systems
  • Powered exhaust systems.
defensive ppv advantages
Defensive PPV - Advantages
  • Rapid removal of gases
  • Cooler and easier working conditions
  • Hot spots seen easier - have hose line to deal with.
ppv sequence of operations
PPV sequence of operations
  • Isolate unaffected areas
  • Position the fan
  • Crew members to open exhaust vent
  • Start the fan
  • Check smoke taking expected route
  • Monitor until fan stopped.
offensive ppv
Offensive PPV
  • Used before the fire is out
  • Part of firefighting tactics
  • If not used effectively can cause fire spread.
summary
Summary
  • Note and use prevailing wind
  • Consider and use correct tactic
  • Do firefighters need to withdraw
  • Outlet first - high and downwind
  • Cover outlet vents with charged hoselines
  • Start inlet vent
  • Communications
  • Monitor.
confirmation assessments will be based on this lesson and the corresponding study note
ConfirmationAssessments will be based on this lesson and the corresponding study note

Learning Outcomes

  • Describe the effects of forced and natural ventilation on the development of a range of fires.