Air & Smoke Movement in and
around High Rise buildings
(Air Tracks)
Mark Fishlock
2011
Understanding the dynamics of
air or smoke movement is
critical to safely working in
high rise buildings!!
Affecting Factors FRS Operations:
Wind Effect
Built-in ventilation systems -HVAC
Fire pressurisation systems
Fire shafts
Lift shafts (Piston affect)
Stack Effect
Combustion pressure
Compartmentation breeching
AND THEY CAN ALL COMBINE!!
Built in Ventilation systems
Common on newer buildings ie HVAC
Will have over-rides (either manual or automatic)
Built in smoke control and detection
Fire Pressurisation systems
Usefulness now brought into
doubt by BRE bd2410 (2005)
PPV ?
Fire fighting shafts
Requirement of Approval
Document B
BS 9999 / BS 5588 Part 5: 2004.
Naturally vented with AOV on roof
and shutters dampers on each
floor
Research FR 11.24
Lifts and Lift Shafts
Normal lift are not/can not be smoke tight
Lift shafts can have a micro-climate
Lift movement can create a noticeable air flow
Lift shafts
Piston Effect
Lift shafts
Piston Effect
Lift shafts
Piston Effect
Lift shafts
Piston Effect
Stack Effect
(or Chimney effect)
Combustion Pressure
High Rise are designed as
hermetically sealed buildings
BRE bd2410 (2005) shown pressure
increases in small mixed load fire
(plastic/carbonaceous domestic) @ 1.5 MW is
35 Pascal's .00035 Bar
Applying water increases it to 190 Pascal's
Pressurised protection of buildings
aims for 50 Pascal’s
WIND
• Wind is the flow of gases on a large scale.
• Measures in KPH (MPH) or Knots
• Strongest gust UK (1989) 146mph (low
level)
• Strongest sustained wind UK (1971)
73MPH
Wind
Wind: Behaviour
Winds can go from still state to Hurricane
force in under 5 minutes (RAF
Lossiemouth 1981)
Wind can change direction by up to 90
degrees in 20 mins (RN Boatcraft D3)
Wind: Pressure
• Wind blowing on an object creates
pressure
Wind: Pressure
• Wind blowing around an object can create
a reduced pressure
Wind: Pressure
The basic formula for wind pressure is:
P = .00256 V2
where
P = the wind pressure (pounds per square foot)
V = wind speed (miles per hour)
The force created by the wind on a structure is:
F = P × A × Cd
where
P = the wind pressure
A = the flat projected area of the structure (square feet)
Cd = drag coefficient for the shape of the structure’s members.
The coefficient for a flat surface is 2.0.
Wind: Pressure
SO for a failed window opening
4’ x 3’ and a wind of 40mph
P = .00256 V2 = 4 psi
18PSI = 128.6% increase
Effectively 27% O2 (Dalton law of partial pressure)
F = P × A × Cd = 98 pounds
Wind: Pressure
SO for a failed balcony patio door
7’ x 6’6” and a gust of 60mph
P = .00256 V2 = 9.2 psi
23.2PSI = 166% increase
Effectively 35% O2 (Dalton law of partial pressure)
F = P × A × Cd = 839
pounds
Wind Effect
Wind effect modelling
Wind and fire compartment
Primarily has two effects:
To create wind driven fire (an air pathway) or to
pressurise or depressurise a compartment.
Wind driven fires are FORCE VENTILATED
Pressurised fires are Oxygen rich
De-pressurised fires can be under ventilated
Wind driven fire
There are inlet AND outlet to compartments
creating an air path
Very high energy release rates 17Mw +
Fuel used quickly
Wind driven fire
If air pathway runs FROM the fire
compartment and travels inside building
then extremely hazardous to Ff’s
Wind driven fire
If air pathway runs FROM inside the building
and travels to the fire compartment then
less hazardous to Ff’s
C
WIND DIRECTION
C
WIND DIRECTION
C
Compartment pressurisation
There is no simple air path. (An in and out)
Fire compartment has opening(s) on same
face
Fire is ventilated and fed from same window
CONTAIN &
Let it burn
out???
Compartment pressurisation
Wind blowing onto opening (+ Pressure)
Smoke bleeding into corridor
Fire could be well ventilated
Very dangerous to enter !!
Compartment pressurisation
Wind blowing across or away from opening
(-Pressure)
Air being sucked from corridor.
Ensure its not a developing
Backdraft: Confirm its vented
Safer but still poses serious risk to enter
Unventilated compartment.
MAY BECOME VENTILATED AT ANY TIME
(DOOR OPENING/WINDOW FAILIURE).
May be sucking or blowing depending of
phase of fire.
Risk of sudden escalation or Backdraft upon
Ff entry.
May be impossible to externally ventilate.
Dangerous to enter
Wind Effect
sometimes called the “Blow torch effect” ??
Has the greatest bearing on abnormal fire
development in High Rise Incidents
Window failure or Fire-fighters ventilating
create direct air tracts
Fire energy is rated as its energy release over a period of
time (MW). One of the primary effectors of this time span is
availability of O2 and wind can greatly enhance this supply
SAFETY
•
FIREFIGHTERS WORKING IN THE BUILDING CHANGE ITS DYNAMICS
•
KNOW THE BUILDING LAYOUT AND ITS FIXED SYSTEM
•
KNOW ITS VENTILATION SYSTEM AND HOW IT WORKS
•
KNOW THE STATE OF THE HOUSEKEEPING
•
ALWAYS BE AWARE OF UNPREDICTED SMOKE TRAVEL (Safety officers)
•
MINIMISE USE OF LIFTS
•
STRIVE TO MAINTAIN COMPARTMENTATION (especially to stairwells)
•
BE AWARE THAT WEATHER (WIND & TEMP) WILL HAVE A SERIOUS EFFECT
ON AIR/SMOKE TRAVEL
THANK YOU
Any Questions?