Basic Ventilation Flashcards
Ventilation defintion
• The planned methodical and systematic removal of pressure, heat, smoke, toxic gases, and flame from an area and with the replacement of these products with cooler, fresh air.
Reasons for ventilation
a. Removal of smoke, heat, and fire gases
b. Improved visibility (locate victims faster)
c. Reduced potential harm to victims
d. Reduced stress for firefighters
e. Assists with control and extinguishment
i. Localizes fire
ii. Removes trapped heat and smoke which helps perpetuate fire
iii. Aids in property conservation
How does ventilation work?
a. Heat and smoke rise and create pressure
b. They take the path of least resistance
c. Openings release pressure
i. Pulls heat and smoke and fire into the opening
ii. Creates a chimney when there wasn’t one
d. Double edged sword
i. Will eventually make fire worse (chimney)
ii. Poorly placed ventilation openings will pull fire to them
Fuel limited fires facts
i. Relatively quick growth
ii. Once they hit peak after flashover, they start to peter out due to lack of fuel
Ventilation limited fires
i. A fire in which heat release rate or growth is controlled by the amount of air available to the fire
ii. The fire tries to grow exponentially, but the lack of oxygen makes it stifle itself. Then Mr. Freelancer breaks all the windows….
Outside fire vs Compartment fire
a. Outside fire
i. Heat and fire gases escape
ii. Fuel is the limiting factor
b. Compartment fire
i. Radiant heat is absorbed by other materials (makes igniting easier)
ii. Smoke and hot air rise and transmit heat (makes igniting easier)
iii. Smoke provides fuel air mixture
iv. Oxygen limiting factor
v. Hit it hard from the yard
Types of ventilation
Vertical
Horizontal
Built-in
Vertical self ventilation
- Misnomer. Just say “Fire has burned through roof.”
- Compromised structure: not safe to be on or under
- Think about transitioning to defensive attack
- Again, if it’s not safe to be on it attacking, it’s not safe to be under it attacking!
FD initiated vertical ventilation
- Most effective avenue to exhaust smoke and fire gases
a. Naturalized convection currents are utilized
b. Localized the fire
c. Roof opening should be at the highest point, as directly over the fire as safely possible - Can help prevent backdraft by allowing smoke and hot gases to exit the vent hole prior to the introduction of oxygen
Factors to consider before vertical ventilation
a. Life safety hazards
i. Find victim first
ii. Is it safe to ventilate?
b. Visible smoke conditions
c. Aspects of the building involved
d. Is there a need to ventilate
e. Where to ventilate
f. Type of ventilation
Tools for V ventilation
a. PPE
b. Tools
c. Ladders
d. Hose line
e. Radio
f. Saws/axes
g. Rubbish hooks
h. TICs
Before getting on the roof……
a. Is there fire showing from the roof?
b. Any roof sag?
c. Type of roof?
d. Is there smoke or fire?
Slate or tile that will make roofing difficult?
Rules to ventilate by (lots)
a. Have 2 ladders, non-adjacent
b. Full PPE including air
c. Hose line to the ground (ideal)
d. Start saw on ground
e. Read roof as you approach
f. Utilize roof ladder or use aerial ladder if roof is steep
g. Sound the ground! Break tiles if you have to
h. Walk on solidest points (Beams, ridges)
i. Coordinate with attack teams for location and timing
j. Use existing openings
i. Scuttle doors
ii. Skylights
iii. Stairwells
k. 1 large hole is better than small holes
i. 4’x4’ for residential
ii. 8’x8’ for commercial
iii. 10% of roof’s surface
l. Cut with wind to your back
m. Cut towards your ladder
Vertical ventilation cautions…
a. Never direct hose stream through vent hole
b. Use vertical ventilation in conjunction with forced ventilation: you need to know the fire’s status
c. Do not use on attic fires
Types of vertical ventilation holes
a. Vertical ventilation hole
i. Normal residential roof
ii. Commercial flat roof
b. Inspection hole
i. Kerf cut
ii. Triangle cut
c. Trench cut
i. Defensive measure meaning you are writing off a portion of the building
ii. Need hose lines to defend trench
iii. Nobody should be on fire side of trench
Horizontal ventilation
the venting of heat, smoke, and fire gases through wall openings such as windows and doors
i. Used on smaller fires that don’t require vertical ventilation
ii. Used on buildings that cannot be vertically ventilated easily, such as high rises or two story building or basements
iii. Also used in case of compromised roof structure
Natural H ventilation
Using the wind to ventilate structure
- Open leeward side first, highest point
- Open windward side next, lowest point
- Remove screens if possible as they obstruct airflow by 50%
Forced H ventilation
Using fans, smoke ejectors, or other means to push or pull smoke out of a building
- Advantages
a. More positive control over fire
b. Supplements natural ventilation
c. Speeds removal of contaminants
d. No additional damage to roof
e. Reduces smoke damage which is good PR - Disadvantages
a. Introduces large quantities of fresh air (cottonwood AZ)
b. Power source dependent
c. Need equipment
Positive pressure H ventilation
Uses hi-pressure fans to create higher pressure, forcing smoke out
b. Equally effective horizontal or vertical
c. Advantages over NPV
i. FF’s not exposed to environment
ii. Fans normally not blocking entrance or egress
iii. Twice as effective as NPV
iv. Contaminates not drawn through ejector
d. PPV efficiency can be improved by pressurizing small areas of the house via doors and windows
e. Cone of air must cover opening entirely
f. Can use two or more fans in sequence
g. Maintain one exit point at a time
h. Exit should be same size or smaller than entry to maintain positive pressure
Negative pressure H ventilation
the use of smoke ejectors to create negative pressure in a building to pull smoke out
a. Place fans so they exhaust with the wind
b. Keep flow straight as possible (turbulence)
c. Disadvantages
i. Personnel subjected to environment
ii. Contaminants drawn through ejector
iii. Doorways/windows obstructed
d. Need to occlude doorways to avoid churning
e. 50% as effective as forced horizontal ventilation
Hydraulic ventilation
a. Used to clear a room of smoke, heat, steam, and fire gases after a fire is under control
b. Uses air movement of a fog stream to draw out products of combustion
c. Disadvantages
i. Increased water damage
ii. Drain on water supply
iii. Firefighters exposed to environment
iv. Need to swap out firefighters when SCBA runs out
d. Place nozzle 2ft from opening
e. Set fog to cover 85-90% of opening
f. Nozzle flowing at 95GPM will move 5000 CFM
g. Very effective quick technique for clearing fire room. Put out the fire, then use HV to clear it to make the search easier
Built in ventilation
– heating, ventilation, or HVAC systems
i. May draw heat and smoke and spread fire
ii. System may shut down automatically when smoke or heat is detected in the air ducts or FFs may have to shut it down manually
iii. FF should not attempt to operate smoke control system during fire conditions
iv. Building operators should be called in to operate smoke control systems at the direction of the fire personnel
Two types of fires that are hard to ventilate
High rise fires
Basement fires
High rise ventilation
i. Stack effect may spread smoke to multiple floors
ii. Will require 4-6x times as much staffing as residential
iii. Typically ventilate utilizing a stairwell with roof access hatch
iv. Make sure roof access blocked open or removed
v. All doors unlock or stop-locked
vi. Not simultaneous with evacuation in same stairwell.
