Chapter 11 - Ventilation Flashcards
Tactical ventilation
Planned, systematic and coordinated removal of heated air, smoke, gases or other airborne contaminants from a structure
It is used when
To control a fire and during overhaul and loss control to evacuate smoke from a structure after the fire has been extinguished.
Controlling exhaust openings can also improve visibility inside the structure for interior ops.
True
Ventilation and FA must be what to maximize effectiveness
Coordinated
An effective way of controlling ventilation is to cover what rather than creating more openings
Cover openings, such as closing exterior doors, windows and smoke control control devices
At what temperature does your polycarbonate face piece soften at
149C (300F)
Maximum temperature for PPE
260C (500F)
Flashover temperatures
593C (1100F) or higher
Ventilation without coordination will lead to
Flashover
No amount of additional ventilation will cause the fire to become fuel limited or prevent flashover
True
Ventilation takes advantage of what of fire gases, allowing them to escape
Buoyancy
As the less dense, higher pressure, hot gases escape, they create a lower pressure that draws in cooler ambient air down low
True
The primary mode of heat transfer from one compartment to another in a structure fire is
Convection
Water application to the fire compartment begins to transition the fire from vent limited to
Fuel limited
Life safety
Applies to occupants who may be trapped in structure and the FF who must enter to rescue them. Tactical vent can be used to alter flow path away from trapped occupants
Applications of vent during overhaul
Accelerate the clearing of smoke and hot gases . Can make structure more tenable and easier to find victims. Also minimizes smoke damage to the structure.
Unplanned ventilation
Failure of windows, doors and structural members as a result of heat/fire exposure.
FF should make 2 assumptions about any structure fire to guide their decisions when ventilating
- The structure itself consists of lightweight construction
- The fire in the structure is vent limited.
Wind conditions
Use wind to your advantage (work with wind at your back) during vent. Winds as slow as 10 mph (15 kph) can affect structure fires.
Internal exposures
Building occupants, contents and any uninvolved rooms or portions of the building.
Window mounted air conditioning or HVAC intake vents may draw smoke into adjacent buildings.
True
Indications of possible roof collapse include
- melting asphalt
- smoke coming from roof
- fire coming from roof
- building systems such as HVAC units sagging or leaning
- spongy roof (sag when pushed or walked on and spring back into shape)
Horizontal ventilation
Natural, mechanical and hydraulic.
Natural horizontal vent
Involves opening doors and windows to allow air currents and pressure differences to remove smoke and heat.
- downwind side is low pressure side
- upwind side is high pressure side
- opened to permit fresh air to enter forcing the smoke toward exhaust openings
- can allow FF to apply water with a straight stream from the exterior
Mechanical horizontal vent
Involves the use of fans and ejectors to create pressure differences.
- used when natural flow of air currents are insufficient
- can create neg pressure (low pressure inside structure) to draw air in
- can create pos pressure (high pressure inside) to force smoke and gases out
- coordination with other crews and ops is paramount.
Even in the absence of fire, contaminated atmospheres must be cleared quickly and thoroughly from building or other confined spaces (low O2)
Careful if gas powered fans are being used. They can add additional CO. Monitor closely.
NPV
Negative pressure ventilation.
- draws smoke and hot fuel gases out of structure and draws fresh air in
- requires that opening around the fan be sealed to prevent air from being drawn in around the fan
- not as effective as other vent options for removing smoke
PPA
Positive pressure attack
- used during initial stages of incident to make structure safer for FA
- work best on fires confined to a compartment
- creates a slightly higher pressure in adjacent compartments and force the products of combustion to the exterior through exhaust openings that exist or are created as close to the fire as possible
2 main considerations for PPA
Fire location and exhaust to intake size ratio (greater than 1:1). Exhaust openings must be located in fire compartment.
- remember, as fire grows so does its pressure
- size of exhaust must exceed the intake to fire compartment
- crews enter or exit from intake side only
PPV
Positive pressure ventilation
- used for purposes other than to assist FA
- accelerates natural vent of structure
- exhaust smoke, heat and toxic gases to the exterior after fire suppression
- goal is to increase pressure to a level higher than exterior of structure
- careful of smoldering fires as they can be intensified
Hydraulic vent
Uses water streams to vent compartments and create pressure differences
- fog nozzle wide enough to cover exhaust opening through which smoke will be drawn or pulled
- farther you get from exhaust opening and the larger the opening will entrain more air
Vertical ventilation
Creating openings in a roof or using exhaust openings to channel smoke, hot gases and products of combustion out
- to be effective, horizontal inlet at or below level of fire is needed to provide a flow path for fresh air to enter
Warning
Never direct a fog stream into an opening when interior FA are inside structure.
Sounding
Striking the surface of a roof to determine its structural integrity.
- provides no info about structural members beneath the sheathing
Tiles or slates cannot be sounded; must be removed to reveal the underlying structure
True
Before cutting any type of vent hole, you should cut an inspection hole in the roof to assess for fire and construction.
Kerf cut (single straight cut) and triangle cut (3 overlapping cuts)
- if fire present, leave area and abandon vent
Square or rectangular openings are most common types of cuts made in what roof style
Flat
- made between roof trusses or with truss in the middle of the opening
Cuts on shingle covered pitch roofs
Cut a few inches below the peak on the downwind side. Always cut exhaust openings at or very near highest point on roof when possible
Battens
Strips of wood attached to rafters.
Metal roofs
Thin metals roofs can be sliced open with an axe, carbide tip chain saw, or rotary saw and peeled back. On thick metal roofs, may be easier to open skylights, monitors or scuttle hatches.
Trench cut
Trench or strip ventilation. Create a defensible line ahead of the fire spread. Can attack this area with hose streams.
Basement fire
- most challenging
- unless vents installed, heat and smoke will spread quickly upward into building
- access can be through interior/exterior doors, cellar doors, windows or hoist ways
Venting basements
- horizontal if ground level windows present
- stairwells or hoist way shafts can be used to evacuate heat and smoke
- breaching floors to vent
- subfloor construction limited to wood or concrete
Windowless buildings usually require what for removal of smoke
Mechanical vent
High rise fires
- fire, smoke and toxic gases can spread rapidly through pipe chases (shafts), stairways, elevator shafts, unprotected ducts and other openings
- contribute to the stack effect; creating an upward draft and interfering with evacuation and vent
- heated smoke and fire gases travel upward until they reach top of building or they are cooled to temp of surrounding air. When this equalization of temp occurs, smoke and gases will stop rising and spread horizontally and stratify (form layers). Can collect on floors below top floor
Horizontal smoke spread
Can also occur when an exhaust opening does not match the fire size
High rise continued
- in many, only 1 stairwell penetrates the roof. Can be used like a chimney to vent smoke, heat and gases
- door control paramount
- PPV fans set up at bottom floor of secondary enclosed stairways used for evacuation to keep smoke from entering it
PPP
Positive pressure pressurization
- fans to over pressurize an enclosed compartment preventing additional smoke, heat, and gases from entering area
- exhaust opening generally not created for PPP
- placed at entry point where fire is uninvolved and where IC wants to protect
Positioning of high output fans
Single (basic setup): used to vent most residential fires
Series (30% more air): 2 fans placed, 1 behind the other.
Parallel (wider openings): depends on how wide opening is
Combination (wider openings): series and parallel combined
V-point (highest air volume): highest volume of air. 2 fans parallel to and several feet away from one another in a V point config. One can seal top of entrance and the other bottom. 10% more air then series or parallel option
Purpose of PPA
- reduce backdraft or flashover
- area more tenable for victims and FF
- enables crews to advance more rapidly to seat of the fire
- help protect FF who are at the fire by removing steam
- only assigned by IC or operations chief
Advantages of PPA
- move smoke, heat and fire away from FA teams
- improves chances of victim survival
- reduce amount of unburned fuel present in structure
Disadvantage of PPA
- communication, noisy
- constant supervision
- can spread fire and smoke if improper setup
- cause fire to grow until water is applied
- can reduce time of flashover if used incorrectly
Incomplete seal of door
- can create additional convection currents
- smoke mixing which makes flashover occur sooner
- flashover might exit through the entrance
Stop PPA if pre flashover conditions occur at the entrance
Free burning fire, thick black smoke, rollover and extreme heat
Potential problems caused by improper PPA
- door not completely sealed or exhaust opening not adequate, convection may occur leading to a more rapid onset of flashover
- exposure line is directed into the window rather than across it, may spread smoke and fire onto interior crews
- fire, smoke and heat come out exhaust opening. If not monitored, nearby exposures and personnel can be put in danger
Advantage of PPV
- move heat and smoke away from overhaul teams
- improves visibility
- reduce smoke and toxic gases
- reduces humidity and heat created by overhaul
Disadvantage of PPV
- communication, noisy
- can increase CO
- constant supervision
- can rekindle fire
Rekindle
- open early and often
- consider class A foam
- all areas involved in fire must be monitored without use of PPV for 10-15 minutes prior to leaving scene
Examples of PPP
- prevent fire expansion into adjacent occupancies in a strip mall
- confine garage fire and pressurize the adjoining house
- confine an attic fire and pressurize rooms below
- prevent fire extension into adjacent houses (ie townhouses)
When burned, plastic will produce 300 times the amount of smoke per pound, than wood.
True
Ventilation priorities
I. Venting For Life Safety (Offensive)
II. Venting for Fire Containment (Defensive)
III. Venting for Property Conservation
When setting up an exhaust opening for mechanical ventilation, approximately what size should it be?
The exhaust opening should be 3/4 to 1 3/4 the size of the entrance to where the fan is placed. Bigger is better.
