IFSTA CH 11 Ventilation Flashcards
Tactical Ventilation
the planned and systematic removal of heated air, smoke, gases or other airborne contaminants from a structure, replacing them with cooler and/or fresher air to meet the incident priorities of life safety, incident stabilization and property conservation
reasons for tactical ventilation
It is a tool to help firefighters control a fire
Also used during overhaul and loss control to evacuate smoke from structures after the fire has been extinguished
Being in control of the fire means using ventilation and water application to control its behaviour
An effective way of controlling ventilation is to cover openings rather than creating more openings
Controlling Oxygen Availability
As the oxygen inside the room or structure gets consumed, the fire burns less efficiently and the amount of unburned fuel in the combustion products increases
If the compartment or structure does not ventilate before consuming most of the available oxygen, the fire enters a state of ventilation-limited decay
Tactical ventilation that is implemented during or after suppression can create an interior environment or egress path with the following, more tenable conditions:
Increased oxygen concentration
Reduced concentration of toxic products of combustion
Reduced temperature levels
Increased visibility to aid in fire fighting operations and primary search operations
SAFETY CONSIDERATIONS WHEN VENTILATING
Careful planning
Communication of scene observations to the IC
Systematic application of procedures for removing the contaminants
Coordination with other fireground activities
Recognition that all openings are ventilation
Recognition of the advantages and disadvantages of environmental conditions at the scene
Wind Conditions
Winds as slow as 10mph can affect structure fires, potentially making them wind-driven
If winds are at these speeds or faster, firefighters are safest working with the wind at their backs
Elements that may contribute to roof failure during a fire
Lightweight roof trusses
Open floor plans under wide expanses with limited truss supports
Prior structural damage to the roof
Indications of possible roof collapse
Melting asphalt
Smoke coming from the roof
Fire coming from the roof
Building systems such as HVAC units sagging or leaning
Spongy roof
natural ventilation
Involves opening doors and windows to allow air currents and pressure differences to remove smoke and heat from the building
door control is another form of natural ventilation
mechanical ventilation
Involves the use of fans and ejectors to create pressure differences
hydraulic ventilation
Uses water streams to ventilate compartments and create pressure differences
Wind Assisted Ventilation
When the IC gives the order, windows and doors on the downwind side of the structure should be opened first to create an exhaust point. Openings on the upwind side of the structure are then opened to permit fresh air to enter forcing the smoke toward the exhaust openings
Creating negative pressure
Means artificially lowering the pressure inside the structure so that fresh air from outside moves in more quickly
creating positive pressure
Artificially raising the pressure inside the structure so that smoke and fuel gases move toward lower-pressure openings more quickly
Mechanical Horizontal Ventilation Before and During Fire Suppression
Accelerates the exchange of fresh air into a structure filled with smoke and hot gases
Some limitations of mechanical ventilation include the following:
Depends upon a power source
Requires special equipment
Requires more resources and personnel than natural ventilation
Mechanical Horizontal Ventilation uses after Fire Suppression
Clearing contaminated structures of smoke reduces smoke damage and improves relations with home or business owners
Some advantages of using mechanical ventilation to clear contaminated atmosphere are:
Supplement and enhances natural ventilation
Ensures more control of air flow
Speeds the removal of contaminants
Reduces smoke damage
Promotes good public relations
Negative-Pressure Ventilation (NPV)
Air movement equipment is used to develop artificial air flow to pull smoke from the structure or to enhance natural ventilation
Requires electricity, generally supplied by a cord run from a generator to the fan
Requires that the opening around the fan be sealed to prevent outside air from being drawn in around the fan
Positive-Pressure Attack
The intent is to use high-volume fans to create a slightly higher pressure in adjacent compartments and force the products of combustion (smoke) to the exterior of the structure through exhaust openings that either exist or have been created
intake
Opening where the fan is set up and air flow is introduced
exhaust
Location where the intended products of combustion will be exhausted from the structure
two main considerations for PPA
fire location
exhaust-to-intake size ratio
Hydraulic Ventilation
May be used in situations where other types of forced ventilation are unavailable
Can be used to clear a room or building of smoke, heat, steam and gases after a fire has been controlled
Uses a spray stream from a fog nozzle to entrain smoke and gases and carry them out of the structure through a door or window
Requires firefighters to operate the nozzle within the contaminated atmosphere
Hydraulic Ventilation disadvantages
water damages may increase within the structure
depletes the water supply, a more common problem during rural fire fighting operations where water shuttles are being used
more ice will form on the ground surrounding the building when temperatures are below freezing
the firefighters operating the nozzle must remain in the heated, hazardous atmosphere throughout the operation
VERTICAL VENTILATION
involves creating openings in a roof or using existing openings to channel smoke, hot gases and products of combustion out of the structure
for vertical ventilation to be effective, a horizontal inlet opening at or below the level of the fire is needed to provide a flow path for fresh air to enter the structure
sounding the roof
striking the surface of a roof to determine its structural integrity
provides no information about the structural members beneath the sheathing, sheathing may sound solid but will fail under your weight
inspection holes
help to determine the location of a fire, the presence of fire below the roof and construction features of the roof
comparing observations from multiple inspection holes can provide information about the fire spread
two primary types of inspection holes
kerf cut
triangle cut
kerf cut
easiest and fastest inspection hole to cut
make a single cut in the roof surface using a rotary saw, chain saw or axe
triangle cut
may provide a better view of conditions beneath the roof
Ventilating Flat Roofs
square or rectangular openings are the most common types made in a flat roof
these openings can be made between the roof trusses or with the truss in the middle of the opening
when the truss is in the middle of the opening a louver cut is used
Ventilating Shingle-covered Pitched Roofs
cut a few inches below the peak on the downwind side
always cut exhaust openings at or very near the highest point on the roof when possible
Ventilating Slate or Tile-Covered Pitched Roofs
can be sliced open with an axe, carbide tip chain saw or rotary saw and peeled back
Creating Trench Cuts
the purpose of trench cuts is to create a defensible line ahead of the fires spread
are created ahead of the advancing fire: how far ahead is based upon the fires rate of growth
generally the distance is far enough to ensure that the fire will not reach the personnel creating the cut before they have finished their work
trench cut is created in two steps
make two parallel cuts that extend form one exterior wall to the opposite exterior wall
remove the roof material between the cuts and push down the ceiling material below
trench cut should be 4 or more feet wide and extend the width of the building
advantages of trench cuts
can be used to establish a defensive position in the attic space for fire attack among structures with a common attic
works well in large buildings
disadvantages of trench cuts
can be time-consuming or physically taxing on personnel
can place firefighters in the dangerous position of working ahead of the fire
if it is created improperly or at the wrong time, it can cause the fire to spread more rapidly and potentially destroy the structure
Methods for Ventilation Basements
if the basement has ground level windows or even below ground level windows in wells, horizontal ventilation can be employed effectively
High-Rise Fires
fire, smoke and toxic gases can spread rapidly through pipe chases (shafts), stairways, elevator shafts, unprotected ducts and other vertical and horizontal openings in high-rises
these openings contribute to a stack effect* creating an upward draft and interfering with evacuation and ventilation
horizontal smoke spread* and hot gas layer development can also occur when an exhaust opening does not match the fire size
