Ch11 Mechanical Ventilation/Tactical Ventilation

Question 1

Tactical ventilation is 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… p493

Answer 1

Correctly implemented, tactical Ventilation helps to achieve incident priorities of “Life Safety, Incident Stabilization, and Property Conservation.” (LIP)

Question 2

What is Positive Pressure Attack? p509-510

Answer 2

PPA is used in the initial stages of an incident to make the structure safe for fire attack.

This is when a fan is set up at a door way to increase the pressure inside the structure relative to the atmospheric pressure outside the structure.

This pressure differential carries toxic smoke, gases, and heat from the entrance where fans were placed to an exhaust opening located as close to the fire as possible.

The two main considerations for PPA are fire location and exhaust to intake ratio (CFD wants .75 to 1.75 greater exhaust size to intake size ratio).

The ratio compares the surface area of all exhaust openings with the surface area of all intake openings.

Question 3

What is Positive Pressure Ventilation? p511-512

Answer 3

This is when a fan is setup at a door way of a structure and is used to positive pressurize the structure to assist in overhaul to remove smoke and gases after fire suppression. This accelerates natural ventilation.

Question 4

Positive Pressure Pressurization…

Answer 4

This uses one or more high-output fans to over pressurize an enclosed compartment and preventing additional smoke, gases, and heat from entering an area.

PPP could be used to:
Prevent fire extension into adjacent occupancies in a strip mall
Confine a garage fire and pressurize the adjoining house
Confine an attic fire and pressurize rooms below
Prevent fire extension into adjacent townhouses

PPP would not be an appropriate tactic when:
The fire location has not been established
The fire is known to be spreading beyond origin
There are natural gas leaks

Question 5

What is a flow path?

Answer 5

The volume between an inlet and an outlet that allows the movement of heat and smoke from the higher pressure within the fire area towards the lower pressure areas accessible via doors and windows within a structure.

Question 6

When setting up an exhaust opening for mechanical ventilation, approximately what size should it be?

Answer 6

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.

Question 7

At what angle should fans be placed at a door way before being started?

Answer 7

90 degrees to door way. Once the IC has given the order, place in front of doorway so sufficient air cone coverage of doorway.

Question 8

What fan positioning option has the most output?

Single (basic)

Series (one fan is placed behind another)

Parallel (two fans are placed side by side)

V-Point (two fans positioned parallel and point in a V configuration towards the door)

Answer 8

Answer: V-Point. This option provides the highest volume of air.

Single (basic)

Series (one fan is placed behind another, 30% more than single)

Parallel (two fans are placed side by side, 30% more air)

V-Point (two fans positioned parallel and point in a V configuration towards the door. This combination has 10% more air flow than SERIES or PARALLEL)

Question 9

Tactical ventilation is the planned and systematic removal of heater air, smoke, gases or other airborne contaminants from a structure, replacing them with cooler and/or fresher air… p493

Answer 9

Correctly implemented, tactical ventilation helps achieve incident priorities of life safety, incident stabilization, and property conservation. However, if ventilation is incorrectly applied, the results can traumatize occupants, firefighters, and the structure.

Question 10

Being in control of the fire means using ventilation and water application to control its behaviour. In terms of ventilation, firefighters control the flow of oxygen, smoke, and hot gases to then control the rate of fire growth and spread… p494

Answer 10

ventilation also allows firefighters to control where hot gases and smoke exhaust from a structure. Controlling exhaust openings may improve visibility inside the structure so that interior crews can work more effectively. Exhaust openings can also be used during overhaul to facilitate the removal of smoke or toxic gases after fire extinguishment.

Question 11

To control the flow path, firefighters can be positioned at doors that the crew passes through along their entry path… p494

Answer 11

Normally, this is just the entry door in residential fires. Their role would be to close any doors as much as hoselines will allow.

Question 12

An effective way of controlling ventilation is to cover openings rather that creating more openings. Before interior attack, closing exterior doors and windows or using smoke control devices and/or wind control devices to cover ventilated windows will reduce the oxygen available to the fire… p495

Answer 12

Closing any openings hinders fire growth until an attack can be planned and established. In general, closing openings helps control the fire unless closing those openings goes against an established incident strategy.

Question 13

Rapid fire development potential… p495
A growing fire can generate temperatures in excess of structural PPE limits in a few minutes. If the existing ventilation can support fire growth, flashover may occur less than five minutes after ignition. These environments are untenable for occupants and firefighters in full PPE.

Answer 13

When oxygen from ventilation is introduced into the room, the heated gases can quickly reignite, causing rapid fire development. Firefighters and occupants cannot survive rapid fire development conditions.

To prevent rapid fire development from occurring, you must use the appropriate water stream application techniques to cool the heated gases and know how and when to properly release those gases with appropriate ventilation methods and procedures.

Question 14

Ventilation without coordination will lead to flashover. No amount of additional ventilation will cause the fire to become fuel limited to prevent flashover. The longer the structure or compartment is allowed to ventilate without water being applied, the sooner the flashover occurs… p496

Answer 14

To prevent flashover, ventilation needs to be coordinated with fire attack almost immediately, at the very least within a short amount of time when ventilation alone improves conditions. Ventilation and water application are both necessary to bring a fire under control.

Question 15

The primary mode of heat transfer from one compartment to another in a structure is from heated gases and smoke movement known as… p497

Answer 15

Convection. This occurs because the natural buoyancy of smoke moves toxic gases and heat from one room to another. If not coordinated, the same ventilation operation changes that the flow path within the structure can move additional heat and smoke to areas not originally involved in the fire.

Question 16

What best describes how hot fire gases flow during ventilation operations? p497

Answer 16

During ventilation operations, gases flow from interior to exterior because the interior gases, heated by the fire have become less dense.

Gases less dense than air are buoyant, tend to rise, and move toward areas of low pressure. As the less dense, higher pressure, hot gases escape, they create lower pressure that draws in cooler ambient air down low.

Question 17

Water application to the hot gas layers combined with tactical ventilation can minimize the effect of the new air on fire growth… p498

Answer 17

Water application to the fire compartment begins to transition the fire from vent limited to fuel limited conditions. Vent alone will not achieve this transition.

Question 18

Tactical ventilation that is implemented during or after fire suppression can create an interior environment or egress path with the following, more tenable conditions… p498

Answer 18

Increased oxygen concentration
Reduced concentration of toxic products of combustion
Reduced temperature levels
Increased visibility to aid in firefighting operations and primary search operations

Question 19

Firefighters should make two assumptions about any structure fire to guide their decisions when ventilating a structure… p500

Answer 19

The structure itself consists of lightweight construction

The fire in the structure is vent limited

Question 20

Wind conditions… p500-501
Any opening in a building, whether part of the building design or created by the fire, allows the surrounding atmosphere to affect what is happening inside the building.

Answer 20

Whenever possible, firefighters should use the wind to their advantage during ventilation. Winds as slow as 10mph/15kph can affect structure fire, potentially making them wind driven. If winds at these speeds or faster, firefighters are safest working with the wind to their backs.

Question 21

Spongy roofs will sag when pushed or walked on and spring back into shape. Spongy roofs generally indicate that the roof decking is failing…

Indications of possible roof collapse include… p503

Answer 21

Melting asphalt
Smoke coming from the roof
Building systems such as HVAC units sagging or leaning
Spongy or springy feel to roof

Question 22

Horizontal ventilation… p506
Natural, mechanical, and hydraulic ventilation are all varieties of horizontal ventilation. Natural horizontal ventilation involves opening doors and windows to allow air currents and pressure differences to remove smoke and heat from the building.

Answer 22

Mechanical ventilation involves the use of fans and smoke ejectors to create pressure differences. Hydraulic ventilation uses water streams to ventilate compartments and create pressure differences.

Question 23

Wind assisted ventilation… p506

Answer 23

When the IC gives the order, windows and doors on the down wind side of the structure (low pressure side) should be opened first to create an exhaust point. Openings on the up wind side of the structure (high pressure side) are the opened to permit fresh air to enter forcing smoke toward the exhaust openings.

Question 24

Mechanical horizontal ventilation… p507

Answer 24

Mechanical ventilation may be necessary when the natural flow of air currents and currents that the fire creates are insufficient to remove smoke, heat, and fire gases from the structure. Mechanical ventilation is accomplished using fans, blowers, and smoke ejectors to create negative or positive pressure.

Question 25

Mechanical horizontal ventilation accelerates the exchange of fresh air into a structure filled with smoke and hot gases. If the fire is not under control, this accelerated exchange of gases can do more harm than good. Mechanical horizontal ventilation will add air to the structure more quickly than natural ventilation… p507

Answer 25

Some of the limitations of mechanical vent are…
Depends on a power source
Requires special equipment
Requires more resources and personnel that natural ventilation

Question 26

Mechanical horizontal ventilation uses after fire suppression… p508
Even in the absence of fire, contaminated atmospheres must be cleared quickly and thoroughly from a building or a confined space.

Answer 26

Some of the advantages of using mechanical vent to clear contaminated atmospheres are…
Supplements and enhances natural ventilation
Ensures more control of air flow
Speeds the removal of contaminants
Reduces smoke damage
Promotes good public relations

Question 27

Negative pressure ventilation… p508
Air movement equipment is used to develop artificial air flow to pull smoke from the structure or to enhance natural ventilation. The negative pressure created draws smoke and hot fuel gases out of the structure and draws fresh air into the structure.

Answer 27

Fans can be placed in windows, doors, or roof vent openings to exhaust the smoke, heat, and gases from inside the building to the exterior.

Question 28

Hydraulic ventilation… p513
To perform hydraulic ventilation, set a fog nozzle wide enough to cover the exhaust opening through which the smoke will be drawn or pulled. The farther you get from an exhaust opening, the more air entrains into the fog pattern. The more air entrained, the more heated gases get ventilated from the room.

Answer 28

Hydraulic ventilation has its disadvantages…
If done incorrectly, water damage may increase inside structure
Depletes water supply
More ice will form on ground surrounding the building
Firefighters must remain inside heated building and operate the nozzle

Question 29

Vertical ventilation… p514-515
Vertical vent involves creating openings in a roof or using existing openings to channel smoke, hot gases, and products of combustion out of the structure. Cutting a hole in a roof above the fire, opening existing roof access door, scuttles, or skylights are all examples of vertical vent.

For vertical vent 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.

Answer 29

Some common factors that can reduce the effectiveness of vertical vent are…
Improper use of mechanical vent
Uncoordinated vent
Fog streams directed into vent openings
Burn through of the roof, floor, or walls
Additional openings between the attack team and the upper opening
Improper location of vertical vent opening

Question 30

Before stepping off a ladder, parapet wall, or other place of safety on to the roof of a burning building - especially if smoke or darkness obscures the roof - firefighters should strike the roof surface with the blunt end of a pike pole, rubbish hook, or axe… p516

Answer 30

When a tool strikes a roof, roofs with intact sheathing will feel solid, and the tool will tend to bounce off the surface. Striking the roof will only determine if its sheathing is intact.

Question 31

Before cutting any type of vent hole, you should make an inspection cut. These holes determine the location of a fire, presence of a fire below the roof, and construction features of the roof.

There are two types of inspection cuts… p518

Answer 31

Kerf cut - is the easiest and fastest. Make a single cut in the roof using a rotary saw, chain saw, or axe. The resulting hole is the width of the saw or axe.

Triangle cut - May provide better view of conditions beneath the roof. Using a power saw, cut a triangle hole in the roof with overlapping cuts.

Question 32

Venting shingle covered roofs… p519
On shingle covered pitched roofs, cut a few inches below the peak of the roof on the downwind side. Always cut exhaust openings at or very near the highest point on the roof when possible.

Answer 32

Work from a roof ladder with the hooks attached to the ridge line. On extremely steep roofs, it may be necessary to work from an aerial.

Question 33

Creating trench cuts… p520
A trench cut is created as a defensive line ahead of the fire’s spread. Firefighters can attack this defensible area with hose streams when the fire ventilates at the trench cut. A trench cut is usually ordered when the IC has determined that the body of the fire is too large to extinguish.

Answer 33

Trench cuts are created ahead of the advancing fire: how far ahead is based upon the fire’s growth. Generally the distance is far enough that the fire will not reach personnel making the cut before they have finished work.

Question 34

Basement fires… p522
Ventilating basement fires must be coordinated with fire attack. It is also more important to determine what the fire’s stage is before ventilating a basement.

Answer 34

Unless the basement has vents installed, heat and smoke will quickly spread upward into the building. Without effective ventilation, access to the basement is difficult because firefighters would have to descend through the intense rising heat and smoke to get to the seat of the fire.

Question 35

Methods for ventilating basements… p523
Basement ventilation can be accomplished in several ways. If the basement has ground level windows or even below ground level windows, horizontal ventilation can be used effectively. Piercing nozzles can be used before ventilation to reduce the associated risks with venting a windowless basement.

Answer 35

Natural paths from the basement, such as stairwells and hoist way shafts, can be used to evacuate heat and smoke if there is a way to expel the heat and smoke to the atmosphere without placing other portions of the building in danger.

Question 36

Breaching floors… p523
Breaching a floor assembly may be necessary to ventilate an area, apply water to a fire, or rescue trapped occupants. The breaching tools and methods used will depend on the type of floor construction.

Answer 36

The feasibility of opening a floor during a fire fighting operation depends upon how it was constructed and from what material. A wood floor does not ensure that it can be penetrated easily. Many are installed over a concrete slab. The type of floor construction should be determined through pre incident planning.

Question 37

Fires in windowless buildings… p523
Venting this type of building can be difficult, and the problems involved vary depending on the size, occupancy, configuration, and type of construction materials used. Windowless buildings usually require mechanical vent for the removal of smoke. Most buildings of this type are automatically cooled and heated through ducting.

Answer 37

HVAC equipment can sometimes effectively clear the area of smoke; unless specifically designed for this purpose, these systems are more likely to cause the spread of heat and fire. In windowless high rise structures these systems need to be brought under fire department control as soon as possible.

Question 38

High rise fires… p525
Because there are more occupants in high-rise buildings than in other structures, life safety considerations are an even higher priority. Tactical vent in a high-rise building must be carefully coordinated to ensure the safest more effective use of personnel, equipment, and extinguishing agents.

Far more personnel are required for search and rescue operations in high-rise buildings.

Answer 38

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.

Question 39

High rise fires… p525-526
Heated smoke and fire gases travel upwind until they reach the top of the building or they are cooled to the temperature of the surrounding air. When this equalization of temperature occurs, the smoke and fire gases stop rising, spread horizontally and stratify (form layers).

Answer 39

In some cases, such as high-rise buildings, these layers of smoke and fire gases will collect on floors below the top floor. Additional heat and smoke will eventually force these layers to expand and move upward to the floor of the top building.

Question 40

High rise fires… p526

DO NOT use stairwells or elevator shafts simultaneously for evacuation and exhaust path.

Answer 40

The exhaust path will carry heat and byproducts of combustion through the shaft making it untenable to occupants and firefighters.

Question 41

Advantages and disadvantages of PPP…
Advantages:
Confine fire to area of origin
Prevent fire from spreading to exposures
Reduce the personnel required for exposure protection
Prevent smoke damage in adjacent compartments and structures

Answer 41

Disadvantages:

Reduced communication due to fan noise

Question 42

Ensuring that there is a total seal…

Running the fan without a total seal on the door may create additional convection currents…

Answer 42

This can lead to fuel (smoke) mixing, which makes flashover occur sooner. Without a total seal on the door, the flashover might exit through the entrance, thereby endangering firefighters and victims.

Question 43

Purpose of PPA

It may be used for any or all of the following…

Answer 43

To reduce the risk of backdraft or flashover occurring to facilitate rescue.
To make an area more tenable for victims and firefighting to remove toxic, explosive, and superheated gases.
To enable crews to advance more rapidly to the seat of the fire.
To help protect firefighters who are extinguishing the fire by removing steam.

Question 44

Deciding whether to use PPA…

The following are some examples of situations in which PPA might be required…

Answer 44

Conditions are untenable for firefighters.
The construction is unsuitable for natural ventilation due to the lack of vertical shafts or horizontal openings.
The fire is below ground level, in a confined space, or when entry is difficult to gain.
The IC deems it advantageous.

Question 45

PPA may not be the appropriate tactic if…

Answer 45

Signs of impending backdraft are apparent.
The location of the fire has not been established.
Potential exhaust openings are inaccessible.
Victims in exhaust opening.
The exhaust opening has been used for rescue or may be needed for rescue.

Question 46

High rise fires… p526
When performing tactical ventilation using stairwells in a high rise, where will additional personnel need to be assigned?

Answer 46

During a fire, the doors on uninvolved floors must be controlled so occupants do not accidentally enter a ventilation stairwell as they are evacuating. Doors to the stairwells should be controlled, and firefighters should be assigned to monitor doors.

Question 47

In general, closing an opening helps control the fire unless… p495

Answer 47

it goes against an established incident strategy.

Question 48

What is true about a kerf cut?

Answer 48

It only shows whether or not smoke or flame is escaping or not

Question 49

For positive pressure attack to be effective…

Answer 49

The exhaust opening keeps the pressure in the fire room lower than the rest of the structure. p510

Question 50

To perform hydraulic ventilation, set a fog nozzle on a pattern wide enough to cover the exhaust opening through which the smoke will be drawn or pulled.

Answer 50

The farther you get from an exhaust opening, the more air entrains into the fog pattern. The more air entrained, the more heated gases get ventilated from the room.