Chapter-11: Tactical Ventilatioin

Winds as slow as 10 mph:

Can affect structures fires, potentially making them wind-driven.

Venting Metal Roofs

Thin metal roofs can be sliced with an axe, carbide tip chain saw, or rotary saw and peeled back. Metal cutting tools or power saws with metal cutting blades can be used to open thick metal roofs. Use power saws, axes, or sheet metal cutters for sheet metal roofs

Hose lines and nozzles

Used for hydronic ventilation and resetting fire

Flexible ducts

Used to control the flow of fire gases and smoke during ventilation operations

Fires in windowless buildings

Usually require mechanical ventilation. Creating the openings needed may delay the operation for a considerable amount of time. HVAC can sometimes effectively clear the area of smoke. Unless specifically designed for this purpose, these systems are more likely to cause spread of heat and fire.

Tactical ventilation is performed during fire attack to:

help control the fire by control of the flow of oxygen, smoke, and hot gases to then control the rathe of fire growth and spread. (Creating openings in the structure or closing/covering openings)

FF should make two assumptions about any structure fire to guide their decisions when ventilating a structure:

1. Structure itself consists of lightweight construction. 2. Fire in structure is ventilation limited.

Kerf cut

A cut that is only the width and depth of the saw blade. It is used to inspect cockloft spaces from the roof. Provides whether or not smoke or flame is escaping the cut. Does not allow visual inspection. If flames come through do not proceed and leave area.

Exhaust openings must be located in the fire compartment

Additional exhaust openings remote from the fire compartment can draw air and pressure out of the established flow path and weaken the fans ability to force smoke and heat toward the fire compartment exhaust openings. This can raise the pressure in fire compartment higher than the pressure in the rest of the structure and draw heat and smoke to new exhaust point.

Radiation and/or direct flame contact can:

Affect external exposures, including structures located adjacent to the fire building.

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.

(Mechanical) Creating negative pressure means:

Artificially lowering the pressure inside the structure so that fresh air from outside moves in more quickly. Requires that the opening around the fan to be sealed to prevent outside air from being drawn in. (Not as effective as other operations)

(Mechanical) Creating positive pressure means:

Artificially raising the pressure inside the structure so that smoke and fuel gases move toward lower pressure openings more quickly.

Temperature Tenability

As temperature increases in a structure on fire increases, the tenability for victims and fire fighters within the structure decreases.

Air movement devices

Blowers, fans, and smoke ejectors that generate air flow.

Axes

Breaking windows and chopping holes through roof decking

If not coordinated, ventilation operations that change the flow path:

Can move additional heat and smoke to areas not originally involved in the fire

Successful Ventilation should be conducted in conjunction with fire attack depends on:

Carful planning, communication, systemic applications, coordination, recognition of environmental conditions both helpful and not, and all openings are ventilation.

Exhaust-to-intake size ratio

Compares the surface area of all exhaust openings with the surface area of all compartment intake openings.

Positive pressure attack (PPA)

Controlling flow during initial stages of fire before suppression. Intended to force heat and smoke toward desired exhaust openings to reduce thermal effect.

An effective way of controlling ventilation is:

Cover openings rather than creating more openings. (Closing any openings hinders fire growth until an attack can be planned and established).

Trench cuts are used to:

Create a defensible line ahead of an advancing fire. Usually order when fires are too large to extinguish. 6-10 FF usually assigned to create this cut to complete it quickly enough to be effective. They should have charged hose line present in case they can not complete the cut in time and need to attack fire while retreating. A trench cut should be 4ft or more wide and extend width of building.

Tactical ventilation that is implemented during or after suppression can:

Create an interior environment or egress path with the following: increased oxygen concentration, reduced toxic product of combustion, reduce temperature levels, increase visibility.

On shingle-covered roofs where should you cut for vertical ventilation?

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 whenever possible.

Triangle Cut

Cut consists of three overlapping cuts that form a triangle. Can provide a better view of conditions below the roof deck. Heated smoke, gases and sometimes fire will exit this inspection hole. If fire is present, report it to IC and suspend ventilation.

Power and chain saws

Cutting holes through roof decking or other obstacles.

Limitations of Mechanical Ventilation

Depends on power source Requires special equipment More resources and personnel to use Can add carbon monoxide to a structure during overhaul. Ventilation after fire suppression should lower CO levels. If not, gas powered fans may be the reason.

Effective PPV operation actions:

Ensure exhaust surface area exceeds the intake area, monitor ppv fan operation, communication (IC, IAT, PPV operator) , wind conditions

Unplanned Ventilation

Failure of windows, doors and structural members as a result of heat/fire exposure. It can significantly influence fire behavior in ventilation limited fires.

Stack Effect

Fire, smoke and toxic gases can spread rapidly there, pipe, chases stairways, elevator, shafts, and unprotected ducts, and other vertical and horizontal openings and high-rises. These openings contribute to a stack effect, creating an upward draft interfering with evacuation and ventilation. > heated smoke and fire gasses travel upward 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 in some cases, such as high-rise buildings. These layers of smoke and bar gases will collect on floors below and top floor. additional heat and smoke will eventually force these layers to expand, and move upward to the top floor of the building.

Ventilation without coordination will lead to:

Flashover (No amount of additional ventilation will cause the fire to become fuel-limited or prevent flashover). The longer the structure or compartment is allowed to ventilate without water being applied, the sooner flashover occurs.

Wind Control Device (WCD)

Heavy curtain or similar device used to cover exterior window and door openings to limit ventilation and/or prevent wind from adversely affecting ventilation conditions

Hydraulic Ventilation disadvantages

If done incorrectly, may increase water damage Depletes water supply More ice in freezing temps FF operating it must remain in heated, hazardous atmosphere throughout the operation.

positive pressure ventilation

Increases pressure to a level higher than the exterior of structure, not higher than the fire can produce. This allows for more exhaust openings to create more flow after fire suppression to decrease gas concentration and increase visibility.

Consider internal and external exposures:

Internal exposures include the building occupants, contents, and any uninvolved rooms or portions of the building.

Natural Horizontal ventilation

Involves opening doors/windows to allow air currents and pressure differences to remove smoke and heat from building. (Involves not additional personnel or equipment to setup/maintain) (only provides a small amount of time, maybe less than a minute for FF to use improved conditions)

Mechanical ventilation

Involves the use of fans and ejectors to create negative or positive pressure differences. Assists with natural ventilation.

Tactical Ventilation

Is the planned systematic and coordinated removal of heated air, smoke, gases or other airborne contaminants from a structure. It is a tool to help FF control a fire and for loss control.

Structural elements that contribute to roof failure:

Lightweight trusses Open floor plans under wide expanses with limited truss suppoort Prior structural damaged to roof (If roof is suspected or known to be unstable, personnel should not be placed under it).

Breaching Floors

May be necessary to ventilate and area, apply water to a fire, or rescue occupants trapped by a structural collapse. Subfloor construction is limited to either wood or concrete with a variety of covering materials. Determine floor construction during pre-incident planning.

High-rise fires

May contain hospitals, hotels, apartments or offices. More occupants which means more life safety considerations and are a higher life safety priority. Personnel required for search and rescue and firefighting operations is often four to six times greater.

Indications of possible roof collapse.

Melting asphalt Smoke/fire coming from roof Building systems like HVAC sagging or leaning Spongy roof (sags when pushed or walked on and spring back into shape, indicates roof decking is failing).

Square or rectangular ventilation opening

Most common in flat roofs. Made between roof trusses or with the truss in middle of opening.

Ventilation and fire fighting operations:

Must be coordinated to maximize effectiveness. (Breaking windows unnecessarily or freelancing disrupts the ventilation strategy, which in turn loses control of the fire)

Ventilating Basement fires

Must be coordinated with fire attack. Determine what the fires stage is before ventilating a basement. If it has windows horizontal venting can be used. Piercing nozzles can be used before ventilation to reduce risks with windowless basement venting.

If convection carries hot fire brands or ambers aloft:

Nearby structures and vegetation can be ignited. Fire may be drawn into exterior windows or opening of the adjacent exposures.

Do not upset the effects of horizontal ventilation

Opening upwind side first before creating exhaust opening on downwind side may pressurize building and intensify the fire, and cause it to spread to uninvolved areas.

Stacking and hanging devices

Position air movement devices in door/windows

Pike poles

Pulling or opening ceilings

Rapid fire development

Refers to the rapid transition from the growth stage or early decay stage to a ventilation limited, fully developed stage. (Flash overs, smoke explosions))(Firefighters and occupants cannot survive rapid fire development conditions).

Venting Slate or tiled-covered pitched roofs

Removing individual roofing tiles or using sledgehammer to smash them. If a sub roof is solid, then a vent hole is cut in the standard manner for pitched roofs.

If fire is vented through the roof or has been burning under the roof prior to arrival:

Roof ventilation should not be considered until after fire has been suppressed and roof structure can be evaluated. (Sound roof ahead)

Roof integrity

Roofs construction and building layout can help gauge and identify elements that may contribute to roof failure during a fire.

lightweight construction materials

Roofs may feel solid even though the structural members supporting the decking have burned or weakened. The roof WILL NOT feel spongy

Inspections of ventilation equipment:

Should be well documented. Equipment that fails inspection should be marked out of service

Spongy roofs

Some roofs are spongy with no fire involvement. Usually associated with flat roofs, but condition can apply with pitched roofs. Whether or not the roof springs back is an important piece of information about integrity but not the only indicator.

Sounding roofs

Strike roof surface with blunt end of pike pole, or axe. (Should feel solid and tool will tend to bounce off the surface) only determines if sheathing is intact. Provides no information about the structural members beneath sheathing.

Disadvantages of PPV

Structure must have remaining compartmentation, can add CO to a structure from gas powered fans, hidden fires may be accelerated and spread.

Advantages of mechanical ventilation

Supplements and enhances natural ventilation. Ensures more control of air flow. Speeds the removal of contaminants. Reduces smoke damage. Promotes good public relations.

Flow Path Control

The tactic of controlling or closing ventilation points, which will: 1. Limit additional oxygen into the space thereby limiting fire development, heat release rate and smoke production. 2. Control the movement of the heat and smoke conditions out of the fire area to the exterior and to other areas within the structure.

Hydraulic ventilation

Uses water streams to ventilate compartments and create pressure differences. Set a fog nozzle on a pattern wide enough to cover the exhaust opening thorough which the smoke will be drawn or pulled. *the further 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. The larger the opening, the faster ventilation will occur.

Vertical ventilation

Ventilating at a point above the fire through existing or created openings and channeling the contaminated atmosphere vertically within the structure and out the top. Done with openings in the roof, skylights, roof vents, or roof doors. *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. (VV is often impractical or impossible)

Controlling the process is key and requires water application to ventilation.

Water application to the hot gas layers combined with tactical ventilation can minimize the effect of the new air on fire growth. (Begins transition from ventilation-limited to fuel limited) Venting alone will not achieve this transition.

Safety precautions with Vertical ventilation

Wind at your back, don't cut main structural supports, guard vent opening, use lifelines or roof ladders, use caution around wires, full PPE, stay out of operation range of tools and overhead obstructions, ladders are 3 rungs above the edge and secure ladders, cut away from body, check structural integrity, walk along load bearing walls when possible.

Wind Assisted Ventilation

Windows and doors on the DOWNWIND side of structure (low pressure side) should be opened first to create an exhaust point. Openings UPWIND side of structure (high pressure side) are then opened to permit fresh air to enter forcing the smoke towards exhaust openings.

To prevent flashover, ventilation needs to be coordinated with what?

With fire attack almost immediately. At the very least within the short amount of time when ventilation alone improves conditions. Proper ventilation alone decreases the rate of fire spread and increases visibility for a short period. Ventilation and water application are both necessary to bring fire under control.

Before cutting any type of ventilation hole:

You should cut an inspection hole into the roof.

Gases less dense than air are:

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

The primary mode of heat transfer from one compartment to another in a structure fire is:

convection - occurs because the natural buoyancy of smoke moves toxic gases and heat from one room to another.

Tactical ventilation should be delayed until:

lines are charged and crews are ready. (Keep the fire ventilation limited as long as possible to prevent fire spread).

basement ventilation tactics

most challenging fires, ventilate opening opposite entry point the fire and smoke can be pushed toward the opening by ppv > natural paths from basement such as stairwells and shoots way shafts can be used to evacuate heat and smoke if there is a way to expel it into the atmosphere without placing rest of building in danger > as a last resort, an opening may be cut in the floor near a ground level door or window then use a ppv fan > interior vertical ventilation: only use this tactic when you are sure the floor will support the weight of necessary personnel. Floors may be weakened above fire. Sound floor to assess stability.

Because fires inside the structures are almost always ventilation limited, tactical ventilation may:

provide the fire with the necessary oxygen to grow, rather than creating a more tenable environment. (Only effective if coordinated with an immediate fire attack)