|Strip Ventilation Tactics
by John W. Mittendorf
Your fire department receives an alarm at 1330 hours for a
structure fire. You are the officer in command of a truck company responding to the
alarm. On arrival you observe a 60' x 200', one story mini-mall with heavy smoke
showing from an occupancy at one end of the structure and you see dark smoke pushing from roof vents over two units adjacent to the involved store. You quickly conclude that the fire in the end unit has extended into the common attic space and will quickly expose the entire structure.
Your options are limited. You are the only truck company on the first-alarm
response--the second-due truck is a mutual-aid response. For the critical initial stages of the operation, it's only you, your driver and one firefighter. You direct the firefighter to force entry into several units ahead of the extending attic fire as you and your driver ladder the roof and prepare to ventilate the building.
In this scenario, the truck officer has correctly identified a potential
problem. The fire in the end unit has extended into the common attic space and will extend horizontally to the other end of the building unless it is stopped. When the officer and driver reach the roof, strategic objectives will be as important as tactical operations
if the truck officer is to be effective within minimal time and staffing constraints.
The strategy for roof ventilation operations will be offensive or defensive.
The primary focus of offensive roof ventilation is to create a ventilation opening over or as
close to a fire as possible, as safety permits. This type of ventilation is designed to do
If possible, offensive ventilation should be conducted before defensive ventilation
and can be accomplished using natural construction openings such as skylights,
scuttle covers, bulkhead doors, etc. or by cutting an opening over the fire area
with a power saw and/or an axe. It is important to ensure the proper location
of these openings in relation to the fire area; a misplaced vertical vent opening
will quickly pull heat, smoke and fire toward uninvolved areas.
- vertically channel a fire and its by-products
- limit horizontal extension in a structure
- remove heat and smoke from a structure
- minimize the potential for flashover and backdraft
- increase the safety of fireground operations
If offensive roof ventilation operations have been completed, if they cannot
be performed for safety reasons, or if fire already has self-vented through the roof, defensive
roof ventilation operations should be completed if necessary. The purpose of defensive
roof ventilation is to create an opening ahead of a horizontally extending fire to change
the horizontal direction and extension of fire, heat, and smoke to a vertical direction,
thereby reducing or eliminating the horizontal fire spread.
Defensive roof ventilation is usually accomplished by the strip (or trench) vent.
The strip vent is a long, narrow opening in the roof decking, generally from exterior wall to
exterior wall (or fire wall to fire wall) and approximately three feet wide, ahead of the
horizontally extending fire. This opening allows you to strategically channel and redirect the
fire, slowing horizontal extension and facilitating knockdown.
With a strip vent you are, in effect, "drawing your line in the sand"
against the fire. Usually, committing to a strip vent means that you have a well-advanced
structural fire that is moving horizontally over a large area at such a rate that you cannot
stop it with offensive venting tactics, given on-hand resources. (Editor's note: The
term "defensive" ventilation is convenient because it rightly differentiates between the
strip vent and other methods of roof ventilation. However, there is not connection between
defensive fireground strategy. The strip vent is only "defensive" from the aspect of
"letting the attic fire come to you." Venting of any kind is inherently an aggressive
operation. Likewise, effective strip venting requires aggressive, offensive tactics by
engine and truck crews operating from interior positions--for example, pulling ceilings
and knocking down fire in adjacent occupancies/exposures, etc.)
The strip vent has been used successfully as the primary vent opening
in a variety of fire situations in a variety of structure and roof types, but all these
successful operations shared common factors--the fire was such that offensive venting
either could not be accomplished or had limited effectiveness, fire was in control of a large
area of common attic or cockloft space, an aggressive interior attack still could be made
from unburned or partially involved portions of the structure, there was a significant attic area
over which the fire had to spread, the strip vent could be made in an effective and timely fashion,
and a strategic decision by the commanding officer was made to "sacrifice" the heavily
involved portion of the structure to save the rest.
Many factors influence the strategic decision to vent defensively.
These include building and roof construction, fire conditions, fire load, manpower,
building dimensions, firefighter experience and training, and so on. Time is critical.
The officer must ask himself, 'Given my resources, the extent of the fire, roof construction,
personnel safety, and so forth, can my personnel make a 30' or 50' or 70' long, 3' wide
opening in the roof in the time it will take the fire to reach that point? What is my
return on investment for this tactic? Will a sizable vertical vent (offensive) opening
as close as possible to the fire area delay fire spread significantly and, most
important, improve conditions such that personnel can operate effectively and safely in
interior positions?' The officer in command must weigh many factors. Communication with
fireground companies is essential to acquire the needed information on which sound decision
making is based.
General roof venting tactics
Prior to a roof-cutting operation perform/address these tactical and procedural
Ladder and approach from the uninvolved area. A minimum of two
ladders should be raised away from or opposite the location of a fire. This allows personnel
to start and return to the strongest portion of the building and their means of egress.
Ladder the strong areas of the building roof. Normally, the
strongest portions of the building are at the corners. Avoid placing ladders over
horizontal openings (that is, windows, doors, etc.). Other areas that offer strength
are hips, valleys, and ridges.
Raise the fly of an extension ladder/aerial above a parapet or roof
for visibility. If a ladder is a primary means of egress from a roof, make it easy to
locate. Therefore, do not limit the extension of a ladder above a roof/parapet to three or
Deploy properly equipped and adequate personnel. Roof ventilation operations are
simplified and safety and accountability increased when a minimum of two firefighters
are used. Consider the following equipment the basic minimum necessary to accomplish roof
General features that make a chain saw an effective roof ventilation
- complete turnout gear and SCBA
- portable radio
- pickhead axe (used for prying and as a backup for power saws)
- pike pole, trash hook, or other suitable tools for removing cut sections of
- power saws--Historically the rotary saw has been widely used as a viable roof
ventilation tool although size, weight and the "gyroscopic" effect of the blade often
detract from its effectiveness. In applications other than metal-deck roofs, the modern
chain saw has proven to be a superior roof ventilation tool because of its effectiveness and ease
of use--which often translates into firefighter safety.
Read the roof. Before leaving a ladder and walking across a
roof, personnel must take the time to observe the roof and any visible conditions. A few
- minimum four-cubic-inch engine size, adequate for multiple layers of
- 16" to 20" sprocket tip guide bar (cooler running chain and reach)
- large air cleaner (increased time in smoky conditions)
- muffler guard (usually a piece of aluminum on the front of the muffler,
which minimizes maintenance and cleanup operations)
- carbide-tipped chain (superior to standard chains). A new carbide chain
can successfully cut through 14-gauge steel without ruining the chain).
Determine the type of roof. This can be easily accomplished by prefire
planning or quickly removing a small piece of composition (or other material) from the roof
covering only. This is easily done with an axe or power saw and will reveal the type of roof
decking below the roof covering. For example:
- What is the fire's location and is fire showing through the roof?
- Is the roof stable? Is a portion of the roof sagging? Are there heat blisters?
- Does the roof have ventilators, vent pipes, or skylights, and are they issuing smoke?
- What are interior/attic conditions? Communicate with interior fire attack crews and
the incident commander.
Determine the location and extension of fire. Prior to any roof
ventilation, you must determine the location and/or extension of fire. With your knowledge of
the type of roof, you can quickly determine the feasibility of a strip ventilation operation
before leaving the route of egress (ladder). You can determine the location and extension of fire by:
- corrugated metal indicates a metal-deck built-up roof with open web bar joists
- 1" x 6" sheathing indicates a conventionally constructed roof
- plywood on a newer building is an excellent indicator of lightweight construction.
Consider the following four conditions showing from an inspection opening:
fire; black, hot, pressurized smoke; white, lazy smoke; or nothing. Always remember to consider
the smoke's pressure, colour, and temperature.
- visual size-up (what areas of the roof are issuing fire or smoke?)
- small inspection/indicator openings (kerf cut, etc.) which can be cut with an axe
or power saw in the roof decking and used to determine the location and extension of fire.
Sound the path of travel. Sounding with an axe, pike pole, trash hook,
or other suitable tool in front of your intended path of travel will help verify the roof's safety.
Remember, don't sound with your feet--they are connected to your body.
Work toward the ladder/means of egress. Ventilation cuts should be
designed to start in the weakest portion of a roof (toward the fire) and finish in the strongest
portion of roof (away from the fire).
Keep the wind at your back. When possible, ventilation cuts should be
planned to keep the wind at the back of personnel.
Cut only as deep as necessary. Unless otherwise necessary, ventilation
cuts should be cut through roof decking only. Cuts deeper than roof decking increase the possibility
of cutting through structural members.
Predetermine your path(s) of egress. Always know how to safely exit a
roof. Generally, exit a roof from the same area you used to walk onto it. Never get cut off by fire
from your means of egress.
Strip vent tactics
Consider the principle of distance for time. Strip ventilation can be a time-
and personnel-consuming operation. Therefore, if strip ventilation is necessary, place enough distance
between the extending fire and the strip operation to allow the strip to be completed before the fire can
travel pass the strip opening.
Consider timing in strip ventilation operations. Since strip ventilation operations
can be a time- and resource-intensive operation and an opening can accelerate the travel of fire toward
its location, conduct strip operations as two distinct operations. The first operation is to cut the strip;
the second is to open the strip.
Coordinate interior attack operations with strip ventilation operations.
To be successful, strip operations also require the ceiling under (or as close as possible to)
the strip opening be removed to allow access for a hose line into the attic to extinguish the attic
fire. This operation requires coordination and communication between roof and interior personnel.
Make sure the strip cut is made from wall to wall. If not, fire could
pass around the ends, destroying the vent's effectiveness.
The roof must be walkable. The strip vent operation is a power-saw operation.
While the strip cut originated in flat-roof applications, experience has shown that it can be used
successfully on pitched roofs, provided the pitch does not compromise firefighter safety.
Wood roofs--against the construction. Strip ventilation openings that are cut against
the construction will require additional cuts and time to complete compared with strip ventilation
openings cut with the construction. To cut against the construction:
Wood roofs--with the construction (centre rafter).
- Make two parallel cuts about three feet apart across the rafters and section of roof to
be ventilated. Depending on staffing and equipment, these cuts may be made singularly or simultaneously.
- Make cuts between the rafters every 16 or 24 inches, depending on the spacing of roof
members. This produces small sections nailed to single rafters. These panels are easily hinged in
the form of louvers or removed.
- Remove or hinge the panels. Pry up with a suitable hand tool to remove or hinge the
Wood roofs--with the construction (between the rafters).
- Make two parallel cuts on either side of a rafter. These cuts should be near the outside
- Make crosscuts between the parallel cuts about every four to six feet. This enhances removing plywood
and/or multiple layers of roofing materials.
- Remove the cut panels of decking. Each 4' to 6' panel is nailed to the centre rafter and is
easily removed or louvered.
In this operation, the cut section of decking will fall into the building or attic.
Although this method drops material into a building or attic, a strip is quickly completed (particularly when
time is a primary concern) without personnel having to manually remove cut sections of decking
material. If an attic is not encountered, ensure there are no personnel working below this operation.
- Make the first cut along the length of the rafter, as close as possible to the rafter
without cutting it.
- Mirror this cut along the second rafter, again as close to it as possible.
Metal-deck roofs. Although the methods necessary to strip ventilate metal-deck
roofs are similar to those of wood roofs, initiating a strip ventilation operation in a metal-deck roof
is enhanced by a two-step process that consists of removing the insulation or composition covering
and then removing the metal decking from the bar joists. This is due to the fact that metal cutting
blades are not effective in cutting through the insulation/composition covering. For example, a strip
opening cut against the construction can be accomplished as follows:
Each strip ventilation method has its advantages and disadvantages. Using a particular
method will depend on the type of incident and roof, staffing, individual preference,
and your ability--which is developed by training and experience.
- Using a chain saw or rotary saw with a wood-cutting blade, make two parallel cuts about
three feet apart. It is only necessary to cut through the layers of composition and insulation. Let the
teeth ride on top of the metal corrugations.
- Make crosscuts every four feet between the parallel cuts. This ensures that the cut sections
of composition/insulation are easily removed.
- If the metal decking under the cut sections is cold, strike the sections to be removed with
an axe or similar tool. This will loosen the tar or adhesive bond between the metal corrugations and the
layers of composition/insulation, facilitating removal. If the metal decking is warm, the cut sections
should be easily removed.
- Remove the cut sections and place on the roof away from the fire.
- Two parallel cuts are now made through the metal decking with a rotary saw and metal-cutting blade
similar to cuts made in the insulation/composition layers.
- Crosscuts are then made between the metal bar joists. This process ensures that each of the metal
sections is attached to a single bar-joist only and is easily louvered and removed with minimal effort.
- Although this task is easily accomplished, it is a time- and blade-consuming operation.