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Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
Page 1 of 13 Supersedes – SOP
Date:
1 PURPOSE 1
2
To describe guidelines and procedures for controlling ventilation at a structure fire. 3
2 SCOPE 4
Applies to all department members. 5
6
3 ACCREDITATION REFERENCE 7
8
5E 9
10
4 PROCEDURE 11
12
Ventilation considerations are a key component of the Incident Action Plan (IAP) at a structure 13
fire. The tactics used for ventilation will depend on the circumstances of each incident. Since 14
fires are dynamic events, ventilation efforts and their effects must be managed and assessed 15
throughout an incident. 16
This SOP is not intended to describe all possible combinations of tactics, and assignments for 17
ventilation at every possible type of fire. It explains how ventilation will be assigned within the IAP 18
and provides guidelines for ventilation and tactics. 19
20
Ventilation Guidelines 21
22
Ventilation changes a fire’s growth and behavior. When coordinated with fire attack, the right 23
ventilation tactic, at the right time, will protect victims and interior crews, and speed 24
extinguishment with minimum damage to property. 25
By contrast, incorrect ventilation can make the situation much worse. Incorrect ventilation can 26
take many forms. It could be as simple as choosing the wrong tactic for the incident. 27
Horizontal ventilation on the windward side of a structure on a windy day. 28
Positive Pressure Ventilation in a structure without adequate exhaust openings. 29
It could also be performing the correct tactic but at the wrong time. 30
Ventilating before the attack team is in position, allowing the fire time and oxygen to row. 31
Turning in the fan for Positive Pressure Ventilation before the lines are opened up. 32
In all cases, incorrect ventilation can increase the intensity and spread of the fire, increase the 33
risk to firefighters and victims, and increase the damage caused by the fire. 34
If possible, ventilation openings should be controlled – able to be closed again if needed. 35
Breaking glass (while commonly needed) should only be done after ensuring there is not a 36
method of opening a door/window that will allow it to be sealed again. 37
Unless an immediate life hazard is present, firefighters must not break glass or otherwise 38
create openings into the structure without orders from the IC/Fire Attack. Uncoordinated 39
ventilation can dramatically change the fire’s dynamics, endangering firefighters and civilians. 40
Ventilation tactics must be chosen deliberately, after proper size-up, and in conjunction with 41
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
Page 2 of 13 Supersedes – SOP
Date:
the IAP. Firefighters and officers who are assigned to ventilation must understand more than 42
what they are ordered to do, they must know why they are doing it, and what effect they should 43
expect to see if it is working. 44
If a ventilation tactic does not appear to make sense in context of the total firefighting effort, or 45
it might put firefighters or victims in danger, alert the officer or the IC. 46
Likewise, if the fire does not behave as expected after ventilation, notify the IC. 47
In both cases, the information provided allows the IC to adjust strategy/tactics, and protect 48
firefighters from serious injury or death. 49
Ventilation Methods 50
Detailed instructions on every ventilation tactic is beyond the scope of this SOP, which is not a 51
substitute for training, practice, and experience. Instead, this section will provide a broad 52
overview of the most common ventilation tactics. For the purposes of this SOP, Vent-Enter-53
Isolate-Search (VEIS) is considered a Search/Rescue tactic and not covered, except how its 54
use relates to other ventilation tactics. 55
Horizontal Ventilation 56
Horizontal ventilation uses openings in the walls of the structure as exhausts to allow the high-57
pressure smoke and heat from the fire to escape. Typically, these are pre-existing openings in 58
the structure, such as doors or windows 59
60
When creating a horizontal ventilation opening, remove all obstructions (sash, curtains, 61
screens, etc.) from the opening, so it can be used as an emergency egress if conditions 62
deteriorate. 63
64
Horizontal ventilation is typically performed from the exterior, and focused on managing the 65
behavior and growth of a fire. 66
67
68
69
Indications Contraindications Tactical Considerations
Attack lines flowing water into the fire area
Attack lines are reasonably expected to be flowing water into the fire area before the fire can grow after venting
Firefighters or victims operating in the flow path between the fire and the intended vent opening
Backdraft conditions
High winds in the directions of the intended ventilation opening.
The door through which the Fire Attack hand line enters, if left open, is a horizontal ventilation opening.
Exposures close to the intended ventilation opening must be monitored.
The fire can extend to the exterior of the structure, such as the siding or soffit.
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
Page 3 of 13 Supersedes – SOP
Date:
Vertical Ventilation 70
71
Vertical ventilation typically takes longer than horizontal ventilation, and is inherently more 72
hazardous because it requires crews to operate above a fire, often on a pitched surface. 73
When properly performed, the hazards can be minimized and some fires may require this 74
tactic. Therefore, it is essential firefighters are familiar with it and prepared to carry it out. 75
The first step is size-up to determine where the vertical hole will be cut. If the location chosen 76
for ventilation does not have access to the fire area, ventilation will be delayed and the effort 77
wasted, and the hole may draw fire into a previously intact area. Once a location for ventilation 78
is identified, select a landmark to stay oriented while on the roof. This could be a ladder, a 79
tree, or a feature on the roof. 80
A firefighter should make the cuts working from the weak side to the strong side and ensure a 81
path to the escape route remains clear while the Company Officer continuously monitors the 82
roof and fire conditions for changes. 83
Cuts should be no deeper than necessary to remove the roof decking. 84
85
86
Modern building construction and 87
home furnishings will need large 88
openings. In a normal wood frame 89
home, a 4’ x 8’ ventilation hole is 90
standard. The safest and more 91
efficient method to create this 92
opening is the 7-9-8 cut, as shown 93
Indications Contraindications Tactical Considerations
Horizontal exhaust openings are unavailable
Tactical considerations require a vertical exhaust opening
Pre-existing vertical openings (roof access hatches, skylights, etc.)
Heavy fire in attic/concealed space
Impervious/dangerous roof coverings (tile, concrete, etc.)
Hazardous weather conditions (lightning, snow/ice)
Hazardous building construction (lightweight construction, bow string truss, etc.)
Must be performed above the fire area, which should be determined from size-up
Need 2 routes of egress (ladder, aerial, etc.) off the roof
Minimize number of firefighters involved, and spread out to avoid concentrating weight
Avoid operating around heavy loads (HVAC, etc.)
Cut inspection hole to determine conditions below
Figure 1: Cut pattern for 7-9-8 ventilation hole
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
Page 4 of 13 Supersedes – SOP
Date:
in Figure 1: 94
When the decking is louvered to create a vent opening, crews may need to use long pike 95
poles to break out the ceiling that separates the exhaust opening from the fire area. 96
Firefighters must be cautious not to overbalance when breaking out ceiling below the vent 97
opening. 98
Limited Ventilation, (“Door Control”) 99
100
Limited ventilation, or “Door Control” is based on modern fire science research. Most fires are 101
ventilation-limited by the time firefighters arrive on scene. The act of opening a door and 102
advancing an attack line into structure introduces a great deal of oxygen to the fire. This 103
combines with the heat and fuel already present to greatly increase the extent of the fire and 104
draw it toward attack crew. 105
Firefighters have a 106 very short period of time to begin applying water 107 to the fire before this occurs. A good rule of thumb 108 is they have 100 seconds in a 1-story house, and 109 200 seconds in a 2-story house. 110
Door Control involves 111 intentionally restricting the amount of air that can 112 enter or exit the structure through the fire attack 113 entrance. The simplest method is to have a 114 firefighter assigned to keep the door mostly closed 115 behind the attack crew, and feed them hose 116 around the door. Other methods might involve 117 assigning additional firefighters to push 118 hose around the door, or using a device such 119 as a smoke curtain to block the flow of air into the 120 structure.
If done correctly, this 121 tactic can extend the time available to interior 122 crews to advance to the seat of the fire before it 123 begins rapid growth and interior conditions 124 become untenable 125
126
127
128
129
130
131
132
133
134
135
136
Figure 2: A firefighter performing door
control
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
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137
Positive Pressure Ventilation 138
Positive Pressure Ventilation (PPV) uses fan(s) to create a pressure gradient in a building that 139
will force smoke out of one or more exhaust openings. When performed correctly, PPV can 140
dramatically improve visibility after knock down, and minimize firefighter and victim exposure to 141
thermal disruption and steam resulting from firefighting efforts. This improves victim 142
survivability and firefighter safety, and expedites completing search operations. 143
For greatest effect, this tactic should be started immediately after interior crews achieve a 144
knock down on the fire. If the IC intends to use this tactic, at least one firefighter should be in 145
position at the doorway, awaiting orders to turn in the fan. That firefighter must remain by the 146
fan, prepared to shut it down until the effectiveness and safety of this tactic is confirmed and 147
he or she is released by the IC or D/G Supervisor. 148
Indications Contraindications Tactical Considerations
Building layout/content or other incident factors will prevent rapid advancement to the seat of the fire.
Fire has exhausted available oxygen, but high heat and smoke will cause rapid fire growth and expansion with introduction of oxygen.
Thick turbulent black smoke puffing from small openings that has died away prior to application of water – this is a sign that the fire is only waiting for enough oxygen to flare back up rapidly on interior crews.
Door or other openings near the fire attack entrance are unable to be controlled (broken glass, etc.).
Tactical situation requires frequent entry/exit, which will prevent this tactic from working.
Fire attack entrance on the leeward side of a structure with a wind driven fire.
At least 1 firefighter must be dedicated to maintaining door control at all times. Or saw (rip) an 18” section off the bottom of the door for hose advancement.
Ideally, one firefighter at the door will maintain door position, and a second firefighter will hump hose to the door.
Firefighter on door control must be alert for signs the interior crew is evacuating.
Entry/exit into structure must be minimized until fire is under control, which can delay additional assignments (search, overhaul, and back-up).
This tactic only delays O2 introduced by the fire attack entrance. O2 introduced from any other part of the structure (i.e., a window failing) can cause rapid fire progression and endanger interior crews.
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
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149
Positive Pressure Attack (PPA) 150
Positive Pressure Attack (PPA) is similar to PPV, with the key difference that the PPA occurs 151
BEFORE fire attack crews make entry. 152
When all indications are present, PPA can dramatically improve visibility and reduce heat as 153
firefighters advance the attack line, allowing them to place the fire under control and search for 154
victims much more rapidly. However, if even a single indication is absent, or one of the 155
contraindications is present, PPA is extremely dangerous. Introducing large amounts of fresh 156
air to a fire with uncontrolled flow paths will accelerate its growth and cause conditions to 157
worsen rapidly. 158
In addition, the benefits of PPA are negated if it will significantly delay getting water on the fire. 159
Therefore, if PPA is to be used effectively, the initial company officer must quickly identify the 160
fire as a candidate for this tactic, and be able to establish the inlet and exhaust openings with 161
the first arriving companies. 162
If PPA is attempted, be alert for changing conditions that indicate the tactic ineffective, or 163
actively endangering firefighters. Examples include increased smoke from areas/openings 164
other than the designated exhaust opening, or no change to smoke from designated exhaust 165
opening. Both of these observations indicate that the air/pressure from the fan is not following 166
the intended flow path. PPA efforts should be immediately ceased in such cases, and not 167
resumed unless the cause can be identified and immediately fixed. 168
169
Indications Contraindications Tactical Considerations
Fire under control/knocked down
Vertical/horizontal ventilation openings established, and adequate for the volume of smoke to be removed.
Use when specific exhaust opening(s) are preferred, to steer smoke away from bystanders and other hazards.
PPV is often indicated in large structures with numerous compartments, and other special situations, which are addressed in more detail in Section 4.
Unknown extent and location of fire
Exhaust opening not established.
Turning fan into building before being ordered by IC or interior crews.
Presence of explosive gasses above the UEL (upper explosive limit).
Exhaust opening on windward side of building, during high wind conditions.
Use caution in structures with large void spaces that may be concealing fire (balloon frame, common attic, etc.)
Consider using this tactic to remove the heavy smoke after knockdown of a fire when door control/anti-ventilation have been used.
Use of gas-powered fans will introduce a small amount of CO into a structure from their exhaust. This is negligible in the case of heavy smoke, but when attempting to remove a light haze, electric fans are preferred.
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
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Date:
*Applies to fires in small/medium size structures. Large/multistory non-combustible buildings are addressed in Section 4. 170
171
Hydraulic Ventilation 172
Hydraulic ventilation uses the air flow entrained by an interior hose stream directed out of a 173
window or exterior doorway. This tactic should not be used before knockdown, as it would 174
draw smoke and fire toward the interior crew operating the hand line. It can be used in 175
combination with other post-knockdown tactics such as PPV. 176
177
178
179
180
Indications Contraindications Tactical Considerations
Fire in a known location
An exhaust opening larger
than the inlet opening (at
least 2-3 times the size of
the inlet).
Exhaust opening is in same compartment as fire.
Air can freely move from fan location → fire → exhaust opening
At least one firefighter can be assigned to stand by the fan and adjust/shut down as needed.
Fire location/compartment unknown
Exhaust opening cannot be established in the fire room
Exhaust opening smaller than inlet
Structure with vaulted ceilings or large open floor plan
Exhaust opening on windward side of structure
Firefighters or victims in windows or doorways (includes VEIS operations)
Significant openings in structure other than intended inlet & exhaust openings
Fire in void spaces of structure
Firefighters working interior prior to placement of fan
Backdraft conditions, or abnormal contents such as flammable gasses
Exhaust opening must be created prior to turning in fan*
Interior crews must be withdrawn (or confirmed to be in safe interior location) prior to beginning this tactic.
Minimize delay between turning in fan and applying water to seat of fire.
Both the inlet and exhaust opening must be constantly monitored for changing conditions.
A firefighter must be assigned to stand by the fan to shut down immediately, if needed.
Protect exposures near the exhaust opening
Buildings larger than 5000 sq. ft. will require more than one fan.
Hose streams should not be operated into an exhaust opening. Don’t try to combine PPA with a transitional attack.
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
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181
TACTICAL CONSIDERATIONS 182
High-Rise Buildings 183
Ventilating high-rise fires presents many challenges. Flow path considerations become more 184
important, as does use of building layout. Most high rises are noncombustible or limited 185
combustible, so the danger of collapse is decreased, but the difficulty in accessing the fire is 186
increased. Ventilation of fires in these structures will usually not be performed by the first 187
arriving company, but instead be assigned to another company or a Ventilation Group. This 188
makes coordination the key to safe and successful ventilation. 189
High-Rise: Vented vs. Not Vented 190
If a high-rise fire has not vented, the IC (or designee) should determine where the ventilation 191
opening will be, and coordinate with the attack crews as to when to create it. This may be 192
accomplished by breaking glass from an adjoining balcony, or striking it from above with a 193
hand tool suspended from a rope. The company or Ventilation Group should not create any 194
openings until requested by the attack crew, and monitor the condition of windows in the fire 195
area for signs of failure. 196
If a high-rise fire has vented, the IC (or designee) must determine the flow through the 197
ventilation opening. 198
High Rise: Wind Effects 199
Because of the increased danger posed by wind driven fires in a high-rise fire, the IC (or 200
designee) should constantly monitor all inlets/exhaust openings to the fire area for signs of 201
unidirectional inward flow or other wind driven fire behavior. Interior crews must also be aware 202
of the danger and be prepared to take refuge in internal compartments on the same face of the 203
building as the fire area. 204
205
Indications Contraindications Tactical Considerations
Fire under control
Presence of firefighters interior with charged hand line
Small area requiring ventilation.
Fire not under control
Freezing conditions
Have clear visual of area that will be sprayed by hose stream. Avoid people, energized electrical lines, etc.
Position nozzle about 2 feet from window.
Avoid blocking air flow to window with your body.
Water spray should be directed to the exterior to limit property damage.
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
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High-Rise: Post-Fire Smoke Removal 206
Some high rises are equipped with HVAC systems that can aid in removing and replacing the 207
air inside the structure much faster than normal PPV methods. Their use should only be 208
considered if building maintenance personnel are on scene and the fire is definitively under 209
control. The IC must be informed before activating such systems. 210
Commercial Buildings 211
Large assembly, retail, and manufacturing buildings may have less windows and exterior doors 212
than a residential occupancy or high rise, which can make establishing an exhaust opening 213
adequate for the volume of fire present difficult. 214
Such buildings lack a standard layout, making universal guidelines difficult to define. In 215
general terms, attempt to establish the fire’s location, and locate the nearest existing or 216
potential ventilation openings. Ventilation efforts must be in line with the overall strategy, and 217
take advantage of building features that may allow them to create a ventilation opening, or 218
isolate the fire to a specific area within the building. Fires in these buildings may go defensive 219
if not extinguished early in the event, and a defensive fire eventually self ventilates. 220
Basement Fires 221
Basement fires are as difficult to ventilate as they are to extinguish. Ideally, they can be 222
ventilated and attacked from the same level, such as in a walk-out or daylight basement. If at 223
all possible, ventilation (and fire attack) should take place from the exterior, as opposed to 224
having crews operating above an active fire. This may involve breaching an exterior wall. 225
Another option, may be to delay active ventilation until the fire can be knocked down (or at 226
least “reset”) by exterior water application. 227
Basements that are completely below grade on all sides. In such cases, the only way to 228
effectively ventilate the structure will be through the basement stairwell. Before opening the 229
stairwell, ensure there is a single clear and unobstructed flow path for the smoke to travel to 230
the outside of the structure before opening the doorway to the basement stairs. Once the 231
basement stairs are opened, assuming this is the only opening into the basement, bi-232
directional flow should create a small layer of cool air traveling down the stairs which can be 233
used by attack crews making an advance down the stairs. 234
Another option on basement fires is to use limited ventilation tactics. This means avoiding 235
making large openings that will provide the fire with oxygen and allow it to grow, and applying 236
water to the fire area through a small hole to apply water. This could be through the floor 237
above the fire, or an exterior wall. Water can be applied by a spear nozzle, cellar nozzle, or 238
fog nozzle. The disadvantage is that any victims in the fire area will be exposed to large 239
amounts of steam for an extended period. Therefore, this tactic should only be used when no 240
survivable spaces are believed to exist in the fire area. 241
Strip Mall Fires 242
Strip malls may have a much higher fire load than a residential house, depending on the 243
business occupancy. The occupancies usually have existing openings limited to the narrowest 244
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
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two sides, the storefront and the rear. There typically a common attic space which can allow 245
smoke and heat to spread to exposures. Their roof construction is heavier and more time 246
consuming to cut through. 247
Ventilation tactics must be coordinated with fire attack. An early ventilation survey of the 248
structure must be performed. Note the location of any possible ventilation openings and fire 249
breaks. If crews will be making an interior attack, the flow from the nozzle will generate 250
pressure like a positive pressure fan (although less pressure in total) so if an exhaust opening 251
can be created on the opposite side of the structure, smoke and heat will tend to flow away 252
from the fire attack team. 253
Such openings may require more manpower and equipment than in a residential structure. 254
Early allocation of sufficient resources is needed to ensure the opening can be created in 255
conjunction with fire attack. Establishing a Ventilation Group will allow the IC to coordinate the 256
overall incident efficiently. 257
Some fire service texts teach setting PPV fans into exposures on either side of the fire 258
occupancy, with the idea that they will pressurize the exposures and prevent smoke/fire from 259
extending into them. However, fires generate far more pressure than a fan, and many strip 260
malls have common attics. Therefore, such a tactic is unlikely to prevent fire extension and 261
may even contribute to fire spread by introducing additional oxygen. 262
Balloon Frame Buildings 263
Balloon frame houses are common in older areas of Lawrence. Lacking fire stops between 264
floors, fire can spread much easier than in newer buildings. For these reasons, use of a 265
blower fan for PPA or PPV is contraindicated unless the fire is definitively extinguished, and 266
even then should be used with caution. 267
Limited ventilation tactics such as door control may be most useful, as they will deny a fire the 268
oxygen with which to grow in void spaces until the main body of the fire is extinguished. 269
Opening exterior walls from the outside instead of the inside can be effective and exhausting 270
smoke and heat to the atmosphere instead of allowing it to travel to different areas within the 271
structure. However, this must not be done one the windward side of the structure as such 272
openings would allow wind to introduce far more oxygen than a fan would provide, and cause 273
rapid fire growth. 274
If smoke and heat are accumulating in the attic, an exhaust opening must be created quickly to 275
prevent having fires in two locations. This could be through vertical or horizontal ventilation, 276
but should be one of the first ventilation considerations in fires that have grown past the 277
incipient stage. 278
APPENDIX / KEY CONCEPTS 279
Ventilation-Limited Fires 280
A vent limited fires growth is determined by the amount of available oxygen. Every opening 281
into a structure is a ventilation opening, whether it’s a broken window, a hole in the roof, or the 282
fire attack door. In all cases, these openings will ultimately allow more oxygen to reach the 283
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
Ventilation Effective Date: Draft
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fire, which in turn will increase the size and extent of the fire. With a few exceptions, the 284
growth of the fire will be in the direction of opening. 285
Therefore, all ventilation efforts must be coordinated with the fire attack. The method, location, 286
and timing of these efforts must be purposeful and deliberate. Ventilation that occurs too early 287
or in the wrong place can increase the fire and endanger firefighters. 288
Controlled vs. Uncontrolled Ventilation Openings 289
Controlled ventilation openings are created by using existing openings in the buildings (e.g. 290
opening doors, hatches, windows, etc.), and can be re-closed if needed. Uncontrolled 291
ventilation openings are permanent openings, typically created by cutting or breaking some 292
part of the structure, and cannot be re-closed during the incident. 293
Controlled openings are preferred if available. For instance, if it will not otherwise delay 294
operations, forcing a lock on a tempered glass door is better than breaking the glass, because 295
if the door remains intact the opening can later be closed if ventilation needs change. 296
However, many buildings do not offer controllable openings in the quantities and locations 297
needed to provide adequate ventilation and uncontrolled openings must be created. 298
The Attack Door IS Ventilation 299
Interior fire attack will almost always involve opening an exterior door and advancing a hose 300
line through it to the seat of a fire. One of the key findings from modern fire science research 301
is that when this door is opened it serves as a significant ventilation opening, which was often 302
overlooked in years past. This means that the high-pressure smoke and heat flow toward that 303
opening, drawing the fire toward the attack crew. It also allows fresh air, with additional 304
oxygen to be drawn toward the fire at the floor level, intensifying the fire. 305
Research suggests that from the time the front door is opened crews have only a few minutes 306
to advance to the seat of the fire before the additional oxygen creates a rapid growth of fire. A 307
rule of thumb is that this will happen within 100 seconds in a 1-story house, and within 200 308
seconds in a 2-story house. Forcible entry efforts should attempt to preserve the door intact, 309
and a door should not be left open until the attack crew is making entry. 310
Flow Paths 311
A fire produces hot air and gasses as a product of combustion. These are at a higher 312
pressure than the rest of the environment. In a structure, this causes air pressure to build up 313
in the fire compartment. Since gas pressures always try to equalize, the atmosphere in the fire 314
compartment will flow into adjacent lower-pressure areas. This is how the fire spreads 315
pressure, heat, and smoke throughout the structure. 316
At the same time, as the fire consumes the oxygen present in the fresh air around it, it will 317
create a localized LOW pressure around its base. This low pressure will draw in fresh air from 318
any areas that have a higher pressure to the seat of the fire. 319
The fire’s flow path refers to the route taken by fresh air to the seat of the fire, and by the heat 320
and smoke travelling away from the seat of the fire. The flow path can change as the 321
exhaust/inlet openings change, and in response to firefighting tactics. 322
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Understanding the effect of flow paths on a fire, and of firefighting tactics on flow paths is 323
essential to safe and efficient firefighting. Monitoring the changes in a fire’s flow path allows 324
firefighters to determine if ventilation and fire attack tactics are working. 325
Unidirectional Flow Path 326
A unidirectional flow path occurs when the air flow in a given pathway to/from a fire is all going 327
the same way. A simple example of this would be a building that has a ventilation opening on 328
its roof, so that the fire draws fresh air in through the ground level door, and exhausts smoke 329
and heat through the hole in the roof. 330
Bi-Directional Flow Path 331
A bi-directional flow path is one in which fresh 332
air is drawn in to the fire on the floor level, 333
while superheated smoke and gas are pushed 334
away from the fire at the upper level of the 335
same path. A simple example of this would be 336
a fire in a room with a single opening. Most 337
doorways firefighters enter for interior attack 338
will have bidirectional flow. 339
The Neutral Plane 340
The neutral plane is the level in an 341
opening with bidirectional flow where the 342
exhaust flow and the inlet flow meet. This 343
level will change in response to fire 344
growth and firefighting tactics. Monitoring 345
the behavior of neutral planes throughout 346
a structure helps gauge the 347
effectiveness of these tactics. 348
The neutral plane of ventilation 349
openings can change for a number 350
of reasons. Therefore, it is 351
important to confirm that any 352
observed changes match expected 353
behavior. If they do not, it may be 354
an early warning sign of additional 355
unrecognized incident factors and 356
dangers. 357
If the neutral plane is descending, 358
as seen in Figure 5, the opening 359
is serving as an exhaust for more 360
products of combustion. This might 361
be due the fire growing in response 362
Figure 3: Unidirectional flow path
Figure 5: Neutral plane in doorway
Figure 4: Bi-Directional flow path
Lawrence-Douglas County Fire Medical Procedure 207.42 Title:
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to getting additional oxygen or fuel. However, the neutral plane could also descend in 363
response to changes in other openings affecting the ventilation profile. For instance, if an 364
open door that was serving as an exhaust outlet for half of the heat and smoke is closed, then 365
the other openings may see their neutral planes descend. 366
Any opening through which crews are operating interior should be monitored for signs that the 367
neutral plane is descending. This may be a sign that the fire is intensifying and expanding in 368
the direction of interior firefighters. 369
If the neutral plane is rising, it is typically a sign that the opening is being used more to draw in 370
fresh air and acting less as an exhaust outlet. This may be a good sign, suggesting the fire 371
growth is being checked by attack efforts. However, it may also be a sign of caution, 372
suggesting the fire is growing rapidly in another direction. This is especially true when the 373
opening under consideration is on a lower story than other openings. 374
Dangers of Operating in an Exhaust Flow Path 375
The exhaust flow path is the route taken by the hot air and smoke to the outside of the 376
structure. 377
Almost all interior fire attacks will require firefighters to operate in a flow path at some point. 378
This is not a contraindication, but firefighters must be aware that operating in an exhaust flow 379
path can cause PPE to fail earlier than expected. Just as wind makes cold air feel colder, 380
rapid movement of hot air past a firefighter transfers much more heat energy than relatively still 381
air of the same temperature. 382
There are several solutions to this issue which may be possible, depending on tactical 383
considerations. They include: 384
Opening hand lines into the flow path. This protects crews and also creates an interior 385
pressure back toward the fire as the hose stream entrains air in the direction of the water flow. 386
This may also check the growth of the fire until the line can be advanced to the seat for knock-387
down. 388
Withdrawing crews to change tactics or repositioning them to enter via a different attack 389
opening. This is especially true for firefighters operating interior above the fire level. 390
Isolating crews from the flow path – in a high rise or other building with long hallways, crews 391
may avoid the exhaust flow path by sheltering in place in a nearby compartment that can be 392
isolated from the flow path and the exterior. 393
Opening additional exhaust vents – this should be done in a coordinated manner, as described 394
in this SOP. 395
Partially or totally closing the exhaust vent – if the exhaust vent is the attack entrance, it cannot 396
be completely sealed due to the hose line in the doorway. However, it can be significantly 397
sealed by limited ventilation tactics (described above) such as door control or smoke curtains. 398
This will not cool the temperatures in which the crews are operating, but it will decrease the 399
rate at which the superheated air flows past their protective gear, and thereby prolong its 400
efficacy. 401
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