Fire Attack Tactics, Ventilation & Overhaul

Fire Attack Tactics, Ventilation & Overhaul

Translating size-up decisions into fireground success requires mastery of interior attack methods, precise ventilation timing, and thorough overhaul procedures. Fire officers must select attack modes based on fire progress and coordinate ventilation to prevent explosive thermal events.

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Modes of Structural Fire Attack

The choice of fire attack mode depends on compartment temperature, visibility, fire location, and structural integrity. Firefighters utilize three primary offensive water application modes:

1. Direct Fire Attack

• Method: Water stream (solid, straight, or narrow fog) is applied directly onto the burning fuel surface at the seat of the fire.
• Operational Advantage: Maximizes cooling of solid fuels, reduces steam production in the upper air layer, and minimizes thermal discomfort for attack crews inside the room.
• Indication: Visible seat of fire, manageable thermal conditions, and clear access to the burning fuel.

2. Indirect Fire Attack

• Method: Firefighters direct a wide fog stream into the superheated upper gas layer near the ceiling from an exterior doorway or window without entering the compartment.
• Mechanism: Water droplets vaporize in superheated air (above 1,000°F / 538°C), expanding rapidly into steam (1:1,700 expansion ratio at 212°F / 100°C; over 1:4,000 at superheated fire temperatures). Steam displaces oxygen and rapidly cools the ceiling space.
• Warning: Must not be used in occupied spaces or where firefighters are located inside the compartment, as expanding steam will cause severe thermal burns to personnel.

3. Combination Fire Attack

• Method: Combines ceiling layer cooling with fuel surface application. Attack personnel move the nozzle in a structured geometric pattern—such as a 'Z', 'O', or 'T' shape.
• Execution: The narrow fog or straight stream is first directed high across the ceiling to cool upper toxic gases, then swept down across the floor and burning fuel bed to extinguish solid burning materials.
• Indication: Heavy interior heat buildup, rollover operating in the upper atmosphere, and severe thermal threat to advancing hose crews.

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Structural Ventilation Principles & Methods

Tactical Ventilation is the systematic, controlled removal of heated air, smoke, and toxic gases from a structure, replaced with cooler, fresh air. Coordinated ventilation lowers interior temperatures, improves visibility for primary search teams, and drastically reduces the probability of Flashover (simultaneous ignition of all combustible contents) and Backdraft (smoke explosion caused by sudden oxygen introduction into an oxygen-depleted room).

+-------------------------------------------------------------------------+
|                    TACTICAL VENTILATION CLASSIFICATION                  |
|                                                                         |
|                         /                     \                         |
|            [NATURAL VENTILATION]       [MECHANICAL VENTILATION]         |
|            (Windows, Doors, Roofs)              |                       |
|                                    +------------+------------+          |
|                                    |            |            |          |
|                                  [PPV]        [NPV]     [HYDRAULIC]     |
|                                (Positive)   (Negative)   (Fog Nozzle)   |
+-------------------------------------------------------------------------+

Natural vs. Mechanical Ventilation

• Natural Ventilation: Relying on ambient wind currents and natural thermal convection currents (stack effect) by opening doors, windows, and roof scuttle hatches.
• Mechanical Ventilation: Utilizing powered fans, blowers, or hose streams to force air movement:

1. Positive Pressure Ventilation (PPV): Placing a high-capacity powered blower outside the entry door, blowing fresh air inward. This creates positive atmospheric pressure inside the building, forcing smoke and heat out through a single, pre-selected exhaust opening on the leeward side.
   • Requirement: Strict door control and a controlled opening-to-exhaust area ratio (exhaust opening should be 75% to 150% of the entry doorway size).
2. Negative Pressure Ventilation (NPV): Suspending smoke ejector fans inside upper windows or doorways to pull smoke out of the building, exhausting it to the exterior.
3. Hydraulic Ventilation: Operating a wide fog stream out a window or doorway from 2 to 4 feet inside the room, covering 85–90% of the opening. The high-velocity water movement creates a Venturi effect that draws smoke and gases out of the compartment.

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Horizontal vs. Vertical Ventilation

Horizontal Ventilation

Releasing heat and smoke through openings on the same level as the fire (windows, exterior doors, wall cuts). Highly effective for single-story structures or compartmented room fires.

Vertical Ventilation

Cutting openings in roofs or opening existing vertical shafts (skylights, scuttle covers, stairwell penthouses) to release heat and smoke directly upward. Vertical ventilation operations require strict safety precautions due to roof structural collapse hazards.

Roof Cutting Techniques & Safety Protocols

• Kerf Cut: A single continuous saw blade cut made into the roof decking to inspect for heat, smoke, or fire presence directly underneath.
• Triangular Inspection Cut: A small three-sided cut used to determine roof deck thickness, rafter direction, and structural integrity.
• Louver Cut (Rectangular Cut): Cutting roof decking between rafters and tilting sections on the rafter axis to create a wide exhaust opening.
• Trench Cut (Strip Cut): A defensive vertical ventilation cut executed across the entire width of a roof assembly ahead of an advancing fire in large commercial structures or attics. The trench cut acts as a firebreak to prevent horizontal fire propagation.

Overhaul Operations & Rekindle Prevention

Overhaul is conducted after the main body of fire has been extinguished. Its purpose is to locate and extinguish hidden pockets of fire in wall cavities, cocklofts, floor voids, and furniture, ensuring the fire is completely out and preventing a rekindle.

+-------------------------------------------------------------------------+
|                       OVERHAUL SAFETY & EXECUTION                       |
|                                                                         |
| [Main Fire Extinguished] ---> [Structural Inspection & Utility Safety]  |
|                                                  |                      |
|                                                  v                      |
| [Rekindle Prevention] <--- [TIC Scanning & Wall/Ceiling Breaching]      |
+-------------------------------------------------------------------------+

Overhaul Safety Precautions

• Continuous SCBA Use: Toxic off-gassing of carbon monoxide (CO), hydrogen cyanide (HCN), and carcinogenic particulates remains extremely high during overhaul; full SCBA is mandatory.
• Structural Assessment: Fire weakens structural joists, rafters, and floor assemblies. Officers must inspect for sagging floors, cracked masonry, and heavy water accumulation prior to sending crews inside.
• Utility Disconnection: Electrical, gas, and solar PV system feeds must be isolated and locked out before opening walls.

Thermal Imaging Cameras (TIC)

A Thermal Imaging Camera (TIC) detects infrared radiation emitted by heat sources, converting temperature differences into a visual grayscale or color image.

• Overhaul Application: TICs allow firefighters to rapidly scan walls, plaster ceilings, insulation, and baseboards to pinpoint hot spots (represented as bright white/yellow/red regions) without needlessly tearing down intact structural surfaces.
• Search & Rescue Application: TICs assist in locating unconscious victims through dense smoke and identifying thermal footprints on furniture.