Ventilation Tactics: When to Go Vertical, When to Go Horizontal, and When to Wait

Ventilation is one of the most misunderstood and most dangerous operations on the fireground. Done correctly and at the right time, ventilation saves lives. It lifts the smoke layer, improves visibility for interior crews, reduces temperatures, and channels the products of combustion out of the structure in a controlled manner. Done incorrectly, at the wrong time, or without coordination, ventilation can accelerate fire growth, push fire into uninvolved areas, and create conditions that injure or kill firefighters and trapped occupants.

The decision of when and how to ventilate is not something you figure out on the roof. It is a decision that requires an understanding of fire behavior, building construction, flow path dynamics, and the current tactical situation. You need to know the principles cold so you can apply them under pressure.

What Ventilation Actually Does

At its core, ventilation is the exchange of air within a structure. You are removing hot gases, smoke, and combustion products and replacing them with cooler, cleaner air. This exchange improves conditions for interior crews and any occupants who are still inside.

But here is the critical reality: when you remove hot gases and bring in fresh air, you are also providing oxygen to the fire. A ventilation-limited fire that has consumed most of the available oxygen in a compartment will react aggressively when it receives a fresh air supply. If the fire is ventilation-limited and you provide oxygen before water is applied, you are feeding the fire. This is the fundamental tension in ventilation operations. You want to remove the bad air and improve conditions, but doing so can make the fire bigger before it gets smaller.

This is why coordination between ventilation and fire attack is not optional. It is the most important tactical coordination on the fireground.

Vertical Ventilation

Vertical ventilation involves cutting a hole in the roof directly over the fire and allowing the heat, smoke, and combustion products to vent straight up through the opening. This takes advantage of the natural tendency of hot gases to rise and is the most effective form of ventilation for removing heat from a structure.

The ideal vertical ventilation hole is directly over the seat of the fire or as close to it as possible. The hole should be at least four feet by four feet, though bigger is generally better. Cut the roof decking, pull the ceiling below if necessary, and the thermal column of hot gases will rise through the opening, dramatically improving conditions below.

Vertical ventilation is most effective on peaked roof residential structures where the fire is on the top floor. The roof pitch creates a natural collection point for hot gases at the ridge, and a vent hole at or near the peak gives those gases a direct path out.

FSRI at fsri.org has published extensive research on ventilation timing and coordination. Their studies demonstrate that vertical ventilation performed before an attack line is in place and flowing water can cause rapid fire growth on the floor below. The fresh air supply entering through the vent hole and other openings feeds the fire, and without water to control it, conditions can deteriorate quickly. Their recommendation is clear: coordinate ventilation with suppression.

Vertical ventilation requires firefighters to work on the roof, which introduces significant risks. You need to assess roof structural integrity before committing personnel. Sound the roof with a tool as you advance. Stay on structural members, not the middle of spans. Watch for spongy decking, sagging areas, and lightweight truss construction. If the roof is compromised, get off it. No ventilation hole is worth a firefighter falling through a roof into a working fire.

Horizontal Ventilation

Horizontal ventilation involves opening or removing windows, doors, and other wall-level openings to allow smoke and hot gases to exit horizontally. This can be accomplished by breaking windows, opening doors, or using mechanical fans to push air through the structure.

Horizontal ventilation is simpler to execute than vertical ventilation because it does not require roof operations. However, it is less effective at removing heat because hot gases naturally rise. Pushing them out horizontally requires either wind or mechanical assistance to be truly effective.

The most common form of horizontal ventilation is positive pressure ventilation, or PPV, using a mechanical fan placed at the entry door. The fan pushes fresh air into the structure, pressurizing the interior and forcing smoke and hot gases out through an exhaust opening on the opposite side, typically a window near the fire.

PPV is extremely effective when done correctly, but it requires precise coordination. The exhaust opening must be created before or simultaneously with the pressurization. If you pressurize the structure without an adequate exhaust opening, you simply push the smoke and heat deeper into the structure, potentially into areas where occupants or firefighters are located.

The exhaust opening should be positioned to create a flow path that channels smoke and gases away from interior crews and any known or suspected victim locations. This requires communication between the ventilation crew and the interior attack team.

When to Ventilate

The timing of ventilation is as important as the method. Here are the key decision points.

Ventilate when the attack line is in position and water is being applied. This is the fundamental coordination requirement. Water controls the fire while ventilation clears the environment. Done together, conditions improve rapidly. Done separately, ventilation alone can make things worse.

Ventilate when there is a known life hazard and ventilation will improve conditions for the victim. If you have a confirmed rescue situation with an occupant trapped in a smoke-filled area, ventilation may be necessary even before the attack line is in place. This is a risk-based decision. You are accepting the risk of increased fire growth in exchange for improving survivability for the victim. This decision should be made deliberately by the incident commander, not freelanced by individual firefighters.

Do not ventilate when the fire is ventilation-limited and no attack line is in position. If the fire has consumed most of the available oxygen and is smoldering or pulsing, providing fresh air without simultaneous suppression can cause a rapid increase in fire intensity. Read the signs: pulsing smoke at openings, dark staining around closed windows, and little visible flame despite heavy smoke all suggest a ventilation-limited fire.

Do not ventilate when you do not know the fire location. If you do not know where the fire is, you cannot predict the effect of ventilation. Opening a window on the wrong side of the structure can pull fire toward the opening and into the path of interior crews. You need to locate the fire before you start modifying the ventilation profile of the building.

Hydraulic Ventilation

Hydraulic ventilation uses the fire attack stream to create airflow and clear smoke from the interior. By positioning the nozzle near a window or door opening with a fog pattern that covers approximately 85 to 90 percent of the opening, the moving water droplets entrain air and create a draft that pulls smoke out of the space.

Hydraulic ventilation is the safest form of ventilation because it does not require separate roof operations, does not require opening additional ventilation points, and is performed by the attack crew who are already inside with water. It is particularly useful in situations where vertical ventilation is not feasible and conditions do not support PPV.

The limitation of hydraulic ventilation is that it is less powerful than mechanical ventilation and requires the attack crew to dedicate their stream to ventilation rather than fire suppression for the duration. It is most effective after the fire has been knocked down and you need to clear the space for overhaul and search.

The Coordination Imperative

The single most important principle in ventilation operations is coordination. The engine company, the truck company, and the incident commander must be communicating about the timing and location of all ventilation actions. No one should be breaking windows or cutting roof holes without authorization and coordination.

On the modern fireground, freelance ventilation, meaning uncoordinated opening of ventilation points by individual firefighters acting on their own, is one of the most dangerous behaviors that occurs. A well-intentioned firefighter who breaks a window to improve conditions in one area can push fire into another area where crews are operating. This is not theoretical. It has killed firefighters.

Every opening you create on the fireground changes the flow path. Every change in the flow path affects conditions throughout the structure. If you understand this principle, you understand why ventilation must always be deliberate, coordinated, and tied to the overall tactical plan.

First Due Co. puts ventilation coordination into every fire scenario, teaching you to think about timing, position, and flow paths before you cut or break anything. Train with purpose at firstdueco.com.