Horizontal ventilation and PPV: Back-to-basics tactics
While not the preferred method of ventilation in the modern era, horizontal ventilation remains a valid option in some circumstances
Horizontal ventilation is as old as the fire service itself. Likely with little to no understanding in the early years, horizontal ventilation was really the first method employed by firefighters to release heat and toxic gases from a structure.
While not necessarily the preferred method of ventilation these days, horizontal ventilation has stood the test of time and, even today, in the era of mechanically assisted positive pressure ventilation (PPV), the traditional form of horizontal ventilation could still be your only option in certain circumstances. As such, it’s important to understand the process and how our efforts will impact fire conditions.
Horizontal ventilation is not simply breaking windows
Horizontal ventilation requires some thought and planning before initiating any action. We have learned, through experience and research, that one action leads to another. In regard to horizontal ventilation, the action of opening a window or a door creates a flow path, essentially a path of least resistance for heat and toxic gases to flow from the fire area to that opening, potentially worsening conditions interior.
However, we also know, again through experience and research, that if we put a little thought into our horizontal ventilation effort, we can control the flow path to a certain extent. Taking into consideration available openings, wind direction and the advancement of the attack team, we can choose the best possible openings that will yield better ventilation results or even change the current flow path.
Of course, improper timing and randomly breaking windows can result in unexpected and unintended results. When we make the decision to ventilate, we must take into account the possible flow paths we are creating – and maintain control of it. Improperly initiating horizontal ventilation can lead to extended ventilation efforts, draw fire and smoke into areas not already involved and, in some situations, can even endanger or injure the attack crew.
Horizontal ventilation is a coordinated and synchronized process
As professionals, we are not looking to randomly break windows. When done correctly, horizontal ventilation is a step-by-step process. In fact, a better descriptor of the action would be “coordinated/synchronized horizontal ventilation.” What does that mean exactly?
Coordinated: Horizontal ventilation should be coordinated with the attack crew in whatever method they determine is best for their attack methods, whether it’s before or after the application of water. If we are launching an interior attack, we want to coordinate our ventilation effort.
Synchronized: Synchronized horizontal ventilation involves closing the doors to every room in the structure, isolating them from the room of origin and the bigger rooms (living room/ kitchen), and ventilating the bigger open rooms first, using the front and back doors or larger windows (open, not break when possible). We would then open the door to one room at a time to ventilate that room by opening a window in that room. Once that one room is clear, we close the door to that room and open a door to a new room to ventilate. We can open all the windows to all the rooms at the same time as long as we isolate the individual rooms first by keeping the door closed. This will allow some ventilation to occur while those individual rooms are waiting to be better ventilated by opening the door.
By using this method, we control any flow paths we create from the beginning to end of the ventilation process.
Adding positive pressure into horizontal ventilation efforts
When positive pressure fans are added to our ventilation efforts, isolating the individual rooms is particularly important. It is more critical here to control the flow path than in any other form of ventilation. Failure to understand and control our flow path can lead to a catastrophic event.
When performing positive pressure ventilation (PPV), we are simply adding the positive pressure element to our horizontal process. We place the fan at the door and can use the opening already made by the fire, or we create an opening to the fire room, usually the window in the room of origin, as our vent point. This is truly the only window that should be broken from the outside when using positive pressure fans.
By isolating all the other rooms, we do two things at once: 1) We eliminate or lessen the chance that we will spread the fire or make conditions worse, and 2) when the fire is contained, we speed the ventilation process of the rest of the structure.
There is no ventilation fan on the market that can effectively ventilate a 2,500-square-foot house with all the windows and doors open. It is faster, more efficient and more effective to have one entrance and one exit (flow path) open at a time, ventilating one room at a time. This applies to natural horizontal ventilation and adding PPV into the ventilation efforts.
When presented with windowless basements, subfloors or buildings with limited openings, PPV is required to expedite the ventilation process. However, we cannot simply set up our fan and pressurize the area. We will need to have a plan.
One plan is to use the staircase as our vent point. This is effective if we have two staircases – one staircase for intake of fresh air and one staircase as our vent point.
If we only have one staircase available for ventilation, however, ventilation ducting will be required to streamline the operation. There must be enough ventilation ducting to place the fan about 10 feet from the door to the area to be ventilated to the side of the door, not directly in front of the door. This will help avoid reintroducing any smoke we are venting. Then we need enough to reach the back room, make a 180-degree turn and aim the ducting back at our entrance point or door/staircase, essentially using the intake as our vent point. To enhance this operation, you could use one or two old-school smoke ejectors hanging from the upper part of the door as well.
If ventilation ducting is not available, placing the positive pressure fan in the doorway and using a salvage cover around the fan and halfway up the door will enhance the ventilation effort, with fresh air being introduced at the lower portion of the doorway opening and smoke exiting the upper portion of the doorway. In this scenario, we are manufacturing our own “neutral plain” and bi-directional flow mechanically through PPV, where fresh air is brought in from the bottom and the byproducts of fire are forced out the top. While this is not an ideal scenario, it is more effective than using the old-school smoke ejectors or simply pointing the fan at the door and hoping for the best results.
PPV of an exposure building
Your positive pressure fan can be used for more than just ventilation of a structure; it can also help prevent exposures from becoming an involved structure in the first place.
In this scenario, we would not open any windows or create any additional exterior openings other than the opening needed for the fan. We want to pressurize the entire house. Simply open the front door and any attic space or cockloft opening, set the fan at the appropriate distance to “seal” the door, and let the pressurization of the structure keep the heat and any fire impingement from entering or traveling through the structure. It’s controversial and not meant as a long-term solution to an exposure problem, but it could be effective under certain circumstances to prevent any significant spread or at least slow the spread significantly.
Ventilation fans: The good and the bad
Let’s now turn to the different types of ventilation fans and what’s required to use them.
Smoke ejectors: Smoke ejectors were the first form of mechanically assisted ventilation fans on the market. They move between 3,700 cfm and 11,800 cfm, depending on the manufacturer. Smoke ejectors were intended to essentially suck the smoke out of the structure. If no additional openings were made, in theory, you would be creating a vacuum inside the structure and getting very little movement or improvement. After the fire is controlled, opening an additional door or window would make this option more efficient. This is the slowest way to ventilate a structure.
Positive pressure fans: Positive pressure fans also come in many forms, with most moving 12,800 cfm or more, depending on the manufacturer.
Gas-powered was one of the first and more popular versions. While these fans were the most effective at moving large amounts of byproducts from the structure quickly, they also produce a fair share of carbon monoxide. On several occasions, I have had to ask myself if it was the byproducts of the fire or the CO created by the running gas-powered motor of the fan that was making me feel bad, one time bad enough to require transport to the ER for evaluation.
If using a gas-powered fan during extended ventilation operations or multiple gas-powered fans for even a short time, air monitoring should be assigned to a safety officer for continuous air monitoring, including for a period after the fans are shut down until CO levels are deemed acceptable and natural ventilation of remaining CO levels can continue without the presence of fire department personnel.
In recognizing the problem with the production and buildup of CO levels inside a structure associated with fuel-powered fans, manufactures produced electric-powered positive pressure fans, but that required a source of power, either from the building being ventilated, which is not always possible, or from a generator on the apparatus. The manufacturers do, however, now offer the option to eliminate the CO problem altogether.
Recently, battery-powered fans have been introduced to the fire service. These fans are slimmer, lighter, more user-friendly and just as effective in moving large amounts of air inside a structure. The drawback is maintaining the batteries and replacing them when necessary.
Have a plan
Regardless what method of ventilation you use, in today’s fire service there is no excuse for a crew not to approach their ventilation efforts without a well-educated and thought-out plan.
Coordinate with the attack crew and synchronize for flow path management, when possible, for the best results. Simply smashing windows and putting a fan at the door without understanding what the results could be is one of the fastest ways in today’s fire service of showing a high degree of incompetence.
Get out and train! Be safe!