Ventilation conceptually is the same for both low-volume and very-high-volume facilities. But as Fort Worth has shown, ventilating large structures is significantly more involved.
Firefighters hold strong beliefs about strategies and tactics, and have experiences that they draw on to back up their viewpoints. In some cases though, firefighters’ perspectives may be based more on what they’ve been told or what they’ve read rather than on what they actually have experienced themselves.
Such “synthetic experiences” can be helpful in dealing with situations that one hasn’t encountered directly. On the other hand, they might lead firefighters to believe and even perpetuate practices or tactics that aren’t based on evidence.
Take, for example, ventilation. Most firefighters would agree that ventilation is a hallmark firefighting tactic. And most firefighters have significant experience in ventilating structures. Depending on their backgrounds, however, many would debate when, where and how to ventilate.
Let’s focus on ventilating very large occupancies, such as grocery stores, warehouses, office buildings, industrial facilities and high-rise buildings. A relatively small fire could produce significant losses in terms of life and property without timely and adequate ventilation.
Fires in such buildings might be considered low-frequency/high-risk events. While some firefighters have significant first-hand experience with ventilating these structures, most firefighters’ ventilation experience involves clearing relatively smaller occupancies like residential and commercial buildings.
Firefighters probably have more synthetic experience in the form of department procedures or fire-service literature than direct experience when it comes to very-high-volume structures.
These procedures usually detail a sequential process that begins with the exhaust opening, followed by the inlet opening and then other openings depending on the occupancy and the location of the smoke. Positive-pressure fans generally are used to displace the air inside the building. This creates a positive pressure inside the structure and a negative pressure at the exhaust opening, thereby moving the air from the inside to the outside of the building.
This practice seems to be very logical in most situations where ventilation is needed. In fact, the concept is virtually the same for relatively low-volume facilities and very-high-volume facilities. There is nothing wrong with the concept, but the reality is that ventilating large structures is significantly more involved.
The concepts of applying high gallons of water per minute to overcome high volumes of British Thermal Units and displacing high volumes of contaminated air with high volumes of fresh air are similar. However, most fire departments have the capability to apply large volumes of water through master streams, but do not have the capability to displace large amounts of air.
Where Concept, Reality Differ
This is where the reality of high-volume ventilation usually differs from firefighters’ preconceived notions of ventilating large structures. Most fire departments rely on electric or gasoline fans that move 12,000 to 14,000 cubic feet of air per minute. While more than sufficient to ventilate the average structure, these fans fall far short when attempting to displace air in very large buildings.
Multiple fans wouldn’t move enough air to create sufficient positive pressure to eject contaminated air in a timely manner, especially if the inlet opening is large, as is the case with overhead doors. Additional openings throughout the structure will lessen the potential for positive pressure inside the structure even further. The only realistic solutions for ventilating large structures are to rely on the building’s ventilation system, if it is equipped with one or to have a fan capable of moving tremendous amounts of air.
When available, the building’s ventilation system can be useful, as it is engineered to move air in a timely manner based on the building’s size. Also, many buildings have ventilation systems that are designed to create safe areas, such as stairwells, in high-rise buildings. However, open stairwell doors can limit severely the building’s ventilation system by creating large floor areas to pressurize. In addition, relying solely on the building’s system can be problematic, as there is no assurance that the system has been maintained or will even be in operation when needed. Even worse are buildings that do not have a ventilation system capable of pressurizing critical areas. The Cook County Administration Building fire in Chicago, where six people died in an upper-floor stairwell in 2003, falls into this category.W
The most realistic and reliable solution to displace large amounts of air in a structure resides in firefighters’ ability to either assist a building’s engineered ventilation system, or to produce the large volume of air needed with a fan capable of displacing millions of cubic feet of air in a timely manner. Fans are available that will produce hundreds of thousands of cubic feet of air per minute.
This volume of air can clear a 100,000-square-foot warehouse or grocery store in a relatively short time frame. Even larger occupancies of several hundred thousand square feet can be cleared in a reasonable amount of time. This is especially true when the ventilation process is prioritized.
Keep in mind that the floor area is only a fraction of the building’s cubic feet of space. Most ceiling heights are at least eight feet and easily can exceed 20 feet in some occupancies. A building with 200,000 square feet easily could have 2 million cubic feet of space. The ventilation process should follow the same set of priorities as the incident goals. Sequentially stated, we should ventilate to save the most lives, stabilize the incident, and save the most property.
While each incident requires very specific ventilation tactics to achieve priorities, generalities can be discussed here for the sake of gaining experience, even if the experience is synthetic. For instance, placing high-volume fans to clear means of egress certainly would support our No. 1 priority: life safety. Also, maintaining clear stairwells in high-rise buildings can support all three priorities simultaneously by allowing occupants to exit and firefighters to gain access to upper floors to manage the situation.
High-rise buildings represent the extreme high-volume structure because they can have very large floor areas stacked on top of each other. High-rise hospitals, nursing homes, dormitories and detention facilities present extreme situations where high-volume ventilation can be invaluable.
In some cases, pressurizing critical-care or occupant areas in these structures will limit the potential harm to occupants while firefighters extinguish a fire in another area of the building. Laundry, mechanical and utility areas are especially common fire areas. Maintaining tenability in the occupant areas while limiting the spread of the fire from these areas is a strategy we all can agree on.
But while we might agree in concept, we might disagree on the specifics of when and where to inject high volumes of air into a structure. Feeding fire tremendous amounts of air is certainly a serious concern, especially if firefighters haven’t located the fire in a very large structure. Even if they have located the fire, firefighters should have the gallons per minute needed to overcome the Btu before possibly intensifying the fire.
Wind-driven fires have received tremendous attention in recent years. wind-driven fires in residential structures and even high-rise buildings. Serious concerns about creating similar artificial wind-driven fire situations must be considered. However, the possibility of using high-volume, positive-pressure ventilation to counteract natural wind might also be considered. Without the empirical data to support this tactic at this time though, a word of caution is in order.has linked several firefighter fatalities to the overwhelming nature of
Caution should be used when considering not only the concepts of when, where and how to ventilate, but whether we actually can perform timely and adequate ventilation in high-volume structures. If your department has the necessary equipment, specifically a high-volume fan, you might consider discussing the way it will be used before setting it up on location.
Discussing possibilities ahead of time and testing our thoughts through training evolutions are great ways to determine whether our planned response is actually a realistic approach to mitigating serious incidents. Following our sequential priorities of life safety, incident stabilization and property conservation will provide general guidance, but each incident will require specific direction due to the dynamic nature of our business and the particular strategy needed to resolve the incident.
Basically, separating the realities of high-volume ventilation from the myths should be done over a cup of coffee and not on the scene. Consider whether your department actually has the ability to displace millions of cubic feet of contaminated air in a reasonable time. Though no amount of debate will change the fact that traditional practices and equipment will not get it done, fire hall discussions can provide valuable opportunities for separating ventilation fact from fiction.
Tim Hatch is a battalion chief with the Fort Worth (Texas) Fire Department.