There has been a lot of focus the past few years on controlling ventilation. Controlling the vent point goes against what many were originally taught and the opposite of what we practiced for many years. Because of the greater understanding of fire dynamics and ventilation-induced fire behavior, many departments, including some of the largest departments like Los Angeles County (CA), the Fire Department of New York (FDNY), and Chicago (IL) have adopted new best practices that have been successfully instituted on the fireground. Is it perfect? Absolutely not. Do we still have to use our experience and knowledge to make intelligent fireground decisions that may go against what had been previously taught? Yes! However, those situations should be few and far between.
To Vent Or Not To Vent?
One area that some firefighters have trouble understanding with controlling the vent point is what we’ve seen and felt on the interior when we don’t open up and actually shut it down instead. In the past, when we performed ventilation, we achieved a lift of smoke, heat, and unburned products of combustion, giving us a clearer view at the floor level. This lift and clearer view gave us the ability to work faster and more efficiently by giving us the ability to work in an environment we could see, and it gave us the perception that it was cooler in temperature. When we do not perform ventilation and instead shut/control doors, we are allowing the environment to continue to fill with the smoke, heat, and unburned products of combustion. This places us in an environment that we have been taught is bad for us and bad for the occupants.
What we can’t see when operating on the fireground are the things that are truly happening to the gas and heat levels when we ventilate and when we do not ventilate. When we ventilate, temperatures will rise. This rise in temperature is because of the most basic form of the fire dynamics. Fire needs oxygen to burn. The more oxygen we provide, the fire gains in size and intensity. Regardless if the “hole” is a window, door, or 4 × 4 roof hole, the temperatures will rise because we are supplying more oxygen.
When we do not ventilate (until water is applied), we are decreasing the amount of available oxygen. Therefore, the fire decreases in size or slows its growth. This allows less heat and energy to be created. However, the smoke and unburned products of combustion will drop to the floor, exposing a potential trapped victim to poisonous gas. The part that we need further understanding of is what is actually occurring to the environment. The poisonous gases already exist at levels that can be deadly, and excess moisture from the burning synthetic materials already exists prior to water application. The more heat that is generated by allowing oxygen will increase the gas concentrations and temperatures that the victims are exposed to. While visually it appears to be counterproductive to shut down ventilation, when we step back and review the data from research studies, we are increasing victim survivability by controlling the vent point.
Research on Governors Island, New York, found that one of the important outcomes was quantifying how much more hazardous ventilation can make fire conditions. In one experiment, the first-floor living room was reignited, creating a fuel-rich, ventilation-limited environment. The front door was then opened and bedroom windows were vented, creating a flow path from the front door through the open bedroom window.
The bedroom door was then closed, blocking the flow path. Less than 90 seconds after the front door was opened, and before the bedroom windows were vented, the temperature at the front door rose from approximately 75°F to more than 550°F. At the same time, the temperature in the living room (front and rear), where the fire had started, almost doubled, reaching flashover.
The Governors Island experiments showed that adding ventilation or being in the exhaust flow path of the fire reduced potential survival time. Importantly, it demonstrated the viability of closing the door behind the firefighters once vent, enter, isolate, and search (VEIS) operations have commenced. The idea of firefighters entering a burning building and closing the door behind them is both contrary to traditional practice and counterintuitive. However, the experiments definitively show that closing the door interrupts the flow path, reducing oxygen in the structure, lowering its temperature, and improving both victim and firefighter survivability.
Another important and counterintuitive finding in the Governors Island experiments relates to the impact of venting on oxygen and carbon dioxide levels in the open bedroom. Opening the front door and the windows in the open and closed bedrooms led to a decrease of oxygen in the air in the open bedroom from 21 percent to eight percent. At the same time, the carbon dioxide levels rose to nine percent of the air, creating a highly hazardous environment for any occupants in that room. Closing the door to the bedroom almost immediately began to reverse the effects. Within two minutes, oxygen had risen to 16 percent of the air, while carbon dioxide dropped to four percent.
The experiments also showed that interrupting the outlet of a flow path can help slow a fire. In one experiment, the front door was closed after the basement reached flashover. This interrupted the flow path that had run from an open basement window and Bilco door to the previously open front door. While opening the front door led to flashover in several areas of the home, closing the door reduced room temperatures by as much as 70 percent.
More To Do
If we are truly concerned about the victim, there are many more components we need to look at and adopt. Does your department promote residential sprinklers? Does your department promote Close Before You Doze? Are you altering your search techniques to be more efficient? Are you applying water in the quickest manner possible, regardless of if that is from the interior or exterior?
Remember, the fire does not know where the water is coming from! If it comes in the window or down the hall, the temperatures will be reduced. If we promote keeping interior doors closed and we promote getting water on the fire in the quickest manner possible, we will lower temperatures and decrease gas concentrations—increasing the chance of survival.
Underwriters Laboratories, “Interrupting the Flow Path,” New Science Fire Safety Article, http://newscience.ul.com/wp-content/themes/newscience/library/documents/fire-safety/NS_FS_Article_Interrupting_Flow_Path.pdf.
P.J. Norwood is a deputy chief training officer for the East Haven (CT) Fire Department and has served four years with the CT Army National Guard. He is a FDIC classroom, workshop, and H.O.T. instructor; Fire Engineering advisory board member; and Fire Engineering book and video author and served on the ULFSRI technical panel for the Study of Residential Attic Fire Mitigation Tactics and Exterior Fire Spread Hazards on Fire Fighter Safety. Norwood is certified to the instructor II, officer III, fire marshal, and paramedic level. He has lectured across the United States as well and overseas.
Sean Gray is a 24-year veteran of the fire service and is a lieutenant with Cobb County (GA) Fire and Emergency Services. He has been a member of multiple technical panels involving firefighter safety research and is an appointed member of the UL Firefighter Safety Research Institute Advisory Board. Gray is an NFPA committee member for fire hose and fire service training facilities. He recently coauthored a Fire Engineering DVD and book, The Evolving FireGround. Gray has also been published in multiple fire service magazines, is an FDIC H.O.T. lead instructor, runs the Web site stopbelievingstartknowing.com, and delivers evidence-based tactics training courses across the United States. He has a bachelor’s degree in fire safety engineering and is working toward furthering his education.