Fire ventilation tactics you must know
The impact of ventilation is much more dramatic than many of us realize
Some days what I seem to be able to control diminishes with the passage of each minute. I’m sure we all have and will continue to have such days. Some days I question the impact of my mere presence, let alone my efforts.
But the reality is that all of our actions or inactions have an impact on what goes on around us.
Albert Einstein did not like the thought that the reality of our universe couldn’t be measured accurately and predicted, that things could be random. Einstein actually felt that randomness was simply an indicator that we were ignorant of some fact.
We often think that structure fires are repeatable, measurable events; that they are not random, that they can be categorized and that if we simply perform the same actions over and over again, we’ll achieve the same outcome.
What we often fail to realize is that although many of a building’s components are made to react in certain ways, we, the firefighters, often disrupt and have an impact on fire progression — and NOT in a positive way.
For those who don’t know, Underwriters Laboratories does more than just put their logos on electrical appliances. UL tests items both to make sure they meet standards, such as those by the NFPA, but also conducts tests to see if what those standards suggest really work.
They also see if the things that underwriters (the real money behind insurance, think Lloyds of London and such) are getting protected.
In 2008, the Department of Homeland Security funded an experiment with UL to find out how the introduction of fresh air and removal of the products of combustion (ventilation) impacted fire growth and tenability in structures.
They performed 15 burns in identical one- and two-story structures to see what the impact would be on fire spread and combustion rates. The outcomes are well worth watching — check out the extensive presentation here — and the impact on tactical considerations worthy of review.
We must recognize that our primary function is life safety and property conservation. I always say, “Our lives, their lives, their stuff, our stuff.”
That is to say, our priorities are our own lives, then the civilians’ lives. We can’t kill ourselves for the unsavable civilian. At the same time, they paid for our equipment so we can use it till it breaks to save their property. All efforts must be directed toward trying to ensure tenability of life inside the building and to limit property damage.
The UL study determined that often our ventilation activities, including forcible entry, severely and negatively impact tenability and property protection; that today’s room contents not only lead to more dangerous fires but that the impact of ventilation is much more dramatic than many of us realized.
To that end, the study addressed several tactical considerations which are well worthy of our attention:
Stages of fire development
The stages of fire development change when a fire becomes ventilation limited. It is common with today’s fire environment to have a decay period prior to flashover, which emphasizes the importance of ventilation.
Forcing the front door is ventilation: Forcing entry has to be thought of as ventilation as well. While forcing entry is necessary to fight the fire, it must also trigger the thought that air is being fed to the fire and the clock is ticking before either the fire gets extinguished or it grows until an untenable condition exists, jeopardizing the safety of everyone in the structure.
No smoke showing
A common event during the experiments was that once the fire became ventilation limited, the smoke being forced out of the gaps of the houses greatly diminished or stopped altogether. No smoke showing during size-up should increase awareness of the potential conditions inside.
If you add air to the fire and don’t apply water in the appropriate time frame, the fire gets larger and safety decreases. Examining the times to untenability gives the best case scenario of how coordinated the attack needs to be.
Taking the average time for every experiment from the time of ventilation to the time of the onset of firefighter untenability conditions yields 100 seconds for the one-story house and 200 seconds for the two-story house.
If a vent location already exists because the homeowner left a window or door open, then the fire is going to respond faster to additional ventilation opening because the temperatures in the house are going to be higher. Coordination of the fire attack crew is essential for a positive outcome in today’s fire environment.
Smoke tunneling and rapid air movement through the front door: Once the front door is opened, attention should be given to the flow through the front door. A rapid in-rush of air or a tunneling effect could indicate a ventilation limited fire.
During a VES operation, primary importance should be given to closing the door to the room. This eliminates the impact of the open vent and increases tenability for potential occupants and firefighters while the smoke ventilates from the now isolated room.
Every new ventilation opening provides a new flow path to the fire and vice versa. This could create very dangerous conditions when there is a ventilation limited fire.
Can you vent enough?
In the experiments where multiple ventilation locations were made, it was not possible to create fuel-limited fires. The fire responded to all the additional air provided.
That means that even with a ventilation location open, the fire is still ventilation limited and will respond just as fast or faster to any additional air. It is more likely that the fire will respond faster because the already open ventilation location is allowing the fire to maintain a higher temperature than if everything was closed.
In these cases, rapid fire progression if highly probable and coordination of fire attack with ventilation is paramount.
Impact of shut door on occupant tenability and firefighter tenability: Conditions in every experiment for the closed bedroom remained tenable for temperature and oxygen concentration thresholds. This means that the act of closing a door between the occupant and the fire or a firefighter and the fire can increase the chance of survivability.
During firefighter operations, if a firefighter is searching ahead of a hose line or becomes separated from his crew and conditions deteriorate, then a good choice of actions would be to get in a room with a closed door until the fire is knocked down or escape out of the room’s window, with the closed door providing more time.
Potential impact of open vent already on flashover time
All of these experiments were designed to examine the first ventilation actions by an arriving crew when there are no ventilation openings. It is possible that the fire will fail a window prior to fire department arrival or that a door or window was left open by the occupant while exiting. It is important to understand that an already open ventilation location is providing air to the fire, allowing it to sustain or grow.
There were no temperature spikes in any of the rooms, especially the rooms adjacent to the fire room when water was applied from the outside.
It appears that in most cases the fire was slowed down by the water application and that external water application had no negative impacts to occupant survivability. While the fog stream “pushed” steam along the flow path, there was no fire “pushed.”
No damage to surrounding rooms: Just as the fire triangle depicts, fire needs oxygen to burn. A condition that existed in every experiment was that the fire (living room or family room) grew until oxygen was reduced below levels to sustain it.
This means that it decreased the oxygen in the entire house by lowering the oxygen in surrounding rooms and the more remote bedrooms until combustion was not possible. In most cases surrounding rooms such as the dining room and kitchen had no fire in them even when the fire room was fully involved in flames and was ventilating out of the structure.
The report is well worth the time it takes to review and is certainly worth sharing during drill, even if just some parts of the overall report. Ultimately it shows how little we can control. What we can always control, however, is our own actions including learning and training – we truly can have an impact.