UL: Impact Of Fire Behavior, Ventilation

Underwriters Laboratory provides you with a wealth of new information on ventilation and fire behavior in the modern home.

Underwriters Laboratories, and more specifically Steve Kirber (author), have put together research information funded by an AFG grant on ventilation practices on fire behavior in the modern home geometry.

At a Underwriters Laboratories facility in Northbrook, IL researchers built two homes. The first was a one-story, 1,200 sq.ft., 3 bedroom, 1 bathroom house with 8 total rooms. The was a two-story 3,20sq.ft., 4 bedroom, 2.5 bathroom house with 12 total rooms. The second had a modern open floor plan, two-story great room and open foyer. 15 tests were done varying the ventilation locations and the number of ventilation openings.

Scenarios included:
– ventilating the front door only
– opening the front door and a window near and remote from the seat of the fire
– opening a window only and ventilating a higher opening in the two-story house.

One scenario in each house was done three times to view repeatability. You can read the full report here, “Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction”

An online training program featuring the research and results is also available. Click on the image.

The results should cause us to rethink current of traditional strategies. “Several tactical considerations were developed utilizing the data from the experiments to provide specific examples of changes that can be adopted based on a departments current strategies and tactics.” I find the data on flow paths, VES and pushing fire personally interesting.

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.

Vent Enter Search (VES): 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.

Flow paths: 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 hoseline 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 more time provided by the closed door.

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.

Pushing fire: 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.

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