Assessing the ventilation is a key task for exterior firefighters and officers. Inside crews are often not able to judge if the ventilation is effective or not.

This video is from a training fire and it shows an example of fan assisted post knockdown ventilation.

At the start of the video

In the top camera views we can see firefighters that has suppressed the fire compartment on the top floor and are backing out.

At 5 seconds

The PPV-fan is started and directed into the entry door at ground floor.

In the lower left camera view we can see that the flow of smoke from the fire compartment on the top floor is quickly increasing when the fan is started.

Assessing the flowpath

The initial result of smoke being pushed out of the fire compartment is an indicator that the flowpath is clear from the fan inlet to the outlet.

This is the exterior crews first task, to assess and report the effectiveness of the ventilation both to the inside crew and to the officer.

The interior crew might not be able to assess the effectiveness of the ventilation due to lack of vision.

At 7 seconds

In the lower right camera view we can see the room at the top of the staircase on the top floor.

At the start of the video, the lower part of the room has good visibility. But when the fan is started the turbulent airflow make the visibility worse for some time before enough smoke is pushed outside.

Horizontal ventilation will increase turbulence and possibly push smoke down to the floor. Although with the supply of fresh air the amounts of toxic gases will probably be low.

At 15 seconds

In the top left camera view we can see the door to the fire compartment self closing due to the passing air flow.

The interior crew does not know this is happening due to lack of vision. It is a good practice to prop the interior door open.

At 17 seconds

In the lower left view we can see the pushed flow of smoke from the fire compartment suddenly decrease.

This change in flow must be noticed and reported by the exterior crews to the interior crew and officer.

When the interior door closes, the fan is increasing turbulence and pressure inside the building but without increasing visibility. This is probably not a good thing.

Ventilation is dynamic

Fire and smoke conditions are clues to assessing the effectiveness of any ventilation action and changes may happen very fast.

All ventilation requires continuous monitoring and evaluation, both from inside and outside, to be safe and effective.

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