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Positive pressure ventilation: The rights and wrongs

When it comes to PPV, everyone has an opinion and everyone considers themselves correct

In our next installment of the “Coordinating Fire Attack” series, we move onto the discussion of ventilation and the significant role this tactic plays on the ability to influence actions on the fireground.

This tactic is one that can make or break a team’s ability to complete other assignments such as rescue, fire attack, confinement and even something as simple as being able to enter a structure to complete the above required suppression acts.

In this article, we will briefly discuss what ventilation is, how it can be used to our benefit and most importantly how it can impact our ability to remain safe while completing other fireground tasks.

The process
Ventilation is the process of removing heat and products of combustion from a structure by use of natural, negative, hydraulic or mechanical means. Ventilation is one of the tactical necessities during the evolution of a fire that can be initiated at any point of the scenario to enhance a team’s need to attack fire and make rescues.

That means that ventilation can be utilized at the onset of a fire attack such as seen in the positive pressure fire attack process, or it can be used at the end of a fire attack such as when a fire has been extinguished quickly enough that clearing a structure of smoke is one of the final acts necessary for investigation.

Ventilation is a tactic that can greatly contribute to a team’s ability to accomplish basic firefighting objectives. This tactic assists in many different means.
Primarily, ventilation increases visibility for victims and rescuers, which reduce the hazardous impacts associated with primary search and fire attack. This in effect allows the interior teams to be more rapid in their completion of tasks while reducing the possibility of injury.

This allows for quicker and easier entry of attack crews to locate the seat of a fire. Rapid location of the seat of the fire reduces the ability of the fire to spread beyond its area of origin, find where fire may have spread and stop fire growth/expansion.

Flashover and backdraft
Ventilation also reduces the chances that environmental parameters may be moving toward a flashover or backdraft. Ventilation assists in cooling areas that are pre-flashover by moving the larger quantities of heat out of that general area and allowing fuel in the area to cool and prevent the auto-ignition possibility from fuels in the fire area.

Ventilation reduces the possibility of a backdraft by removing high heat from an area and venting that to the environment, reducing flammable / explosive fire gases that are looking for fresh sources of oxygen to deflagrate. Properly accomplished ventilation increases the effectiveness of most operations.

A final, but primary cause for ventilation is that ventilation saves lives! A victim’s environment becomes more survivable by the removal of heat and smoke and reduces dangers to trapped occupants.

In addition, the improved environment also serves to save those lives of firefighters operating inside a structure by removing heat, steam and smoke. The need to crawl through the fuel-laden smoke is removed and improves the firefighter’s operating environment.

In my previous article, “The Basics of Ventilation,” I went into detail describing the four means of ventilation and how to utilize them. In this article I will not cover details regarding negative or hydraulic ventilation.

I will, however, discuss positive pressure ventilation as it plays a significant role in today’s fire attack processes.

Everyone has an opinion
Positive pressure ventilation is one of those decisions that can be likened to one’s personal selection of a nozzle. Everyone has an opinion and everyone considers themselves correct.

While everyone has the right to have a preferred ventilation style, once a preference is made, one must be careful not to try to fit that preference to apply to every circumstance.

Positive pressure ventilation is one of the primary methods utilized by the fire service today. When utilized appropriately, it is a great problem solver.

Effectively, when air is forced into a structure through an opening, it will seek the path of least resistance to find its way out of a structure. If the opening it utilizes as an exit is three quarters or less the size of the initial opening, there remains a residual positive pressure in the compartment where the air is being forced in to.

This positive pressure pulls the smoke and heat inside a compartment and moves it out of the controlled ventilation exit with the air being forced through the front ventilation opening.

It is critical that there be only one entrance for the ventilation unit and only one exit for the removal of smoke and heat. This exit must be smaller than the opening or there will be no build-up of positive pressure to pull the by-products of the fire.

More fire and gases
Positive pressure tactics have the ability to move fire and fire gases (this is the ventilation part). This also can cause a rapid increase in fire development. Attempt to place the ventilation opening between your firefighters and the fire or between the fire and trapped victims.

It is critical to know where the fire is and where it is going to move once this tactic is selected. If you initiate positive pressure in conjunction with your attack crews, know what this method is going to do to your crews.

Positive pressure is a tool to be utilized when a size-up confirms this ventilation tactic will assist with rapid fire suppression, quick location of victims and will not increase the risk/benefit profile for interior crews. Don’t simply utilize this tactic because “we have always done it this way.”

In the next part of this article, I’ll be focusing on what you should know about vertical ventilation.

Michael Lee teaches firefighters the ‘Street Smarts’ they need to survive in some of the most dangerous situations they encounter: ice rescues, basement fires, and structural collapses. Read Lee’s advice in his FireRescue1 exclusive column.