Chapter 11 Set 04: Positive-Pressure Attack and Ventilation in Firefighting

What is positive-pressure attack, or PPA?

Using positive-pressure fans to control airflow during the initial attack before fire suppression is completed.

What is positive-pressure ventilation, or PPV?

Using positive-pressure fans after suppression to remove smoke, heat, and toxic gases.

On what type of fire does positive-pressure attack work best?

A fire confined to a compartment.

How does PPA direct combustion products outside?

Fans raise pressure in adjacent compartments and push gases toward an exhaust in the fire compartment.

Why can fire pressure make PPA difficult?

A growing fire creates pressure that may overcome or redirect the fan-produced airflow.

What may happen if the PPA fan does not create sufficient pressure?

Smoke may move toward the intended intake instead of the exhaust.

What is the benefit of correctly applied PPA for interior crews?

It can reduce their heat exposure during interior operations.

What is the danger of incorrectly applied PPA?

Rapid fire development and fire spread may increase.

What is the intake in a positive-pressure operation?

The opening where the fan introduces air.

What is the exhaust in a positive-pressure operation?

The opening through which smoke and combustion products are intended to leave.

What determines the correct positioning of a positive-pressure fan?

The fan's design, manufacturer recommendations, and departmental SOPs.

What are the two main PPA considerations identified in the outline?

Knowing the fire location and achieving the proper exhaust-to-intake area ratio.

What does the exhaust-to-intake ratio compare?

The total surface area of exhaust openings with the total surface area of intake openings to the compartment.

What exhaust-to-intake ratio does the outline specify for effective PPA?

Greater than 1 to 1, meaning exhaust area exceeds intake area.

Where must PPA exhaust openings be located?

In the fire compartment.

Why can an additional exhaust remote from the fire compartment be dangerous during PPA?

It can divert airflow, weaken the intended pressure pattern, and draw heat, smoke, or fire toward the new opening.

How do fire pressure and fan pressure interact?

Together they can create unexpected flow directions unless openings and suppression are coordinated.

What helps keep fire-compartment pressure below the pressure in surrounding compartments?

A sufficiently large exhaust opening in the fire compartment.

How can firefighters influence unsafe pressure conditions during PPA?

Control the airflow produced by the fan and apply water to cool the fire.

Why must search and ventilation crews coordinate closely during PPA?

Opening doors can change the flow path and cut crews off from escape routes.

Where should crews enter and exit during PPA?

Through the designated intake, without blocking it.

What restriction does the outline place on searching compartments during PPA?

Search open compartments, because opening closed interior doors changes the established flow path.

When should crews apply water during PPA?

As soon as their streams can reach the fire.

How does water application improve PPA?

It lowers temperatures and fire-generated pressure, improving control of airflow and the approach path.

What pressure is PPV intended to exceed after suppression?

Exterior atmospheric pressure, rather than pressure generated by an actively growing fire.

How does PPV affect natural ventilation?

It accelerates natural airflow and moves smoke toward selected exhaust openings.

How does the exhaust-to-intake ratio differ in importance between PPA and PPV?

It is especially critical during PPA, while post-suppression PPV places less emphasis on it.

What exhaust-area guidance does the outline still give for effective PPV?

Ensure that exhaust surface area exceeds intake area.

Why can more exhaust openings be useful during post-suppression PPV?

They can increase airflow and help return the interior toward outside conditions faster.

When should PPV begin after suppression when it is selected for smoke removal?

As soon as it can be safely established and coordinated.

What interior conditions can effective PPV improve?

Temperature, toxic-gas concentration, and visibility.

What operations benefit from improved conditions produced by PPV?

Search and rescue, overhaul, and salvage.

How can PPV conceal or worsen hidden fire?

Airflow may hide signs of extension while supplying oxygen to smoldering materials.

How can crews check for hidden extension after PPV improves conditions?

Briefly stop the fan or close the intake so crews can reassess smoke conditions.

What coordination is needed to maintain effective PPV?

Monitor the fan, use wind appropriately, and maintain communication among the IC, interior crews, and fan operator.

What setup advantage does PPV have over NPV?

PPV blowers can be placed without entering the smoke-filled area.

How does PPV compare with NPV in smoke and heat removal?

The outline describes PPV as more efficient and effective with either horizontal or vertical exhaust arrangements.

How can pressurization help protect exposures?

It can help keep smoke and fire from entering adjacent compartments or exposed buildings.

What are the main disadvantages of PPV?

It requires remaining compartmentation, gas-powered fans may add carbon monoxide, and airflow may intensify hidden fires.

Where should positive pressure generally be introduced in a multistory building?

At the lowest point, usually ground level.

How is positive-pressure airflow directed through a multistory building?

By coordinating the opening and closing of doors.

What can be done if one fan does not provide enough pressure and airflow?

Position additional PPV fans at upper floors and the entry point, following the coordinated plan.

Which floor should generally be cleared first during floor-by-floor smoke removal?

The floor most heavily charged with smoke.

What two approaches can remove smoke one floor at a time?

Cross-ventilating the floor or directing smoke up a designated stairwell and out a rooftop opening.

What equipment may be needed for large-volume or multistory buildings?

Blowers larger than those normally carried on engine or ladder apparatus.

What is a major coordination problem during aboveground PPV operations?

Controlling stairwell doors and other openings so pressure is not lost.

How can stairwell opening control be managed during PPV?

Assign one person to direct pressurization, use portable radios, and have firefighters monitor stairwells and hallways.