Chapter 11 Set 03: Types and Techniques of Horizontal Fire Ventilation

What are the three types of horizontal ventilation?

Natural, mechanical, and hydraulic ventilation.

What is natural horizontal ventilation?

Using doors and windows, natural air currents, and pressure differences to remove smoke and heat.

What is mechanical ventilation?

Using fans, blowers, or smoke ejectors to create pressure differences and move gases.

What is hydraulic ventilation?

Using a water stream to entrain air and carry smoke and gases out of a compartment.

What is an equipment advantage of natural ventilation?

It does not require additional air-moving equipment or personnel to set up and maintain.

In coordinated wind-assisted ventilation, which side is opened first?

The downwind, lower-pressure side is opened first to establish an exhaust.

What is the purpose of an upwind opening during wind-assisted ventilation?

It admits fresh air from the higher-pressure side and directs flow toward the established exhaust.

What roles can a single open door serve during a fire?

Both an air intake and a smoke exhaust.

How can an exterior door or window opening assist water application?

It may provide access for a straight stream to cool the fire compartment before a follow-up interior attack.

How can doors be used to control natural ventilation?

Open or close them strategically to change the available flow path.

Why should firefighters not ventilate a burning structure and simply walk away?

The opening continues supplying oxygen and can allow the fire to grow.

How long might natural ventilation alone provide temporarily improved conditions?

Possibly less than one minute.

What is a potential disadvantage of creating multiple openings after suppression?

It may remove smoke faster but cause additional property damage.

When may mechanical ventilation be necessary?

When natural air currents and fire-generated currents do not adequately remove smoke, heat, and gases.

What is negative-pressure ventilation?

Lowering pressure inside a structure by exhausting gases so outside air is drawn in.

What is positive-pressure ventilation in terms of airflow?

Raising interior pressure so gases move toward selected lower-pressure exhaust openings.

What can happen if an upwind intake is opened before a downwind exhaust is established?

The building may become pressurized, intensifying the fire and spreading it into uninvolved areas.

How can an obstruction at an intake affect ventilation?

It can reduce or eliminate the intended airflow.

Can mechanical ventilation be used with both horizontal and vertical openings?

Yes, although it is most often used for horizontal ventilation.

What are the two general ways mechanical equipment moves smoke?

Pulling gases out through an opening or pushing air inside to displace gases through an exhaust.

When should mechanical ventilation equipment be activated?

Only after it is positioned and its operation is coordinated with other tactics and crews.

Why can mechanical ventilation worsen an uncontrolled fire?

It introduces fresh air faster than natural ventilation and can accelerate fire growth.

What must be ready before mechanical ventilation supports an interior operation?

Equipment must be positioned and all crews coordinated before openings are established and fans are started.

What are the resource limitations of mechanical ventilation?

It requires a power source, specialized equipment, and additional personnel or resources.

Why must a fog stream never be directed into a horizontal exhaust while interior attack crews are inside?

It can force smoke, heat, and steam back toward them.

How can mechanical ventilation help after suppression or in a contaminated space without fire?

It can remove smoke or toxic gases and replace contaminated or oxygen-deficient air, with appropriate safety controls and monitoring.

What are the main benefits of mechanical ventilation after suppression?

Faster contaminant removal, greater airflow control, less smoke damage, and improved conditions for occupants and crews.

What hazard can gasoline-powered ventilation fans introduce?

Carbon monoxide from their exhaust.

What should firefighters do while using gas-powered fans in a contaminated structure?

Continue using SCBA and monitor the atmosphere until it is confirmed safe.

What might explain carbon monoxide levels that do not decrease during post-fire ventilation?

Exhaust from a gas-powered fan may be adding carbon monoxide.

Where can negative-pressure smoke ejectors be positioned?

In doors, windows, or roof ventilation openings to exhaust gases outside.

What power source does the outline describe for negative-pressure smoke ejectors?

Electricity, commonly supplied through a cord from a generator.

Why should the opening around a negative-pressure fan be sealed?

To prevent outside air from being drawn around the fan instead of smoke being removed from the structure.

How does the outline compare NPV with other smoke-removal options?

It describes NPV as less effective than some other ventilation options.

What should be kept clear of a smoke ejector's intake and blades?

Debris, clothing, curtains, drapes, people, and anything else that could obstruct or be drawn into it.

How should a smoke ejector be moved?

Turn it off and carry it by its handles.

Why should firefighters avoid standing in a smoke ejector's outlet area?

The discharged air may carry flying debris.

When may hydraulic ventilation be used?

After the fire is controlled, especially when other forced-ventilation equipment is unavailable.

How does hydraulic ventilation remove smoke?

A fog stream entrains smoke and gases and carries them outside through a door or window.

Where must the nozzle operator work during hydraulic ventilation?

Inside the contaminated compartment.

How should the fog pattern be sized for hydraulic ventilation?

Wide enough to cover the exhaust opening while avoiding unnecessary interior water damage.

How does nozzle distance from the exhaust affect hydraulic ventilation?

Greater distance allows more air to be entrained in the fog pattern.

How does exhaust-opening size affect hydraulic ventilation?

A larger opening allows faster ventilation.

What are the disadvantages of hydraulic ventilation?

Possible additional water damage, depletion of the water supply, ice formation in freezing weather, and continued firefighter exposure to a hazardous atmosphere.

Why is hydraulic ventilation's water use especially important in rural operations?

Water supplies may depend on limited supplies or water shuttles.