Fire Ventilation Guidelines

Ventilation Guidelines

• Guidelines enable Fire Rescue personnel to make decisions about using mechanical or natural ventilation.
• Ventilation is used to remove an Immediately Dangerous to Life or Health (IDLH) atmosphere from an area.
• Ventilation can be done horizontally or vertically.
• Positive or negative pressure techniques are used based on specific conditions.
• The Fire Rescue Administrator is in charge of the process
• The guideline applies to all Emergency Operations personnel.
• Attachments include the Super Vac P164 Series Fan Manual and the RAMFAN Manual.

General Information

• Ventilation efforts increase the safety of civilians and firefighters.
• Ventilation must be coordinated with Fire Attack operations.
• Specialized situations may need ventilation methods not in this guideline.

Basics of Ventilation

• The three basic principles of ventilation are:
  • Vent for Life Safety
  • Vent for Fire Containment
  • Vent for Property Conservation
• Ventilation clears contaminated atmospheres for occupant survival.
• Releasing contaminated atmospheres to the exterior stops it from spreading inside.
• Ventilation limits property damage.
• The Incident Commander decides the ventilation type (vertical or horizontal) and method (natural or mechanical).

Types of Ventilation

Vertical Ventilation:

• Vertical ventilation uses the natural rise of heat.
• It involves openings in roofs or floors for contaminated atmospheres to escape.
• Pathways for vertical ventilation are stairwells, exhaust vents, and roof openings (skylights, scuttles).
• Creating openings involves cutting holes in roofs or floors.

Horizontal Ventilation:

• Horizontal ventilation is usable in basic ventilation situations.
• It uses doors, windows, and other horizontal openings on the same level as the fire.
• Horizontal ventilation is safer and faster than vertical ventilation.

Methods of Ventilation

Natural Ventilation:

• Natural ventilation relies on convection currents, wind, and natural air movements.
• This allows contaminated atmospheres to flow out of a structure.
• Wind speed and direction are important during natural ventilation.

Mechanical Ventilation:

• Mechanical ventilation uses fans or other equipment.
• It is used to exhaust contaminated atmospheres or introduce clean air.
• The three methods of mechanical ventilation are:
  • Negative pressure
  • Positive pressure
  • Hydraulic ventilation

Negative Pressure Ventilation:

• Negative pressure ventilation uses fans to exhaust contaminated atmospheres.

Positive Pressure Ventilation:

• Positive pressure ventilation uses fans to introduce clean air and push contaminated atmospheres out.
• Clean air follows the path of least resistance.

Hydraulic Ventilation:

• Hydraulic ventilation moves air using fog or broken-pattern fire streams.
• It creates a pressure differential behind and in front of the nozzle.

HVAC Systems:

• Some buildings have HVAC or designated smoke management systems.
• These systems can provide mechanical ventilation using positive or negative pressure.

Vertical Ventilation Considerations

• Consider alternative ventilation options if resources are limited.
• Consider building construction and the risks to firefighters.

Horizontal Ventilation Procedures

Negative Pressure Ventilation:

• Fire Rescue uses an electric fan, Super Vac P164 Series.
• The electric fan should be placed high in a door or window on the leeward side.

Positive Pressure Ventilation (PPV):

• Fire Rescue uses a high-volume velocity fan, RAMFAN.
• The fan is used for positive pressure ventilation. -The high-volume velocity fan provides up to 13,000 cubic feet per minute (cfm) of air.
• The high-volume velocity fan is placed on the windward side with 4-10 feet outside the ventilation opening.
• The cone of air from the fan should cover the opening completely.
• When selecting an exhaust opening for PPV, select the leeward side, close to the fire, 1-2 times the size of the ventilation opening.
• Smaller exhaust opening sizes may be used when cooler gases with less energy are being ventilated.
• Doors to rooms may be closed to speed up the process.

When NOT to Use PPV

• PPV should not be used if:
  • The seat of the fire is not located.
  • The fire is not under control.
  • There are pre-flashover conditions.
  • There may be hidden fire in void spaces.
  • There are no exhaust openings.
  • There are strong winds against the exhaust opening.

Pre-Flashover Conditions

• Impending signs of pre-flashover conditions include:
  • High heat.
  • Thick, turbulent, black smoke.
  • Roll-over.
  • Uncontrolled fire in the interior.
  • Auto-ignition (a.k.a. vent-point ignition) of smoke at exhaust openings.