8.2 Vertical Ventilation & Ventilation Tools (JPR 4.3.12)

8.2 Vertical Ventilation & Ventilation Tools (JPR 4.3.12)

Vertical Ventilation Principles

Vertical ventilation opens a hole in the roof above the fire to use the natural buoyancy of hot gases. Hot smoke rises; an opening at the highest point of the structure lets the smoke escape upward, drawing cooler air in at the lower floors and clearing the interior. Vertical ventilation is the most effective method for large commercial buildings, deep-seated fires, and any fire where horizontal openings are blocked or unavailable. NFPA 1001 Firefighter I requires the candidate to perform vertical ventilation on a pitched roof as part of a team.

When to Choose Vertical Ventilation

• The fire is below a pitched or flat roof that can be safely accessed from a ladder.
• The fire is in a large undivided commercial space where horizontal openings do not provide enough exhaust area.
• Wind speeds above 25 mph make horizontal ventilation hazardous.
• The roof is the only accessible opening above the fire room.

Roof Construction Hazards

The most important safety decision in vertical ventilation is whether to go on the roof at all. Roof construction type drives that decision.

Stable Roof Types

• Dimensional lumber (2x joists, tongue-and-groove decking): Holds up well under fire, gives visible warning before failure, and is generally safe to vent.
• Concrete or gypsum on metal deck: Stable and can be cut with a rotary saw using a concrete blade.

Dangerous Roof Types

• Lightweight wood trusses (pitched chord trusses): Fail in 5 to 10 minutes under direct fire exposure because the metal gusset plates expand and pop off. The roof can fail with no visible warning.
• Engineered I-joists (OSB web with dimensional lumber flanges): Lose strength rapidly under fire exposure and have been associated with sudden collapse.
• Metal corrugated deck on bar joists: Conducts heat and can sag or buckle without warning. Falls are a primary hazard.

Roof Size-Up

Before stepping onto any roof, the Firefighter I team must perform a roof size-up:

1. Construction type: From below or from the aerial view, identify the roof system (pitched truss, flat dimensional, lightweight I-joist, metal deck).
2. Fire location: Determine where the fire is relative to the roof area to be cut. Never cut directly over a working fire in a lightweight structure.
3. Time: Estimate how long the fire has been burning. Beyond 10 minutes of direct fire exposure on lightweight construction, vertical ventilation is generally not attempted.
4. Access: Plan a second means of egress off the roof (a second ladder on the opposite side).
5. Sound the roof: Once on the roof, the firefighter crawls and uses a tool (pike pole, axe) to sound the roof ahead of every move. Hollow or bouncy sections indicate compromised decking and are avoided.

The Ventilation Opening

The standard vertical ventilation opening for Firefighter I operations is approximately 4 feet by 4 feet (1.2 m by 1.2 m) cut at the highest point directly above the fire. The opening is made directly above the fire room so the hot gases rise straight up rather than travelling horizontally across the underside of the roof deck. The opening is kept clear of personnel; once the cut is complete, the cut section is pushed or pulled down into the fire room to ensure the hole is open.

Cut Patterns

• Coffin cut: A rectangular 4x4 foot opening made with four cuts, with one corner left uncut so the panel can be hinged downward. Used on flat roofs.
• Louvre cut: Multiple parallel cuts made close together; the strips are pushed down to create a continuous opening. Used for fast openings on pitched shingled roofs.
• Trench cut: A long narrow cut (typically 3 to 4 feet wide) made across the entire roof to stop fire spread along a common attic. Used in row fires and strip-mall fires where fire is running the cockloft.

Ventilation Tools

• Pike pole: A 6-foot, 8-foot, 12-foot, or 16-foot pole with a hook on one end used to pull ceiling, break windows, sound a roof, and remove cut sections.
• Chain saw or circular saw: The primary cutting tool for vertical ventilation. Carbide-tipped blades cut wood; abrasive or diamond blades cut metal deck and concrete.
• Flat-head axe: Used as a striker, a sounding tool, and to chip through composition shingles.
• Roof ladder: A single ladder with folding hooks that anchors over the ridge. It distributes firefighter weight across the rafters and provides a stable working platform.
• Thermal imaging camera (TIC): Used from the roof or aerial platform to identify the hottest section of the roof and the location of the fire below.

Operational Sequence for Vertical Ventilation on a Pitched Roof

1. Confirm with command that the attack line is in place.
2. Raise a roof ladder to the ridge and anchor the hooks.
3. Raise a second ladder at the opposite end of the roof as a secondary egress.
4. Two firefighters climb to the ridge, crawling on the roof ladder with full PPE and SCBA on air.
5. Use a TIC or visual cues to locate the area directly above the fire.
6. Sound the roof ahead of every move with a pike pole or axe.
7. Make the cut pattern with the saw at full throttle, kneeling on the roof ladder.
8. Push the cut section down into the fire room with the pike pole.
9. Report the opening to command and observe smoke conditions.
10. Withdraw from the roof via the secondary ladder when ordered.

Vertical Ventilation Dangers

• Roof collapse on lightweight construction exposed to fire for more than 10 minutes.
• Falls through weakened decks, skylights, scuttles, or unreinforced ceilings.
• Backdraft when an opening is cut over a ventilation-limited compartment.
• Electrical contact with overhead lines near the roof edge or parapet.
• Saw kickback if the blade binds in the cut or contacts hidden fasteners.