Post-Knockdown Ventilation in a Sprinkler-Controlled Restaurant Fire
You are the ventilation group supervisor at a single-story 6,000-square-foot restaurant fire. The fire began in a deep-fat fryer in the kitchen and the sprinkler system, which is flowing, has knocked it down. Interior crews report light smoke, moderate heat, visibility about 10 feet, and no extension beyond the kitchen. Windows on the A side are intact; the front door on the A side is open. The roof is flat built-up with a small scuttle. Wind is 15 mph from the A side. Crews have been inside 14 minutes; the IC wants smoke cleared so overhaul can proceed.
1. Do you start positive-pressure ventilation now? State the conditions that must be met first and where the fan and the exhaust opening go.
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Not yet, and not because of the wind. PPV is a coordination tool, not a smoke-removal convenience - starting it while crews are working the interior can push heat and smoke into void spaces and unburned areas, and can unbalance a crew that is not expecting the change.
Conditions before starting:
- Fire confirmed knocked down (satisfied here - sprinkler-controlled, no extension).
- Interior crews informed and in agreement, with a charged line still at the door.
- An exhaust opening established and controlled - a window on the C or D side, opened by a firefighter, not left to chance.
- Crews told what to expect: the smoke layer will lift and move, and visibility will change quickly.
Placement: fan at the A-side front door, upwind, with the cone sealed over the opening so it pressurizes the building rather than blowing past it. Exhaust on the downwind side, away from the kitchen and away from the side where crews are operating.
The trap: with wind already from the A side, the building is partly self-ventilating. Adding PPV on the same side without a controlled exhaust just pushes smoke through the structure.
2. The IC asks whether to cut the roof. What is your recommendation and the reasoning behind it?
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Recommend against vertical ventilation.
Reasoning:
- Roof ventilation exists to release heat and smoke from a compartment where interior crews are working below a fire that is still producing them. Here the fire is out and the remaining problem is residual smoke - a horizontal-ventilation problem, not a vertical one.
- A flat built-up roof means cutting is labor-intensive, creates a large water-entry path, and adds roof-level risk (skylights, HVAC units, a built-up roof that hides deterioration) for a benefit the smoke ejector already provides.
- Cutting also commits a crew to the roof that is better used for overhaul.
What to do instead: use the scuttle or a controlled C/D-side window as the exhaust point, protect the interior with covers over stock and equipment, and clear smoke by horizontal ventilation.
When the answer changes: if crews report heat increasing, a visible fire in a void, or fire extending into the attic/truss space, vertical ventilation becomes relevant again - but at that point the fire attack decision comes before the ventilation decision.
3. When and how do you shut down the sprinkler system, and what are the consequences of getting that wrong?
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Do not shut the system down yet - and when you do, do it as a controlled operation, not a valve turn.
Sequence:
- Overhaul first: pull ceiling, check void spaces, and use a thermal imager on the fryer area, hood, and duct. A deep-fat fryer fire commonly extends into the hood and duct, and that is where rekindle comes from.
- Once the IC confirms no hot spots, close the control valve, and record the time. Many systems also send a signal to a monitoring company - notify them so they do not dispatch on the flow.
- Where only one or two heads are flowing, use sprinkler stops or plugs instead of shutting the whole riser. That preserves protection for the rest of the building and reduces water damage.
Consequences of getting it wrong:
- Shutting down early with a hot duct or a smoldering void allows rekindle in a building full of overhaul crews.
- Leaving it flowing for the whole overhaul produces escalating water damage and can compromise ceilings and floors.
- Failing to restore the system before leaving leaves the occupancy unprotected.
Handoff: the valve status and the reason for it go in the report to the owner and the IC, because the fire department owns that decision until it is documented.