Summary: Choosing the right nozzle pattern in vent-limited fires can make or break your interior attack. Through side-by-side testing at the Connecticut Fire Academy, Episode 11 of Fully Involved reveals how fog patterns significantly increase air entrainment, especially when working in the exhaust. Whether you're using a smooth bore, straight stream, or fog pattern, understanding how your stream moves air is critical for safer, more effective fireground tactics.
How Nozzle Pattern Affects Air Entrainment in Vent-Limited Fires
If you’ve ever found yourself taking heat while making a hallway push, this episode is for you. In Episode 11 of Fully Involved, the crew runs a series of nozzle tests to show just how much your stream pattern can work against you or with you when it comes to air entrainment and ventilation.
What Is Air Entrainment and Why Should You Care?
Air entrainment is the air movement created by your nozzle stream and your hose handling. In a vent-limited environment where the fire doesn’t have enough oxygen and the only opening is behind you, everything you push forward, from air to smoke to heat, wants to come right back at you.
That’s a problem if your nozzle pattern is cranking up turbulence instead of controlling it.
Four Nozzle and Ventilation Scenarios Put to the Test
The crew ran controlled burns using:
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A smooth bore nozzle
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A fog nozzle in straight stream
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A fog nozzle in fog pattern
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A Vortex (adjustable smooth bore)
Each setup was tested in both vent-limited and partially ventilated environments. The goal was to visualize air movement using streamers and flaps to see how different patterns impact flow path and air entrainment.
Vent-Limited Plus Fog Pattern Equals More Turbulence
In the vent-limited scenarios, the smooth bore and straight stream patterns caused minimal air movement. But once the fog pattern was introduced, flaps and streamers lit up, showing major backdraft of air and gases toward the nozzle team. Not good.
If you’re advancing with a fog pattern in a hallway where the only opening is behind you, you’re basically blowing hot smoke and fire gases back on yourself.
The Vortex Adds Control Without Sacrificing Flow
Switching to the Vortex pattern, an adjustable smooth bore, provided high air movement similar to a fog but at smooth bore pressures and flows. This allows for controlled hydraulic ventilation when needed without the high turbulence of a traditional fog pattern.
Tailboard Talk: Choose the Stream That Matches the Job
Instructor Pete Morotto wraps it up by breaking down stream choice. Use fog for exposure protection and cooling radiant heat from outside, but for interior work, especially in residential structures, smooth bore or straight stream gives you the reach and control needed to make the push and manage the environment from a position of advantage.
Key Takeaways for Nozzle Teams
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Know your fire environment. Vent-limited versus partially ventilated changes the game.
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Straight stream or smooth bore means less air movement and a safer interior attack.
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Fog patterns generate more turbulence. Use with intention and coordination.
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Vortex can be a tool for hydraulic ventilation. Know when and where to use it.
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Slow, steady nozzle movement distributes water better and keeps air entrainment low.
Want to see these stream effects in action? Episode 11 of Fully Involved breaks it all down with visuals and live commentary from the Connecticut Fire Academy team.
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