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Questions and Answers
What is the primary reason for the existence of Stack Effect in structures?
When is Stack Effect typically most pronounced?
What contributes to air leaving and entering a structure?
What can Stack Effect cause in a fire?
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In what type of structures can Stack Effect exist?
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What can cause wind-driven conditions in a fire, even when there is no wind?
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What is the primary cause of negative pressure at the bottom of a structure during a fire?
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What term is used to describe smoke moving downwards within a building during the summer?
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What is the purpose of installing revolving doors or two separate doors at ground level in High Rise buildings?
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During the winter, what happens to air on the lower floors of a building?
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What is the term used to describe the area in a building where the in-flow is equal to the out-flow and air is not moving in either direction?
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What should firefighting crews consider when responding to a structure fire?
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Study Notes
Stack Effect
- Stack Effect is the natural movement of air in and out of a structure, which can dramatically affect a fire and its byproducts.
Why Stack Effect Exists
- Structures are not airtight, allowing air to constantly enter and escape through windows, doors, and ventilation features.
- Pressure differences between the atmosphere outside and inside the structure dictate the flow of air.
When and Where Stack Effect Exists
- Stack Effect exists in any structure, from bungalows to high-rise buildings, and is more pronounced in extreme weather conditions.
- The taller the building, the greater the Stack Effect.
- Stack Effect is more pronounced in cold weather due to the large temperature difference between the inside and outside of the structure.
- In cold weather, hot air rises through stairwells, elevator shafts, vents, and cracks, causing a negative pressure at the bottom of the structure.
- In warmer weather, the temperature difference is less drastic, but Stack Effect still exists, with cool air falling within the building and exiting near the bottom.
How Stack Effect Affects Firefighting
- Stack Effect affects the movement of smoke and fire within a building.
- Smoke may move up shafts and hoist-ways and exit the top of the structure naturally in winter, and move down within the structure in summer.
- Reverse Stack Effect occurs when smoke moves downwards within a building.
- Ventilation sectors can utilize Stack Effect to their advantage when removing smoke from a structure.
- A neutral pressure plane, typically near the middle of a building, has equal in-flow and out-flow, with no air movement.
Mitigating Stack Effect
- Engineers use features like revolving doors, separate doors, and walls to separate elevator shafts and stairwells to decrease Stack Effect.
- Firefighters should consider these features to aid in mitigating emergencies.
Summary
- In winter, lower floors suck in air, while upper floors push air out.
- In summer, upper floors suck in air, while lower floors push air out.
- This can present wind-driven fire conditions, even without wind, and disperse smoke and fire byproducts throughout a structure.
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Description
Learn about the Stack Effect, a crucial concept in firefighting that affects fire behavior and safety. Understand its causes and implications for efficient incident response.
