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Fire Alarm -- Description

Outside Air is used to push smoke out of a stairwell
When there's a fire, clean outside air is forced by a Stair Pressurization Fan into a stairwell. The pressurization is used to push back on smoke, keeping the smoke out of the escape route.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer






What is a Stair Pressurization Fan (SPF)?

By Douglas Krantz

In case of fire in a high rise building, a Stair Pressurization Fan (SPF) uses clean outside air to pressurize the air in stairwells. The pressurized air helps people escape the fire and firefighters battle the fire.

Stairways are Fire Escape Routes

Nowadays, stairwells have better fire ratings than the rest of the building. In other words, so people can get out when the rest of the building is on fire, stairways don't burn.

Stairways Full of Smoke

The stairways may not burn, but they can still fill up with smoke. The smoke can not only make it harder to see as one is getting away from a fire, but it can:
  • Make it harder to breathe - possibly causing injury or death
  • Close off the escape route - possibly causing people to seek another pathway of escape

Open Doors

The problem is, as people are escaping the fire, they have to open the door to the stairway. When the door is open, preventing the stairway from being used by later escapees, smoke follows and billows into the stairway.

Smoke Push Back

The idea behind the stair pressurization is that during a fire the stairway should have more pressure than the rest of the building. That way, when the doors open, the higher pressure in the stairwell pushes the smoke back onto the floor, keeping the escape route clear of smoke.

The smoke free escape route also doubles as a smoke free entrance route for the firefighters as they combat the fire.

Turning On the SPF

Except when there's smoke, the stair pressurization fans aren't needed, so normally they're turned off. When the fire alarm system detects smoke, they're automatically turned on.
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As firefighters battle the fire, if the fire alarm system has not turned on the stair pressurization fans, they're turned on by the firefighters.

Escape

As people are escaping a fire, and open the doors to get into the stairways, smoke would naturally billow from a fire floor into the stairwell. Keeping the smoke out of the stairwell by pushing it back onto the floor, a Stair Pressurization Fan pressurizes the air in the stairwell.






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Describing How It Works
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Electrical Flow


On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

Conventional current flow, positive charges that appear to be moving in the circuit, will be specified when it is used. The positive electrical forces are not actually moving -- as the electrons are coming and going on an atom, the electrical forces are just loosing or gaining strength. The forces appear to be moving from one atom to the next, but the percieved movement is actually just a result of electron movement. This perceived movement is traveling at a consistent speed, usually around two-thirds the speed of light. To explain the effects of electrostatic forces, the movement of positive charges (conventional current) is best.

See the explanation on which way electricity flows at www.douglaskrantz.com/
ElecElectricalFlow.html
.