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Why do the fans shutdown verses go to full exhaust when fire alarm system within building sounds?
So you don't feed the fire with more air.
I've forgotten more than I remember.
Even though it's exhaust, it's creating negative air pressure in the area, which draws in more fresh air from the surroundings. Great for clearing smoke after the fact but definitely hazardous in a real fire. Also, the system is shut down to prevent other AHUs from sucking in smoke and blowing it to other areas of a building, since smoke is toxic.
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