Exhaust stack fans deenergize whan Fire alarm activates at panel

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New User
New User
Posts: 1
Joined: Thu Feb 15, 2018 8:04 am
YouTube Username: hingusus

Thu Feb 15, 2018 8:07 am

Why do the fans shutdown verses go to full exhaust when fire alarm system within building sounds?
Old fire alarm guy
Fire Alarm Technician
Fire Alarm Technician
Posts: 43
Joined: Tue Apr 05, 2016 7:09 am

Fri Feb 16, 2018 10:19 am

So you don't feed the fire with more air.
I've forgotten more than I remember.
Casual Participant
Casual Participant
Posts: 139
Joined: Wed Mar 08, 2017 9:09 am
Location: Central MA

Mon Feb 19, 2018 9:56 pm

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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