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Old 05-29-2019, 10:42 PM   #1
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Default Fire suppression and MUA

City engineer says he wants the kitchen fan to go on when fire suppression is activated and for MUA to be de-energized. Does that make sense?
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Old 05-29-2019, 10:53 PM   #2
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Quote:
Originally Posted by 99cents View Post
City engineer says he wants the kitchen fan to go on when fire suppression is activated and for MUA to be de-energized. Does that make sense?
Yes. I assume the kitchen fan is an exhaust?

MUA off so it does not feed the fire, kitchen exhaust on to get rid of smoke.
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Old 05-29-2019, 11:08 PM   #3
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Makes perfect sense.
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Old 05-29-2019, 11:24 PM   #4
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Old 05-30-2019, 08:40 AM   #5
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YES, completely!

The smoke needs to be removed and the air supply to the fire needs to be cut off.
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Old 05-30-2019, 09:56 AM   #6
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It makes sense but if you are exhausting a space without bringing in air, the air needs to be replaced some how. Also if your exhaust is still on, that is air flow that may reduce the effectiveness of the suppressant.
I would think and have wired in the past were if the F/A goes off, you kill the power to both the MUA and exhaust. No air movement. The fire department sets up the exhaust fans once the fire is out.


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Old 05-30-2019, 10:14 AM   #7
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It makes sense but if you are exhausting a space without bringing in air, the air needs to be replaced some how. Also if your exhaust is still on, that is air flow that may reduce the effectiveness of the suppressant.
I would think and have wired in the past were if the F/A goes off, you kill the power to both the MUA and exhaust. No air movement. The fire department sets up the exhaust fans once the fire is out.


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Then why does an atrium require a smoke control system?

And why do they chainsaw through the roof of a burning building to ventilate?

And why do they smash windows to ventilate?

They want the products of combustion (smoke) evacuated while fighting the fire, whenever possible. It aids in fighting the fire as well as rescue.
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Old 05-30-2019, 10:39 AM   #8
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Consider the fluid dynamics of the entire physical phenomena... Running the exhaust whilst simultaneously restricting fresh air intake is an attempt to draw a vacuum in the room. It's a really, really, poor vacuum because the building is leaky, but that's the goal nonetheless.

A fire hates a vacuum way more than a smokehouse. A smoldering fire will produce combustible gases through pyrolysis and now you have an explosive mixture. That's also why firemen cut holes: The immense rising hot air and smoke cause a partial vacuum in the structure. Fire hates vacuum.
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Old 05-30-2019, 11:01 AM   #9
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That's how we've always done it here.
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Old 05-30-2019, 11:06 AM   #10
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Maybe I’m missing something but the air flow is above the hood near the ceiling and above the fire. I don’t see how it makes any difference.

This guy has some strange ideas but maybe he has this one right, I dunno.

Another question: The little fire suppression activation box has three wires (a common and NO and NC). Fire guy says to hook up to NO. How does this thing actually work? I don’t want it to dump by mistake.
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Old 05-30-2019, 11:18 AM   #11
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What do you mean airflow is above the hood?
It should be the hood exhaust which gets powered during fire condition.
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Old 05-30-2019, 12:17 PM   #12
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I'm aware of the FD opening up holes to fight fires.
In my case I'm thinking of rooms where we have suppression systems and the rooms have to be sealed for it to work. All air flow is shut down during a fire and the doors must remain closed so the suppression can work until the FD shows up.


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Old 05-30-2019, 12:42 PM   #13
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Quote:
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I'm aware of the FD opening up holes to fight fires.
In my case I'm thinking of rooms where we have suppression systems and the rooms have to be sealed for it to work. All air flow is shut down during a fire and the doors must remain closed so the suppression can work until the FD shows up.


Tim.
Like an Ansul system (FM200) in a data room or other critical control area.

That dilutes the O2 in the air by flooding it with N2 limiting the ability of the fire to propagate.
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Old 05-30-2019, 12:58 PM   #14
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Quote:
Originally Posted by 99cents View Post
Maybe I’m missing something but the air flow is above the hood near the ceiling and above the fire. I don’t see how it makes any difference.

This guy has some strange ideas but maybe he has this one right, I dunno.

Another question: The little fire suppression activation box has three wires (a common and NO and NC). Fire guy says to hook up to NO. How does this thing actually work? I don’t want it to dump by mistake.
An intake air fan will spray the fire with fresh air. You want that off. The exhaust fan is pulling smoke and heat off the fire. Sure, air in the room will move toward the fire as the fan operates, but that air is limited by the doors and windows and walls. The fan is trying to draw a vacuum.

I don't think you can dump the system by wiring the microswitch wrong. What I like to do is use my meter to make sure we are all in agreement about what NO and NC mean in any given system. With the system full and cocked, the microswitch should energize an ice cube relay that allows the manual switch to operate the exhaust and MUA fans. When it trips, the ice cube relay should drop out and the circuit to the MUA fan should open, and the exhaust fan circuit should close, bypassing any manual switches.
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Old 05-30-2019, 04:20 PM   #15
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Hey 99

Why don't you ask to move this thread, it is in new introductions section. I know it is a rough day.

Cowboy.

PS I need to add posts so I can PM cricket
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Old 05-30-2019, 11:05 PM   #16
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Quote:
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Hey 99

Why don't you ask to move this thread, it is in new introductions section. I know it is a rough day.

Cowboy.

PS I need to add posts so I can PM cricket
How TF did that happen?
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Old 05-31-2019, 12:40 AM   #17
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Quote:
Originally Posted by CoolWill View Post
An intake air fan will spray the fire with fresh air. You want that off. The exhaust fan is pulling smoke and heat off the fire. Sure, air in the room will move toward the fire as the fan operates, but that air is limited by the doors and windows and walls. The fan is trying to draw a vacuum.

I don't think you can dump the system by wiring the microswitch wrong. What I like to do is use my meter to make sure we are all in agreement about what NO and NC mean in any given system. With the system full and cocked, the microswitch should energize an ice cube relay that allows the manual switch to operate the exhaust and MUA fans. When it trips, the ice cube relay should drop out and the circuit to the MUA fan should open, and the exhaust fan circuit should close, bypassing any manual switches.

You mean like this guy:

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