Post-Fire Smoke Exhaust Requirements

[Josh Koci]

Back again with another exhaust question.

We are currently working on a large exhibition hall approximately ~100,000 SF and ~30ft tall located in Florida. They currently have 4 x 65,000 CFM exhaust fans. With no real knowledge of why they are present. My higher ups believe they are there for Carbon Monoxide control or post-fire smoke removal. However, after PPM calculations of plausible CO emissions I have concluded they are not their for CO purging.

So, the only reasonable option left would be smoke purging, but again I cannot see why this would be required. After many hours of scouring IBC and FBC I cannot find a requirement for such a system in a A-3 group class exhibition hall anywhere in the code. I found FBC 403.4.7 requires a minimum of 4 ACH by mechanical means for a post-fire smoke purge system, but this is for a high rise building. According to the definition, that I found, of a high-rise our building would not be considered high rise.

Our client is asking if we can drastically reduce or remove the existing exhaust system mentioned above. Can anyone shed some light on this topic? I want to tell them to remove the existing exhaust system, but I feel as the previous engineers had a reason for designing it the way they did.

 

[mtlogcabin]

When was the building constructed and where? Dade and Broward counties where under their own codes in the 70's and 80's and we installed a few of these systems in a number a "A" occupancies. In all honesty they usually did not work as intended. The idea was they could pull the smoke up from the floor and protect the occupants.

 

[Josh Koci]

Early 80's and Volusia County. I'm guessing it is along the lines of what you are referring too, but can't find any current codes supporting the need to keep them.

 

[mtlogcabin]

If the current code does not require them then you have to find what if any new code requirements there are so you can document why you removed them.
For example does the suppression system have quick response heads through out the area?
[F] 903.3.2 Quick-response and residential sprinklers.
Where automatic sprinkler systems are required by this code, quick-response or residential automatic sprinklers shall be installed in the following areas in accordance with Section 903.3.1 and their listings:

1. Throughout all spaces within a smoke compartment containing care recipient sleeping units in Group I-2 in accordance with this code.

2. Throughout all spaces within a smoke compartment containing treatment rooms in ambulatory care facilities.

3. Dwelling units and sleeping units in Group I-1 and R occupancies.

4. Light-hazard occupancies as defined in NFPA 13.

 

[Josh Koci]

So what you are saying is, verify that the current FP is code compliant and use the code compliance to justify the removal of preexisting redundant exhaust system, based on the lack of a code requirement for the current exhaust system?

If so, that makes perfect sense to me. I will have to contact someone to verify but this seems like a good solution to my dilemma. Thank you.

 

[Builder Bob]

Old smoke protected system - common thought in the 70's and 80's = before fire sprinkler system were common place or with newer technology that has drastically changed the spray patterns and placement requirements for fire sprinkler heads..... for example, old sprinkler design could be done using pipe schedule design.

 

[cda]

You might check history

Might have been required as part of original design, so the question would be does it have to stay

Might be part of a engineered exiting system.

The city should have plans and comments

 

[Josh Koci]

So I was a bit mistaken. The original building was built in early 1980's, however, the part we are looking at was a exhibition hall expansion built in the mid 2000's. The fans are referred to on the drawing as "Exhibit Hall General Purge Fans" and say "shall be activated through the BAS in accordance with the pre-programmed schedule, or by operator activation..." later in the control specifications it refers to them as "Truck Dock Purge Fans" with the exact same note copy and pasted. So to divert a bit, can anyone think of a reason these would have been installed or required at such a high CFM in the mid to late 2000's. The CFM of the combined exhaust fans equals to a bit over 4.3 ACH.

 

[Josh Koci]

Also, there are only 6 truck dock stations. Even if the docks were occupied with Heavy Duty Diesel Vehicles (HDDV) idling for 8 hours straight you would barely break the 9 PPM Carbon Monoxide (CO) EPA regulated threshold. Which mind you is only broken once the CO levels have been at 9 PPM for 8 hours straight. So the idea of this being a "Truck Dock Purge Fan" problem does not seem very likely to me.

 

[steveray]

Not necessarily required, but let me ask you this, have you ever tried to get smoke out of a large building after a fire? Could be the difference between the building being closed for days or months....

Smoke protected seating?
Atrium smoke control?
Stage ventilation?

 

[mtlogcabin]

Might be simply to purge the odor and has nothing to do with life safety. Check the mechanical codes 403 & 502.14

 

[cda]

So I was a bit mistaken. The original building was built in early 1980's, however, the part we are looking at was a exhibition hall expansion built in the mid 2000's. The fans are referred to on the drawing as "Exhibit Hall General Purge Fans" and say "shall be activated through the BAS in accordance with the pre-programmed schedule, or by operator activation..." later in the control specifications it refers to them as "Truck Dock Purge Fans" with the exact same note copy and pasted. So to divert a bit, can anyone think of a reason these would have been installed or required at such a high CFM in the mid to late 2000's. The CFM of the combined exhaust fans equals to a bit over 4.3 ACH.

So are the fans over

The exhibit area

Or

Truck dock

Or both??

 

[cda]

I am thinking the plans approved for this area need to be looked at with the city Building and fire dept,,,

To see what they say

 

[Josh Koci]

Might be simply to purge the odor and has nothing to do with life safety. Check the mechanical codes 403 & 502.14

This right here, I am fairly certain is the correct answer. After discussing this further with those in charge this system has nothing to do with life safety or fire/smoke control, therefore NFPA does not apply. As far as they know this system is solely for odor removal and best design practice. No code requirements. No safety precautions.

So I will be doing more research into best practice of odor removal.

Not necessarily required, but let me ask you this, have you ever tried to get smoke out of a large building after a fire? Could be the difference between the building being closed for days or months....

Smoke protected seating?
Atrium smoke control?
Stage ventilation?

 

[cda]

This right here, I am fairly certain is the correct answer. After discussing this further with those in charge this system has nothing to do with life safety or fire/smoke control, therefore NFPA does not apply. As far as they know this system is solely for odor removal and best design practice. No code requirements. No safety precautions.

So I will be doing more research into best practice of odor removal.

That is a new one

I am thinking it has to do with exiting design

 

[Msradell]

Our client is asking if we can drastically reduce or remove the existing exhaust system mentioned above. Can anyone shed some light on this topic? I want to tell them to remove the existing exhaust system, but I feel as the previous engineers had a reason for designing it the way they did.

Looking at it from a different way, why does the client want them removed? Are they affecting the energy efficiency of the building? Unless they are running I don't see why they would be to any degree. If their location sucks that they are an eyesore or take up space that could be better used for something else?

You may be better off trying to determine why they went and removed and overcoming that instead of trying to figure out how to remove them.

 

[Builder Bob]

I am sure the thermal envelope is affected by six large penetrations and if not properly installed and maintained, may allow water to drip thru the vertical fan install..... now it is a slipping hazard on the floor system below.

 

[Josh Koci]

Looking at it from a different way, why does the client want them removed? Are they affecting the energy efficiency of the building? Unless they are running I don't see why they would be to any degree. If their location sucks that they are an eyesore or take up space that could be better used for something else?

You may be better off trying to determine why they went and removed and overcoming that instead of trying to figure out how to remove them.

They want the fans removed for the intent of lowering operating costs and sound levels during fan operation. We have determined from the owner that these systems are not used for fire and life safety.

 

[cda]

They want the fans removed for the intent of lowering operating costs and sound levels during fan operation. We have determined from the owner that these systems are not used for fire and life safety.

And the ahj’s position ?

 

[steveray]

When and what triggers them to operate at all?

 

[Msradell]

They want the fans removed for the intent of lowering operating costs and sound levels during fan operation. We have determined from the owner that these systems are not used for fire and life safety.

If they aren't using them on a regular basis and they are creating a sound problem or using energy. You just leave them where they are and don't use them you're not going to incur additional cost by removing them nor cause a potential code problem in the future. I really don't see any justification for removing them. It sounds like it's just something that the building owners want to do without any true reason.