Dampers Required for Room with Clean Agent?

2/20/2023

We have a project where we're adding a sound (anechoic) chamber and and protecting it with clean agent.

A question came up as to whether or not dampers are required for the HVAC system that provide supply and return air to the pre-manufactured chamber.

Is an anechoic chamber required to have dampers for limiting the migration of the clean agent?

My thinking is that the clean agent will be activated by an air sampling system, so there should be no meaningful amount of smoke in the chamber.

That said, do the dampers have to be listed for fire/smoke?

Any help with getting specifics from code or a clearer understanding is always appreciated from the community so thanks in advance.

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8 Comments

Glenn Berger

2/20/2023 08:05:51 am

You want smoke dampers to contain the clean agent in the protected volume.

schulman

2/20/2023 08:07:27 am

to do the job for the clean agent system the dampers just need to stop the hole so you don't have pressure loss ... smoke/fire requirements would be for other code reasons such as wall rating or compartmentalization for egress ...

Jesse

2/20/2023 08:58:16 am

Determining the amount of agent needed requires a volume calc. So without the dampers, you would need to include the area beyond where the damper would be. Otherwise you agent concentration won't be correct.

Todd E Wyatt

2/20/2023 09:43:20 am

Per the scoping Code (2021 IBC), a “clean-agent system” (904.10) which is an “Alternative Automatic Fire-Extinguishing System” (904) is required to be “be designed, installed, inspected, tested and maintained” in accordance with 2018 NFPA 2001 Standard on Clean Agent Fire Extinguishing Systems.

NFPA 2001 references (10) instances of “DAMPER” (see REFERENCES below) ...
• Chapter 7 Approval of Installations, 7.2.3.7 When applicable for system operation, fan coastdown and DAMPER closure time shall be verified that they are in accordance with the system design criteria.
• Chapter 9 Marine Systems A.9.7.2 Automatic shutdowns are the preferred method for shutting down a ventilation system. Shutdowns requiring personnel to find and manually close DAMPERs far from the fire extinguishing system discharge station should not be permitted.
• Annex C — Enclosure Integrity Procedure ... (8) instances ... This annex is not a part of the requirements of this NFPA document but is included for informational purposes only.

These DAMPER references do not require the use of dampers in “Clean Agent Fire Extinguishing Systems” although DAMPERS can be a part of the system to achieve the “Enclosure Integrity Procedure” (Section 7.5)

REFERENCES
2021 IBC
Section 904 Alternative Automatic Fire-Extinguishing Systems
904.1 General
Automatic fire-extinguishing systems, other than automatic sprinkler systems, shall be designed, installed, inspected, tested and maintained in accordance with the provisions of this section and the applicable referenced standards.
904.2 Where Permitted
Automatic fire-extinguishing systems installed as an alternative to the required automatic sprinkler systems of Section 903 shall be approved by the fire code official.
904.10 Clean-Agent Systems
Clean-agent fire-extinguishing systems shall be installed, maintained, periodically inspected and tested in accordance with NFPA 2001 and their listing. Records of inspections and testing shall be maintained.

2018 NFPA 2001
Chapter 7 Approval of Installations
7.2* General.
7.2.3 System Acceptance Testing.
7.2.3.7
When applicable for system operation, fan coastdown and DAMPER closure time shall be verified that they are in accordance with the system design criteria.
7.5 Review of Enclosure Integrity.
7.5.1
It shall be determined that the protected enclosure is in general conformance with the construction documents.
7.5.2
All total flooding systems shall have the enclosure examined and tested to locate and then effectively seal any significant air leaks that could result in a failure of the enclosure to hold the specified agent concentration level for the specified holding period.
7.5.3*
Quantitative results shall be obtained and recorded to indicate that the specified agent concentration for the specified duration of protection is in compliance with Section 5.6, using an approved blower fan unit or other means as approved by the authority having jurisdiction. (For guidance, see Annex C.)

Chapter 9 Marine Systems
9.7 Enclosure.
9.7.1*
To prevent loss of agent through openings to adjacent hazards or work areas, openings shall be one of the following designs:
(1) Permanently sealed
(2) Equipped with automatic closures
(3) Equipped with manual closures outfitted with an alarm circuit to indicate when these closures are not sealed upon activation of the system
A.9.7.1
A well-sealed enclosure is vital to proper operation of the system and subsequent extinguishment of fires in the protected space. Gastight boundaries of the protected space, such as those constructed of welded steel, offer a highly effective means for holding the fire extinguishing gas concentration. Where the space is fitted with openings, avenues for escape of the gas exist. Automatic closure of openings is the preferred method of ensuring enclosure integrity prior to discharge. Manually closed openings introduce added delay and an added human element into the chain of proper operation of the system. Failure of personnel to properly close all openings has been a recurring cause of gaseous systems not performing as intended. It is recognized that some openings in the enclosures, such as maintenance hatches and watertight doors, cannot be fitted with automatically operated closers due to personnel hazards or other limitations. In those cases, an indicator is required to alert the system operator that an opening has not been closed as required and thus the system is not ready for operation.
9.7.1.1
Where confinement of agent is not practical, or if the fuel can drain from one compartment to another, such as via a bilge, protection shall be extended to include the adjacent connected compartment or work areas.
9.7.2*
Prior to agent discharge, all ventilating systems shall be closed and isolated to preclude passage of agent to other compartments or the vessel exterior. Automatic shutdowns or manual shutdowns c

Franck

2/20/2023 11:07:29 am

If you want to keep your gas concentration for at least 10 minutes, you will probably need dampers.
And you may also need “overpressure” dampers to eliminate the overpressure at the initial stage of the discharge.

This being said, are you sure that gas protection is the best solution to protect your anechoic chamber ?
It might depend on your configuration, but most anechoic chambers have cones made of some type of combustible foam material.
If the fire is inside this cones structure, you will have a quick spreading fire and deep seated, so probably difficult to extinguish with your gas.
The question is : what are you protecting ? The room from a fire coming from the equipment being tested, or the equipment itself ?
Most anechoic chambers I have seen were sprinkler protected, and only a few of them had a gas protection in addition (not instead).
Be careful if you provide sprinklers, they have to be installed upside down (water is to be delivered towards the cones, not inside the room). And when provided on telescopic branch lines (to limit perturbations inside the room), it may become problematic from a maintenance en operational point of view.

Another underestimated issue with gas protection : over the time, dust accumulate over the cone surface. When activating the gas protection, because of the pressure and release of gas, the dust will be spread all over the room. If you test equipment that are very sensitive to dust, such as mirrors for space industry, it could be a disaster.

Chad

2/21/2023 08:47:15 am

Be careful if you provide sprinklers, they have to be installed upside down (water is to be delivered towards the cones, not inside the room).

That is a darn good point! I can imagine someone arguing it but you are certainly right.

Franck

2/20/2023 11:16:10 am

For the “overpressure” dampers, I have a “funny” real story.
A very large anechoic chambers was protected by sprinklers and gas (nitrogen, or something similar). This large chamber was used to test satellites, so they wanted to be sure that the system was working.
Why sprinkler + gas ? Because they had a fire in this chambers that damaged a several hundred million dollars satellite.

Sprinkler arms operations were tested with air pressure.
For the gas protection system, they wanted to make an actual release with concentration measurements at several heights.
But when they discharged the gas (several dozens of cylinders… the test cost a fortune), the overpressure was such that it activated the anti-panic bars on the entrance door and opened them widely, releasing the gas out of the chamber immediately!

To a certain point, this failure was a good thing as they could remediate the issue… Imagine if that had happened during a fire !

Frank Savino link

12/26/2023 10:47:05 am

You need to imagine that your clean agent protected room is a large swimming pool that you are trying to fill up with water. Most clean agents like Novec 1230 (aka FK 5-1-12) or FM-200 (aka HFC227es) are heavier than air. The water and clean agent will leak out through all of the openings in the walls, doors, and floor. It will not leak out upward through openings in the ceiling. The HVAC supply and returns grills are at the ceiling and agent will leak upwards. If the HVAC is allowed to continue to run after agent discharge, you will dilute your extinguishing concentration. The best and easiest way to deal with that is to electrically interlock your clean agent to automatically shut down the HVAC upon agent discharge. You do not need dampers. Most of the time, HVAC shuts down instantaneously. If not, you can time delay the agent discharge to give time for the HVAC to shutdown. Keep in mind that if you have HVAC openings in walls or the floor, these will likely need to be dampered. Remember the swimming pool analogy.

Doing it this way will save a lot of money in damper installation, and wiring. One issue that you will need to address is passing the room integrity test because you have room openings through the open HVAC ducts at the ceiling. The test procedure allows you to temporarily close those duct openings at the ceiling with cardboard and duct tape for test purposes.

Inert gas agents like Inergen, ProInert, Nitrogen, or Naturara are very close to the same density as air. They very much stay suspended in the room and their hold time is far superior to the other clean agents. You will need to also be sure to shut down the HVAC electrically to prevent agent loss from dilution. Same rules apply as in the first example i gave.

The inert gas agents require that a lot of agent be discharged into the protected space compared to the other clean agents. You have to do a calc to make sure that you do not over pressure the room and cause a wall in the room to rupture. You might need a pressure operated pressure relief vent to prevent over pressurization. This is weighted damper that automatically opens upon pressure increase and closed when the pressure normalizes. You need to make sure that you don’t over pressurize an adjacent space. You might need to duct this to the outside of thr building. Doing this over pressure calc is very important. It is described in NFPA 2001 and the integrity test people can help you with this. Please note that NFPA 2001 requires all clean agent systems be calculated for over pressurization but it is especially important to do for inert gas agents.

If you do use dampers, they should be fail safe ( fail in the state you want them to be in a fire). Also, they must be at least 99% airtight. Many are very leaky and will cause agent dilution. In my opinion, they do not need to be fire listed but I am not sure about the listing question.

Bottom line is avoid dampers if you can. They usually are not needed.

Dampers Required for Room with Clean Agent?

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