Clean Agent System Venting

[fireguy2001]

thread184-267644

I should apologize ahead of time, this is my first post on this forum, and unfortunately extremely long. The subject matter is simple in substance but complicated in design.

I am hoping that one or more of you good folks can help me with a design conundrum brick wall that I recently ran into. A few months ago one of my clients approached me with a task to essentially become an expert in the field of clean agent systems, and more specifically IG-541 (Trademarked as “Inergen” by Tyco Corp.’s Ansul). After months of research I can now say that I am almost an expert. I have to say that had I known the depth of the rabbit hole I was plunging into I might have been a little reluctant.

Anyway the conundrum is as follows:
I now understand that there are two main considerations with regards to the protected enclosure (room being protected):

1.) The enclosure must be of tight enough construction that the clean agent gas does not leak out of the room too quickly. In essence the design concentration (as measured by the percentage of gas concentration within the room mixed with air) must be maintained at the minimum required level (in this case 34.2% for a class C fire hazard) for a minimum of 10 minutes. This translates to the need to perform an enclosure integrity test by depressurizing and then pressurizing the room with a door fan to verify that the room is not too “leaky”. This establishes the Effective Leakage Area (“ELA” for the remainder of this post). The ELA is expressed as a maximum value depending on the design concentration for clean agent gas retention within the enclosure.

2.) The enclosure is going to be subjected to a lot of pressure when we dump all that gas (a time frame as little as 10 seconds for the halocarbon agents and 60 seconds for the Inert gas agents). This pressure differential is a considerable increase for the inert gas agents and a considerable initial decrease for the halocarbon agents with an eventual increase above the normal “static” pressure within the enclosure. As a result we have to have a minimum amount of Free Vent Area (“FVA” for the remainder of this post) through the walls/ceiling/floor to allow enough of the air to escape as the gas fills the room or we could literally blow the roof off or blow the walls out (I’m not joking here, I have seen photographs of enclosures that have failed as a result of discharge and they aren’t pretty; ceilings obliterated; CMU wall blocks blown across the floor of a facility, etc.).

Are you sensing the conundrum yet? Well here is the whole nut including the shell.

The amount of pressure we can impose upon an enclosure is dependent on the effective strength of the enclosure (walls, ceilings, floors). In my team’s case the ceilings and floors are typically concrete and, thus very strong. The walls, however, are a different matter altogether and are sometimes simply corrugated metal haphazardly attached to girts or other framing.

The amount of gas we can “dump” into enclosures of this type can be quantitatively measured as a function of the wall strength (typically expressed as pounds of pressure per square foot of wall surface or lbs/sq.ft. – 5 lbs/sq.ft. is typically considered at the low end of the scale but my team has some that should be considered lower than that)

So - I need to rest my fingers after all of this typing, my apologies (fwheww)

So I have done some calculations and discovered that the MINIMUM FVA that our enclosures typically require is about 1.5 times larger than the MAXIMUM ELA we are allowed for the minimum retention requirements. Oh the conundrum at last.

So, now I have some documentation that recommends the use of special vents that open upon system discharge and then close either after some period of time or stabilization of column pressure within the enclosure. This is the only solution my team has been able to find for this daunting design problem. We have identified three types of vents as follows:

1.)Static/Gravity vents – these are essentially spring operated vents that open when subjected to a certain amount of pressure and close when that pressure has been reduced. Our concern about these is the extremely dusty environment we are working in and potential failure due to seize-up when needed.

2.)Electric Motor Operated – these vents have louvers that are opened by an electric motor and would need to be controlled by our release panel. Our concern here is that we would have yet one more working part that could fail, again giving consideration to the environment.

3.)Pneumatically Operated – Operates through application of a pressurized gas to a switch or lever. We use nitrogen pilot lines to open our cylinders already so these are a possibility but we would have the same concerns as with the other vents.

My questions for the group are as follows:

1.) Do any of you good folks have any experience with any of these vents?

2.) If so which type(s) have you used?

3.) Do you know of any other types of vents other than the 3 I mentioned?

4.) Could you recommend any high quality manufacturers with products with a good track record for extremely dusty environments?

Thanks for any help you can provide and thanks for taking the time to read this extremely long post.

JMO

 

[b1ueshift]

The amount of gas discharged by an Inergen system is such that some has to escape. Fortunately air is very light and low in viscosity and quickly gets out any openings like the gap under the room door. Most designers seem to assume that there is sufficient leakage (like under the door as well as some service penetrations) that will let the gas escape.

I recall reading in the Tyco Engineering Guild that if the designer is concerned about overpressure, they should use a type of vent which is a small damper held closed by gravity and opens when subject to a positive pressure. The amount of pressure required to open a damper like this is very small compared to the amount of pressure required to blow a door off it's hinges.

As for the condition of the damper, I think you should be equally concerned about every other component in the system which is subject to failure. The system (including damper) should be inspected at intervals recommended by NFPA 25 in order to ensure reliable operation.

 

[DM2]

Man...I had to put my monitor in Portrait mode to read your post...a good Post.

Some additional information however:
1. I suspect you've gone through NFPA 2001. The requirement for the hold time (NFPA 2001, 2008 edition, section 5.6) limits the hold time to the "...highest level of combustion...". Most would interpret this to mean the highest level of equipment, which is considered to be a cabinet. Some may argue that it's higher due to the location of cable trays. Door fan testing that we've conducted has always been to the top of the equipment.

2. The next edition of NFPA 2001 was scheduled for 2011, however due the filling of several NITMAM (Notice of Intent to Make a Motion) it will likely be delayed until this next fall. The NITMAM's have to do with a debate over the safety factor for Halocarbon agents. In the US the margin of safety uses a 1.2 multiplier over the extinguishing concentration. The equivalent ISO standard uses a 1.3 multiplier (there's a long story behind this but for another post maybe). The standard was revised to use the 1.3 safety factor and as a result several manufactures posted their objection in two (2) NITMAM's. I wrote all of that to write this...The next edition of the standard will revise the extinguishing time for Inert agents to 2 minutes for Class A hazards. Now...A Class C hazard becomes a Class A hazard when you remove the power, which is typically done for most suppression systems.

The folks that make Inert Gas systems have been fighting the 1 minute discharge time for years and each year the NFPA 2001 committee votes against extending it to 2 minutes. Looks like this year they got part of it passed. The point being the check if you're going shutdown the electrical and can therefor class the area as a Class A fire hazard and then use the 2 minute discharge time. This will greatly reduce you're vent size.

3. The 5 lbs/sq. ft. is something that I suspect you may have gotten from the IBC. In our area most of the buildings exceed this due to wind loading, but then I'm in the gulf of Mexico.

I can't speak from experience on the dampers as we, being a fire suppression company, don't actually supply them...the HVAC contractor does. I can say that we have always used the gravity version. We did however have a project going to the North Slop of Alaska where the electrical building manufacture used blow off vent used for "Arc Fault Protection" (I may have gotten the description wrong). These provided great sealing, but had to be replaced if a discharge occurred and I can't remember any brand names.)

In an offshore application, we had to use dampers that had an offshore A-60 rating. Here again we didn't supply them but they were made by Ruskin (

http://www.ruskin.com)

As we distribute Ansul products, I called them for their recommendation. They recommended one company called "Greeheck" (

http://www.greenheck.com)

but don't have any information beyond that.





Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[pipesnpumps]

My recommendation , wearing my HVAC engineer hat, is the gravity type, but have it discharge into an adjacent interior space above the drop-in ceiling if possible.. Maybe into a vented attic, room next door, etc.

If you are doing a stand-alone building that is entirely protected by the system, then I would go with the spring type, the reason for that suggestion is the wind can tend to open and close gravity types, so you get the flap,flap effect. I suppose either gravity or spring return "relief dampers" (the HVAC term for what you describe) can seize up, but I have never heard of such a thing..

Its a very reliable piece of metal with a hinge, can get much simpler than that..

 

[DM2]

Discharging in to an joining space isn't recommended unless the space is sufficiently large. Keep in mind you're adding 40% volume into the existing space and the air already in that space has to go somewhere. If the walls in the other space aren't sufficiently strong enough, they too will be damaged.

Ansul has a document that it intended to be handed over to HVAC contractors. I believe it includes formulas to account for the changes in direction of the duct work as this would have an effect on evacuating the volume of air already in the room.

I'm a big believer in Inergen systems but I do have video of doors blowing open and the resulting damage due to lack in accounting for adequate venting.

Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."