Nitrogen for Ice Plugs 3

[nitrosup]

We distribute nitrogen generators that filter the oxygen out of air to leave nitrogen present as a supervisory pressure for dry fire protection systems. The main market for this product is the prevention of corrosion in dry fire protection systems. There may be an important market we are missing altogether. We believe that nitorgen will provide a tremendous advantage over simply trying to dry compressed air as by eliminating the oxygen, as well as continuing the drying process, you virtually eliminate condensation. Plus, nitrogen can shrink or even eliminate existing ice plugs. Has anyone had success with nitrogen as a supervisory agent in dry systems for cold storage?

 

[stookeyfpe]

DFW airport is using compressed N2 in pre-action and dry pipe systems primarly for control of MIC.

 

[nitrosup]

We have seen fairly large usage of nitrogen as a response to corrosion issues in fire protection systems. With the elimination of oxygen, the corrosion process is inhibited.
I am wondering about ice plugs in cold storage applications. I have come to find that these dry systems protecting cold storage or freezers, may have ice plugs that have developed between the interface of the cold air and the warm air of the supplied air compressor that prevents the systems from working properly when called upon and there is no required testing or maintenance procedures required to determine if ice plugs are present.
Can anyone weigh in on this idea?

 

[TravisMack]

NFPA 13 has a detail for how you are to provide piping and a gauge system when you are using shop air as the air to a dry system in a cooler/freezer. That method req'd is to help determine if an ice plug is formed at the interface you described.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[nitrosup]

Travis: Thank you for the response. I will check with NFPA 13 as I find it difficult to understand how contractors or AHJ's can ignore this possibility.

 

[FFP1]

Nitrogen is approved for "refrigerated area systems" (i.e. freezers & coolers).........this approach works very well and essentially eliminates the possibility of ice plugs. Any moisture will inevitably lead to condensation and ice plugs in air systems; this problem can be prevented as long as several specific design schemes are included. The information and requirements for both nitrogen and air supplies for refrigerated area systems are clearly outlined in NFPA & FM Global documents. The primary problems associated with nitrogen is limited supply during emergency incidents and the cost of nitrogen in comaprison with air. Air systems require less space, provide unlimited volume and also cost less than nitrogen when filling the system. The initial cost between the two options is close to the same; however, the long term maintenace cost is higher with the nitrogen system approach........then again, if you have ice plug(s) one time, the nitrogen approach quickly starts to sound like the better approach. Most contractors and customers go with the air systems with regen. dryers and ALL of the required piping arrangements with are required for these applications.

 

[LCREP]

Do not forget NFAP 25 regarding ice obstructions, see below. This is where ice problems are hopefully being picked up. Problem is dry systems have been protecting these occupancies a long time before NFPA 13 changed the air supply requirements. This came about as a result of some fire in these occupancies and FM doing investigations as to teh cause. Take a look at FM Data Sheet 8-29 great info and nice photos of ice plugs. FM data sheets are free on line.

from NFPA 25, 2011

14.4 Ice Obstruction. Dry pipe or preaction sprinkler system
piping that protects or passes through freezers or cold storage rooms shall be inspected internally on an annual basis for ice obstructions at the point where the piping enters the refrigerated area.

14.4.1 Alternative nondestructive examinations shall be permitted.

14.4.2 All penetrations into the cold storage areas shall be
inspected and, if an ice obstruction is found, additional pipe shall be examined to ensure no ice blockage exists.

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Fire Sprinklers Save Firefighters’ Lives Too!

 

[nitrosup]

I have received two very insightful responses to my question concerning the use of nitrogen in dry systems protection cold storgae applications. I am wondering if we can answer one more?
I have been told that if nitorgen is used as the supervisory pressure as opposed to air, that the nitrogen will not allow condensation to form because the oxygen is no longer present in the compressed air and that with the use of nitorgen, the nitorgen will actually shrink or completely eliminate any existing ice plugs that may be present.
Doea that sound factual?

 

[TravisMack]

To transform from a solid state to a liquid state, you need heat. Unless the nitrogen is going to react with the frozen H2O to produce an exothermic reaction, I don't see how it could melt an existing ice plug.

Once the existing ice plug is removed, the nitrogen could be used to reduce or eliminate the occurrence of future plugs. But, it doesn't seem feasible for it to eliminate a current ice plug - unless I am missing something from my basic chemistry days.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[FFP1]

System piping needs to be "dry" and filled with nitrogen in accordance with approved procedure. I am not aware of any claims that nitrogen will eliminate existing ice plugs. I also do not believe this is possible........the ice plugs would remain solid as long as the system temperature is maintained below freezing. Thawing the system piping to allow the ice to melt and simply filling the system with nitrogen might or might not work.........the moisture would still be in the system and condensation would eventually accumulate in the section(s) of sprinkler piping where the temperature drops below 32F (i.e. all freezer wall penetrations). Even if this approach works......it is not considered acceptable based on NFPA or FM Global guidelines.

 

[nitrosup]

Two last questions concerning ice plugs if possible:
1. Are the majority of ice plugs in cold storage applications seen at the interface of the cold/warm temperature or are they seen primarily at the drum drip location?
2. When there is an ice plug present, is there a drop in pressure that would register on an air gauge down stream of the plug or does the plug lock in the air pressure?
Thanks for your help with tihs!!

 

[LCREP]

Two last questions concerning ice plugs if possible:

1. Are the majority of ice plugs in cold storage applications seen at the interface of the cold/warm temperature

YES If the air does not come out, the valve, dry or pre-action ( if double locked) does not trip, the fire is not controlled.


2. When there is an ice plug present, is there a drop in pressure that would register on an air gauge down stream of the plug or does the plug lock in the air pressure?

Nope only location of the gauges is at the sprinkler valve, if the ice is plugged you would have no idea by looking at the gauge.

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[TravisMack]

If you install per FIGURE 7.9.2.7.1.1(a) then you would be able to tell an ice plug is present if you have different readings on gauge P1 and P2. That is the purpose of that configuration, so you can determine the ice plug upon visual inspection.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[LCREP]

Travis,

The gauges and pipe are still on the riser side before a plug where the cold and warm meet I do not see how this would work.

Did I miss something??

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[LCREP]

disregard I was looking at preaction arrangement FIGURE 7.9.2.7.1.1(b). which is different then the dry arrangement!

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[nitrosup]

Guys: I am told that the "easily removed pieces of pipe" section is very rarely used by fire protection contractors although you can easily see why it should. If there is no visual inspection of an ice plug, will there be differential pressure between the two air gauges that would indicate a plug? I am wondering if an ice plug wouldn't lock in the pressure downstream of the plug.

 

[TravisMack]

It is rarely used by contractor's that are not installing per NFPA 13. It is a pretty blatant requirement.

I have to assume that the people that write the standards are far more intelligent than myself and I recall there being a pretty thorough description of the new piping requirements (this came about in the 2002 edition) was so that a pressure differential would indicate an ice plug.



Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[FFP1]

It is possible to have a lower air pressure downstream of the ice plug IF the system components downstream have leaks or a leak; however, gauges are not considered (and shoud not be considered) an indicator that the system does not have ice plugs!

Some ice plugs are solid (100% blockage). Many of the ice plugs in these systems create severe obstructions with partial ice plgs which develop inside the pipe with an open hole in the center (imagine a donut with a very small hole in the middle that runs 6-8 feet long down the length of the pipe). I have seen instances were 90-95% of the pipe cross section of the 8 in. diameter pipe is obstructed by ice. Either way..........the fire protection system will not operate as designed!

The primary location for the ice plugs will be the first few feet as the pipe enters the refrigerated area (caused by condensation over time). ANY moisture inside the sprinkler system piping will eventually find it's way to this section of pipe over time due to condensation laws. This is one of the many reasons why standard dry-pipe valve systems should NOT be used to protect refrigerated area systems; the priming water is drawn into the system and creates the ice plug & also leads to dry rotted rubber seat at the dry-pipe valve.......VERY common problem and a significant percentage of the people in our industry are simply are unaware of this issue. If these "sprinkler people" were knowledgeable in this arena, we would not see standard dry-pipe valve systems protecting these areas and we would see most or all of the NFPA & FM Global required components (including the "easy to remove sections of pipe" for ice plug inspections!).

Instead, many customers think I am trying to make them spend money for expensive alterations simply because some jack-leg sprinkler contractor was the low bidder! I end up spending a significant amount of time explaining the problem and removing sections of sprinkler piping to show the customer the ice plugs; however, this is not enough proof to spend $10,000, so I have to explain the entire condensation process, show them the NFPA documents outlining the proper design and convince them the system is not reliable as installed. WOW, that is a really long run-on sentence!!

 

[nitrosup]

Dear FFP1: Thank you for taking the time to explain this problem in detail. It was exactly the info that I was looking for. I am trying to determine if nitrogen and specifically, a nitorgen generator could be a potential solution to this problem and your explanation was very helpful.
Many people are looking towards a regenerative dryer a s asolution to the problem and while this may be helpful, it is not the total solution. If you can eliminate the oxygen through the use of nitrogen as the supervisory pressure, would that prevent condensation from forming?

 

[TravisMack]

This is just basic chemistry. If you don't have Oxygen, then you obviously can't get H2O to form. If you were to eliminate all of the oxygen and only have N2 in the piping, then you will not form H2O. I doubt there would be enough H2 in the air / piping to cause the N2 to react forming NH3. So, yes, if you eliminate Oxygen by displacing it with Nitrogen, there is no way for condensation (H2O) to form unless it is introduced to the piping from other means.

Now, if the system trips, you will have to be sure to eliminate all of the water and fully displace the O2 in the piping with N2 again to prevent the condensation from developing.

The N2 plan seems more foolproof than the air dryer, but if the system is properly maintained per NFPA 25 with the air dryer, then I would assume that would be effective as well. Again, proper maintenance is the key.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com