Engineered Corrosion Solutions: Fire Safety for Cold Storage

Posted by ORR Protection on Mar 10, 2021 9:30:00 AM

Bill Aaron, Director of Training at ECS, discusses corrosion management of fire sprinklers in a cold storage application. In particular, understanding the industry guidelines for maintaining these sprinklers, installing and maintaining these sprinkler systems, and the current technologies that are available.


Video Transcript:

My name is Bill Aaron. I'm the Director of Training for Engineered Corrosion Solutions. And I want to thank you for taking time out of your schedule to meet with us today. What we'd like to discuss is corrosion management of fire sprinklers in a cold storage application.

Some of the objectives that we'd like to discuss today is how we maintain an operational sprinkler system and refrigerated space. Understanding better the industry guidelines for maintaining these sprinklers, installing and maintaining these sprinkler systems, and the current technologies that are available. When we started looking at maintaining an operational fire sprinkler system, there's a few things we want to consider. Number one, we want to protect against corrosion between this fire sprinkler riser and the refrigerated space. We also want eliminate ice plugs and frost accumulation in the refrigerated space. We also want to consider and look at reducing maintenance costs and operational costs and extending the life cycle of the equipment. From an industry guideline standard. We want to look at NFPA 13, which is the standard for installation of sprinkler systems, NFPA 25, which is the standard for inspecting testing and maintenance, and FM Global's property loss prevention for refrigerated storage space. From a current technology standpoint, there are three basic technologies that are available. The three, are dry air packs, nitrogen based, and vacuum based. We're going to discuss the dry air packs and nitrogen based today. The vacuum based is still a relatively new technology and has some limited applications. So we're going to discuss that at a future presentation.

The biggest concerns when you're working with refrigerated spaces is the potential of the sprinkler system freezing up and making it inoperable. In the field examinations by FM global, what they've found that they have found ice plugs in over 50% of the freezers that they've examined and these ice plugs are found within the first 15 feet of the pipe, as it goes inside the cold storage area. NFPA 13, the standard for installation defines the differences between sprinkler systems at those systems that are above 32 degrees and those that are below 32 degrees. When we're working with these sections of NFPA for areas that are below 32 degrees, then we need to consider the, what is defined in the refrigerated spaces. The intent is to minimize the chances of ice plugs inside the sprinkler system and protect those freezers.

NFPA 13 tells us that our supply of gas has to be one of the three of the following. One, if it's air, it must come from the lowest temperature to reduce the moisture content. It can also come from a compressor dryer package that's listed for the application, or the third is compressed natural gas from cylinders in lieu of compressed air. One thing to remember is taking the air supply from the coldest room then doesn't compromise the fact that you could be moisture free. The best thing we can do is to ensure that that gas is at least 20 degrees below the lowest nominal temperature.

When we're looking at the supply of gas, we've got two possible options. One is using air as the air supply, and the other is using nitrogen. When you're working with the air supply, you need to provide two easily removable supplies for that air to get into the connected to the sprinkler system. And those need to be six feet long so that they can be easily removed. When you're working with nitrogen, you only need a single six foot long supply. The other couple of other things you need to remember is priming water can evaporate and migrate into the freezer and cause an ice plug and also excessive leaks in the sprinkler system can cause excessive air compressor runtime, which will then increase more moisture, which then can cause additional ice accumulation.

Now even though NFPA 13 does not specifically call out that we can use a nitrogen generator for cold storage applications. What it does say that anywhere that the term air is used, it can also include nitrogen or an approved gas and that nitrogen or approved gas has to be supplied from a reliable source. And it can either be generated onsite or in storage containers. So by doing this, this will allow us to use a nitrogen generator instead of cylinders for cold storage application. Also, when you start talking about the air supply and meeting the 30 minute fill requirement. When you're working with cold storage applications, that timeframe is increased to 60 minutes instead of the 30 minutes. So if your refrigerator space is below five degrees Fahrenheit, you're now allowed to be able to extend the time from 30 minutes to 60 minutes to meet the fill requirement. And the purpose for that is by slowing down the gas, going into the sprinkler system and filling it slower.

There's less potential of additional moisture or ice accumulation during the fill time. NFPA 25, which is standard for inspection testing and maintenance tells us that loading of sprinklers is detrimental to the performance of that sprinkler. And if there's any severe loading or corroded sprinklers, they need to be reported as a deficiency or an impairment. The other thing too, is this tests have shown that the loss of color in the sprinkler glass classification does not affect the operation of the sprinkler system. And these sprinklers can remain in service. NFPA 25 also tells us that refrigerated spaces in other areas of a building where the temperature is maintained at or below 40 degrees cannot be wet pipe systems. They must be dry pipe systems. Also any air dryers must be maintained in the courts of manufacturer's instructions. And that compressors used in conjunction with dry pipe systems need to be inspected and maintained in accordance with chapter 13 and the manufacturer's instructions .

NFPA 25 also requires us to check the pressure gauges on at the air compressor and at the sprinkler system monthly to ensure that the pressures stay the same, because the difference in those pressures is an indication of a freeze up in the line. Also pre action systems and dry pipe systems when they're trip tested must be done in a manner that doesn't introduce moisture into the piping of the freezers. In spaces that have a temperature below 32 degrees, they need to be inspected annually for ice obstructions. And any, if any ice instructions are found, then additional pipe must be examined to ensure that there's no ice obstructions or ice blockages. FM global has requirements for, uh, refrigerated storage spaces. Some of those requirements include that the, uh, re regenerative or dehydrated air has to be in a FM approved system, and that if their detection portion of the refrigerated area is pneumatic, it must come from a separate or independent air supply than the sprinkler system piping. Also the dry pipe and pre action systems need to be FM approved and also need to be, uh, connected to an adequately sized dehydrator.

FM tells us that we need to use an approved air supply package, and we have to dehumidify that air to a dew point of 200 degrees below the lowest nominal temperature. We also have to take the source air from the freezer with the lowest temperature, and we have to have duplex lines from the compressed air source through the freezer. In addition, we need to install a check valve between the valve assembly and the disc start charge line to block any moisture migration. In the event of a trip, the entire system needs to be inspected each branch line and each cross main. If ice plugs are found, the entire system needs to be disassembled taken to a warm area and allowed to unthaw. You cannot use open flames or any kind of heaters to mitigate any of that ice buildup.

So now let's start talking about the gas sources for these refrigerated space sprinkler systems. And first we're going to start with the dry air packs. There's currently three different models of dry air packs available. One is 500 gallon capacity. Second one is a thousand gallon capacity and the third one is 2000 gallon capacity. Now, the, what they require or recommend is that you limit to three sprinkler systems per dry air pack. So in the case of the 500 gallon, that means you could put three, 500 gallon systems on that model. What, we have found and what history is demonstrated to us is that even though dry air packs are installed in refrigerated spaces, especially if they're not maintained, there is a history of ice accumulation. From an operating dew point, the dry air packs can get the dew point to between minus 40 and minus 60 degrees Fahrenheit.

Some of the things that we found with our dry air pack is that they are very labor intensive to, to install and to maintain. As an example, when you initially set one up, the current installation manual requires that you run the dryer for a half hour before you connect to the sprinkler system. However, earlier, versions of that same installation manual tells you how to run it for eight hours before you connect to the sprinkler system. And in turn, when you start looking at maintenance on the dry air pack, number one, the current edition is telling us that we need to replace the desiccant every three years. For previous models of that installation manual said need to replace desiccant once every one to two years. Also, once you replace that desiccant the runtime for the dryer needs to be a half hour before you connect it back to the sprinkler system.

And you need to remove the purging mufflers during that process. The older version previously was running for eight hours, remove the mufflers during the first two hours, and then re-install them. So what we're saying is that it is very labor intensive to maintain the dry air packs. And if they're not maintained properly, they're not going to work properly. And when they don't work properly, you have, you're more susceptible to, um, ice plugs in these freezer systems. So now let's look at a comparison between a dry air pack and a nitrogen system as it results to corrosion within that sprinkler system. And as an example, let's use a thousand gallon sprinkler system and let's use NFPA 13's allowable rate of a pack one and a half PSI in 24 hours. If you were to allow a pack or one and a half PSI leakage rate in a 24 hours, what you would be doing is adding 21.3 gallons of oxygen.

Because remember, at a thousand gallons, 21% is oxygen, the rest is nitrogen. But you'd be adding 21.3 gallons of oxygen would be drawn into that system each day. And 21.3 gallons of oxygen would provide, create an additional 0.8, four pounds of iron oxide. Whereas with a nitrogen system, same pound and a half, one and a half PSI drop in 24 hours, you'd only be allowing 2.1 gallons of oxygen to be drawn in which then would create 0.8 pounds of iron. So the bottom line is that a dry air pack could result in 950% more corrosion in a sustained operation. So now I start looking at using nitrogen for these dry pipe systems and cold storage applications. First of all, nitrogen is a very dry gas. The operating dew point is minus 100 degrees Fahrenheit at 98% pure. When you start looking at a nitrogen generator, you can connect up to 22 sprinkler systems to a single nitrogen generator. How that equates is we looked at thousand gallon systems, 22 of them, two for a total of 22,000 gallons of system capacity. The largest nitrogen generator offered by ECS can handle up to 22,500 gallons. So in reality, whatever the combination of systems and total volume that can be connected to a single nitrogen generator, can be as much as 22,500 gallons. What we have found by using nitrogen in lieu of dry air or air is that by using nitrogen, in our case studies, we have found no ice accumulation in these cold storage sprinkler applications.

Now let's look at the initial setup, operation and maintenance of a nitrogen generator. For a nitrogen generator, your connections you've got electrical power, you've got the power for the generator itself, which is 120 volt power. Depending on the size of the system will determine whether you need a separate air compressor or not, which is the source air for the nitrogen generator. And you'll need a power requirements for that. Typically that it would be a three-phase connection. Then you'd have the plumbing from the air compressor air source to the nitrogen generator and the plumbing to the, um, from the nitrogen generator to the sprinkler systems. Then we can set up our operation going through the other maintenance devices. From an operational standpoint, we would go through the 14 day startup pair or a nitrogen inerting period. If you're using a manual vent, it's open a ball valve, come back 14 days later, close the ball valve.

If you're using a smart vent, what you would do is push the vent button, which would initiate the 14 days. And then once it's done the night generator will provide all the supervisory gas. From a maintenance standpoint, the, on the nitrogen generator, we need to replace the filters annually. And then as far as the air compressors change oil every 500 hours. Other than that, there is no additional maintenance that needs to be done to the nitrogen generator. Far less labor-intensive a lot easier and a lot less expensive to operate and maintain. So now let's look at a comparison between a dry air pack and nitrogen generators. In a dry air pack you've got a fluctuating dew point and the lowest dew point is between minus 40 and minus 60 degrees Fahrenheit. It is maintenance dependent. There is the potential of ice plugs and there is no corrosion protection. From a maintenance or labor standpoint, it is very extensive required. There is quarterly inspection or procedures of annual procedures, and there's replacing the desk and every three years. Along with being limited to three sprinkler systems per dry air pack. Whereas with a nitrogen generator, we're producing 98% pure nitrogen. That dew point, it could be as low as minus 100 degrees Fahrenheit. It is consistent. We've eliminated ice plugs, we've eliminated corrosion. There's minimal maintenance, only annual. And the nitrogen generator is really based on the total size of the system capacity.

So now let's look at a couple of case studies where we've used nitrogen generators in lieu of dry air pack. And the results from that. This is case study number one, and what it is. It's a cold storage facility that's kept at minus 10 degrees Fahrenheit. It was a single pre action system. The supervisor gas was a dry air pack, and they were doing quarterly inspections. The problems they were running into was had frost and ice plugs were consistently being found during the quarterly inspections. So what was done was the dry air pack was removed and the nitrogen generator was installed. The result, no ice plugs, no frost accumulation in subsequent quarterly inspections. And this project was completed in September of 2017. Case study number two is a cold storage facility that's over a million square feet. At a supervisor gas was provided by eight dryer pack units, and they had annual inspections.

The problems they were running into was frost and ice plugs were consistently found during the annual inspections and the dry air pack maintenance was cumbersome and costly. The solution, and this was during a test to see how the, see, how we could compare the differences between the dry air packs and a single nitrogen generator. So for the dryer packs remained, and four, excuse me, four of them were removed and replaced with a single nitrogen generator. The results were, there was no ice and frost accumulation in the systems that was connected to the nitrogen generator during the annual inspections, while the four systems that were connected to the dry air packs, were still seeing frost and ice plugs. This project was completed in May of 2016, since that time ECS as completed numerous projects in cold storage applications, where we've used nitrogen generators in lieu of any other gas source. And what we've found in all of these applications is that using nitrogen in lieu of air has stopped ice plugs and frost in these sprinkler systems. So using nitrogen is the best means for mitigating ice plugs in cold storage application. So what have we learned today?

Well, number one, field examinations have revealed that 50% of the existing freezers have ice plugs. Number two NFPA and FM global have specific requirements for refrigerated spaces where the temperatures are below 32 degrees to minimize ice plugs. Number three NFPA 25 requires piping in that piping in or passing through refrigerated spaces below 32 degrees need to be inspected annually for ice obstructions. Number four, dry air pack require quarterly and annual maintenance and recommend a maximum of three sprinkler systems connected to a single dry air pack unit. Number five, nitrogen generators require only maintenance and are compatible with new and existing systems. And a single nitrogen generator can serve as much as 22,500 gallons of system capacity. And number six, using nitrogen in refrigerated spaces eliminates ice plugs.

We hope this was informational for you, and we really appreciate you taking time out of your schedule. And we thank you. If you have any questions, please contact us or go to our website at for white papers, case studies, a lot of valuable information that can be used to help you and assist you with your cold storage needs. If you have any questions or need any assistance, don't hesitate to call us. Again, thank you very much.

Topics: Fire Protection Systems, Leaks and Corrosion, Featured Article, Video Blogs, Featured Blog, MCFP, Cold Storage

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