Storage Capacity for Existing OH Pipe Schedule?

10/12/2020

NFPA 13, 2016 Chapter 11 and Chapter 23 provide information on systems that were designed as a Pipe Schedule System (as defined in Section 3.4.9). Section 11.2.2 and 23.7 provide information regarding "Ordinary Hazard" pipe schedule systems, but the storage capabilities in NFPA 13 are based on specifically Ordinary Hazard Group 1 and Ordinary Hazard Group 2 (specifically referencing chapter 13 in this situation for Miscellaneous storage).

I am working in an existing building with an "Ordinary Hazard" pipe schedule system, what are the storage capabilities of the existing system (assuming it does not adequately calculate)?

I did try hydraulically calculating the system just to see if it would work, but there wasn't enough pressure for the existing pipe configuration. A few people I have talked to agreed to stick to OH1 storage capabilities without any upgrades, but I am looking for formal guidance if anyone knows of any.

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8 Comments

Dan Wilder

10/12/2020 08:41:58 am

Let's not forget the OH3 curves. The old curves used to be ".1" ".18", ".24", & ".30" for the 1500 square foot design areas (understanding that this isn't a hydraulic question but Ordinary Hazard had a third option for a time).

My question is what changed to bring you in to perform work? If the owner was being questioned by the AHJ as to system capability (with no modifications ongoing), then I would write up your findings stating the system does not work per current standards (design area & density + current water supply).

If you have a calc plate or system as builts, then the allowable design criteria should be available and the capabilities/limitations of the system need to be maintained (unless your AHJ has outright struck the IFC/NFPA references to use of pipe schedule systems). Without the original system design, the safest non-calculation method would be the approach you mentioned of the lowest OH design available. Luckily, the LH & OH pipe schedules are well defined and not an issue to prove intent.

Beyond that, to evaluate the system would require current NFPA guidance and, as you stated, the system does not work as currently configured.

Noah Koski

10/12/2020 10:10:07 am

Hey Dan, good questions. The occupant of the space is changing and the new occupant intends on storing a different commodity in a different configuration than the previous occupant. The AHJ typically makes us verify the existing system is adequate for a new occupant when they pull a building permit with new rack plans.

The building owner is the 3rd owner of the building since 1973 so there are no as-builts or hydraulic placards. The pipe schedule of the existing system is a textbook OH pipe schedule. It sounds like OH1 would be the safest storage capability to communicate to the building owner since the system does not work hydraulically.

10/12/2020 10:32:17 am

Yes, with no info the OH1 (Class 1 to <12' & Class 2 to <10' - nothing else) approach would be the safest with the caveat that you provide something in the letter stating that hydraulic calculations to current standards would be in the best interest of all parties and that your review/conclusion is only at a basic level of compliance as to the original design intent and per NFPA (site sections and adoption year).

If he pulled a rack permit that is a little worrisome.

Mike

10/12/2020 10:48:14 am

If you are saying you calculated the system for OH1 and there wasn't enough pressure, why would you stay with OH1 storage capabilities. You now have prior knowledge of an inadequately designed system for a new/changed occupancy.

Wouldn't this become a liability to your company in case of a fire?

If it were me, I'd present it to the new owner. There is also the insurance underwriter that may want plans and calculations.

I have done some of these reports and the owner has had to upgrade the system to comply with the occupancy when the existing system was deficient.

Casey Milhorn

10/12/2020 12:15:26 pm

Dan has some great info and good points and I would definitely approach it as Mike is suggesting. I have done a number of these and you have to put on your lawyer hat first. You do not want to be sitting on the stand being grilled by a lawyer 5, 10, 30 years down the line for something you did or did not do. My letters always state the info I received, where I got it from, the date I got it, and the 2nd part of my letter is analyzing existing storage (hopefully classified by owner, you don't want to do that for them if at all), 3rd part is analysis of what the system is capable of doing, and then the last part is the conclusion of if it works, or if it doesn't. Be very clear that water supplies can and do change over time, any information supplied by others is assumed accurate, and that you will not be liable for changes in occupancy/storage heights/storage types/storage scenarios, that could affect the system's capability of proper protection. In my opinion, this is not something you want to half A do. Be very clear of your scope, what you are doing, and then be very detailed. Or wash your hands early and put it back on owner. Don't get caught playing in the middle of the road on something like this. You should always assume its not if there is a fire event, but when will there be a fire event at this location.

Franck

10/13/2020 10:45:43 am

I fully agree with Mike's comments.

Working for an insurance company for more than 25 years, I would definitely require an upgrade of the sprinkler system.
With the information you provided, if this is a correct understanding from my side:
- you have a pipe schedule system for OH
- when you do calculations, you can not achieve the demand for OH (in that case, your system is actually not an OH, but something weaker... maybe LH ?)
- the new owner want to install racks... and you know that in rack storage you may find in the future very different adverse conditions than what they ware approved (with your system, you will limit both the commodity classification and the height of storage... but everybody knows that if more plastic need to be stored, it will be stored, and if you can store higher, you will store higher...).

I would call this a scary situation...

In you case (again, as an insurer's point of view), the question is "will you be confident that a fire in the new configuration will be controlled". So far, I am not convinced. And the AHJ would probably be not convinced either.

10/13/2020 12:10:47 pm

NFPA 13, 2016 section 11.2.2.3 allows pipe schedule methods for additions or modifications to existing pipe schedule systems. If the water supply requirements of Table 11.2.2.1 are met, why would the system need to be modified if the maximum storage is kept to the OH1 storage limitations. NFPA 13, 2016 doesn't provide any guidance on upgrading existing pipe schedule system based on hydraulic calculations except for Extra Hazard occupancies. I hear what you're saying from an insurance perspective, but that sounds like an opinion above and beyond the standards of NFPA 13, 2016 since there is nothing that recommends doing that. The hydraulic calculations were for the owner, but doing calculations doesn't change the fact that pipe schedule systems are allowed. My understanding is that most pipe schedule systems don't work hydraulically. If the intent is to upgrade a system every time someone decides to try a hydraulic calculation (knowing that it probably won't work), why would NFPA 13, 2016 11.2.2.3 allow the pipe schedule method to be permitted?

10/13/2020 12:41:22 pm

I would have to agree with Franck as well on this. The question is how many pipe scheduled systems have not had any changes on what is being stored, how its being stored, the height, etc... it comes down to who has asked for this "analysis" and why. Also remember that an ordinary hazard occupancy is not the same as a storage occupancy using ordinary hazard density and area for protection. There are some nuances there that you should be very careful of making from Chapter 11 to Chapter 13, or vice versa. Like 11.2.2.1 water supply requirements mention light or ordinary hazard occupancies, they don't mention storage occupancies protected by ordinary hazard design requirements. Little bit of a rabbit hole there. Now that you have proof that the system doesn't work hydraulically (even if you didn't do an analysis of storage type, height, arrangement, etc..) you are in a precarious position.

Storage Capacity for Existing OH Pipe Schedule?

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