Mix K-Factors and Temperatures in Same Room?

2/14/2019

Are there any requirements pertaining to mixing fire sprinkler k-factors or temperatures in the same room?

We often come across unit heater placement, so at least on the temperatures I suspect that mixing in the same room happens fairly commonly to accommodate heat sources.

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7 Comments

Corey

2/14/2019 10:02:52 am

Yes, you can mix temperatures within the same area. See NFPA 13, 2016 edition 8.3.2.5 for more detail.

Dan W

2/14/2019 10:24:14 am

If you are using the different K-Factors to minimize over discharge a system, then not allowed (23.4.4.9.2-16'). 23.4.4.9.3 & 23.4.4.9.4 allows different orifices within small rooms (exposure protection & directional spray sprinklers) with the Annex explanation giving a little more insight.

PETE

2/14/2019 10:24:22 am

Mixing K-factors is acceptable, however, you will want to either designate areas that certain K-factors are to be used, or be very knowledgeable about fluid dynamics. If you have one K-factor in one area, and another K-factor in another area- both areas should be calculated. This also applies to standard and extended coverage in portions of systems.

I had one instance in which I was designing a deluge system for an industrial chemical complex that was on city water, and I was trying to satisfy and insurance underwriter's safety cushion requirement. I had to use a plurality of screwed pipe sizes and orifices in order to minimize over-flow and over pressure situations, as every head was required to flow.

PETE

2/14/2019 10:30:44 am

I should add, after reading DAN W's comment above: the example I gave was a directional nozzle deluge system for a pumping station near an exterior dock; in which non-flammable non-combustible liquids were being pumped- mainly ammonia.

2/14/2019 01:49:16 pm

Adding to what others have said.
- Mixing temperature ratings is permissible, and fairly common. For example: NYC apartments and condos, I would use regular temp heads throughout, but switch to medium- or high- temp if the sprinkler is too close to a stove, dryer, fireplace, etc.
- Mixing k-factors is NOT allowed for "balancing" or to try and reduce your hydraulic demand. It is (in general) allowed if you need a different k-factor for a specific reason. However - the requirement to separate different k-factors is "by room" or "by area" not by sprinkler system. It is important to review NFPA definitions for these, as the NFPA definitions may not align with an Architect's "common sense"
- As I understand it, mixing Ordinary Response sprinklers with FR/QR sprinklers is NOT allowed.

Dan W

2/14/2019 05:52:42 pm

For the FR/QR/SR comment, it can be done in accordance with 8.3.3.5 '16. This has saved me on a couple of projects with EC sprinklers.

Franck Orset

2/19/2019 11:06:26 am

Mixing K-factor is not a good idea, unless you have good reasons for it (such as a deluge system where the K factor may different depending on the area for the entire surface coverage, but this is not a sprinkler system...).
Mixing different temperatures can be deemed necessary because of possible change of local room temperature (sprinkler heads next to a heater, below a skylight...).
In the 2019 Edition, the chapter is now 9.4.2 (& 9.4.2.5 for a list of examples), and not 8.3.2 (& 8.3.2.5).
You could mix K-factor in the same room (as well as T° rating) if you have a change of occupancy that would require this particular change.
For example, if you have a processing area (let's say OH Gr 1 activity with ordinary rated temperature sprinkler heads), but a dedicated storage area representing a higher fire challenge (a few racks, or a idle pallets storage). In that case, you might need to have larger orifice sprinkler heads and/or higher temperature rated sprinkler heads.
But there are rules, as indicated above, because you will need to extend the most demanding area beyond the area of protection (or provide a draft curtain/fire barrier).
This is part of chapter 20.10 of NFPA 13 (2019 Edition) : Adjacent hazards or design methods.

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