Ordinary Hazard within Light Hazard "Building"?

1/16/2020

What should I do about a sprinkler contractor who insists that rooms of dedicated Ordinary Hazard occupancy (storage, janitors, mechanical etc.) within an otherwise Light Hazard occupancy building can be protected as Light Hazard?

NFPA 13 clearly provides direction for adjacent and multiple hazard classifications. I think Chapter 5 and 11 (and common sense) are clear on this. Classroom Labs are even another matter that NFPA has addressed. Do you all run into this "it's all light hazard" belief as well?

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10 Comments

Mike L

1/16/2020 09:05:18 am

We run into this situation very often. We design the sprinkler heads for the Storage areas as Ordinary Hazard (reduced head spacing with a density of 0.15 gpm/sf) but with a light hazard (30 minute) water supply.

We do this as long as the Storage Areas do not exceed 30% of the area. (I recall reading somewhere that less than 30% is considered ancillary space and thus permitting the light hazard water supply for the ordinary hazard)

Colin link

1/16/2020 10:23:56 am

You may only use the 30-minute water supply if Ordinary Hazard rooms are limited to "single rooms less than or equal to 400 sq.ft.". This is in Chapter 11.1.6.1 of 2016. There is no 30% allowance that I am aware of.

Julianne

1/16/2020 10:20:49 am

You are right, the sprinkler contractor is wrong. The AHJ will tell them the same thing; give them a call.

Colin link

1/16/2020 10:22:23 am

"What should I do about a sprinkler contractor who insists that rooms of dedicated Ordinary Hazard occupancy (storage, janitors, mechanical etc.) within an otherwise Light Hazard occupancy building can be protected as Light Hazard?"

Easy; tell them they're wrong, and show them the code/standard! As design professionals, it's our job to educate the contractors on proper design, and to fight the "but this is how we've always done it" attitude.

To what Mike L. said: You may only use the 30-minute water supply if Ordinary Hazard rooms are limited to "single rooms less than or equal to 400 sq.ft.". This is in Chapter 11.1.6.1 of 2016. There is no 30% allowance that I am aware of.

Nhat Nguyen

3/30/2020 10:05:52 pm

Dear Collin,

It's clear that water supply duration is 30 min for hose in this circumstance, but the standard does not mentions about water demand duration for sprinkler system. So when i calculate the capacity of tank, what the duration shall i use for the sprinkler system?

Colin link

3/31/2020 11:43:38 am

Nhat,

You use the 30-minute duration. The durations listed in the tables in chapter 11 are "water supply duration requirements", and are not limited to just the hose streams; they ALSO apply to the fire sprinkler system. So in any situation, you take the highest gpm waterflow demand, whether it's the hose stream or the sprinkler system or the standpipe system, and multiply that by the required duration.

Nhat Nguyen

3/31/2020 08:18:21 pm

Dear Colin,

I understand, thank you very much. In my local code, to calculate the capacity of tank, we must summary all water demand of all fire protection system in a building, but does not state about this situation of mixing hazard, so i can refer to NFPA

Regards,
Nhat

Max

1/16/2020 11:38:27 am

It is also worth noting in a remote area such as this the hose streams for the higher hazard must be included in the hydraulic calculation.

Colin link

1/16/2020 11:41:21 am

Unless the Ordinary Hazard area is a single room less than 400 sq.ft., then you may still use the Light Hazard hose stream for calculations.

Henry S.

1/16/2020 12:06:11 pm

While most sprinkler contractors I work with are generally up on code or at least are open to being pointed out where they are wrong (I catch a lot of common, but unintentional mistakes). But as Colin said, I also get a lot of "that's the way we've always done it." Julianne brings up an interesting point too about calling the AHJ. I have rarely done that, but I may consider that more often, especially when I already have a working relationship with that AHJ, since they are the ones with the teeth. Some AHJ's are very knowledgeable, while others simply are not. One AHJ told me he only has about 30 minutes to review any given submittal, so leaves a lot up to the integrity of the contractor. Some contractors are better than others as far as in-house continuing education in design (to me, a good indicator is if they active in NFSA or AFSA), and the increasing use of outside designers who may be in another geographical region can create problems. And there are too many ways to circumvent licensing requirements and ethics. Good discussion.

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Ordinary Hazard within Light Hazard "Building"?

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