Tank Sized Based on Light or Ordinary Hazard?

6/6/2024

I'm looking at a building that is a convent home (residential) but has a chapel, bedrooms, dining room, kitchen area and a few mechanical support spaces.

I would think the building would be classified as light hazard because that is what a majority of the building is. But some could argue that some of these spaces are Ordinary Hazard 1.

Should the tank be sized on the Ordinary Hazard 1 demand or the Light Hazard demand?

Thanks for you help,

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9 Comments

Dan Wilder

6/6/2024 07:12:20 am

What is the official building occupancy as designated by the Architect? that will provide the needed information and also what is considered ancillary to the main occupancy.

The chapel leads me towards light hazard, the ancillary nature of the mechanical and storage rooms wouldn't sway things. The kitchen area would likely be no different than a large home kitchen (no overhead kitchen hood, no large fryers, no large open grill type cooking equipment).

The tank sizing will likely be defined by the pump at 150% more than a 4 sprinkler calc or a reduced hydraulic remote area.

Pete H

6/6/2024 07:59:50 am

Completely agree with Dan, just posting to reinforce that a larger kitchen can push you into ordinary. And I could see that actually being a decent size if they try to cook for the nuns en masse.

Jesse

6/6/2024 08:06:54 am

While the majority is Light Hazard, you do have some OH1 areas that will drive your density for AS as well as well as your tank size. You'll need to size your tank for the greatest demand.

Mike Morey

6/6/2024 08:12:17 am

Is it 13 or 13R? 13R if the rooms are 500 sq ft or less you can limit the demand to a 4 head calc even for OH. If 13 or over 500 sq ft you may still be able to limit the volume using the QR reduction etc. In that case arguably you'd still have to provide the "phantom flow" to reach whatever the minimum design area you can squeeze down to is x density even if you don't have to calculate that many sprinklers. Also unless you're providing hydrants or hose valves you can throw out the hose flow. Lastly, assuming there's a reasonably good refill source you may be able to size it down using the break tank rules if you provide the appropriate automatic refill apparatus.

Glenn Berger

6/6/2024 08:16:07 am

Completely agree with Jesse.

Since you did not give the sizes of the various spaces, Given some of the megachurches that are being built, you cannot just assume the mech/elect support spaces are always minor. The project location will determine how much cooling / heating will be provided and this will drive the electrical loads.

Franck

6/6/2024 08:26:05 am

Fully agree with Jesse & Glenn

Should be designed for higher demand. Higher demand could be LH if OH is on a limited number of sprinklers, but duration is another factor to consider…
You might end up with size of the pump related to LH and size of tank related to OH demand.

So not possible to answer with no more details on the different areas.

Anthony

6/6/2024 08:27:00 am

I also agree with those indicating the tank shall be sized to the greatest demand.

Jack G

6/6/2024 10:55:30 am

In agreement.
If a 4 head calc and the pump is sized so that 140% of pump equals the demand then it won’t matter. Tank sized at 150% of pump rating would be approximately the same.

David C

6/6/2024 07:22:45 pm

The A occupancy(Assembly) is the highest order of concern here in my eyes, as referenced earlier. (Yes a full code review including separation walls between mechanical and storage are the normal order of things)

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Tank Sized Based on Light or Ordinary Hazard?

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