Single-Interlock Subject to Water Delivery Time?

1/19/2024

Topic: Water Delivery Time in Single Interlock Preaction Systems Question:

I'm currently designing a single-interlock preaction system and I'm seeking clarification about the water delivery time requirements under NFPA 13 (2013).

Section 7.3.2.2 mentions that the system size cannot exceed 1,000 automatic sprinklers but doesn't specify the water delivery time for single interlock systems.

On the other hand, Section 7.3.2.3 clearly states that double interlock preaction systems must deliver water within no more than 60 seconds.

Does this mean that single interlock systems are not required to adhere to a specific timeframe for water delivery?

In my view, it makes sense to not include a delivery time for single interlock systems, since water should already be at the sprinkler prior to activation. I'm interested in others' views or experiences in this area.

Thanks in advance!

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5 Comments

Dan Wilder

1/19/2024 07:24:30 am

You are correct, no water delivery time requirements for a single interlock. In the later 2022 edition, the enhanced content explains why:

"...The detection systems for the single interlock and non-interlock systems typically have a lower temperature rating than the system sprinklers. When so configured, the single interlock and noninterlock systems are expected to operate more quickly than the double interlock or dry pipe systems..."

It's been years since I have designed a single interlock but being able to loop and grid a single interlock (when not protecting storage) was a big plus.

Jesse

1/19/2024 09:04:37 am

Yep what Dan said. These will operate in a time similar to a wet system.

Franck

1/19/2024 10:56:19 am

Double interlock is considered as a dry pipe system with same restrictions (time, increase of designed area) while a single interlock is considered as a wet system for the reasons mentioned by Dan.

Dave

1/19/2024 11:04:25 am

When it comes to preaction systems, I often have to explain to clients, "double" is not automatically better than "single," there is a time and place for each. Especially if it is an FM Global project.

Glenn Berger

1/19/2024 11:54:40 am

Franck response is spot on.

Single-Interlock Subject to Water Delivery Time?

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