Does My Unit Require a Duct Smoke Detector?

1/29/2020

On every project containing fire alarm design I come across the same question repeatedly - does this unit require a duct detector?

In short, there's two prevailing standards that determine whether duct detection is required. The first (and most common in the United States), is the International Mechanical Code (IMC). Section 606.2 identifies areas where smoke detection is required for the purpose of mechanical unit shutdown.

The other prevailing standard is NFPA 90A, the Standard for Installation of Air Conditioning and Ventilating Systems. I'll address those requirements in a later post.

Back to the question at hand - there's essentially six different scenarios a mechanical unit can fall into under the International Mechanical Code. These do not include the requirement for multi-level duct risers over 15,000 CFM, but rather whether an individual unit requires detection at the unit.

Here is a quick cheatsheet summary concerning those scenarios:

GET THE DUCT-DETECTOR CHEATSHEET

If you review or design fire alarm systems regularly, take a look and let me know what you think.

If you know someone who might also benefit from cheatsheets like this, send them a link or tell them to subscribe here.

Hope you find this helpful and have a great rest of your week!

Rusty Scott

1/29/2020 01:36:18 pm

Don't forget about those Remote Alarm LED indicators and key test switches. NFPA 72-2013 & 2016 17.4.7 where "detectors more than 10ft above finished floor or in arrangements where the detector's alarm or supervisory indicator is not visible to responding personnel, the detectors shall be provided with remote alarm or supervisory indication in a location acceptable to the authority having jurisdiction."

I've seen some engineers try to rely on specifications for the contractor to locate the remote indicators on performance design type projects. I believe this may be due to on NFPA 72-2013 (under 7.4 Shop Drawings Installation Documents) 7.4.8 "Typical wiring diagrams shall be provided for all initiating devices, notification appliances, remote indicators, annunciators, remote test stations, and end-of-line and power supervisory devices." So it's putting it off on the contractor to coordinate. I don't believe this is the best/correct/only method, I believe engineers should be discussing & coordinating this information with architects about locating on the floorplan drawings for AHJ's initial review for permitting.

I'm assuming FA contractors price this equipment whether shown on floorplans or not in some way?? I'd be curious to know, because I've never heard any complaints when they weren't shown. I'd be interested to hear someone's thoughts on this if anyone has any experience on it. The person who normally makes the most noise is the architect when walking around the finished product.

Jon Sullivan

2/3/2020 03:53:34 pm

I see these missed a lot, and have missed them myself. I do not think many HVAC engineers are aware of this requirement even though IMC requires NFPA 72 compliance. IMC requires requires the supervision of detector by the fire alarm system and as well as a version of the requirements of NFPA 72 17.4.7. Perhaps many engineers think that the supervision of the detector by the fire alarm system is also assumed to be the visual and audible supervisory signal required at a constantly attended location by both NFPA and IMC.

Joshua Smith

6/12/2020 09:37:49 am

My question is this. Who ultimately is responsible for where duct detectors should be located? I work at an MEP firm and the mechanical engineers refuse to take responsibility for locating them. I see it as a fire alarm device that is located by the mechanical engineer. They do not show them on there documents either.

WES

6/12/2020 09:43:40 am

It's up for debate. Used to work at a large MEP firm and I did a location callout on the fire alarm plans to locate "on return side of mechanical unit" but to refer to the mechanical for exact ductwork and unit locations.

Just my experience, but non-fire people tend to very much not care about fire things.

6/12/2020 10:25:16 am

Since the locations are dictated by the IMC and NFPA 90A which are all mechanical code requirements how can it be up for debate? I worked for another firm who only did fire alarm design. In all my years there I never had a mechanical engineer not locate the the duct detectors or not show them on their documents.

I agree about the non-fire people not caring. But if it is a requirement of the code of which you are designing to you must own it in my opinion.

6/12/2020 10:29:11 am

Well said. You convinced me.

... now you just need to convince those mechanicals....

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Does My Unit Require a Duct Smoke Detector?

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