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:
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!
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Joseph Meyer, PE, owns/operates his own Fire Protection Engineering practice in St. Louis, Missouri. See bio on About page.