Smoke detectors under raised floor

[reko19]

Hi everyone. Working on a project with a raised floor area utilized as a plenum. Rooms are used for the electrical distribution equipment, NOT a data center covered by article 645.

I believe requirements for the smoke detectors inside a plenum are covered by 2024 NFPA 90A, a standard for the Installation of Air-Conditioning and Ventilating Systems. According to Chapter 8, Plenums; Paragraph 8.5, Raised Floor Plenums, section 8.5.5.10, smoke detectors are NOT required to meet the requirements of this section providing materials under raised floor are non-combustible and meet certain requirements.

Any thoughts on the subject?

Thank you.

 

[ron]

I doubt NFPA 90A is the adopted mechanical code for your jurisdiction, as very few use it versus the IMC.

Detection is directed by the adopted building code. For sprinklers, if it is concealed (using their definition from NFPA 13), no sprinkler coverage is required, which is a similar thought process.

 

[gadfly56]

You want to be very certain of that "non-combustible" requirement for the under-floor materials. If it isn't all in conduit, then it's probably combustible.

 

[reko19]

Unfortunately i cant find any under raised floor detection requirements in IBC or IMC. The NEC has relaxed the requirements with the data center raised floor where it is no longer required.

NFPA72 refers to NFPA 90A, we do have internal duct detectors at each unit supplying the under raised floor, so I believe we are in compliance with NFPA71 17.5.3.1.4(2)?

 

[gadfly56]

Unfortunately i cant find any under raised floor detection requirements in IBC or IMC. The NEC has relaxed the requirements with the data center raised floor where it is no longer required.

NFPA72 refers to NFPA 90A, we do have internal duct detectors at each unit supplying the under raised floor, so I believe we are in compliance with NFPA71 17.5.3.1.4(2)?

View attachment 2574095

You're probably fine with the return air detection, especially if the HVAC units serve only the space with the underfloor plenum.

 

[ron]

Unfortunately i cant find any under raised floor detection requirements in IBC or IMC. The NEC has relaxed the requirements with the data center raised floor where it is no longer required.

NFPA72 refers to NFPA 90A, we do have internal duct detectors at each unit supplying the under raised floor, so I believe we are in compliance with NFPA71 17.5.3.1.4(2)?

View attachment 2574095

In many modern data centers, there are no detectors under the raised floor if there are no combustibles (plenum rated cable if not in raceway), and because the adopted Mechanical Code doesn't require duct detectors if the CRAH/CRACs just recirculate air, no detection in the air handlers.