NFPA 90A is entitled Standard for the Installation of Air Conditioning and Ventilating Systems. It is the basic instruction needed for the installation of not only ducting, but also smoke detectors within that air ducting. By following the guidelines and procedures contained in this document, you will be helping to prevent the spread of fire and smoke through the ductwork in heating and air conditioning systems, should the situation arise.
A special note here is that you should always familiarize yourself with any local codes that are more stringent than these guidelines and update your copy of NFPA 90A to ensure you have the most current information.
NFPA 90A is fairly specific in its requirements for commercial installations and the reasons for having them in the first place. Since that is the case, and we are discussing the installation of smoke detectors, we need to ask:
Where should you install these smoke detectors in the ducting?
The short answer is based on the size of the system:
In HVAC systems greater than 2000 CFM, they are installed downstream of the conditioning filtering media and upstream of any installed branch ducts.
In the event that your system is installed in a multi-story structure, based on a common return and having a greater than 15,000 CFM capacity, a detector should be installed on each floor. It is important that this be installed before a connection to the common return and/or re-circulation/fresh air inlet associated with the return air systems.
In dealing with NFPA 90A code requirements and duct smoke detectors, there are two exceptions to the above requirements.
These two are:
1. Venting fan systems that are used to move air from inside to outside the building are excluded from the above requirements, and 2. Duct smoke detectors are not required if the occupied space is served by an area smoke detector system.
There are other smoke detector safety concerns in air conditioning and heater systems, and they can be found in the following reference material:
The ASHRAE “Handbook of Smoke Control Engineering”
NFPA “Life Safety Book for Health Care Organizations”
U.L. Standard 269A, “Standard for Smoke Detectors for Duct Applications”
The NFPA 90A Code Requirements for Large 2000 CFM VAV Air Handling Units addresses Life and Safety Systems and how they are to be treated as far as installation and appropriate safety systems that are necessary for those elements that can be considered dangerous to life and health in any commercial structure.
It not only addresses the installation of smoke and fire dampeners, but also all ventilation systems. The vast majority of engineering drawings will have the location of these important elements of safety noted. However, they are not always recorded, and NFPA 90A will assist ongoing work so as not to delay the project any more than is necessary.
A certified technician will have a copy of this document at hand when employed in this area and have all components pre-positioned for rapid completion of his or her task.
The manufacturer’s guidelines, instructions and recommendations should also be considered when installing and testing the finished work within the ducting. The fire, code and building commission inspectors will follow up on this, so appropriate compliance with this document is critical.
It is important to know that the subject of this code, the duct smoke detectors, are not supposed to be a substitute for adequate area smoke detection systems. They are simply to complement them, not to be the primary source of early warning, although they are a critical part of the overall balanced safety systems. NFPA 90A is not written in such a way as to knowingly confuse technicians. However, if there are any questions about it, consult an engineer in your industry.