Duct smoke detectors work by sampling airflows in ventilation systems to determine if smoke or fumes are present. When one of the two is detected, the device closes the duct flaps, turns off the fans and blowers to eliminate the oxygen source to prevent the spread of the fire, and triggers an acoustic and visible signal on the fire control panel. The International Mechanical Code has installation requirements for duct smoke detectors. NFPA 90A has installation requirements for duct smoke detectors. In addition, the intention to use ducted smoke detectors should not replace area smoke detectors. Nor should it serve as an early warning system. Therefore, they should complement the building`s fire alarm system and not serve as a primary fire alarm system. Also, always follow the code requirements for each project. If you don`t understand the code or requirements, ask the technician or other qualified person for the project.
I have a problem with a single retail space that has (5) AHU in an open space, each is 1850cfm and has its own supply channels. Is there not an exception that detectors are not necessary because the devices all power the same room? NFPA 90A requires duct detectors to be installed on the supply side of ventilation systems with airflows of more than 2,000 cubic feet per minute (cfm). The standard also requires a duct detector on the return side of each unit with air flows greater than 15,000 cfm serving more than one floor of a building. Section 606.2 of the ICD 2009 states that smoke detectors must be installed in return air systems of more than 2,000 cfm and in front of filters or exhaust or outdoor air fittings. The BMI and NFPA 90A require that the detectors be installed in accordance with NFPA 72 and connected to a fire alarm system if necessary. Both also have exceptions that allow the cancellation of return smoke detectors when the operated area is powered by area smoke detectors and they are configured to control the HVAC system in the same way as sewer detectors. NFPA 72 also states that a ducted smoke detector should not replace a surface smoke detector, primarily because the detector would not detect smoke if the ventilation unit (AHU) does not work. Therefore, duct smoke detectors are generally considered to be mechanical equipment devices rather than life safety devices. The BMI and NFPA 90A state that if multiple ventilation systems serve the same area and the combined air volume is greater than 2,000 cfm, detectors are required. Both also have exceptions that duct smoke detectors would not need if the air conditioner only served one room, as the smoke could not be distributed to other locations.
The objective of NFPA 90A is to prevent the spread of smoke and fire through piping and ventilation systems for high-capacity air conditioning and heating systems. Always make sure to check the latest codes for up-to-date information. In addition, some municipalities have stricter codes. Therefore, it is advisable to review the requirements for the local code in addition to the existing national codes. Channel detectors are wired to a printed circuit board. When smoke is detected, the device sends a signal to the PCB. Most PCBs are equipped with several different relays that are used to send signals to various other systems, including the fire alarm panel to trigger the alarm and the HVAC control system to close the shock absorbers and turn off the fans. There will also be a relay to report to the Supervisory Board.
The location of the sewer detectors is documented in the installation and acceptance documentation and kept in the protected area in the document box, where this information is present on site and in the records, the testing and maintenance of the sewer detectors are completed at the time of operation, without the need to go back and forth for elevators and access. First, determine what the control codes are for your particular project. If BMI is the accepted code, smoke detectors are required in the return channels. This may be the only code requirement. NFPA 90A is not referenced in the ICD. However, you should also check the requirements of firefighters in the project jurisdiction. If they have adopted NFPA 101 or other NFPA standards related to NFPA 90A, compliance with the requirements of NFPA 90A may be ordered by firefighters. If this is the case, place the smoke detectors in the inlet and return channels. The conflicting demands are obvious.
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