Air duct service openings
It’s next to impossible to properly maintain your fire and smoke dampers unless you have adequate
access to them. To that end, NFPA 90A requires that service openings be provided in air ducts adjacent
to each damper [see Sec. 2-3.4.1]. Obviously, the openings need to be conveniently located and large
enough to allow for maintenance and resetting of the devices. It’s important to note that there could be
times when it may be necessary to get two arms into the duct. While no specifics are spelled out in the
standard, NFPA 90A(99), Sec. A-2-3.4.1 offers the following guidance relating to service openings:
• Where the size of the duct permits, access doors should be at least 18 inches x 16 inches in size.
• Where fire dampers are too large to allow them to be reset and the fusible link replaced from
outside the duct, the access doors should be increased to at least 24 inches x 16 inches in size to
allow a person to enter the duct.
• The doors for fire dampers should be located so that the spring catch and fusible links are
accessible when the damper is closed.
• The doors should be located as close as practicable to the dampers.
• It’s recommended that access doors be located on the underside of ducts rather than on the side.