All ducting systems must be seismically restrained, unless they are:
- a rigid duct work system suspended by hangers that are less than 200 mm long from the top of the duct to the structural support or
- a flexible ducting system that is less than 1.5 m long.
Where a restraint system is required and the duct work is suspended with cables, the restraints must restrict movement of the ducting in all directions. Cable suspension is recommended to isolate vibrating equipment.
Suspended components that are installed in line with the duct system and have an operating weight greater than 10 kg shall be supported and laterally braced independently of the duct system. Examples of components are fans, heat exchangers and humidifiers.