Typically, pressurisation ductwork is subject to demonstrable product certification on the basis of fire testing (for eampmple, ISO 6944). In the United States, additional hose-stream testing is required to achieve product certification, as the system includes not just a section of ductwork tested in a full scale floor furnace, but also a firestop, which must survive the hose.
Pressurisation systems are evaluated for exterior fire exposure. Grease ducts, on the other hand, are evaluated for interior fire exposures.
There are two means of providing fire-resistance rated ductwork:
The use of drywall shaftwall systems has been common for many years. 3-D full scale fire testing (e.g., ISO 6944) resulted in the first certification listing for an inherently fire-resistant duct. Drywall systems were tested as flat walls and a three-dimensional solution surrounding a real duct with four corners was never done, but are currently accepted in construction.