Methods of protecting compartmentation
The Building Regulations require that new buildings must be divided into fire compartments in order that the spread of smoke and fire in the building be inhibited, and to stop the spread of smoke and fire from one compartment to another for given periods of time.
There are obvious areas of weakness, which include doors, windows and ventilation ductwork passing from one compartment to another.
BS 9999:2017 - Fire safety in the design, management and use of buildings. Code of practice
When considering ductwork systems, the aim of BS9999 is to ensure the design and construction of ductwork systems prevent them becoming the means by which fire, smoke and other products of combustion can spread from one compartment to another, or prejudice the safe use of escape routes.
Where air handling ducts pass through fire-separating elements such as compartment walls or the enclosures to protected escape routes, then the integrity of those elements should be maintained, using one or a combination of the following four methods:
- Method 1: thermally actuated fire dampers;
- Method 2: fire-resisting enclosures;
- Method 3: protection using fire-resisting ductwork;
- Method 4: automatically actuated fire and smoke dampers triggered by smoke detectors.
Note 1: These methods are not mutually exclusive, and in most ductwork systems a combination of them will best combat the potential fire dangers.
Note 2: Further information on fire-resisting ductwork is given in the ASFP Blue Book  and the ASFP Blue Book (European version) 
Fire-resisting ductwork should meet the appropriate fire resistance of integrity and insulation time period for the specific application it is being used for and the compartmentation through which it penetrates, when tested in accordance with BS EN 1366-1,8,9 and classified in accordance with BS EN 13501-3 and BS EN 13501-4 by a recognised NAMAS/UKAS accredited laboratory.