Compartmentation is the act of subdividing a building into smaller compartments using fire resistant materials in order to control/slow the spread of fire and create more manageable areas of risk. The fire resistant materials used must prevent the passage of fire between individual compartments for a certain amount of time giving the fire service more time to arrive and efficiently extinguish the fire. This is done through the use of fire resistant materials and methods such as fire doors, cavity barriers in voids above false ceilings, looking at the intumescent materials used throughout the building, and ensuring that any penetrations that may have compromised the integrity of a wall are filled.

Larger and/or more complex buildings such as blocks of flats rely even more on fire compartmentation. Each flat is usually treated as its own compartment to limit the risk of fire spreading between flats. Dependent on the size of the flat the rooms within it may also be treated as separate compartments in order to protect the occupants means of escape. It is also important to consider the needs of any occupant who may have mobility issues that may not be able to use the stairs without aid, especially since it is not advised to use a lift as an emergency escape route during a fire something that compartmentation can help with. By successfully using passive fire protection methods including compartmentation refuge areas can be created to protect anyone unable to be safely evacuated in the early stages of a fire.