Fire compartmentation

Fire compartmentation is the division of a building into firecells or compartments enclosed by fire-resisting construction. Its purpose is to limit the spread of fire, smoke and heat between those spaces and to preserve required functions for occupants and firefighters. It uses walls, floors, doors, dampers, firestops and other details as one separating system.

A firecell is any space or group of contiguous spaces enclosed by fire separations, external walls, roofs and floors. Internal floors between firecells are themselves fire separations. This makes compartmentation a three-dimensional arrangement rather than a collection of unrelated walls.

A firecell is a complete separating system. Based on Ministry of Business, Innovation and Employment (2025), p. 64.

Compartmentation can delay fire spread and provide time for detection, evacuation, suppression and structural response. It does not guarantee containment, because openings, penetrations, conduction and failure of individual components can defeat the intended boundary.

Separating elements

Fire resistance supplies the performance criteria for compartment boundaries. Structural adequacy, integrity and insulation must be maintained as applicable for the required duration. C/VM2 reports these in that order, with durations determined from standard tests or verified calculation methods.

A Fire wall separates buildings or subdivides a building to prevent fire spread through fire resistance and, where required, structural stability. Its ends, roof junctions and connections must also be detailed so that fire cannot bypass the main wall. A wall is effective only as part of that complete boundary.

A Fire door protects an opening in a fire-resistive wall and has a specific fire resistance rating. It normally closes and latches automatically if it is not already closed, while still allowing occupants to pass. Door operation, seals, frames and hardware are part of the opening's performance.

A Fire damper automatically seals an air-distribution opening to resist heat and flame. It preserves the rating of the wall, partition or floor penetrated by the duct, using a fusible link or remote activation signal. Both its fire resistance and its airflow closure behaviour matter.

Firestopping seals penetrations and narrow gaps around services and joints. C/VM2 requires the fire stop to have a rating no less than the fire separation in which it is installed. A continuous barrier therefore needs appropriate products and installation for its orientation and use.

Fire spread and failure modes

Fire spread can occur through openings, radiation, direct flame contact, burning debris and conduction through solid boundaries. Compartmentation addresses these pathways differently. A barrier that stops direct flame can still transmit enough heat to ignite material on its unexposed side.

Conductive failure occurs when sufficient heat passes through an intact barrier to meet a failure criterion. There may be no cracks or collapse, so visual integrity alone does not demonstrate protection. The combustibles and their arrangement on the receiving side must be included in the assessment.

Compartment boundaries can fail thermally, through integrity or through stability. Based on Australian Building Codes Board et al. (2005), p. 1.6-7.

Loss of integrity involves cracks, fissures and failed firestopping, allowing flames and hot gases through. Loss of stability involves collapse of the barrier and creates a much larger opening. These modes can occur at different times and should be evaluated separately.

Openings change with occupancy and firefighting. Doors can open for evacuation, glazing can break and ventilation components can operate, altering both fire spread and oxygen supply. Compartmentation must therefore be assessed as a changing system, not as a fixed drawing of closed boundaries.

Passive protection as a system

Passive fire protection prolongs fire resistance without manual, mechanical or other initiation, replenishment or sustainment during the incident. Compartmentation is a central example because walls and normally closed barriers perform in their normal orientation. Other passive measures include insulation, coatings and noncombustible construction.

The complete assembly determines performance. A strong wall can be undermined by an unprotected penetration, an open door or an unsuitable damper, while a well-detailed system can delay spread without looking unusual in normal use. Product choice and installation are therefore inseparable from the rating.

Active systems can complement compartmentation by detecting and suppressing fire, but they do not remove the need for a sound boundary. A fire barrier can be intended to work together with sprinklers, while a fire wall may be intended to remain stable and uncompromised during an uncontrolled fire. These roles should not be confused.

Fire compartmentation also supports other passive goals. It can protect structural members, preserve safe paths and limit smoke movement, but each has its own criteria and timescale. A single rating cannot demonstrate all of these without the relevant assessment.

Openings and penetrations

Service penetrations create potential weak points for flames, smoke and heat. Cables, pipes, ducts and trays require seals appropriate to the barrier and the service arrangement. Unsealed or unsuitable penetrations can allow a fire to move around an otherwise effective compartment wall.

Openings and junctions can bypass a fire-rated wall. Based on Australian Building Codes Board et al. (2005), p. 1.6-7 and U.S. Nuclear Regulatory Commission (2005), p. 17-7.

Fire walls also need protected ends and roof junctions. NUREG-1805 lists fire-resistant exterior wing walls and a parapet extending through and above the roof deck as ways to prevent spread around the wall. Pipes, conduits and cables may be routed to floor level to reduce damage if the structure on either side collapses.

Concealed spaces need attention because they can connect compartments without obvious openings. Cavity barriers close openings within those spaces against fire and smoke spread. Their location, integrity and relationship with the main fire separations must be assessed.

Fire doors and smoke control doors need correct operation during evacuation. C/VM2 assumes self-closing doors are closed except when being used, allowing three seconds per occupant at low load and continuous opening during queuing. This changes the boundary during the very period when protection is needed.

Fire engineering and evacuation

Compartmentation can preserve tenable conditions in adjacent spaces long enough for evacuation. Fire models compare the time available for escape with the time occupants need, and the boundary's condition affects both smoke spread and fire growth. ASET analysis includes only those separations and closures needed to demonstrate safe evacuation.

Fire spread and barrier-failure times can also become inputs to new compartment design fires, evacuation and firefighting assessments. The analysis is therefore sequential: one compartment's conditions determine when the next becomes hazardous. A building-wide model must preserve those links.

Firefighters may also rely on compartment boundaries for access and intervention. C/VM2 has a dedicated firefighting scenario, while its general fire-safety-system definition includes restricting fire spread and limiting structural instability. The required performance should be identified before assigning a rating or modelling a boundary.

Compartmentation can change during the incident as occupants escape and firefighters enter. Those door states change smoke and oxygen transport, so an ASET calculation should use the actual sequence rather than assuming all barriers remain closed. This makes compartmentation part of the evacuation scenario, not only a construction detail.

Design and regulation

C/VM2 defines firecells and fire separations within New Zealand's 2025 second edition. It also requires construction detailing to match the design and proprietary fire stops to suit their orientation and separating element. Those requirements are jurisdiction-specific and should not be replaced with a generic wall label.

The rating alone does not describe the whole fire scenario. Compartment geometry, fuel inventory, openings, active systems and occupants determine whether the boundary provides the intended benefit. Performance-based analysis must show those interactions rather than simply declaring the compartment fire rated.

Historic standards provide useful construction evidence but should not be turned into universal values. NUREG-1805 gives typical fire resistance for brick and concrete-block walls and separate expectations for fire walls and fire barriers. Those examples come from a US nuclear reference and do not replace project-specific testing or current local requirements.

The World Trade Center investigation illustrates a different regulatory pathway. Local rules allowed floor-area compartmentation or sprinklers, and passive protection was chosen to achieve required ratings. It shows that compartmentation is one option within a wider fire-safety strategy, not the only possible form of compliance.

Reliability and maintenance

Compartmentation depends on construction matching the design. Doors can be wedged open, seals can be damaged, coatings can be missing and penetrations can be altered during refurbishment. Those changes can invalidate an otherwise sound original design.

The WTC passive-protection review specifically evaluates insulation thickness, gaps and adhesive or cohesive strengths. These details affect whether the protection remains in place and performs as intended. Compartment boundaries should therefore be inspected as physical systems rather than only as drawings.

Test evidence should match the assembly and its orientation. A product tested in one wall, floor or penetration arrangement may behave differently in another. C/VM2 explicitly calls for appropriate proprietary products for orientation and use, and fire-resistance ratings require relevant standard-test evidence or verified calculation.

Maintenance must preserve operation as well as material condition. Fire doors must close and latch, dampers must activate, and seals must remain continuous. A compartment that appears intact during inspection can still fail if these functions are not maintained.

Limits and common misunderstandings

Compartmentation is not a single fire-rated wall. It is the complete arrangement of enclosing elements, openings, penetrations and junctions. Any weak or altered detail can become the pathway that determines spread.

A fire rating does not guarantee zero fire or smoke spread. Conduction, radiation, debris, open doors and failed components can still expose adjacent spaces. The analysis must state which pathways and criteria are included.

Noncombustible construction is not automatically fire resistant. Materials can deform, crack, lose stability or transmit heat, and those failures can compromise the compartment. Material choice and assembly performance are different questions.

Finally, compartmentation does not replace evacuation, detection or suppression. It provides time and space for those responses, but their effectiveness depends on the complete scenario and on maintaining the separating system.

A system review should map every boundary and every opening, including those that are normally concealed. Each path should be assigned a closure, a firestop or an explicit assumption, so that no route is left without analysis. This is more reliable than reviewing only the largest walls.

The receiving compartments should be included in that map. Their fuel, occupants and active systems determine what happens if heat or smoke crosses, and their own separations affect later spread. A barrier can therefore be evaluated properly only as part of a sequence of connected firecells.

Junctions deserve particular attention because they join different assemblies and exposure conditions. Roof decks, exterior walls, shaft walls and floor intersections can all change the heat and structural path. A rating for one straight wall segment does not establish those junction details.

For evacuation, the boundary should be evaluated at the times when people actually pass. Door opening, queuing and fire service access can change both smoke transport and the available escape time. The model should preserve that sequence instead of treating the compartment as sealed throughout.

For structural assessment, boundary failure can be both a cause and a result of fire damage. Heat can weaken a wall or its supports, and collapse can create an opening that changes ventilation. This links compartment performance with the structural analysis rather than treating them as separate reports.

Evidence should be checked against the actual products and installation. Proprietary closures and firestops need appropriate orientation, while an older rating may rely on details that no longer exist. Inspection and documentation should confirm that the analysed assembly is the one present in the building.

A final review should distinguish intended containment from demonstrated performance. The design may intend to restrict fire, but tests, calculations and incident evidence determine how long and under what conditions it works. Reporting those conditions makes compartmentation a verifiable safety measure rather than a generic label.

A final check is whether the compartment's actual fire scenario supports the intended separation. Fuel, openings and occupants can change which boundary is needed and when it must perform. The assessment should use those conditions rather than assigning the same rating to every compartment.

The report should also identify which criteria have and have not been verified. Structural adequacy, integrity and insulation require appropriate evidence, while smoke movement and escape require a scenario analysis. Keeping those outputs separate prevents a general fire rating from being mistaken for a complete safety result.

For final acceptance, the complete sequence of boundaries, openings and active systems should be reviewed together. A compartment is only protected when the intended separation, its closures and the scenario assumptions agree. This prevents a rating on one component from being treated as proof of building-wide containment.

See also

• Cavity barrier
• Fire resistance criteria
• Fire safety strategy

References

• Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). International fire engineering guidelines (2005 ed.). Australian Building Codes Board.
• Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), SFPE handbook of fire protection engineering (3rd ed.). National Fire Protection Association.
• Ministry of Business, Innovation and Employment. (2025). C protection from fire: Verification method C/VM2 (2nd ed.). New Zealand Government.
• National Institute of Standards and Technology. (2005). Passive fire protection (NIST NCSTAR 1-6A). U.S. Department of Commerce.
• Rockett, J. A., & Milke, J. A. (2002). Conduction of heat in solids. In P. J. DiNenno (Ed.), SFPE handbook of fire protection engineering (3rd ed.). National Fire Protection Association.
• U.S. Nuclear Regulatory Commission. (2005). Fire dynamics tools: Quantitative fire hazard analysis methods for the U.S. nuclear regulatory commission fire protection inspection program (NUREG-1805). Author.
• Van Rossum, E. (2027). Introduction to Fire Safety Engineering. Fire Safety Academy.
• White, R. H. (2002). Analytical methods for determining fire resistance of timber members. In P. J. DiNenno (Ed.), SFPE handbook of fire protection engineering (3rd ed.). National Fire Protection Association.