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Contents
  1. 1The compartment boundary
  2. 2Routes by which fire can spread
  3. 3Thermal, integrity and stability failures
  4. 4Doors, ducts and service penetrations
  5. 5Smoke separation and pressure differences
  6. 6Representing openings in an analysis
  7. 7Integration with the fire safety strategy
  8. 8Construction, alterations and continued performance
  9. 9See also
  10. 10Notes
  11. 11References

Fire compartmentation is the division of a building into spaces separated by construction intended to restrict the spread of fire and its effects. Walls, floors, closures and protected penetrations work together as a boundary. Its performance depends on maintaining the required structural, integrity and heat-transmission functions under the relevant exposure.[1][2][3]

The separation is not defined by a wall alone. Doors, ventilation openings, service penetrations, junctions and supporting construction can determine how a fire reaches another space. Some routes exist from the outset, while others develop through opening, damage or structural failure. Concealed voids and shafts can connect spaces beyond the room of origin.[4]

Smoke movement adds a further consideration because intact construction can still contain leakage paths. Pressure differences drive flow through those paths and through open doors. Compartmentation consequently interacts with evacuation, ventilation and smoke control, as well as the fire resistance of its materials and assemblies.[5][6]

The compartment boundary

A compartment is a volume separated from other spaces by construction intended to restrict fire effects, and its boundary can include walls, floors, a roof and closures within those elements. New Zealand's C/VM2, second edition of 2025, calls the enclosed volume a firecell. Its definition allows contiguous spaces on the same or different levels, rather than limiting a firecell to one room.[3]

The boundary is therefore a complete system of construction and protected openings. The definition of a fire barrier in NUREG-1805 includes supports, penetration seals, closures, doors and dampers alongside walls and floors. That report was prepared for the United States nuclear regulatory inspection programme. Its terminology usefully identifies the interacting components without establishing requirements for every other building type.[2]

Firecell bounded by walls, floor, roof, fire door, damper and penetration seals.
A firecell is a complete separating system. Based on Ministry of Business, Innovation and Employment (2025), p. 64.

Fire resistance describes how the construction maintains specified functions under an exposure. Those functions include structural adequacy, integrity and insulation where applicable: the first concerns load-bearing performance, the second passage of flames or hot gases, and the third heat transmission. A compartment boundary can lose one function while retaining another.[1][7][3]

A Fire wall is one form of separating construction, but its precise role depends on the governing framework. Iqbal and Salley distinguish a wall intended to remain stable through an uncontrolled fire from a barrier used with other protective measures. That distinction belongs to their discussion of United States practice. It does not make every internal partition a structurally independent fire wall.[8]

Routes by which fire can spread

Fire spread between compartments can follow openings that already exist or openings created during the fire, and the 2005 International Fire Engineering Guidelines treat both categories explicitly. Doors and windows may be open initially, while glazing breakage or damage can create further routes. The state of each route can change as the event develops.[9][10]

An opening can also result from missing or inadequate sealing around services. Pipes, cable trays and ventilation ducts cross boundaries to perform normal building functions. Those crossings need their own representation in the separating system. A sound wall surface does not describe the behaviour of an unprotected opening through it.[10][11]

Concealed spaces can connect locations that appear separate in an occupied room, and the guidelines identify ceiling voids, hollow construction, spaces under floors and spaces behind external cladding. Shafts and large service ducts can provide vertical routes. In the analysis, these spaces become further enclosures with their own connections and boundaries.[10]

The route can also pass outside the building before re-entering another space, and the guidelines discuss flames projecting from windows, radiation and burning debris. Adjacent buildings can be exposed through openings or external surfaces. Compartmentation therefore cannot be assessed solely by tracing internal partition lines on a floor plan.[12]

Fire and smoke passing through a door, duct, cable penetration, cavity and wall end.
Openings and junctions can bypass a fire-rated wall. Based on Australian Building Codes Board et al. (2005), p. 1.6-7 and Iqbal and Salley (2004), p. 17-8.

Thermal, integrity and stability failures

Heat can pass through an intact boundary by conduction. The unexposed surface may then become hot enough to breach an insulation criterion or ignite nearby material under suitable conditions. This mechanism does not require a visible hole. The thermal properties, thickness and exposure history influence the resulting temperature distribution.[6][13]

Loss of integrity introduces a path through the boundary. Cracks, fissures and failed penetration protection can permit hot gases or flames to pass. Whether adjacent material ignites depends on its location and response to the exposure. The International Fire Engineering Guidelines distinguish this physical sequence from a simplified analysis that equates barrier failure with spread.[14]

Loss of stability means that the barrier or its supporting construction can no longer remain in place, so a wall can fail because another structural element supporting it fails. The guidelines identify this dependency explicitly. The endurance of an isolated wall specimen is therefore not sufficient evidence for a boundary whose support fails earlier.[15]

Three panels: heat through an intact wall, cracks with smoke and a collapsed wall.
Compartment boundaries can fail thermally, through integrity or through stability. Based on Australian Building Codes Board et al. (2005), p. 1.6-7.

These mechanisms can interact during the same fire. An opening can change ventilation as well as permit spread into another enclosure. Structural loss can damage several boundaries together. The analysis therefore follows changes in the building and exposure, rather than assigning every component an unrelated failure time.[16][17]

Doors, ducts and service penetrations

A Fire door protects an opening that must also permit normal access and evacuation, and its closed-state performance is part of the compartment boundary. Its open state creates a different route for heat and smoke. The International Fire Engineering Guidelines consequently connect door-opening times to the analysis of occupant movement.[3][6]

A Fire damper addresses the internal path through a ventilation opening or duct. Iqbal and Salley describe devices that close in response to a fusible link or remote signal. Their account distinguishes the fire-resistance function from the conditions under which the damper can close against airflow. Those conditions depend partly on whether ventilation is stopped.[18]

Firestopping addresses gaps and penetrations that would otherwise weaken the separation. Around a duct, it protects the path between the duct assembly and the surrounding boundary. Closing the air passage inside the duct is a different function. A design can therefore need both a closure and a suitable seal at the same crossing.[18][19]

New Zealand's 2025 C/VM2 construction provisions connect these details to the completed design, and its commentary calls for proprietary firestopping suited to the orientation and the separating element. It also identifies testing of rated closures under an internationally recognised standard. These provisions concern the installed construction, not a material name or an isolated product label.[20]

Smoke separation and pressure differences

Restricting fire spread and restricting smoke movement are related but distinct functions. Smoke can pass through cracks and leakage paths while a boundary remains intact. Klote identifies gaps around doors, pipe penetrations and wall-to-floor junctions as examples. The pressure difference across the boundary determines the driving force for that leakage.[21]

Several forces can create the pressure difference. Klote discusses buoyancy from heating, stack effect, wind and mechanical ventilation, and these can act together, so smoke movement is not determined by temperature alone. Stopping ventilation fans removes one influence but does not eliminate movement driven by the others.[22][23]

Mechanical smoke control can use pressure differences across closed boundaries and airflow through open doorways. The appropriate assessment changes when a door opens. A pressure difference across a mostly closed barrier is not equivalent to the airflow required through a large opening. Klote therefore distinguishes closed-door and open-door conditions.[24]

C/VM2, second edition of 2025, likewise distinguishes fire separations, smoke separations and unrated construction within the trial design. The method applies different assumptions to their continued presence during a fire. Those assumptions describe the analysis framework and the evidence attributed to each separation. They are not predictions that every physical partition disappears at one identical temperature.[25]

Representing openings in an analysis

The International Fire Engineering Guidelines begin with the enclosure geometry, openings and properties of barriers and structural elements. They also require the location and ignition characteristics of material in adjacent spaces, and this information establishes what can be exposed if a route opens. A boundary failure and the ignition of another fuel item are separate events unless the method deliberately combines them.[12]

The guidelines permit simplifying assumptions for specified analyses. Examples include treating barrier failure as spread or using flashover as an opening-related event. They also identify conditions that can invalidate a simplification, such as direct flame contact on an unrated boundary. An assumption is therefore part of the model definition, rather than an observed fact about every fire.[10]

Door use provides a practical example. Under New Zealand's 2025 C/VM2, a self-closing fire or smoke-control door is assumed closed except when occupants use it. With low occupant demand, it is modelled open for three seconds per occupant. Where occupants queue, the method instead considers the sustained opening associated with that queue.[26]

The same document uses half the door width for smoke-flow modelling while the door is being used for egress. Its commentary explains that a moving leaf and passing occupants restrict the unobstructed opening, and this is a smoke-modelling assumption within C/VM2. It is not a rule that halves the physical escape width of every doorway.[27]

The concealed-space scenario in New Zealand's 2025 C/VM2 provides a specific example of protecting a route that is not visible from an occupied room. It applies within the stated scope to buildings containing rooms with more than 50 occupants and concealed spaces. The document identifies separating elements, suppression and detection as approaches to that scenario. Their acceptance depends on the scenario conditions, rather than an unrestricted exchange between systems.[28]

Where its separating-element approach is used without automatic detection, C/VM2 specifies at least 30 minutes for integrity and insulation and limits the concealed-space area to 500 m². These figures belong to the particular 2025 New Zealand scenario; they do not define a universal compartment size or barrier rating. The example shows how the route, detection assumptions and separating construction are connected within a stated method.[28]

Integration with the fire safety strategy

Compartmentation forms part of Passive fire protection, but it interacts with systems that operate during an incident. A door may need to close, and a ventilation closure may depend on a signal or the state of a fan. The International Fire Engineering Guidelines distinguish static barriers from operable closures. Describing the whole strategy as having no operational dependencies would conceal those differences.[29][18]

The expected duration of separation follows its purpose in the strategy. The guidelines connect times of spread and structural failure to evacuation, firefighting and protection of adjoining property. Different objectives can therefore require different outputs from the same physical analysis. A nominal duration without an endpoint or objective does not define the required performance.[30][16]

Compartmentation can also be evaluated alongside suppression. Iqbal and Salley's distinction between fire walls and barriers specifically refers to whether other protective measures are credited. The consequences of losing that support differ from the behaviour assumed when it operates. The design basis therefore identifies which systems and operating conditions form part of the assessment.[31]

Structural support is another dependency within the strategy. A protected boundary may rely on columns, beams or floors to remain in place. The guidelines require consideration of failure of those supporting elements and its effects on other boundaries. Treating each rating independently would omit a physical route by which several protections can be lost together.[17]

Construction, alterations and continued performance

Construction and commissioning establish whether the intended boundaries exist and their components match the specification. The International Fire Engineering Guidelines identify barrier integrity, specified materials and operation of automatic closures as distinct checks. They also include operation and maintenance documents. The completed system therefore includes both physical construction and information about its required functions.[29]

Later repairs or alterations can change that system. The guidelines note that passive barriers are liable to be overlooked during building modifications. Their continued identification helps connect a new service opening or construction change to the original fire strategy. Without that connection, a local alteration can change a boundary whose role is not visible from the room alone.[29]

Static barriers and operable closures have different maintenance needs. The guidelines describe relatively limited routine maintenance for passive barriers, while calling for operational testing of automatic closures. Inspection and records preserve evidence about both. A wall remaining in place and a door closing correctly are separate observations within the same compartmentation system.[29]

Evidence of performance remains tied to the construction and conditions assessed. A standard test demonstrates specified functions of its assembly, while modelling represents selected exposures, openings and dependencies; their combined interpretation identifies where the boundary is expected to remain effective. It also identifies the assumptions that cease to hold when the building or its operating conditions change.[32][33]

See also

Notes

  1. ↑ 1.0 1.1 Kodur and Harmathy (2002), p. 1-155.
  2. ↑ 2.0 2.1 Iqbal and Salley (2004), p. F-24.
  3. ↑ 3.0 3.1 3.2 3.3 Ministry of Business, Innovation and Employment (2025), p. 64.
  4. ↑ Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-8.
  5. ↑ Klote (2002), pp. 4-277–4-279.
  6. ↑ 6.0 6.1 6.2 Australian Building Codes Board et al. (2005), p. 1.6-7.
  7. ↑ Milke (2002), pp. 4-210–4-211.
  8. ↑ Iqbal and Salley (2004), pp. 17-7–17-8.
  9. ↑ Australian Building Codes Board et al. (2005), p. 1.6-1.
  10. ↑ 10.0 10.1 10.2 10.3 Australian Building Codes Board et al. (2005), p. 1.6-6.
  11. ↑ Iqbal and Salley (2004), p. 17-8.
  12. ↑ 12.0 12.1 Australian Building Codes Board et al. (2005), pp. 1.6-5–1.6-7.
  13. ↑ Van Rossum (2027), §5.2.
  14. ↑ Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-7.
  15. ↑ Australian Building Codes Board et al. (2005), pp. 1.6-7–1.6-8.
  16. ↑ 16.0 16.1 Australian Building Codes Board et al. (2005), p. 1.6-4.
  17. ↑ 17.0 17.1 Australian Building Codes Board et al. (2005), p. 1.6-8.
  18. ↑ 18.0 18.1 18.2 Iqbal and Salley (2004), p. F-19.
  19. ↑ Iqbal and Salley (2004), p. F-44.
  20. ↑ Ministry of Business, Innovation and Employment (2025), p. 13.
  21. ↑ Klote (2002), pp. 4-277–4-278.
  22. ↑ Klote (2002), p. 4-274.
  23. ↑ Klote (2002), p. 4-277.
  24. ↑ Klote (2002), pp. 4-278–4-279.
  25. ↑ Ministry of Business, Innovation and Employment (2025), pp. 14–15.
  26. ↑ Ministry of Business, Innovation and Employment (2025), p. 15.
  27. ↑ Ministry of Business, Innovation and Employment (2025), pp. 15–16.
  28. ↑ 28.0 28.1 Ministry of Business, Innovation and Employment (2025), p. 41.
  29. ↑ 29.0 29.1 29.2 29.3 Australian Building Codes Board et al. (2005), p. 1.6-9.
  30. ↑ Australian Building Codes Board et al. (2005), p. 1.6-2.
  31. ↑ Iqbal and Salley (2004), p. 17-7.
  32. ↑ Milke (2002), pp. 4-209–4-210.
  33. ↑ Australian Building Codes Board et al. (2005), pp. 1.6-5–1.6-9.

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. Australian Building Codes Board.
  • Iqbal, N., & Salley, M. H. (2004). Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program (NUREG-1805). U.S. Nuclear Regulatory Commission.
  • Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
  • 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., pp. 1-155–1-181). National Fire Protection Association.
  • Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
  • Ministry of Business, Innovation and Employment. (2025). C protection from fire: Verification method C/VM2 (2nd ed.).
  • Van Rossum, E. (2027). Introduction to Fire Safety Engineering. Fire Safety Academy.
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