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Contents
  1. 1Performance criteria
  2. 2Standard exposure and testing
  3. 3Fire compartmentation
  4. 4Structural fire engineering
  5. 5Passive fire protection
  6. 6Reaction to fire and combustibility
  7. 7Analysis and validation
  8. 8Limits and common misunderstandings
  9. 9See also
  10. 10Notes
  11. 11References

Fire resistance is the duration for which a building element satisfies specified performance criteria during fire exposure. These criteria concern structural adequacy, integrity and insulation, with the required functions depending on the element. Fire resistance is therefore a performance property of an assembly, not simply the combustibility of the materials from which it is made.[1][2]

Structural adequacy concerns load-bearing performance and stability, integrity concerns preventing flame and hot-gas passage, and insulation concerns limiting temperature transmission. C/VM2 presents a fire resistance rating as three numbers giving the minutes for which each criterion is satisfied, always in that order. The criteria can have different durations.[1][3]

Fire resistance can be established through standard tests, special experiments or analytical techniques supported by experimental evidence. The result depends on the exposure, loading, restraints, geometry and end conditions. It should not be transferred to another assembly without assessing those differences.[4][3]

Performance criteria

Fire resistance criteria define the functions an element must maintain and the conditions for judging failure. A load-bearing column needs structural support, while a separating wall may need to prevent flame passage and limit unexposed-side temperature. The appropriate criteria follow the element's purpose.[2][3]

Structural adequacy is not only avoidance of collapse. Deflections, strains and stress levels can be compared with established limits, and load-bearing performance must continue for the required period. Actual loading and end restraint can therefore change the result.[4][3]

Integrity limits the passage of flame and hot gases through an assembly. Cracks, joints and failed firestopping can create paths even when the main element remains in place. ASTM E119 also includes ignition of cotton waste as an endpoint related to flame and hot-gas transmission.[3]

Insulation limits heat transmission and temperature rise on the unexposed side. ASTM E119 includes average and single-point temperature endpoints, including an average of 139 °C and a single point of 181 °C for walls and partitions in the cited method. These values belong to that test method and should not be treated as universal criteria.[5]

Wall with average 139 °C and single-point 181 °C temperature-rise criteria marked on the unexposed side.
ASTM E119 wall-insulation endpoint examples (temperature rise). Based on Milke (2002), p. 4-211.

C/VM2 requires its three criteria to be reported in the order structural adequacy, integrity and insulation. A rating can consequently communicate different durations for different functions rather than implying one uniform period of complete performance.[1]

Three panels for load support, flame separation and limited heat transmission.
Fire resistance has three distinct performance criteria. Based on Ministry of Business, Innovation and Employment (2025), p. 64.

Standard exposure and testing

The Standard fire curve provides a specified furnace temperature-time exposure for fire-resistance testing. ASTM E119 uses such a curve to represent severe room-fire exposure, while acknowledging limitations for exterior members. The curve is a test input, not a prediction of every real compartment fire.[3][6]

A Fire resistance test subjects an assembly to that furnace environment and records when the relevant endpoint is reached. Tests can be conducted with or without load, and structural assemblies can be restrained or unrestrained against thermal expansion. These arrangements influence the measured performance.[4][3]

ASTM E119 evaluates structural integrity, temperature, flame passage, cotton-waste ignition and, in some cases, hose-stream response. Unloaded tests can have a relaxed structural criterion requiring only that the component remains in place. The test report must therefore state the loading and endpoint arrangement.[3]

Standard furnace curve heats an assembly and leads to structural, flame and temperature endpoints.
Fire-resistance testing links exposure to assembly endpoints. Based on Milke (2002), pp. 4-209–4-210.

Furnace and specimen dimensions limit the test. Milke notes that continuous beams, actual full floor or roof systems and long columns may not be tested in full, making the result comparative. Actual performance requires appropriate analysis and validation rather than assuming literal full-scale reproduction.[3]

C/VM2 permits a rating from a standard test or from a specific calculation method verified by experimental data from standard fire-resistance tests. This establishes a link between analytical methods and experimental evidence within New Zealand's 2025 framework.[1]

Fire compartmentation

Fire compartmentation divides a building into enclosures intended to limit fire and smoke spread. Fire resistance enables the enclosing elements to preserve that separation for the required time. It is one part of a wider strategy that also addresses openings, penetrations and active systems.[7][1]

Conductive heat can expose the unexposed side even when integrity and stability remain intact. Combustibles there can then ignite, so insulation and the disposition of adjacent fuel must be assessed together. A wall that remains standing is not necessarily preventing every form of fire spread.[7][8]

Loss of integrity creates cracks and paths for flame and hot gases, while loss of stability creates larger openings through collapse. These are distinct failure modes and can occur at different times. Fire-resistance analysis should track them separately.[7]

Doors, glazing, dampers and penetrations are part of the same separating system. Their ratings and operation affect the assembly's overall performance, and a stronger wall does not compensate automatically for a weaker penetration. The whole construction must be assessed.[1][7]

Structural fire engineering

Structural fire engineering evaluates how fire exposure changes temperatures, material properties, deformations and load-bearing behaviour. It links a fire-exposure model with heat-transfer analysis and structural mechanics. All three are required for a defensible fire-resistance assessment.[4][2]

Fire exposure describes gas temperatures and heat flux over time. Heat transfer then determines the temperature distribution within the member, including surface resistance, conduction and, where relevant, internal radiation and convection. Finally, structural analysis evaluates strength, stiffness, stability and deformation under elevated temperatures.[4]

Material properties often change substantially during heating. Conductivity, heat capacity, strength and elastic modulus can vary, and microstructural changes can make the material different from its ambient condition. Temperature-dependent data are therefore necessary for many assessments.[9][10]

Loading and restraint affect both stress and deformation. Thermal expansion can be resisted by connections and adjacent construction, creating additional forces or changing stability. The actual framing and end conditions must be represented rather than assuming a generic simply supported member.[3][11]

Passive fire protection

Passive fire protection uses construction, materials and details to resist fire without requiring activation. Fire-resistant walls, floors, doors, coatings and firestops contribute by preserving separation, protecting members and limiting heat transfer. Their performance depends on installation and continuity.[1][12]

Protective membranes delay heating and can preserve member capacity for longer. White's component-additive discussion assigns times to membranes and framing based on ASTM E119 evidence, while warning that fastener type and spacing can be critical. Installation details therefore belong in the assessment.[12]

Intumescent and other coatings can add an insulating layer, but adhesion and durability under deformation matter. A coating that performs in a small test may fail when a member bends or cracks. Full-scale evaluation is needed where those conditions apply.[13]

Passive protection also includes limiting ignition of adjacent fuel and preventing flame and smoke passage. Its effectiveness should be judged against structural adequacy, integrity and insulation rather than only against visible flames. Thermal exposure can continue after the initial fire has declined.[8][7]

Reaction to fire and combustibility

Reaction to fire concerns how a material contributes to ignition, heat release, spread and smoke. Fire resistance instead concerns an assembly's continued performance under exposure. A combustible member can be protected to achieve a rating, while a noncombustible member can still fail structurally or transmit excessive heat.[1][14]

Noncombustibility does not guarantee fire resistance. Materials can melt, spall, expand, lose strength or allow heat transmission without burning. The assembly's functions and failure modes must be evaluated explicitly.[2][9]

Combustible content can also change the exposure of other elements. If an assembly ignites, it can add heat release and weaken separation, while if it remains protected, it can delay the fire's development. Reaction and resistance therefore interact but remain distinct measurements.[15][7]

Analysis and validation

Analytical methods range from empirical correlations to heat-transfer and structural calculations. Empirical methods are limited to the exposure, loading and span represented in their supporting tests. Other conditions require an appropriate heat-transfer or structural model.[4]

Heat-transfer analysis estimates the time to a critical temperature or supplies temperatures for structural analysis. Its accuracy depends on exposure description and temperature-dependent properties. Structural analysis then requires loading, end conditions and elevated-temperature material behaviour.[4]

Testing remains necessary to validate calculations and assess interactions between members, insulation and other components. Calculation can extend test results and reduce the need for additional experiments, but it does not eliminate the need for evidence.[3][1]

Results should include their exposure and endpoint definitions. A rating based on one furnace curve and load arrangement does not automatically cover a natural fire, different restraint or another assembly. Any extrapolation should be justified and documented.[3][6]

Limits and common misunderstandings

Fire resistance is not the time until an element first shows damage. It is the time for which specified criteria continue to be met. Local damage can occur without failure, and different criteria can fail at different times.[1][3]

A rating is not a universal property of a material. It belongs to an assembly under its test or verified analytical conditions. Changing thickness, joints, loading or exposure can change the rating.[4][12]

An intact barrier does not necessarily provide adequate insulation. Heat can be conducted through it and expose occupants or fuel on the other side. Integrity, stability and insulation must be evaluated separately.[7][8]

Finally, the standard curve is not every real fire. Natural fires can have different growth, peak, duration and decay, and those differences affect performance. Fire-resistance assessment must state which exposure is being represented.[6][16]

The evidence should be assigned to the correct part of the assembly. A furnace-average temperature, a steel or reinforcement temperature and an unexposed-surface temperature describe different aspects of performance. Reporting them as one value can conceal which criterion actually failed.[3][11]

Protection should be assessed as a complete system rather than a thickness alone. Membrane continuity, fasteners, joints and attachment determine whether the intended thermal path exists throughout exposure. A nominally identical material can therefore produce different ratings when installed differently.[12][13]

Loading should remain consistent with the structural evaluation. A member that remains in place under self-weight is not equivalent to one carrying its full design load, and restrained expansion can add further forces. Test and analysis reports should state those conditions before comparing results.[3]

Exposure duration and decay also matter. A member can pass an early criterion and fail later as heat penetrates, or it can remain vulnerable after the furnace has stopped heating. Fire-resistance assessment should therefore consider the complete relevant thermal history.[8][6]

For compartmentation, the receiving side must be included. Insulation criteria limit temperature rise, but actual ignition also depends on combustible material and its arrangement there. A numerical insulation result does not by itself prove that fire will not spread to the next enclosure.[7][17]

For structural fire engineering, alternative load paths and local failures can change system behaviour. Connections and adjacent elements may provide restraint or additional capacity, but they also conduct heat. A system-level review is needed where member-only analysis cannot represent those interactions.[11][18]

A final report should distinguish tested performance, calculated performance and regulatory acceptance. Test data support a rating, calculations extend it to defined conditions, and the authority's rules determine how it may be used. Keeping those roles separate prevents an analytical result from being presented as direct test evidence.[1][3]

The concept should finally be interpreted as time under specified performance, not time until any damage occurs. An assembly can deform, crack or lose material while still satisfying a selected criterion, and another can appear intact while allowing excessive heat transmission. The endpoint definitions determine what the rating means.[1][3]

Ratings should therefore be read with their exposure and assembly details. Changing the fire curve, protection, joints, loading or restraint can change when each criterion fails. A single duration cannot be separated from those conditions without losing its technical meaning.[4][6]

Where the intended scenario differs, the analysis should be repeated with the relevant exposure and acceptance criteria. This can use additional tests or verified calculations, but the supporting evidence must remain explicit. That approach is more defensible than transferring a rating solely because two elements share a material name.[1][3]

A clear rating therefore belongs to the complete tested or analysed assembly and its exposure. It records the functions preserved, the criteria applied and the evidence used to verify them. Without that context, a numerical duration can create a misleading impression of universal performance.[1][3]

For final acceptance, each criterion should be evaluated at the required time and under the intended exposure. Structural adequacy, integrity and insulation can pass or fail independently, so a summary should not hide an early failure in one of them. The rating is meaningful only when those separate outcomes are visible.[1][3]

See also

Notes

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 Ministry of Business, Innovation and Employment (2025), p. 64.
  2. ↑ 2.0 2.1 2.2 2.3 Kodur and Harmathy (2002), p. 1-155.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 Milke (2002), pp. 4-209–4-210.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 Milke (2002), p. 4-209.
  5. ↑ Milke (2002), p. 4-211.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Lie (2002), pp. 4-201–4-203.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 Australian Building Codes Board et al. (2005), p. 1.6-7.
  8. ↑ 8.0 8.1 8.2 8.3 Rockett and Milke (2002), p. 1-29.
  9. ↑ 9.0 9.1 Kodur and Harmathy (2002), p. 1-163.
  10. ↑ Fleischmann and Buchanan (2002), pp. 4-241–4-242.
  11. ↑ 11.0 11.1 11.2 Fleischmann and Buchanan (2002), p. 4-242.
  12. ↑ 12.0 12.1 12.2 12.3 White (2002), pp. 4-259–4-260.
  13. ↑ 13.0 13.1 White (2002), p. 4-260.
  14. ↑ Janssens (2002), pp. 3-38–3-39.
  15. ↑ Kodur and Harmathy (2002), p. 1-157.
  16. ↑ Cadorin et al. (2003), pp. 429–430.
  17. ↑ Kanury (2002), pp. 2-231–2-232.
  18. ↑ Cadorin et al. (2003), p. 430.

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.
  • Cadorin, J.-F., Pintea, D., Dotreppe, J.-C., & Franssen, J.-M. (2003). A tool to design steel elements submitted to compartment fires: OZone V2. Part 2: Methodology and application. Fire Safety Journal, 38, 429–451.
  • Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno (Ed.), SFPE handbook of fire protection engineering (3rd ed.). National Fire Protection Association.
  • Janssens, M. (2002). Calorimetry. In P. J. DiNenno (Ed.), SFPE handbook of fire protection engineering (3rd ed.). 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.). National Fire Protection Association.
  • Lie, T. T. (2002). Fire temperature-time relations. In P. J. DiNenno (Ed.), SFPE handbook of fire protection engineering (3rd ed.). 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.). National Fire Protection Association.
  • Ministry of Business, Innovation and Employment. (2025). C protection from fire: Verification method C/VM2 (2nd ed.). New Zealand Government.
  • 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.
  • 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.
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