Fire door

A fire door is a rated doorset that protects an opening in a fire separation. It allows access through the boundary while providing specified resistance when closed. The thermal and integrity functions concern the complete construction, while closing and latching establish the operating state on which that performance depends.

A door is consequently more than its leaf material: its installation, associated components and evidence of assembly performance matter to the claimed rating. Smoke control may require additional performance beyond the fire-resistance function. New Zealand's C/VM2, second edition of 2025, distinguishes those requirements explicitly.

A fire door also forms a changing part of Fire compartmentation. Occupants open it during evacuation, while pressure differences can move smoke through gaps or the open doorway. Understanding its role therefore requires both the closed-state evidence and the conditions under which it opens and closes during the event.

The complete doorset

A fire door belongs to the separating construction surrounding its opening. New Zealand's C/VM2, second edition of 2025, defines it as a single-leaf or multiple-leaf doorset with a specified rating. The definition includes automatic closing and self-latching during fire if the door is not already closed. Smoke-control capability is an additional feature in specified situations.

The word doorset keeps attention on the assembled opening protection. A door leaf operates within a frame and a surrounding separation, while the closing and latching functions establish its intended state. A claim about one material does not describe all these functions. The rating concerns the construction and conditions supported by the relevant test evidence.

A fire door is a complete doorset, not only a leaf. Based on Ministry of Business, Innovation and Employment (2025), p. 64 and Iqbal and Salley (2004), p. C-10.

An Intumescent material swells during heating and can change the thermal path through an assembly. Van Rossum describes that general protective mechanism without defining the performance of a particular doorset; its presence does not replace evidence for the complete door. The construction, operation and claimed fire performance remain separate parts of the assessment.

Fire-resistant glazing likewise concerns a complete assembly rather than glass alone. C/VM2's definition includes the glazing, frame, fixings and associated components, and the source therefore distinguishes a rated glazing arrangement from an unspecified glazed opening. A glazed door requires evidence relevant to the assembled construction in which that glazing is used.

Fire resistance and smoke performance

Fire resistance criteria identify the functions evaluated under the prescribed exposure. Integrity addresses the passage of flames or hot gases, while insulation addresses heat transmission; a separating element may require different evidence for these outcomes. Neither can be inferred solely from the appearance or combustibility of the door material.

Smoke movement introduces leakage paths and pressure differences. Klote identifies cracks around closed doors as paths through which gases can move, so a closed leaf does not imply an airtight boundary. The amount and direction of movement depend on both the available path and the forces acting across it.

New Zealand's 2025 C/VM2 explicitly separates fire-door and smoke-control-door provisions. A fire door with smoke-control capability must satisfy both sets of provisions identified by that method; this distinction prevents a fire rating from being read as a complete smoke-leakage specification. It also identifies which function is being credited in the analysis.

A smoke separation need not have the same fire-resisting capability as a fire separation. C/VM2 applies different assumptions to their continued presence as conditions become more severe, and its discussion explains why a boundary credited early in a fire may not be credited after flashover. That is a modelling distinction, not a universal physical failure temperature for every door.

Testing and interpretation of ratings

A Fire resistance test places the doorset under a defined exposure and evaluates specified endpoints. The 2004 NUREG-1805 report summarises United States NFPA 252 door-assembly testing, and it describes tests continuing to the selected rating period or an earlier performance failure. The report is a historical technical summary, not the full standard or a current product approval.

The summary includes rated periods such as 20, 30, 45, 60, 90 and 180 minutes; these durations belong to the reported test framework. They do not establish a universal duration required for every door or every location. The required performance follows the building context and the applicable classification and design provisions.

The same summary describes a hose-stream exposure following the fire-endurance test, and its purpose is to apply impact, erosion and cooling to the heated assembly. The report identifies an exception in which the hose stream is optional for the stated 20-minute-rated assemblies. It is therefore inaccurate to describe this stage as mandatory for every door test worldwide.

Fire-door testing includes endurance and hose-stream response. Based on Iqbal and Salley (2004), p. C-10.

Test evidence also retains its construction context. New Zealand's 2025 verification method requires details during construction to match the developed design; its commentary connects rated closures to testing under an internationally recognised standard. This links the installed doorset to its evidence instead of assigning a rating from its thickness or material name alone.

Door use during evacuation

A door protecting Means of escape must be considered in both its closed and open states. When occupants pass through, they temporarily change the separating boundary, and the International Fire Engineering Guidelines therefore obtain opening times from the evacuation analysis. A closed-door furnace result does not describe those periods of use.

C/VM2, second edition of 2025, provides a specific modelling convention for this interaction. Fire and smoke-control doors with self-closers are assumed closed unless occupants are using them. For low occupant demand, the model allows three seconds of opening per occupant. The commentary connects that interval to opening the leaf, passing through and allowing it to close.

Where a queue keeps occupants passing continuously, the same document treats the door as open for the queuing period. This is a different physical state from isolated short openings. Applying the low-demand convention while a continuous queue holds the leaf open would misrepresent the intended assumption. The distinction belongs to the New Zealand method's movement and smoke analyses.

Fire-door state changes during evacuation. Based on Ministry of Business, Innovation and Employment (2025), p. 15.

For smoke-flow calculations during egress, C/VM2 represents the open door using half its width. The commentary explains that the moving leaf and occupants obstruct part of the opening; this is an effective opening assumption for that analysis. It does not redefine the constructed door width or the width available under separate escape provisions.

Pressure differences and open doorways

A closed door and an open doorway present different airflow problems. With a closed door, the paths may consist mainly of small gaps. With an open door, a much larger passage connects the spaces. Klote distinguishes pressure control across mostly closed barriers from airflow control through large openings.

Mechanical pressurisation can oppose smoke entry through leakage paths, and its intended airflow is from the protected side towards the smoke-exposed side. When a door opens, however, low air velocity may permit smoke to flow back through part of the opening. The closed-door pressure condition does not by itself establish the open-door performance.

The forces moving smoke can also come from outside the mechanical system. Buoyancy, stack effect and wind affect the pressure field within a building. Klote explains that fan shutdown alone does not stop movement through all available paths. A door's leakage and operating state therefore interact with the surrounding building conditions.

These interactions explain why fire separation and smoke control cannot be assessed as completely independent systems. The same opening can support evacuation, interrupt a smoke boundary and influence airflow. The analysis identifies which state is assumed during each part of the event. It then connects that state to the function attributed to the doorset.

Closing functions and commissioning

A rating establishes performance under its tested conditions; it does not prove that an installed door will reach the necessary closed state. Closing and latching are operating functions in C/VM2's definition. Their role is distinct from the material's thermal response. Both are needed where the strategy relies on an automatically closed opening.

The International Fire Engineering Guidelines include operable systems among construction and commissioning checks. Components must match the specification, and automatically closing doors must perform their intended function. The guidelines also include operating and maintenance information. This creates an evidence chain from the design description to the completed and functioning installation.

The state assumed in a model can depend on use and management. C/VM2 explains its short opening convention through a well-maintained self-closing door and intermittent occupant arrivals. That convention does not describe a door permanently held open. Its use therefore rests on the operational condition stated in the method.

Inspection, alterations and continuing evidence

The 2005 International Fire Engineering Guidelines distinguish routine inspection of static barriers from operational testing of active closures. A fire door may combine both types of concern: the physical separation and the movement required to restore it. Inspection of the wall alone cannot demonstrate the closing function. An operating check alone cannot establish the wall's complete fire-resisting construction.

Repairs and modifications can affect the original boundary. The guidelines note that passive components may be overlooked during building changes. Continued identification of the separation links local work to its wider fire-safety role. That includes the opening protection as well as the surrounding construction.

Maintenance records identify the required functions and document observed outcomes. The guidelines do not prescribe one universal inspection interval or one component specification for every doorset. Those details require the applicable standard and product evidence. The general framework preserves the connection between the designed boundary, the installed assembly and its continuing operation.

See also

• Passive fire protection
• Stair pressurisation
• Protected escape route
• Fire-induced pressure

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.