Fire-resistant glazing - Revision history

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

2026-11-02T21:32:49Z

Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

← Older revision		Revision as of 22:32, 2 November 2026
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	Ordinary window glass usually breaks in a fully developed fire, and its failure changes the fire. C/VM2 (second edition, 2025) assumes that exterior windows without fire resistance break and fall out at the earlier of two moments. These are an average upper layer temperature of 500 °C and the point at which the fire becomes ventilation-limited.<ref name="MBIE25-16" /> A comment in C/VM2 explains that it is hard to predict when glass falls out, and that 500 °C represents a rapid onset of flashover.<ref name="MBIE25-16" /> Windows with non-fire-resisting glazing are therefore counted as openings that supply air to the fire when the fire severity is calculated.<ref name="MBIE25-19">Ministry of Business, Innovation and Employment (2025b), p. 19.</ref> Fire-resistant glazing, in contrast, may be assumed to stay in place up to its rated time.<ref name="MBIE25-16" />		Ordinary window glass usually breaks in a fully developed fire, and its failure changes the fire. C/VM2 (second edition, 2025) assumes that exterior windows without fire resistance break and fall out at the earlier of two moments. These are an average upper layer temperature of 500 °C and the point at which the fire becomes ventilation-limited.<ref name="MBIE25-16" /> A comment in C/VM2 explains that it is hard to predict when glass falls out, and that 500 °C represents a rapid onset of flashover.<ref name="MBIE25-16" /> Windows with non-fire-resisting glazing are therefore counted as openings that supply air to the fire when the fire severity is calculated.<ref name="MBIE25-19">Ministry of Business, Innovation and Employment (2025b), p. 19.</ref> Fire-resistant glazing, in contrast, may be assumed to stay in place up to its rated time.<ref name="MBIE25-16" />

	The International Fire Engineering Guidelines make a similar distinction. For analysis, fire may be assumed to spread through a closed window at flashover if the window is of ordinary glass, but not if it is toughened or wired.<ref name="IFEG-1.6-6">National Research Council of Canada et al. (2005), p. 1.6-6.</ref> They add that fire can spread to an adjacent building through the glass of a fixed or closed window by radiation, without any breakage.<ref name="IFEG-1.6-7">National Research Council of Canada et al. (2005), p. 1.6-7.</ref> More on how and when glass fails is given in [[Glass breakage in fire]]. In zone models, the failure of glass or polycarbonate parts of the building envelope can be included as the opening of a vent at a set temperature or rate of temperature rise.<ref name="VR-9.3a">Van Rossum (2027), §9.3 (How a zone model works).</ref><ref name="VR-9.3b">Van Rossum (2027), §9.3 (Results from zone models).</ref>		The International Fire Engineering Guidelines make a similar distinction. For analysis, fire may be assumed to spread through a closed window at flashover if the window is of ordinary glass, but not if it is toughened or wired.<ref name="IFEG-1.6-6">National Research Council of Canada et al. (2005), p. 1.6-6.</ref> They add that fire can spread to an adjacent building through the glass of a fixed or closed window by radiation, without any breakage.<ref name="IFEG-1.6-7">National Research Council of Canada et al. (2005), p. 1.6-7.</ref> More on how and when glass fails is given in Glass breakage in fire. In zone models, the failure of glass or polycarbonate parts of the building envelope can be included as the opening of a vent at a set temperature or rate of temperature rise.<ref name="VR-9.3a">Van Rossum (2027), §9.3 (How a zone model works).</ref><ref name="VR-9.3b">Van Rossum (2027), §9.3 (Results from zone models).</ref>

	A NIST test for the World Trade Center investigation shows the difference between glass types. A 2.4 m by 2.4 m window assembly held two double-pane tempered glass units with a gel insulation layer between the panes and two single-pane tempered units.<ref name="HMMOA-11">Hamins, Maranghides, McGrattan, Ohlemiller, and Anleitner (2005), p. 11.</ref> The lower single-pane unit cracked and fell out about 185 s after ignition and the upper one about 212 s after ignition.<ref name="HMMOA-55">Hamins, Maranghides, McGrattan, Ohlemiller, and Anleitner (2005), p. 55.</ref> The double-pane units never fell out.<ref name="HMMOA-55" /> The extra ventilation from the broken panes probably caused the highest peak heat release rate of the test series, almost 16 MW.<ref name="HMMOA-55" />		A NIST test for the World Trade Center investigation shows the difference between glass types. A 2.4 m by 2.4 m window assembly held two double-pane tempered glass units with a gel insulation layer between the panes and two single-pane tempered units.<ref name="HMMOA-11">Hamins, Maranghides, McGrattan, Ohlemiller, and Anleitner (2005), p. 11.</ref> The lower single-pane unit cracked and fell out about 185 s after ignition and the upper one about 212 s after ignition.<ref name="HMMOA-55">Hamins, Maranghides, McGrattan, Ohlemiller, and Anleitner (2005), p. 55.</ref> The double-pane units never fell out.<ref name="HMMOA-55" /> The extra ventilation from the broken panes probably caused the highest peak heat release rate of the test series, almost 16 MW.<ref name="HMMOA-55" />

Lisa: Add Intermediate SVG figures with Fire Safety Academy watermark at planned locations; preserve article text

2026-11-02T17:12:40Z

Add Intermediate SVG figures with Fire Safety Academy watermark at planned locations; preserve article text

← Older revision		Revision as of 18:12, 2 November 2026
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	Fire-resistant glazing lets designers keep light and views in places where a solid wall would otherwise be needed. Typical uses in the sources are vision panels in fire doors, windows in external walls close to a boundary, and glazed panels beside escape routes.<ref name="ABCB20a-C7-212">Australian Building Codes Board (2020a), Data Sheet C7, p. 212.</ref><ref name="MBIE25-45">Ministry of Business, Innovation and Employment (2025b), p. 45.</ref><ref name="MBIE25-34">Ministry of Business, Innovation and Employment (2025b), p. 34.</ref> Some products only keep flames and hot gases back, while insulated products also limit the heat on the unexposed side.<ref name="MBIE25-35">Ministry of Business, Innovation and Employment (2025b), p. 35.</ref> The difference matters for people who pass close to the glass, because heat radiation through uninsulated glazing can still be high.<ref name="MBIE25-35" />		Fire-resistant glazing lets designers keep light and views in places where a solid wall would otherwise be needed. Typical uses in the sources are vision panels in fire doors, windows in external walls close to a boundary, and glazed panels beside escape routes.<ref name="ABCB20a-C7-212">Australian Building Codes Board (2020a), Data Sheet C7, p. 212.</ref><ref name="MBIE25-45">Ministry of Business, Innovation and Employment (2025b), p. 45.</ref><ref name="MBIE25-34">Ministry of Business, Innovation and Employment (2025b), p. 34.</ref> Some products only keep flames and hot gases back, while insulated products also limit the heat on the unexposed side.<ref name="MBIE25-35">Ministry of Business, Innovation and Employment (2025b), p. 35.</ref> The difference matters for people who pass close to the glass, because heat radiation through uninsulated glazing can still be high.<ref name="MBIE25-35" />

			[[File:fse-fire-resistant-glazing-v1.svg\|thumb\|upright=1.5\|alt=Three glazed openings in a fire: ordinary glass falls out, uninsulated fire glass stays but passes heat, insulated fire glass limits heat.\|Ordinary glass, uninsulated fire-resistant glazing and insulated fire-resistant glazing in a fully developed fire. Based on Ministry of Business, Innovation and Employment (2025b), pp. 16 and 35.]]

	== Fire resistance criteria for glazing ==		== Fire resistance criteria for glazing ==
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	The example also shows how distance helps. Calculating the view factor for larger distances shows that the radiation from this panel falls to 10 kW/m² at about 2.0 m with uninsulated fire-resistant glazing, and only at about 3.0 m with ordinary glass.<ref name="VR-5.4" /> At 1.0 m the design needs another solution, such as insulated glazing of at least -/30/30, listed window wetting sprinklers or an alternative escape route.<ref name="MBIE25-35" />		The example also shows how distance helps. Calculating the view factor for larger distances shows that the radiation from this panel falls to 10 kW/m² at about 2.0 m with uninsulated fire-resistant glazing, and only at about 3.0 m with ordinary glass.<ref name="VR-5.4" /> At 1.0 m the design needs another solution, such as insulated glazing of at least -/30/30, listed window wetting sprinklers or an alternative escape route.<ref name="MBIE25-35" />

			[[File:fse-fire-resistant-glazing-v2.svg\|thumb\|upright=1.5\|alt=Line chart of radiation at an escape route against distance from a 2 m by 2 m glazed panel, for ordinary and fire-resistant glazing, with a 10 kW/m² limit.\|Radiation opposite the centre of a 2.0 m by 2.0 m glazed panel with an emitted flux of 83 kW/m², for ordinary glass (k = 1.0) and uninsulated fire-resistant glazing (k = 0.5). Based on Ministry of Business, Innovation and Employment (2025b), pp. 34 to 35, and Van Rossum (2027), §5.4.]]

	== External walls and boundaries ==		== External walls and boundaries ==
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	The maximum area of each glazed area depends on the distance to the boundary, the fire load and whether the firecell is sprinklered. In an unsprinklered firecell, each area is limited to 1.0 m² up to 0.4 m from the boundary, whatever the fire load.<ref name="MBIE25-74">Ministry of Business, Innovation and Employment (2025b), p. 74.</ref> At 1.0 m the limits are 6.0 m², 3.5 m² and 1.5 m² for fire load energy densities up to 400, 400 to 800 and above 800 MJ/m².<ref name="MBIE25-74" /> For a fire load of up to 400 MJ/m², the area is unlimited beyond 1.7 m; for higher fire loads it never exceeds 15 m².<ref name="MBIE25-74" /> Sprinklers relax the limits considerably: with a fire load of up to 400 MJ/m² there is no limit at all.<ref name="MBIE25-75">Ministry of Business, Innovation and Employment (2025b), p. 75.</ref>		The maximum area of each glazed area depends on the distance to the boundary, the fire load and whether the firecell is sprinklered. In an unsprinklered firecell, each area is limited to 1.0 m² up to 0.4 m from the boundary, whatever the fire load.<ref name="MBIE25-74">Ministry of Business, Innovation and Employment (2025b), p. 74.</ref> At 1.0 m the limits are 6.0 m², 3.5 m² and 1.5 m² for fire load energy densities up to 400, 400 to 800 and above 800 MJ/m².<ref name="MBIE25-74" /> For a fire load of up to 400 MJ/m², the area is unlimited beyond 1.7 m; for higher fire loads it never exceeds 15 m².<ref name="MBIE25-74" /> Sprinklers relax the limits considerably: with a fire load of up to 400 MJ/m² there is no limit at all.<ref name="MBIE25-75">Ministry of Business, Innovation and Employment (2025b), p. 75.</ref>

			[[File:fse-fire-resistant-glazing-v3.svg\|thumb\|upright=1.5\|alt=Step chart of maximum fire-resistant glazing area against distance to the boundary for three fire load bands in unsprinklered firecells.\|Maximum area of each fire resisting glazed area in an unsprinklered firecell, by distance to the relevant boundary and fire load energy density (C/VM2, New Zealand). Based on Ministry of Business, Innovation and Employment (2025b), p. 74.]]

	== Glazing inside buildings ==		== Glazing inside buildings ==

Daan: New FSE wiki article: Fire-resistant glazing (written by Claude Opus 5.5)

2026-11-01T22:42:53Z

New FSE wiki article: Fire-resistant glazing (written by Claude Opus 5.5)

New page

'''Fire-resistant glazing''' is glazing that, together with its frame, fixings and glazing beads, has a specified fire resistance rating. It can therefore form part of a fire separation or a fire-rated external wall.<ref name="MBIE25-64">Ministry of Business, Innovation and Employment (2025b), p. 64.</ref> New Zealand's Verification Method C/VM2 (second edition, 2025) calls it fire resisting glazing and defines it as a complete fixed or openable assembly, not as a type of glass alone.<ref name="MBIE25-64" /> Its main difference from ordinary windows is that it stays in place during a fire for its rated time. Ordinary exterior windows are assumed in C/VM2 to fall out at an upper layer temperature of 500 °C or when the fire becomes limited by ventilation.<ref name="MBIE25-16">Ministry of Business, Innovation and Employment (2025b), p. 16.</ref>

Fire-resistant glazing lets designers keep light and views in places where a solid wall would otherwise be needed. Typical uses in the sources are vision panels in fire doors, windows in external walls close to a boundary, and glazed panels beside escape routes.<ref name="ABCB20a-C7-212">Australian Building Codes Board (2020a), Data Sheet C7, p. 212.</ref><ref name="MBIE25-45">Ministry of Business, Innovation and Employment (2025b), p. 45.</ref><ref name="MBIE25-34">Ministry of Business, Innovation and Employment (2025b), p. 34.</ref> Some products only keep flames and hot gases back, while insulated products also limit the heat on the unexposed side.<ref name="MBIE25-35">Ministry of Business, Innovation and Employment (2025b), p. 35.</ref> The difference matters for people who pass close to the glass, because heat radiation through uninsulated glazing can still be high.<ref name="MBIE25-35" />

== Fire resistance criteria for glazing ==
Glazing is rated by the same [[fire resistance criteria]] as walls and doors. In New Zealand, a fire resistance rating (FRR) gives three times in minutes, for structural adequacy, integrity and insulation, always in that order.<ref name="MBIE25-64" /> Integrity is the time for which a test specimen prevents the passage of flame or hot gases. Insulation is the time for which it limits the transmission of heat through the specimen.<ref name="MBIE25-66">Ministry of Business, Innovation and Employment (2025b), p. 66.</ref> These times come from a furnace test that follows the standard fire curve. The ''Introduction to Fire Safety Engineering'' stresses that this curve is an agreed temperature course for comparing constructions, not a model of a real fire.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref>

The Australian data sheets give the criteria of the test standard AS 1530.4 in some detail. Integrity is lost when a cotton pad held over a crack ignites, or when a through gap larger than 150 mm by 6 mm or 25 mm in diameter appears. Flaming for 10 s or more on the unexposed face also counts as failure.<ref name="ABCB20a-C7-211">Australian Building Codes Board (2020a), Data Sheet C7, p. 211.</ref> Insulation is lost when the average temperature of the unexposed face rises by 140 K, or the maximum temperature at any point by 180 K.<ref name="ABCB20a-C7-212" /> A fire door with glazing must also not fail by radiation through any glazed part during its integrity period.<ref name="ABCB20a-C7-211" />

For glazed areas in fire doors, AS 1530.4 and the Australian National Construction Code add a separate radiation criterion. The heat flux at 365 mm from the vision panel may not exceed 10 kW/m² for the period of the integrity rating.<ref name="ABCB20a-C7-212" /> At that level, combustibles stored more than 365 mm from the door are not expected to ignite, and the measured flux also shows the risk to people walking past.<ref name="ABCB20a-C7-212" /> The limit makes the role of [[thermal radiation]] explicit: integrity alone does not stop heat from passing through clear glass.

In the United States, NUREG-1805 summarises the window test standard NFPA 257. Fire ratings of windows were once limited by the failure of wired glass at about 870 °C (1,600 °F).<ref name="IS-C-10">Iqbal and Salley (2004), p. C-10.</ref> Advances in glazing technology have since raised the available ratings of window assemblies to 20, 30 and 45 minutes. Ratings of 60, 90 and 180 minutes or more are available under the general fire resistance test NFPA 251.<ref name="IS-C-10" /> Within 2 minutes after the fire test, the fire-exposed side of the window assembly is subjected to a standard hose stream.<ref name="IS-C-10" />

== Behaviour compared with ordinary glass ==
Ordinary window glass usually breaks in a fully developed fire, and its failure changes the fire. C/VM2 (second edition, 2025) assumes that exterior windows without fire resistance break and fall out at the earlier of two moments. These are an average upper layer temperature of 500 °C and the point at which the fire becomes ventilation-limited.<ref name="MBIE25-16" /> A comment in C/VM2 explains that it is hard to predict when glass falls out, and that 500 °C represents a rapid onset of flashover.<ref name="MBIE25-16" /> Windows with non-fire-resisting glazing are therefore counted as openings that supply air to the fire when the fire severity is calculated.<ref name="MBIE25-19">Ministry of Business, Innovation and Employment (2025b), p. 19.</ref> Fire-resistant glazing, in contrast, may be assumed to stay in place up to its rated time.<ref name="MBIE25-16" />

The International Fire Engineering Guidelines make a similar distinction. For analysis, fire may be assumed to spread through a closed window at flashover if the window is of ordinary glass, but not if it is toughened or wired.<ref name="IFEG-1.6-6">National Research Council of Canada et al. (2005), p. 1.6-6.</ref> They add that fire can spread to an adjacent building through the glass of a fixed or closed window by radiation, without any breakage.<ref name="IFEG-1.6-7">National Research Council of Canada et al. (2005), p. 1.6-7.</ref> More on how and when glass fails is given in [[Glass breakage in fire]]. In zone models, the failure of glass or polycarbonate parts of the building envelope can be included as the opening of a vent at a set temperature or rate of temperature rise.<ref name="VR-9.3a">Van Rossum (2027), §9.3 (How a zone model works).</ref><ref name="VR-9.3b">Van Rossum (2027), §9.3 (Results from zone models).</ref>

A NIST test for the World Trade Center investigation shows the difference between glass types. A 2.4 m by 2.4 m window assembly held two double-pane tempered glass units with a gel insulation layer between the panes and two single-pane tempered units.<ref name="HMMOA-11">Hamins, Maranghides, McGrattan, Ohlemiller, and Anleitner (2005), p. 11.</ref> The lower single-pane unit cracked and fell out about 185 s after ignition and the upper one about 212 s after ignition.<ref name="HMMOA-55">Hamins, Maranghides, McGrattan, Ohlemiller, and Anleitner (2005), p. 55.</ref> The double-pane units never fell out.<ref name="HMMOA-55" /> The extra ventilation from the broken panes probably caused the highest peak heat release rate of the test series, almost 16 MW.<ref name="HMMOA-55" />

Glazing also matters for smoke. In C/VM2, smoke separations that include glazing and comply with the relevant product specification stay in place up to their rated temperature or until flashover, whichever comes first.<ref name="MBIE25-14">Ministry of Business, Innovation and Employment (2025b), p. 14.</ref> A separation that consists simply of toughened glass, not designed to a standard, is assumed to disappear once the average upper layer temperature reaches 200 °C.<ref name="MBIE25-15">Ministry of Business, Innovation and Employment (2025b), p. 15.</ref>

== Radiation through glazing along escape routes ==
People who escape past a window or glazed panel must not receive so much radiation that they feel pain. C/VM2 (second edition, 2025) sets a maximum exposure of 10 kW/m² for occupants in exitways or on external escape routes.<ref name="MBIE25-34" /> Without fire-resistant glazing, all occupants must also have passed the window within 10 minutes after ignition.<ref name="MBIE25-34" /> The method calculates the radiation at the point opposite the centre of the window, at a height of 2.0 m or at mid-height of the glazing, whichever is lower.<ref name="MBIE25-35" /> It multiplies the heat flux emitted by the window by a view factor, the emissivity of the fire gases and a glazing factor:<ref name="MBIE25-35" />

<math display="block">\dot{q}''_r = F_w \, \varepsilon \, k \, \dot{q}''_w</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot{q}''_r</math> || maximum incident radiation at the escape route || kW/m²
|-
| <math>F_w</math> || view factor from the window to the point on the escape route || –
|-
| <math>\varepsilon</math> || emissivity of the fire gases, taken as 1.0 || –
|-
| <math>k</math> || glazing factor: 0.5 for fire resisting glazing, 1.0 for all other glazing || –
|-
| <math>\dot{q}''_w</math> || design heat flux emitted from the window: 83, 103 or 144 kW/m² for a fire load energy density up to 400, 400 to 800, or above 800 MJ/m² || kW/m²
|}

The glazing factor expresses that radiation through uninsulated fire-resistant glazing may be taken as half that through other glazing.<ref name="MBIE25-35" /> The relation applies to a single window; several windows need a more detailed, time-dependent analysis.<ref name="MBIE25-34" /> It is not meant for occupants who are likely to be mobility-impaired.<ref name="MBIE25-35" /> No analysis is needed where insulated glazing with an FRR of at least -/30/30 is used, or where window wetting sprinklers listed for that purpose are installed.<ref name="MBIE25-35" />

A worked example takes a glazed panel 2.0 m wide and 2.0 m high in a firecell with a fire load energy density of at most 400 MJ/m², so that <math>\dot{q}''_w</math> = 83 kW/m².<ref name="MBIE25-35" /> An escape route passes 1.0 m in front of the panel. Using the table method of the ''Introduction to Fire Safety Engineering'', the panel is split into four squares of 1.0 m by 1.0 m, each with a view factor of 0.139.<ref name="VR-5.4">Van Rossum (2027), §5.4.</ref> The total view factor is 4 × 0.139 ≈ 0.56, and with ordinary glass (<math>k</math> = 1.0), the radiation is 0.56 × 1.0 × 1.0 × 83 ≈ 46 kW/m². With uninsulated fire-resistant glazing (<math>k</math> = 0.5) it is about 23 kW/m², still more than twice the limit of 10 kW/m².<ref name="MBIE25-34" />

The example also shows how distance helps. Calculating the view factor for larger distances shows that the radiation from this panel falls to 10 kW/m² at about 2.0 m with uninsulated fire-resistant glazing, and only at about 3.0 m with ordinary glass.<ref name="VR-5.4" /> At 1.0 m the design needs another solution, such as insulated glazing of at least -/30/30, listed window wetting sprinklers or an alternative escape route.<ref name="MBIE25-35" />

== External walls and boundaries ==
Glazing in external walls is one of the routes for [[fire spread between buildings]]. In New Zealand, building code clause C3.6 limits the radiation received at the relevant boundary to 30 kW/m², and to 16 kW/m² at 1 m beyond it.<ref name="MBIE25-43">Ministry of Business, Innovation and Employment (2025b), p. 43.</ref> In the C/VM2 method, non-fire-rated window and door assemblies count as unprotected areas that radiate heat.<ref name="MBIE25-44">Ministry of Business, Innovation and Employment (2025b), p. 44.</ref> The design emitted flux from such areas is 83, 103 or 144 kW/m² for unsprinklered firecells, depending on the fire load energy density.<ref name="MBIE25-44" /> For sprinklered firecells the values are lower, at 58, 72 and 101 kW/m².<ref name="MBIE25-44" /> The rest of the wall must keep its integrity through the full burnout design fire and have enough insulation to meet clause C3.7.<ref name="MBIE25-44" />

The ''Introduction to Fire Safety Engineering'' applies the same logic to openings in a facade. Its worked example has two openings of 1.8 m by 1.2 m, 2.4 m apart, that radiate 120 kW/m² towards a facade 6 m away.<ref name="VR-5.4" /> The radiation received there is 3.84 kW/m², below the limit of 15 kW/m² used in the example, so no further measures are needed.<ref name="VR-5.4" /> If the result had exceeded the limit, the openings would have to be made fire-resistant or another measure would be needed.<ref name="VR-5.4" />

Close to a boundary the rules become strict. Within 1.0 m of a relevant boundary, C/VM2 permits no unprotected areas except small ones of up to 0.1 m² and areas of fire resisting glazing.<ref name="MBIE25-45" /><ref name="MBIE25-72">Ministry of Business, Innovation and Employment (2025b), p. 72.</ref> The glazing must be rated for integrity, and its FRR, like that of the wall, is derived from the full burnout design fire.<ref name="MBIE25-72" /> Neighbouring areas of fire-resistant glazing in the same space must be spaced horizontally by at least the greater of their widths, and vertically by at least the greater of their heights.<ref name="MBIE25-72" />

The maximum area of each glazed area depends on the distance to the boundary, the fire load and whether the firecell is sprinklered. In an unsprinklered firecell, each area is limited to 1.0 m² up to 0.4 m from the boundary, whatever the fire load.<ref name="MBIE25-74">Ministry of Business, Innovation and Employment (2025b), p. 74.</ref> At 1.0 m the limits are 6.0 m², 3.5 m² and 1.5 m² for fire load energy densities up to 400, 400 to 800 and above 800 MJ/m².<ref name="MBIE25-74" /> For a fire load of up to 400 MJ/m², the area is unlimited beyond 1.7 m; for higher fire loads it never exceeds 15 m².<ref name="MBIE25-74" /> Sprinklers relax the limits considerably: with a fire load of up to 400 MJ/m² there is no limit at all.<ref name="MBIE25-75">Ministry of Business, Innovation and Employment (2025b), p. 75.</ref>

== Glazing inside buildings ==
Inside buildings, fire-resistant glazing forms part of the walls and doors that maintain [[fire compartmentation]]. Vision panels in a [[fire door]] are one such case, and they are the reason for the radiation criterion of 10 kW/m² at 365 mm in Australian door tests.<ref name="ABCB20a-C7-212" /> Glazed panels beside escape routes fall under the C/VM2 radiation check, and any openable part must close automatically when smoke or heat is detected.<ref name="MBIE25-35" />

Older and current American codes show how glass has long been accepted in protected openings. The BOCA Building Code in force when the World Trade Center was designed allowed openings in shafts to be protected with approved fire doors, curtains, shutters or fixed metal sash with wired glass.<ref name="RG-22">Razza and Grill (2005b), p. 22.</ref> The current (2003) New York City Building Code allows atrium enclosure walls of wired, laminated or tempered glass instead of 2 hour rated construction.<ref name="RG-63">Razza and Grill (2005c), p. 63.</ref> In that case sprinklers no more than 6 ft (1.8 m) apart must protect the glass on the occupied side.<ref name="RG-63" />

== Limits and uncertainty ==
A fire resistance rating describes performance in a standard furnace test, not in a real fire. The ''Introduction to Fire Safety Engineering'' recommends comparing the thermal load in a natural fire with the load in the fire test. A zone model can estimate when glazing fails if a limit temperature or rate of rise is known.<ref name="VR-9.3b" /> The temperature in a real fire depends on room size, openings, insulation and heat release rate, so a test curve cannot reproduce a specific fire.<ref name="VR-8.6" />

Several simplifications in the design rules point to remaining uncertainty. C/VM2 states that it is hard to predict reliably when glass falls out of a window.<ref name="MBIE25-16" /> The fixed glazing factor of 0.5 treats all uninsulated fire-resistant glazing alike, and the escape route method is limited to a single window.<ref name="MBIE25-34" /><ref name="MBIE25-35" /> The NIST test also showed that the breakage time of ordinary panes can change the ventilation and the heat release rate of a fire.<ref name="HMMOA-55" />

== See also ==
* [[Fire curtain]]
* [[Intumescent material]]
* [[Fire wall]]
* [[Passive fire protection]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Hamins, A., Maranghides, A., McGrattan, K. B., Ohlemiller, T. J., & Anleitner, R. L. (2005). ''Experiments and modeling of multiple workstations burning in a compartment'' (NIST NCSTAR 1-5E). National Institute of Standards and Technology.
* 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, Office of Nuclear Reactor Regulation.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Razza, J. C., & Grill, R. A. (2005b). ''Comparison of codes, standards, and practices in use at the time of the design and construction of World Trade Center 1, 2, and 7'' (NIST NCSTAR 1-1E). National Institute of Standards and Technology.
* Razza, J. C., & Grill, R. A. (2005c). ''Comparison of the 1968 and current (2003) New York City Building Code provisions'' (NIST NCSTAR 1-1F). National Institute of Standards and Technology.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]