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Contents
  1. 1Types of curtain barriers
  2. 2How a deployable curtain is released
  3. 3Fire resistance and smoke leakage
  4. 4Use in design
  5. 5Reliability and limits
  6. 6See also
  7. 7Notes
  8. 8References

A fire curtain is a barrier that hangs from a ceiling or closes an opening, in the way of a curtain or shutter, to limit the passage of fire or smoke.[1][2] Fire engineering sources treat such barriers under several names. Draft curtains are barriers suspended from the roof of a structure to limit the spread of smoke.[1] Roller shutters, rolling fire doors and automatic fire shutters are closures that can stay open in normal use and close automatically, for example when smoke detectors operate.[2][3]

A closed curtain acts as part of a smoke barrier or a fire separation. Its task is then the same as that of a wall: to keep smoke within one zone long enough for escape and fire service intervention.[4] Two questions decide whether it works. The first is whether the closure is in place at the right moment, which depends on detection, release devices and maintenance.[5] The second is how much smoke and heat pass through and around it once it is closed, which depends on its leakage and its rating against the standard fire.[6][7]

Types of curtain barriers

The first type is the fixed or deployed draft curtain at ceiling level. In the SFPE Handbook, Notarianni describes a draft curtain as a barrier that extends a certain distance down from the roof or ceiling, installed to subdivide a large area and corral heat and smoke.[8] Cooper describes ceiling-mounted screens or draft curtains that divide a large space into separate curtained compartments.[9] Their purpose is to limit the smoke to the curtained compartment where the fire started.[9]

The second type is a full-height closure in an opening of a fire or smoke separation. The sources mention roller shutters, rolling fire doors and automatic fire shutters.[2][3][10] A guidance document on fire safety in Dutch car parks names fire screens between vehicles and fire-resistant rolling shutters as ways to divide a car park into fire compartments.[11] In the tenant guidelines of the World Trade Center, automatic fire shutters could be used to maintain the fire rating of a tenant space.[10]

Left: a curtain hangs part-way down from a roof and holds smoke on the fire side. Right: a shutter closes a full-height opening in a wall.
Two types of curtain barrier: a draft curtain at ceiling level (left) and a full-height closure in an opening of a separation (right). Based on Notarianni (2002), p. 5-45, Cooper (2002b), p. 3-220, and Ministry of Business, Innovation and Employment (2025b), p. 15.

The word "curtain" also has meanings that have nothing to do with these barriers. In fire service usage, a smoke curtain is a set of salvage covers that firefighters place around an area to stop smoke from causing further damage.[12] Ordinary curtains and draperies are fuel: they are combustible and can spread fire quickly over large surfaces.[13]

How a deployable curtain is released

A closure that stands open in normal use needs a signal to close. For fire and smoke doors, the Australian data sheets describe an automatic hold-open device that releases the door when a heat, smoke or fire sensing device operates.[14] These devices can be connected to the fire alarm system: the fire indicator panel then sends the release signal to doors with hold-open devices, as well as to smoke dampers and vents.[15] NIST also lists automatic door hold-open devices and smoke dampers among the features that complete compartmentation once smoke is detected in a zone.[16]

The World Trade Center shows a fail-safe arrangement. When the towers were designed, the Port Authority chose to provide fail-safe automatic closers for the overhead rolling fire doors between the below-grade truck dock and the elevator lobby.[3] These doors were arranged to close when smoke detectors operated.[3] An Australian worked example shows why fail-safe action matters. If the detection system fails completely, which was estimated at about 20 %, no alarm sounds and smoke doors with hold-open devices do not close.[17]

Flowchart from smoke or heat detection via the fire indicator panel to release of the hold-open device and closure, with a failure branch.
Release chain of a deployable closure and the effect of a detection failure. Based on Australian Building Codes Board (2020a), Data Sheet C3, p. 98, and Data Sheet C7, p. 201, and Australian Building Codes Board (2020b), p. 100.

A closed curtain or shutter may also trap people. The World Trade Center tenant guidelines therefore required a safe means of egress for persons who remain inside a space after its automatic fire shutter has closed.[10] The 1968 New York City Building Code did not allow vertically sliding doors, rolling shutters or folding doors to serve as exit doors or corridor doors.[18] The Dutch car park guidance likewise starts from the idea that people must be able to escape from every fire compartment.[11]

Fire resistance and smoke leakage

A curtain that forms part of a fire separation is judged by the same fire resistance criteria as a wall or door. In New Zealand, the fire resistance rating consists of three times in minutes, for structural adequacy, integrity and insulation, always in that order.[19] Integrity is the time for which a specimen prevents the passage of flame or hot gases, and insulation is the time for which it limits heat transmission.[20] These ratings come from tests with the standard fire curve, which is meant for comparing tested constructions, not for reproducing a real fire.[21] For sliding doors and roller shutters, the Australian data sheets note that the insulation criteria may differ from those of hinged doors.[7]

Smoke barriers are also tested at lower temperatures. The Australian data sheet on smoke barriers uses three exposure classes: ambient at 20 ± 10 °C, medium at 200 ± 20 °C, and high, representing a fully developed fire.[4][22] In New Zealand, C/VM2 (second edition, 2025) assumes that a smoke separation tested for use as a smoke barrier stays in place up to its rated temperature or until flashover, whichever comes first.[23] An untested, non-fire-rated but imperforate separation is assumed to remain in place only until the average upper layer temperature reaches 200 °C.[23]

The smoke that passes a closed barrier flows through its leakage paths: gaps, cracks and the edges of the closure. The flow is driven by the pressure difference across the barrier.[24] Klote writes the volume flow through such a path as the product of a flow coefficient, the leakage area and a velocity that grows with the square root of the pressure difference:[24][6]

V˙=CA2Δpρ

Symbol Description Unit
V˙ volume flow rate through the leakage path m³/s
C flow coefficient (0.6 to 0.7; 0.65 is commonly used) –
A flow area, also called leakage area m²
Δp pressure difference across the path Pa
ρ density of the gas entering the path kg/m³

The square-root form is reasonable for all flow paths except extremely narrow cracks.[24] The flow coefficient depends on the geometry of the path, turbulence and friction.[24] The same idea appears in the Introduction to Fire Safety Engineering, where the effective area of an opening is its real area times a contraction factor, for example 0.65.[25] The density of hot gas follows from the ideal gas law; at 200 °C it is about 0.75 kg/m³.[26]

A worked example uses the values that the Australian data sheet gives for a smoke-proof wall. Including general service penetrations, the leakage area is 1.5 × 10−4 m² per square metre of wall.[27] With C = 0.65, 25 Pa and smoke at 200 °C, the flow per square metre is 0.65 × 1.5 × 10−4 × √(2 × 25 / 0.75) ≈ 8.0 × 10−4 m³/s.[27][26] That is about 2.9 m³/h per square metre, close to the 3 m³/h per square metre stated in the data sheet.[27] Because the flow is proportional to the leakage area, a curtain with twice the gap area passes twice as much smoke at the same pressure. The data sheet warns that gaps in shutter assemblies, for example around the barrel of a roller shutter, are harder to protect and can allow significantly greater smoke spread.[7]

Line chart of leakage flow per square metre of barrier against pressure difference, for gas at 20 °C and at 200 °C.
Leakage flow per square metre of a smoke barrier with a leakage area of 1.5 × 10⁻⁴ m² per m², calculated with the orifice equation and C = 0.65. Based on Klote (2002), p. 4-280, and Australian Building Codes Board (2020a), Data Sheet C5, pp. 149 to 150.

Use in design

Closed curtains and shutters form part of the barriers used for compartmentation. Compartmentation is a passive smoke control approach that uses smoke barriers between smoke zones and keeps the openings in these barriers small.[16] NIST, quoting NFPA 92A, defines a smoke barrier as a continuous vertical or horizontal membrane that restricts smoke movement and that may or may not need a fire resistance rating.[16] In New Zealand, C/VM2 asks the designer to identify all separations and closures in the trial design.[23] Closures such as roller shutters are modelled as closed unless they are explicitly designed to open in the event of fire.[2]

In large open spaces, barriers work differently. Milke explains that smoke control by pressure differences and physical barriers is not feasible within atria and covered malls, so smoke spreads freely through the whole volume.[28] In atrium smoke control, physical barriers are one of several approaches, next to limiting the fire size and ventilation, and they serve to limit smoke spread to adjacent spaces.[29][30] How well such a barrier works depends on its leakage and on the pressure difference across it, and it must withstand smoke at elevated temperature.[30] In a tall atrium the smoke layer may be only slightly warmer than the ambient air.[30]

Draft curtains under a roof need a minimum depth. Cooper, following NFPA 204, recommends a depth of at least one fifth of the height between the base of the fire and the ceiling.[31] Once the smoke layer in the curtained space drops below the bottom edge of the curtain, smoke starts to flow under it into the adjacent spaces.[32] The ceiling jet under the roof is about one tenth of that height deep, and the smoke layer can only be modelled reliably once it is thicker than the jet.[31] A ceiling 10 m above the base of the fire, for example, needs curtains at least 2 m deep.[31]

Section under a roof: fire plume, thin ceiling jet, and a draft curtain at least one fifth of the fire-to-ceiling height deep.
Minimum depth of a draft curtain: at least 0.2 times the height from the fire base to the ceiling, twice the depth of the ceiling jet. Based on Cooper (2002b), pp. 3-229 and 3-234.

Closures are not always the best answer. The Dutch car park guidance accepts compartments of up to 1,000 m², based on the 2012 Building Decree, and allows fire-resistant rolling shutters between them.[11] It warns that smaller compartments can heat up faster towards flashover and make it harder to find the burning vehicle.[11] For that reason it prefers an open, clearly arranged area with a sprinkler system to further division into compartments.[11]

Reliability and limits

A deployable barrier depends on mechanical and electronic parts that must work during the fire. Data from the Tokyo Fire Department, reported in the Australian data sheets, put the reliability of fire doors with automatic closers at 97 %.[5] With an added hold-open device the value was 91 %, which implies about 94 % per hold-open unit.[5] The data sheet notes that it is unclear whether this estimate covers common mode failures.[5] Gaps around shutter assemblies add a second source of underperformance once the barrier is closed.[7]

In New Zealand, C/VM2 (second edition, 2025) contains design scenario RC, which tests what happens when a key fire safety system fails.[33] Key fire safety systems include fire doors, smoke control doors "or similar fire closures", and any feature that needs a mechanical or electronic component to activate during the fire.[33] The check applies where failure of a key system could expose, for example, more than 150 people to untenable conditions.[33] Each key system is assumed to fail in turn, and ASET must still exceed RSET.[34] Doors with hold-open devices to BS 7273.4, released by the fire alarm, are exempt in sprinklered buildings, but the text names doors rather than other closures.[33]

See also

Notes

  1. ↑ 1.0 1.1 Iqbal and Salley (2004), p. F-21.
  2. ↑ 2.0 2.1 2.2 2.3 Ministry of Business, Innovation and Employment (2025b), p. 15.
  3. ↑ 3.0 3.1 3.2 3.3 Lew et al. (2005), p. 163.
  4. ↑ 4.0 4.1 Australian Building Codes Board (2020a), Data Sheet C5, p. 147.
  5. ↑ 5.0 5.1 5.2 5.3 Australian Building Codes Board (2020a), Data Sheet C7, p. 216.
  6. ↑ 6.0 6.1 Australian Building Codes Board (2020a), Data Sheet C5, p. 149.
  7. ↑ 7.0 7.1 7.2 7.3 Australian Building Codes Board (2020a), Data Sheet C7, p. 196.
  8. ↑ Notarianni (2002), p. 5-45.
  9. ↑ 9.0 9.1 Cooper (2002b), p. 3-220.
  10. ↑ 10.0 10.1 10.2 Fanella et al. (2005b), p. 263.
  11. ↑ 11.0 11.1 11.2 11.3 11.4 Van der Graaf et al. (2021/2023), p. 35.
  12. ↑ Nolan (2000), as cited in Iqbal and Salley (2004), p. F-51.
  13. ↑ Babrauskas (2002b), p. 3-15.
  14. ↑ Australian Building Codes Board (2020a), Data Sheet C7, p. 201.
  15. ↑ Australian Building Codes Board (2020a), Data Sheet C3, p. 98.
  16. ↑ 16.0 16.1 16.2 Ferreira and Strege (2005), p. 6.
  17. ↑ Australian Building Codes Board (2020b), p. 100.
  18. ↑ Grill and Johnson (2005b), p. 22.
  19. ↑ Ministry of Business, Innovation and Employment (2025b), p. 64.
  20. ↑ Ministry of Business, Innovation and Employment (2025b), p. 66.
  21. ↑ Van Rossum (2027), §8.6.
  22. ↑ Australian Building Codes Board (2020a), Data Sheet C5, p. 148.
  23. ↑ 23.0 23.1 23.2 Ministry of Business, Innovation and Employment (2025b), p. 14.
  24. ↑ 24.0 24.1 24.2 24.3 Klote (2002), p. 4-280.
  25. ↑ Van Rossum (2027), §6.8.
  26. ↑ 26.0 26.1 Van Rossum (2027), §3.2.
  27. ↑ 27.0 27.1 27.2 Australian Building Codes Board (2020a), Data Sheet C5, p. 150.
  28. ↑ Milke (2002b), p. 4-292.
  29. ↑ Milke (2002b), p. 4-293.
  30. ↑ 30.0 30.1 30.2 Milke (2002b), p. 4-294.
  31. ↑ 31.0 31.1 31.2 Cooper (2002b), p. 3-234.
  32. ↑ Cooper (2002b), p. 3-229.
  33. ↑ 33.0 33.1 33.2 33.3 Ministry of Business, Innovation and Employment (2025b), p. 58.
  34. ↑ Ministry of Business, Innovation and Employment (2025b), p. 59.

References

  • Australian Building Codes Board. (2020a). Data sheets: Fire Safety Verification Method (Handbook annex, Print version 1.1).
  • Australian Building Codes Board. (2020b). Handbook: Fire Safety Verification Method (Print version 1.1).
  • Babrauskas, V. (2002b). Heat release rates. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 3-1–3-37). National Fire Protection Association; Society of Fire Protection Engineers.
  • Cooper, L. Y. (2002b). Smoke and heat venting. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 3-219–3-242). National Fire Protection Association; Society of Fire Protection Engineers.
  • Fanella, D. A., Derecho, A. T., & Ghosh, S. K. (2005b). Maintenance and modifications to structural systems (NIST NCSTAR 1-1C). National Institute of Standards and Technology.
  • Ferreira, M. J., & Strege, S. M. (2005). Smoke management systems (NIST NCSTAR 1-4D). National Institute of Standards and Technology.
  • Grill, R. A., & Johnson, D. A. (2005b). Fire protection and life safety provisions applied to the design and construction of WTC 1, 2, and 7 and post-construction provisions applied after occupancy (NIST NCSTAR 1-1D). 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.
  • Klote, J. H. (2002). Smoke control. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-274–4-291). National Fire Protection Association; Society of Fire Protection Engineers.
  • Lew, H. S., Bukowski, R. W., & Carino, N. J. (2005). Design, construction, and maintenance of structural and life safety systems (NIST NCSTAR 1-1). National Institute of Standards and Technology.
  • Milke, J. A. (2002b). Smoke management in covered malls and atria. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-292–4-310). National Fire Protection Association; Society of Fire Protection Engineers.
  • Ministry of Business, Innovation and Employment. (2025b). Verification Method C/VM2: Framework for fire safety design (2nd ed.).
  • Notarianni, K. A. (2002). Uncertainty. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 5-40–5-64). National Fire Protection Association; Society of Fire Protection Engineers.
  • Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). Fire safety of indoor car parks accommodating electrically powered vehicles. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
  • Van Rossum, E. (2027). Introduction to Fire Safety Engineering. Fire Safety Academy.
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