Skip to content
Upcoming courses

Fire hydrant

Tools
From Fire Safety Academy Wiki
Revision as of 19:36, 2 November 2026 by Mark (talk | contribs) (Revise against the FSE wiki writing guidelines: corrections after independent fact-check (revised by Claude Opus 5.5))
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Contents
  1. 1Definition and types
  2. 2From hydrant to nozzle
  3. 3Flow, pressure and testing
  4. 4Location and access rules
  5. 5Water supply behind the hydrant
  6. 6When the supply fails
  7. 7Maintenance, information and limits
  8. 8See also
  9. 9Notes
  10. 10References

A fire hydrant is a device that provides a water supply to fire department pumpers for use in fighting structure fires.[1] Fire engines connect to it and pump the water onwards, through hose lines to the fire or into the fire department connections of a building.[2][3] Those connections let the fire department pump water into the fire protection systems of the building, such as its sprinklers and standpipes.[4][5] In the defence-in-depth approach used for US nuclear power plants, fire hydrants, hose stations and water supply systems are among the measures that limit fire spread.[6]

The water a hydrant can deliver depends on the mains behind it, and hydrants serve as the measuring points when the flow and pressure of a supply are tested.[7] Rules for hydrants differ between countries. In New Zealand, Verification Method C/VM2 (second edition, 2025) accepts, for example, a pumping appliance parked so that every point of a building can be reached within 75 m, about three hose lengths.[8] In Australia, the fire brigade intervention scenario of the Fire Safety Verification Method Standard 2022 requires external hydrants for every building and internal hydrants in larger or taller ones.[9] A hydrant is only as reliable as its supply: after the World Trade Center (WTC) towers in New York collapsed in 2001, there was no usable water in lower Manhattan's hydrant system.[10]

Definition and types

The glossary of NUREG-1805, a report of the US Nuclear Regulatory Commission, defines a hydrant by its purpose: it supplies water to fire department pumpers.[1] A fire department connection works the other way round. It is a device through which the fire department pumps water from its trucks into a fire protection system.[4] A standpipe system is the piping, risers, valves and hose connections that supply fire hoses inside a building for occupants or firefighters.[11] A hydrant selected to measure the water flow available from a supply is called a flow hydrant.[12] Its list of abbreviations also names double-outlet and quadruple-outlet fire hydrants and wall hydrants.[13]

The word covers more than the street hydrant on a public main. The NIST investigation of the WTC cites the American standard NFPA 14 as the Standard for the Installation of Standpipe, Private Hydrant, and Hose Systems.[14] The SFPE Handbook names NFPA 24 as the standard for the installation of private fire service mains and their appurtenances.[15] In New Zealand, C/VM2 refers to an internal hydrant installed to NZS 4510, Fire hydrant systems for buildings, and lists its 2008 edition with Amendment 1.[8][16] Inside tall buildings, standpipes supply the hose connections on each floor, a subject covered under Dry and wet risers.[5] In WTC 7, one standpipe in a stairway supplied hose valves on the 45th to 47th floors and also a manifold roof hydrant.[17]

In the International Fire Engineering Guidelines (2005 edition), the hydrant layout is an input to the analysis of fire service intervention, agreed in the fire engineering brief.[18] The guidelines state that the location of hydrants and other fire service facilities affects the efficiency of fire suppression.[19] They also count the amount of available firefighting water among the factors that govern the capability of a fire service.[19] Before the attack can begin, vehicles, hoses and other equipment may first need to be moved into position.[20]

From hydrant to nozzle

In firefighting, a hydrant does not put out a fire on its own. An engine connected to it pumps the water onwards, either through hose lines or into the fire department connections of a building.[2] In the second case, the standpipes and sprinklers of the building carry the water further.[5] The NIST timeline of the 2001 WTC response records engines that hooked up to hydrants that still worked and relayed the water to other engines.[3] One engine took water from a hydrant on West Street, laid an 89 mm (3½ in.) supply line to a tower ladder and also supplied the standpipe of a neighbouring building.[3]

Source, hydrant, pumper, hoses and nozzle form a chain to the fire.
A hydrant supplies a pumping appliance rather than extinguishing directly. Based on Iqbal and Salley (2004), p. F-26 and Evans et al. (2005), p. 18.

The New York City fire department (FDNY) used two kinds of pumper at fires in high-rise buildings. Conventional pumpers had two-stage pumps of 4 or 8 m³/min (1,000 or 2,000 gal/min).[21] High-pressure pumpers had a third stage that could supply 2 m³/min (500 gal/min) at 4.8 MPa (700 psi).[21] The FDNY high-rise manual advised feeding a standpipe system with at least two pumpers at two different fire department connections.[21] Its recommended pump pressures allowed for the nozzle pressure, the height of the floor and the friction losses in the building's pipes and in the hose lines.[21]

The flow a fire needs can be far more than one hose line delivers. Using standard fire service methods, the NIST report on the emergency response estimated that about 4,700 L/min (1,250 gal/min) would be needed to extinguish a fire on half a floor of a WTC tower.[22] That half floor measured about 1,350 m², and the flow corresponds to roughly five hand lines of 63.5 mm diameter.[22] A full floor would have needed about 9,400 L/min and some ten hose lines, an operation for at least 15 to 20 engine companies.[23]

For car fires, the Netherlands Institute for Public Safety (NIPV) gives much smaller rules of thumb. A high-pressure jet of 125 L/min is generally sufficient up to a heat release rate of 2.5 MW, and a low-pressure jet of 450 L/min up to 10 MW.[24] Introduction to Fire Safety Engineering explains that fire engines can work at low, medium or high pressure, each with a different volume flow.[25] Knowing the heat release rate of a burning object helps crews judge whether a fire can still be fought with a given flow.[25]

Flow, pressure and testing

The flow a hydrant can give depends on the pressure in the main and on the outlet. In the SFPE Handbook chapter on hydraulics, Titus explains that water discharging into the open air from a tank, hydrant or nozzle is affected by the area and shape of the opening.[26] The flow from a hydrant outlet is normally found from the outlet diameter, the pressure measured with a pitot gauge in the stream and a coefficient for the outlet shape.[27] For full flow across a standard 63.5 mm (2½ in.) outlet, that coefficient is usually taken as 0.90.[27] Without a pitot gauge, the flow can be estimated from the outlet height and the distance the stream travels, a method Titus calls relatively inaccurate but useful as a bounding guide.[27]

Hydrants are also the usual measuring points when a public or private water supply is tested. In the method that Fleming describes in the SFPE Handbook, the static pressure is read from a gauge on one hydrant.[7] The residual pressure is read from the same gauge while water flows from another hydrant, preferably downstream.[7] The static pressure mainly reflects elevated tanks and running pumps, while the drop to the residual pressure reflects friction and other losses in the pipes.[7] The resulting water supply curve is therefore a fingerprint of the supply and its piping.[7] NUREG-1805 lists NFPA 291, Recommended Practice for Fire Flow Testing and Marking of Hydrants (2002 edition), among the American standards.[28]

Because a public supply is rarely without any flow, the static reading represents the network carrying only its ordinary demand.[7] Fleming gives a worked example. A supply tested at a static pressure of 6.9 bar (100 psi) fell to a residual pressure of 5.5 bar (80 psi) while 3,785 L/min (1,000 gpm) flowed.[7] Read from the plotted supply curve, the same supply would still give about 6.2 bar (90 psi) at 1,703 L/min (450 gpm).[7] In the American sprinkler design practice that Fleming describes, the demand of the system, including an allowance for hose streams, should lie below this curve.[7]

Real networks differ widely. Around the WTC, the city supply was a gridded network of ductile iron mains of about 510 and 300 mm (20 in. and 12 in.) diameter.[29] Water could flow along many paths through this grid, which kept friction losses small while large volumes were flowing.[29] The standard flows of about 1,900 L/min (500 gal/min) in the smaller mains and about 2,800 L/min (750 gal/min) in the larger ones typically caused no recognisable pressure drop.[30] The average static pressure of the grid was about 340 kPa (50 psi).[31]

Location and access rules

Where hydrants and fire engines must be placed is set by national rules, and these rules differ. In New Zealand, Verification Method C/VM2 (second edition, 2025) sets out the Building Code clauses for firefighting operations.[32] Clause C5.3 requires fire service access for vehicles to a hard-standing with an unobstructed path to the building within 20 m of the firefighter entrance and of any sprinkler or hydrant inlets.[32] Clause C5.5 requires the means to deliver water for firefighting to all parts of the building.[32]

C/VM2 accepts two ways to meet clause C5.5. The first is a pumping appliance parked so close that any point in the building lies within 75 m, about three hose lengths.[8] The second is an internal hydrant installed to NZS 4510 or approved by the National Commander of Fire and Emergency New Zealand.[8] For intermediate floors, a comment accepts a hydrant in a safe path no more than 40 m from the most remote point. This corresponds to about two hose lengths, with some allowance for an indirect route.[33]

The 2013 commentary on the first edition of C/VM2 explains the purpose of these clauses. For the officer in charge to judge an attack safely, information must be available on arrival and a protected route must lead to the upper floors.[34] Firefighting water must also be available near the fire.[34] In the commentary's example of a sprinklered hotel, a pumping appliance parked within 5.0 m of the building takes water from street hydrants. Every point of the ground floor then lies within three hose lengths (75 m), while building fire hydrant systems in the stairways serve the upper floors.[35]

Pumper at hard-standing connects to hydrant and hoses reach fire through protected access.
Firefighting access includes vehicles, connections, internal routes and safe egress. Based on Ministry of Business, Innovation and Employment (2025b), pp. 53–55.

The second edition also sets conditions for the moment firefighters first apply water in some unsprinklered firecells. These are firecells within 15 m of a relevant boundary with a fire load above 20 TJ or a floor area above 5,000 m².[32] At that moment, the radiation at 1.5 m above the floor may not exceed 4.5 kW/m², and the smoke layer must be at least 2 m above the floor.[32] The moment may be taken as 1,200 s after ignition, or 1,000 s where automatic detection is directly connected to a remote receiving centre.[8]

In Australia, the Fire Safety Verification Method Standard 2022 includes a fire brigade intervention scenario for buildings within 50 km road travel of a fire station. Compliance is shown with the Fire Brigade Intervention Model of the Australasian Fire and Emergency Service Authorities Council (AFAC).[9] Table 2.8 of the standard requires external fire hydrants for every building. Internal hydrants are required in buildings of more than three levels. They are also required where the distance to all points exceeds 100 m in a sprinklered building, or 70 m in one without sprinklers.[9]

Where the water is not enough, tactics change. A fire service with too little water or too few firefighters may switch from fighting the fire to stopping its spread to adjoining buildings, according to the International Fire Engineering Guidelines.[36] For indoor car parks in the Netherlands, NIPV notes that the time needed to bring water to the fire affects how the fire develops.[37] A dry riser can shorten the attack, because less hose has to be rolled out. NIPV therefore advises placing it where the fire service enters the car park.[37]

Water supply behind the hydrant

Every hydrant depends on the fire water supply behind it: the mains and, in larger systems, tanks, pumps and connections. The NIST investigation describes such a system at the WTC in detail. The complex took its water from the city distribution system through a fire main that looped the site.[38] This main was fed by two redundant connections of about 410 mm (16 in.), and electric fire pumps maintained its operating pressure.[38] Emergency generators provided back-up power, and tanks of about 19 m³ (5,000 gal) in the towers held the first water for the fire brigade or the fire department.[38] Without refilling, these tanks gave the maintenance staff about 10 minutes to start the manual fire pumps.[38]

Redundancy only helps when the supply routes are independent. The towers had two connections, at Vesey Street and Liberty Street, with isolation valves so that either main could operate on its own.[31] Fourteen fire department connection stations at street level let the fire department add water and pressure.[38] WTC 7, by contrast, was fed by two connections only about 3.7 m (12 ft) apart from the same city main.[31][39] A loss of power to its automatic fire pump or significant damage to that main could interrupt the supply to the sprinklers on floors 1 to 20.[40] In New York, the fire department routinely provided a supplemental supply, which was considered infinite in duration.[41]

Municipal main, reserve tank, fire pump and fire department connection feed one distribution system, with shared failure points.
Redundant supplies require independent availability when needed. Based on Hopkins et al. (2005), pp. xxxiv–xxxv and pp. xxxix–xli.

When the supply fails

Many causes of a failed supply lie away from the hydrant itself. For sprinkler systems, NUREG-1805 lists a closed water supply valve, a broken supply header and an empty water tank.[42] An electric fire pump may fail to start after a power failure, and a diesel pump through poor maintenance, dead batteries or a lack of fuel.[42] For US nuclear power plants, NUREG/CR-6850 asks whether an earthquake could disable fire pumps, water piping, standpipes and tanks at the same time.[43] It reports concern about cast-iron fire mains, because cast iron is seismically weak.[44] It also asks whether an alternative source of firefighting water, and enough hose to use it, is available.[45]

The attacks of 11 September 2001 showed how a hydrant network can fail in a large incident. The collapse of the two towers damaged the city water system in the surrounding streets.[46] Around 11:30 a.m., there was no water in the hydrant system or in the standpipes of WTC 7.[47] An FDNY engine at the corner of WTC 7 was still connected to a hydrant with its pump running, although the engine itself was on fire.[48] Fire boats on the Hudson River began stretching lines towards the site, and engines elsewhere relayed water from hydrants that still worked.[48][3]

Rescue work, care for the injured and the loss of hydrant water meant that the fire department could not consider fighting the WTC 7 fires until about 1:00 p.m.[49] At about 2:30 p.m. it ordered its personnel to withdraw from the building. The reasons included growing fires, possible structural damage, the loss of many fire department assets and the lack of usable water in the hydrant system.[10] The city mains had also been the only supply for the sprinklers on the lowest 20 floors. Fires on the 7th to 13th floors therefore went unchecked by sprinklers.[21][47]

Maintenance, information and limits

A hydrant only helps if crews can reach it and it works when needed. The International Fire Engineering Guidelines list perimeter roads for fire service access and equipment such as hydrants among the items whose design and maintenance effective intervention needs.[50] In some jurisdictions, essential safety provisions may secure that maintenance.[50] The guidelines also note that the fire service part of a design may change over a building's life, through changes in fire stations, budgets, equipment and traffic.[51] The 2013 commentary on C/VM2 reads New Zealand Building Code clause C5.8 as requiring hydrants and other fire safety systems to meet acceptable standards for design, construction, installation and maintenance.[52]

Firefighters also need to know what each connection serves. New Zealand's clause C5.7 requires clear information so that firefighters can locate the fire and identify the fire safety systems in the building.[32] It also requires information on any hazardous substances or processes in the building.[32] In New York, colour-coded caps showed whether a fire department connection fed a standpipe, a sprinkler system, a combined system or a high-pressure supply.[21] The operations and maintenance manual of WTC 7 included a riser diagram showing the arrangement of the valves.[47]

Introduction to Fire Safety Engineering stresses that a positive result of a fire safety engineering analysis does not mean the fire service will attack from inside.[53] That decision always rests with the crews at the scene.[53] The International Fire Engineering Guidelines likewise state that the analysis of occupant evacuation should not rely on fire service intervention.[54] It is misleading to give hydrants a fixed score in a risk checklist. The SFPE Handbook notes that the relative value of hydrants, sprinklers and extinguishers depends on other features of a building's form and use.[55]

See also

Notes

  1. ↑ 1.0 1.1 Iqbal and Salley (2004), p. F-26.
  2. ↑ 2.0 2.1 Evans et al. (2005), p. 18.
  3. ↑ 3.0 3.1 3.2 3.3 Lawson and Vettori (2005), p. 229.
  4. ↑ 4.0 4.1 Iqbal and Salley (2004), p. F-25.
  5. ↑ 5.0 5.1 5.2 Evans et al. (2005), p. 9.
  6. ↑ Iqbal and Salley (2004), p. 1-2.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Fleming (2002), p. 4-81.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Ministry of Business, Innovation and Employment (2025b), p. 54.
  9. ↑ 9.0 9.1 9.2 Australian Building Codes Board (2022), pp. 15–16.
  10. ↑ 10.0 10.1 McAllister et al. (2008), p. 304.
  11. ↑ Iqbal and Salley (2004), p. F-62.
  12. ↑ Iqbal and Salley (2004), p. F-32.
  13. ↑ Iqbal and Salley (2004), pp. G-3, G-9 and G-11.
  14. ↑ Hopkins et al. (2005), p. xxxii.
  15. ↑ Fleming (2002), p. 4-73.
  16. ↑ Ministry of Business, Innovation and Employment (2025b), p. 60.
  17. ↑ Evans et al. (2005), p. 28.
  18. ↑ National Research Council of Canada et al. (2005), p. 1.9-3.
  19. ↑ 19.0 19.1 National Research Council of Canada et al. (2005), p. 1.9-5.
  20. ↑ National Research Council of Canada et al. (2005), p. 1.9-4.
  21. ↑ 21.0 21.1 21.2 21.3 21.4 21.5 McAllister et al. (2008), p. 77.
  22. ↑ 22.0 22.1 Lawson and Vettori (2005), p. 41.
  23. ↑ Lawson and Vettori (2005), p. 77.
  24. ↑ Van der Graaf et al. (2021/2023), p. 45.
  25. ↑ 25.0 25.1 Van Rossum (2027), §8.6.
  26. ↑ Titus (2002), p. 4-62.
  27. ↑ 27.0 27.1 27.2 Titus (2002), p. 4-65.
  28. ↑ Iqbal and Salley (2004), p. E-6.
  29. ↑ 29.0 29.1 Hopkins et al. (2005), p. xxxiii.
  30. ↑ Hopkins et al. (2005), p. xxxiv.
  31. ↑ 31.0 31.1 31.2 Hopkins et al. (2005), p. xxxix.
  32. ↑ 32.0 32.1 32.2 32.3 32.4 32.5 32.6 Ministry of Business, Innovation and Employment (2025b), p. 53.
  33. ↑ Ministry of Business, Innovation and Employment (2025b), p. 55.
  34. ↑ 34.0 34.1 Ministry of Business, Innovation and Employment (2013), p. 151.
  35. ↑ Ministry of Business, Innovation and Employment (2013), p. 196.
  36. ↑ National Research Council of Canada et al. (2005), p. 2.9-4.
  37. ↑ 37.0 37.1 Van der Graaf et al. (2021/2023), p. 66.
  38. ↑ 38.0 38.1 38.2 38.3 38.4 Hopkins et al. (2005), p. xxxv.
  39. ↑ Hopkins et al. (2005), p. xl.
  40. ↑ Hopkins et al. (2005), p. xli.
  41. ↑ Hopkins et al. (2005), p. xlii.
  42. ↑ 42.0 42.1 Iqbal and Salley (2004), p. 10-2.
  43. ↑ Nowlen et al. (2005b), p. 13-7.
  44. ↑ Nowlen et al. (2005b), p. 13-2.
  45. ↑ Nowlen et al. (2005b), p. 13-8.
  46. ↑ Hopkins et al. (2005), p. xxxi.
  47. ↑ 47.0 47.1 47.2 McAllister et al. (2008), p. 78.
  48. ↑ 48.0 48.1 Lawson and Vettori (2005), p. 110.
  49. ↑ McAllister et al. (2008), p. 627.
  50. ↑ 50.0 50.1 National Research Council of Canada et al. (2005), p. 1.9-8.
  51. ↑ National Research Council of Canada et al. (2005), p. 1.9-2.
  52. ↑ Ministry of Business, Innovation and Employment (2013), p. 35.
  53. ↑ 53.0 53.1 Van Rossum (2027), §9.3 (Results from zone models).
  54. ↑ National Research Council of Canada et al. (2005), p. 1.9-1.
  55. ↑ Watts and Hall (2002), p. 5-5.

References

  • Australian Building Codes Board. (2022). Fire Safety Verification Method Standard 2022.
  • Evans, D. D., Peacock, R. D., Kuligowski, E. D., Dols, W. S., & Grosshandler, W. L. (2005). Active fire protection systems (NIST NCSTAR 1-4). National Institute of Standards and Technology.
  • Fleming, R. P. (2002). Automatic sprinkler system calculations. 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. 4-72–4-87). National Fire Protection Association; Society of Fire Protection Engineers.
  • Hopkins, M., Schoenrock, J., & Budnick, E. (2005). Fire suppression systems (NIST NCSTAR 1-4B). 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.
  • Lawson, J. R., & Vettori, R. L. (2005). The emergency response operations (NIST NCSTAR 1-8). National Institute of Standards and Technology.
  • McAllister, T. P., Gann, R. G., Averill, J. D., Gross, J. L., Grosshandler, W. L., Lawson, J. R., McGrattan, K. B., Pitts, W. M., Prasad, K. R., Sadek, F. H., & Nelson, H. E. (2008). Structural fire response and probable collapse sequence of World Trade Center Building 7 (NIST NCSTAR 1-9, Vols. 1–2). National Institute of Standards and Technology.
  • Ministry of Business, Innovation and Employment. (2013). Commentary for Building Code clauses C1–C6 and Verification Method C/VM2.
  • 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.
  • Nowlen, S. P., Najafi, B., Wyant, F. J., Forester, J., Kazarians, M., Kolaczkowski, A., Joglar, F., Funk, D., Hannaman, G., & Anoba, R. (2005b). EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Vol. 2. Detailed methodology (NUREG/CR-6850; EPRI 1011989). Electric Power Research Institute; U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research.
  • Titus, J. J. (2002). Hydraulics. 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. 4-44–4-71). 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.
  • Watts, J. M., Jr., & Hall, J. R., Jr. (2002). Introduction to fire risk analysis. 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. 5-1–5-7). National Fire Protection Association; Society of Fire Protection Engineers.
Retrieved from "https://fire-safety.academy/w/index.php?title=Fire_hydrant&oldid=2800"