Skip to content
Upcoming courses

Fire hydrant: Difference between revisions

Tools
From Fire Safety Academy Wiki
← Older edit
VisualWikitext
Sanne (talk | contribs)
Bots
337 edits
Add diagrams fse-fire-hydrant-v1.svg, fse-fire-hydrant-v2.svg, fse-fire-hydrant-v3.svg (level-1 visual plan)
Mark (talk | contribs)
Bots
284 edits
Revise against the FSE wiki writing guidelines: corrections after independent fact-check (revised by Claude Opus 5.5)
 
(One intermediate revision by the same user not shown)
Line 1: Line 1:
A '''Fire hydrant''' is a device that provides water to fire department pumpers for firefighting. It forms a connection point between the available water infrastructure and the equipment used to deliver water to a fire. Its usefulness depends on access, flow, pressure, valve condition and the complete supply network.<ref name="NUREG-F25">U.S. Nuclear Regulatory Commission (2005), p. F-25.</ref><ref name="CVM2-53">Ministry of Business, Innovation and Employment (2025), p. 53.</ref>
A '''fire hydrant''' is a device that provides a water supply to fire department pumpers for use in fighting structure fires.<ref name="IS-F26">Iqbal and Salley (2004), p. F-26.</ref> 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.<ref name="Evans-18">Evans et al. (2005), p. 18.</ref><ref name="LV-229">Lawson and Vettori (2005), p. 229.</ref> Those connections let the fire department pump water into the fire protection systems of the building, such as its sprinklers and standpipes.<ref name="IS-F25">Iqbal and Salley (2004), p. F-25.</ref><ref name="Evans-9">Evans et al. (2005), p. 9.</ref> 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.<ref name="IS-1-2">Iqbal and Salley (2004), p. 1-2.</ref>


A hydrant does not itself extinguish a fire. Water must be transported through suitable hoses and applied by trained personnel, while the supply must remain available during operations. The hydrant's location and condition therefore need to be assessed together with vehicle access, hose deployment and fire conditions.<ref name="CVM2-54">Ministry of Business, Innovation and Employment (2025), pp. 53–55.</ref><ref name="Hopkins-xxxi">Hopkins, Schoenrock, and Budnick (2005), pp. xxxi–xxxv.</ref>
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.<ref name="Fleming-81">Fleming (2002), p. 4-81.</ref> 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.<ref name="MBIE-54">Ministry of Business, Innovation and Employment (2025b), p. 54.</ref> 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.<ref name="ABCB22">Australian Building Codes Board (2022), pp. 15–16.</ref> 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.<ref name="McA-304">McAllister et al. (2008), p. 304.</ref>


Hydrants are also distinct from sprinkler inlets and standpipes, although these provisions can be located close together. A fire department connection can supplement an installed system, while a standpipe distributes water to hose outlets within a building. Each provision has its own function and dependencies.<ref name="NUREG-F61">U.S. Nuclear Regulatory Commission (2005), pp. F-61–F-62.</ref><ref name="Hopkins-xxxv">Hopkins, Schoenrock, and Budnick (2005), p. xxxv.</ref>
== Definition and types ==


== Function and system boundary ==
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.<ref name="IS-F26" /> 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.<ref name="IS-F25" /> A standpipe system is the piping, risers, valves and hose connections that supply fire hoses inside a building for occupants or firefighters.<ref name="IS-F62">Iqbal and Salley (2004), p. F-62.</ref> A hydrant selected to measure the water flow available from a supply is called a flow hydrant.<ref name="IS-F32">Iqbal and Salley (2004), p. F-32.</ref> Its list of abbreviations also names double-outlet and quadruple-outlet fire hydrants and wall hydrants.<ref name="IS-G">Iqbal and Salley (2004), pp. G-3, G-9 and G-11.</ref>


The hydrant's primary function is to make water available to a pumping appliance. The appliance and its crew then deliver water through their hose systems. This makes the hydrant one part of a chain that includes municipal or private supply, connection, pumping, hoses and nozzles.<ref name="NUREG-F25" /><ref name="Hopkins-xxxv" />
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''.<ref name="Hopkins-xxxii">Hopkins et al. (2005), p. xxxii.</ref> The SFPE Handbook names NFPA 24 as the standard for the installation of private fire service mains and their appurtenances.<ref name="Fleming-73">Fleming (2002), p. 4-73.</ref> 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.<ref name="MBIE-54" /><ref name="MBIE-60">Ministry of Business, Innovation and Employment (2025b), p. 60.</ref> Inside tall buildings, standpipes supply the hose connections on each floor, a subject covered under [[Dry and wet risers]].<ref name="Evans-9" /> In WTC 7, one standpipe in a stairway supplied hose valves on the 45th to 47th floors and also a manifold roof hydrant.<ref name="Evans-28">Evans et al. (2005), p. 28.</ref>
[[File:fse-fire-hydrant-v1.svg|thumb|upright=1.5|alt=Source, hydrant, pumper, hoses and nozzle form a chain to the fire.|A hydrant supplies a pumping appliance rather than extinguishing directly. Based on U.S. Nuclear Regulatory Commission (2005), p. F-25 and Hopkins, Schoenrock, and Budnick (2005), pp. xxxi–xxxv.]]


[[Fire water supply]] includes the sources and infrastructure needed to provide that flow. NIST's WTC analysis describes municipal distribution, reserve tanks, pumps and fire department connections as different components. Those sources can have different capacities and failure modes.<ref name="Hopkins-xxxii">Hopkins, Schoenrock, and Budnick (2005), pp. xxxii–xxxv.</ref>
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.<ref name="IFEG-1.9-3">National Research Council of Canada et al. (2005), p. 1.9-3.</ref> The guidelines state that the location of hydrants and other fire service facilities affects the efficiency of fire suppression.<ref name="IFEG-1.9-5">National Research Council of Canada et al. (2005), p. 1.9-5.</ref> They also count the amount of available firefighting water among the factors that govern the capability of a fire service.<ref name="IFEG-1.9-5" /> Before the attack can begin, vehicles, hoses and other equipment may first need to be moved into position.<ref name="IFEG-1.9-4">National Research Council of Canada et al. (2005), p. 1.9-4.</ref>


A hydrant's static condition does not demonstrate adequate flow during an incident. Pressure can change as demand increases and as losses occur in the distribution network. The relevant assessment therefore includes the operating condition and not only the presence of a connection.<ref name="Hopkins-xli">Hopkins, Schoenrock, and Budnick (2005), pp. xli–xlii.</ref>
== From hydrant to nozzle ==


Water supply can be affected by physical damage or loss of power. NIST identifies city-main damage, pump-power loss and infrastructure failure as possible interruptions in its scenarios. A hydrant at a usable location can consequently be unable to support the intended operation.<ref name="Hopkins-xli" /><ref name="Hopkins-xlii" />
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.<ref name="Evans-18" /> In the second case, the standpipes and sprinklers of the building carry the water further.<ref name="Evans-9" /> 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.<ref name="LV-229" /> 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.<ref name="LV-229" />
[[File:fse-fire-hydrant-v1.svg|thumb|upright=1.5|alt=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 complete boundary also includes valves and isolation arrangements. Valves can allow parts of a network to be isolated, but an incorrect position can prevent supply. Inspection and operational information should make those dependencies visible to the responding personnel.<ref name="Hopkins-xxxv" /><ref name="NUREG-10-2">U.S. Nuclear Regulatory Commission (2005), p. 10-2.</ref>
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).<ref name="McA-77">McAllister et al. (2008), p. 77.</ref> High-pressure pumpers had a third stage that could supply 2 m³/min (500 gal/min) at 4.8 MPa (700 psi).<ref name="McA-77" /> The FDNY high-rise manual advised feeding a standpipe system with at least two pumpers at two different fire department connections.<ref name="McA-77" /> 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.<ref name="McA-77" />


== Municipal and private supplies ==
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.<ref name="LV-41">Lawson and Vettori (2005), p. 41.</ref> That half floor measured about 1,350 m², and the flow corresponds to roughly five hand lines of 63.5 mm diameter.<ref name="LV-41" /> 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.<ref name="LV-77">Lawson and Vettori (2005), p. 77.</ref>


Municipal networks distribute water through underground mains. NIST describes a gridded lower-Manhattan network with several possible flow paths, which reduces sensitivity to restrictions in any one path. That description is specific to the WTC area and is not a universal municipal arrangement.<ref name="Hopkins-xxxiii">Hopkins, Schoenrock, and Budnick (2005), p. xxxiii.</ref>
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.<ref name="NIPV-45">Van der Graaf et al. (2021/2023), p. 45.</ref> ''Introduction to Fire Safety Engineering'' explains that fire engines can work at low, medium or high pressure, each with a different volume flow.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref> Knowing the heat release rate of a burning object helps crews judge whether a fire can still be fought with a given flow.<ref name="VR-8.6" />


The same account reports expected flows in the local mains with little recognisable pressure reduction under normal conditions. Those values are observations for that system and period. They cannot be used to infer available flow or residual pressure in another network.<ref name="Hopkins-xxxiii" />
== Flow, pressure and testing ==


Reserve tanks can provide an initial or secondary supply. NIST describes tanks that allowed time for personnel to start pumps manually, while also providing a finite quantity. The intended response must account for how that finite duration interacts with pump activation and subsequent supply.<ref name="Hopkins-xxxv" />
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.<ref name="Titus-62">Titus (2002), p. 4-62.</ref> 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.<ref name="Titus-65">Titus (2002), p. 4-65.</ref> For full flow across a standard 63.5 mm (2½ in.) outlet, that coefficient is usually taken as 0.90.<ref name="Titus-65" /> 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.<ref name="Titus-65" />


Fire pumps can increase pressure to the required distribution system. They depend on suitable power, operation and maintenance. A pump that fails to start or loses power can make an otherwise intact pipe network unavailable.<ref name="Hopkins-xxxv" /><ref name="NUREG-10-2" />
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.<ref name="Fleming-81" /> The residual pressure is read from the same gauge while water flows from another hydrant, preferably downstream.<ref name="Fleming-81" /> 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.<ref name="Fleming-81" /> The resulting water supply curve is therefore a fingerprint of the supply and its piping.<ref name="Fleming-81" /> NUREG-1805 lists NFPA 291, ''Recommended Practice for Fire Flow Testing and Marking of Hydrants'' (2002 edition), among the American standards.<ref name="IS-E6">Iqbal and Salley (2004), p. E-6.</ref>


Redundancy can involve more than one source or supply route. NIST describes municipal connections, reserve tanks and fire department connections as supporting provisions. Their independence must be assessed, because shared mains, power or valves can still create common failure points.<ref name="Hopkins-xxxv" /><ref name="Hopkins-xli" />
Because a public supply is rarely without any flow, the static reading represents the network carrying only its ordinary demand.<ref name="Fleming-81" /> 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.<ref name="Fleming-81" /> 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).<ref name="Fleming-81" /> 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.<ref name="Fleming-81" />
[[File:fse-fire-hydrant-v2.svg|thumb|upright=1.5|alt=Municipal, tank, pump and fire-department supplies feed hydrants, with shared failure points.|Redundant supplies require independent availability when needed. Based on Hopkins, Schoenrock, and Budnick (2005), pp. xxxiv–xxxv and pp. xli–xlii.]]


== Firefighting access ==
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.<ref name="Hopkins-xxxiii">Hopkins et al. (2005), p. xxxiii.</ref> Water could flow along many paths through this grid, which kept friction losses small while large volumes were flowing.<ref name="Hopkins-xxxiii" /> 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.<ref name="Hopkins-xxxiv">Hopkins et al. (2005), p. xxxiv.</ref> The average static pressure of the grid was about 340 kPa (50 psi).<ref name="Hopkins-xxxix">Hopkins et al. (2005), p. xxxix.</ref>


[[Fire service access]] must allow a pumping appliance to reach a position from which personnel and hoses can be deployed effectively. C/VM2 uses a hard-standing and an unobstructed path to the building as part of its New Zealand firefighting scenario. The relevant connections must also remain accessible.<ref name="CVM2-53" />
== Location and access rules ==


C/VM2 refers to access within 20 m of firefighter entry points and installed sprinkler or hydrant inlets in its cited clause. This is a requirement of the second-edition New Zealand method, not a universal hydrant spacing rule. Other jurisdictions and building layouts must use their own criteria.<ref name="CVM2-53" />
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.<ref name="MBIE-53">Ministry of Business, Innovation and Employment (2025b), p. 53.</ref> 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.<ref name="MBIE-53" /> Clause C5.5 requires the means to deliver water for firefighting to all parts of the building.<ref name="MBIE-53" />


Access includes more than vehicle arrival. Personnel must reach the fire floor, search the area and protect their means of egress. Building information should help them identify the fire location, available systems and hazardous substances or processes.<ref name="CVM2-53" />
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.<ref name="MBIE-54" /> The second is an internal hydrant installed to NZS 4510 or approved by the National Commander of Fire and Emergency New Zealand.<ref name="MBIE-54" /> 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.<ref name="MBIE-55">Ministry of Business, Innovation and Employment (2025b), p. 55.</ref>
[[File:fse-fire-hydrant-v3.svg|thumb|upright=1.5|alt=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 (2025), pp. 53–55.]]


Hose deployment can determine whether a connection is practically usable. C/VM2 offers one provision based on reaching any point within a building within 75 m of a pumping appliance, approximately three hose lengths. That is a scenario-specific method, not a guarantee of safe or direct hose routing.<ref name="CVM2-54" />
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.<ref name="MBIE13-151">Ministry of Business, Innovation and Employment (2013), p. 151.</ref> Firefighting water must also be available near the fire.<ref name="MBIE13-151" /> 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.<ref name="MBIE13-196">Ministry of Business, Innovation and Employment (2013), p. 196.</ref>
[[File:fse-fire-hydrant-v3.svg|thumb|upright=1.5|alt=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.]]


Structural stability also affects access. C/VM2 calls for specified structures supporting firefighter access and rescue to remain stable during and after fire. A hydrant and hard-standing may be usable initially but become inaccessible if the building's condition changes.<ref name="CVM2-53" /><ref name="CVM2-54" />
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.<ref name="MBIE-53" /> 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.<ref name="MBIE-53" /> 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.<ref name="MBIE-54" />


== Hydrants and standpipe systems ==
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).<ref name="ABCB22" /> 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.<ref name="ABCB22" />


A [[Dry and wet risers]] system distributes water vertically within a building to hose outlets. NUREG-1805 defines a standpipe as piping, risers, valves and connections used by occupants or fire department personnel. Wet standpipes are permanently charged with water, while manual standpipes rely on the fire service to supply them.<ref name="NUREG-F61" />
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.<ref name="IFEG-2.9-4">National Research Council of Canada et al. (2005), p. 2.9-4.</ref> For indoor car parks in the Netherlands, NIPV notes that the time needed to bring water to the fire affects how the fire develops.<ref name="NIPV-66">Van der Graaf et al. (2021/2023), p. 66.</ref> 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.<ref name="NIPV-66" />


A hydrant can provide water to a pumping appliance, while a fire department connection can feed a standpipe or sprinkler system. These functions should not be conflated merely because they share a location or connection hardware. Their downstream networks and intended users differ.<ref name="Hopkins-xxxv" /><ref name="NUREG-F61" />
== Water supply behind the hydrant ==


NUREG-1805 describes standpipe classes according to intended use. Class I serves fire service or personnel trained in heavy streams, Class II concerns incipient-fire hose use, and Class III combines those features. Those classes are not the same as fuel-based fire classes.<ref name="NUREG-F61" />
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.<ref name="Hopkins-xxxv">Hopkins et al. (2005), p. xxxv.</ref> This main was fed by two redundant connections of about 410 mm (16 in.), and electric fire pumps maintained its operating pressure.<ref name="Hopkins-xxxv" /> 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.<ref name="Hopkins-xxxv" /> Without refilling, these tanks gave the maintenance staff about 10 minutes to start the manual fire pumps.<ref name="Hopkins-xxxv" />


NIST's WTC account describes standpipes in stairwells supplying pre-connected hoses on each floor. It also describes ground-level fire department connections that could supplement those systems. This illustrates how internal distribution and external supply can work together.<ref name="Hopkins-xxxiv">Hopkins, Schoenrock, and Budnick (2005), pp. xxxiv–xxxv.</ref>
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.<ref name="Hopkins-xxxix" /> Fourteen fire department connection stations at street level let the fire department add water and pressure.<ref name="Hopkins-xxxv" /> WTC 7, by contrast, was fed by two connections only about 3.7 m (12 ft) apart from the same city main.<ref name="Hopkins-xxxix" /><ref name="Hopkins-xl">Hopkins et al. (2005), p. xl.</ref> 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.<ref name="Hopkins-xli">Hopkins et al. (2005), p. xli.</ref> In New York, the fire department routinely provided a supplemental supply, which was considered infinite in duration.<ref name="Hopkins-xlii">Hopkins et al. (2005), p. xlii.</ref>
[[File:fse-fire-hydrant-v2.svg|thumb|upright=1.5|alt=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.]]


A [[Firefighting]] assessment must therefore identify the complete path. Municipal or reserve water reaches the hydrant or inlet, passes through pumps and risers, and reaches hose teams or fixed outlets. A failure at any stage can change the water available at the fire.<ref name="Hopkins-xli" /><ref name="NUREG-F61" />
== When the supply fails ==


== Flow, pressure and hose deployment ==
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.<ref name="IS-10-2">Iqbal and Salley (2004), p. 10-2.</ref> 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.<ref name="IS-10-2" /> 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.<ref name="Nowlen-13-7">Nowlen et al. (2005b), p. 13-7.</ref> It reports concern about cast-iron fire mains, because cast iron is seismically weak.<ref name="Nowlen-13-2">Nowlen et al. (2005b), p. 13-2.</ref> It also asks whether an alternative source of firefighting water, and enough hose to use it, is available.<ref name="Nowlen-13-8">Nowlen et al. (2005b), p. 13-8.</ref>


Hydraulic assessment considers available flow and pressure after losses through the network. NIST used minimum delivered density and pressure requirements to evaluate installed systems under specified conditions. Those criteria and design areas belong to the cited standards and analysis, not to every building.<ref name="Hopkins-xli" />
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.<ref name="Hopkins-xxxi">Hopkins et al. (2005), p. xxxi.</ref> Around 11:30 a.m., there was no water in the hydrant system or in the standpipes of WTC 7.<ref name="McA-78">McAllister et al. (2008), p. 78.</ref> 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.<ref name="LV-110">Lawson and Vettori (2005), p. 110.</ref> Fire boats on the Hudson River began stretching lines towards the site, and engines elsewhere relayed water from hydrants that still worked.<ref name="LV-110" /><ref name="LV-229" />


The analysis found capacity to control several small fires under normal operating assumptions, but performance degraded as the assumed operating area increased. This illustrates the difference between available hydraulic capacity and the fire's actual demand. A system can have excess capacity for one scenario and be overwhelmed by a larger one.<ref name="Hopkins-xli" />
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.<ref name="McA-627">McAllister et al. (2008), p. 627.</ref> 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.<ref name="McA-304" /> 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.<ref name="McA-77" /><ref name="McA-78" />


NIST also found one booster pump undersized relative to the cited NFPA 14 requirement, while noting it met the local code. This shows the importance of distinguishing different acceptance bases. A component can satisfy one code and still fall below another engineering benchmark.<ref name="Hopkins-xli" />
== Maintenance, information and limits ==


Hose length and route add operational losses and deployment time. C/VM2 uses approximate hose lengths in its method to address whether water can reach all parts of the building. Actual routes can be indirect and must be considered with the firefighters' access and exit conditions.<ref name="CVM2-54" />
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.<ref name="IFEG-1.9-8">National Research Council of Canada et al. (2005), p. 1.9-8.</ref> In some jurisdictions, essential safety provisions may secure that maintenance.<ref name="IFEG-1.9-8" /> 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.<ref name="IFEG-1.9-2">National Research Council of Canada et al. (2005), p. 1.9-2.</ref> 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.<ref name="MBIE13-35">Ministry of Business, Innovation and Employment (2013), p. 35.</ref>


The fire environment affects whether water can be applied safely. C/VM2 sets conditions for radiation and smoke-layer height at first water application in particular unsprinklered firecells. Those criteria apply to the specified New Zealand scenario and do not guarantee safe conditions later.<ref name="CVM2-53" />
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.<ref name="MBIE-53" /> It also requires information on any hazardous substances or processes in the building.<ref name="MBIE-53" /> 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.<ref name="McA-77" /> The operations and maintenance manual of WTC 7 included a riser diagram showing the arrangement of the valves.<ref name="McA-78" />


== Reliability and common failures ==
''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.<ref name="VR-9.3">Van Rossum (2027), §9.3 (Results from zone models).</ref> That decision always rests with the crews at the scene.<ref name="VR-9.3" /> The International Fire Engineering Guidelines likewise state that the analysis of occupant evacuation should not rely on fire service intervention.<ref name="IFEG-1.9-1">National Research Council of Canada et al. (2005), p. 1.9-1.</ref> 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.<ref name="WH-5-5">Watts and Hall (2002), p. 5-5.</ref>
 
A hydrant and its connection can be physically intact while water is unavailable. NUREG-1805 lists empty tanks, broken headers, closed valves and pump failures as possible sprinkler-supply failures. The same systems-thinking is necessary when evaluating hydrant-supported manual firefighting.<ref name="NUREG-10-2" /><ref name="Hopkins-xli" />
 
Shared infrastructure can defeat apparent redundancy. Several outlets connected to one damaged main or pump can lose supply together. NIST's evaluation considers initial damage to risers and water-supply components when estimating system performance during the incident.<ref name="Hopkins-xlii" />
 
Reserve arrangements need realistic timing. A tank with limited duration may support only the period before pumps or alternative supplies operate. That duration must be compared with detection, response, deployment and activation times rather than treated as unlimited backup.<ref name="Hopkins-xxxv" />
 
Damage to distribution outside the building can matter as much as damage within it. NIST describes water-system damage in the streets around the WTC after the collapses. Access to an external hydrant therefore does not guarantee that the municipal supply remains available.<ref name="Hopkins-xxxi" />
 
Reliability assessment should distinguish availability, delivered flow and suppression outcome. A source can be available without providing sufficient pressure, and water can reach the fire without controlling it. Each stage needs relevant evidence rather than one general reliability claim.<ref name="Hopkins-xli" /><ref name="Fleming-4-73">Fleming (2002), p. 4-73.</ref>
 
== Inspection and operational information ==
 
Inspection should confirm the hydrant's identity, access and supply arrangement. A connection that is blocked by vehicles or altered surroundings can be unavailable even if its mechanical condition is satisfactory. Access should be reviewed as part of the operating building, not only on the original plan.<ref name="CVM2-53" /><ref name="IFEG-1-8-14">Australian Building Codes Board et al. (2005), pp. 1.8-13–1.8-14.</ref>
 
Operational information should identify which parts of the network each connection serves. Isolation valves and multiple inlets can create different supply paths. Responding personnel need clear information about available systems and hazardous conditions to use those paths appropriately.<ref name="CVM2-53" /><ref name="Hopkins-xxxv" />
 
Maintenance should preserve valves, pumps, tanks and connections as a functioning chain. Testing only one component can miss a failed common path. Restoration after impairment should verify the supply at the relevant outlet and operating condition.<ref name="NUREG-10-2" /><ref name="ABCB-130">Australian Building Codes Board (2020), pp. 129–130.</ref>
 
Documentation should include the source, supply route and relevant standards of record. NIST reconstructed these arrangements from drawings, specifications, procedures and other collected records. Such records make it possible to evaluate capability and interpret changes over time.<ref name="Hopkins-xxxii" />
 
Changes to roads, hard-standing, building entrances and internal routes can alter effective access. A hydrant that was once easy to reach may become difficult to use without any change to the hydrant itself. Periodic review should include those physical and operational changes.<ref name="CVM2-54" /><ref name="IFEG-0-3-8">Australian Building Codes Board et al. (2005), p. 0.3-8.</ref>
 
== Evaluation and common misunderstandings ==
 
A hydrant is not a guarantee of unlimited water. Available flow depends on the municipal or private source, pumps, tanks, distribution and continued operation. The duration and independence of each source must be evaluated for the scenario.<ref name="Hopkins-xxxv" /><ref name="Hopkins-xli" />
 
A hydrant is also not the same as a standpipe or a sprinkler inlet. These provisions can share connections and water sources, but they serve different downstream purposes. The system being supplied must be identified before assessing performance.<ref name="NUREG-F61" /><ref name="Hopkins-xxxv" />
 
Location alone does not prove accessibility. Vehicle hard-standing, unobstructed paths, hose deployment and fire conditions all affect whether water can be applied. C/VM2's scenario addresses these as connected firefighting requirements rather than as a simple distance check.<ref name="CVM2-53" /><ref name="CVM2-54" />
 
Historical calculations and case studies do not establish universal flow or pressure. NIST's WTC analysis uses building-specific infrastructure, design criteria and fire assumptions. Those conditions must be retained when drawing lessons from its results.<ref name="Hopkins-xli" />
 
The useful assessment therefore traces water from source to application. It checks connection access, supply reliability, pressure, hose deployment and firefighter safety. A hydrant provides valuable protection only when that complete sequence remains functional.<ref name="NUREG-F25" /><ref name="CVM2-53" />
 
Hydrant assessment should also distinguish normal system availability from incident conditions. A routine flow test may demonstrate performance at one demand, while a larger fire or damaged main produces a different result. The scenario used for assessment should state the demand, supply route and any impairments being considered.<ref name="Hopkins-xli" /><ref name="Hopkins-xlii" />
 
Operational maps should support the connection between source and destination. They can show which valves, risers and zones supply a particular area and where alternative connections are located. This helps responders understand whether a failed path can be isolated and another used without assuming that every connection is equivalent.<ref name="Hopkins-xxxv" /><ref name="CVM2-53" />
 
For fire service planning, the time to establish supply belongs in the response sequence. Detection, appliance travel, hose deployment and pump activation occur before water reaches the fire. C/VM2 provides method-specific intervention times for its scenarios and also permits another time supported by a brigade intervention model.<ref name="CVM2-54" />
 
The review should end with a clear statement of the conditions under which the hydrant can deliver its intended function. That statement should identify source, access, pressure and flow evidence, operating assumptions and any remaining uncertainty. It should not imply that the connection alone proves successful fire control.<ref name="Hopkins-xli" /><ref name="NUREG-F25" />


== See also ==
== See also ==


* [[Dry and wet risers]]
* [[Hose reel]]
* [[Fire water supply]]
* [[Fire extinguisher]]
* [[Firefighting]]
* [[Firefighting lift]]
* [[Fire classes]]


== Notes ==
== Notes ==


<ref name="Hopkins-xlii">Hopkins, Schoenrock, and Budnick (2005), pp. xli–xlii.</ref>
<references />
<references />


== References ==
== References ==


* Australian Building Codes Board. (2020). ''Fire safety verification method data sheets'' (Version 1.1). Author.
* Australian Building Codes Board. (2022). ''Fire Safety Verification Method Standard 2022''.
* 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.
* 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 (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* 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.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.). New Zealand Government.
* 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.
* U.S. Nuclear Regulatory Commission. (2005). ''Fire dynamics tools: Quantitative fire hazard analysis methods for the U.S. nuclear regulatory commission fire protection inspection program'' (NUREG-1805). Author.
* 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.


[[Category:Firefighting & Fire Service]]
[[Category:Firefighting & Fire Service]]

Latest revision as of 19:36, 2 November 2026

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"