Technical·8 min read
Fire Hydrant System, Hose Cabinets and Fire Department Connection: A Design Guide
A facility's firefighting water is built in three layers: the hydrant system outside, fire hose cabinets inside, and the fire department connection that links both to the fire engine. We cover hydrant spacing, pipe specs, frost depth, bedding/sleeving, NRS valve and Post Indicator requirements, and FDC design from an engineering perspective.
A-Pro Engineering
A facility’s firefighting water is not a single component; it is made of complementary layers: the outdoor hydrant system surrounding the building, the fire hose cabinets that enable first response inside, the landing valve from which firefighters draw water off the standpipe, and the fire department connection (FDC) through which a fire engine pumps water into the system from outside. All of these are fed by the fire pump and water tank behind them. In this article we cover each layer — spacing, pipe specs, frost protection, valve requirements and design detail — from an engineering perspective.
1. Fire hydrant system (external response)
The hydrant system lets the fire brigade and external response teams reach high-flow water fast. Above-ground hydrants are placed at set intervals along an underground main that rings the building.
Spacing and performance (BYKHY Article 95)
- The spacing between hydrants is set by the risk class: no more than 50 m very-high-risk, 100 m high-risk, 125 m medium-risk, 150 m low-risk.
- Hydrants are normally sited 5–15 m from the protected building, at accessible points a fire engine can pull up to.
- At the hydrant outlet the system must deliver at least 700 kPa (7 bar) pressure and at least 1900 L/min flow; in organised industrial estates and large industrial plants this flow rises much higher depending on the risk level.
Pipework and pipe specifications
The hydrant main is the backbone that carries the highest flow in the system, so pipe selection is critical:
- Diameter: An underground hydrant supply main cannot be smaller than DN150 — a smaller diameter creates excessive pressure loss at the required flow.
- Pressure class: It must be at least PN16.
- Material: The underground hydrant main uses HDPE (PE100) pipe; being corrosion-resistant, flexible and welded at the joints into a leak-tight, continuous line, it is the most suitable material for buried pressurised water mains.
Frost depth and burial depth
The greatest enemy of an underground main is frost. A frozen main gives no water in a fire:
- The pipe is buried below the region’s frost depth — typically at least 30 cm below the frost line. In continental climates like Ankara’s this depth increases further.
- Above-ground hydrants use a dry-barrel design: the main valve sits below the frost line and, after use, the water in the barrel drains automatically, so no water is left to freeze in the barrel. The hydrant length is chosen to suit the region’s frost depth.
NRS valve and Post Indicator (PIV) requirement
Main control valves on the hydrant main are essential for maintaining, modifying or isolating a section of the line; in a fault or repair they let you shut only the affected section without leaving the whole system without water. Underground, NRS (non-rising stem) valves are used for this: because the stem stays inside the body, it takes no room below ground and is protected from external impact.
The biggest drawback of an NRS valve, however, is that you cannot tell from outside whether it is open or closed. This is exactly the most common critical failure in water-based systems: a valve accidentally left closed after maintenance or testing. In that case the system looks intact and the pump runs, but in a fire no water reaches the hydrant — the firefighting water is entirely out of service and the response ends before it begins.
To eliminate this risk, the NRS valve is used together with a Post Indicator Valve (PIV). The PIV makes the underground valve’s status (OPEN / SHUT) visible via an indicator read above ground, and its lockable design prevents the valve from being closed without authorisation or by accident. At critical facilities the valve position is also wired to the fire alarm panel with a tamper switch, so a closed valve raises an immediate alert.
Field-type hydrant cabinet
The hydrant itself is only a water outlet; equipment is needed to respond. A field-type hydrant cabinet sits next to the above-ground hydrant and holds the response equipment (lay-flat hose, nozzle, hydrant key, adaptors/reducers, Storz couplings). Its purpose is to make the hydrant ready for use: it lets the facility team or the brigade respond directly, without hunting for equipment, until the fire brigade arrives. It is designed to be weatherproof, locked yet accessible for emergencies.
2. Indoor fire hose cabinets (first response)
Fire hose cabinets allow response to a fire in the first minutes — before the brigade arrives. Working correctly depends on layout and equipment detail (BYKHY Article 25):
- Layout and spacing: Cabinets are placed on every floor and in every compartment separated by fire barriers, no more than 30 m apart and so that every point can be reached with the hose. Where the building has full sprinkler protection, this distance may be increased to 45 m. Escape routes, corridors and areas near exit doors take priority; the cabinet is positioned so it does not obstruct escape.
- Hose type: Under BYKHY, indoor fire hose cabinets must use semi-rigid hose (TS EN 671-1). The semi-rigid (reel) hose is essential for indoor first response because it can deliver water without being fully unrolled and can be used easily by one person, even an untrained user. TS EN 671-2 lay-flat hose cabinets are used as a complement in industrial/special areas where trained personnel are present.
- Pressure and flow: Adequate pressure and flow for suppression must be guaranteed at the nozzle tip; too high a pressure makes the hose hard for one person to control, so a pressure reducer is used where needed.
- Standpipe design: The vertical standpipes feeding the cabinets are sized by hydraulic calculation to provide the required flow and pressure even at the most unfavourable (highest/farthest) cabinet; in high-rise buildings this standpipe can also be fed from the fire department connection.
3. Landing valve (firefighters draw water)
The landing valve (Turkish “itfaiye su alma ağzı”) is, as the name says, an outlet valve from which firefighters draw water off the building’s fixed standpipe. Instead of running long hose from outside, the crew goes up to the floor and connects their own hoses to this valve to attack the fire directly. This shortens response time significantly, especially in large-floor and high-rise buildings. Design details:
- Requirement and distance (Article 25): On floors where one dimension exceeds 60 m, a landing valve must be provided together with the hose cabinet; within the floor, the distance from any point to the landing valve must not exceed 60 m.
- Connection: The outlet has a 50 mm or 65 mm Storz coupling compatible with the brigade’s standard equipment. The valve ties into the standpipe, which is fed by the pump/tank.
- Location: It is placed where firefighters can reach it safely — protected from smoke, such as a stair landing — and connect their hoses.
4. Fire department connection / FDC (firefighters feed water in)
The fire department connection (FDC) works in the opposite direction to the landing valve: it lets a fire engine pump water into the building’s suppression system from outside. When the building’s pump or tank falls short, or in a prolonged fire, the brigade supplies reinforcement water with its own pump. Technical details to watch in design:
- Location: The connection is placed on the façade where a fire engine can easily pull up, at a visible and accessible point, at a suitable level (a height convenient for the engine connection). Its front is not blocked by parking/obstacles.
- Connection and equipment: It has adaptors compatible with the Storz coupling size the brigade uses, a check valve preventing backflow into the system, and — between the check valve and the connection — an automatic drain (drip valve) preventing freezing in winter. The connection ties into the correct point of the system (sprinkler/hose-cabinet standpipe) so the pumped water reaches the protected space.
- Marking: It is clearly labelled with what it feeds, and distinguished so it is not confused with the landing valve.
Standards
These three layers rest on mature international standards alongside BYKHY:
- BYKHY Article 25 — Fire hose cabinets and fire department connection.
- BYKHY Article 95 — Hydrant system (spacing, flow, pressure).
- NFPA 24 — Private Fire Service Mains and hydrants: burial, valve, PIV rules.
- NFPA 14 — Standpipe and fire department connection systems.
- TS EN 671-1/-2/-3 — Fire hose cabinets (semi-rigid / lay-flat hose / maintenance).
- TS EN 14384 — Pillar-type above-ground hydrants.
Summary
Firefighting water is a set of complementary layers: the hydrant system outside, the fire hose cabinets inside, the landing valve from which the brigade draws water, and the fire department connection (FDC) through which the brigade feeds water in. On the hydrant main, spacing follows the risk class (50–150 m), the pipe must be at least DN150/PN16 HDPE (PE100) and below the frost line; against the risk of being left closed, main valves must be made visible and inspectable with an NRS + Post Indicator (PIV). Indoor cabinets are designed to the 30 m rule (45 m when fully sprinklered) with mandatory semi-rigid hose, and the landing valve to the 60 m rule. At A-Pro we design hydrant, fire hose cabinet and fire department connection systems on the basis of BYKHY and NFPA 24/14; explore our water-based suppression systems, and contact us for a facility-specific design with a free site survey within Ankara.
This content is for informational purposes. A binding, facility-specific assessment requires project-based work with a fire engineer and using the current edition of the relevant standards.
© 2026 A-Pro Mühendislik. This is original technical content produced by A-Pro Engineering; all rights reserved. Copying, reproducing or republishing it in whole or in part without attribution and permission is prohibited.
Frequently asked questions
What should the spacing between hydrants be?+
Under Turkish Fire Code (BYKHY) Article 95 the distance between hydrants depends on the risk class: no more than 50 m in very-high-risk zones, 100 m in high-risk zones, 125 m in medium-risk zones and 150 m in low-risk zones. Hydrants are normally sited 5–15 m from the protected building; the system must deliver at least 700 kPa (7 bar) pressure and at least 1900 L/min flow at the hydrant outlet (much higher in special/industrial areas).
Which pipe should a hydrant supply main use, and how deep should it be buried?+
An underground hydrant supply main cannot be smaller than DN150 and must be at least PN16 pressure class; the material used is HDPE (PE100) pipe — corrosion-resistant, flexible and welded at the joints to form a leak-tight, continuous line. The pipe is buried below the region's frost depth — typically at least 30 cm below the frost line; in continental climates like Ankara's this depth increases further.
Why is an NRS valve required on a hydrant main, and what happens without one?+
Main control valves are needed to maintain the line or isolate a section; underground, NRS (non-rising stem) valves are used for this because the stem stays inside the body. But you cannot tell from outside whether an NRS valve is open or closed. A valve accidentally left closed cuts off water entirely during a fire — the system looks intact and the pump runs, yet no water reaches the hydrant. This risk is removed with a Post Indicator Valve (PIV), which makes the valve position visible above ground and can be locked; at critical facilities the valve is also wired to the alarm panel via a tamper switch.
How are indoor fire hose cabinets positioned, and which hose is used?+
Under BYKHY Article 25, fire hose cabinets are placed on every floor and in every compartment separated by fire barriers, no more than 30 m apart (45 m where the building is fully sprinkler-protected) and so that every point can be reached with the hose. Escape routes, corridors and areas near exits take priority. Indoor fire hose cabinets must use TS EN 671-1 semi-rigid (reel) hose; it can deliver water without being fully unrolled and can be used easily even by an untrained person.
What is the difference between a landing valve and a fire department connection (FDC)?+
A landing valve (Turkish 'itfaiye su alma ağzı') is an outlet valve from which firefighters draw water off the building's standpipe; instead of running hose from outside, they go up to the floor and connect their hoses there. A fire department connection (FDC) is the opposite: it lets a fire engine pump water into the system from outside. BYKHY Article 25 requires a landing valve together with the hose cabinet on floors where one dimension exceeds 60 m, and the distance from any point to the landing valve must not exceed 60 m.
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