A building's fire suppression systems only work if they are fed with enough water at enough pressure. The Turkish Regulation on Fire Protection of Buildings (BYKHY) sets the framework for the fire water tank, the fire pump station, hydrants and hose cabinets, while the technical design follows standards such as NFPA 20, NFPA 13 and EN 12845. This article summarises the logic of tank sizing, the components of the pump station and the requirement for standby and diesel pumps.
The Basic Logic of Tank Sizing
The volume of a fire water tank reduces to one relationship:
Tank volume = required flow × required duration
The "required flow" is the total water demand of the systems expected to operate simultaneously in the worst-case fire scenario. The "duration" is the period over which the system must sustain that flow without interruption, and it varies with occupancy and hazard class. Both must be chosen correctly so the tank is neither undersized (inadequate protection) nor oversized (unnecessary cost).
Which Systems Are Assumed to Operate Simultaneously?
The tank is sized for the worst case. The common approach assumes that the flow of the most hydraulically demanding sprinkler area operates simultaneously with some combination of hydrant and hose cabinet flow. Which systems are counted together depends on the chosen standard and the risk class:
| System | Function | Effect on tank volume |
|---|---|---|
| Sprinklers | Automatic suppression and control | Most critical area flow times duration — the main load in most facilities |
| Hydrants (site) | External fire service intervention | Added to the demand where assumed simultaneous |
| Hose cabinets | First-aid firefighting inside the building | Number of simultaneous cabinets times their flow |
Some frameworks assume sprinkler and hydrant simultaneity, others take the "largest single system" approach. Choosing the correct simultaneity scenario is critical to arriving at a realistic tank volume.
Components of the Fire Pump Station
A tank alone is not enough; a pump station is required to deliver the necessary flow and pressure. A typical station comprises:
- Main fire pump: delivers the required system flow at the design pressure.
- Standby pump: of the same capacity as the main pump, usually diesel driven.
- Jockey (pressure maintenance) pump: makes up small leaks and holds system pressure, preventing unnecessary starting of the main pump.
- Controllers: separate control for the electric and diesel pumps.
- Suction and discharge headers, test line and flow meter: for commissioning and periodic testing.
- Pressure switches and gauges: for automatic operation and monitoring.
The suction conditions of the pump room (positive suction is preferred), ventilation, drainage, and the fuel tank and exhaust arrangements for the diesel pump are all integral parts of the design.
Redundancy and the Diesel Pump
A pump failing during a fire is not acceptable, so redundancy is fundamental. In practice one main plus at least one standby pump is provided. The energy independence of the standby pump matters: the system must operate during a power outage. Therefore:
- Where there is no reliable second electrical source (independent feeder or generator), a diesel standby pump becomes effectively mandatory.
- In critical buildings such as high-rise blocks, large warehouses and shopping centres, an electric main pump is generally supplemented by a diesel standby.
- The diesel pump fuel tank must have capacity for at least a defined minimum run period.
Hose Cabinet and Hydrant Criteria
Fire hose cabinets are the first-aid firefighting hose systems inside the building. Design is based on achieving a defined minimum flow and nozzle pressure at the most remote or most critical cabinet. The number of cabinets assumed to operate simultaneously is set by the size of the facility and feeds through into tank and pump capacity.
The hydrant system is installed so the fire service can take water from outside the building, and becomes mandatory in structures above a defined size or occupancy threshold. Spacing between hydrants, hydrant flow and network pressure are set by the regulation and the chosen standard. As a site grows, hydrant numbers and total flow demand increase, which directly enlarges the tank and pump.
Tank Compartmentation and Continuity
So that the system is never left without water during maintenance or a fault, the fire water tank should preferably be divided into at least two compartments. One compartment can then be cleaned while the other continues to feed the system. In addition:
- The tank should be fed from a clean water source with an automatic level make-up arrangement.
- Tank material should be corrosion resistant and stagnation of the water prevented.
- In critical facilities, continuity is assured by a compartmented tank rather than a single large one.
How BYKHY Relates to NFPA 20 and EN 12845
BYKHY sets the general framework and the obligations; the technical design of the pump station and water supply is left to international standards:
- NFPA 20 — installation of fire pumps: pump type, driver, control, testing and redundancy.
- NFPA 13 / EN 12845 — sprinkler water supply flow and duration.
- EN 17451 — referenced separately for pump sets following the 2026 update to EN 12845.
Standards must be chosen consistently on a project. Mixed approaches — sizing sprinklers to EN 12845 and the pump to NFPA 20 — can create inconsistencies in water supply duration and flow definitions.
Frequently Asked Questions
How does BYKHY determine fire water tank capacity?
The tank volume is the required flow of the fire systems present - sprinklers, hydrants and hose cabinets - multiplied by the duration for which that flow must be sustained. BYKHY expects the tank to have capacity to feed the systems for at least a defined period, which varies with occupancy and hazard class. The exact duration and volume should be taken from the current regulation and the chosen design standard.
Which systems are assumed to operate simultaneously in tank sizing?
The tank is sized for the worst case. The general practice assumes the flow of the most critical sprinkler area operating together with hydrant or hose cabinet flow, but which systems are counted together depends on the chosen standard and the risk class of the facility. Some frameworks assume sprinkler plus hydrant simultaneity, others take the largest single system. The tank volume must therefore be calculated with the correct simultaneity scenario.
Is a standby fire pump mandatory under BYKHY?
Redundancy is expected in fire pump stations against the possibility of the main pump being out of service. In practice a main pump, at least one standby pump of the same capacity, and a jockey pump for making up small leaks are provided. The energy independence of the standby matters, which is why it is usually diesel driven. The level of redundancy follows the size and criticality of the facility and the chosen standard.
When is a diesel fire pump required?
A diesel fire pump is the energy-independent standby that keeps the system operating even during a power failure. Where there is no reliable second electrical source such as an independent feeder or generator, or where the facility is highly critical, a diesel pump becomes effectively mandatory. High-rise buildings, large warehouses and shopping centres generally use an electric main pump with a diesel standby. The final requirement depends on the current regulation and the authority's approval.
What flow and pressure are required at a fire hose cabinet?
Fire hose cabinets are the first-aid firefighting hose systems inside a building. BYKHY requires each cabinet to provide a defined minimum flow and nozzle pressure, and in practice the design is based on meeting those minimums at the most remote or critical cabinet. The number of cabinets assumed to operate simultaneously is set by the size of the facility. Exact flow and pressure values should be checked against the current regulation.
When is a hydrant system mandatory?
An external site hydrant system is installed so the fire service can take water from outside the building, and becomes mandatory in structures above a defined size or occupancy threshold. Spacing between hydrants, hydrant flow and network pressure are determined by the regulation and the chosen standard. As site size and building density increase, hydrant numbers and total flow demand rise, which directly affects the fire water tank and pump capacity.
What equipment is in a fire pump station?
A typical station comprises the main fire pump, a standby pump (usually diesel), a jockey pump, pump controllers, suction and discharge headers, pressure switches, a test line with flow meter, and pressure gauges. Suction conditions (positive suction preferred), the test flow arrangement, and pump room ventilation and drainage are also part of the design. Equipment selection follows the chosen standard, NFPA 20 or EN 12845.
How is the most critical scenario chosen for tank sizing?
The tank is sized on the scenario with the highest water demand among the facility's systems. In sprinkler design the most disadvantaged hydraulic area is selected, its flow multiplied by the required duration, and any simultaneous hydrant or hose cabinet flow added. As the storage hazard class rises, both flow and duration increase. Choosing the critical scenario correctly is what keeps the tank from being either oversized or undersized.
Is a single tank sufficient, or is a divided tank required?
So the system is not left without water during maintenance or a fault, the fire water tank should preferably be divided into at least two compartments, allowing one to be cleaned while the other continues to feed the system. In critical facilities this is an important continuity requirement. Tank material, clean water supply and an automatic level make-up arrangement are also considered. The need for compartmentation is assessed against facility criticality and the chosen standard.
How do BYKHY, NFPA 20 and EN 12845 relate?
BYKHY sets the general framework and obligations, while the technical design of the pump station and water supply is left to international standards. NFPA 20 is used for pump selection and station design, and NFPA 13 or EN 12845 for the sprinkler water supply calculation. Following the 2026 update to EN 12845, pump sets are additionally referenced to EN 17451. Standards should be chosen consistently; mixing EN sprinkler design with NFPA pump design creates inconsistency.
Are the values in this article legally binding?
No. This article explains the fire pump and water tank requirements under BYKHY in a general and practical framework; exact flow, pressure, duration and volume values and their exemptions can change over time. What is binding is the current text of the Regulation on Fire Protection of Buildings in force, the selected design standard and the approval of the authority having jurisdiction. Always check the current official text and consult a fire safety specialist where necessary.
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Download MEP Calc on the App StoreThe flow, pressure, duration and volume statements in this article describe the general design logic under the Turkish Regulation on Fire Protection of Buildings (BYKHY); exact values and exemptions vary with the regulation and the chosen standard. Technical design references: NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection; NFPA 13; TS EN 12845; EN 17451 (pump sets).