Additional Water Demand for Hose Cabinets and Hydrants: BYKHY Annex 8/C and TS EN 12845

If sprinklers, hose cabinets and hydrants in a building are fed from the same tank, the tank volume cannot be calculated from the sprinkler water alone; the water for the hose cabinets and hydrants also enters the calculation. The Turkish Regulation on Fire Protection of Buildings (BYKHY) gives this additional water as numbers: Annex 8/C is the table "Additional Water Demand to Be Added for Hose Cabinets and Hydrant Systems" (unofficial translation). TS EN 12845, on the other hand, gives no numbers on the same subject; it sets a rule for how a combined water supply is to be sized. This article puts the two approaches side by side and works through an example tank calculation for the same building.

The Annex 8/C table

BYKHY Annex 8/C gives the following values according to the building hazard class (Article 19, Annex 1):

The duration column is the same as Article 92(3): the water tank volume is based on 30 minutes for low hazard, 60 for medium hazard and 90 for high hazard. The flows in the table are the values added to the sprinkler flow in the preliminary tank calculation of Article 92(5).

The design values of the hose cabinet and hydrant themselves are in other articles:

• Hose reel with round semi-rigid hose (TS EN 671-1, no fire brigade outlet inside): design flow 100 l/min, design pressure 400 kPa; if the pressure at the nozzle inlet exceeds 900 kPa, a pressure reducer is used (Article 94(1)(b)(5)).
• Lay-flat hose cabinet (TS EN 671-2, in buildings required to have trained firefighting staff): design flow 400 l/min, design pressure at least 400 kPa (Article 94(1)(b)(6)).
• Hydrant system: design flow at least 1,900 l/min; the flow is increased according to the building hazard class; 700 kPa is required at the hydrant outlet (Article 95(2)).

Article 92: four routes to the tank volume

Article 92 has the water tank volume calculated by four routes, depending on which systems the building has:

There are two complementary rules. If a hydraulic calculation has been made, the volume found by the hydraulic calculation governs (Article 92(4), last sentence). The part of the tanks reserved as fire reserve may not be used for any other purpose; it serves the extinguishing systems only (Article 92(2)). If the building has hose cabinets only and the use area is not in the high hazard class, the hose cabinets may be connected to the building's domestic water system (Article 92(6)). Article 92(6) does not give the number of hose cabinets operating simultaneously.

Annex 8/B: the sprinkler flow in 92(5)

The sprinkler flow in Article 92(5) is the design density in Annex 8/B multiplied by the area of operation:

The Annex 8/B note applies TS EN 12845 to storage areas and use areas with different characteristics. In the High Hazard 1 row the regulation states 7.7 mm/min; TS EN 12845+A2:2026 Table 3 gives 7.5 mm/min for the same class (HHP1). Since Article 96(5) ties sprinkler design to TS EN 12845, the standard's value is used in sprinkler design.

How are Annex 8/A and Annex 8/C read together?

The title of Annex 8/A is "Minimum Water Tank Volume for the Preliminary Calculation of Sprinkler System, Hose Cabinet and Hydrant Design" (unofficial translation). Read literally, the table value also covers the hose cabinet and hydrant water. On the other hand, the numbers in Annex 8/A (preliminary calculation, minimum volume) are identical to TS EN 12845 Table 9, and the standard (clause 9.3.2.2) allocates these volumes to the sprinkler system alone. There are therefore two readings:

• Literal reading: the Annex 8/A (preliminary calculation, minimum volume) value also covers the hose cabinets and hydrants; Annex 8/C is not added separately.
• Cautious reading: the Annex 8/A (preliminary calculation, minimum volume) value is sprinkler water; for the hose cabinets and hydrants, the Annex 8/C flow × duration is added.

The regulation does not state clearly which one applies. The fire water tank calculator uses the cautious reading by default and shows the other with a toggle. Clarify with the competent authority which one is to be used on the project.

TS EN 12845: a rule, not a number

TS EN 12845+A2:2026 is the standard for sprinkler systems; in its foreword it points to a separate series of standards (EN 671) for hose reel and hydrant systems and gives no flows for them. The subject comes up in three places.

Town mains (clause 9.2). The mains must be able to meet the pressure, flow and duration requirements while also taking into account the additional flow needed for manual intervention (hydrants, hose reels, etc.). The standard does not give the amount of the additional flow.

Combined water supplies (clause 9.6.4). If the water supply feeds more than one fixed firefighting system (e.g. hydrants, hose reels and sprinklers), it must be a superior single or duplicate supply and must meet the following four conditions:

1. The systems shall be fully calculated.
2. The supply shall be able to deliver the sum of the simultaneous maximum calculated flows of the systems; the flows are adjusted to the pressure of the system demanding the highest pressure.
3. The duration of the supply shall not be less than that required for the most demanding system.
4. A duplicate pipe connection shall be made between the supply and the systems.

A note in the standard points out that some countries may not allow a sprinkler system to be fed from a combined supply. Clause 8.1.1 also refers to 9.6.4 if the water supply serves other extinguishing systems. Durations are LH 30, OH 60, HHP and HHS 90 minutes. For calculated systems, the minimum effective water volume is the maximum flow demand (Q_max) multiplied by this duration (clause 9.3.2.3).

Connections to other services (clause 8.3, Table 8). Water may be taken from the sprinkler system for other services only if conditions are met: the connection is made upstream of the control valve set, with an isolating valve; the system must not be high-rise and must not protect a multi-storey building. Under Table 8, with a town main supply of at least 150 mm, one connection of at most 50 mm diameter may be made for hose reels. Sprinkler pumps are separate from hydrant pumps unless a combined supply complying with 9.6.4 is used (clause 8.3).

Side-by-side comparison

In Turkey the two texts are applied together: Article 96(5) ties sprinkler system design to TS EN 12845, while the hose cabinet and hydrant flows come from BYKHY.

Example: one building, three results

Consider an Ordinary Hazard 3 building with wet sprinklers, semi-rigid hose reels and a hydrant system, all fed from the same tank. The height between the lowest and the highest sprinkler head does not exceed 15 m.

Route 1 — Article 92(5):

• Sprinkler flow (Annex 8/B): 5.0 mm/min × 216 m² = 1,080 l/min
• Annex 8/C, Ordinary Hazard 3-4: hose cabinet 100 l/min + hydrant 1,000 l/min
• Total: 2,180 l/min × 60 min = 130.8 m³

Route 2 — Article 92(4), literal reading: Annex 8/A (preliminary calculation, minimum volume), Ordinary Hazard 3 wet, h ≤ 15 m → 135 m³

Route 3 — cautious reading: Annex 8/A (preliminary calculation, minimum volume) + Annex 8/C: 135 m³ + (100 + 1,000) l/min × 60 min = 135 + 66 = 201 m³

Looking at the same building from the TS EN 12845 side:

• If the supply serves the sprinklers only: for a pre-calculated OH3 system the Table 9 volume is 135 m³, and this volume is allocated to the sprinklers only.
• If the hose cabinets and hydrants are fed from the same supply: under clause 9.6.4 all systems must be fully calculated. The volume is the sum of the simultaneous maximum calculated flows multiplied by the longest duration (60 minutes for OH). Since the density over the area of operation cannot be less than the design density (clauses 7.1 and 13.4.1), the calculated sprinkler flow does not fall below 1,080 l/min; the hose cabinet and hydrant flows come from BYKHY.

The difference between the results is a difference of method: 92(5) gives a quick lower value from density × area, the Annex 8/A (preliminary calculation, minimum volume) table is the sprinkler volume of a pre-calculated system, and in the final design the hydraulic calculation result governs (Article 92(4)). You can compare the values on your own project with the fire water tank calculator and the hose cabinet and hydrant flow calculator.

Common mistakes

• Confusing Annex 8/C with the design values: Annex 8/C is for the preliminary tank calculation; the hose cabinet design flow and pressure are in Article 94, the hydrant values in Article 95(2).
• Sizing the hydrant network with the Annex 8/C flow: under Article 95(2), the design flow of the hydrant system is at least 1,900 l/min with 700 kPa at the outlet.
• Taking the Table 9 volume as the shared tank: TS EN 12845 allocates the Table 9 volume to the sprinkler system only; if the hose cabinets and hydrants are fed from the same supply, clause 9.6.4 applies.
• Taking the duration from a single system: in a shared supply the duration may not be less than that of the most demanding system (EN 12845 9.6.4 c); in BYKHY the duration follows the building hazard class (92(3)).
• Sharing the fire reserve with domestic water: the part reserved as fire reserve may not be used for any other purpose (Article 92(2)). In buildings whose use area is not in the high hazard class and which have hose cabinets only, however, the hose cabinets may be connected to the building's domestic water system (Article 92(6)).

You can see in which buildings hose cabinets, fire brigade outlets, fire brigade inlets and hydrants are mandatory with the requirement checker. The tank calculation is covered in detail in Fire Water Tank Volume: Annex 8/A or Hydraulic Calculation?, and the supply options in EN 12845 in EN 12845 water supply selection: single, duplicate, combined.

FAQ

How much water is added to the tank for hose cabinets and hydrants under BYKHY?

Under Annex 8/C, depending on the building hazard class: low hazard, hose cabinet 100 l/min and hydrant 400 l/min, 30 minutes; Ordinary Hazard 1-2, 100 and 400 l/min, 60 minutes; Ordinary Hazard 3-4, 100 and 1,000 l/min, 60 minutes; high hazard, 200 and 1,500 l/min, 90 minutes. Under Article 92(5), these flows are added to the sprinkler flow found from Annex 8/B and the total is multiplied by the duration of the hazard class.

Is the Annex 8/C water added on top of the Annex 8/A volume?

The regulation does not say so clearly. The title of Annex 8/A gives the table for the combined preliminary calculation of sprinklers, hose cabinets and hydrants; in this reading nothing is added separately. However, the numbers in Annex 8/A (preliminary calculation, minimum volume) are the same as TS EN 12845 Table 9, and the standard (clause 9.3.2.2) allocates this volume to the sprinkler system only; in the cautious reading the Annex 8/C water is added. Clarify with the competent authority which one is to be used.

Does TS EN 12845 give an additional water quantity for hose reels and hydrants?

No, it gives no numbers. Clause 9.2 requires the town main to also meet the additional flow needed for manual intervention (hydrants, hose reels); clause 9.6.4 requires, for a combined water supply, that the systems are fully calculated, that the supply delivers the sum of the simultaneous maximum calculated flows and that the duration is not less than that of the most demanding system. In Turkey the hose cabinet and hydrant flows come from BYKHY.

Is the hydrant flow 1,900 l/min or the Annex 8/C value?

They are separate provisions. Article 95(2) requires the design flow of the hydrant system to be at least 1,900 l/min with 700 kPa at the hydrant outlet. The 400, 1,000 and 1,500 l/min in Annex 8/C are the hydrant flows added to the sprinkler flow in the preliminary tank calculation of Article 92(5). In a building with external hydrants only, the tank supplies at least 1,900 l/min × 90 minutes under Article 92(7). The regulation does not explain the relationship between these values; clarify it with the competent authority on the project.

What tank volume results for an Ordinary Hazard 3 building?

For an OH3 building with wet sprinklers, hose cabinets and hydrants, where the height between the lowest and highest sprinkler head does not exceed 15 m: the Article 92(5) route (5.0 × 216 = 1,080 l/min + 100 + 1,000 = 2,180 l/min, × 60 min) gives 130.8 m³; the Annex 8/A (preliminary calculation, minimum volume) table gives 135 m³; adding the Annex 8/C water to Annex 8/A (preliminary calculation, minimum volume) gives 135 + 66 = 201 m³. In the final design the hydraulic calculation result governs (Article 92(4)).

References

1. Turkish Regulation on Fire Protection of Buildings (BYKHY), Official Gazette 19.12.2007/26735 and amendments (current consolidated text); Articles 19, 92, 94(1)(b), 95, 96(5); Annex 8/A (preliminary calculation, minimum volume), Annex 8/B, Annex 8/C. mevzuat.gov.tr
2. TS EN 12845+A2:2026-05 (EN 12845:2015+A2:2026), Fixed firefighting systems — Automatic sprinkler systems — Design, installation and maintenance: Foreword, clauses 7.1, 8.1.1, 8.3 and Table 8, 9.2, 9.3.2, 9.6.4, 13.4.1, Table 3, Table 9.

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