EN 12845 Pre-calculated Design for HHP and HHS: Clause 13.3.5 and Tables 32-35

Source: TS EN 12845+A2:2026 (EN 12845:2015+A2:2026), Clauses 7.3.2, 12.2, 13.1, 13.3.5, 13.4.4 and Tables 7, 19, 32, 33, 34, 35.

In the high hazard class, pre-calculated design does not rest on a single pipe table as it does in LH and OH, but on a pair of tables that depends on which block of Table 7 the water supply conforms to. For the same density there are four different combinations of pipe tables and four different required pressures. This article deals with that matching and with its limits.

First the limit: when pre-calculation is not allowed

Clause 13.1 (TSE p.85 / EN p.82) says pipe sizes shall be determined by one of two methods: pre-calculated systems (13.3), where some of the sizes are taken from tables and some are calculated, and fully calculated systems (13.4), where all sizes are determined by hydraulic calculation. The designer may choose between the two; but full calculation shall always be used in two cases:

• layouts with HHS intermediate sprinklers,
• gridded or looped layouts.

Clause 7.2.3.4 (TSE p.40 / EN p.37) says the same thing from the storage side: in-rack sprinklers and their associated ceiling sprinklers shall always be fully calculated. The note to the clause recalls the minimum pressure: the minimum pressure at any operating sprinkler is 2.0 bar (13.4.4).

The heading of Clause 13.3.5 repeats it too: "High hazard - HHP and HHS (excluding intermediate sprinklers)".

Four parameters: Clause 13.3.5.1

Clause 13.3.5.1 (TSE p.92 / EN p.89) lists in four items what determines the pipe size:

1. the design density,
2. the spacing of the sprinklers,
3. the K-factor of the sprinklers used,
4. the pressure/flow characteristic of the water supply.

And a single absolute lower limit: no pipe shall have a nominal diameter smaller than 25 mm.

The water supply: the four blocks of Table 7

Clause 7.3.2.1 (TSE p.43 / EN p.40): the water supply shall be capable of providing not less than the flow and pressure specified in Table 7 at the highest design point. Table 7 gives the pressure at the highest design point (pd) according to the area of operation per sprinkler (6, 7, 8 or 9 m²) and is divided into four blocks:

The maximum demand flows of Table 7 depend on the density, not on the block. Example rows (TSE p.43 / EN p.40):

At the same density the required pressure falls as the block changes. For 10.0 mm/min and 9 m² per sprinkler: Table 7 (1) → 3.90 bar, Table 7 (2) → 3.00 bar, Table 7 (3) → 1.60 bar, Table 7 (4) with K115 → 0.95 bar. In other words, larger pipe tables (34, 35) and a larger K-factor let you achieve the same density with a lower supply pressure.

The note to Table 7: where there are sprinklers in the array higher than the design point, the static head from the design point up to the highest sprinklers shall be added to pd.

Matching rules and range pipe limits

Clause 13.3.5.2: Table 7 (1) with K80

In installations whose water supplies conform to Table 7 (1) and whose sprinklers have a K-factor of 80, Table 32 (range) and Table 33 (distribution) apply. No more than four sprinklers shall be connected to any range pipe. Range pipes shall not be connected to distribution pipes of a diameter greater than 150 mm.

Clause 13.3.5.3: Table 7 (2) with K80

In installations whose water supplies conform to Table 7 (2) (or are modified by 7.3.2.6) and which use K80 sprinklers, Table 32 and Table 34 are used. Again, a maximum of four sprinklers per range; range pipes shall not be connected to distribution pipes exceeding 150 mm. An additional constraint: in 4-end-side systems no distribution pipe of a diameter smaller than 65 mm shall be used.

Clause 13.3.5.4: Table 7 (3) with K80 or Table 7 (4) with K115

Table 34 and Table 35 are used. Here the number of sprinklers per range depends on the arrangement:

• in end-side arrangements, a maximum of six sprinklers on a range pipe,
• in 2-end-centre arrangements, a maximum of four sprinklers.

Range pipes shall not be connected to distribution pipes greater than 150 mm and, in 4-end-side systems, no distribution pipe smaller than 65 mm shall be used.

The pipe size tables

Table 32 - Range pipe sizes (for Table 7 (1) or (2)), TSE p.93 / EN p.90:

Table 33 - Distribution pipe sizes downstream of the design point (for Table 7 (1)), TSE p.93 / EN p.90:

Table 34 - Distribution pipe sizes downstream of the design point (for Table 7 (2), (3) or (4)), TSE p.94 / EN p.91:

Table 35 - Range pipe sizes (for Table 7 (3) or (4)), TSE p.95 / EN p.92:

The design point and everything above it

Clause 13.3.2.1 (TSE p.88 / EN p.85): the design point is located where a horizontal distribution pipe connects to a range pipe, to a riser or drop pipe connecting ranges to the distribution pipe, or to a pipe feeding a single sprinkler.

Table 26 (TSE p.89 / EN p.86) gives the position of the design point for HH: where there are more than 48 sprinklers on one distribution pipe in a room, the design point is at the junction with the distribution pipe of the range carrying the 49th sprinkler, and this applies to all range arrangements.

Clause 13.3.5.5 (TSE p.95 / EN p.92) binds everything above the design point: the pressure loss between the design points and the control valve set shall be determined by calculation. The sum of the pressure loss at the flows shown in Table 7, the pressure required at the design point and the static pressure equal to the height difference between the highest sprinkler and the control valve set shall not exceed the available pressure. Where the highest sprinkler is upstream of the design point, the section requiring the higher static head shall have its own distribution pipe. Pressure losses in the distribution pipes feeding each section of the risk may be balanced by sizing the distribution pipe appropriately.

Sprinkler layout and type

Table 19 (Clause 12.2, TSE p.73 / EN p.70) gives a single row for HHP and HHS:

There is no separate 7.5 m² value for HHS. Under Clause 12.4.1, the maximum distance to walls and partitions shall not exceed half of the maximum distance in Table 19, that is 1.85 m, nor the other values listed in the clause; the smallest of these values is selected.

Clause 12.1.2 (TSE p.73 / EN p.70): in HHP and HHS a clear space of at least 1.0 m shall be maintained below the deflector of ceiling and roof sprinklers.

Table 37a (TSE p.107 / EN p.104) binds the sprinkler type and the K-factor:

Clause 14.2.2 (TSE p.107 / EN p.104): ceiling, flush, recessed and concealed sprinklers shall not be installed in OH4, HHP or HHS areas. Clause 14.2.3: in HH installations sidewall sprinklers may be used only for the protection of corridors, cable ducts and columns.

Minimum pressure

Clause 13.4.4 (TSE p.105 / EN p.102) binds the pressure at the hydraulically most unfavourable sprinkler while all sprinklers in the area of operation are operating. The pressure required to achieve the design density applies, or the following values, whichever is the higher:

• 0.50 bar in HHP and HHS (excluding in-rack sprinklers),
• 1.00 bar for in-rack K115 sprinklers,
• 2.00 bar for in-rack K80 sprinklers.

Frequently Asked Questions

What is the maximum area of coverage per sprinkler in HHP and HHS?

Table 19 (Clause 12.2, TSE p.73 / EN p.70): for HHP and HHS the maximum area per sprinkler is 9.0 m2, with S and D of 3.7 m maximum in standard layout and 3.7 m maximum for S and D in staggered layout as well. There is no separate, smaller value for HHS.

On what basis are the pipe size tables selected in pre-calculated HH design?

Clauses 13.3.5.2, 13.3.5.3 and 13.3.5.4 (TSE p.92-94 / EN p.89-91) match them to the block of Table 7 that the water supply conforms to, and to the K-factor. Table 7 (1) with K80: Tables 32 and 33. Table 7 (2) with K80: Tables 32 and 34. Table 7 (3) with K80 or Table 7 (4) with K115: Tables 34 and 35.

How many sprinklers may be connected to a range pipe in HH?

Where Tables 32 and 33 apply, no more than four sprinklers shall be connected to a range pipe (13.3.5.2). Where Tables 34 and 35 apply, a maximum of six sprinklers may be connected in end-side arrangements and a maximum of four in 2-end-centre arrangements (13.3.5.4).

What is the minimum sprinkler operating pressure in HHP and HHS?

Clause 13.4.4 (TSE p.105 / EN p.102): 0.50 bar in HHP and HHS excluding in-rack sprinklers. For in-rack sprinklers it is 1.00 bar for K115 and 2.00 bar for K80.

Can systems with in-rack intermediate level sprinklers be pre-calculated?

No. Clause 13.1 (TSE p.85 / EN p.82) requires full calculation at all times for layouts with HHS intermediate sprinklers, and Clause 7.2.3.4 also requires in-rack sprinklers and their associated ceiling sprinklers to be always fully calculated. The heading of Clause 13.3.5 likewise says excluding intermediate sprinklers.

References

• TS EN 12845+A2:2026 Clause 7.2.3.4 (TSE p.40 / EN p.37)
• TS EN 12845+A2:2026 Clause 7.3.2.1, Table 7 (TSE p.43 / EN p.40)
• TS EN 12845+A2:2026 Clauses 12.1.2, 12.2, Table 19 (TSE p.73 / EN p.70)
• TS EN 12845+A2:2026 Clause 12.4.1 (TSE p.75 / EN p.72)
• TS EN 12845+A2:2026 Clause 13.1 (TSE p.85 / EN p.82)
• TS EN 12845+A2:2026 Clause 13.3.2.1 (TSE p.88 / EN p.85), Table 26 (TSE p.89 / EN p.86)
• TS EN 12845+A2:2026 Clauses 13.3.5, 13.3.5.1, 13.3.5.2 (TSE p.92 / EN p.89)
• TS EN 12845+A2:2026 Table 32, Table 33, Clause 13.3.5.3 (TSE p.93 / EN p.90)
• TS EN 12845+A2:2026 Table 34, Clause 13.3.5.4 (TSE p.94 / EN p.91)
• TS EN 12845+A2:2026 Table 35, Clause 13.3.5.5 (TSE p.95 / EN p.92)
• TS EN 12845+A2:2026 Clause 13.4.4 (TSE p.105 / EN p.102)
• TS EN 12845+A2:2026 Table 37a, Clauses 14.2.2, 14.2.3 (TSE p.107 / EN p.104)

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