EN 12845 Zone Test and Drainage Facilities

Inspector test connection, alarm test valve, low-point drain, drainage branch. Properly designed drainage is what makes a system genuinely testable; inadequate drainage means years of tests that were never really carried out.

At one logistics facility, opening the zone test connection released about 1500 L of water across the floor, so for four years the team cut the test short to protect the wall finishes. No drainage had been designed — just a cap. An insurer audit established that the quarterly tests had been abbreviated, and the report was reissued as "test could not be performed". The premium rose sharply at renewal. If the drainage branch required by the installation clauses is missing, every test in the maintenance clauses is left hanging.

Drainage provisions

System drainage

Every control valve set has a main drain valve for emptying the system. Sizing:

• Minimum DN50 main drain
• Discharge capacity of at least 25 % of the design flow
• DN80 or DN100 on large systems
• Discharge route vented and protected against back-siphonage

Inspector test connection

Taken from the most remote or hydraulically most demanding point of the system, with a test orifice matching the smallest K-factor orifice in the system. During the flow simulation:

• The flow alarm switch must operate within about 30 s
• The water motor gong, where fitted, must sound
• The pressure switch must close and transmit an alarm
• The signal must reach the fire service or central monitoring station

Low-point drains

Water collects at the low points of horizontal pipework, which is a freezing risk in a dry system in particular. The solution:

• At least one low-point drain every 90 m
• DN15–25 diameter
• An accessible position — not above a suspended ceiling
• Labelled and locked, so that it is not opened by mistake
• Discharge to a pit, channel or container

Hydraulic sizing of the drainage branch

System size	Design flow (L/min)	Drain size	Drain capacity (L/min)
LH small	225	DN50	about 250
OH2 medium	540	DN50	about 250
OH3 large	900	DN65	about 450
HHP3	1620	DN80	about 700
HHS3	3250	DN100	about 1200
HHS4	4875	2 × DN100	about 2400

The 25 % figure is the practical floor. Where the insurer or authority requires drainage at full design flow, a separate test loop is designed.

Test loops and water reuse

A test sends a large fraction of the design flow to drain for three to fifteen minutes. The water loss is significant:

• An OH2 system at 540 L/min for 10 min: 5400 L per test
• An HHS3 system at 3250 L/min for 5 min: 16 250 L
• Four quarterly tests a year: 20–65 m³ lost

Where it does not compromise tank cleanliness, test water can be returned to the pump suction as a closed-loop test. This is the preferred design for water conservation, but flow and pressure measurements must then be taken with a calibrated flow meter.

Field error — the drainage pit overflowed

At a textile warehouse a 0.5 × 0.5 × 0.3 m drainage pit had been built beside the control valve. When the quarterly test started 540 L/min flowing, the pit filled in twenty seconds and water spread across the warehouse floor, soaking 200 m² of raw fabric. No capacity calculation had been done; "a small pit will do" had been the assumption. The drainage clause requires capacity at 25 % of design flow — which means a connection to an open channel or gully, not a pit.

Drainage route design rules

• Main drainage falls at 1° or more, so it self-empties
• No air traps — no low points along the route
• Sized to pass the design flow
• Air gap at the outlet, as back-flow protection
• Freeze protection in cold areas
• Discharge to a rainwater drain if the water counts as clean, or to industrial drainage if it does not
• A separate disposal line for glycol-filled systems

Fire service connection and drainage

A drain valve is provided on the fire service connection so that residual water can be removed after the fire service has finished pumping. In freeze-prone areas the connection pipe is kept dry, with automatic drainage beneath the main check valve. Check it visually daily and functionally each year.

Comparison with NFPA 13 and NFPA 25

NFPA 13 requires a main drain capable of carrying the full flow — at least 2 in, roughly DN50 — which is effectively the same as EN 12845 in practice. NFPA 25 requires the inspector test connection to be at the most remote point with an orifice matching the smallest K-factor, the same approach as EN 12845. Low-point drains appear on the NFPA side as "auxiliary drains", located at each drum drip rather than at a fixed interval. The two standards run parallel on drainage philosophy.

Link to Turkish regulation

BYKHY has no separate drainage clause; it is applied through the EN 12845 and NFPA references. Because of that gap, drainage branches in Turkey are frequently left at the level of "empty it with a bucket". This is one of the most common deviations recorded in insurance audits: if the quarterly test cannot be reported, the periodic inspection is downgraded to conditional. Drainage design has to be verified physically on site, not only on paper.

Quick check list

• Main drain valve at least DN50, sized for 25 % of design flow.
• Inspector test connection at the most remote and highest point, with the smallest K orifice.
• Low-point drains every 90 m, labelled and locked.
• Drainage route falls at 1°, with no air traps.
• Discharge to an open channel or gully — not a pit.
• Separate drainage line for glycol systems.
• Fire service connection drain protected against freezing.
• The test water route is documented.

Frequently Asked Questions

How large must the main drain be?

At least DN50, with a discharge capacity of 25 % of the design flow. Large systems need DN65 to DN100, or twin DN100 runs on the highest-demand storage systems.

Where is the inspector test connection taken from?

From the most remote or hydraulically most demanding point of the system, with a test orifice matching the smallest K-factor orifice installed.

Is a drainage pit acceptable?

Generally not. A pit of a few hundred litres fills in seconds at design flow. The discharge needs a connection to an open channel or gully sized for the drain capacity.

How often are low-point drains needed?

At least one every 90 m of horizontal pipework, DN15–25, in an accessible position, labelled and locked so they are not opened by mistake.

SprinkCalc — Fire Sprinkler Design Across Three Standards

SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.

Download SprinkCalc on the App Store

MEP Calc — 86+ Engineering Calculators

MEP Calc bundles 86+ engineering modules in one iOS app: 21 fire calculations plus heating, cooling, HVAC, plumbing, steam and natural gas.

Download MEP Calc on the App Store