EN 12845 Frost Protection Strategies

Dry systems, alternate wet and dry, glycol antifreeze and heat tracing. Freeze protection is not in competition with fire protection; inadequate protection begins with a flange bursting in winter, and the damage climbs into the millions within hours.

At a logistics base in eastern Turkey, a February morning at −18 °C burst a wet pipe flange under an unheated canopy. Not a sprinkler — just a connecting flange. Over 24 hours some 850 m³ of water spread across the warehouse floor and destroyed a large quantity of stock. The designer's assumption had been that the canopy was enclosed and would not freeze. The freeze protection clause makes that assumption impossible — every metre of pipe that could fall below 4 °C must be protected.

Methods of freeze protection

Limits on wet systems

A wet system may be used where the ambient temperature stays continuously between 4 °C and 70 °C. The 4 °C figure is a safety margin against 0 °C, covering the temporary dips caused by thermal bridges, doors opening and heating interruptions.

Dry pipe systems

The pipe is filled with pressurised air, typically 2–4 bar. When a sprinkler opens the air escapes, the dry valve trips and water follows. This is the standard solution in freeze-prone areas. The constraints:

• Maximum water delivery time to the most remote sprinkler: 60 seconds
• A practical volume limit of around 1500 L
• Dry valve, air compressor and drain points kept in a heated space
• Pipework pitched at 0.4°, with a low-point drain every 90 m

Alternate wet and dry systems

Wet in the warm months and dry in winter, with a manual changeover at each seasonal transition. Common in older facilities and rarely chosen for new projects, because the risk of a changeover error is high.

Antifreeze (glycol) systems

For small freeze-prone branches only. The constraints:

• A maximum of 20 sprinklers or 40 L of glycol solution, whichever is smaller
• Glycol concentration set from the table for the lowest expected temperature
• Propylene glycol in food and beverage areas, ethylene glycol elsewhere
• Annual concentration measurement with a refractometer
• Separated from the main system by a check valve; back-flow of the solution is prohibited

Heat tracing

EN 12845 does not accept electrical trace heating as a primary method; it is supplementary only. Protection is lost the moment the power fails. It requires a supervised alarm connection, a duplicate circuit and insulation protection.

Glycol concentration against temperature

Target temperature	Propylene glycol (% by volume)	Ethylene glycol (% by volume)
−5 °C	20	15
−10 °C	30	25
−15 °C	35	30
−20 °C	40	35
−25 °C	45	40
−30 °C	50	45

Above about 50 % glycol, suppression performance falls away because of the flammable vapour risk; larger branches move to a dry system.

Dry system sizing — the 60 second rule

Water must reach the most remote sprinkler within 60 seconds of it opening. The larger the pipe volume, the longer the delay. As a practical check:

• Volume below 1500 L: a single dry valve is usually adequate
• 1500–3000 L: add an accelerator or exhauster, or subdivide the area
• Above 3000 L: multiple dry valves, with the area split

Timing the delivery is mandatory during commissioning, and systems that exceed the limit are re-sized.

Typical freeze-prone areas

• Cold stores (dry or pre-action)
• Unheated roof voids
• Enclosed car parks near external walls
• Canopies, awnings and covered walkways
• Loading dock aprons
• Underground external crossings above the frost line
• The above-ground section of the fire service inlet
• External valve sets at the water tank

Field error — glycol assumed full strength, actually diluted

A food factory installed a 35 % propylene glycol system. In year five the concentration was not measured before annual service — "closed system, what could happen?" A snowy weekend produced a freeze and four sprinklers cracked. The measurement afterwards read 18 %: a leaking connection on the fill line had let water in and diluted the solution. When the annual concentration check is skipped, glycol protection becomes non-functional. A refractometer reading takes three minutes.

Pre-action and double interlock for cold stores

At −20 °C and below, even a standard dry system is marginal. The solutions:

• Pre-action: the pipe is dry and fire detection (smoke or heat) opens the valve, reducing the risk of accidental discharge.
• Double interlock: both detection and sprinkler operation are required — the most common arrangement in data centres and cold stores.
• Valve, compressor and air chamber stay in a heated space; only galvanised dry pipe enters the cold area.

Comparison with NFPA 13

NFPA 13 treats antifreeze more strictly: since 2010 only factory premixed solutions may be used rather than site-mixed concentrate, with an upper limit of 38 % propylene glycol in residential applications. EN 12845 leaves the concentration table open. The 60 second dry system rule is the same in NFPA 13, and the pre-action definitions are parallel. NFPA 25 requires annual concentration measurement explicitly; EN 12845 covers it under general annual checking, so the maintaining contractor must schedule it.

Link to Turkish regulation

BYKHY requires fire water to be protected against freezing and references the EN 12845 and NFPA 13 methods. Turkey's eastern and inland provinces are continuous frost zones, and canopy or external sprinklers there should be treated as requiring dry systems. Insurers add standard contract conditions on this point. Even in central Anatolia, a wet system is risky where night temperatures reach −10 °C.

Quick check list

• A winter minimum temperature map produced for the whole pipe run.
• Every area below 4 °C on dry, alternate, glycol or pre-action.
• Glycol limited to 20 sprinklers or 40 L.
• Dry system 60 s delivery test recorded at commissioning.
• Heat tracing not relied on as the primary method.
• Annual glycol concentration measurement scheduled.
• Cold stores on pre-action or double interlock.
• Fire service inlet and external valve sets protected.

Frequently Asked Questions

Below what temperature must a wet system be avoided?

Wet systems are permitted only where ambient temperature stays continuously between 4 °C and 70 °C. The 4 °C figure is a margin against transient dips.

What are the limits on glycol systems?

A maximum of 20 sprinklers or 40 L of solution, whichever is smaller, with concentration set from the table for the lowest expected temperature and measured annually.

What is the 60 second rule for dry systems?

Water must reach the most remote sprinkler within 60 s of it opening. Above roughly 1500 L of pipe volume, an accelerator or a subdivided area becomes necessary.

Can heat tracing be the primary freeze protection?

No. EN 12845 treats it as supplementary only, because protection is lost the moment the power fails. It needs supervised alarms and a duplicate circuit.

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