Wet pipe freezes, so freezers use dry pipe or preaction
A freezer can't hold wet sprinkler pipe. Standing water below 0 C turns to ice, splits the pipe and leaves the building with a system that fails when it's needed. So cold storage protection keeps the pipe dry until there's a reason to fill it. The winterization checklist covers the unheated spaces around a cold-storage building, such as dock areas and valve rooms.
| System | How it works | The catch |
|---|---|---|
| Dry pipe | Pipe holds pressurised air or nitrogen. A head opens, the pressure drops, the valve trips and water follows | Water arrives late, the gas has to stay dry, and it needs more testing than wet pipe |
| Single interlock preaction | Pipe stays dry until the detection system trips the valve, then water waits for a head to open | Detection now has to work properly in the cold |
| Double interlock preaction | The valve opens only after detection and a head operating | The slowest to deliver water. Some AHJs favour it for deep-freeze rooms |
Double interlock is common in freezers because accidental water in the pipe is expensive there (ice on the floor, ruined product), and Reliable Automatic Sprinkler's design guidance lists single interlock as an option for coolers and freezers too. Our view: don't default to the slowest system because it sounds safest. Decide how costly a bumped head or a burst pipe really is, then settle it with the designer and the AHJ before drawings are issued. A cooler held above freezing might use wet pipe, but only if no pipe ever sees a sub-zero draught, and near evaporators and dock doors that's harder to guarantee than it looks. Some freezers are covered instead by dry-type sprinklers dropped in from a wet pipe that stays in the heated space outside.
Ice plugs and the air supply
Warm, moist air gets into a dry system, condenses and freezes. Ice plugs turn up most often in the feed main where the pipe passes from a warm space into the freezer, and one full blockage means a system that looks fine on the riser gauge and can't flow. The air or nitrogen supply is the defence: NFPA 13's annex guidance ties how dry it must be to the lowest temperature the space will hold. Your designer sets that number, and it's worth asking what it was.
Detection has its own rule. NFPA 13 bars rate-of-rise detectors in refrigerated spaces and expects fixed-temperature detection to operate below the sprinkler's rating. Section numbers moved between editions, and Alberta's codes reference the 2019 text, so have the designer confirm the clause. Fog from door openings and defrost cycles can trip smoke detectors too. Air-sampling detection, which we list among our fire alarm options, is one to consider, provided its rated temperature range covers the room.
Foam-core panels and the fire behind the skin
Most cold rooms are built from insulated metal panels, and many have a foam core, expanded polystyrene or polyurethane, between two metal skins. The core adds fire load, and once fire gets inside a panel it travels through concealed spaces no sprinkler can reach. Insurers such as FM Global steer owners toward noncombustible cores like mineral wool, or panels approved to FM Approval Standard 4880.
The risky moment is a renovation. Cutting a new door opening or adding a conveyor penetration means hot work near foam. The fire code (NFC(AE) 2023, 5.2.3.6 and 5.2.3.7) asks for at least one portable extinguisher in the hot work area and a fire safety plan where one's required. Take that as the floor. If your building is already clad in foam panels, ask your supplier for their fire test listing and file it with the building records. Our guide to construction site fire safety plans in Alberta explains what a plan has to cover.
Defrost heaters, door frames and other quiet heat sources
A freezer is full of small heat sources next to foam and packaging: electric defrost elements on evaporator coils, drain-line heaters, door-frame heaters, and wiring that lives in wet, cold rooms. None is exotic. A heater that fails on stays on. They belong on the maintenance schedule as much as the sprinkler valves do, and if your electrical contractor does infrared scans, put these on the list.
Ammonia and other refrigerants
Sprinklers are there for the building fire. The refrigerant is somebody else's design. In Alberta, CSA B52, the mechanical refrigeration code, is declared in force under the Pressure Equipment Safety Regulation. ABSA, the province's pressure equipment safety authority, publishes AB-538, which sets out what owners of ammonia systems must have in place for integrity management and reminds them that B52 applies in its entirety. The NFC(AE) 2023 has its own article on indoor storage of anhydrous ammonia and other toxic gases (3.2.8.3), which matters if you keep cylinders or vessels inside.
Ammonia detection, machinery room ventilation and emergency shutdown come from the refrigeration engineer. How a refrigerant alarm talks to the building fire alarm is a design-stage question, so raise it early. Sign-off responsibilities depend on the facility, so make ABSA and your AHJ the first calls.
Testing sprinklers in a room that's well below freezing
NFPA 25-2017 asks for a yearly trip test on dry and preaction valves, a full-flow trip test every 3 years, and valve room temperature checks in cold weather (daily, or weekly if a low-temperature alarm is supervised). In a freezer, a full-flow trip test is planned like a small construction job: the product may need to move or be covered, the air gets dried afterward, and every low point is drained before the room returns to temperature. Skip that last step and you've made your own ice plug. Extinguishers need the same thought. Each has an operating temperature range on its label, and one hung in a freezer has to be rated for it.
The inspection page has the general schedule, and the wet vs dry sprinklers piece explains the winter maintenance habits that carry over.
What we can design, install and service in a cold building
- design and installation of dry pipe and preaction sprinkler systems (see fire sprinkler systems)
- addressable fire alarms and air-sampling detection, with monitoring integration
- portable extinguishers through Amerex (portable extinguishers)
- inspection and maintenance to NFPA 25-2017
- code consulting on occupancy classification and panel or layout changes
We don't design refrigeration plants, ammonia detection or the insulated panels themselves. If the building is also a distribution centre, read warehouse and logistics for the storage-height side, and food processing if product is made there as well. To talk through a specific room, use the contact page.
Frequently asked questions
Can a freezer use wet pipe sprinklers?
No. Water standing in pipe below 0 C freezes and can split it. Freezers use dry pipe or preaction systems, or dry-type sprinklers fed from a wet pipe kept outside the cold room. A cooler held above freezing may get away with wet pipe, but only if no part of the pipe sees sub-zero air, and evaporators and door drafts make that hard to promise.
Is double interlock preaction required for freezers?
Not automatically. It's common because accidental water in a freezer is costly, and some AHJs favour it for deep-freeze rooms, but single interlock is also used in coolers and freezers. Water arrives later with double interlock, so the choice is a trade the designer and the AHJ should settle before drawings are issued.
How do ice plugs form in a dry sprinkler system?
Moist air enters the pipe, condenses on the inside and freezes, most often where the feed main passes from warm space into the freezer. Dry supply air, drained low points and careful re-setting after a trip test are the defences. Ask what dew point your supply air is designed to.
Who regulates ammonia refrigeration systems in Alberta?
CSA B52 is in force under the Pressure Equipment Safety Regulation, which ABSA administers, and ABSA's AB-538 sets integrity management requirements for owners of ammonia systems. Fire code requirements sit alongside that. Ask ABSA about the refrigeration plant and your AHJ about the building.
Sources
- National Fire Code 2023 Alberta Edition, National Research Council Canada
- Preaction Sprinkler System Design Guide, Reliable Automatic Sprinkler
- NFPA 13 2022 vs 2025 Edition, Engineered Fire Systems
- Integrity Management Requirements for Mechanical Refrigeration Systems Containing Ammonia (AB-538), ABSA