Data Center Cold Aisle Containment Curtains

Pre-Design Considerations

Assuming you’ve met the prerequisite of managing all the bypass airflow in your computer room, you can move onto the next step of pre-qualifying the computer room for design changes. The biggest potential obstacle to curtains in the data center is fire detection and fire suppression.

Fire Detection and Suppression

A curtain installation will, in many cases, create physical zones which are isolated from existing fire detection systems such as smoke detectors and VESDA inlets. Smoke inside the containment zone will not reach the detectors in their current location. This is a very serious life-safety and property loss issue.

There have been equipment fires in curtained zones which were not detected because the curtain zone was unprotected. It is very important that you consider this issue in your aisle containment layout.

The fire suppression issue is parallel to fire detection. Regardless whether you utilize gas or water, if the suppressant can’t reach the fire because curtains are in the way, the consequences can be dire.

The Three Alternatives to Addressing Fire Suppression & Detection
in the Computer Room

1. Add additional detection and suppression elements to support the isolated zones. This may make sense if other construction or remodeling changes in the computer room coincide with a curtain installation.

2. Hang the curtains at least 18” below the level of the ceiling or the sprinkler heads/suppression nozzles, whichever is lower.

   Note: 18” below sprinkler heads is the generally accepted minimum separation between sprinkler heads and interferences or combustible material while still achieving effective sprinkler spray pattern and fire suppression.

3. 
   Thermal Links

   Install the curtains using a fusible link which can allow the curtains to fall away from the ceiling in the event of a fire event. Mechanical fuse links are temperature sensitive and are heat activated – like a sprinkler head. Electrical fuse links are electrically activated by smoke alarms or other detection systems. The choice depends on the type of fire suppression system used in the computer room.

Electrical links

For computer rooms with traditional heat activated water sprinkler systems (wet or dry pipe) thermal links are used. The thermal links are designed to break apart at 135° F. Most commercial sprinkler heads are rated at 155° F. The curtains will fall before the sprinklers activate.

For computer rooms with gas-based suppression systems activated by smoke sensors, electrical links are used. The electrically activated link can be triggered by the existing fire alarm system using user specific activation criteria.

Using Lanyards - The 18” Separation Rule

Lanyard

With either water or gas based fire suppression systems,the hook bead bar and curtains remain supported with 18” lanyards. When the links activate, the thin aircraft cable lanyards limit the curtain drop to 18” to prevent equipment damage and/or personal injury.

Sometimes, following the 18” Separation Rule up front avoids any conflict with the local fire inspecting agency: if the rack height is such that the rack to ceiling distance is already less than 18” then the curtains should be mounted to no higher than the rack.

Mechanical Obstructions

Physical obstructions need to be considered early, as it affects both layout and implementation. Curtain designs can accommodate these obstructions but the designer needs to include the modifications in the initial design.

DCT Steps Around Light

Will the curtains pass across lay-in light fixtures and prevent re-lamping?
Typically, the diffuser on these common fixtures hinges down to allow bulb and ballast changes.

Cut Around Cable Tray

Will the curtains pass across a building HVAC diffuser or other component?
Sometimes the containment layout can be adjusted or the fixture relocated to avoid an obstruction. Harder to move is cable tray or buss ducts for power.

 Note: Depending on the hang length, containment curtains can be hung up to 18” offset from the face of the equipment.

Entrance and Egress

The next consideration is computer room traffic patterns, convenience and life safety.

• Will the curtain layout obstruct a popular walkway?
• Can the design be modified to minimize walkway obstructions and still provide the intended isolation?

Will the curtain layout realistically impede rapid exit from the room in the event of emergency or will the curtains prevent personnel from hearing or seeing emergency warning annunciators?

Again, can the design be modified to prevent such obstructions?

Material Selection
Softwall aisle containment curtains are available in three materials which offer different price and performance characteristics:

1. PolySim
   Originally designed for NASA, this material features superior long-term physical stability and has become the gold standard for containment curtains. PolySim is made from an inherently static dissipative polyurethane. Outgassing is extremely low because no plasticizers are used. This product is both fire-rated and anti-static and can help you meet sustainability goals because it is a urethane, as opposed to a PVC-based vinyl.
2. FlexSim FR AS
   FlexSim FR AS has all the features of FlexSim FR with the addition of built-in ESD inhibitors. Product cost is roughly 40% less than PolySim.
3. FlexSim FR.
   FlexSim FR vinyl was developed especially for use in data center applications. It is low-outgassing and fire rated. Product cost is roughly 50% less than PolySim.

Aesthetics

Many managers complain that they don’t want their data center looking like a meat locker or a loading dock. This can be a show stopper. Usually, the performance benefits from containment curtains easily outweigh the aesthetic concern, but not always. A helpful approach is to implement only one aisle as a trial showcase.