Matching the theoretical to reality provides the peace of mind for fire suppression and environment stability.

Once a Server room/Data Centre is built, the critical contents seem to be forever evolving and growing with the needs of the business. Conversely, the building envelope remains static, often accumulating new penetrations (holes) from trades or tech staff over time.

Computer room Air leakage under false floor

Note the Blue arrows. Air leaving under the floor puts the room above the floor in Negative pressure, sucking air from above.

The one thing that doesn’t seem to get much attention within a computer room is the building fabric/building envelope and its ability to contain and suppress a fire, while at the same time ensuring key environmental stability. This assists hardware longevity and low energy costs for controlling humidity and temperature.

Before we move onto more detail, it’s imperative that we explain two important things that all Data Centre/Server Room operators should have a basic understanding of:

  1. Fire Suppression Systems Operate in Two Primary Forms (Regardless of Gas Type: FM200, Novec, IG-55)
    • Continuous Mixing: With air conditioners operational, suppressant gas circulates and escapes through holes/high-pressure points.
    • Descending Interface: Without air conditioners, heavier-than-air suppressants gradually leak out through low-lying openings.
  2. Understanding Baseline/Bias Pressure:
    • Bias pressure is the normal everyday pressure acting in a room depending on HVAC systems, external wind pressures, and the envelope’s integrity.

The single most important point of failure that can compromise a fire suppression system, energy efficiency, and humidity/temperature lies in the under false floor plenums or ductwork that distributes air to and from air handlers. Areas where elevated pressures up to 10 Pascals exist to keep equipment at an optimum temperature must be almost entirely airtight. Air tightness is extremely critical for both Continuous Mixing and Descending interface but for different reasons. The leakage you are specifically looking for is located under walls or through walls, particularly when hundreds of cables have been pulled through a wall.

For Example…

Uncaulked plaster wall

Comments:  Leakage under a false floor where the concrete slab meets the plaster wall

Hole under corner plaster

Comments:  Leakage under a false floor where the concrete slab meets a cornered plaster wall.

Cutout through wall for cables

Comments:  Leakage below a false floor, especially where power cables are penetrating a wall. This contractor gets 10 points for the fire pillow, but fire pillows themselves are not air tight. It’s a good idea to use Rockwool board combined with a fire rated acrylic mastic instead.

With high pressures inside a leaky floor/supply plenum, that air which is leaving needs to be made up on the return side forcing unfiltered/uncontrolled air into the air conditioning system.

Things to focus on in-house:

  • Testing on whether air conditioners shut down or stay running should be thoroughly tested and reported on.
  • Check the state of all penetrations under the false floor or your return air plenum. Resolve any penetrations that are evident.
  • It should be reported what the bias/baseline pressure is in a computer room during normal operation because it will give you clues of potential issues in the room. Even though a computer room might pass an integrity room test when everything is turned off, high operating bias pressures are unacceptable. It could also indicate considerable leakage under a false floor, which is not desirable for both descending interface and continuous mixing fire suppression system.
  • Consider relief vents in airtight computer rooms. When a fire suppression system goes off, depending on the airtightness of the building envelope, momentary pressures can go up to 1000Pa and damage the structure.  Some agents cause more negative pressure, and the peak pressure is related to “leakage to Volume” ratio.  Seek professional advice.
  • Does the room behave, as it should in the event of a triggered fire suppression system?
    • Do extraction fans turn off and also damper?
    • Do dampers to the Building HVAC system close?
    • Does the Pressure relief vent work complimentary to your gas fire suppression system?

To ensure your data centre is prepared for an incident while also improving the performance of your computer room, do the following:

  1. Air tight floor or supply plenum and returnRegular Inspections: New penetrations, especially under supply or return plenums, ensuring contractor awareness of expectations.
  2. Annual Fire Integrity Testing
  3. Baseline/Bias Pressure Measurements:
    • During normal operation.
    • Optionally, with all systems off (especially for Descending Interface setups). Ensure reports reflect realistic measurements (e.g., -0.17Pa) rather than idealized zeros.

Currently hot/cold aisle containment solutions are quite popular. These solutions can do wonders, but it’s important to ensure you don’t lose site of the big picture when retrofitting these types of solutions into computer rooms. Make sure you consult your fire integrity consultant before moving forward with a containment solution.

Think of integrity room testing as a means of understanding air tightness/energy efficiency as well as protecting your equipment and you will get more out of the whole exercise.

 

By John Konstantakopoulos