High Airflows, High Risks: Protecting Datacenters
Aspirating sensor technology offers a high level of protection for datacenters while addressing the unique conditions and complications of these environments.
Ceiling aspiration air sampling points are recommended for this configuration with more predictable airflow patterns. Hot air returns, such as ducts or plenum spaces, are key areas for sampling points.
Raised floors that supply air are also recommended sampling point locations when combustible cables or construction features are present.
Similarly, the contained approach also uses a supply and return air distribution system, where the IT equipment supply and/or return airflow is completely or partially enclosed to minimize or eliminate air mixing. These contained approaches are also known as hot aisle/cold aisle configurations. For reasons of energy efficiency and cooling effectiveness, hot and cold aisle designs are now common in datacenters.
Although spot detectors are some-times considered for these containment applications, their performance is often impaired by high airflow and the limitation of detecting smoke at a spot location subject to high airflows. Air sampling detection can overcome these limitations and offer advantages over spot detectors.
“Accommodating the hot aisle/cold aisle scenario changes your detection strategy. Hot and cold issues make detection more challenging,” explains Jeffrey Tubbs, PE, FSFPE, Arup principal and Boston fire group leader. “This configuration changes the detection strategy as detection needs to account for the compartments created by the equipment. For example, detectors may need to be placed in the hot aisle exhaust components, and these detectors need to be appropriate to and listed for expected velocities and temperatures.”
Aspiration in IT Equipment Spaces
Concealed spaces are common within datacenters, such as areas above ceilings and below raised floors; such spaces are generally protected with detection systems yet do not meet appropriate standards. NFPA 75 and insurance carriers have specific requirements for areas above ceilings and below raised floors that contain cables. Highly protected risk insurance standards tend to prefer very early warning fire detec
tion provided by aspirating detection system technology.
“The decision to use early and very early detection typically is based upon tier level, the criticality of the facility, and the risk tolerance of the stakeholders,” says Tubbs. “For a business’ most critical operations, enhanced detection, either through very early detection or addition-al detection, can be important. For these cases, aspirated systems or multicriteria detectors are a viable solution.”
Raised Floors and Cabling Pathways
NFPA 75 requires automatic detection systems below raised floors of IT equipment areas that contain combustible cables. Both thermal and nonthermal damage can result if PVC cables or other plastics ignite. Early detection provided by air sampling technology can minimize the risk of damage to equipment from ignited plastic cables.
Furthermore, these systems can provide condition alerts in the raised floor to prompt appropriate personnel to remove tiles and locate the issue.
Above Ceiling/Below Floor Spaces
The ceiling plenums and below floor/ within wall spaces that define the IT equipment space are often used for air circulation from other building spaces. Consequently, there may be smoke dampers or other protective openings for air return or supply. NFPA 75 requires detection to initiate closing these openings, as well as smoke dampers to eliminate smoke contamination of the IT equipment space.
NFPA 75 requires one or more of the following three methods to be used:
- Detection throughout the above ceiling space or below floor air circulation space
- Detection at each smoke damper
- Detection at other locations where smoke may be transported into the IT equipment space (e.g. door opening from a non-IT equipment space)
Aspirating technology can easily identify smoke contamination from IT equipment space fires: install air sampling points at each damper location to sense smoke and initiate the damper closing operation. If a large number of dampers or other openings need to be controlled, then it may be beneficial to install detection sampling points throughout the ceiling plenum or raised floor plenum. This can be an effective installation because these concealed spaces may have wiring and cables that warrant detection.
Automatic Detection at Ceiling Level
Airflow path locations, such as return air grills or in-duct air sampling points, are often convenient locations for air sampling points. NFPA 75 requires early warning automatic detection systems at the ceiling level throughout IT equipment areas. Although various types of detection could fulfill this requirement, NFPA 75 does note that air sampling detection devices should be considered due to the high-airflow nature of the datacenter environment.
Aspirating detection systems operate over a wide range of airflows (0 to 4,000 feet per minute) and can be programmed for sensitivities ranging from early warning to very early warning-type detection. Aspirating detection at the ceiling fulfills basic or high sensitivity detection throughout the space, whether the data-center is operating in full air movement mode or undergoing a service outage or equipment replacement. Packaging materials and combustible boxes can present a transient fire risk during equipment upgrades and layout changes, but continuous ceiling-level air sampling detection monitors such combustible fire risks.
HVAC systems, usually referred to as CRAC or CRAH units in datacenters, monitor and maintain the temperature, air distribution and humidity in a network room or datacenter. Fan motors, fan belts, power wiring, and filters are potential ignition and fire sources. A smoldering wire or small filter ignition can introduce smoke into the cooling airstream. Consider placing aspiration air sampling points downstream of the filters on the supply air side of the CRAC or CRAH units to recognize smoke before it circulates through sensitive electronics.
Aspirating smoke detection systems, which actively monitor the ambient air throughout a datacenter, can provide the high sensitivity and continuous sampling of low quantities of smoke that may be distributed and easily diluted by high air-flow. Digital equipment designed to high standards (UL 60950, NEBS GR63) have components and shutdown features that minimize the production of smoke, yet an incident may only have a chance of being detected with an aspiration system.
Ideal air management and equipment rack cooling schemes use in-rack cooling systems integrated with plenums and aspiration air sampling ports at the top of the cabinet just before the fan location.
As datacenters keep evolving, fire protection technologies and strategies acclimate to provide integrated solutions.
David George is Director of Marketing Communications for System Sensor.
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