(1) Site Selection
(2) Space Planning
(3) Cooling
(4) Redundancy
Now it comes to the firefighting operations which can be critical for your facilities and planning.
An average 15,000 sq. ft data center carries around 2,700 kW load and releases nearly 750 tons of heat daily. Generated by small blade servers and overcrowded racks, loads of this size burden the data center’s electrical circuits, which may not be properly grounded, causing equipment to overheat in areas without proper cooling.
This is typically found in some data center built in several years ago (usually before 2000) and inside an old / pre-existing industrial / commercial buildings in which the original purpose is not for data center and the renovation and facilities' improvement are far more complicated and difficult.
Specifying the appropriate fire detection and suppression systems for each data center will increase its survivability. Most fires in mission critical facilities can be prevented if fire detection and suppression systems are properly designed, installed and commissioned in accordance with applicable standards.
FIRE DETECTION SYSTEMS
The unique airflow patterns within a data center create a challenge for smoke and fire detection systems. Unlike a typical commercial building, the data center is outfitted with hot and cold aisles and underfloor and overhead spaces, each separated to contain airflow within the space. For this reason, conventional detection methods don’t meet the data center’s needs. Instead, additional fire detection strategies need to be considered concurrently to achieve reliable protection.
Each data center will determine whether the facility needs an Early Warning Smoke Detector (EWSD) or a Very Early Warning Smoke Detector (VEWSD). The EWSD system provides detection typically at the first sign of smoke, while a VEWSD will expose an incipient fire smoldering for hours or days before a flame ignites.
Early Warning Smoke Detector (EWSD)
Automatic spot-type detectors are the most common form of EWSDs, available in ionization and photoelectric types. Using ceiling sensors, these passive detectors rely heavily on high airflow for their optimal performance. Duct detectors are installed in the supply and return ducts of HVAC systems to prevent smoke spread by initiating control of fans, dampers, etc. As they sense particles of combustion, they transmit a supervisory alarm to the fire alarm panel urging it to shut down the air handling unit.
The International Building Code requires high-rise buildings with air in the return and exhaust air plenums with a capacity greater than 2,000 cfm to have a duct smoke detector in a serviceable area downstream of the last duct inlet.
Very Early Warning Smoke Detector (VEWSD)
An aspirating smoke detection system, on the other hand, is an active VEWSD, constantly sampling particles of air for the presence of visible or invisible smoke, with its piping network, an aspirating fan and a highly sensitive detector. Less dependent on the airflow in the room to transport smoke to the detector, the VEWSD carries extremely low accidental discharge rates, with a maximum transport time from the most remote sampling port not to exceed 120 seconds. Air sampling systems are specified where very early detection is crucial, in data centers and other high-tech communications facilities.
Cross-zoned Detection
A critical facility should consider employing its smoke detectors as part of a cross-zoned scheme, which requires the installation of two smoke detectors in the same area that are run on separate circuits.
In this case, when a fire is detected, the panel will require activation of both circuits before the release of a fire-extinguishing agent. Cross-zoned detection systems minimize possibility of accidental discharge due to false alarm and may provide an additional opportunity for on-site personnel to eliminate an impending risk factor. (In a data center, only smoke detectors should be cross-zoned, heat detectors need not be.)
FIRE EXTINGUISHING SYSTEMS
While detection is crucial to alerting personnel in the room, fire damage can be minimized where an effective extinguishing system is installed and properly maintained. Both water and gas-based fire suppression systems can be found in today’s data centers.
Water-based Suppression Systems
Water-based extinguishing systems fight fires in two dimensions, both in the air and on the equipment, but not underneath equipment cabinets and other computer room fixtures. Ideal for structural protection, water-based extinguishing systems are available in either wet or pre-action configurations.
"Wet Configuration"
Pipes in a wet system are filled with water at all times, discharging it over the fire when the sprinkler head fuses due to heat build-up. Although the accidental discharge rates of a wet sprinkler system are minimal, an accidental discharge due to a damaged sprinkler activation pipe or fitting leak could cause considerable damage to information technology equipment, possibly resulting in a large or even fatal loss in data processing.
"Pre-action Configuration"
The more appropriate water-based extinguishing system for a data center is a pre-action system, available in both single and double interlock options, as its pipes remains dry until a reliable fire condition is detected.
The single interlock pre-action system requires the activation of heat or smoke detectors before water enters the piping, discharging it over fire upon fusion of a sprinkler glass bulb or solder link due to heat buildup in the space. The Loss of air due to a damaged sprinkler will transmit a supervisory alarm at the control panel.
With the double interlock system, water again enters the pipes upon heat detection and loss of air due to fusion of glass bulb or solder link. In both cases, when the sprinkler is merely damaged or there is a simple pipe leak, the pre-action system will transmit the supervisory alarm signal, but keep the piping networks dry.
"Water Mist System"
Recently developed very fine fire spray or a water mist system provides another option for fire suppression systems. Requiring less water to suppress a fire than traditional sprinkler systems, the water mist method extinguishes a fire by absorbing its heat and by discharging very fine droplets of water.
Water mist systems require unique hardware such as steel pipes, water container, pump, gas, nozzles, strainers, detection, and a panel. Water mist may provide a similar level of protection as a sprinkler system. For data centers, water mist systems use stainless steel pipes to avoid corrosion which causes the development of pin leak holes in sprinkler piping.
Gaseous Suppression Systems
Gas-based fire suppression systems fight fires in three dimensions, in the space itself and under the equipment cabinets. Designed to protect the equipment and data in process, gas-based systems do not leave a residue or require any clean up of the equipment after it discharges.
Similar to the pre-action system, clean agent extinguishing pipes contain no gas. Gas will discharge upon activation of the cross-zoned detection system and subsequent mechanical and electrical systems shut down, flooding the room in 10 sec (with the exception of inert gases, which are required to discharge in 60 sec). Gas in the room is specified to maintain concentration for as long as 10 min to obliterate smaller fires in any hard-to-reach places.
When the gas is discharged, your data center space has to be air-tight, with all door, floor, and ceiling openings sealed. The gases used, including FM 200, FE 25 (HFC 125), Novec 1230 and inert gasses including Inergen and argon, are odorless, non-toxic, non-corrosive, electronically non-conductive, and environmentally-friendly.
Kindly note the gas storage tanks need to be refilled and preparation for another incident. For this reason, some mission critical facilities are now reserving back-up tanks, maintaining twice as much gas storage at all times.
Integrated Systems
A typical data center will be outfitted with both water-based fire extinguishing systems and gaseous systems. If the fire isn’t suppressed by the gas system, the sprinkler system will subsequently activate, but is otherwise maintained as the official back-up extinguisher.
DATA CENTER FIRE CODES
A number of NFPA fire codes are applicable to the data center environment. Each governing a different aspect of the facility from design through maintenance, these standards work in concert to protect your mission critical facility from the threat of a fire. Here are examples
NFPA 10 Standard for portable fire extinguishers
NFPA 25 Standard for inspection, maintenance and testing of water-based fire protection systems
NFPA 72 National Fire Alarm Code
NFPA 75 Standard for protection of information technology equipment
NFPA 76 Standard for fire protection of telecommunications facilities
Please refer to the complete list of NFPA standards from National Fire Protection Association.
About the Blogger
Strategic Media Asia Ltd (SMA) is one of the Approved CPD Course Providers of the Chartered Institution of Building Services Engineers (CIBSE). SMA exists to provide an interactive environment and opportunities for members of IDC industry and engineers to exchange professional views and experience on data center design, critical infrastructure system, electrical and mechanical facilities, etc.
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