Data center fire suppression

The average 14,000-sq.-ft data center pushes a 2,400 kW load and 700 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.

05/01/2008


The average 14,000-sq.-ft data center pushes a 2,400 kW load and 700 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.

 

A simple equation applies: Large loads + combustible scenarios = the greatest threat to the data center’s 24/7/365 existence: a computer room fire.

 

Flames and their smoke cause irreversible damage to a facility and its data processing equipment, often forcing the facility to close its doors. According to the U.S. National Archives and Records Administration , College Park, Md., as many as 93% of companies that lose their data centers for 10 days or more due to a disaster file for bankruptcy within one year.

 

Designing today’s critical facilities for their survivability is key. Minimizing the risk of fire by maximizing detection and suppression with the right systems will mitigate the threat that large loads and combustible scenarios pose to any data center’s uptime.

 

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.

 

The architectural and mechanical layout of 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.

 

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.

 

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.

 

After evaluating EWSD and VEWSD systems, 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. (Note: 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.

 

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.

 

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. 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.

 

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 (100 to 120 micron) 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. Underwriters listed water mist systems for data centers using stainless steel pipes to mitigate micro biologically-influenced corrosion (MIC), 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. Clean agent extinguishing systems suppress fire in the incipient stage.

 

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). Although it takes under two minutes to suppress the flames, done by absorbing the fire’s heat, 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.

 

In order for gaseous systems to be effective, though, the space has to be air-tight, with all door, floor, and ceiling openings sealed. The gases used, including FM-200 (HFC 227), FE-25 (HFC-125), 1230 Novec, and inert gasses including inergen (IG-541) and argon, are odorless, non-toxic, non-corrosive, electronically non-conductive, and environmentally-friendly. (Note: Venting of the space is required when high-pressure inert gasses are used.) Once a gas discharge has taken place, however, its storage tanks need to be refilled. Very often, depending on the location of the data center and its proximity to a vendor, it can take as long as 24 to 48 hours to replace the gas agent needed to suppress another fire. For this reason, some mission critical facilities are now reserving back-up tanks, maintaining twice as much gas storage at all times.

 

Integrated systems

Most local jurisdictions require water-based fire extinguishing systems, while gaseous systems often provide the preferred protection for computer room equipment. In order to satisfy each requirement, a typical data center will be outfitted with both. Here’s how it works: 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.

 

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.

 

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.

 

1. NFPA 10 Standard for portable fire extinguishers. This code requires the installation of portable fire extinguishers throughout the premises. The use of a portable extinguisher will suppress a fire in its incipient stage and preserve activation of the fixed extinguishing system, conserving resources and expenditure. Hand-held, clean agent fire extinguishers should be used because of their colorless, odorless, non-conductive suppression agent.

 

2. NFPA 25 Standard for inspection, maintenance and testing of water-based fire protection systems. This code specifies which tests and frequency of tests need to be performed weekly, monthly and yearly. For example, water flow switches are tested once a year, while control valves are inspected weekly.

 

3. NFPA 72 National Fire Alarm Code. This standard outlines the requirements for spacing detection systems, including how many are needed and where they are to be installed as well as the locationand installation of audible and visible appliances, addressing their frequency and maintenance requirements. For example, manual pull stations are required within 5 ft. of each exit, while the fire alarm panel must annunciate all the suppression, detection and notification zones.

 

4. NFPA 75 Standard for protection of information technology equipment. This code governs data center construction, in regard to the requirements of its fire protection and detection systems, its HVAC equipment and power supply requirements, including disconnecting and grounding. The Standard requires the installation of automatic detection devices both above the suspended ceiling (plenum) and below the raised floor, with a spot type detectors or air sampling system.

 

5. NFPA 76 Standard for fire protection of telecommunications facilities. This standard governs the fire protection of telecommunications facilities where telephone, data, cellular, internet, voice over internet protocol and video services are rendered to the public.

 

For a complete list of NFPA standards, visit

 

Commissioning fire detection and suppression systems

Commissioning a data center’s life safety system can be just as crucial as its initial design. Documenting and validating the system’s viability throughout the project assures both the specifying engineer and the owner that building operations match projected performance criteria.

 

The following is a short list of life safety systems that need to be commissioned and their appropriate testing criteria:

 

1. Underground fire mains shall be tested in accordance with NFPA-24 by flushing before backfilling, performing a hydrostatic test, inspecting the location of thrust blocks, and completing contractor material and test certificate.

 

2. Sprinkler system commissioning includes a pneumatic test of the dry and pre-action systems, the valve supervisory devices, and a hydrostatic test of the wet, dry, and pre-action systems; a trip test of the dry system and detection devices; a loss of air test and a solenoid release of the pre-action system.

 

3. The clean agent extinguishing system shall be evaluated in accordance with NFPA 2001 by testing smoke detectors at the ceiling and under the raised floor by activating manual pull stations and abort switches, sampling the power shut to the equipment and by performing a flow (puff) test to make sure that pipes and nozzles are free of obstructions, a pneumatic test of piping and by verifying trouble and alarm status at the building fire alarm panel.

 

4. The fire alarm system shall be tested in accordance with NFPA 72 by verifying the monitoring of fire suppression trouble and alarm zones, testing alarm initiating devices, activation of duct smoke detectors, air handling shut down, activation of notification appliances verifying the sound levels of audible devices, elevator recall and the tie in of fire alarm panels to the UL-listed central station; verifying the sound levels of audible devices.

 

5. The VEWSD shall be tested for the travel time of its smoke alarm (maximum of 120 sec), verifying alert, action fire 1 and fire 2 status as well as trouble and alarm status at the building fire alarm panel and verifying flow pressure of sampling holes.

 

Additional references:

 

• International Code Council:

 

• Society of Fire Protection Engineers:

 

• Fire Protection Handbook:

 

Author Information

Salwan is a registered PE in both Illinois and California as well as a technical committee member for NFPA Standards 14, 24, 72, 75, 291 and a member of the Society of Fire Protection Engineers. As a senior associate at ESD, Salwan supervises the design and implementation of fire suppression and life safety systems in a variety of mission critical, residential, healthcare, education, commercial, and industrial projects.



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