Data center fires often go unreported — to minimize insurer response, limit public knowledge, and various other reasons.
This denial regarding risk can contribute to complacency when it comes to data center fire protection. However, according to UL’s Consumer Technology, “Fires are perhaps the least predictable cause of data center outages, as well as the cause that poses the greatest potential hazard to the health and safety of workers.”
Fires may not be the most common cause of data center downtime, but they do occur and can cause major service interruptions. Data center consulting company Capitoline reports that, after IT-related issues, fire incidents are the leading cause of data center outages, and they account for the longest periods of downtime — in excess of 24 hours on average. After power issues, fire incidents account for 21% of data center outages, according to the companu.
The costs of a data center fire can range from life safety impact and economic losses (both direct and indirect) to data loss and the cost of redundant systems. Another cost may be the most difficult to recover from, and that’s the loss of a facility’s professional reputation. Whether the computing environment encompasses far-flung data closets for edge computing or modular containers added to quickly scale computing capabilities, protecting data center facilities with automatic fire suppression should be given careful consideration.
With data stored and backed up in multiple locations, there may be a reduced need for automatic fire suppression systems. A fire or other catastrophic event, at worst, would result in the loss of relatively inexpensive servers and racks, while data center operations could be seamlessly transferred to another redundant location.
However, even a small fire can lead to a system collapse causing economic loss and potential brand damage. When a faulty piece of power control equipment at a data center for a major U.S. airline hub caught fire in 2016, sparking a surge that knocked out power, servers that did have backup power were unable to communicate with those that did not, taking down the airline’s system and causing the delay or cancellation of over 4,000 flights. The incident illustrates that cloud computing has not eliminated the need for data centers to protect their physical systems from disruptive events like fire.
Fire Suppression Challenges
Data centers present more complex challenges for fire suppression than most conventional office buildings, largely due to four main features they typically possess: open areas, sensitive equipment, climate control, and standby power.
Data center IT equipment is placed in open areas referred to as white space. These spaces can either be densely or sparsely packed. Both have their challenges. White spaces that are densely packed with equipment make it difficult to pinpoint the source of smoke, while the open spaces can add challenges for identifying and suppressing a fire.
Data storage equipment is very sensitive to temperature changes. Even a moderate increase in temperature due to a fire can create serious problems for servers and other equipment, which means equipment can be damaged even if a fire is contained in a relatively small area. Server rooms require fire suppression systems that are safe for people and nondamaging to sensitive electronics.
The need for climate control to dissipate the heat generated by increasingly high-density servers is a major design (and energy consumption) factor for data centers. Most facilities still depend on air conditioning to combat server-generated heat. However, these HVAC systems can actually help a fire spread by transporting smoke and heat to other parts of the facility and feeding the fire with fresh air, literally fanning the flames. Furthermore, the system’s exhaust vents can remove smoke from a room before it can reach and activate detectors.
Finally, the standby power generation equipment that data facilities depend on for power quality and reliability can be a potential source of fire. In fact, fire risks associated with backup power equipment are probably the risk best understood by data centers. Backup generator rooms contain hydrocarbon fuel (typically diesel) and are subject to intense fires. Other fire hazards in electrical closets and generator rooms include overload or short circuit of electrical components; technical faults in a generator or battery units; and ignition of fuel, plastics, or batteries.
Switchgear, UPS systems, transformers, and diesel backup generators all require fast-acting, automatic suppression that can extinguish electrical and high-energy hydrocarbon fires. The increasing adoption of new battery technologies for energy storage brings fire risk that may not have been considered or planned for. The most widely used system today is lithium-ion (li-ion) battery technology and, due to its energy density and potential for thermal runaway (where excessive heat creates even more heat), can lead to fire or explosion, requiring rapid suppression.
It’s important that facilities have fire sensors and smoke detectors installed in all areas of the data center so, wherever a fire may start, it can be detected as soon as possible and suppressed. There should also be an adequate supply of a fire suppression agent and enough dispersion nozzles installed to properly protect valuable equipment and data.
FIRE SUPPRESSION ALTERNATIVES
Fire suppression systems need to quickly control fire without damaging a data center’s contents or endangering its occupants — and do so without leaving messy residue or discharging large amounts of water. The most frequently used suppression methods that fit these requirements are clean agents and water mist, respectively.
Clean agent fire suppression
A clean agent is defined by The National Fire Protection Association (NFPA) as “an electrically nonconducting, volatile, or gaseous fire extinguishant that does not leave a residue upon evaporation.” Clean agent systems disperse the extinguishant from storage cylinders to quickly suppress a fire before it reaches the flame/heat stage that activates the building’s code-required sprinkler system. Once a fire is suppressed, clean agent gases are easily removed by ventilation. Since they leave no residue, there is no equipment damage and no costly, time-consuming cleanup needed.
Clean agents typically include halocarbons, fluorinated ketones, or inert gases (such as nitrogen or argon or blends thereof). Halocarbons and fluorinated ketones suppress fires by a combination of physical (80%), due to their relatively high heat capacity, and chemical (20%) mechanisms without affecting the available oxygen. Inert gases suppress fires by means of reducing the oxygen content within a room to the point at which fire can no longer burn.
Inert gases are a special class of clean agents that are considered the most “green” as measured in terms of global warming potential (GWP). The inert gases used are naturally present in the atmosphere and make no known contribution to the depletion of the ozone layer. While adoption in the U.S. is expected to increase in due course, Europe already favors inert gas fire suppression because of the European Union’s (EU’s) F-gas regulation to phase down “highly warming fluorinated gases.”
Water Mist Fire Suppression
Water is the most commonly used suppression agent in buildings of all kinds since conventional water sprinklers are required by nearly all state and local fire codes. Sprinkler systems are intended to protect structures and are minimally concerned with protecting the building’s contents. However, putting a data center fire out with a large amount of water — between 30 to 36 gallons per minute from a single sprinkler head —can be a case where the solution is worse than the problem. Fortunately, there is an alternative water-based fire suppression solution, which can greatly reduce the amount of water needed to suppress fires and has been specifically tested for data center fire suppression under FM Approvals 5560: Water Mist.
Water mist consists of finely atomized water droplets. In a high-pressure water mist system, 99% of the droplets measure less than 100 microns in size, thus providing a larger surface area for heat transfer. This permits more of the water mist to be vaporized into steam and provides the radiant heat blocking and cooling effect necessary for fire extinguishment. The larger droplet sizes of both low-pressure water mist and traditional sprinkler systems do not evaporate as quickly; therefore, greater volumes of water are required for fire extinguishment.
Since much of the water is vaporized during the suppression process, water mist systems minimize damage to property and critical assets. They also address other disadvantages of conventional sprinklers, such as the enormous amount of water that sprinklers discharge. Particularly in locations with limited water supply or where municipal water pressure is low, the fact that water mist suppression uses 50% to 90% less water than conventional sprinkler systems is significant. Also, while sprinkler systems often use the same water supply as fire hydrant lines (water that can contain sediment and other impurities), water mist systems use potable water, free of contaminants.
Suppression system design approaches
Data centers have many different sizes and configurations, which are important factors in determining the appropriate design of a fire suppression system. Areas requiring fire protection can range from an entire building to a single floor, a room, or just specific equipment or assets.
Total flooding suppression
Computer rooms within data centers are typically protected by a “total-flooding” clean agent system. When a fire occurs, the entire room is flooded with the fire suppression agent. The quantity of agent required for fire suppression is calculated based on the overall volume of the protected room. The agent gas must be mixed homogeneously throughout that space to achieve an effective suppression concentration.
In order to contain the clean agent long enough to suppress a fire, the room or enclosure must be airtight. This requires the complete sealing of all walls, floors, return air ducts, and ceiling slabs, including doorways and other possible openings, and potentially shutting down HVAC systems that may cause the agent to be removed from the room through return air ducts.
On the other hand, installing a water mist system may not require special alterations to a room/space or an HVAC shutdown. This is especially beneficial in the protection of data centers.
Clean agent and water mist systems can be deployed effectively in facilitywide fire suppression. The choice between the two is often based on the potential hazard, economics, and overall fire protection objectives. Traditionally, gaseous clean agent systems have been installed in addition to standard building fire sprinkler systems as an effective first line of defense for sensitive electronics. Gaseous systems tend to be more economical in spaces of under 8,500 square feet and with 15-foot ceilings.
Water mist can be deployed in the same spaces as clean agents and can also cover spaces within the facility not normally protected by clean agents, such as office or storage areas that may exist in the same building envelope and be served from the same water mist pump. This means that a water mist system can be a facility’s primary fire suppression system, eliminating the need for sprinklers.
Rather than protecting an entire data facility, fire suppression systems can be designed to protect a smaller localized part or even specific equipment within it. This may be more economical than total-flood suppression, depending on the facility’s size and equipment.
Local applications within a data center can include areas with potential fire sources, such as HVAC, power and communication cables (often located in subfloors or above floor cable trays) and power rooms (including backup generators, UPS, and battery rooms).
During the design and installation of a local-application water mist system, closed, fusible-link, discharge heads must be carefully selected and positioned to provide the required coverage, activation temperature, flow, and distribution pattern for the protected area. In the event of a fire, this system will only discharge water mist in the spaces where a fire’s heat signature is detected.
Hot and cold aisles
Hot and cold aisles are very effective at controlling temperatures in data centers, but they can present a challenge to fire suppression systems. The high airflow velocities in the aisles can make smoke difficult to detect. For a clean agent system, airflow can create difficulties in maintaining the required concentration of gas for effective fire suppression.
The placement of air containment partitions in the aisles must also be taken into account in fire suppression system design in order for the water mist to distribute properly or for clean agent gases to attain the necessary concentration. Depending on their placement, containment partitions can become obstructions, impacting fire detection and suppression. In situations where containment partitions are moved, fire suppression systems already installed may need to be reconfigured.
Modular, micro and containerized data centers
Modular and containerized units offer a portable method of deploying data center capacity wherever it’s needed. A fire suppression system for these units will be affected by both the size and shape of the container and also by the amount of space between the unit’s contents and its ceiling (which determines how much room there is for distribution nozzles.) In addition, there must be enough space for the water mist or the clean agent to vaporize, especially in the case of clean agents that are converted from liquids into gases after discharge from the nozzles.
Micro data centers can be deployed as a single unit in a location such as a small office, warehouse, or factory floor, or in sets of multiple units for larger capacities in a location such as an edge computing data center. Depending on the size of a micro unit, clean agents can be used as an effective fire suppression system. The gas is dispersed inside the cabinet in the event of a fire. A cost analysis should be performed to determine the choice between protecting multiple individual cabinets versus flooding the room.
The risk of data center fires is real. Whether the computing environment is a large data center, far-flung data closets for edge computing, or modular containers added to quickly scale computing capabilities, adding automatic fire suppression can help mitigate risk. The costs of being unprepared can be high — in life safety impact, economic losses, and long-term damage to a facility’s professional reputation.
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