Sometimes the unimaginable happens. A fire can threaten to destroy a data center. To protect the valuable equipment and information housed in the facility, it is critical to install a fire suppression system adequate to the size, type and operational responsibilities of the complex. By definition, a fire suppression system is a combination of fire detection and extinguishing devices designed to circumvent catastrophic business loss as a result of a fire. This loss includes not only the cost of equipment replacement, but also the cost of recovering lost data or business-specific applications.
Detection Systems: The First Line of Defense
A critical component of any suppression system is smoke detectors. Depending on the application, they can be of the photoelectric or ionization type. Detectors perform several vital functions:
- Warn facility occupants of possible fire.
- Shut down all electrical service to the equipment so as not to “fuel the fire.”
- Activate the suppression medium.
If it is properly designed, the detection system can also be used to limit business loss due to power-off interfaces by detecting a system failure rather than an actual smoke condition.
A highly effective detection system is one we call an “intelligent” system. It uses a software-based early warning system to provide an accurate means of detection and verification at the ceiling plane and underfloor plenum.
Water and Clean Agent Gas: Common Suppression Media
Suppression medium is activated if a true emergency is detected. The two most commonly used media to put out a fire are water and clean agent gas such as FM200, Inergen, and NAFS-III.
Determining which type of suppression medium to use depends in large part on the requirements of local code enforcement authorities, building and/or landlord stipulations, and input from insurance underwriters. It also depends on user preference, which is influenced by such factors as cost, business risk relative to data recovery, existing systems, and so forth.
Water sprinkler systems
Water sprinkler systems are found in most buildings regardless of the presence of a data center. As a general rule, where sprinkler systems exist, it is less expensive to convert to a pre-action sprinkler system than to install a clean agent system. Pre-action sprinklers are the water-based choice for data centers and refer to systems that control the flow of water to pipes in the ceiling plane. Smoke and heat activate a valve that advances the water to the ceiling plane. That way, inadvertent damage to equipment from leakage or accidental discharge is prevented. (By comparison, with an ordinary sprinkler system, water is contained in pipes in the ceiling plane at all times.)
Water is highly effective at putting out fires and is well suited for areas like printer rooms that contain combustible materials like paper and toner. The downside of water-based systems is the messy and lengthy clean up and recovery time after a water discharge.
There are primarily three clean agents presently vying for acceptance in the marketplace, FM200, NAF S-III, and Inergen. These agents were developed in response to the phase-out of Halon and the development of NFPA 2001, which was adopted in the Fall of 1994.
Consideration of these agents as alternatives to CO2 in under floor applications is viable. The costs of these systems has dropped in recent years due to more competition in the market place with competing vendors offering these various gas options.
- FM-200 (Heptafluoropropane – HFC-227EA) is a colorless, liquefied compressed gas. It is stored as a liquid and dispensed into the hazard as a colorless, electrically non-conductive vapor. It leaves no residue. It has acceptable toxicity for use in occupied spaces when used as specified in the United States Environmental Protection Agency (EPA) proposed Significant New Alternatives Policy (SNAP) program rules. FM-200 extinguishes a fire by a combination of chemical and physical mechanisms.
FM-200 is an effective fire-extinguishing agent that can be used on many types of fires. It is effective for use on Class A Surface-Burning Fires, Class B Flammable Liquid, and Class C Electrical Fires.
On a weight of agent basis, FM-200 is a very effective gaseous extinguishing agent. The minimum design concentration for total flood applications in accordance with NFPA 2001 shall be 7.0%.
- NAF S-III is a clean, non-conductive media used for the protection of a variety of potential fire hazards, including electrical and electronic equipment. NAF S-III is a clean gaseous agent at atmospheric pressure and does not leave a residue. It is colorless and non-corrosive.
NAF S-III acts as a fire-extinguishing agent by breaking the free radical chain reaction that occurs in the flame during combustion and pyrolysis. Like Halon 1301, NAF S-III has a better efficiency with flaming liquids than with deep-seated Class A fires.
NAF S-III fire extinguishing systems have the capability to rapidly suppress surface-burning fires within enclosures. The extinguishing agent is a specially developed chemical that is a gas at atmospheric pressure and is effective in an enclosed risk area. NAF S-III extinguishes most normal fires at the design concentration by volume of 8.60% at 20° C.
NAF S-III is stored in high-pressure containers and super-pressurized by dry nitrogen to provide additional energy to ensure rapid discharge. At the normal operating pressure of 360 psi (24.8 bar) or 600 psi (42 bar), NAF is in liquid form in the container.
Once the system is activated, the container valves are opened and the nitrogen propels the liquid under pressure through the pipe work to the nozzles, where it vaporizes. The high rate of the discharge through the nozzles ensures a homogeneous mixture with the air. Sufficient quantities of NAF S-III should be discharged to meet the concentration required and the pressure at each nozzle must be located to achieve uniform mixing.
- Inergen is composed of naturally occurring gases already found in Earth’s atmosphere (nitrogen, argon, and CO2). Inergen suppresses fire by displacing the oxygen in the environment. Inergen, however, is not toxic to the occupants because of the way it interacts with the human body. The level of CO2 in Inergen stimulates the rate of respiration and increases the body’s use of oxygen. This compensates for the lower oxygen levels that are present when Inergen is discharged.
Inergen is stored as a dry, compressed gas and is released through piping systems similar to those utilized in other gaseous suppression systems.
- FE-25 fire suppression agent is environmentally acceptable replacement for Halon 1301. FE-25 is an odorless, colorless, liquefied compressed gas. It is stored as a liquid and dispensed into the hazard as a colorless, electrically non-conductive vapor that is clear and does not obscure vision. It leaves no residue and has acceptable toxicity for use in occupied spaces at design concentrations. FE-25 extinguishes a fire by a combination of chemical and physical mechanisms. FE-25 does not displace oxygen and therefore is safe for use in occupied spaces without fear of oxygen deprivation.
FE-25 has zero ozone depleting potential, a low global warming potential, and a short atmospheric lifetime.
FE-25 closely matches Halon 1301 in terms of physical properties such as flow characteristics and vapor pressure. The pressure traces, vaporization, and spray patterns for FE-25 nearly duplicate that of Halon 1301. The minimum design concentration for FE-25 systems is 8.0% meaning that about 25% more of FE-25 agent will be required. Fe-25 requires about 1.3 times the storage area of Halon.
When retrofitting existing Halon 1301 system, the nozzles and cylinder assembly will need to be upgraded, however, the piping system likely will not need to be changed, which is cost-effective retrofit that minimizes business interruption.
- FE-13 is a clean, high-pressure agent that leaves no residue when discharged. FE-13 efficiently suppresses fire by the process of physiochemical thermal transfer. The presence of FE-13 absorbs heat from the fire as a sponge absorbs liquid. FE-13 is safe for use in occupied spaces up to a 24% concentration. Design concentration for total flood application is 16%.
- Novec 1230 is the newest clean-agent gas available on the market. It is marketed as a long-term sustainable alternative to FM-200 and Halon. Novec 1230 has a 0.0 ozone depletion potential (equivalent to FM-200), but has an atmospheric lifetime of only five days, compared to FM-200’s half life of over 20 years. Novec 1230 has a zero global warming potential. Novec 1230 is designed to a concentration level of 4-6%, which will require less gas than other clean agent. Novec 1230 extinguishes the fire by heat absorption, and is heavier than air, so the gas will sink in the room. Novec 1230 is also safe for electronic equipment, so the data center may not have to be shut down in the event of a gas discharge.
Novec 1230 will require the same amount of tanks as FM-200, and is stored as a liquid under pressure. Under normal atmospheric conditions, it will exist as a gas. The system is approximately 5-7% more expensive than FM-200.
|Table – Relative Cost Comparison of Extinguishing Methods|
(1) Total flooding.
(2) Does not include the cost of fire alarm and detection system. Probable cost < $4,000.
(3) Assume a fully sprinklered building and
(4) Includes the cost of the extinguishing agent.
|Extinguishing Agent||Design Concentration, Density||Agent Quantity||Installation Cost (4)||Recharge Cost||Design Basis|
|FM-200||7.44 % by volume||364 lbs||20% more than Inergen||Almost twice the cost of Inergen||(1) + (2)|
|FE-25||96% by volume||335 lbs||Parallel to FM-200 less gas||20%-25% less than FM-200||(1) + (2)|
|Inergen||37.5 % by volume||4780-cu-ft||(1) + (2)|
|NAF S-III||8.60 % by volume||___||___||___||(1) + (2)|
|Pre-Action Sprinklers||0.1 gpm/s.f water||N/A||1/4 the cost of Halon or Inergen||N/A||(2) + (3)|
Note: NAF S-III does not appear to have the market presence to be a viable alternative.