A question commonly proposed to fire protection engineers called on to design a computer room fire suppression system for a new facility goes like this: “What type of fire protection is appropriate for our computer rooms and data storage areas?” The answer to this question depends on many factors and in fact, leads to viable answers given today that may very well be quite different from the answer given five or ten years ago.
Two common suppression systems no longer used for computer rooms are Halon and carbon dioxide. It wasn’t too long ago that computer rooms around the globe represented an immense market for Halon 1301 systems. Halon 1301 was once recognized as the most effective chemical fire suppression agent developed. But today, halogenized agents (newly produced ones) are not a protection option since we now know that all halons are ozone depleters. The bromine atom in Halon 1301 reacts readily to destroy ozone molecules. The production of halon itself has essentially ended as of January 1, 1994. Another non-option for Computer Room Fire Suppression is carbon dioxide extinguishing systems. Since CO2 displaces oxygen, it’s discharge would cause asphyxiation or suffocation to any occupants present. A low-pressure carbon dioxide system, which would cost about double what a halon system would to install, could realistically be installed in the computer room sub-floor space only. This is environmentally acceptable, and would require no clean-up whatsoever.
Computer Room Fire Suppression – Halon is Extinct
With the phase-out of Halon 1301 (and 1211), several chemical companies set out to find suitable alternate replacement agents. No one has ever really come up with a “drop-in” pound-for-pound mimic of halon. The first qualification to be realized is US EPA approval, particularly from their Atmospheric Protection Division. The Clean Air Act requires the US EPA to research and report to the public the status of potential halon substitutes. The US EPA publishes their findings in the Significant New Alternatives Policy (SNAP). The EPA designates agents as either acceptable, unacceptable, or pending. Through all this, the NFPA has established a new technical committee. In 1991 the committee’s task was to prepare a design standard to be ready for the commercialization of the agents. Now known as NFPA 2001, “Standard on Clean-Agent Extinguishing Systems,” this internationally accepted standard shows which agents are acceptable for occupied space protection. This determination is made by comparing the minimum design concentration for the agent with the highest acceptable toxicity exposure. NFPA 2001 requires that inert gas systems be designed with an agent concentration of 43% or less and an oxygen concentration of 12% or more if personnel are not able to evacuate the area within one minute. Currently, NFPA 2001 (and SNAP) has recognized eleven Halon replacement agents. Two that are in wide use today are IG-541 (better known as Inergen) and HFC-227 (commonly called FM-200). Both are used for the protection of sensitive electronic equipment and other highly critical environments not suitable for water-based extinguishment. Each agent has its pros and cons with respect to chemical composition, equipment hardware, installation restrictions, and system recharge cost, just to mention a few.
Computer Room Fire Suppression – Understanding Your Needs
The question that you need to put to the business owner is, what value do you place on the operation of the computer room? Does your business depend on uninterrupted 24-hour operation of the computer room in order to survive? Typically, the Computer Room Fire Suppression system desired must be comprised, in part, of the following essential features:
• an agent that is non-toxic
• a fast-responding system
• a system that does not bring about a major clean-up problem
• an electrically non-conductive medium
A critical component in the planning stages for computer room fire suppression is understanding the potential losses to consider, including not only the loss of computer hardware, but the loss of computer down-time. If continued operation of the computer room is imperative, then you will want to investigate the (fairly costly) installation of quick-responding chemical agent systems. Once more, two of the more popular gases that are both habitable (people-safe) and environmentally-friendly are FM200 (produced by Great Lakes Chemical) and Inergen (made by Ansul). If systems do activate, the down-time when using either system is very short.
Computer Room Fire Suppression – Inergen Systems
Inergen is a very clean agent, which makes it a popular choice (at least) for the sub-floor space and also for switchgear rooms, tape storage, vaults, process equipment, and any electronic area containing irreplaceable equipment. It is also widely used for the computer rooms, and its discharge time is anywhere from 45 seconds to a full minute. It is an inert gas with superior flow characteristics. It is a mixture of three naturally occurring atmospheric gases: (52%) nitrogen, (40%) argon, and (8%) CO2. The Inergen gas curtails and extinguishes fire by lowering the oxygen content beneath the level that supports combustion. But it should be noted that due to the CO2 present in Inergen, the brain continues to receive the same amount of oxygen in an Inergen atmosphere as it would in a normal atmosphere, for reasonable periods of time. Also, the agent does not produce a fog, so visibility in a compartment remains adequate for evacuation purposes. Designed for versatility, Inergen cylinder valves can be opened electrically, pneumatically, or manually. Inergen has zero Ozone Depletion Potential (ODP), zero Global Warming Potential (GWP), and a zero atmospheric lifetime. When Inergen is released, its components simply resume their normal role in the earth’s life cycle. Its installation requires the presence of one or more large alloy steel cylinders (similar to that of CO2 cylinders), which holds the gas at vapor pressures in excess of 2000 psi at 70F. The amount of agent required is calculated in cubic feet rather than pounds. Pressure reducers in the cylinder manifold are a necessary system component, as is the use of Schedule 80 steel pipe up to the union orifice where pressure is reduced. Because Inergen is required to reach 95% of its design concentration within 45 seconds, coupled with its higher vapor pressure, the Inergen fire suppressant cylinders can be stored a fairly long distance from the protected hazard utilizing smaller diameter discharge piping. The major advantage of an Inergen system is its quick response and the larger extent to which it can be reliably effective.
Computer Room Fire Suppression – FM-200 Systems
FM200 is a chemical blend (heptafluoropropane), stored as a liquid within the agent cylinder similar to that of Halon-type cylinders. FM200 has zero ODP, a GWP of 0.3 to 0.6, and an atmospheric lifetime of 31-42 years. This is in strict compliance with environmental regulations. It is thermally stable and on the SNAP list. The FM-200 discharge piping utilizes Schedule 40 pipe. FM200 requires less of a footprint to hold agent in a cylinder. The supply tank will be proportionately smaller. It lays in pipe at approximately 60 psi, and discharges quickly for a duration of about ten seconds to achieve a 7% concentration. Due to the typical 7-10% concentration design, the agent storage requires minimal space. But due to the relatively low (59-60 psi) vapor pressure, the FM-200 cylinders are required to be within close proximity of the hazard. Actually, the physical properties of FM200 considered along with its traditional extinguishing requirements, allow its use in the same type of equipment that would be used for Halon 1301, requiring minimal hardware alteration for retrofit situations. Usually the same detection and control panels can be used. Installation of the first commercial FM-200 system began in December of 1992.
In addition to computer rooms, typical applications for this clean, gaseous agent include telecommunication equipment facilities, data processing libraries, emergency power facilities, flammable liquids storage rooms, museums, clean rooms, process control centers, and so on. It does create hydrogen chloride as a byproduct, which may attack existing documents or other “archive” materials. It will not, however, corrode sensitive electronic equipment, and contains no particulates or oily residues. In fact, it leaves very little residue and is a quite popular extinguishing agent in use today for the protection of computer rooms. Proponents of FM-200 boast code-compliant, cost-effective system configurations. For these reasons the FM-200 systems are currently the most popular non-water based computer room fire suppression systems.
Computer Room Fire Suppression – Preaction Systems
If you are working with tight budget considerations, then you may want to investigate the installation of a Preaction system for computer room fire suppression. BOCA defines a Preaction system as a fire sprinkler system employing automatic sprinklers attached to a piping system containing air with supplemental fire detection that is installed in the same area as the sprinklers. Actuation of the fire detection or smoke detection system automatically opens a valve that permits water to flow into the sprinkler piping system and to be discharged from any open sprinklers. Preaction systems historically have had limited use in electronics-intensive applications, where the mere mention of the word “water” is probably dangerous.
Some modifications are advisable. As an example, a time delay can be built into the preaction control panel, creating a time lapse before water commences to fill the system. This delay provides the building staff with a chance to investigate the incident prior to the introduction of water at the scene. As additional safety measures, on/off sprinkler heads and floor drains may be installed. Also, smoke detectors can be cross-zoned, so that two detectors must go into alarm before the preaction system is charged with water. A Preaction system, while a less expensive option, is really insurance for protection of the building structure itself. The loss of the entire building will be protected effectively by a properly installed Preaction system, although the degree of water damage may sacrifice the equipment data center in the process. The loss of down-time may be considerable. However, the Preaction system will not activate until there surely is fire present.
The question presented to the business owner is always: what type of protection do you want? Again, the type of protection generally desired for a computer room is total flooding fire extinguishment, suppression that occurs quickly before any damaging smoke is generated, and without wetting equipment and contents of the enclosed room. The desired qualities of gaseous agents present near the fire origin must include quick-response time, near-zero ozone depletion, short atmospheric life, and low toxicity. If fire suppression is accomplished within ten seconds of system activation, the release of toxic and/or corrosive gases (acidic products of decomposition under fire conditions) will be minimized. When you need to guard absolutely against water damage to sensitive electronic gear or high-value areas, a gaseous agent is a wise choice for fire protection. The question of which agent is best suited is not simply this one or that one. Neither is the “better” gas. It should be obvious to any discerning mind that neither agent, nor any of the 11 recognized by NFPA 2001, is the most optimum for all possible applications. Many issues with respect to hazard definition, size of hazard, agent cylinder storage size, locations, installation cost, and agent recharge cost must be addressed. As an example, while the FM-200 gas may cost 8-10% less up front, it has a higher replacement cost. When choosing between FM200 and Inergen, you have to look at the total situation, talk to a professional, and make a choice. The effectiveness of clean-agent systems is always dependent on the integrity of system interaction with process controls. And the designer must determine an adequate amount of agent to supply, in accordance with recommended design concentrations for the cubic-foot volume of the computer room. With regard to clean-agent system design, there are several “red-flags” that the engineer must strive to avoid:
- room smoke detectors must not be placed within close proximity of air diffusers
- doors must be self-closing, and never “blocked open”
- inadequate pressure venting may result in over pressurization of the enclosure
- too much air-handling equipment may result in loss of agent during discharge
- cable and ventilation openings must be minimized
- incomplete fire separations will allow exposure from external fires
- concentration levels (esp. for flammable-liquids hazards) must be adequate
- deficient fire barriers will fail to contain the gaseous agent
Computer Room Fire Suppression – Water Mist Systems
One final option that is growing in the fire suppression arena for computer room fire suppression is water mist systems. The efficiency of these systems is well documented, and they may be economically advantageous as halon alternatives in many applications. Their fine water spray absorbs heat, cools flame by diluting oxygen with steam, and reduces overall heat intensity. The water-cooling effect is enhanced as a result of the division of water into small drops, which also maximizes evaporation. The creation of fine droplets increases the surface area available for heat absorption. Similar to the result firefighters obtain with fog streams, the mist allows a fuller interaction with air currents, which will scatter the droplets over a larger area, blocking the transfer of radiant heat to nearby combustibles. This process will extinguish fire and not cause unacceptable levels of water damage.
Water mists systems can provide protection for much larger areas than the popular gas alternatives. Like most of the fire suppression technology the equipment used in water mist systems has advanced significantly in just the last 5 years, making it a viable alternative. The US Navy and other government buildings are now using water mist system for protection in a variety of environments. An informed choice for the selection of the most appropriate fire detection and suppression system for computer rooms is a critical step for the fire protection designer. And regardless of the system selected, containment of the protected space and separating it from the rest of the building is equally important.