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| A reduced-oxygen fire-prevention system differs from conventional fire-extinguishing systems in that it provides a continuous level of prevention rather than a one-time discharge of extinguishing agent when a fire has been detected. Photo credit: ©istockphoto.com/Baran Özdemir |
I have noticed a lot of Web traffic lately regarding the evolution of data centers and their supporting technologies.
The methods of building these data centers vary from onsite builds, modular construction with site adapt, somewhere in between, or they can be part of a larger multi-tenant data center available via cloud with scalable capacity.
Sabey Corp.’s Integrate. Manhattan project is an example of a facility offering scalable, remote data storage. The project is coming online to offer 600,000 sq. ft. of multitenant data-center space in a renovated high-rise.
One question comes to mind when reviewing proposed fire-suppression systems for these high-dollar, limited-access, mission-critical facilities. Instead of adding fire-suppression systems such as gaseous clean-agent, total flooding suppression and complex dry pipe/preaction sprinkler systems, why not go back to the technologies of reduced oxygen environments? To ask the question a different way, why not prevent flame instead of waiting for it to ignite, grow to detectable size and then suppress it with a complex system?
Consider that a spark or a small fire can cause a catastrophic loss and downtime in ammunition storage areas, art galleries, banks, cold storage areas, computer facilities, document archives, libraries, security control and command rooms, underground car parks, vehicle paint facilities, vaults and warehouses — not to mention data centers.
A reduced-oxygen fire-prevention system differs from conventional fire-extinguishing systems in that it provides a continuous level of prevention rather than a one-time discharge of extinguishing agent when a fire has been detected.
Before a fire can actually occur, four things must be present in the correct proportions: an ignition or heat source, a fuel source (materials that burn), an oxidizer (gases that increase oxygen concentration and support combustion) and an uninhibited chemical chain reaction. These elements are known as the fire tetrahedron. When the components converge in the proper proportions, a fire quickly can ignite. If any component is not present in its correct proportion, a fire will not be able to ignite.
In normal circumstances, air is a mixture of oxygen and nitrogen together with small quantities of argon, carbon dioxide and other gases. Oxygen is the critical element that supports both life and combustion. When the oxygen content is intentionally lowered for special applications, the resulting gas is called hypoxic air or reduced-oxygen air.
Hypoxic fire prevention
The fire ignition threshold of air is 16.2% oxygen. By constantly maintaining a hypoxic state of air in the prevention area of 14% to 16%, ignition of Class A, B and C fires can be prevented. The reduced-oxygen atmosphere reaches everywhere the air reaches, even in enclosed spaces such as server cabinets and drawers.
Keep in mind we normally breathe in atmospheric air with an oxygen concentration of about 21%. When the atmospheric pressure is reduced to 15%, such as on a plane or at high altitude, we may feel groggy until acclimated to the new environment. The same condition is experienced with exposure to a reduced-oxygen environment, or hypoxic atmosphere.
According to http://www.nfpa.org/NFPA’s 2001 Clean Agent Fire Extinguishing Systems report, 12% minimum oxygen corresponds to a no adverse-effect level in humans and 10% corresponds to a low adverse-effect level in humans.
Hypoxic fire prevention and suppression is approved under the Environmental Protection Agency’s Significant New Alternatives Policy. EPA states this technology “does not require further review and can be marketed,” and it has a “zero toxicity and zero atmospheric damage factor.”
Confined space training
Since some people are sensitive to a hypoxic environment, OSHA requires reduced oxygen environments be treated as permit-required confined spaces. Occupational Safety and Health Standard 29 CFR 1910.146 defines a space with an “atmospheric oxygen concentration below 19.5% or above 23.5%” to be hazardous. A space that contains or has the potential to contain a hazardous atmosphere is defined as a permit-required confined space (permit space).
The United Kingdom’s Health and Safety Executive mandates that areas with reduced-oxygen atmospheres also classify as confined spaces. Generally, all personnel are to be evaluated and trained prior to gaining access to confined spaces due to health and safety risks of the space configuration, its contents and atmosphere. Warning signs at space entrances are required where oxygen content is reduced to 17%. More stringent safeguards are required as oxygen content parameters are reduced to 15%. European standardization information, drafted and presented within the last year, is available at www.cowiprojects.com.
Application in a space depends on the leakage rate of the space. How drafty is the building? An oxygen-reducing system will have to work much harder or have a larger capacity to keep up with outside air increasing the air oxygen level in the protected space. Therefore, a reduced-oxygen system is more effective in a tightly constructed, conditioned space commonly used for data centers. Building leakage rates also affect gaseous suppression systems as minimum agent concentration hold times are required, but only during total flooding activation.
A conventional fire-detection system is not necessarily required within the protected area. However, it is recommended to install an air-aspirating smoke-detection system to detect the presence of smoldering or pyrolysis.
The installation design must incorporate a minimum of two oxygen-independent sensors in different locations in each protected area. The sensor outputs are sent as required to monitoring and control points (e.g., the fire alarm panel and the building management system). The location of the oxygen sensors must not be influenced by the injection of hypoxic air or nitrogen. The readings from the oxygen sensors reflect the homogeneity of the hypoxic air environment.
Design and installation of hypoxic air fire-prevention systems should follow a suitably detailed hazard and risk assessment, including consideration of the suitability of such a system for the specific application at its location and any protective measures required for the health and safety of all persons having access to the protected space.
