Maintaining the operability of computer networks, Web sites, and communications has become an absolute necessity, consider the importance of computer operations on air traffic control, nuclear power generation, national defense, surgical procedures, and financial transactions. That means fire protection engineering is an absolute necessity, too.
There are a number of ways that businesses use fire protection engineering to ensure their reliability. This article will discuss the way fire protection engineering systems, both passive and active, are engineered to meet the important goal of continuous operation and mission continuity. In order to fully understand the way fire protection systems are engineered and used to protect modern data centers and telecommunications facilities, it is important to understand the relationship between the computer hardware and the electrical and mechanical systems that serve them.
This relationship is most evident by the amount of heat that is generated by modern digital equipment, such as computer servers and telephone switching equipment. Older systems, as could be expected, were much larger and bulkier than today's digital equipment. Current digital hardware takes up far less space than earlier generation equipment occupied and generates a large amount of heat that must be continuously removed. Depending on the specific equipment and its physical configuration, failure can occur within a matter of ten or fifteen minutes if continuous cooling is not provided. Fire protection engineering has to take into consideration such problems.
This "compression of technology" has obvious benefits, but there is another more intrinsic price to be paid. For example, telecommunications switching sites can now process calls at much higher rates in relatively small facilities, serving very large geographical areas as a result. Consequently, the importance of an individual site becomes that much more critical, since a fire at a single facility can have such a widespread effect.
Another example of this is a facility that maintains Web site hosting for businesses. Web site addresses have become as essential to a business as a phone number, allowing clients and customers the opportunity to view products and services, and more importantly, make transactions. As the value of Web sites increases, the need to have them continuously available increases as well, and many businesses expect guaranteed operability of the Web hosting center. Continuous operation of a telecommunications facility, Web hosting center, or data center requires reliable, and in many cases, redundant power, cooling, fire protection, and security systems. It is Fire Protection Engineering that provides the most essential of these.
FIRE PROTECTION ENGINEERING DETECTION STRATEGIES
Sophisticated fire alarm and detection systems, fire prevention engineering and practices, compartmentation, fire suppression, and, in some instances, smoke management also serve to provide redundant levels of fire protection. Perhaps the most critical of these fire protection systems is in the area of detection. Detection systems serve the basic function of alerting building occupants of a fire condition, but are also used routinely to control the release of fire suppression systems such as preaction sprinkler and clean agent systems.
Normally, these functions are controlled by standard spot type ionization and photoelectric smoke detectors, although heat detection, flame detection, and other methods may be used where they are more appropriate for the specific hazard or application. Standard spot type smoke detectors and other devices that detect fire conditions prior to the time at which they threaten the building or occupants are referred to as Early Warning Fire Detection (EWFD). EWFD is critical to sound fire protection engineering.
FIRE PROTECTION ENGINEERING: BEYOND TRADITIONAL FIRE DETECTION
A reduction in spacing may be sufficient to accomplish the goal of detecting a fire condition and releasing a suppression system before the occupants of the facility are threatened. However, EWFD is generally considered to be incapable of detecting an incipient fire condition prior to the time at which it affects modern digital computer equipment. According to the FCC's Network Reliability Council Report to the Nation, as much as 95 percent of all damage caused to computer and digital switching equipment by fires can be characterized as non-thermal damage. What this shows is that the biggest risk to continuous operation in these facilities from fire is the smoke, not the fire itself. Smoldering combustion of one or two circuit boards may produce a heat release rate of one or two kilowatts. By comparison, the heat release rate from a typical trash can fire is on the order of 15 kW 2 or higher. However, relatively small amounts of smoke and hydrochloric acid, a common byproduct of combustion of PVC cables and digital circuit boards, can very effectively damage digital servers and switches.
Detecting combustion by-products from these low energy fires requires a more sophisticated technology. Two common methods of detecting fires of this magnitude are through the use of air sampling smoke detection systems or high sensitivity laser spot detectors. Detectors such as these that can detect products of combustion before they substantially threaten equipment in the space are referred to as Very Early Warning Fire Detectors (VEWFD).
FIRE ALARM SYSTEM FEATURES
The overall fire protection engineering design also plays an important role in maintaining continuous operation. For larger facilities having many detectors, the number of addressable points on a system can reach the thousands. Displaying alarm information clearly through the use of graphic displays, PCbased annunciators, and traditional LCD annunciators should be considered. In addition, providing multiple annunciators or paging systems can enhance the speed with which the facility staff can locate and isolate the source of the fire. Identifying each detector (or addressable point) by its room designation, column grid, and location (above ceiling, below floor, etc.) can also decrease the time needed to identify the source of the alarm and correct the problem. Offsite monitoring is also important, particularly for facilities that may not be normally occupied. In many cases, the building code will require offsite monitoring of the fire alarm and suppression systems. Monitoring the system in accordance with Central Station requirements should be considered in most cases, unless equivalent reliability and performance can be provided by some other method. In some instances, it may be beneficial to transmit the alarms to a remote facility monitored by the owner.
PASSIVE FIRE PROTECTION STRATEGIES
Compartmentation, housekeeping, and regulation of equipment also play important roles in fire protection design for these facilities. Smoke and fire barriers, dampers, fire doors, and staff training are essential to confining products of combustion and minimizing the damage should even a small fire develop. It may also be appropriate to locate the facility in a building of protected construction, particularly where evacuation may be impractical or a multi-tenant occupancy exists. Selection of equipment may also be an issue when the data center, particularly a Web hosting or co-location facility, is subject to transitory equipment and multiple clients. Equipment should be evaluated to ensure it is listed and is constructed of materials that do not have an unreasonable fire potential. Where the performance of equipment is questionable, segregation or elimination of the components should be considered as part of good fire protection engineering. Similarly, maintaining critical areas free of materials that simply have no place in a data center or telecommunications facility is also important. Contractor staging during renovations or new equipment installation should be confined to appropriate areas, so that excessive fuel loads that could overcome the fire protection systems do not exist within critical areas
CLEAN AGENT SUPPRESSION SYSTEMS
In many cases, clean agent suppression systems can provide a level of fire suppression performance that sprinklers do not, allowing critical systems to continue to operate during system discharge. They also require very little cleanup following a discharge and are generally safer for building occupants than carbon dioxide or traditional inert systems. Two of the more common suppression agents are FM200™ and Inergen™, although FE13™, Argon, and others exist as well. Both systems operate in a manner similar to Halon systems in that the agent is stored in fixed containers and is discharged through fixed piping to discharge nozzles. The properties of these alternative agents, however, do not allow them to be used as a direct substitute for existing Halon installations. Therefore, piping systems, agent storage containers, is of an electrical nature, as can be the case with cable fires, the energy source should be interrupted in order for the suppression system to be effective. One very unique feature about Inergen™ systems is the ability for occupants to remain in the protected area following system discharge. Inergen™ is actually a combination of three gases (nitrogen, argon, and carbon dioxide) that basically inert the protected volume. Depending upon the design concentration selected, this would typically reduce oxygen concentrations within the protected area to approximately 12 percent, which is sufficient to extinguish fires involving most ordinary combustibles. While this concentration is also less than that required for humans to survive, the presence of additional carbon dioxide stimulates the body to breathe more deeply, increasing the absorption of oxygen by the body. This physiological effect allows humans to breathe normally, even in an oxygen depressed atmosphere. Another key difference between FM200™ systems and Inergen™ systems is the delivery method and agent discharge time. FM200™ systems are more like Halon systems in this regard and require the agent storage containers to be located inside or within close proximity to the protected area. This is driven by the dynamics of the twophase flow that occurs when the system discharges. Also, since FM200™ is a halogenated system, it must be completely discharged within 10 seconds. Inergen™, on the other hand, is stored and discharged as a gas. It operates at a higher pressure (approximately 15 MPa [2,175 psi] vs. 2.5 MPa [360 psi]), which be effective in localized extinguishment of fires involving electronic equipment, their use as a total flooding system is still relatively new and unproven. Water mist systems are an emerging technology that may prove to be an effective system for critical facilities in the near future. Clean agent suppression and similar fixed systems necessarily rely on the integrity of the enclosure to help maintain appropriate concentrations of the agent and effectively control or suppress the fire. If the integrity of the enclosure is not maintained (for example, opened doors or holes in walls where cables have been run), then the agent would be less effective, or not effective at all. This is one reason that local authorities may not permit a direct "tradeoff" between alternative suppression systems and traditional sprinkler systems. Both National and local fire codes need to be considered as part of your fire protection engineering plan.
CONCLUSION
The fire protection engineering methods that have been discussed by no means represent a complete list of all the systems and strategies that are available to the fire protection professional. The best overall fire protection strategy for a specific facility is very much a function of acceptable risk levels, minimum code requirements, and interoperability of systems. System designs should be based upon a total fire protection approach, not simply individual systems pieced together by different trades. Only a total fire protection concept approach will integrate with the facility's goal of ensuring continuous operation.
