Computer Fire

Fire-protection design for computer rooms doesn't need to be an expensive guessing game. But it's true that when companies attempt to protect these most valuable electronic assets, the stakes are higher and the fire-protection systems become more complex and costly. For example, in most cases, the conventional wet sprinkler system plays only a secondary role. When it comes to protecting electronic equipment, clean agent systems take over, because an owner cannot afford to let fire conditions reach the level where the wet sprinkler system is activated.

With the development of newer, clean agent fire-protection systems (National Fire Protection Assn. 2001), end users no longer need to use the ozone-depleting gas halon, as suggested in NFPA 12a. The new clean agent systems currently available to protect the computer room environment are perfectly suited for the task and do not harm the electronic equipment, disks, tapes or servers.

Clean agents are just that—clean, environmentally-friendly gases. They leave no residue, there is no water and they are very efficient at extinguishing fires in the very early stages of development without environmental damage.

For more than 10 years now, the industry has been using a clean agent gas called HFC-227ea, heptafluoropropane, with excellent results. Similar to halon, this gas requires constructing an airtight seal or box around the computer room. Walls need to be constructed to full height above and below the raised floor. In addition, openings for conduits, pipe, wiring and ductwork must be sealed where they penetrate the wall and floors. Doors at the room perimeter must be gasketed and have automatic closures. Also, automatic dampers need to be provided at both fresh air and exhaust ducts supplying the room.

To determine the necessary quantity of HFC-227ea, the volume of the room is calculated, and using the ambient temperature of 70ºF, a 7% concentration of the gas has been determined to be the optimum. This percentage is based on the amount of gas required to extinguish the fire and still support life in case someone is in the room when the gas discharges. The gas is stored in containers at 360 psig and released by piercing the rupture disc or similar device on the tank outlet. The piping system, usually schedule-40 galvanized steel pipe, delivers the gas to nozzles that are strategically placed around the room. NFPA requires all of the gas to be discharged to the room within 10 seconds. It's important to note that the discharge sound resembles a mild explosion and can be very startling to individuals remaining in the space.

Recently, HFC-125, Pentafluoroethane, has become available for use as a clean agent for data center fire protection. This clean agent is nearly a perfect match and replacement for the old halon systems. From a fire-protection engineering design perspective, the chemical properties are so close to halon that in most retrofit cases, the existing halon piping system can be saved and reused. Only the discharge nozzles and agent tanks need replacement. This simple retrofit is especially beneficial for data centers, since the existing piping system becomes intertwined with the cabling and raised floor equipment.

Equally important to the type of gas employed in a fire-suppression system are the sensors used to detect fire. Since the extinguishing system only takes 10 seconds to fully discharge, the detection system must be equally sensitive to the changes within the data center and signal that a fire condition is brewing. The first products of combustion create smoke. Therefore, smoke detection is one of the most important ingredients in the detection system.

There are two common types of smoke detection systems, passive and active. In the passive system, the smoke must pass through the detector. One type of passive detection is photoelectric. Photoelectric detectors are located in a uniform pattern on the data center ceiling and below the raised floor to sense smoke in the air and sound the alarm. These detectors can be wired and are uniquely identified by a control panel to provide the occupants with the exact location of the origin of the smoke. This may be very beneficial to the manager of the data center as immediate attention to a precise location could head off a more damaging event.

The active type of detection takes samples of the room air, like a vacuum cleaner, at various locations and analyzes the change in density or obscurity of the air. If a variance exists, an alarm is sounded. These air-sampling systems are extremely sensitive, but the exact source of the smoke cannot be pinpointed, so the source could be anywhere in the room.

The third component of a gas fire-suppression system is the control panel. The control panel must be capable of accepting all of the information and perform the other requirements to satisfy NFPA and the legal fire authorities. The panel ties all of the components together into a complete system.

Clean, environmentally friendly gases are an essential component to protecting valuable computer equipments. To protect these assets, an owner can't wait for the sprinklers to activate. A fire calls for fast-acting agents that will not harm equipment.