By Bronwen Ledger
Building Systems: Fire protection of Internet Data CentresEngineering
Gunnar Heissler, P.Eng. of the ECE Group, electrical and mechanical consulting engineers in Toronto, says that one of the critical issues in designing fire protection systems for computer-intensive fa...
Gunnar Heissler, P.Eng. of the ECE Group, electrical and mechanical consulting engineers in Toronto, says that one of the critical issues in designing fire protection systems for computer-intensive facilities such as internet data centres, web hosting facilities and switching centres is coping with the very turbulent air conditions in these spaces. The turbulence is caused by the high air volumes necessary to cool the extensive computer equipment.
The most crucial factor, Heissler says, is to avoid a fire or false alarms and the exorbitant costs that result from the equipment downtime. He therefore recommends the use of Vesda (very early smoke detection and alarm) systems. These super-sensitive early warning systems alert the facility operators to the fact that something may be wrong before smoke or fire occurs.
A conventional smoke and fire detector either responds to visual obscurity or the presence of combustion products. Vesda systems can detect changes in the atmosphere (such as “smelling” VOCs produced when equipment gets hot). A sensitive monitoring system can respond to changes in the draw of electrical current.
Once alerted to the danger, the operator can immediately shut the offending equipment down, localizing the problem rather than having to close down the whole facility.
In case a fire actually does break out, systems have to be in place to extinguish it. There are no specific codes governing the fire protection of these facilities. Data hotels are essentially industrial in function, with only a handful of operators on site. However, Heissler says that if an internet centre is located in a downtown office tower it might be expected to conform to commercial occupancy fire protection codes.
Fire extinguishment is provided by water sprinkler systems or gas suppression systems, which essentially starve the fire of oxygen. Heissler cautions that the heat travels in the turbulent air, and so the sprinkler head may mistakenly fuse and be triggered to release over the wrong equipment. Sprinkler systems, in his opinion, are necessary, but are most effective in controlling fully developed fires.
Gas suppression systems are an alternative often used, though since halon has been banned because it depletes the ozone layer, there is debate over what is the safest alternative (the National Research Council’s Institute for Construction does research in this area, and NFPA 2001 — Clean Agent Fire Extinguishing Systems — is a standard).
For smoke management, according to Heissler, the first aim is to confine the contaminated air in the immediate fire zone and to evacuate it quickly by supplying fresh air through the fire fighting access route. This approach allows firefighters to enter the compartment safely. The fresh air should be supplied at low pressure to limit the force required to open the emergency exit doors to 3.3 lbs. of force.
Removing the smoke quickly helps to minimize damage to the equipment from the combustion products and to speed the mop up process. By keeping the space at negative pressure the smoke is confined within the problem area and kept from spreading.
Heissler reckons that the cost of a smoke exhaust system can be in the range of $2-$10 per cfm of air flow, and the cost of a Vesda expert detection system might cost between $5-$10 per square foot. Again, he stresses that the operating word with these facilities is “avoidance.”