Sunday 09 October 2011
Fire is one of the main enemies of a datacenter. Because of the large density of equipment and cables, a short circuit in a cable or a defect in the equipment can easily lead to fire. And because of the air flow in the datacenter and the frequent use of raised floors fires can spread around very quickly.
Even if a fire starts outside of the datacenter’s computer room, the smoke of such a fire could damage equipment in the datacenter. I know of occasions where the fire was not in the computer room, but in an office. The smoke was not entering the datacenter at all, but the fire fighters demanded to have the power of the entire building (including the datacenter’s UPS) shut down before they could start extinguishing the fire.
Smoke should be taken seriously as well. Even if there is no fire breakout, smoke exposure alone can cause extensive damage to the electronic equipment within the data center. A report by the FCI states that less than 5% of fire damage results from direct thermal damage, while the rest is contributed to non-thermal reasons such as smoke and the inherent gases in it.
Suppressing fire in the datacenter consists of four levels:
- Fire prevention – measures to avoid a fire in the first place
- Passive fire protection – measures to limit the exposure of the fire once it has started
- Fire detection systems – systems to detect smoke and fire
- Fire suppression systems – systems to extinguish the fire once it is detected
Each of the levels above should be taken care of. They are described below.
The best way to avoid fire damage is to ensure fires do not start at all. Respecting regulations and implementing fire prevention guidelines is of course a good measure. In datacenters the most common source of fires is overheating of equipment or cables. Avoiding “cable spaghetti” is a very useful step in fire prevention, as is not overloading the power supply connections.
Passive fire protection
Passive fire protection limits the exposure of fire once it has started. Measures include the installation of fire resistant walls, floors and ceilings to keep the fire from spreading fast and firewalls around parts of the datacenter to restrict the fire to a certain datacenter compartment.
Be aware of vulnerable entry points, such as cable penetrations, coolant tube penetrations and air ducts. These entry points should be filled with fire resistant material.
Fire detection systems
Fire detection systems allow investigation, interruption of power, and manual fire suppression before the fire grows to a large size. Smoke detectors, flame detectors and heat detectors are usually installed to provide early warning of a developing fire.
Installation of these detectors is a delicate task, as the air flow of the datacenter’s cooling systems must be considered. Early warning signs should enable staff to investigate the alarm and if possible stop the fire using for instance hand fire extinguishers, or simply shutting off the power to overheated equipment.
Fire suppression systems
Fire needs three components: heat, fuel and oxygen. If any of these three lack, a fire will stop. So in general there are three ways to stop a fire:
- Reduction or isolation of fuel
- Reduction of heat
- Reduction or isolation of oxygen
Putting out a fire by reducing heat using water (as used by sprinkler systems or firemen) is not preferred in a datacenter. The damage created by the water might be worse than the fire itself. Therefore in the early days of datacenters fire extinguishing was mostly done using Halon gas, reducing the oxygen the fire needs. Halon extinguishes fire without damaging electronic equipment by replacing the oxygen in normal air with inflammable Halon gas. However Halon is bad for people, as it causes dizziness - not a good combination with a spreading fire.
Today gas based extinction systems are still in use, but they use mostly other types of inert gases, like Argon and special patented gas types (usually combinations of Argon and for instance Nitrogen in a special mix). They have all the benefits of Halon but none of its disadvantages.
Because releasing fire suppression gas in the datacenter increases the pressure in the datacenter with some 50% in a very short time, the pressure peak can break windows, or hurt people. This means that proper vents must be installed when gas based fire extinguishing is used.