ENCLOSURES FEATURE
Protecting IT systems from fire
Fire risk is an underlying threat to all IT operations. Typically, they are caused by defective capacitors, power packs or other short circuiting components. Early detection systems, along with fire extinguishers, are both vital in ensuring a major disaster can never occur
A
ccording to research conducted by the German Institute for Damage
Prevention and Damage Research, the primary cause of fires in data centres, not surprisingly perhaps, is a failure in electronic components. Fire protection is, therefore, an important factor in risk management, given how highly dependent companies are on IT systems. The first step, before choosing a fire
protection system, will be to determine the impact that loss of data will have on different commercial operations, and which of these operations are critical. The next step is to decide on whether an extinguishing system is needed for the entire room or whether a rack-level system is sufficient. Room solutions can lead to a number of follow-on investments. For example, if a room is to be flooded with nitrogen then an additional pressure-relief system will be needed, while measures must also be taken to protect people in the proximity. Small IT applications, with a low number of server enclosures, often only need fire protection at the rack level. A series of fire alarm and extinguisher systems, such as the Rittal DET AC III range, can be installed in closed server cabinets. These usually consist of a combined early fire detection and extinguishing system.
EARLY DETECTION Alongside highly sensitive smoke detectors, there also needs to be an active air sampling system. Air from the entire enclosure should be monitored continually. This can be done by drawing the air through an integrated pipe system, which passes it over the smoke detectors. The pipes have a number of holes drilled within them; how they are laid down is dependent on the airflow through the enclosure. Without this system, a fire may only be detected when it has taken hold.
THE RIGHT EXTINGUISHING MEDIUM It is clearly important that the extinguishing medium does not damage the electronics within the data centre, so that it can be up and running again quickly after a fire has been put out. This means the extinguishing medium must not be conductive nor must it leave any residues. Water or aerosol extinguishing media are not suitable, but inert gases such as argon or nitrogen, or chemical extinguishing agents, such as Novec 1230, work well. They displace the oxygen which deprives the flames of heat and is neither corrosive nor electrically conductive. Success depends on both the IT rack - including enclosures and any bayed cooling units - being leak- proof, while cable and conduit entries must be sealed both to the frame and to each other, as must any floor elements. The Rittal DET-AC III fire alarm and active
extinguishing system, for example, holds two litres of extinguisher medium in a 19-inch rack, and only takes up one height unit. This is sufficient to extinguish a fire with a volume of 2.8m³, according to tests by the VdS, an international testing institution focusing on fire prevention.
AUTOMATED POWER CUT-OFF Of course, it would be impossible to get a completely air-tight hermetic seal, and as a result, the concentration of extinguishing medium in the enclosure will gradually decline. Because the medium has a higher density than air, this will start to happen from the top of the enclosure. Within the holding time - the time in which a concentration capable of extinguishing can be maintained - all electrical components should be disconnected from the power supply. You can do this automatically with the help of a switchable power distribution unit (PDU) and a monitoring system. Without this capability, the fire may be
unwittingly re-kindled. The horizontal circulation of air within a cooling system helps improve holding times because it will support an even distribution of the extinguishing medium.
OTHER CRITERIA A built-in emergency power supply with rechargeable batteries means that fire protection can still be maintained should there be a temporary loss of power. Rittal’s DET-AC III, for example, can run for up to four hours without any mains power. The batteries are trickle charged when under power. It’s also worth bearing in mind that the smoke detection system should have a two-stage design to improve security and avoid false alarms. These employ highly sensitive optical sensors which can detect very small smoke particles early on and trigger a pre-alarm. Current technology can detect 0.25 per cent obscuration per metre which might indicate a possible fire. When the second sensor also detects smoke, the main alarm is triggered and the extinguishing medium is released. Finally, it should be possible to integrate
the fire protection system with building management systems. Rittal’s DET-AC III uses an integrated CAN bus interface which allows direct access to CMC III monitoring system that supports such protocols as http, SNMP, MODBUS over TCP/IP and OPC UA. Easy access to the components, via USB interface for example, is important for equipment maintenance and avoids the need for removing the 19-inch rack- mounted assembly. All these precautions help deliver both a
fail-safe operation, and improve risk management across the organisation.
Rittal
www.rittal.co.uk
ELECTRICAL ENGINEERING | NOVEMBER 2016 37
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