As more and more of our lives have moved into the digital realm, the data centres that store so much of our personal and business information have become ever more critical to our society and economy. As recently as September 2024, the U.K. government designated data centres as critical national infrastructure, giving them comparable priority for protection during times of crisis with water and electricity supplies, and government itself. In this article, we discuss aspects of best practice in protecting these buildings from the threat of fire, particularly for high-ceiling data centres that comply with U.S.-based regulatory requirements, such as those from UL and NFPA.
The financial investment in data centres globally is immense. Protecting that investment, not to mention the reputations and livelihoods of the businesses whose data is stored ‘in the cloud’, is essential – even brief outages can have far-reaching consequences. However, records show that data centre fires, while not exactly common, are by no means unheard-of events. This is because of three particular aspects of these buildings:
- Data centres consume unusually large amounts of energy, both to power the servers that store the data and to keep those servers cool enough to run at their optimum efficiency.
- Servers, like all computing devices, have become steadily more powerful, but with that increased performance comes higher operating temperatures and the ever-present risk of overheating. This threat is exacerbated when, as is often the case, more servers are squeezed into a smaller space to increase the storage and processing power of the data centre.
- Some data centres contain uninterruptible power supplies (UPSs) to ensure continuity of operation in the event of the main power supply failing. These often rely on lithium-ion batteries, which are particularly difficult to extinguish if they catch fire.
All these aspects of data centre design present opportunities for fires to start, and demand new approaches to reduce the risk to the lives of workers and the possibility of prolonged downtime of the facility.
New solutions for an old challenge
One problematic aspect of traditional fire protection technologies is that they can often do more harm than good where data centres are concerned. Water sprinkler systems will probably extinguish a fire in a server room, but would also cause extensive damage to all the sensitive electrical equipment in that space, not only the parts involved in the fire. Even clean gaseous extinguishing agents can damage servers due to the sound energy generated during the discharge. Sometimes the best solution is to detect the fire in its incipient stage early and take steps to save data, replace components as a maintenance activity and contain the incident manually. For example by turning off the air conditioning in that area and saving data the operators using hand extinguishers could tackle the fire at its source or best case scenario remove the threat of fire proactively with maintenance measures.
As part of this strategy of balancing the need to tackle a fire with the effect on operations, the protection of a data centre can be broken down into levels. At one level, the rooms in the building require a smoke detection system to comply with traditional building fire codes or standards such as NFPA 75, which addresses the fire protection of IT equipment (an aspect we will return to later). Then, at a second level, comes the servers themselves with their valuable cargo of data; these have their own ‘early warning’ monitoring system installed close to or even inside the racks and cabinets where servers are mounted or where forced air movement for cooling could take the incipient smoke. This system is intended to give very rapid identification of smoke before it is picked up by the room’s smoke detectors, allowing server fires to be tackled while they are still small and localised. In many cases, this may even avoid the need to activate the building’s fire extinguishing system, which would inevitably cause an interruption in service.
An ideal technology for the early detection of the smouldering fires caused by overheating electrical components is Aspirating Smoke Detection (ASD), which uses an aspirator to pull air continuously through a network of pipes. These pipes contain multiple inlets through which the air in the vicinity is filtered and sampled. The sampled air travels to a high sensitivity detection chamber where the presence of smoke particles can be detected by their scattering effect on light. Due to the way that the air is sampled and analysed, even very low concentrations of smoke can be detected and, critically, distinguished from dust particles to help prevent false alarms.
The contained space within a server cabinet has made ASD the preferred solution for the early warning detection systems in data centre server rooms. Recent introduction of the 7th edition of the UL268 regulations for ASD makes the deployment of Aspirating Smoke Detection systems much more reliable It’s been developed to prevent nuisance alarms and enhance the requirement for early detection in “special applications” such as Telco/ data/ warehouses/power gen etc. Though this change in the 7th edition will have far-reaching implications for such systems in the United States, Latin America, Middle East and Asia. It does recognise the unique benefits of “Early Detection” within these critical applications. The new regulations have reduced the allowable time between sampling the air and analysing for the presence of smoke by up to 80% in some applications. The allowable number of sampling holes and pipe length have also been reduced all with the objective of achieving true early detection in these spaces.
The result of these changes will be that newly commissioned systems will be certified to monitor smaller volumes than previously. Furthermore, older systems installed under the previous regulations may require modifications to remain in service; these could include turning up the sensitivity of the system, However, the extra protection given by the very rapid smoke detection that ASD provides more than offsets these challenges, the earlier smoke is reliably detected the more appropriate the response can be, in some cases removing the risk of a flaming fire all together.
Detection systems of last resort
The facilities needed by a modern office building, such as power supplies, air conditioning, and electrical cabling, are also required in data centres but to a much greater extent. As a result, the rooms within the data centre need monitoring in the areas above server racks, below ceilings and in voids between rooms. These are the systems that notify the building’s fire control panel of a fire, initiate alarms and evacuation, and finally activate the fire extinguishing system. Although used as a last resort in data centres, such systems are vital for protecting the lives of workers and the fabric of the building.
Standards such as NFPA 75 stipulate the use of smoke detection in specific areas of data centre buildings, such as near ceilings and underneath raised floors. However, a prescriptive approach can be difficult to define, as the air flow patterns within the rooms will be very different from those in a normal office. This is due to the demanding cooling requirements of the servers, which is often met by compartmentalising the hot and cold air streams (known as ‘aisle containment’). As a result, the selection of the most effective smoke detection solution depends on the specifics of each data centre and requires careful assessment.
Beam detectors offer an excellent option for protecting the large room volumes often found in data centres. A single beam can routinely protect almost 24,000 ft2 (2,230 m2), whereas comparable networks of point detectors are more expensive to install and maintain, not helped by some fire codes stipulating a higher density of such detectors in high-risk applications (typically 215 ft2 (20 m2) per detector). Furthermore, engineers have more flexibility when mounting beam detectors (which need not be mounted at ceiling height), an aspect which can be important in rooms with unusual air flow patterns. Some beam detectors are now equipped with a ground-level controller to assist with monitoring and aligning the system without the need to climb ladders to reach the units themselves, further enhancing their useability.
Monitoring performance
Regular testing of fire protection systems is, of course, essential to ensure they are functioning correctly. The condition of ASD systems is constantly monitored by measuring the volumetric air flow rate through the pipe network. This ensures that the pipework remains free from breaks or blockages. However, the most accurate test is to ensure regular maintenance is carried out typically checking the systems performance to test smoke and verifying flows through the sampling pipework is within design parameters – This is not a complex and time-consuming process and is usually combined with the general maintenance regime of the building fire alarm system. Maintenance pays dividends when smoke from overheating components can be detected so rapidly.
At room level, point detectors need to be tested individually, typically via a manual operation where each detector is exposed to an aerosol designed to simulate smoke, and its response is checked. In contrast, the testing of beam smoke detectors can be accomplished simply by either partially or completely blocking the beam. Furthermore, systems that include a ground-level controller usually have a remote fire test feature which allows the performance to be checked quickly and easily without having to access the detectors themselves.
Summary
The key factor that underpins all data centre fire protection strategies is early and reliable fire detection, but as more data centres are built, the cost of their construction and ongoing operation and maintenance will become ever more important. While ASD systems remain the best choice for finding the very earliest signs of fire inside server cabinets, beam detectors offer a cost-effective, complementary solution for delivering rapid and accurate smoke detection in the rooms of the data centre, as an essential part of the entire building’s fire protection system. Combining the two technologies gives the optimum solution for protecting these critical pieces of national infrastructure.