Aisle containment must be fire aware

Businesses are required to design disaster recovery and business continuity plans as part of their corporate governance. Rarely are these plans integrated with facilities management processes. The most serious disaster that can befall a data centre is a fire because of its destructive nature.

It is not just the physical melting of components but the damage caused by smoke, residue from electronics and especially water. Building a fire resistant environment must be part of the initial facility plans and these plans should be updated as the usage of the data centre changes. This already happens with power and cooling but facility management teams must pay equal attention to their fire suppression systems.

The changing face of the data centre
Over the last decade, data centres have undergone a revolution driven by an ever increasing demand for more compute power and storage. To meet this demand, IT has brought in highly dense computing such as blade servers and increased the use of virtualisation. Increased utilisation of hardware generates greater power loads which in turn create heat and cooling issues.

For many data centres, this change in power, cooling and utilisation has come at a significant cost. Open plan halls full of racks have made it difficult to manage the hot spots created by blade servers, dense switch environments and large data storage systems. To create environments where power and cooling can be more effective has meant either extensive refurbishment to create smaller halls or the introduction of hot and cold aisle containment systems.

Benefits of aisle containment
The introduction of aisle containment has given data centres, new and old, the ability to prevent hot and cold air mixing inside the aisle. Preventing mixed airflow means that cooling can be more effective and delivered at a lower cost. Aisle containment can be either designed from scratch or retrofitted to existing environments and there are three types of aisle containment, hot, cold or complete.

Hot aisle containment encloses the hot aisle drawing exhaust air away from equipment and sent directly to the cooling system via a ceiling plenum. While this increases the temperature of the hot aisle, it does prevent other equipment ingesting already warm air.

Cold air containment enables higher utilisation of space as air can be directed to the equipment that needs it the most. By preventing hot air being pulled into the aisle, it ensures that input temperatures can be held constant. Service Level Agreements (SLAs) over input air temperature are starting to become more common and cold air containment is a key technology to meeting demand. When cold air containment and in-row cooling are combined, rack density can be substantially increased, providing there is enough power to support the additional equipment.

When the cooling efficiency of both cold and hot aisle containment are compared to rooms with no aisle containment, they use between 40% and 50% less power to dissipate heat than a non-contained environment. For data centre owners, this delivers both a substantial reduction in the cost of running IT equipment and the ability to increase density without increasing cooling capacity.

While aisle containment is about increasing efficiency, reducing energy consumption and, where applicable, security, it does not deal with fire suppression or detection.

Disaster recovery is more than just failover power, cooling and IT equipment
IT’s focus on disaster recovery inside the data centre is around keeping IT systems running. Uninterruptible Power Supplies (UPS), generators, spare high voltage air conditioning units and even synchronously backing up critical IT systems to other data centres are all high on IT's agenda.

The data centre facilities team have a different agenda. They are responsible for the building fabric and the essential services used inside the building.

The recent storms in the UK and US have shown that high winds causing physical damage and the increased risk of flooding are now a yearly risk and not a once in a lifetime risk. This means that data centre facility teams need to overhaul their entire risk profile for the facility.

Part of that risk assessment must include fire suppression systems that are already reviewed annually. For those with large halls and no containment, this is perfectly fine. However, the rise of containment systems has created a lot of press, often misguided, about the dangers that increased aisle containment can bring to detecting and extinguishing fires.

Incorporate fire detection sensors into aisle containment
One of the big charges made against aisle containment systems is that they inhibit the proper detection of fire. With badly installed systems this could be the case but the issue here is not the aisle containment but the implementation of the fire detection and suppression systems.

Over the last decade the rise of Data Centre Information Management (DCIM) systems has enable data centre operations teams to manage their environment more effectively. Sensors make up a significant part of the tools that are used in DCIM solutions and many of these are installed inside the racks in the data centre.
It should come as no surprise that taking the fire detection systems from the ceiling and including them in the racks or the aisle containment is a relatively simple task. More importantly, it not only makes it possible to detect any risk inside the aisle containment but also enables much earlier detection.

Where to place the fire suppression systems
While sensors are relatively easy to move, fire suppression systems are not. Many facilities have perfectly adequate systems in the roof of each hall but worry about how to deal with fire suppression in a contained aisle.

One solution that is often talked about is extending the suppression system into the aisle. It might sound easy but in reality it is not. Without knowing exactly what is in each rack could mean that the amount of suppression being delivered through the system is insufficient for the fire. At the same time, the dispersal pattern of the suppressant may well be impaired due to the equipment in the aisle and where it is located.

One risk that can easily be overlooked is health and safety. The type of suppressant, especially gas, may cause injury to staff. Therefore, changes to the dispersal pattern must ensure that there is sufficient opportunity for staff to get to safe areas before the gas is released.

Any changes must also be tested and very few data centres have the spare capacity to do this testing. This means testing in a live data centre with all the attendant risks of damage to equipment. A bigger challenge that no facilities management team wants to address is that every time there is a change to the room layout and changes to the way fire suppression is deployed, there is a need to retest the system.

As a result, the best practice is to keep the suppression systems where they are already installed, in the ceiling space. This does not mean that facility managers can relax, because there is a need for them to constantly review the risks and density of equipment inside the data centre and update systems where appropriate.
Having decided to leave the suppression systems where they are, the next concern is how to deal with enclosed aisles. One solution is to have a mechanism where the panels drop away when the fire alarm is triggered or thermal links. However, should there be anyone in an aisle when this happens, there is a risk of injury.
A better solution is to use an active roof system where the panels open to allow the suppressant in. One of the first actions when fire is detected is to cut the power. For an active roof to function properly, it needs to be independent of power functions. Some require an additional form of power that will trigger the roof to open. This is not difficult to resolve. Most high density racks have some form of UPS installed. Wiring that to the fire detection sensors and the active roof means that there will always be power to open the roof in an emergency but this utilises UPS power and may be an issue.

An active roof will enable a fire to be dealt with effectively but for very old data centres without small rooms, often found in small facilities, the height of the roof may pose another challenge. Systems that use an active roof require greater headroom than those with falling or fixed panels.

Conclusion
Fire is something that no data centre owner wants to consider but must plan for. While aisle containment systems are making it possible to lower power costs, especially on cooling, there is concern that they may inhibit fire detection and suppression systems. Providing that the installation team understand the need for placing sensors in the right place and an active roof design is chosen, aisle containment creates no more risk than any other form of data centre enhancement.