Modern data centres are characterised by spaces filled with ever-increasing numbers of server racks and various types of electronic equipment, and are regarded as mission-critical facilities that must maintain 24 x 365 business continuity. There was a time when temporary business interruptions were a minor and relatively inexpensive inconvenience to the operation of data centres. However, with the increasing reliance of society upon the interconnected global IT infrastructure for much of what we consider everyday life, the loss of data centre service often has a dramatic effect felt far beyond the affected business, impacting clients, suppliers, whole industries, and society at large. Data processing centres store data in the systems memory, and during an interruption only that data which has not yet been placed in permanent memory is lost – but there is much more than just data loss at stake. The uninterrupted use of computers and electronic equipment in modern data centres is critical. According to a 2013 Ponemon Institute report, the cost of data centre downtime is high – and getting higher. From 2010 to 2013, the average cost per minute of data centre downtime increased 41%, from $5617 (£3580) per minute in 2010 to $7908 (£5042) per minute in 2013. The total cost of downtime is not limited to revenue losses, but can ultimately also include : Productivity Losses: Numerous users across an organisation rely on IT-delivered services and applications and any downtime will greatly reduce their productivity, often resulting in work grinding to a halt Customer Disruption: Customers can suffer from disruptions in customer service and support systems, leading to dissatisfied customers who may take their business elsewhere Reputation Damage: Disruptions can negatively impact the reputation of the organisation, leading to a loss in future sales Isolation and Repair Costs: The cost of downtime also includes the costs to find and fix the problem Loss of Data and Records Lawsuits Costs in addition to the loss of revenue can be significant, as seen in Figure 1 below, which summarises the cost of a typical data centre outage. Fire protection options The high value and sensitivity of the electronic equipment found in modern data centres, combined with the consequences of system interruption, makes fire protection a critical component of any data centre risk assessment. Fires do occur in these types of facilities – as evidenced in Table 2, which includes a selection of data centre fires that have been reported within the last several years. Table 2. Data centre fires Date Location Data centre 2014 Thailand Cowboyminers 2014 South Korea Samsung 2014 Argentina Iron Mountain 2014 USA Iowa Legislative Building 2013 USA NSA Spy Centre 2012 Canada Shaw Data Centre A. Water-Based Fire Suppression Systems The primary objective of a sprinkler system is not fire extinguishment but fire control: Confining a fire to its point of origin (preventing fire spread) and controlling ceiling temperatures to prevent structural damage. Sprinkler systems use water, at a typical flow rate of 25 gallons per minute. Water has obvious disadvantages around electronics and electrical systems due to its electrical conductivity. In the event of activation, water damage to the facility and equipment can be substantial, often worse than the fire damage itself, and the cleanup required after sprinkler system activation can be extensive. Sprinkler standards such as NFPA 13 typically require a 30 minute supply of water, and it is common for the two heads nearest the fire to activate – this translates to 1500 gallons of water dumped on the facility’s electronic equipment. Sprinkler heads are activated by a thermally sensitive frangible bulb or fusible link which releases water only after the head reaches a preset minimum temperature, usually 135oF or higher. By this time fires are well-developed and considerable direct fire, smoke, and water related damage can be expected (See Figure 2). The extensive cleanup after a sprinkler system discharge, and resulting business interruption, will add to the business cost of a fire. Water is not a three dimensional agent, and cannot readily extinguish hidden or obstructed fires, such as an in-cabinet or in-rack fires. For these reasons, sprinkler systems are best suited for the protection of structures, not for the protection of mission-critical assets located within those structures. Water mist systems are a more recent entrant into the water-based fire suppression arena. Such systems generally require high pressure pumps and special nozzles to distribute a fine water mist into the protected space. Typical delivery rates for water mist systems are on the order of 8 gpm for high pressure water mist systems: A 30 minute discharge from the two closest heads would result in 480 gallons of water dumped on the facilities electronic equipment. Water mist primarily extinguishes via oxygen dilution: Steam produced from the mist near the fire displaces oxygen and puts out the fire. Water mist systems perform well on large energetic fires, but have exhibited poor performance on small fires. Water mist, like water, does not fully flood a space and as a result is not suitable for the extinguishment of hidden or obstructed fires, such as an in-cabinet or in-rack fires. While lesser in volume than sprinklers, these systems do leave residual water following system discharge, necessitating cleanup and added service interruption. Potential water damage to electronics and the incompatibility of water and electricity remain a concern. For these reasons water mist systems, like sprinkler systems, are not recommended for the protection of high value electronic assets and services located within a structure. Figure 2. Aftermath of pre-action sprinkler activation on an in-cabinet fire B. Clean Agents The primary objective of a gaseous clean agent system is to extinguish the fire quickly, limiting fire damage to the object(s) involved in the origin of the fire. Hence, the primary purpose of a gaseous clean agent system is to protect the valuable, sensitive and mission-critical assets within the enclosure. This is clearly fundamentally different from the primary objective of sprinkler systems, as illustrated in Figure 3. The primary advantages of total flooding clean agents are: Clean