Protecting Data Centers Using Water Mist Fire Suppression

By Dennis Phillips

Suppressing fires in buildings often requires customized solutions to mitigate risk and reduce the loss of high-value assets. Some of the most challenging spaces to protect are data centers. Fires that ignite in these facilities can cause significant damage to hard disk drives (HDDs) and result in the disruption of business operations. Recently, several newsworthy events involving data centers led to the loss of millions of dollars and, in turn, significant damage to the reputation of those companies.

Fire Suppression In Data Centers

There are three main challenges to suppressing fires in data centers. First, data centers are ventilated to maintain an optimal temperature and keep operations up and running. However, ventilation can increase the spread of fire by transporting smoke and heat to other areas of the building and providing fresh air into the space. Data centers also contain high-density cables that are typically stored in trays positioned above the servers, which can further propagate fire. Finally, HDDs in data centers can also be damaged from acoustic levels from some suppression systems such as clean agent (inert gas).

While traditional pre-action water sprinklers can quickly suppress fires in data centers, the amount of water required for extinguishment may cause widespread damage. Fortunately, a solution exists that can greatly reduce the amount of water needed to suppress fires – water mist.

How Does Water Mist Suppression Work?

Water mist suppression uses less water than a traditional sprinkler system, which minimizes damage to property and critical assets. Nozzle design, along with pre-determined pressure criteria, creates a mist of small water droplets. Those smaller droplets absorb heat at a faster rate than larger droplets due to the higher surface-area-to-mass ratio. As a result, a rapid absorption of heat occurs, causing temperatures to drop while oxygen is displaced due to the expansion upon water evaporation.

Faster vaporization allows oxygen to be rapidly displaced in the area of the fire to disrupt the fire tetrahedron, which consists of fuel, heat, oxygen and a chemical reaction. Any air the fire draws in becomes saturated with these droplets and vaporization occurs. Water mist also helps pre-wet and block the transfer of radiant heat to adjacent combustibles which decreases the risk that the fire will grow and spread.

How Does Water Mist Benefit Data Centers?

The main benefit of water mist is that it uses less water than a traditional sprinkler system. This minimizes damage to property and critical assets. Also, lower water requirements allow the system to use smaller diameter piping, reducing both material cost as well as the overall installation cost of the system.

Shutting down ventilation in data centers is not viable due to the impact it will have on operational efficiency. Some water mist suppression systems have been tested and approved to operate in ventilated conditions, allowing operators more freedom in designing ventilation applications.

Previously, fire protection systems only provided protection for non-fire-propagating cables. Water mist solutions that are FM (Factory Mutual) approved can further protect against the additional hazard inherent in fire-propagating cables, allowing greater flexibility in cable selection. Specifiers should also look for a water mist suppression solution that offers design flexibility for different layouts and has been extensively tested to provide protection below floors, in cable voids or wherever cable trays are located.

A Sustainable Solution

A water mist system may use less water; but it typically requires higher pressure than what a municipal water main can provide. One solution is to use a positive displacement pump, which provides a high-pressure output at lower water volumes, or by using stored nitrogen or air cylinders as a propellant for the water.

Since water demand is lower, water mist systems are suitable for standalone applications where access to water may be limited. In such situations, a water tank or cylinder(s) filled with water and pressurized by stored nitrogen can be used to supply the pump with water. However, with these standalone solutions there is a finite discharge duration due to the limited amount of stored water.

Selecting A Water Mist Solution For Your Data Center

Specifying the appropriate water mist solution is not only about extinguishing the fire but also about protecting the contents of the building and minimizing water damage. Look for a solution that meets the specific needs of your data center and has been designed and rigorously tested to meet all applicable local and state requirements to ensure compliance.

Dennis Phillips is Senior Business Development Manager for the Fire Protection business of Johnson Controls. He is a NICET S.E.T. Level IV in water-based applications, a Level II for special hazards applications and holds a certification in Industrial Fire Protection from Eastern Kentucky University.

Dennis brings more than 35 years of experience from inside the fire protection industry to his current role, having worked in design, contracting, sales and business development. He enjoys working with clients to understand and solve their fire protection problems, while working with the Johnson Controls research and development teams to create solutions that meet customers’ needs.