While data center fires remain relatively rare, fire-related outages can be costly. According to the 2025 Uptime Institute Report, 54% of respondents noted their most recent significant data center outage cost more than $100,000, with 20% reporting costs exceeding $1 million (https://bit.ly/4sTulkl).

While the causes of data center fires are underreported, contributing causes of recent fires in data centers include electrical faults, battery failures, cooling system malfunctions and human error. As artificial intelligence technologies continue to advance, these fire-related risks within data centers will intensify (https://bit.ly/4sOV1mg).

To add to the challenge, some common fire safety strategies may be damaging to equipment. Often, traditional water-based sprinklers are used as the primary means of active fire protection in data centers, especially in the United States. However, these systems can use significant amounts of water, creating risk to expensive computing equipment. 

Some of those risks can be mitigated by employing a preaction sprinkler system in which the pipes are normally filled with pressurized air instead of water until activated. 

In addition to preaction systems, other fire protection options exist, such as water mist and clean agent (gaseous) systems, that can help mitigate concerns about the risk to equipment from water damage.

Water mist and clean agent systems offer several distinct advantages and limitations in data centers. To determine which type of suppression system is most appropriate for protecting each data center application, it’s important to compare the solutions along with their benefits and limitations.

Comparing suppression systems

Water mist systems produce fine droplets of water, often less than 200 microns in size, at a high pressure. These droplets can suppress fire through three main mechanisms:

Rapid cooling of flame and hot gases;

Oxygen displacement from steam generation;

Blocking radiant heat to prevent fire spread.

Water mist systems can perform these functions while using typically 50% to 80% less water than traditional sprinkler systems, sometimes even smaller amounts. This can help reduce the risk of excess damage to IT equipment and possibly reduce cleanup and environmental concerns around water consumption and runoff. 

Water mist systems do not require air-tight rooms to contain the water mist and are able to function even in areas with low levels of continued ventilation (circa 1.5 m/s or about 3.5 mph). Water mist is non-toxic and safe for humans and the environment.

While water mist systems use less water, they are still water-based, and concerns may still be present about conductivity. This is especially true with live circuits or residual voltage in the protected equipment, as well as possible corrosion of fine electronics because of direct discharge or condensation on exposed components. For some data centers, the end user may see any water-based fire suppression system as unacceptable. 

Certain data centers with high airflow might not be suitable environments for a water mist system, as the airflow may impact the activation and delivery mechanism of water mist, so air handling might have to decelerate on fire alarm activation. 

Water mist is more commonly seen in larger data centers, as the cost of install may not be justified for the protection of small server or data rooms. Clean agent systems are often a better choice for small spaces.

Clean agent systems can lower risk of equipment damage. Halocarbon chemical agents (or inert gases) work to extinguish a fire by reducing available oxygen or interrupting the chemical reaction of combustion and absorbing heat from a fire. 

These systems are typically paired with a detection system that can detect the very early stages of a fire and deploy the agent well before a fire has grown large enough to activate a traditional sprinkler system, which significantly reduces the risk of damage to the equipment. 

Clean agent systems have minimal required cleanup after a system discharge and, depending on the specific agent used, can have little to no impact on the environment. There is typically no need for water usage, which is very appealing for data center operators, especially where continued electronics operation is a necessity. 

A common configuration is to pair a clean agent with a preaction sprinkler system backup to satisfy code requirements. These systems are more frequently used in mission-critical spaces where little to no downtime is strongly desired.

Note: Clean agent systems have requirements for room integrity to retain the appropriate concentration of the agent in the area containing the fire for a period of time. There are also normally requirements for pressure venting to avoid damage to walls and ceilings. 

These systems are typically better for small areas; large data centers may be dissuaded due to the cost and cylinder storage space needed. 

Preaction system considerations

When it comes to both water mist and clean agent systems, in many cases, the locally-adopted codes and standards in the United States do not currently recognize these as full alternatives to a traditional sprinkler system. Often, these types of systems would still require a backup sprinkler system. 

The cost of providing a primary and a backup system can be daunting and essentially come down to what level of risk the data center operator is willing to accept. They may find that they are willing to rely on a water-based traditional sprinkler system only, given their perceived improbability of fire.

As opposed to a traditional dry-pipe system, a preaction system is equipped with some form of supplemental detection. This detection can be in the form of smoke detection, heat detection or other form of fire detection at an early stage. Other examples include air-sampling detection and special cameras or linear beam devices to detect smoke. 

Preaction systems can be non-interlock, single-interlock or double-interlock systems, depending on the mechanism with which water is introduced from the main preaction system valve into the sprinkler pipes.

• Non-interlock: Water is introduced into the system piping when fire is detected by either the supplemental detection or sprinkler activation. This could permit the system to still function in a fire even if the supplemental detection is somehow impaired.

• Single-interlock: Water is introduced into the system piping when the supplemental detection system is activated. Operation of a sprinkler, or damage to a sprinkler or pipe that causes a drop in air pressure, will not trigger the preaction valve to release water into the system.

• Double-interlock: Water is only introduced into the system piping when both the supplemental detection has been activated and a sprinkler has operated due to the heat of a fire. These systems were primarily developed for the protection of cold spaces where accidentally introducing water into the system piping could result in freezing and pipe rupture, requiring repair and/or replacement of the system piping.

Many data centers built today are protected with double-interlock systems, as they are perceived to have the smallest chance for accidental discharge. However, some elements of a double-interlock preaction system do not necessarily make it the ideal choice for protecting an occupancy with very expensive or high-risk equipment. 

Since a double-interlock system will not release water until both the detection system has been triggered and a sprinkler has operated, the system must wait for water to arrive at the open sprinkler(s) before it can begin to control the fire. This gives the fire additional time to grow, potentially resulting in additional damage. 

Perhaps more importantly in system planning, it also requires a larger design area, and thus more water than if the sprinkler discharges water immediately upon its activation. 

When a fire occurs in a data center, the suppression system should work to control or suppress that fire as soon as possible. Therefore, a single-interlock preaction system may be a more preferred choice of the building owner or stakeholders, such as the insurer. It is expected that the early stage of a fire will trigger the supplemental detection prior to sprinkler activation. 

Once the supplemental detection picks up on these earlier warnings of a fire, water is introduced into the pipe and will be ready and waiting once the fire has grown just large enough to operate the sprinklers, discharging water almost immediately in most cases. 

For this reason, a single-interlock system is calculated as a wet-pipe system with none of the design penalties that are imposed with a dry-pipe system calculation.

Ultimately, fire protection system selection should be based on careful consideration of various factors. This can include performing a full risk assessment to compare the cost of the protection system to the potential fallout of downtime or equipment loss. 

Robust, redundant systems such as clean agent with sprinkler backup might be costly but desirable — even necessary — for certain types of data centers. This is especially true where downtime is extremely undesirable as we move to more remote and inherently more impenetrable facilities. 

Melisa Rodriguez is senior manager, industry relations with Johnson Controls. She is a licensed fire protection professional engineer with 21 years of industry experience, and NICET-certified Level IV in water-based systems layout. Rodriguez serves on the Minnesota board of licensure, is vice-chair of the Minnesota Governor’s Council for Fire Prevention and Control, and a member of multiple fire protection industry committees. She is past president of the Minnesota Chapter Society of Fire Protection Engineers.