By MELISA RODRIGUEZ, Senior Manager, Fire Suppression Products, Johnson Controls 

From their sprawling, cloaked exteriors to their extreme heat and power-generating interiors, data centers are drastically different from any other commercial or industrial building. And while operating under these unique conditions, data centers are also expected to meet aggressive uptime requirements. 

To successfully maintain around-the-clock operation, these facilities depend on systems developed with redundant design principles to prevent failures, maintain uptime and support continuous workloads. Redundancy ensures that if one element of that system fails, a backup element takes over right away. This most often applies to cooling systems, power systems, networks and computing — but these principles should also extend to fire protection. 

Rather than designing a fire suppression system that meets minimal code requirements, it's critical to design systems that can help maintain uptime and enable rapid recovery after a fire event. 

System designers can achieve this redundancy by incorporating a combination of effective fire suppression solutions like clean agent, water mist and preaction sprinkler systems to create a multilayered solution. This overlapping defense can address fire events quickly with early detection and quick suppression, simplify cleanup after discharge and help to preserve data center equipment and hardware. 

Why redundant fire suppression in data centers? 

Although the number of reported data center fire events has been statistically low, the rise in high-density AI computing workloads increases thermal risk. The intensification in electrical load and power density, which can be more than 100 kW per rack, in a smaller footprint changes the hazard profile of the infrastructure. 

However rare, the consequences of a fire-related outage can be substantial. According to the 2025 Uptime Institute Report, 54% of respondents state their most recent significant data center outage cost more than $100,000, with 20% reporting costs exceeding $1 million. 

The length of data center downtime after a fire event is not limited to the duration of the event itself. It extends beyond into cleanup of the suppression agent and replacement of damaged equipment. On their own, each fire suppression system is designed to effectively suppress fire during an event. However, each suppression agent can result in different outcomes after the fire is out.  

Water mist and clean agent systems can help reduce post-discharge cleanup and minimize damage to sensitive equipment. However, in many U.S. jurisdictions, they are not typically accepted as standalone replacements for the water-based sprinkler protection required by adopted building and fire codes. 

For that reason, many data centers employ a layered approach that combines early detection and suppression technologies, such as clean agent or water mist systems, with a code-required preaction sprinkler system. In this configuration, the clean agent or water mist system serves as the first line of defense to suppress a fire quickly and minimize disruption, while the sprinkler system provides the redundant layer of protection needed for life safety and code compliance. 

A redundant suppression solution and resilience-focused fire protection strategy should consider three outcomes: 

1. How quickly can the system detect and suppress the fire? 

2. How much cleanup and recovery will be required? 

3. How will equipment and infrastructure be affected by the suppression agent? 

By considering these three outcomes, system designers can create effective, application-specific system architecture that can help improve data center resilience and uptime. 

Address fire events ASAP with early detection, quick suppression 

Clean agent systems are typically paired with a detection system designed to sense 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. Detection systems can range from standard smoke or heat detection to more specialized systems like air-sampling detection, advanced cameras or linear beam devices to detect smoke. 

When a clean agent system is deployed, halocarbon chemical agents or inert gases reduce available oxygen or interrupt the chemical reaction of combustion to absorb heat from and extinguish a fire. Halocarbon systems typically discharge completely within 10 seconds for rapid extinguishment, while inert gas systems fully discharge within two minutes. 

Because clean agent system efficacy depends on the appropriate concentration of agent in the affected space over a certain time, clean agent systems have requirements for room integrity as well as pressure venting to avoid damage to walls and ceilings. This requirement, paired with the need for cylinder storage space, often makes clean agent systems better for protecting smaller areas, such as small server or data rooms, usually up to about 40,000 cubic feet in size. 

For larger areas, water mist systems offer effective suppression by producing fine droplets of water, often less than 200 microns in size, at a high pressure. These droplets can suppress fire in three different ways:

• absorbing heat to rapidly cool flame and hot gases;
• generating steam that displaces oxygen;
• and blocking radiant heat to prevent fire spread. 

However, because the droplets are so light, areas with high airflow can affect the activation and delivery mechanism of water mist. This means air handling systems might have to slow down when the fire alarm activates for the water mist system to operate effectively. 

This illustrates why suppression systems cannot be designed independently of the rest of the data center infrastructure. Airflow, cooling strategy, room configuration and fire protection must be evaluated as interconnected systems. 

Simplifying cleanup after discharge 

Depending on the agent, the discharge of a fire suppression system can affect the area in different ways and require different levels of cleanup. When there is less to cleanup, spaces can be restored to operation faster. 

As the name suggests, areas protected by clean agent systems typically require post-discharge ventilation after system discharge, but little actual cleanup as there is no residue. 

Water mist systems are designed to suppress fire using around 50% to 80% less water than traditional sprinkler systems, sometimes even less. Releasing a fraction of the water in a space can reduce cleanup compared to that discharged by traditional sprinkler systems. 

In comparison, traditional water-based sprinkler systems can use significant amounts of water. After a traditional sprinkler system discharges, areas tend to require water and wet debris removal. 

Pairing a clean agent or water mist system with a preaction sprinkler system backup allows the system with less cleanup to be the first line of suppression. And considering the reduced water usage, clean agent and water mist systems may also be preferable for the conservation of resources. 

Preserving equipment and hardware 

The effects of fire suppression systems on equipment and hardware is a significant factor in preserving uptime. The amount of water traditional sprinkler systems typically release can damage expensive computing equipment. Water mist systems use significantly less water than traditional sprinklers and can help reduce the risk of excess damage to IT equipment. However, they may still raise concerns 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. 

The speed at which a clean agent system deploys and extinguishes fire gives it an advantage over traditional fire sprinkler systems. The increased speed significantly reduces the risk of thermal damage to equipment while the gas agent itself will not react with hardware and equipment. 

A clean agent with a preaction sprinkler system backup is designed to use little to no water, which is ideal in areas where continued electronics operation is a necessity. 

Selecting the most effective preaction system 

Fire protection should be treated as part of the data center's uptime architecture. The objective is not only to suppress a fire, but also to minimize disruption, protect critical equipment and support rapid recovery. 

Water-based sprinkler systems are available in multiple types with different capabilities and benefits. When selecting a pre-action sprinkler system to help maximize data center uptime, it’s important to understand the difference between the three different types: 

• In a non-interlock system, water is introduced into the system piping when either the supplemental detection or sprinkler activation detects fire. The benefit is that the system can still operate during a fire event even if the supplemental detection is impaired;

• In a single-interlock system, water is introduced into the system piping when the supplemental detection system is activated. This can reduce the risk of accidental discharge as the operation of a sprinkler, or damage to a sprinkler or pipe that causes a drop in air pressure, will not trigger the preaction valve;

• In a double-interlock system, water is introduced into the system piping only when both the supplemental detection has been activated and a sprinkler has operated due to the heat of a fire. These systems are designed to protect cold areas where accidentally introducing water into the system piping could result in freezing and pipe damage. 

As double-interlock systems are generally considered to offer the least risk of accidental discharge among the three types of preaction systems, many data centers built today use them. However, some system elements don't necessarily make double-interlock systems ideal for protecting spaces containing very expensive or high-risk equipment. 

The reason is that very mechanism that prevents accidental water release could also give fire extra time to grow and cause additional damage. As a double-interlock system won't release water until both the detection system has been activated and a sprinkler has operated, the system must wait for water to arrive at the open sprinkler(s) before it can begin to suppress the fire. Double-interlock systems also require a larger design area and more water than if the sprinkler discharges water immediately upon its activation. 

In the interest of speed when suppressing a data center fire, a single-interlock preaction system may be preferred. With a single-interlock system, the early stage of a fire will trigger the supplemental detection before sprinkler activation, allowing water to be introduced into the pipe and ready once the fire has grown large enough to activate the sprinklers, discharging almost immediately in most cases. 

In this case, the sprinkler system that minimizes the probability of accidental water release may not necessarily be the system that minimizes overall business risk. It's critical for system designers to balance accidental discharge risk against fire-growth risk, equipment exposure and recovery objectives. 

Maximizing uptime with effective fire suppression design 

As rack densities increase, fire protection strategies designed around yesterday's data center environment may warrant reevaluation. Greater power density, more concentrated equipment value and increasingly demanding uptime expectations make the speed of detection, suppression and recovery more consequential. 

For mission-critical data centers, code compliance should be viewed as the starting point of fire protection design rather than the finish line, allowing fire protection to also be engineered around operational resilience and recovery. 

Ultimately, fire suppression design for a data center should begin with the operational outcome the facility needs to protect. Codes establish essential life-safety requirements, but operators should also ask what happens after the system activates:

• How quickly will the fire be controlled?
• What equipment could be affected?
• How much cleanup will be required?
• How quickly can the space return to service?
• If the first suppression layer is unsuccessful, what happens next?

Designing around those questions shifts fire protection from a compliance exercise to an integral part of the data center's resilience strategy.

As rack densities and uptime expectations increase, suppression strategies that combine early-response technologies with code-required sprinkler protection can help improve resilience, reduce business risk and support operational continuity. 

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