Data centres are the backbone of the modern digital economy, supporting cloud services, financial transactions, healthcare records and enterprise communications. When a data centre goes offline, the financial consequences are immediate and severe. According to the Ponemon Institute, the average total cost of an unplanned data centre outage was approximately US$690,000 per incident, with individual events ranging from US$74,000 to more than US$1.7 million. The Uptime Institute’s Global Data Center Survey 2025 confirms that outage costs have continued rising, driven by the growing criticality of digital services and increasingly stringent contractual obligations.
Fire stands out as both the least predictable and most consequential cause of data centre downtime. Unlike a hardware fault, which can often be isolated within hours, a significant fire can permanently destroy servers, corrupt irreplaceable data, compromise structural integrity and trigger cascading failures that extend an outage from hours to months. Industry research consistently notes that 25% of businesses never reopen after a fire, and 80% of those that do not reopen within a month ultimately fail. For operators and design professionals responsible for protecting these facilities, a solid, code-compliant fire protection strategy is a necessity.
The detection foundation
Effective fire protection begins long before any suppression system activates. The modern data centre presents a challenging detection environment: dense server equipment generates significant heat requiring high mechanical cooling, and the resulting elevated airflow can dilute and disperse smoke before it reaches conventional ceiling-mounted spot detectors.
The accepted solution for high-airflow environments is aspirated smoke detection (ASD). Rather than relying on smoke to passively migrate to a ceiling detector, ASD systems continuously draw air samples from multiple points via a network of sampling pipes, delivering air to a central detector that analyses it for combustion products. This active sampling approach provides the early warning capability that modern data hall environments require.
Active fire protection: The single-interlock pre-action sprinkler system
A water-based automatic sprinkler system remains the gold standard of active fire protection across virtually every building occupancy, including data centres. NFPA 75 requires that IT equipment areas be equipped with a sprinkler system, a clean-agent extinguishing system, or both. The optimal strategy is a sprinkler system covering the entire building, with gaseous or water mist systems layered on top to protect data halls and peripheral UPS and battery rooms.
For data centre applications, the single-interlock pre-action sprinkler system is the preferred configuration. The piping is normally dry and only fills with water when the primary detection system is activated, preventing water from entering distribution piping due to a single mechanical failure or accidental impact unless a confirmed fire event triggers detection. Once detection is activated, the pre-action valve trips, water fills the piping, and thermally activated sprinklers nearest the fire open and discharge. This two-step sequence delivers proven fire-control performance while substantially reducing the risk of inadvertent water discharge into an equipment-dense environment.
It is worth understanding the design intent: sprinklers are designed for fire control, property protection and life safety, not complete extinguishment of a fire burning inside a server cabinet. They will not penetrate a closed cabinet enclosure. The sprinkler system is the building protection layer; supplemental systems address the equipment protection layer. Both are necessary.
Special extinguishing systems: Capabilities, limitations and the code boundary
Water mist systems discharge extremely fine droplets that suppress fire through heat absorption and oxygen displacement, using substantially less water than conventional sprinklers. They reduce collateral damage and enable faster system reinstatement after activation. Like sprinklers, however, water mist systems control fire spread at the room level rather than extinguishing fires within individual enclosures.
Clean-agent gaseous systems are designed to completely extinguish a fire rather than merely control it. They activate earlier than water-based systems, responding to smoke detection while fires are still incipient, and discharge without leaving residue. These characteristics make them well-suited for protecting high-value equipment where early extinguishment and rapid return to service are paramount. Design professionals should note that traditional HFC-based halocarbon agents are now subject to significant environmental restrictions; agents with negligible global warming potential should be specified where regulatory compliance is a consideration.
A critical code boundary must be clearly understood: the International Building Code does not recognise special extinguishing systems as equivalent to an automatic sprinkler system for purposes of building construction trade-offs. Installing an NFPA 13 sprinkler system throughout a building provides significant design allowances — increased allowable area, additional stories, reduced exterior fire-wall requirements and modifications to egress provisions. A clean-agent or water mist system protecting a server room does not satisfy this requirement, regardless of its technical sophistication.
The appropriate approach treats these systems as complementary. A single-interlock pre-action sprinkler system provides baseline structural protection required by code. Clean-agent and water mist systems are then layered within specific enclosures to provide rapid, equipment-level extinguishment that maximises asset protection and minimises recovery time.
A growing hazard: Lithium-ion battery systems
The proliferation of lithium-ion battery systems used as UPS installations deserves particular attention. Lithium-ion batteries combine high-energy materials with flammable electrolytes, and any damage to the internal separator can trigger thermal runaway: a self-reinforcing cycle of rising temperature that propagates from cell to cell with potentially catastrophic consequences.
The regulatory framework governing these installations has grown substantially. NFPA 855 is the primary installation standard for stationary battery energy storage systems, establishing requirements for siting, separation, detection, suppression and emergency response planning. NFPA 1, Chapter 52, addresses energy storage from a fire code enforcement perspective. NFPA 70, Article 706, governs electrical installation requirements, while NFPA 110 and NFPA 111 establish performance requirements for UPS systems serving emergency power functions. Design professionals should treat this suite as a coordinated framework: an installation satisfying NEC Article 706 but not evaluated against NFPA 855’s separation criteria may still represent a significant unmanaged fire risk.
FM Data Sheet 5-32 explicitly prohibits using clean-agent systems as the sole active protection method for data processing equipment rooms containing distributed lithium-ion battery backup units, confirming that water-based protection is the required baseline for these increasingly common installations.
Current technology has a hard limit: no firefighting system available today can stop thermal runaway once it has begun. Very early detection — ideally through off-gas monitoring before smoke or heat becomes evident — is the most effective intervention point currently available. Battery rooms should ideally be separated from the main data hall or positioned against an exterior wall to facilitate fire service access. Early engagement with the AHJ and thorough review of applicable NFPA and FM standards are prerequisites for a defensible design.
Designing for the full risk picture
The guidance of FM Data Sheet 5-32, NFPA 75 and NFPA 13 is consistent: no single system provides complete protection, and the systems that protect the building and those that protect the equipment serve different but equally essential purposes.
The single-interlock pre-action sprinkler system is the foundation — providing structural fire protection, satisfying NFPA 75 and NFPA 13 requirements, meeting FM’s preferred configuration and enabling the IBC construction trade-offs on which many data centre designs depend. Special extinguishing systems, carefully selected and matched to the specific fire scenarios of each protected space, build on that foundation to deliver equipment-level extinguishment and faster return to service.
For a facility where a single outage can cost hundreds of thousands of dollars and fire remains among the most destructive threats in the risk portfolio, treating fire protection as a risk-management investment — not merely a code-compliance exercise — is readily defensible.
