Prefabricated Modular Data Center Testing and Certification

As artificial intelligence (AI) continues to gain global traction across industries, data centers are increasingly challenged to keep pace with the growing demands of AI-driven workloads.

To meet the surging demand for AI, data center construction is undergoing a dramatic transformation, shifting away from lengthy traditional brick-and-mortar builds toward next-generation, prefabricated modular data centers (MDCs) that enable faster deployment than conventional methods. Prefabricated modular construction offers a scalable, flexible and more efficient way to expand data center capacity to help meet the demands of AI.

This shift toward modular construction is fueling explosive market growth. The global MDC market has experienced unprecedented expansion, growing from $29.3 billion (USD) in 2025 to a projected $128 billion (USD) by 2035, at a compound annual growth rate (CAGR) of 13.8%.¹

Safety risks of data centers

The surge in data center workloads is contributing to heightened safety hazards — particularly an increased risk of fire — driven by several key factors:

Higher power densities — ranging from 100 kilowatts to 1 megawatt per rack, compared to traditional levels of 5 to 10 kilowatts — significantly raise the potential for available fault current, increasing the likelihood of more intense and destructive arc flashes.
Increased thermal loads place greater stress on cooling systems, which can lead to rapid overheating if not properly managed.
Complex cooling systems often rely on flammable liquids, and any leakage can pose a serious fire risk.

Between 2014 and 2023, 22 high-profile data center fire incidents were publicly reported.² These events underscore the serious consequences of fire in critical infrastructure, including loss of essential equipment, extensive property damage, serious injuries and even deaths.

UL 2755:2018, the Outline of Investigation for Modular Data Centers

In 2018, UL Solutions developed UL 2755:2018 in collaboration with manufacturers, end users and regulatory authorities to help address the safety challenges of MDCs and meet the needs of key stakeholders.

UL 2755 is referenced in Article 646 of National Fire Protection Agency (NFPA) 70 — the National Electrical Code® (NEC) — as a recognized method for determining certification requirements. It enables evaluation of both the underlying subsystems and the complete MDC as a single integrated product. As a result, UL Certified MDCs typically require only evaluation of proper installation in the field, helping streamline deployment and reduce time and resource demands. In contrast, MDCs without UL 2755 Certification may be subject to additional evaluations by local code authorities depending on jurisdictional requirements.

UL 2755:2025, the Outline of Investigation for Prefabricated Modular Data Center Systems and Related Modular Units

To meet the evolving demands of modern data center architectures in the face of AI-driven workloads, UL Solutions revised the OOI in 2025. The updated UL 2755:2025 reflects the shift toward distributed modular architectures, where functional modules — such as power, cooling, IT and support systems — are manufactured and deployed independently but operate as an integrated system. This distributed approach enables massive scalability, with individual facilities supporting hundreds of megawatts of power and thousands of racks across multiple buildings and zones.

UL 2755:2025 replaces UL 2755:2018. This proprietary edition of the OOI reflects the evolving requirements for modern data centers and AI-driven demands and enables manufacturers to demonstrate safety and compliance for modern prefabricated data center systems.

Key features of UL 2755:2025 include:

Module type categorization and system integration
Precise testing addresses the safety risks for each module’s functions and applications.
Comprehensive code compliance framework
Evaluation to comprehensive compliance requirements with multiple code systems beyond building and fire codes can help streamline approvals with complex authority having jurisdiction (AHJ) requirements.
Enhanced construction and structural requirements
Comprehensive safety testing to structural engineering requirements includes stacking loads, lifting specifications and seismic considerations — crucial for large-scale data center deployments.
Streamlined pathway to compliance
Our structured process includes a request for quote (RFQ), preliminary review for compliance to UL 2755, preliminary findings and full evaluation to UL 2755.

Why work with UL Solutions?

Leverage our deep technical expertise as you build safer infrastructure that can keep up with modern hyperscale data center requirements. The revamped UL 2755:2025 provides a comprehensive safety framework that addresses real-world deployment scenarios while remaining flexible to support ongoing technological innovations. Available exclusively through UL Solutions, the 2025 edition reinforces us as your trusted provider — helping you navigate safety and compliance challenges and accelerate the deployment of prefabricated MDCs.

What is a modular data center (MDC), and how does it differ from a traditional data center?: An MDC is a prefabricated structure designed for faster deployment, scalability and efficiency in meeting data center workload demands, contrasting conventional brick-and-mortar data centers, which require longer construction times. Legacy facilities and infrastructure may not be designed to meet the performance demands and requirements for modern AI data centers.
What are the primary safety risks associated with data centers?: The main safety risks include more destructive arc flashes associated with higher power densities, rapid overheating stemming from increased thermal loads and overtaxed cooling systems, and flammable liquid leaks from liquid cooling systems — all of which introduce significant fire risks.
What is UL 2755, and why is it important for modular data centers?: UL 2755, the Outline of Investigation for Modular Data Centers, is referenced in Article 646 of NFPA 70 — the National Electrical Code® (NEC). UL 2755 addresses safety challenges and enables manufacturers to have prefabricated MDCs evaluated efficiently, as a single integrated product. This helps streamline the approval process with AHJs. UL Certified MDCs typically require only evaluation of proper installation in the field, whereas without UL 2755 Certification, local code authorities would likely need to conduct additional evaluations.
What changes have been made to UL 2755?: The updated edition, UL 2755:2025, provides a comprehensive safety framework that addresses real-world deployment scenarios while remaining flexible to support technological innovation in modern prefabricated MDCs and the increased capacity required for AI-driven workloads.
Key updates include robust module type categorization, a comprehensive code compliance framework and enhanced construction requirements. As a proprietary OOI available exclusively through UL Solutions, UL 2755:2025 positions us as your provider of choice — helping you demonstrate safety and compliance for prefabricated MDCs and supporting their rapid deployment.