The data center industry is undergoing significant transformation, driven largely by the growing demands of artificial intelligence (AI) and machine learning (ML). As facilities shift from traditional self-contained units to complex, distributed modular architectures, updating the scope of safety and performance standards is critical to address today’s challenges. The revised UL 2755:2025, the Outline of Investigation for Prefabricated Modular Data Center Systems and Related Modular Units tackles these issues and signals a transformative change in how data center projects are planned, executed and inspected.
AI-driven demands of modular data centers (MDCs)
According to Goldman Sachs1, AI workloads account for 13% of global data center demand today and are projected to reach 28% by 2027. Pre-AI data centers were not built to meet today’s demand. Leading systems are projected to contain up to 576 graphics processing units (GPUs) in a filing-cabinet-size rack, consuming up to 600 kilowatts (kW) — enough energy to power 500 U.S. homes.
Meeting the surging demand for AI requires a fundamental shift in data center construction. The industry must move away from lengthy “brick-and-mortar” builds toward next-generation prefabricated MDCs that can be deployed faster and scale more efficiently. These facilities use distributed modular architectures, where power, cooling, information technology (IT) and support systems operate as interconnected but separately manufactured and deployed units. This approach enables massive scalability, supporting hundreds of megawatts and thousands of racks across multiple buildings and zones.
The MDC market is projected to grow from $29.3 billion (USD) in 2025 to $128 billion (USD) by 2035 — a compound annual growth rate of 13.8%.2
Why update UL 2755?
Originally published in 2018 as the Outline of Investigation (OOI) for Modular Data Centers, UL 2755:2018 focused on self-contained MDCs housed in shipping containers. It did not account for the needs of AI-driven or distributed MDC facilities. Since then, the industry has evolved rapidly. Today’s facilities rely on interconnected modules for power, cooling, IT and support systems — often manufactured and deployed separately. This complexity calls for updated requirements for safety and performance.
One key reason for updating UL 2755 is its reference framework, particularly regarding electrical codes and energy storage systems. Since 2018, the National Electrical Code® (NEC) has undergone two major revisions, introducing requirements essential for modern prefabricated MDCs — requirements absent from UL 2755:2018. Without a reference to NEC updates, code authorities lack clear guidelines for assessing energy storage integration, updated electrical distribution demands and enhanced fire safety measures.
Energy storage has also become a core component of data center operations, prompting the creation of safety standards, such as UL 9540, the Standard for Energy Storage Systems and Equipment, and UL 9540A, the Standard for Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems.
Traditional inspection methods designed for conventional construction or simple containerized units do not fully address the complexities of evaluating modern prefabricated data centers’ complex, interconnected systems. UL 2755:2025 incorporates these code and standard updates, while addressing MDC developments.
Key enhancements in UL 2755:2025
The revised OOI addresses critical areas:
- High-density power and cooling requirements – Current requirements for AI/ML workloads include specifications for power densities up to 200 or more kilowatts per rack, with future designs expected to exceed 1 megawatt per rack, excluding cooling systems. These systems require sophisticated direct-to-chip cooling, closed-loop cooling, and the integration of cooling and power systems to help promote safer operation under extreme thermal loads.
- Distributed architecture standards – Interoperability requirements support seamless integration between separately manufactured modules. This includes standardized interfaces for power, cooling, monitoring and fire suppression systems, as well as communication protocols that enable coordinated operation across distributed architectures.
- Enhanced factory acceptance testing (FAT) protocol – Comprehensive FAT protocols that address multi-vendor, multi-location manufacturing. This includes requirements for integrated system testing at neutral sites when modules from different manufacturers must be evaluated together, remote witnessing for global supply chains, and documentation so code authorities can access complete testing records.
- Hyperscale integration capabilities – Modern modular systems must integrate seamlessly with hyperscale data center environments, supporting facility-wide monitoring, control and safety systems. UL 2755:2025 addresses integration with existing facility infrastructure, scalability requirements for phased deployments and coordination with other critical systems — including fire suppression, security and building management systems.
- Implications for construction and facility planning – UL 2755:2025 signals a shift in how data center construction projects must be planned, executed and inspected. This transition requires updated expertise, modified inspection protocols and enhanced coordination to enhance public safety while enabling critical infrastructure deployment.
- Environmental regulatory compliance – MDCs face strict environmental regulations, energy efficiency requirements and sustainability mandates. UL 2755:2025 aligns safety standards with these requirements and establishes that the criteria that supports code compliance is evaluated by the certification body, boosting code authorities’ trust and confidence.
Meeting the challenges of modern MDC deployments
The stakes are high. As AI and ML become central to economic competitiveness and national security, supporting infrastructure must support rapid deployment and safety.
UL 2755:2025 provides the framework for achieving both. Our experts can help you navigate the challenges of complex, multi-module prefabricated MDC deployments.
About the authors
Flore Chiang is a principal engineer at UL Solutions and has more than 20 years of experience in the product compliance and safety field. His areas of expertise include certification schemes/programs, hazard-based safety engineering, standard development processes, lithium-ion battery failure mechanism and safety, data center high-voltage direct current (HVDC) power architecture, liquid cooling for AI/ML workloads, and prefabricated MDC design. In 2024, he was a recipient of the IEC 1906 Award and an invited speaker at the Organisation for Economic Co-operation and Development (OECD) Workshop: “The Impact of Products Incorporating Digital Technology on Consumer Product Safety.”
Dejan Gakovic is a business manager at UL Solutions and has more than 20 years of experience in product compliance and safety. His areas of expertise include IT equipment and data center programs for installers and integrators.
X
Want to learn more about UL 2755:2025?
Learn more about the evolving requirements for modern prefabricated modular data centers. Let's collect some information so we can connect you with the right person.
Please wait…
Characters remaining