White Paper: Requirements for Energy Storage Systems Used in Data Centers, Revision 1.0, Version 1.0 (OCP Ready Facilities, January 2026)

Overview

The paper recalls that modular battery backup units (BBUs) entered the Open Rack design as a decentralised form of UPS, that early deployments favoured lithium-ion for energy density, cycle life and efficiency, and that thermal runaway makes fire risk the central concern. Its aims are to summarise the worldwide codes data centre operators follow, give guidance for safe design, operation, risk mitigation and maintenance, and influence later revisions of the OCP Ready v2 for Hyperscale and OCP Ready for AI self-certification requirements. The revision history marks it as the 30 January 0.2 committee draft; it points to the governing codes rather than replacing them.

The stakeholders and deployment chapter treats ESS for primary backup, grid interaction and load balancing, and says large-scale centralised ESS units are typically over 100 kW, sit in mechanical rooms or containers and interface with main LV or MV switchgear. An architecture table maps DC- and AC-coupled, distributed and centralised, autonomous and coordinated, energy- and power-oriented, hybrid, backup-only and grid-interactive forms to the relevant parts of NFPA 70, NFPA 855 and IEC 62933. The code frame cites NFPA 855 (2026), ANSI/CAN/UL 9540, UL 9540A, the IEC 62933 series, CSA C800 and FM Global data sheets; a future NFPA 800 Battery Safety Code will address storage and transport.

The chemistry chapter compares VRLA (gel and AGM, including TPPL), nickel-zinc (aqueous alkaline, not susceptible to thermal runaway), lithium-ion (LFP, LCO, LMO, NMC, NCA, LTO, all with some thermal runaway potential), sodium-ion and supercapacitors. Supercapacitors lack flammable electrolyte and thermal runaway, but hybrids with lithium-ion cells keep that risk. The insurance section uses FM Global data sheets (5-32, 5-33) and the IEC 62485 series: FM DS 5-33 recommends rooms with at least a 2-hour fire rating and, for indoor Li-ion racks, at least 6 ft (1.8 m) from accessible faces to non-combustibles and adjacent racks and 9 ft (2.7 m) to combustible materials.

On ventilation and detection, hydrogen off-gassing becomes explosive at about 4% by volume (IEC 62485-2) and may continue for an hour or more after charging stops. For suppression of Li-ion, FM DS 5-33 recommends hazard classification HC-3 with a dry pre-action sprinkler design of 12 mm/min over 330 m2 (0.30 gpm/ft2 over 3,500 ft2); water is typically the only recommended agent, with clean agents as supplementary protection. NFPA 855 (2026), UL 9540A (5th Ed.) and Annex G bring large-scale fire testing, NFPA 68 and NFPA 69 cover explosion control, and ventilation required during an ESS fire needs emergency backup power for 24-48 hours or more.

The later chapters cover shipping and on-site storage of UN3480 lithium-ion batteries (IFC Section 320 and NFPA 855 Chapter 14), maintenance and repair, decommissioning plans (NFPA 855 Chapter 8), hazard mitigation analysis (HMA) and first responder planning (NFPA 855 Annex G.10), civil engineering (containers may weigh about 80,000 lb or 36,000 kg), segregated white and grey space, cable penetration sealing and flexibility. Appendices give the OCP Ready ESS requirements matrix and regional lists of codes and standards, for example the Middle East. Data centre staff must not approach an ESS in alarm that shows fault signs (sparks, arcs, flames, gas plumes) and must evacuate and activate the emergency plan.

Key points

1. Large-scale centralised ESS units are typically over 100 kW, in mechanical rooms or containers, interfacing with main LV or MV switchgear.
2. FM Global DS 5-33 (as cited) recommends battery installations in rooms with at least a 2-hour fire rating.
3. Indoor Li-ion ESS racks: at least 6 ft (1.8 m) from accessible faces to non-combustibles and adjacent racks, and 9 ft (2.7 m) to combustible materials (FM DS 5-33).
4. Hydrogen off-gassing becomes explosive at about 4% by volume (IEC 62485-2), and gas emission may continue for an hour or more after charging stops.
5. For Li-ion ESS, FM DS 5-33 recommends HC-3 with a dry pre-action sprinkler design of 12 mm/min over 330 m2 (0.30 gpm/ft2 over 3,500 ft2).
6. Ventilation required during an ESS fire needs emergency backup power, potentially for 24-48 hours or more (NFPA 855 4.1).
7. NFPA 855 (2026) typically requires a hazard mitigation analysis (HMA) for most ESS; explosion control is required except for lead-acid and other aqueous technologies.
8. Nickel-zinc batteries are not susceptible to thermal runaway; supercapacitors lack flammable electrolyte, but hybrids with lithium-ion cells keep the runaway risk.
9. NFPA 855 (2026) Annex G requires large-scale fire testing (LSFT); UL 9540A 5th Ed. and CSA/ANSI C800:25 also form part of the test framework.
10. Large outdoor containerised BESS can weigh about 80,000 lb (36,000 kg) and sit on individual foundations in geotechnically evaluated soil.

Using it in design

• Fix the ESS architecture (DC or AC coupled, distributed or centralised, backup-only or grid-interactive), write the applicable NFPA 70, NFPA 855 and IEC 62933 parts into the design basis, and consult the authority having jurisdiction (AHJ) early.
• Plan the battery room as a compartment with at least 2-hour fire rating per FM DS 5-33, place the 6 ft and 9 ft Li-ion rack clearances on the layout, and design ventilation and gas detection around the 4% hydrogen limit where relevant chemistries are used.
• For Li-ion, weigh HC-3 dry pre-action sprinklers (12 mm/min over 330 m2), explosion control (NFPA 68 or NFPA 69) and the monitoring and detection architecture (BMS, gas, NFPA 72) together with HMA findings.
• Provide emergency backup power for 24-48 hours or more to ventilation, detection and BMS that must run during a fire.
• Prepare the first responder plan (NFPA 855 Annex G.10) with the fire service, and add decommissioning and recycling plans (NFPA 855 Chapter 8) and shipping and storage procedures (UN3480, IFC 320) to operating documents.
• For outdoor container ESS, address geotechnical study, foundation load (up to about 36,000 kg), blast barrier needs, fire service access and personnel egress early.

Who should read it

Electrical and fire-protection engineers who site, protect and specify BBUs, UPS and BESS in data centres, and developers working with insurers and the AHJ.

Document contents

1. Executive Summary and Introduction
2. Scope
3. Abbreviations
4. Compliance with Open Compute Project Tenets
5. Stakeholders, Use Cases, and Deployment Models
6. ESS Architectures & Topologies
7. ESS Technologies (VRLA, nickel zinc, lithium-ion, sodium-ion, supercapacitors)
8. Insurance requirements / Best practices
9. Ventilation and Detection/Alarm
10. UL 9540A and Large Scale Fire Testing
11. Fire Suppression Systems
12. Automated Fire Control and Suppression
13. Explosion Prevention/Control
14. Backup power requirements for ventilation systems
15. Handling of LIB in Data Centers (UN3480, storage, maintenance, decommissioning)
16. Hazard Mitigation Analysis and Emergency Response Planning
17. Civil Engineering Considerations
18. Segregated White Space/Grey Space, Cable Penetration Sealing Solutions
19. Flexibility and Adaptability
20. Appendix A. OCP Ready Requirements for ESS Matrix
21. Appendix B. Codes and Standards

Read the document

Publication details

Authors

Mark Dansie; Shrikanth Venkateshappa; Jim Dietz; Dan Lambert; Kalyan Jana; Mike Pagel; Lance Jennings; Josh Gerber; Ben Gully; Mauro Leuce

Publisher

Open Compute Project Foundation

Year

2026

Document language

English

Source type

Industry body

Access

Open licence — downloadable

Licence

CC BY-SA 4.0 — share with attribution under the same licence

Licence evidence

www.opencompute.org

Citation