Ensuring ESS Safety in Data Centers with NFPA 855 – Part 2

April 7, 2021
ZincFive paper on how the NFPA 855 standards helps ensure ESS safety

Data center safety is a growing challenge as facilities expand in size and number, along with their UPS and battery systems. Now there is a single guiding document, NFPA 855, to help operators manage the potential risk from all that stored energy.

In the first blog post in this two-part series, we provided an overview of regulatory standards and codes from the National Fire Protection Association (NFPA) and the International Codes Council (ICC). We introduced the Underwriters Laboratories (UL) testing method and the best practices from the Institute of Electrical and Electronics Engineers (IEEE). Finally, we met NFPA 855, the fully coherent regulatory framework designed to organize the alphabet soup described above.

In this post, let’s learn more about how to evaluate ESS safety using NFPA 855.

Specific details of NFPA 855

Before the construction of a data center can begin, the operator’s representative will have to submit the chosen ESS supplier’s documentation, along with several other required documents including a Hazard Mitigation Analysis and the test report from an approved large-scale fire test to the AHJ. The information package must provide the AHJ detailed plans of the ESS installation, including the proposed floor layout and the operational parameters of the batteries specified, as well as details about smoke detection systems, thermal management, ventilation and fire suppression systems.

Below these thresholds, ESS systems using the various battery chemistries do not have to meet NFPA 855 requirements. For nickel-zinc (NiZn) and lead-acid this has been set at 70kWh of stored energy, though it should also be mentioned that no one NiZn or lead-acid battery string within an ESS deployment may exceed a 50kWh capacity. In contrast, the thresholds for Lithium-ion, Na-NiCl2 and flow batteries have been placed at just 20kWh.

Under NFPA 855, the maximum energy capacity inside a single battery room within the data center complex may, in some cases, be restricted. Lithium-ion and flow batteries will be restricted to 600kWh in total per fire enclosure area (i. e., battery room), while lead-acid and nickel-based batteries are not limited in capacity in a single fire enclosure area. Lead-acid batteries associated with a UL 1778 listed and labeled UPS system have the least restrictions placed on them, while other, more volatile battery chemistries have spacing limitations (three feet between cabinets and walls, etc.) and enhanced fire protection and explosion control/deflagration requirement that must be met.

These additional requirements, along with the required infrastructure upgrades required, may significantly increase the footprint and the up-front cost of these ESS offers.

Testing brings extra costs 

Other than lead-acid systems, any ESS with an energy storage capacity above the figures outlined in Table 1 will need to be tested in accordance with the UL9540A testing procedure at a certified lab. Carrying out such testing will determine if there is a propensity for thermal runaway to propagate within the battery, whether a fire will spread throughout the whole ESS, and how effective the fire protection measures are at preventing this from happening. It will also determine if flammable gases are given off that could exacerbate the situation. Depending on the report data derived from these tests, it is possible that reductions in spacing between cabinets or increases in storage capacity may be justified.

Since costs associated with UL 9540A testing could easily fall in the range of $50,000 to $100,000 or more, it can have a substantial impact on the total cost of ownership (TCO) of the ESS. There are other impacts as well in terms of the time and inconvenience of the testing process. 

UL 9540A testing costs can easily fall in the range of $50,000 to $100,000 or more.

Thanks to their safer characteristics, ESS installations that are based on either lead-acid or NiZn battery chemistries require less fire suppression apparatus (such as lower sprinkler density) than the lithium-ion equivalents. They also will not require explosion control venting needed for lithium-ion systems. All this adds to the list of TCO disadvantages when utilizing lithium-ion.

Better risk management now and in the future

Data center operators should now refer to NFPA 855 when designing, testing and installing ESS facilities to manage the risks of higher density battery systems. In addition, these new ESS standards are going to dramatically impact how future data center UPS back-up systems are managed and monitored once in operation.

NFPA 855 will also guide some aspects of upgrading and subsequent decommissioning of an ESS as well. If, in the future, a decision is made to apply the UL 9540A standard to existing ESS infrastructure, data center operators may have to retrofit compliant battery hardware too. This is certainly feasible at any installation where the AHJ feels a serious concern.

The arrival of the NFPA 855 means that data center operators and the ESS provider partners have the tools to give due consideration to safety across the full lifecycle of a planned UPS system. They can now understand operational parameters as well as the economic aspects that will have a substantial influence on deciding which battery chemistry should be employed in new installations.

Contact ZincFive if you have additional questions about NFPA 855, ESS safety and the TCO advantages of NiZn UPS batteries.

Dan Lambert, ZincFive Codes & Standards Specialist
Dan Lambert
Senior Product Manager, ZincFive
Dan has over 40 years of commercial and industrial electrical experience and has worked with AC and DC power systems, with a primary focus on mission-critical power systems. Working with stationary battery systems since 1985, Dan has worked with many battery chemistries and has contributed to large scale energy storage analysis projects, as well as testing other storage systems. Dan is currently a member of the IEEE Power and Energy Society serving as the chairperson for the IEEE Energy Storage and Stationary Battery Committee’s IEEE 1679.4 Alkaline Chemistries Working Group and is a member of the Battcon conference Technical Committee.