In Rack UPS Under 20 kWh Considered an ESS?

7/9/2026

I have a project I'm working on for a data center, and the owner is requesting a Hazard Mitigation Analysis (based on NFPA 855). I'm trying to see if NFPA 855 is applicable since it relates to energy storage systems (ESS).

The end user will have a UPS installed in each rack instead of a central UPS, and each rack will only be 0.55 kWh.

FM is also applicable in this case, but FMDS 5-32, Section 2.3.1.4.2 indicates that if your in-rack UPS exceeds 20 kWh, then that pushes the system into an ESS and FMDS 5-33.

But, NFPA 855 indicates that if aggregate quantities within the fire area exceed 20 kWh (which we would be for the data hall), then it's defined as an ESS.

Is the in-rack UPSs below 20 kWh are actually defined as an ESS or if they're just information technology equipment and NFPA 855 doesn't apply?

Thanks in advance.

Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

11 Comments

Joe Mc

7/9/2026 08:48:00 am

IFC 2024 section 1207 and related sub section will mostly govern,
if the AHJ is on an older edition i would still use the 2024 edition for liability issues.

https://codes.iccsafe.org/content/IFC2024V2.1/chapter-12-energy-systems#IFC2024V2.1_Pt03_Ch12_Sec1207

Jack G

7/9/2026 08:53:25 am

Per NFPA an ESS is an energy storage system. It stores energy and releases it later. That usually means lithium ion batteries. These batteries stack together in large racks for hones or businesses.
Some of the rules:
Use standard automatic fire sprinklers and may need a dry system for outdoor units.
System must spray a minimum 3 density over the entire battery area.
Goal is to prevent the fire from rack to rack
All ESS designs must follow NFPA 855.
Yhink of a battery as a hot charcoal grill.Too much heat to blow up. Water soaks the batteries to cool them down fast. This stops the " thermal runnaway."
Nfpa 855 is the primary protection standard for ESS storage. It mandates system listing's to UL 9540, Establishes spacing and ventilation rules, requires fire suppression, and requires site specific HMA, to prevent cascading thermal runaway.
Water is the most effective cooling agent.
TRPP ( thermal runaway prevention) must feature to absorb heat and stop propagation to other cells.
Fire detection systems such as off gas thermal image or radiant energy detectors must incorporated.
For systems exceeding certain energy thresholds, 600 kwh, explosion control and dedicated exhaust ventilation are mandatory
Owners must submit an ERP to the AHJ. Energy planning and response plan.
Nfpa 855 does apply.

Michael Knott

7/9/2026 12:15:12 pm

Appreciate it!

Jocelyn

7/9/2026 08:59:13 am

FMDS 5-32, the IFC, and NFPA 855 all scope their documents a little differently. I agree with your assessment of FMDS 5-32. The IFC also doesn't specify aggregate capacities for Section 1207 applicability, so I would argue Section 1207 doesn't apply to this case either.

But since you are being asked to comply with NFPA 855, the application Table in the Scoping Section 1.3 requires that the standard apply to an aggregate capacity of over 20 kWh per fire area. So although each individual in-rack ESS is less than 20 kWh, in aggregate for the fire area, they exceed 20 kWh, and yes NFPA 855 applies.

7/9/2026 12:13:53 pm

Thanks! If you're the same Jocelyn in the MeyerFire University series on ESS, thank you very much! I started watching those as I was banging my head against the wall and it helped to clear some things up.

7/9/2026 12:31:06 pm

It's me!

Dan Wilder

7/9/2026 09:03:48 am

I have seen this on a couple DC's lately and even with the dispersion or individual ESS components (ITE and the separate ESS components), the aggregate total within area drives the overall design. The designs have been able to utilize information specific to testing results that were provided to the AHJ by the owner as allowed in IFC 1207 for density, area, and configuration requirements and they were allowed to go with a lesser density however the area remained + applicable increases like dry/preaction, air velocity limits...

Between the IFC 1207 & NFPA 75, 800 (new in creation), and 855 they are all trying to keep up with and better define the equipment, hazards, and protection schemes. Try to always use the most current even if the AHJ hasn't adopted it.

As I sit on and/or will possible be accepted into the above referenced NFPA's, the above is my sole opinion and not a representation of any NFPA standard or committee nor a formal or informal interpretation....or something like that.

7/9/2026 12:11:12 pm

Thanks!

Ricardo Gonzales

7/13/2026 01:02:11 pm

You should also check with the Owner and see IF they've done full scale testing. That would and should be listed and identified in an HMA which would allow limited sprinkler and detection schemes.

Raymond Armas

7/15/2026 04:55:14 pm

I believe the Threshold Quantities in table 1207.1.3 is based on the aggregate energy capacity of all ESS in the fire area. Section 1201.3 provides insight to this measurement concept for the Maximum Allowable Quantity threshold in Table 1207.5. I would have to assume the use of aggregate capacity would be the same in establishing the applicability of Threshold Quantities.

Additionally, NFPA 855 applies to energy storage system (ESS) installations that exceed the aggregate capacity values shown in Table 1.3, in each fire area or outdoor installation. The table is titled "Threshold Levels per Each Fire Area or Outdoor Installation," and it establishes thresholds based on the total (aggregate) amount of energy storage present in that area or installation, not individual rack or unit capacity.

Hope this helps.

7/15/2026 05:56:30 pm

I don't agree with that interpretation of IFC Section 1201.3. The section header is for "Mixed system installation" and the section considers the aggregate sum of all ESS types (PV, Fuel Cell, electrochemical ESS) with regards to their respective MAQs, in the event that multiple types of ESS are in the same fire area.

This is akin to Section 1207.5.2.1, which is also in regards to mixed electrochemical energy systems. The word "aggregate" in this section is in reference to the sum of the percentages of each electrochemical ESS type divided by its respective MAQ.

This is supported by the commentary for these sections.

In Rack UPS Under 20 kWh Considered an ESS?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES