IEEE Electrification - December 2021 - 32

System Certification
Since 2017, the National Electrical
Code has required batteries other
than lead acid to be listed, that is, tested
by a nationally recognized testing
laboratory to comply with an applicable
safety standard. For stationary batteries,
that standard is UL 1973, first
published in 2013 and extensively
revised in 2018. Additionally, batteries
such as Li-ion, which incorporate a
battery management system with
safety functions, must demonstrate
compliance with UL 991, UL Standard
for Safety Tests for Safety-Related Controls
Employing Solid-State Devices [Third Edition,
(2010)] and UL 1998, UL Standard
for Safety Software in Programmable
Components [Third Edition (2013)].
Certification is not limited to the battery, however, as
the complete ESS must be certified to UL 9540, first published
in 2016 and revised in 2020. Certification to UL
9540 requires that a UL 1973-listed battery be paired with
a UL 1741-listed power-conversion system, with additional
testing to verify the adequacy of system integration.
The hierarchy of codes and standards applicable to
ESSs is depicted in Figure 3.
Large-Scale Fire Testing
Arguably the most impactful, safety-related document for
batteries is UL 9540 A, which is not a qualification standard
but rather a standardized test method with no pass/
fail criteria. This testing assesses the extent of TR
Standards and Model Codes Hierarchy
Built Environment
* iCodes - IFC, IRC, IBC
* IEEE - C2, SCC 21
* NFPA 1, 5000
Energy Storage Systems
* NFPA 855
* UL 9540
* ASME TES-1
* NFPA 70
* UL 9540 A
* FM GLOBAL 5-33
* DNVGL GRIDSTOR
* NECA 416 and 417
Installation/Application
* IEEE C2
* IEEE 1635/
ASHRAE 21
* IEEE P1578
System Components
* UL 1973
* UL 1974
* UL 810A
* UL 1741
* CSA 22.2 NO. 340-201
* IEEE P2686
Figure 3. The hierarchy of ESS codes and standards. IFC: International
Fire Code; IRC: International Residential Code; IBC: International
Building Code. (Source: Pacific Northwest National Laboratory;
used with permission.)
32
IEEE Electrification Magazine / DECEMBER 2021
* IEEE 1547
* IEEE 1679
Arguably the most
impactful, safetyrelated
document for
batteries is UL 9540
A, which is not a
qualification
standard but rather
a standardized test
method with no
pass/fail criteria.
propagation within the battery and
the effectiveness of fire suppression,
if needed. UL 9540 A testing is referenced
by fire codes and NFPA 855 and
is required whenever it is proposed to
exceed mandatory energy limits or to
reduce mandatory spacing between
battery segments, or between batteries
and exposures. Results of the testing,
including video recordings, are
submitted to the AHJ to inform their
decision making on code variances.
The evolution of UL 9540 A is an
example of the response of the standards-writing
community to unfolding
ESS safety events around the
world and the lessons learned from
those events. Originally published in
2017, the standard was revised twice
in 2018, and most recently, the fourth edition was published
in November 2019.
The test method in UL 9540 A takes a stepwise
approach, with testing starting at the level of individual
cells and continuing to modules, units (racks), and finally,
complete installations. The document is applicable to all
battery technologies that are subject to installed-energy
and spacing restrictions in fire codes or in NFPA 855, and
there are " off ramps, " where systems giving satisfactory
results at one of the lower levels do not have to complete
the higher, more expensive levels. However, if TR or flammable
gas is generated at the cell-level test, the moduleand
unit-level tests are required.
At each level, TR is initiated using an external heater. If
there is venting in the single-cell test, which is normal for
most Li-ion technologies, the overall volume and constituents
of the vented gases are measured. For the modulelevel
test, a single cell is heated to TR, and the adjacent
cells are observed to understand the effects of propagation
of the event. In the absence of sustained propagation,
additional cells may be heated to create a more extreme
event. There has been some discussion of this methodology
as the most likely initiating event in real life is an internal
short in a single cell, and simultaneous internal shorts
in multiple adjacent cells would be statistically highly
improbable. The counterargument is that such multicell
heating could potentially be caused by an arcing event.
The testing moves on to the unit or rack level, with TR
initiation in one module and monitoring for possible module-to-module
propagation and measurement of vented
gases and radiated heat. If there is no flaming outside of
the unit or deflagration risk, testing can be terminated at
this stage.
Testing up to this point is done without fire suppression,
so a lack of propagation in these tests indicates a
good level of intrinsic safety. If flaming occurs outside the
unit or gas generation represents a deflagration hazard,
IEEE Electrification - December 2021

Table of Contents for the Digital Edition of IEEE Electrification - December 2021
