The examine of a lithium-ion battery (LIB) system security dangers usually facilities on hearth potential because the paramount concern, but the benchmark testing methodology of the day, UL 9540A, is eager to position hearth danger as one amongst at the very least three dangers, alongside off-gas and explosion. On this weblog, we’ll shift some focus in direction of off-gas and explosion dangers to know which stakeholders care most about off-gas and explosion potential and why.
The Context of UL9540A
Underwriter Laboratories (UL) launched its 4th and present version of UL9540A “Take a look at Technique for Evaluating Thermal Runaway Fireplace Propagation in Battery Power Storage Methods Customary” in 2019. It’s the present security commonplace to which so many vital different codes and requirements — just like the Worldwide Fireplace Code, California Fireplace Code, NFPA’s 855 “Customary for the Set up of Stationary Power Storage Methods” — level. UL 9540A is very related when a lithium-ion battery (LIB) system undertaking goals for tighter spacing between models/teams or bigger vitality capacities of battery models/teams.
UL 9540A outlines and limits how a acknowledged UL9540A take a look at laboratory is to look at and quantify the initiation and propagation of a hearth situation, referred to as thermal runaway (TR), which could be outlined because the “self-heating of an electrochemical system in an uncontrollable vogue… [that] progresses when the [batery] cell’s warmth era is at the next price than it might probably dissipate, doubtlessly resulting in off-gassing, hearth, or explosion” (NEC 2023, 2020).
The finer-grained particulars and information we are able to seize in regards to the thermal situations at which TR begins in a given product’s cell, the higher. Every take a look at degree— cell, module, unit, set up— establishes and carries over vital quantifiables. The extra information we are able to repeatably acquire relating to the “when”, “at which temperatures,” and “below which thermal ramp charges” the propagation of TR happens at every test-level executed for a given LIB product below take a look at, the higher we are able to assess, design for, and handle TR danger of that LIB product.
In search of a proof of how UL 9540A take a look at methodology pertains to and differs from the UL 9540 itemizing? We’ve obtained you lined.
Off-Gassing begins earlier than and continues by means of TR Onset
One frequent false impression about LIB expertise is that there’s nothing to fret about if we keep away from the onset of TR. Offgassing begins throughout degradation section, previous to a given TR onset temperature. The development of a LIB cell from secure operation to degradation to uncontrollable TR could be visualized by plotting cell temperature over time, as proven under.
How a lot flammable off-gas is an excessive amount of at this cell vent? UL 9540A establishes a quantifiable threshold for unsafe ranges of flammable off-gassing (see Part 7.4 of UL 9540A entitled “Cell vent gasoline composition take a look at”). Right here, a cell is pushed into TR inside a pressurized vessel to gather part gases at venting. Utilizing gasoline chromatography, the gasoline composition and combination are decided.
This mixture of flammable gases is then synthesized in a brand new take a look at protocol and the Decrease Flammability Restrict (LFL) for the artificial gasoline combination is decided, each at ambient temperature and on the cell vent temperature. LFL is commonly reported as a share of air quantity, indicating the focus at which a quantity of air containing the flammable gasoline could be ignited.
As a security precaution, the present UL 9540A stipulates that regardless of the LFL noticed on the cell-level for a given combination of off-gas, the efficiency targets on the unit-level portion of the take a look at embody a threshold of 1 / 4 of that LFL by the overall quantity of related area. This threshold is restated within the under instance 9540A report from TUV, as a unit-level efficiency criterion: “The focus of flammable gasoline doesn’t exceed 25% LFL in air for the smallest specified room set up measurement.”
A historical past of LIB’s concerned in fires, no matter “main” trigger
A short assessment of battery fires reveals that TR alone will not be the primary and even enough trigger for a lot of massive BESS fires. Whereas there’s restricted information in regards to the root causes of battery fires, a number of publicly out there databases exist equivalent to this one from EPRI. The restricted information that’s out there reveals that the majority BESS fires have stemmed from exterior causes or broader system design points equivalent to exterior shorts or water ingress, somewhat than from thermal runaway propagation.
As talked about above, it’s vital to keep in mind that LIB expertise will produce flammable vent gases previous to reaching thermal runaway. These vent gases could then change into a gas supply within the occasion of an exterior failure, which may then result in ignition, explosion, or deflagration.
All lithium-ion chemistries to this point carry inherent flammable off-gassing danger.
It’s much less frequent, however not unusual, to listen to proponents of LIB merchandise declare that TR just isn’t of concern for some LIB chemistries. Sadly, this isn’t an correct depiction.
“Since all industrial Lithium Ion cell applied sciences out there at time of this writing are in a position to be pushed into thermal runaway (and emit flammable gasoline in that course of), Lithium Ion cells commercially out there right this moment don’t meet the CELL and MODULE degree efficiency standards. Because of this, Lithium Ion BESS should at all times full at the very least three take a look at ranges (CELL, MODULE, and UNIT LEVEL).”
The Sustainable Power Motion Committee, Informational Bulletin on the UL 9540 Security Customary and UL 9054A Take a look at Technique (June 2024)
Lithium iron phosphate (LiFePO4) batteries carry larger TR onset temperatures than many others named for numerous cathode supplies. That is, certainly, an advantageous cathode alternative that gives a wider thermal vary of operation earlier than TR onset. However that doesn’t preclude LFP batteries from being concerned in fires.
To state it once more: the flammable off-gassing that happens and propagates on the module degree in all commercially out there LIB to this point, together with LFP applied sciences, oftentimes turns into a primary gas supply for a lot of hearth or deflagration occasions brought on by failures exterior to the battery unit like water ingress, exterior shorts, and many others. We who’re actively working for increasingly more vitality storage deployment to modernize the grid and speed up the inexperienced vitality transition are higher served with correct and candid communication, even round a doubtlessly worrisome set of subjects like hearth and explosion danger administration.
That’s to not say that lithium-ion batteries are prohibitively harmful. All vitality sources pose some inherent security danger, and few established classes are as younger and rapidly evolving as LIB. With our wider neighborhood of stakeholders’ views in tow, we are going to proceed to enhance how we measure, consider, and account for these dangers in our product and system design.
Shield those that defend us below duress.
So the place will we stand: extra lithium BESS installs? A convincing “sure, and.” Extra vitality storage is important to the vitality transition forward of us, however we additionally should achieve this as safely as doable for all stakeholders, of which there are various. In dialogue with a number of former hearth professionals and present AHJ representatives explosion danger is a significant concern, and oftentimes a bigger one than hearth.
From the attitude of fireplace service skilled coaching protocols, solely two states of operation a lithium battery: usually operational or actively on hearth. As a result of every thing in between poses a danger for explosion. Some LIB producers have devised engineering options that embody actively lighting off-gasses at LFL, sacrificing the enclosure, and burning all of the batteries as much as keep away from fastly worsening catastrophic explosion hazard potential.
One SME supplied the motivation shared by hearth professionals and the AHJ’s that advocate for them as follows: “From a primary responder perspective we have to know what that secure degree of engagement is and distance to have the ability to even put an incident command publish. As soon as the unit or system is on hearth, at the very least we all know it’s not going to explode, which feels like a wierd win.”
“We’d somewhat have a identified ongoing battery hearth than an unmanaged off-gassing occasion ripe for deflagration or detonation.”
NFPA explosion terminology examine:
To debate managing off-gassing danger administration for lithium-ion batteries in better element and to satisfy some key stakeholders round UL9540A, be part of us in Austin, TX on October 2nd and third for our first inaugural Training Summit. Register right this moment!
