Dec. 17, 2025

231 - BESS explosion prevention and mitigation with Lorenz Boeck and Nick Bartlett

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Today we cover another branch of safety of Battery Energy Storage Systems (BESS), that is explosion prevention in mitigation. I always thought you can either end with a fire or with an explosion, and boy I was wrong... but we will go back to this later. Now I bring on Dr. Lorenz Boeck (REMBE) and Nick Bartlett (Atar Fire) to unpack how gas released during thermal runaway turns a container into a deflagration hazard, and what it takes to design systems that actually manage the pressure, flame, and fallout. This is a tour through real incident learnings, rigorous lab data, and the evolving standards that now shape best practice.

We start with the fundamentals: from the overview given by NFPA855, why modern BESS enclosures—with higher energy density and less free volume—see faster pressure rise, how gas composition varies by cell and manufacturer, and why stratification matters when lighter hydrogen-rich mixtures sit above heavier electrolyte vapors. From there, we translate UL 9540A outputs—gas quantity, composition, flammability limits, burning velocity—into engineering decisions. NFPA 69’s prevention path typically relies on gas detection and mechanical ventilation designed to keep concentrations below 25% LFL, validated with CFD to capture obstructions, sensor placement, fan ramp, and louver timing. NFPA 68’s mitigation path kicks in if ignition happens, with certified vent panels sized to the actual reactivity and geometry, relieving pressure and directing flame away from exposures.

A major takeaway: the latest NFPA 855 now often pushes for both prevention and protection. Even with active ventilation, partial-volume deflagration hazards remain, especially as cell capacities rise and gas volumes scale up. We dig into venting trade-offs—roof vs sidewall, snow and hail loading, heat flux to back-to-back units—and how targeted sidewall venting can deflect flame upward while reducing weather vulnerabilities. Perhaps most critical, we talk about late deflagrations observed hours into large-scale fire tests, when changing ventilation conditions allow pockets to ignite. Active systems aren’t built to operate throughout a long fire, so passive venting becomes essential during and after ignition.

Whether you’re a fire engineer, AHJ, insurer, or developer, this conversation connects the dots between lab data, CFD, and field realities. You’ll leave with a clearer view of how to apply UL 9540A, NFPA 68, NFPA 69, and NFPA 855 in a world of stacked containers and supersized cells—plus where training can shorten your learning curve.

If you are interested by the course given by colleagues in Lund in January 2026 - here it is: https://www.atarfire.com/event-details/nfpa-855-8-hour-training-lund-university

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The Fire Science Show is produced by the Fire Science Media in collaboration with OFR Consultants. Thank you to the podcast sponsor for their continuous support towards our mission.

00:00 - Why Talk About Explosions Now

05:10 - What Causes BESS Explosions

09:30 - Scale, Free Volume, And Enclosure Effects

13:50 - Gas Composition And Surrogates

18:30 - From UL 9540A Data To Design

23:15 - NFPA 855, 68, And 69 Explained

27:40 - Ventilation Triggers And CFD Validation

32:10 - Detection, BMS, And System Independence

36:25 - Fire Tests And Late Deflagrations

41:10 - Deflagration Venting: Panels And Limits

46:05 - Sidewall Venting And External Hazards

50:00 - Taller, Denser BESS And New Risks

53:30 - Training, Standards, And What’s Next

56:40 - Closing Thoughts And Listener Invite

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Hello everybody, welcome to the Fire Science Show.

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Uh when I posted an episode with Norrider a few weeks ago on battery energy storage systems, it really blew up.

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It was a very popular episode, so I thought uh while I'll have access uh to some really good battery speakers, let's take them on a spin and and make uh perhaps a follow-up, more battery energy storage system content because it really seems it gets a lot of people interested in.

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During my stay in Lisbon when I've attended the SFPE Symposium on Lithium Ion battery safety, I've heard a lot of great talks actually, uh but uh I've heard a really good talk about explosions in battery storage systems, and I thought that I actually never covered explosions in this podcast, not just in the relationship to the battery energy storage systems, but I don't think I really had a proper explosion episode at all in the podcast, which is quite funny.

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230-ish episodes in, and there are still new things that were never ever covered in in the podcast.

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Great to realize that we're not running out of topics in here.

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But on the topic that I wanted, I found a great speaker in in Lisbon.

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Actually, I found more than a great speaker, because I found two speakers.

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For this podcast episode, I've invited Dr.

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Lorez Boeck from Rembe and uh Nick Bartlett from Atar Fire, and they, besides uh being specialists in battery energy storage system fire safety and explosion safety, these guys also run courses on NFPA eight five five, NFP sixty eight, sixty nine, a lot of standards.

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And and this is actually another reason why it's time to do this podcast episode.

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Because we're not talking about hypothetical solutions, we're talking about quite a standardized, I would say quite a major part of fire science right now.

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There are standards that you can follow, there are technical guidances that you can use to design fire safety and explosion safety of your storage systems.

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And all of this we will discuss in this podcast episode.

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So I hope I got your interest quite high up.

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I hope that you will stay with us till the end, you'll learn where you can find our courses.

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And for now, let's spin the intro and jump into the episode.

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Welcome to the Fires Show.

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My name is Wojciech Wegrzynski, and I will be your host.

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As the UK leading independent fire consultancy, OFR's globally established team have developed a reputation for preeminent fire engineering expertise with colleagues working across the world to help protect people, property, and the planet.

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Established in the UK in twelve sixteen as a startup business by two highly experienced fire engineering consultants, the business continues to grow at a phenomenal rate with offices across the country in eight locations, from Edinburgh to Bath, and plans for future expansions.

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If you're keen to find out more or join OFR consultants during this exciting period of growth, visit their website at orconsultants.com.

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And now back to the episode.

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Hello everybody.

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I am joined today by two guests.

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Uh, first, Nicholas Bartlett from Atar fire.

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Hey Nicholas.

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Hey Warchick.

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Good to have in the podcast.

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And together with us, Dr.

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Lorenz Boeck from uh Rembe.

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Hey Lorenz.

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Hey Warchick, thanks for having me.

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Thanks for coming for to the Fire Science Show.

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Uh with the recent podcast episode I had with Noah Rider, which broke some yearly records on listenership.

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I could not miss an opportunity to do another battery energy storage uh podcast episode.

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And Lorenz, I saw your talk in SFP event in Lisbon uh recently.

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I've learned that you are doing some crazy cool things uh uh with training uh battery storage systems.

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So here we are to follow up on that.

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And I hope today I will extract from you some knowledge to my friends who are listening to this podcast about, let's say, explosion protection of battery energy storage system, but also about the landscape, the normative landscape or reference landscape in which people can design those explosion preventions.

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And uh first, I well, that's a general question, but why why should we care about explosion prevent what really is the hazard regarding explosion in battery energy storage systems?

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Lorenz, maybe you would like to start?

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Yeah, for s ure.

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Um so as we all know, uh BES, you know, it's a pretty new and fast-evolving technology.

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It is.

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We've had it around for long enough that we've actually seen some events out there uh that happened, both fires and explosions.

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So we had an opportunity to learn uh not just you know from lab work, from theoretical work, from modeling work, but also from uh real-world uh incidents.

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So the explosions we've seen, most of them go back to some sorts of failures of individual cells or maybe the controls that are supposed to keep the cells happy.

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And as a result of these failures, we think thermal runaway.

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Thermal runaway is something that's it's pretty well known, even in the general population, because it can happen to your phone battery, to any of your personal devices around you.

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And I think the awareness is really growing.

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But what it does in best is it can release flammable gases that can accumulate inside the energy storage system and generate a pretty significant explosion hazard at a scale that is much greater, of course, than just your personal device.

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And uh like it's kind of funny because when you think about storing energy and the late acid batteries, the explosion hazard was always kind of there, but for different reasons, like the hydrogen production when you charge, etc.

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But here it's on a different level.

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Do we care about this explosion hazard only when you're building those mega packs on the desert or any energy storage system?

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It's really something that this risk is real.

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Well, we definitely care about them at all scales, right?

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Going from consumer products to maybe the system you have in your house to store energy from your PV panels all the way up to commercial industrial applications and then grid scale applications.

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And um, those are some of the ones that I personally work on the most, is the larger applications.

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But yeah, we do care throughout the entire range of steels.

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Yeah, I think the hazard does change a little bit depend upon where the energy storage system is located, whether it's outdoors, whether it's indoors.

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But you know, when you have thermal runaway and you're producing hydrogen and CO and some other, you know, hydrocarbons anytime that's of course in an enclosed environment and it can accumulate, then you do have that explosion hazard.

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So, you know, it's just different different settings for the same issue.

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Let's let's try and do an explosion one-on-one in like five minutes to the listeners.

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I didn't have an explosion episode in the fire science show, so let's introduce perhaps some important terms.

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You just drop some stuff that is produced in in the thermal event uh of a battery.

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How does that turn to explosion hazard and like what dictates how big the explosion hazard is?

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Sure.

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So you know, usually when I teach explosion protection uh in one of my classes, that's uh multiple weeks.

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So do this in five minutes, but um I'll try.

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So what we have in BES is basically a gas explosion hazard.

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This is not an energetic material or dust explosion hazard or any of these other great things that we might have to worry about elsewhere, but it's specifically a gas explosion hazard.

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And what makes them unique is the way the gas gets produced, which is from, like we said, the thermal runaway of a battery.

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So now we have the situation where we have a flammable gas inside of an enclosure, so typical container or enclosure of a battery energy storage system.

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The issue is that if that gas ignites, typically it builds so much pressure due to the combustion that this pressure overwhelms the strength of the enclosure.

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So typically these enclosures are built by far not strong enough to contain these deflagration events or these overpressure events.

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That's the issue here.

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So if this happens, you might rupture the container in a very, very worst case scenario.

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Or you might do other things before that happens.

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You might pop open the doors of the system, you might detach ventilation equipment and such.

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And all of that generates a hazard.

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And that hazard could affect the surroundings, could affect people in the surroundings, could affect assets or equipment in the surroundings.

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Those are the things we're trying to prevent, right?

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Really making sure that, first of all, we prevent the occurrence of an explosion, ideally, but if an explosion occurs, we manage it or mitigate it in a way that the outcome is still acceptable.

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So there's a lot of physics, you know, and how these explosions occur, what exactly happens, we can dive as deep as you like into that.

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But in a nutshell, I think that's the issue about best explosions, right?

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If a container with a limited strength, if there is a defigution or an explosion event inside, you build so much pressure that you might cause uh a hazard to the surroundings.

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I would like to book you for a fire fundamentals episode in my podcast.

00:09:12.960 --> 00:09:14.960
We really need to cover explosions.

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I did I did one good one with with Rory on on flammability limits.

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So the listeners are expected to understand what the flammability limits are and they're very important in here.

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How does the volume of the space within the battery energy storage system play a role in here?

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Yeah, so generally the scale of the system plays a strong role because if you have an explosion in a very small space, that basically means that your pressurize will be extremely fast.

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Assume a certain rate of combustion or rate of flame propagation in a very small volume, you have a very fast rise in pressure, and that means we have to protect it in a certain way.

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If you have a large volume, your pressurize tends to be slower, but you also need to possibly relieve much more overpressure, much more gas.

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So the protection or ways of protecting these shifts a little bit.

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And specifically in BES, uh, one of the challenges is, for example, that there is not much free volume inside of these containers anymore.

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And I've already talked to know about this, about design changes over the past years that we see in the industry.

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That was shocking to me.

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Absolutely.

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Like I've knew very little of it, but how much has changed since I've learned a little of that?

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It's it's really insane.

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But sorry, I throw you over.

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No, definitely.

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And and I had the same conversation with a good friend a few days ago where he asked me, well, are these best units still such that you can walk into them and you know look at the batteries left and right of an aisle that goes down the center of these systems?

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And when we talk about containerized systems, that's just not how they look anymore.

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They're densely packed nowadays of thousands of batteries or battery cells inside one of these units, and you're really trying to maximize energy density.

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So from an explosion standpoint, that reduces the free volume inside of these enclosures.

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So you're pushed more and more toward a scenario where you have an explosion and a relatively small effective volume that you need to deal with, that you need to either prevent or mitigate.

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Do you care about the exterior of it as well?

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As in is there like a vapor cloud explosion hazard outside of the enclosure?

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Or you consider that's already good if I got rid out of the gases from from inside?

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Well, so from an explosion protection design perspective, the primary focus is protecting the enclosure itself.

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That's your first step, if you will.

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Making sure that you don't breach the enclosure, making sure you do pressure relief or prevention so that doesn't happen.

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But then of course you need to handle the secondary effects of the explosions in a safe way as well.

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Something that's um covered, for example, in NFPA68, but also other design standards for explosions that tell you how to predict uh the external effects of an explosion.

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For example, extend pressure, right?

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When we talk about explosion venting, you open up panels or rupture panels, then you will have external flame and external pressure propagating from that opening.

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And there are engineering methods and standards that tell you how to predict these effects and then how to consider them to make sure that you're doing this safely, right?

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Again, in the event of an explosion, making sure that you're not creating any unacceptable effects in the surroundings of the equipment.

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Nick, how big is the relationship between the type of a cell and the explosion hazard?

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Like, do we have like explosion safe cells or all of them have the hazard?

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And to what extent the state of charge also plays a role in this?

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Yeah, well, state of charge certainly does play a role in this.

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I mean, 30% state of charge is often cited in various studies where there is, let's just say, less flammable gas produced.

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But what I would say is, you know, generally when I teach NFP 855 is that all lithium-ion batteries have a pretty similar hazard.

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So as the cells get larger and larger, you know, typically you'll have about half a liter to two liters of gases that are produced per amp hour.

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So that will obviously scale.

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And as I know you talked about with NOAA, I mean, today an average cell for an energy storage system is 285 or 314 amp hours, but that is dramatically increasing.

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And we've even seen press releases for a thousand amp hour plus.

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So, right off the bat, you you know without even any testing that your gas volume is increasing, but you're putting it in potentially the same exact box.

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So it definitely changes the hazard as you uh increase the size of the cell.

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Perhaps it's a it's a good moment to move into some of the standards and and specifics because I also like want this to be very practical.

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We obviously are not able to teach you explosion safety, the listener within a podcast episode.

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I hope you don't expect that.

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The the gentleman here uh have a very successful um world tourney with the courses and trainings.

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If you'd like, you'll definitely learn later in the episode how how can you sign for that.

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But there are resources and standards that help you figure out your situation.

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And to what I understood for the cells themselves, there's a UL949540A, which which helps us quantify what I've actually asked, like how how how dangerous is the cell.

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Maybe let's try to briefly talk about uh about the cells, and then we'll move into standards and prevention in in the storage systems.

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So yeah, I think kind of to your point, what I what I teach when I teach NFP 855 is that there are many layers to this.

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It's it's almost like a cake.

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So you know, of course, you have the overall product, the whether it's a uh ISO container, uh, so that has its own certification.

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And then you you get to smaller and smaller levers.

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So the rack itself will have its own testing and certification, then you get down to the module, which would have like what we call a UL 1973 certification, which has, you know, I think over 30 tests just involved in the module.

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You know, they short, short circuit it, they over voltage it, they do whatever they can to the module to fail it.

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And then you get even more granular.

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So the cell usually has UL 1642, and then you know, there's other certifications and standards for all the protective products, like we've already been talking about explosion control.

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So that that's its own standard.

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So what results is this kind of, I don't know, it's almost like a puzzle of different layers of certifications.

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It's not just one standard, and um, you have to consider all of them.

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And I think cumulatively, that's when you get an actual product if it's been evaluated properly, that at least the standards say is safe.

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And and let's let's do the 9540A specifically.

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Right.

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So that standard is critical for us in the end for designing the bright explosion prevention and protection, because that standard tells us about the hazard that the cell produces.

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We talked about this before a little bit, but the hazard from an explosion standpoint is all centered around that flammable gas that is produced.

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So the questions are how much of that gas is released and how reactive is it?

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From an explosion perspective, reactivity is usually quantified by burning velocity and maximum explosion pressure.

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Some of some of these are the critical parameters we're looking for.

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And we get those parameters from UL9540A tests.

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Like Nick mentioned already, also that standard in itself does tests at different layers.

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It starts with a cell level test.

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So it just tests the individual cell, and then it builds it up to a module level test and then to unit level test and an installation level test potentially.

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Um so at all these different levels, there are different tests to be conducted.

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But for us, from explosion design standpoint or protection design standpoint, it's especially the cell level and the module level that matter the most.

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Cell level, what you get is the gas composition, the amount of the gas, the reactivity of the gas, and the flammability limits.

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And then at a module level, you get to understand if there is a potential for propagation from cell to cell or for a cascading thermal runaway scenario that could evolve or involve multiple cells.

00:17:02.399 --> 00:17:08.799
So maybe not just one cell, but maybe there are multiple cells that can thermally propagate and all release a certain amount of gas.

00:17:09.119 --> 00:17:20.559
Yeah, and one of the important distinctions that you know people often get confused is that UL9540 is a certification for a product.

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Whereas another standard he mentioned, 9540A, it has a very similar name.

00:17:26.079 --> 00:17:28.000
So it I can see why it's confusing.

00:17:28.000 --> 00:17:31.839
That is basically a test standard that gives you data.

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It's not a certification.

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So you test your cell, and that's where you get how much gas is produced and what are the constituents, and then you test the module and you get data.

00:17:41.200 --> 00:17:50.559
So 9540A is really just a test that provides data that informs how to design around the data that's produced.

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Whereas 9540 without the A is a product certification.

00:17:55.359 --> 00:17:59.119
So it's really uh important distinction that's quite easy to confuse.

00:17:59.519 --> 00:18:04.319
All my life I've been designing smoke control and we had like NFPA 92B and A.

00:18:04.319 --> 00:18:05.039
Oh yeah.

00:18:05.039 --> 00:18:06.160
So that was fun.

00:18:06.160 --> 00:18:11.680
Uh in terms of uh you said it gives you composition flammability limits.

00:18:11.680 --> 00:18:15.359
So so those compositions are are vastly different.

00:18:15.359 --> 00:18:23.359
Can we say that there's like a single main like element in there, like hydrogen that that drives the behavior, or is it really like about the composition?

00:18:23.599 --> 00:18:28.880
Yeah, there are some elements that you will typically see in most of these tests and for most of these cells.

00:18:28.880 --> 00:18:38.000
Um, those are hydrogen, carbon monoxide, but then also carbon dioxide, then a range of hydrocarbons, and then larger molecules, organic compounds.

00:18:38.000 --> 00:18:43.519
And um, in the end, those are all some sort of decomposition product of the electrolytes of the battery.

00:18:43.519 --> 00:18:53.279
The composition, how much of what you get really depends on the cell chemistry of the makeup of the cell, all the way down to um the specific manufacturer and the form factor of the cell.

00:18:53.279 --> 00:19:02.160
So it's not like you can say, well, I have a certain cell chemistry, LFP, for example, and that will have a certain gas composition, but it really varies from cell to cell.

00:19:02.160 --> 00:19:07.920
And what drives the explosion hazard you already mentioned is especially the hydrogen content.

00:19:07.920 --> 00:19:10.319
But then also the rest does matter, right?

00:19:10.319 --> 00:19:22.160
So it's not like it's not like this is all hydrogen and then a little bit of extra species, but the hydrogen content might range between something like 30% up to maybe 60%, depends what what cell you have.

00:19:22.160 --> 00:19:27.759
But then also the rest matters and contributes to the energy that is released if there is a combustion and explosion.

00:19:28.079 --> 00:19:30.960
I'm looking at a table from sample gas data.

00:19:30.960 --> 00:19:37.519
It's a it's a composition of species that are much lighter than air, species that are that are heavier than air.

00:19:37.519 --> 00:19:47.440
Is this mixture persistently uniform in the time scales that are interesting to you, or are you worried that at some point it's gonna separate into different layers of cake?

00:19:47.759 --> 00:19:51.839
Yeah, we do see stratification in larger scale tests, which is pretty interesting.

00:19:51.839 --> 00:19:59.759
So when you uh put a silent thermal runaway in a larger enclosure in a lab, you will typically see the electrolyte vapor settling down.

00:19:59.759 --> 00:20:03.119
Toward the ground, and then the lighter gas is rising.

00:20:03.119 --> 00:20:08.960
From a UL9540A standpoint, all of this is just reported in relative concentrations, right?

00:20:08.960 --> 00:20:15.119
It's up to us as designers to make sense of that, what that really means in a realistic explosion scenario.

00:20:15.119 --> 00:20:23.680
And what is typically done from what I see is that we mostly focus on the lighter components, mostly because those are also the more reactive ones.

00:20:23.680 --> 00:20:32.160
But it's a bit of an open resource question, I would say, on whether or not we should dig a little deeper into the contribution of those heavier species.

00:20:32.160 --> 00:20:34.000
That was hard to capture, right?

00:20:34.000 --> 00:20:36.960
In tests, a lot of it is condense at ambient temperature.

00:20:36.960 --> 00:20:40.799
So you would have to run the test and sample at elevated temperatures.

00:20:40.799 --> 00:20:50.319
And then even if you wanted to, for example, use synthetic gases to replicate that in other tests, it's pretty challenging to deal with mixtures that have light and heavy compounds.

00:20:51.200 --> 00:20:52.640
Now it's a selfish question.

00:20:52.640 --> 00:21:01.279
Does the industry have some standard surrogate vapor or gas mixture that could be used to study the consequences of those explosions?

00:21:01.279 --> 00:21:02.960
Is there a consensus on that?

00:21:02.960 --> 00:21:17.200
Because if I wanted to like if if I'm only interested in studying the, let's say, the pressure relief or some other mechanism, I would not like to run my simulation a hundred times for 100 different combinations of gases.

00:21:17.440 --> 00:21:23.039
Yeah, so generally the concept of surrogate mixtures is very important here and it's powerful.

00:21:23.039 --> 00:21:28.799
One of the necessities here is that if you're running a test with a battery, there's only so much gas that it produces.

00:21:28.799 --> 00:21:35.920
But you might need a lot more gas to then determine some of the safety parameters, for example, burning velocity or maximum pressure.

00:21:35.920 --> 00:21:45.599
So what is typically done is you look at the composition that you sampled from the actual battery test, and you produce a surrogate gas that now represents that actual battery gas.

00:21:45.599 --> 00:21:52.000
And then you run all these other tests like burning velocity and Pmax, or you could also do, for example, large-scale testing.

00:21:52.000 --> 00:21:53.680
But you need that surrogate gas.

00:21:53.680 --> 00:22:04.160
This way that I described to going from a specific battery to a representative surrogate gas and then continue on is the typical process right now that we see a lot.

00:22:04.160 --> 00:22:10.000
I would not say that there is an industry-wide standard for a surrogate gas for that reason.

00:22:10.000 --> 00:22:12.880
That is due to the variability of the composition, really.

00:22:12.880 --> 00:22:26.319
But I would love to see over the next year some consensus of how, for example, a worst-case battery vent gas could look for a certain set of chemistry, maybe some additional parameters considered harm factor size, capacity, whatever.

00:22:26.319 --> 00:22:36.880
But I would really like that because then that would give us a basis for designing in a conservative way for systems where, for example, we don't have 9540A uh data yet.

00:22:36.880 --> 00:22:42.960
That'd be a powerful starting point that you can then be more specific about in the future once you get the data.

00:22:43.279 --> 00:23:02.400
I think generally speaking, it it would be good to come up with some sort of general agreed-upon surrogate, but you know, then you run into the situation where like we could look at a hundred different cells and probably say that the lower flammability limit is between four percent, which is for hydrogen, and let's say nine percent.

00:23:02.400 --> 00:23:03.920
Like we could all agree on that.

00:23:03.920 --> 00:23:08.400
We could all agree the burning velocity of a hundred tests would be between fifty and a hundred.

00:23:08.400 --> 00:23:13.119
So conceivably we could just make some sort of gas that's very conservative.

00:23:13.119 --> 00:23:28.160
But then kind of what's happened in this industry is that coals and standards are actually, in some regard, limiting the development of technology because we like to benchmark things, we like to standardize things.

00:23:28.160 --> 00:23:31.279
And this is an industry where everything is very novel.

00:23:31.279 --> 00:23:41.599
So, you know, theoretically we could come up with an extremely conservative surrogate gas, but it we'd have to put that in context where you know that that might not actually always be representative.

00:23:41.599 --> 00:23:43.680
It would for certain be worst case.

00:23:44.000 --> 00:23:51.359
Let's maybe venture into the NFPA ecosystem of that, because like Nick, you multiple times mentioned NFPA A55.

00:23:51.359 --> 00:24:04.000
Maybe let's just clarify how the ecosystem of the standards look like, which standard that describes what, and then perhaps we can go deeper into particular uh aspects of the standards.

00:24:04.319 --> 00:24:13.599
Yeah, so if we start, I think at the highest level, it would be NFPA 855, which is the standard for the installation of energy storage systems.

00:24:13.599 --> 00:24:18.400
So timescale-wise, the first edition of that actually came out in 2019.

00:24:18.400 --> 00:24:29.519
So, I mean, I would say globally it probably has the most, I would say, input and refinement of probably any of the global standards out there for safety.

00:24:29.519 --> 00:24:41.119
So it's you know, today it's on its third edition and it's drastically different than what it looked like in 2019, which is, you know, pretty impressive to think it's been six years and it's a completely different document.

00:24:41.119 --> 00:24:48.240
So yeah, you start you start at at with NFP 855, and that covers commercial installations.

00:24:48.240 --> 00:24:52.000
Uh, it does cover residential energy storage systems.

00:24:52.000 --> 00:24:58.319
Actually, it has a chapter on storing and collecting lithium-ion batteries, which is a completely different approach.

00:24:58.319 --> 00:25:12.880
So then, yeah, then from there you just kind of go down with additional standards and and uh it does cover like how did how do we design the actual product, how do we install it, how do we commission it, how do we maintain it.

00:25:12.880 --> 00:25:19.200
It tries to bring together all these aspects because it's not it's not just well, how do we design the deflagration events?

00:25:19.200 --> 00:25:33.680
Of course, that's extremely important, but but there's a whole ecosystem, like you said, where you know, if you miss one one critical aspect, like you you forget to maintain your systems, then you know, of course you're gonna have a problem no matter how well it's designed.

00:25:33.920 --> 00:25:39.200
So it's like equivalent of NFPA 101, life safety code, like uh kind of.

00:25:39.200 --> 00:25:47.279
Okay, and and the two standards that I hear uh very often about NFPA 68, 69, what what are those?

00:25:47.279 --> 00:25:48.400
Uh and what was the role?

00:25:48.720 --> 00:25:53.839
Yeah, those are the explosion prevention and protection standards that 855 points to.

00:25:53.839 --> 00:26:01.039
So instead of reiterating how this is done in 855, we just refer to 68 and 69 as existing documents.

00:26:01.039 --> 00:26:04.319
Uh 69 is the explosion prevention standard.

00:26:04.319 --> 00:26:09.119
So if you think about an accident sequence, the first thing you would want to do is to prevent, right?

00:26:09.119 --> 00:26:12.880
Before you even think about mitigating if the accident happens, but first you want to prevent.

00:26:12.880 --> 00:26:16.559
So in a logical sequence, 69 would be the first one to consider.

00:26:16.559 --> 00:26:24.799
This for BEST specifically would include mechanical ventilation systems that remove flammable gases from the enclosure, for example.

00:26:24.799 --> 00:26:34.480
And then the second standard to consider is NFPA 68, which is the protection standard or explosion mitigation standard, I would say, using defibration venting.

00:26:34.480 --> 00:26:43.119
So that talks about if there is a defibration inside of your system, so if you're not able to prevent it in the first place, then how do you protect the enclosure?

00:26:43.119 --> 00:26:51.680
How do you provide pressure relief in the form of defibration vent panels to keep your enclosure safe and prevent any rupture, any adverse external effects?

00:26:52.000 --> 00:26:52.400
Perfect.

00:26:52.400 --> 00:27:07.279
So let's perhaps try to first of all, like does every battery and the storage system that follows an FPA 855, that does it need both protection and uh prevention solutions on it?

00:27:07.279 --> 00:27:11.279
Is it required like universally, or there's like a scale at which it starts?

00:27:11.599 --> 00:27:19.680
Yeah, generally speaking, in the last edition of NFPA 855, which is 2023, you you could do either or.

00:27:19.680 --> 00:27:22.400
Because that was based on the knowledge at the time.

00:27:22.400 --> 00:27:24.079
You could do one or the other.

00:27:24.079 --> 00:27:27.279
Fast forward lots of discussions between different experts.

00:27:27.279 --> 00:27:44.319
We kind of realized that even if you have the mechanical ventilation, NFPA 69 that Lorenz was talking about, there is often still enough flammable gases that are generated even in the presence of that ventilation system to create what's called a partial volume deflagration hazard.

00:27:44.319 --> 00:27:48.480
So now it actually more or less requires both.

00:27:48.480 --> 00:28:04.079
So you're essentially mandated to do mechanical ventilation now, and you then have to analyze if there is a remaining partial volume deflagration hazard, which would then necessitate potentially installing some sort of deflagration vents.

00:28:04.400 --> 00:28:08.640
When you're having that ventilation system, how does how does it look like?

00:28:08.640 --> 00:28:15.839
Is it like uh, I don't know, uh a fan that you'd install in uh in a toilet on the wall, like a small device that's always on?

00:28:15.839 --> 00:28:22.799
Is it like a huge cooler, chiller that also plays the role as a you know cooling of the what what's the device?

00:28:22.799 --> 00:28:27.359
I don't think I've ever seen a new generation storage facility yet.

00:28:27.359 --> 00:28:30.880
So I am absolutely uh an idiot in terms of that.

00:28:30.880 --> 00:28:32.240
I have no idea how it looks like.

00:28:32.240 --> 00:28:33.519
You have to describe it to me, Nick.

00:28:33.680 --> 00:28:37.920
Well, I think I think you were a little spot on there, so it's a lot simpler than you might think.

00:28:38.079 --> 00:28:43.759
So thank God I mean because fire safety got a lot harder than I thought it would be.

00:28:44.400 --> 00:28:45.119
No, no.

00:28:45.119 --> 00:28:51.440
You're you know smoke control, so you kind of know it's this it's a similar concept, just applied differently.

00:28:51.440 --> 00:28:56.640
So typically, for most of the commercial products, there'll be some sort of gas detection.

00:28:56.640 --> 00:29:08.240
When the gas detection reaches a certain concentration, typically 10% of the LFL of the specific gas, it'll you know, it'll essentially turn an exhaust fan on, open a makeup air inlet.

00:29:08.240 --> 00:29:12.799
It's okay, it draws fresh air in, takes air out, and I mean that's really it.

00:29:13.039 --> 00:29:18.240
So it's not something that it's like continuously operational in the in the storage system?

00:29:18.640 --> 00:29:19.839
Not not typical.

00:29:19.839 --> 00:29:24.880
I have seen a few where they don't they're not really concerned about just running a fan all the time.

00:29:24.880 --> 00:29:30.000
Um, I have seen that application, but 99% of the time it's not running all the time.

00:29:30.400 --> 00:29:40.240
In such a storage system, do you do you actually have some sort of HVC climate control that would be running all the time anyway, or is the the gains are not that big?

00:29:40.480 --> 00:29:45.759
Yeah, I mean I would say thermal control of the actual container is kind of a separate topic.

00:29:45.759 --> 00:29:50.160
So these days, used to be a lot of these had actual HVAC in them.

00:29:50.160 --> 00:29:53.599
There still are some, but a lot of them have liquid cooling.

00:29:53.599 --> 00:29:57.039
So they'll have a chill chiller and they'll be circulating glycol.

00:29:57.039 --> 00:30:02.079
They'll often have some sort of dehumidification because water is not good for batteries.

00:30:02.079 --> 00:30:07.279
Um so they'll have their own separate kind of thermal and humidity control systems.

00:30:07.279 --> 00:30:22.880
So it's not like a drive to to make them all together in one mega ventilation system is like separate rolls and yeah, I haven't haven't seen that so far, not to say it doesn't exist, but I would also be concerned about control logic and sequence and how they all work together.

00:30:23.279 --> 00:30:25.920
And how how do you calculate the efficiency of the genit?

00:30:25.920 --> 00:30:27.920
Like how how does one dimension this?

00:30:27.920 --> 00:30:35.039
How many I don't know, air changes per hour you need per container, or that's the job of the manufacturer and you don't care as a fire safety engineer.

00:30:35.279 --> 00:30:41.680
It all starts again actually with that information that you get from uh URL 9540A, because you need to start with the hazard, right?

00:30:41.680 --> 00:30:44.480
So you need to understand how much gas is produced.

00:30:44.480 --> 00:30:49.680
And critically, when you design 69 systems, also at what rate that gas is released.

00:30:49.680 --> 00:30:55.200
With a 69 system, you're looking to remove the gas at a sufficiently high rate so it doesn't accumulate.

00:30:55.200 --> 00:31:11.359
And that's actually a very interesting conversation because getting that rate of gas release is not easy, both from a testing perspective, but then also right now, just from the perspective of interpreting these uh 9548 test reports, it's not that easy to get reliable numbers.

00:31:11.359 --> 00:31:16.319
But once you have a number that you're happy with and you work with, you can design the ventilation system.

00:31:16.319 --> 00:31:18.720
There are different steps of design, I would say.

00:31:18.720 --> 00:31:21.920
You can do a preliminary design where you can use some hand calculations.

00:31:21.920 --> 00:31:26.720
There are some rule of thumbs in, but also some simple analytical models.

00:31:26.720 --> 00:31:42.079
But then what we see mostly in practice is that you use CFD simulations to actually simulate the true behavior of the specific ventilation system for that specific best geometry, considering things like how obstructed is the geometry.

00:31:42.079 --> 00:31:43.119
It's very important, right?

00:31:43.119 --> 00:31:46.000
Some of these can be hard to ventilate because they're so densely back.

00:31:46.000 --> 00:31:51.200
But then also, for example, how fast does the detection system work once there's a gas release?

00:31:51.200 --> 00:31:54.559
How fast does the fan ramp up and do the louvers open?

00:31:54.559 --> 00:32:02.960
All of these things need to be considered together to really predict how much gas is allowed to accumulate at a worst case time during this entire process.

00:32:02.960 --> 00:32:14.880
And that gets then measured against the performance criterion of 69, saying that at most during this entire process, you're allowed to accumulate 25% of LFL globally throughout the enclosure.

00:32:14.880 --> 00:32:16.559
That's the performance criterion.

00:32:16.559 --> 00:32:18.400
And the simulation will show you that.

00:32:18.400 --> 00:32:23.359
So that is the most typical thing we see in the industry right now, hopefully.

00:32:23.359 --> 00:32:29.200
And actually also as per 855, the ventilation rate needs to be verified once installed.

00:32:29.200 --> 00:32:36.079
So making sure that you're actually getting the air exchange that you have designed for, making sure that you measure that in the actual installed system.

00:32:36.400 --> 00:32:51.839
Yeah, and I I think to add on to that point there, and we were talking about this earlier, is you know, it's really important when you're designing one of these that you have some familiar with familiarity with all these nuances, right?

00:32:51.839 --> 00:33:01.599
Because if you're used to designing buildings and then, you know, somebody comes to you and says, Hey, can you validate this ventilation rate for an explosion control system?

00:33:01.599 --> 00:33:09.680
One of the things we see is that if you just take this 9540A data, right, it's not conservative enough, right?

00:33:09.680 --> 00:33:16.960
So a 9540A failure of a cell is some people would call it a gentle overheating of a cell.

00:33:16.960 --> 00:33:19.119
I mean, that impacts the results, right?

00:33:19.119 --> 00:33:30.480
You're gonna get a certain gas volume, you're gonna get a certain gas release rate, as opposed to, let's say, a multi-cell short circuit, which is very energetic and produces different results.

00:33:30.480 --> 00:33:38.480
So what I've seen in the past is that if you're not familiar with these nuances, like you might just take the data from 9540 and be like, oh, this is great.

00:33:38.480 --> 00:33:40.640
Let's just design the system based on this.

00:33:40.640 --> 00:33:45.599
But that's probably like designing anything, that's probably not the best approach.

00:33:45.599 --> 00:34:01.759
And we, you know, with this new NFPA standard, is actually we've been able to get some content in the annex to kind of explain, yeah, you need to take that data and build in some conservativisms and just like you would with designing any other type of system.

00:34:02.160 --> 00:34:12.480
What kind of time skills are we speaking about from like the failure of the cell that releases a cloud of gases to like you having your control 25% LFL?

00:34:12.480 --> 00:34:15.599
Like, do you have to do it within a minute, five minutes, ten minutes?

00:34:15.599 --> 00:34:17.519
I mean, I've seen minutes to seconds.

00:34:17.519 --> 00:34:18.639
So minutes to seconds.

00:34:18.639 --> 00:34:18.800
Okay.

00:34:19.199 --> 00:34:25.760
When we're talking about well, how long does it take to release all of the volume of gas in a single cell?

00:34:25.760 --> 00:34:28.079
It's usually minutes, right?

00:34:28.079 --> 00:34:34.559
So the cell has a vent on it, it overpressurizes, it'll release gas, then it goes into thermal runaway.

00:34:34.559 --> 00:34:39.840
The the gas release rate will usually change, but that's a minutes time scale.

00:34:39.840 --> 00:34:48.800
And then your time scale for detecting those gases and then turning on the exhaust fin is usually seconds, right?

00:34:49.280 --> 00:34:51.760
And and you're basing it on gas detection.

00:34:51.760 --> 00:35:01.119
It's not that you're monitoring some status of the battery and the BMS is instructing the uh container, oh, you need to ventilate because I'm having some odd uh measurements.

00:35:01.119 --> 00:35:04.400
You base it on measurements of gases inside the free volume.

00:35:04.639 --> 00:35:04.880
Yeah.

00:35:04.880 --> 00:35:05.280
Yeah.

00:35:05.280 --> 00:35:19.920
Typically you see a couple, whether they're a hydrogen detector, CL, similar products, you're monitoring the container for gases, and that's what's triggering the ventilation, not the battery management system.

00:35:20.239 --> 00:35:24.079
Yeah, and that's good practice in safety systems, anyways, to keep those separate, right?

00:35:24.079 --> 00:35:33.920
That's typically a requirement if you look at critical safety systems that they operate completely separate from the process controls or the equipment controls, which in that case would be the BMS.

00:35:33.920 --> 00:35:48.800
Now, of course, the BMS has a critical part in the safety of the overall system to make sure it's kept at a healthy condition and maybe also doing things like early detection of potential upcoming failures of batteries predictive, uh yeah.

00:35:48.800 --> 00:35:49.440
Exactly.

00:35:49.440 --> 00:35:58.320
Yeah, and that's very powerful, of course, now with modern analytics to really trend these batteries and understand is there potential future failure to be expected.

00:35:58.320 --> 00:36:05.679
But um, when we talk about 68 or 69 systems, those are entirely separate from the controls of the battery system itself.

00:36:06.000 --> 00:36:12.800
And if if it's not just uh the cloud, if it's a fire, does this tool operate in the same way?

00:36:12.800 --> 00:36:19.920
Does it have any fire resistance properties of the fans or or it just, I don't know, dies from high temperature or shuts off?

00:36:20.159 --> 00:36:32.239
Yeah, I mean, typically, and this was actually addressed in the newest 855, so the operation of most of these safety systems, it's really only expected to be up until the point where fire occurs.

00:36:32.239 --> 00:36:36.960
So, you know, you might have some resilience, but it's on the minute scale.

00:36:36.960 --> 00:36:40.480
So a lot of the large-scale fire tests are hours, right?

00:36:40.480 --> 00:36:45.199
So, you know, you're not expecting these systems to operate for hours, right?

00:36:45.199 --> 00:36:49.039
Except for potentially passive deflagration events, right?

00:36:49.039 --> 00:37:00.559
I've actually seen in a quite a number of these large-scale fire tests where hours into the test of flaming fire, we've seen pretty large deflagrations.

00:37:00.559 --> 00:37:10.960
So, you know, those passive systems are actually quite important, not just prior to a fire occurring, but even uh over the duration of a fire.

00:37:10.960 --> 00:37:13.840
Because you can get underventilated conditions and things like that.

00:37:14.239 --> 00:37:22.960
You got my attention now because my colleague is doing uh a research grant on post-fire explosion uh resilience of steel uh members.

00:37:22.960 --> 00:37:24.239
So uh what do you mean?

00:37:24.239 --> 00:37:26.400
You had then deflagration hours into fire.

00:37:26.400 --> 00:37:27.119
That's crazy.

00:37:27.119 --> 00:37:27.920
Like why?

00:37:28.320 --> 00:37:28.480
Yeah.

00:37:28.480 --> 00:37:46.960
Well, uh, you know, we've seen this, so a lot of the large-scale fire tests that are being done today on these, you know, giant ISO containers, the way they'll run the test is that they'll open the deflagration vents before the test starts in order to get some, you know, to build up a fully developed fire.

00:37:46.960 --> 00:38:10.559
So one of the phenomena we've seen, and I would say at least half of these tests, is somewhere in the middle of the test, as when the fire gets large enough, I guess the you know, my my theory is that the ventilation conditions inside the container change, you get an underventilated condition, and somehow, and Lorenz could probably speak about this as for sure as well, somehow you get deflagration, right?

00:38:10.559 --> 00:38:20.480
And and sometimes, you know, the the container will deform, you might get projectiles thrown, but it's it's in the middle, could be two hours into a fire.

00:38:20.480 --> 00:38:28.159
And this observation has actually been it's it's pretty new, I would say, because we've been doing these tests this year.

00:38:28.159 --> 00:38:37.760
It's really a key observation for first responders that just because the container is on fire does not mean you cannot have uh deflagration.

00:38:38.079 --> 00:38:40.960
This is like a backtraft kind of mechanism, Lawrence.

00:38:40.960 --> 00:38:41.840
I could imagine.

00:38:41.840 --> 00:38:47.280
I mean, it really depends on whatever mechanism is available to bring oxygen back into the enclosure.

00:38:47.280 --> 00:38:51.039
And I think Nick could speak from his experience seeing these tests live.

00:38:51.039 --> 00:38:53.440
I think a lot of things happen during these tests, right?

00:38:53.440 --> 00:39:01.199
You might have breach of the enclosure in some areas, you might have some deformations, you might have internal collapse potentially.

00:39:01.199 --> 00:39:03.519
It's it's hard to tell really what's going on.

00:39:03.519 --> 00:39:10.639
But the outcome is really that yeah, you see defibrations well into a fire event, which I think is a critical observation.

00:39:10.639 --> 00:39:16.800
And it teaches us something about the scenarios we need to consider for BESS fires and explosions.

00:39:16.800 --> 00:39:26.400
It teaches us that we can't just stop with this uh conventional event tree thinking where you know either you get a fire or an Fire or explosion, yeah, exactly.

00:39:26.400 --> 00:39:27.760
Right.

00:39:27.760 --> 00:39:33.119
That is unfortunately, because it creates complexity, is not sufficient for BES.

00:39:33.119 --> 00:39:35.840
But the branch, let's talk about these branches.

00:39:35.840 --> 00:39:46.800
If you have one branch where there is immediate ignition of the battery event gas, then you are theoretically speaking on the fire branch, which now could lead to a late defigration as well, right?

00:39:46.800 --> 00:39:53.039
So you're on the fire branch, but then there might be another branch off where you might just stay in a fire or you might have a late defigration.

00:39:53.039 --> 00:40:01.199
The other part of the branch is if you're releasing gas and you're not igniting that immediately, then you would go toward conventionally speaking, Explosion branch, right?

00:40:01.199 --> 00:40:03.360
So you're always seeing accumulating gas.

00:40:03.360 --> 00:40:07.840
If there is delayed ignition, then you can have defigration and explosion.

00:40:07.840 --> 00:40:11.199
But so you realize that you have two explosion scenarios here.

00:40:11.199 --> 00:40:18.960
You have one pre-fire explosion, and you have one post-fire or during the fire explosion that we need to understand and consider.

00:40:18.960 --> 00:40:20.880
And that we also need to protect against.

00:40:21.199 --> 00:40:27.920
Okay, well, uh, in that case, your prevention mechanism 69 definitely will not be very helpful if they die into the fire.

00:40:27.920 --> 00:40:29.679
So let's move to 68.

00:40:29.679 --> 00:40:33.360
And uh and how how what what do you do with the flagration?

00:40:33.360 --> 00:40:35.119
And what are your possibilities?

00:40:35.119 --> 00:40:40.159
Because I assume you are in now in a branch in which it is bad.

00:40:40.159 --> 00:40:42.960

231 - BESS explosion prevention and mitigation with Lorenz Boeck and Nick Bartlett

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