Fire Science Show
Fire Science Show
199 - Commercial Timber Guidebook with Danny Hopkin and Luis Gonzalez Avila
We know a whole lot more about mass timber in fire than we did a few years ago (even when I’ve just started the podcast 199 episodes back …). But is this knowledge widely used in engineering practice? Is it used in the same way by different stakeholders? Definitely not.
This is why to move timber into something we would consider “new normal”, we need more than research. We need a consensus on how to apply the outcomes of our research in practice. And this is this podcast episode.
Built by Nature, with a group of investors, property owners, and managers, funded a grant led by Elliot Wood to write a “consensus” guideline on using mass timber in office buildings. A large part of the book covers fire, which we also cover in this podcast episode.
I’ve invited prof Danny Hopkin and Luis Gonzalez Avila from OFR to walk me through the story of the guidebook, its contents of it and we also jump deep into the design philosophy of the book.
https://builtbn.org/knowledge/resources/commercial-timber-guidebook/
In this podcast episode, we try to stay away from explaining how timber burns (sorry!). But if you want to know more about physics, the Fire Science Show has you covered. Check out the timber section of the podcast! Look here: https://www.firescienceshow.com/categories/timber/
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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.
Hello everybody, welcome to the Fire Science Show. I really love to observe how the knowledge base or the experience base of our fire safety community grows over the time and in some cases you can really observe how we know more with every passing year, with every published research project, with every published book. We feel more confident in what we're doing, and one part in which it's very easy to observe this progress for me is mass timber, and this is also something that gives me a lot of joy because, as I reflect on the Fire Science Show, mass timber has been brought in here numerous times and you can even, to some extent, see that evolution as we discussed it with my guests, jumping from some general concepts and problems with mass timber that were quite obvious even years ago up to very sophisticated knowledges and solutions that are presented more recently, and today's episode is no other than that. I have mass timber for you again, and this time in a very useful and actionable form. This time we're not talking about fundamental properties, we're not talking about how timber chars, we're not really talking about the results of scientific research, but we're talking about industry consensus on how to build with mass timber, how to build office buildings in mass timber or in hybrid structures. For this podcast episode I've invited two guests, my colleagues from OFR, dr Danny Hopkins, who you know very well from the podcast, and he's also joined by Luis Gonzalez Avila, and together we are discussing a published piece called the Commercial Timber Guidebook, and on the cover it also has a subtitle Industry Consensus Guidance for Good Practice Mass Timber Office Buildings. And it's exactly that it's. It's something you can consider consensus. You'll learn in the podcast what does that mean in case of this episode and it also covers a lot of good practice on how to use mass timber office buildings. So, going from all the research, all the knowledge base that we've already covered in the podcast so many times and I put some links to the episodes in the show notes so you can perhaps reflect on the journey and on the basis for this After really actionable good practice guidance that moves us closer to designing and building with Mustimber the book itself is open access, so I'll leave you a way to access this publication in the show notes and for now, let's spin the intro and jump into the episode.
Speaker 1:Welcome to the Firesize Show. My name is Wojciech Wigrzyński and I will be your host. The FireSense Show is into its third year of continued support from its sponsor, ofar Consultants, who are an independent, independent, multi-award winning fire engineering consultancy with a reputation for delivering innovative safety-driven solutions. As the UK leading independent fire risk consultancy, ofar'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 plant. Established in the UK in 2016 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. If you're keen to find out more or join OFR Consultants during this exciting period of growth, visit their website at ofrconsultantscom.
Speaker 1:And now back to the episode. Hello everybody, I'm here today with Danny Hopkins from OFR. Hey, danny, hi Bocek and Luis Gonzalez-Avila. Hey, luis, nice to meet you. Hi Bocek, nice to meet you. Thanks for having me and Danny's in the podcast. So we're going to talk about timber. What a very new, fresh topic you brought to the show, danny. I appreciate that. Well, it's a fan favorite.
Speaker 2:Becoming a bit of a one-trick pony, I fear.
Speaker 1:It's a good trick. Anyway, the reason we talk is a very interesting publication that was published last year, if I believe. It's called the Commercial Timber Guidebook and it has a side title Industry Consensus Guidance for Good Practice Mass Timber Office Buildings, and it's a piece that's moving us forward in the discussion about safe use of timber from, let's say, academic considerations to real, actionable guidance that people can actually work in design with. Perhaps it's not the first piece that does that, there were many others, but I find this very interesting and complete. So, first things first. How did it come up to life? Who was doing that Because I see it's a large consortium and how did it start? Yes, you're right.
Speaker 3:Wojciech, I think one of the key things about the guidebook is the huge element of collaboration. So it originated from a grant awarded by Build by Nature in 2023 to the consortium that we were part of in ORFAR and that was together with our partners, structural engineers, elliot Wood, wode Düsseldorf, architects and insurance specialist, lignum Risk Partners. This was with the aim of developing guidance that addressed durability and moisture and fire safety in office buildings of mass timber constructions. Essentially, it was developed with the intent of it being a reference tool, as you were saying, of good practice guidance for designers, but with an element in mind of providing reassurance to insurers that their key concerns are adequately considered.
Speaker 2:So the genesis of the guide was in the grant that was provided by Built by Nature, but recognizing the benefits of some kind of consensus around durability and fire safety. We then got an awful lot of support from the developers people actually ultimately procuring mass timber buildings so there was a very generous group of collaborators who have an interest in developing timber buildings. So there was a very generous group of collaborators who have an interest in developing timber buildings that put additional funding into this to to allow it to happen.
Speaker 3:Yes, definitely so. It's both developers and asset owners that made up that group, some of the largest in the uk, and it consists of berkeley estate asset management, british land derwent, london, hinds. Berkeley Estate Asset Management, british Land Derwent, london, heinz, landsec, lendlease, muse Related, argent and Stanhope. So yeah, as you can see, there was lots of collaboration, starting from the funding through to the development of the book, with our partners. There was also numerous contributions from the insurance sector and other consultants and academics in the fire engineering world and networks, including td uk, timber development uk. So you'll see there's a list of acknowledgments within the guidebook itself.
Speaker 1:It is very impressively long. A question then follows. So if the building owners or managers poured out the money, they must have considered this as an important subject that I find. People randomly give me a lot of money for research, for random purposes. They usually have some points to be solved. Did they come with some clear pain points related to mass timber office buildings when this work was starting? Or it was just blank page?
Speaker 3:Hey guys, fire is a concern, go solve it it comes from their collective intent to really get the ball rolling in in the. You know construction with mass timber. Obviously they all have their sustainability objectives and it's a nice material to work with from an architectural perspective. It has its benefits structural wise. So they do have that in common. But, yes, so the reason why they're all involved is because that objective was in finding a barrier with particular insurance, but also there are barriers in in terms of approvals and it comes to those two main risks that the guidebook covers Especially. You mentioned Fire Voychek obviously this being a fire science show podcast. For fire there was particularly a huge inconsistency in the approach how people address these buildings and what was considered safe. So that was not helping the case in the eyes of the insurers, and this is something that was a key for the developers and funders and for us to be able to contribute to through the production of this guidebook.
Speaker 1:And also, I assume, due to the nature of timber, it being a novel, to some extent innovative, material. So you're really in the performance-based engineering regime. I'm not sure if you call it like that in the UK, but it's something the fire engineers have to craft and if there's no good reference guidance, then everyone does what they think is appropriate, which we all know that in many cases was not. You've mentioned durability, so let's maybe give because I know it's not the part that OFR was largely involved in but let's maybe briefly talk about why durability was involved. What's in that part of guidebook and then we'll move to to fire, yeah absolutely.
Speaker 3:Um. So if we go one page back before the durability part of the book, obviously because this a lot of it comes from the insurance blockers or challenges we and because we have one of our partners who are lignum and they are very well connected and, you know, knowledgeable about all things insurance we do have in the guidebook section that covers insurance provides background and context in particular to to these types of buildings that we're covering in the guidebook. But, yeah, following that section, it provides also background on office buildings of mass timber. That covers general design aspects, structural system types and engineered timber types. And then that's when we dive into the two main topics.
Speaker 3:So, as you were mentioning, wojciech did, first covers moisture and durability Things that are covered in. There are challenges around moisture and risk prevention strategies, mitigation strategies, and we both so the team drafting the durability section and us we're focusing on the fire section we both try to follow a similar sort of approach in that we provided background and specific sort of knowledge on the specific topic and it then concluded with a proposed set of principles, if you like. Well, that's what they're called actually. So there are 10 principles on durability that are proposed by the book as a list of rules, if you like, that you can follow in order to demonstrate that you're addressing adequately that particular risk in the case of durability and moisture.
Speaker 1:I think it's important to understand the requirements coming from different, you know, design objectives people have. The main objective of building is not to not burn down. I mean that's necessary for the building, but we're not building buildings to just survive fires. They have tons of other different functions and understanding those is critical. Okay, let's perhaps move to the fire engineering part. So how does one approach such a vast subject as mass timber office buildings? Perhaps perhaps let's step down a little bit. Why office buildings? Why this particular type of building that is considered by the book?
Speaker 2:we sort of touched on this in in a few podcasts that I've done. So there's the regulatory framework that we have in england, particularly now so, post-gromfell, we've sort of discussed the idea that cladding fires have created concerns around our ability to work safely and responsibly with combustible materials more generally and and therefore the idea of building sort of residential and apartment buildings out of timber has there's definitely been a dip in interest and a dip in confidence in using combustible materials in that context. So that has led to somewhat a bias in the market for mass timber building, sort of moving towards the more commercial type buildings, so the, the offices, the retail sort of applications, education and leisure, that kind of stuff. Um, there's also the fact that we should, we should mention the built by nature separately funded, uh, the new model building, which is um a sort of guide, how to equivalent to our document which sets out some rules of engagement for how you would construct sort of low to medium rise residential buildings out of mass timber. So that was subject to a separate grant that I. I recall ucl and bureau haphold were were heavily involved with alongside war fessleton, who sort of spanned out of mass timber. So that was subject to a separate grant that I recall UCL and Dura Happold were heavily involved with, alongside Warfesselton, who sort of spanned both projects.
Speaker 2:So two elements. One, a guide to some extent already exists to address a particular subset of residential buildings. Two is that market forces are kind of driving more commercial timber construction than they are residential. So the majority of projects that we're working on are commercial projects, and I think it holds true for most other fire safety engineering consultancies, and not only that. It's probably where we're most ambitious, dare I say. So it's where the buildings are getting taller.
Speaker 2:We're using a higher proportion of wooden elements compared to elsewhere. So with that comes potentially higher consequences of fire that need to be addressed. And I suppose the other thing worth noting is that timber has all its great sort of sustainability and embodied carbon benefits. But what it also lends itself to is building quite cleanly, quickly and efficiently in urban areas. So when we're building in city centres and such like, and when we're constrained by site sizes, the number of deliveries that we can have to site, the need to build things quite quickly in those city centres where you have predominantly commercial buildings, it has a use in that respect. So there's lots of reasons as to why we're using timber in that kind of context, and with that demand comes a need for guidance and some level of consistency across the buildings that we're delivering.
Speaker 1:Thanks for bringing back the topic of the residential timber model building code. Mike Woodrow from UCL, who is involved in that is a long list of podcast episodes to be recorded. I hope I'll eventually be able to get one done. But we'll definitely come back to that model code and residential buildings and I echo your opinions on the benefits of timber as construction material outside of your structural properties or aesthetics or other things.
Speaker 1:Why we put it in buildings is just very efficient to build and I I agree with that. I've built numerous clt mock-ups for you even, and I also appreciate how clean and and efficient it is. Even when one has to trim the slab by 10 centimeters because it's not fitting the steel wave that you build. It's much easier to trim a 10 centimeters out of a timber slab compared to trimming it down from a concrete slab. So, yeah, I echo that. Another thing, that there's some distinguishing in the guidebook about the types of buildings, so perhaps we could address that. I wonder to what extent it's related to UK, to what extent it's just general ideas. But you put those buildings in different brackets in terms of their height and in terms whether they are mass timber fully or a hybrid structure. So perhaps let's discuss those brackets like where they came from.
Speaker 2:Sure, there's sort of two, well, three parameters to think about in sort of clustering or grouping mass timber buildings, mass timber buildings. And one is that there's various like I'd refer to them as trigger heights that exist historically in in our fire safety guidance and consequently affect how buildings are designed and operated. So there's certain thresholds at which certain fire safety provisions kick in, like we change typically the way we we approach fire and rescue service access. Around 18 meters in a commercial building, we have triggers for sprinklers and such like. 30 meters in commercial buildings we have new bandings in terms of what it means for external walls and such like 11 and 18 now with these features that come into a building and what it might mean for when you move away from something that is wholly combustible towards seeking to contain things like fire and rescue service provisions inside concrete cores and stuff like that. So there's some practical considerations there in terms of lining up with when these fire safety measures come in. The other thing is, um, we we've spoken a bit about the structural timber association volume safety measures come in. The other thing is, um, we we've spoken a bit about the, the structural timber association volume six guide in in the past.
Speaker 2:So one of the first projects that ofr worked on, in the space and in terms of research at least, was developing this guidance document around under what circumstances a structure should be expected to withstand the full duration of a fire, versus it might potentially have a finite life and at some point potentially collapse in the absence of some kind of third-party intervention.
Speaker 2:And that distinction in structural fire performance objectives was made on the basis of consequence classes, and so consequence classes are something that span all of Europe through the Eurocodes and are present in our approved document A, and they're basically a way of expressing how the consequences of failure of a structure relate to the structural robustness considerations that you should incorporate into your design, in particular when addressing disproportionate collapse, and so that introduces another set of triggers in terms of when your structural objective changes, and so if you're looking to survive burnout, certain types of structural form lend themselves more readily to achieving that outcome than others, and and that might be because we're having to constrain the amount of combustible surface area in the enclosure and therefore we might not want glulam beams with glulam columns, with clt slabs, with exposed walls, and that's kind of a situation where maybe we're in the finite survivability, and there are situations where we want to be more confident, as the consequences are fairly ratcheted up, and that might mean a more hybrid form of a structure where actually our vertical elements are non-combustible.
Speaker 2:They might be steel, they might be concrete. Our cores, where our fire service activities are contained might be non-combustible.
Speaker 1:But by that finite survivability you mean something we ordinarily would call a burnout like can it survive?
Speaker 2:no, no, finite. Finite, as in there is a limited time at which stability is assured. Okay, not infinite. So it's the distinction I draw. So in in the sta sort language, we distinguish it as surviving for a reasonable period versus an adequate likelihood of surviving burnout in terms of those two different objectives. And so yeah.
Speaker 2:So if you're in a situation where, for whatever reason, you're accepting that your structure doesn't need to survive the full duration of a fire without third party intervention, then that gives you a bit more freedom in terms of the amount of combustible structure you might be willing to include, and that is generally appearing in the guide as things that are less tall and therefore have lower failure consequences.
Speaker 2:So those three things ultimately lead us to group the buildings into different height brackets, and then also noting that when we talk about mass timber buildings, a mass timber building can take many forms, so we can have a pure timber building, and by that I mean we're building all of our structure out of timber. So that's glulam frame, cross laminated timber floors, potentially even your cores, formed as, as cross laminated timber. That works to a point from a structural engineering perspective, because glulam isn't as strong as steel, for example, so your vertical elements can get quite big. That means as you go taller, you might consider some amount of hybridization, where you take the benefits of using steel for your vertical elements and potentially your beams. Yeah, so a mass timber building can have elements of mass timber and elements of other materials, and I think we are increasingly making use of the benefits of other materials as the height and the size of the building increases.
Speaker 1:In this hybrid, let's say bracket? Do you also consider buildings Like? You buy a building in a Primal location in London, you clean it inside, you add five floors from CLT. Is that again in your nomenclature a hybrid building or it's something else that's not included?
Speaker 2:um, you know, in totality it's a hybrid building, I suppose, in that you have this sort of melange of materials that you you wouldn't have otherwise had. I think it's important to stress that, for the purposes of the guide, we we specifically excluded that kind of nuance where we're dealing with refurbishments and extensions, because it is in itself a very case-specific, complex thing to resolve.
Speaker 2:So we sort of positioned the guide somewhat conveniently to address sort of wholly new structures that are of of that form. So in that sense when we talk about hybrids we're really meaning the new building is using a selection of materials in concert.
Speaker 1:Yeah, cool. Okay, let's talk compliance pathways, because you even have an entire sub-chapter in the guidebook saying about inadequacy of approved document B, and it mentions the cross-report. I think we've talked about that in extents in previous podcast episodes, danny. Let's talk about what compliance pathways you actually have, and by compliance pathways we obviously refer to the British system, but some of these considerations may be also applicable elsewhere in the world, so I hope it's interesting to the global audience of the Fireside Show. So how does one get timber building compliant, danny Housley, and in what part of that process this guidebook becomes relevant to that process?
Speaker 2:So I guess my first point would be that we don't have a UK regulatory framework. We have all of our devolved nations, so we have separate regulations in England, wales, scotland, northern Ireland. Now there is some commonality in the language they use and how they structure those, but there are also differences. So I'll kind of express this from an englishman's point of view. And that is, if we, if we park the, the building safety act and all the high risk building discussion, as has been covered in a in a podcast by my colleagues in the commercial building worlds, you have the building regulations, where you have regulations b1 to b5 that address effectively escape and warning internal fire spread via the linings internal fast, but via the structure, external fast spread and then fire and rescue service activities. And each one of those regulations and their subparts are what I would call functional or performance based, in that they they are telling you what to achieve.
Speaker 2:So I always use the structure one, because it's the one that sticks in my head, is that the structure should remain stable for a reasonable period in the event of fire. That is the legal test of compliance, if you like, um, and there's similar, similar sentiments expressed like which thou shalt adequately inhibit fire spread over the external surfaces and from one building to another, or something of that sentiment. And so you have that. That is the law, if you like, but the law within it has some vagueness, you might say, or it would require a case by case consideration as to whether you have done something adequately or reasonably. So appealing to those performance based requirements on a case-by-case basis, using first principles, would be really really quite challenging. It would require a huge amount of competency on everybody in the design team, on every single building that you're working on. And so, in parallel with with this change which happened in 1985, which is a stellar year, as you'll appreciate, before we check, absolutely and's the production of approved documents.
Speaker 2:And so the approved documents are a set of recommendations that if you follow them in their entirety and apply them to common building situations, which is not specifically defined by the approved documents, then you can be considered in all likelihood to comply with the building regulations and the building act as the primary legislation would actually say that you would, as a designer, tend towards negative liability if you, if you, did that. So the approved documents give you a set of tools to support compliance for common building situations. Within there is is a series of heuristic shortcuts, rules of thumb that implicitly assume certain features of your building, because these rules or bits of guidance originate from things like the post-war building studies and from a period where construction wasn't especially innovative, to be honest. This and so using and relying on that guidance to demonstrate compliance for a mass timber building potentially has a whole host of pitfalls, because you're taking a material which is combustible and applying it within a guidance-based framework that develops a lot of its rules of thumb from experiences of non-combustible construction.
Speaker 2:And so if you're trying to get a mass timber building ultimately approved so it can be constructed and you can evidence that it complies with the building regulations. You almost have to work through every single one of these requirements and consider the impact of your structure being combustible on the ability to adequately inhibit, support means of escape, whatever it might be, and whether you can sensibly rely on those, those rules of thumb in the guidance, or if they're insufficient because they have certain limitations. And so the I think a mass timber building affects almost every element of the fire strategy and therefore compliance. But if we're going to focus on a few of the ones that get discussed semi-regularly, one is the idea of using fire resistance periods as a proxy for surviving the full duration of a fire, which historically have assumed that your structure is not contributing as a source of fuel.
Speaker 1:Arguably, they were invented to move from timber to non-combustible structures.
Speaker 2:Indeed, they were in fact a response to timber structures and the need to start evidencing the fireproof claims of products in the 1800s 1900s. So at that point, when your structure is involved as a source of fuel, you're going to need to find a way to evidence that it is going to have a reasonable likelihood of surviving the fraudulation of the fire. And that's where your role as an engineer is moving away from the application of I don't use the word prescriptions, because then they're not really but instead of relying on recommendations, you're doing something a bit more involved, a bit more first principles. It might be a fully performance-based assessment, using models or whatever. It might be a semi-qualitative judgment. There's lots of different ways to achieve the same outcome in my mind.
Speaker 2:But in recognizing that there's these bunch of hazards that are not addressed by the guidance, we've got a manual for how to do calculations and evidence the performance of a mass timber building.
Speaker 2:We're still we're still learning about the features of mass timber buildings and what does present a particular challenge and what doesn't, and so there is a real variety in how people are approaching that. It's a real variation in in the amount of diligence that's supplied. There's a variation in the amount of conservatism that's applied. Some of us are a bit more. I'm more of the mind that if there's an uncertainty in design and you can easily remove it, then you should. Others are a bit more liberal in how they might sort of take on that uncertainty and then accept it in their design. That kind of speaks to them. So I was just gonna say that kind of speaks to the motivations of this guide in many respects, because that variation in responses in evidencing the adequacy of a design um creates some nervousness in amongst the insurers and also the approvers, because different people are coming to them with broadly the same sort of designs but presenting the evidence to them in different ways and to different, varying extents of diligence.
Speaker 1:In my view, one can present an analysis, even based on first principles, but just bad assumptions. That a building can be safe with some questionable safety guidance in it, it's possible. It's just how you craft your design. Fire, for example, another person can just mindlessly stack safety margins on top of each other and end up in a structure that's extremely expensive and perhaps inhibits the intended use of that structure. So there is a sweet spot, or there is a good spot to be, and I assume that the principles defined in this manual actually guide people to finding that sweet spot in a more reasonable manner. There's also something called qualitative design review, qdr, mentioned in the guidebook. So if you could perhaps elaborate on that, yes, absolutely.
Speaker 3:Porcek. So I just also wanted to highlight that all of what we're discussing at the minute is almost like a first part of two main parts that form the FHIR section of the guidebook, this part being authored primarily by us in OFR. It's almost setting the scene. So, yeah, we've covered what you guys have just discussed in terms of routes to compliance and in that aspect, the QDR is the process. So yeah, as you mentioned, qualitative design review process that is standardized in terms of a set of steps that comes from British Standard PS 7974. And it's essentially a framework to undertake a fire engineering assessment, from the initial steps of analyzing the architectural design, the architectural proposal, and going through each of the objectives of the stakeholders, clients and the approvers and all the designers, Obviously, for us a key one being life safety, which is a primary objective of any fire safety design, but the specific building can have other objectives.
Speaker 3:We've been talking about insurance here.
Speaker 3:So there is a lot of discussion within these first parts of the fire section of the guidebook about property protection, business continuity. So it's identifying those goals and then establishing the possible fire safety solutions in order to address those goals. Fire safety solutions in order to address those goals that goes with setting the acceptance criteria and how the methods of analysis are undertaken in order to achieve those goals. All of that is something that in an ideal world I say, but actually we believe that's the way it should be done and that's the way we try to do in our projects, believe that's the way it should be done and that's the way we try to do in our projects. That should be part of a conversation with the approvers and all of the key stakeholders. So insurers should be part of the conversation and that's how you so, from the beginning of your project, establish what you're planning to do essentially so how you're going to be demonstrating the life safety or what the other objectives are met and how you can go about showing that to approving authorities.
Speaker 1:I also appreciate that you put structure in this, so it's not just general consideration that what should be done. You propose a list of principles that you, I assume, test against for, or that you should meet in your building, and then you give some considerations on what's the fire engineering approach that's going to meet that principle. I'll take the liberty to quickly list the principles, because it's it's a list of 10 of them. Well, there's sub points, but in general there's 10 of them and they start with zero. There's much more than 10. Come on, guys, it's not 10. I'll go through that.
Speaker 1:Zero fundamental principle, comprehensive fire strategy. That's the first one. Then it's followed by adequate risk to health and safety and adequate risk to health and safety B. Well, adequate risk to health and safety, okay. Then there's assumed redundancies for life, safety design, impact on escape from area of fire origin, mitigating internal and external fire spread, and that subdivides it into vertical and horizontal fire spreads. There's expected performance of structure and compartmentation, survival of burnout with encapsulated mass timber, survival of burnout with exposed mass timber, sensitivity, consequence, consequence analysis and smoldering combustion. So that's the list. I assume that this is the list of principles that the fire engineer should consider when designing them buildings, and then address them one by one, in what way they their engineering design refers to them, meets them. What's the intent between for this structure?
Speaker 3:so, going back first to what I was mentioning, that makes up the fire section. This is that second part. So first part, we have already set the scene. There's also a lot of good content in there. This talking about the way timber burns and the hazards this presents to buildings.
Speaker 1:I have to apologize you for not going in that, because you probably wanted to talk about that, but the listeners of Fire Science Show are very well aware of that after numerous episodes with Dr Hopkins. Absolutely yes, yes no problem.
Speaker 1:I decided to jump straight to the principle, but I also want to actually I want to emphasize the language that's used in the guidebook, the aesthetics of the guidebook, the way it's presented. Also the part about the scientific principle, the description of chemistry, physics of timber fire. It is absolutely superb. It's like that's the top communication on timber I've saw. So I I just want to highlight that and and listeners are very highly recommended to just go see it, even if you're not interested in rumor buildings, just to see how a top scientific communication looks like.
Speaker 3:Let's move to principles yeah, no, thanks for that voice and I, and I was exactly gonna say that.
Speaker 3:You know that is essentially summarizing what has been covered in all the of your episodes in here by colleagues of mine.
Speaker 3:But yeah, so the second main part being the principles, that is something that has been introduced after the outcome of a series of workshops.
Speaker 3:When you mentioned that line in the cover page that talks about consensus, this is a key element in the guidebook that, at least from a FHIR perspective, relates to consensus.
Speaker 3:So we were lucky enough to be able to have a to form a panel of fire consultants and academics, which was formed by Design Fire Consultants Horley, semper, fire Engineering, university of Edinburgh and UCL, together with us, ofr, and together we came up with this list of principles. They primarily propose to enable that demonstration of reasonable standards of health and safety can be achieved in an event of fire in a building this type commercial mass timber building. So they're primarily aimed at life safety a sort of prescriptive list, in any way, but to highlight what are the key rules, if you like, that designers should be considering when they are dealing with a challenge, as is a building structure that can't burn. So in a way, there's still freedom, if you like, as to how to address them. But with the group, with the FHIR panel, we wanted to make it very clear and explicit what the ultimate goal in terms of all of those subheadings that you just listed is.
Speaker 1:Can we have an example? Maybe let's take one principle and go through it in depth, Like how would the process look like?
Speaker 3:Yes, absolutely. Through it in depth, like how would the process look? Like um? Yes, absolutely so. I think internally in ofr we've had some discussion about um, for instance. Uh, it's very weird to start from the, from the bottom.
Speaker 3:But you know the last principle, principle 10, which talks about smoldering combustion, and it's something that's very, very current in terms of research and that is is a big challenge when you're designing a fire strategy.
Speaker 3:So, for instance, that specific principle says that I have knowledge is that it's a secondary hazard, smouldering combustion, and that the fire brigade should be aligned to conventional practices for more traditional forms of construction in the way they tackle a fire with mass construction, and this hazard of smouldering needs to be explicitly acknowledged and communicated to the fire brigade. Now, it doesn't say how. So we talked about QDR before and we were discussing in a previous section the QDR may or may not have input from the fire brigade, for instance. So that might be a moment in the design where this gets communicated, so the designer can find different ways to communicate it, or if maybe in the future there are solutions that don't have to rely in fire brigade intervention to address hotspots, to address smoldering combustion. But at present our view is that the ultimate action of the fiber gate will be necessary for that secondary hazard, if you like, of smoldering combustion.
Speaker 1:So what I'm trying to do here is to understand. I imagine myself in a situation where I'm a fire safety engineer for a mass timber building and I try to put this guidebook into practice. So correct me if I'm wrong, but I assume that you give me a list of principles that I should address and I see principle 10, smoldering combustion. I understand what it is based on the physics description that's provided by the guidebook, and you tell me to provide explicit communication to fire brigade articulating smoldering list. So my task as a fire engineer is to craft a communicate to first reflect on the smoldering combustion hazards in my building, understand them and craft communication fire brigade to help them address that. And if I do that successfully, you would consider me completing that principle.
Speaker 3:or there's more I should be doing If you've adequately so, if you've achieved that communication with the brigade. Yes, you would have addressed the principle.
Speaker 1:And there's also a list of implications related to fire safety principles. What do you mean by those? What do those define?
Speaker 2:So the principles in themselves are a set of objectives, if you like, and to express those in lay terms in terms of what it might mean for your building, in terms of, maybe, the features you are unlikely to be able to have, that's where the implications come in. So we can work through another one of the principles, for example. So if we're looking to, so let's go to 4B we're going to mitigate internal vertical fire spread. So the uncertainty that we're concerned about in addressing this principle are kind of twofold. One is what are the structural implications of multi-story fires in mass timber buildings? So we're not really sure what happens to our columns, our beams, et cetera, et cetera, when the fire is occurring potentially over successive floors. So to address that uncertainty we're not in the space where the research supports a definitive position on it. So it's an uncertainty we're looking to remove. So we're going to basically prevent vertical fire spread. The other uncertainty is that what happens in terms of the envelopment of the building in fire when you have successive stories on fire? So what happens to the external flaming? We know what external flaming from a mouth timber compartment looks like on a single story. But what happens if that's on successive stories and those plumes start to interact and that becomes three stories. Do we? Do we find ourself in a situation where we are going to very readily set fire to our neighbor because we've created a situation where we have this massive wall of external flaming? Again, we're not in a position, from a research perspective, to adequately answer that question, so we try and mitigate it by effectively saying you should prevent it.
Speaker 2:If you're going to prevent vertical fire spread, then you you're going to have to introduce certain features in your building, or maybe you're going to have to eliminate certain features. So an implication would be open atria in timber buildings are probably not a good idea and are unlikely to meet that principle. So that is an implication. If you want to prevent vertical fire spread internally, then don't have open connections between floors. And so you begin to see that the principles and their implications start to set a bit of an envelope in terms of what your building is going to look like. You can eliminate a lot of the, dare I say, more daft ideas of your design by following these principles and just doing a sense check and understanding the implications.
Speaker 2:The same, if you extend the logic to the external wall, if you are trying to prevent story-to-story fire spread. Then having combustible external wall materials with a combustible internal structure is another sort of red flag that you're going to immediately want to eliminate. So again you're you're enveloping the design by, you're removing these combustible elements from the external wall. You might actually want to explicitly include passive measures. So one of the implications of preventing vertical fire spread is you might need to go back to having a spandrel. You might need to introduce projection that deflects the flame away from the building. You might want to stop thinking about your facades in the traditional commercial sense and actually stagger your openings or something that is going to explicitly address this potential for rollover from story to story. So it kind of shapes the design early by setting a bunch of principles about features that you should either be omitting or potentially including to address.
Speaker 1:Yeah, and the fact that it's a list it just makes sure that you do not omit anything like by accident. For example, it's not just smoldering combustion or it's not just external fire spread that you're worried about. Each of those principles is highly impactful on the design. We're low on time, but there's one additional part of the guide which is very interesting, which are the case studies. So the case studies are an example buildings for which you have applied those rules.
Speaker 1:You've done the QDR process to figure out the solutions that would fit them. Those buildings are I'll list them it's a full timber office below 18 meters, up to four stories, so I guess that's your smallest building, but fully timber built. Then there's a fully timber building between 18 and 30, up to 15 stories. Those are very low height stories. If it's 30 meters, then it's hybrid offices between 18 and 30, up to 15 stories. So this one would be a hybrid solution and there's also hybrid offices above 30 meters or above 15 stories. So, luis, maybe you can walk me through the idea of those case studies. And what does a designer take out from them? I assume it's not just like TAKE doesn't build this now, it's more like in one.
Speaker 3:Absolutely yes and actually so. You mentioned QDR, wojciech. So QDR would be something that's project specific. So actually, what we are mentioning at the beginning of this section is that. So, yes, we've tried to come up with these four typologies to sort of show a way in which the principles could take form in a building of these characteristics, however being very explicit that every building will have their specific objectives. So they will need to go through that QDR process. And you see in the so it's a summary table If you look in the guidebook that contains, you know, these four types of buildings and it goes through provisions like whether we think that sprinklers are liable to be required, if the core would need to be combustible or not.
Speaker 3:The number of stairs, because that also in England, wales, it's a subject of discussion. I know Exactly exactly, but for commercial buildings you do have a height up to which you could reasonably have a single-stair building still. So it's all of those elements. There's a list of provisions, including also the type of adhesive that's used, whether heat resistance adhesives are considered probably necessary for that specific type of adhesive that's used, whether you know heat resistance adhesives are considered probably necessary for that specific type of building. Um, but, but this is just like yeah, as you were saying, it's an example, so it's not, by any means it's not intended to be an exemplar or a recipe so it's not your approved document b equivalent for timber.
Speaker 1:It's more like how those principles were applied to those four particular designs and what came out of that. I would also highlight that the designs are pretty. For an example, they're pretty detailed. So you have to take a look in the book. But they give you a lot of description about what the building is like, where it's built, what's construction? Uh, off the offsite category and so on. Does it tells you even if it has a swimming pool or not? So it's a very detailed description of of the building. Uh, not your general consideration that all buildings above 18 meters shall be like this, of course, I like to think of it.
Speaker 2:Void check is a bit of an exercise in managing expectations so when, when a when a client comes along and makes the commitment to build a mass timber building, they probably have a particular vision of what that building's going to look like in their head, and it's.
Speaker 2:It's usually loads and loads of exposed timber, long spans, uh, limited columns, all built out of glue, lamb and the sand.
Speaker 2:The other and it is kind of a bit of a reality check or a sanity check on, if you're going to build this type of building, here's a bunch of features that is probably going to have um, and this is where you're going to end up, and that makes the design process so much easier because you're not sort of swimming against the tide of the expectation of the building they're going to get.
Speaker 2:The expectation has already been managed to some extent in terms of the architecture, the features, fire safety systems, and it's a it's a real sort of ability to test the commitment that if, if you've gone through this list and you think you can accommodate all of this stuff in wanting to move ahead with this kind of building, then in all likelihood it's got it's got a high potential to succeed. If you go into it somewhat blindly, expecting to build it as if it was a concrete building and you've just swapped out the concrete bits for timber bits and forgotten all of these extra considerations and these extra bits on the shopping list, then that might fail as a timber building. So, um, yeah, it's. It's really useful, in terms of almost before we're involved to some extent, to just get the design in the kind of space where it's got legs and it can work, and so I think it'd be very useful in that respect.
Speaker 1:Can I throw a curveball question on you? Go for it. Was there a temptation to put fire safety interventions explicitly for the principles considered? Because now the considerations are separate from interventions and interventions are only found in those examples. So it's there it's. It's not that the principle tells you okay, you have to put sprinklers if it's 18 meters in the box. Was there a temptation to fix it like that, in a more like a person manner? Or you really want it to be the, the qdr of our engineering process?
Speaker 2:tempting, yes, feasible, not really, um, and so it's got the word consensus in the title and consensus. As you can imagine, like you get five or six fire consultants in a virtual room and you ask them to talk about how you should deliver a mass timber building, when you've got a mixture of academics and consultants, you consensus wasn't an easy thing to come by. Uh, and that's on a set of principles which are quite high level considerations for how you're going to design the building. To then extend that to consensus on the specific features a building should have to respond to, those um was really tricky.
Speaker 2:It was a step too far, to be honest and where there is still differing opinions on the specific ways in which some of these problems should be addressed. So we didn't want it to be sort of a timber buildings according to ofr rules, which would have been the alternative. So we feel at this point in time, given the relative immaturity of of how we're approaching these, we should give people the room to to develop the solutions they feel are appropriate that respond to those principles. If, in a couple of years' time, we're converging on something that looks like we can take it a step further, there's the opportunity to do that. But yeah, at this point in time it's just not where we're at.
Speaker 1:I mean we went from timber is stronger than steel because it chars and you see this picture of molten beams on the timber beam to prove my point up to a level where we have 10 workable principles to talk about an engineer around. So I would assume that's a massive step and also cleans up the language, cleans up the definitions, gives a very clear description of what's happening and indicates what the real issues are. So I agree that it's a massive step. It's just the question was due to convenience, like if I just have a check, like going from a list of things I have to consider things I have already in my building sprinklers check, spandrel checks that's even easier way. Perhaps one day I will have a standardized mass timber building with a checklist that tells you that, or else you go QDR. Perhaps we'll use that one. Was the examples also a part of consensus or was it the work of a subgroup from the consortium?
Speaker 3:So no, the examples were done after the consensus was completed. So, yeah, it's part of the author's interpretation of the application of the principles. And also, if I may add, wojciech, in terms of that potential shopping list, dani was saying, yes, it was tempting. But I think also at this point of time where the understanding, knowledge and research around timber buildings is, um, they are challenging buildings and the and the intent of the guidebook is also to highlight that a minimum level of competency is needed for the from the designer. So there's also a danger, if we were providing a very explicit and prescriptive list of, you know, checklist, that you could end up with maybe not necessarily the most competent designer trying to tackle the, the challenge, and it is a big challenge at this point of time.
Speaker 2:So so that was also a reason why they were left, you know, as a high level set of principles yeah, I can give you an example where, where a shopping list would be particularly tricky at this point in time. You mentioned the spandrel void check and you could just have a tick that have I got a spandrel? Well, ultimately, you need to know how big that spandrel needs to be and you need to know what, potentially what, fire resistance it needs from outside to in and inside to out. And so to solve that problem, you need to have a mature method of evaluating the external flaming that you've got from your compartment and the incident heat flux to the spandrel and the flame height.
Speaker 2:Um, we've only been studying that in non-combustible buildings at a relatively small scale, with relatively small openings that are somewhat regular in their geometry. We're not at the point where we're consistently able to estimate flame heights from large enclosures with huge areas of glazing, and especially when you have a lot of surfaces with timber inside of them Exactly. And so to create a generalized recommendation for a spandrel requires both a method and, ultimately, some kind of upper bound, because whatever method you come up with is going to respond to the fact that not all opening geometries are the same, which is going to change that hazard as well, that you do something with your facade, whether you articulate it in a particular way, but I think we're unlikely to get to the point anytime soon where we're specifically saying that we should go back to the 1950s and have a free foot spandrel when the problem goes away.
Speaker 1:It's also that people find clever ways to go around those prescriptive rules when it's convenient for them. So being a step behind and telling them what should be considered sometimes prohibits this clever engineering. And I can give you a very dear to my heart example of green walls, where we've shown that there are potential hazards for fire spread on the external facades of a building and in Poland there's actually a requirement that they're not spreading fire through that exact external facade. And when we told some people that there's this green wall is spreading the fire, their question to us was can you please define wall? Because it's a decoration attached to a non-combustible wall. Therefore it meets the regulation, and I'm like, holy shit, checkmate. Uh, have fun like on the news stories with your building or when it burns down. But that that's the reality. The checklist is also not a complete foolproof thing, and actually stepping back from a checklist to say, hey, your wall should not spread a fire it's very hard to explain that my definition of wall allows me to do a fire spreading wall in that circumstance. So being a step away is also a good idea.
Speaker 1:Okay, guys, I think we're going to finish on that, so let me one more time praise how the document is made like. It really is a masterpiece in communication and, uh, I've praised it online already for that purpose. I mean the contents, of course, are great. The topic is great, but the way how this is given out to the public, the language use, the way how stuff is explained, the way how it highlights the important things and then highlights them again and then highlights them again in the common language for the third time, the illustrations and everything, the way how this document is offset it's really that's the framework of how we should communicate fire safety to public. So huge congratulations to whoever was typesetting or editing this document it's absolutely stunning in that record and also the internal organs of it. The contents are absolutely great as well.
Speaker 1:Any final words to the users. Perhaps I'll ask a question, because this has been published half a year ago. Is there already an experience in applying that in all far? Now? Let's uh take the hat of the authors of the book and put the hat of fire safety engineers in uk. Have you applied this in practice in any projects? Do you have an experience with it already?
Speaker 2:so, so we are, we are applying it. It would be somewhat remiss of us to author it, publish it and then not use it, so, um, it wouldn't be a very good endorsement of the guide. Yeah, so, so we are using it, but but I suppose it's not, it's not really had to fundamentally change anything we've been doing, because these are a bunch of of principles that we've been adopting in our designs for for the best part of five or six years. So it's it's really been sort of a validation and formalization of of what we've been doing in the past, and it just means when we are putting designs forward, the sort of the reasoning is is already apparent to the person receiving that evidence, that analysis, whatever it might be, um, and so it's just easing conversations a little bit.
Speaker 2:Um, I mean, we do have the important note at the beginning of of the principles I I do think is worth reiterating that ultimately, these principles are there in the absence of any project-specific evaluation of what your needs are. So they are an aid memoir in many respects in encouraging people to have the right conversations and the right thoughts. So they are conservative in most instances. They might not always apply, but as a starting point. We feel it's prudent to stick everything in there and have the awkward conversations that need to be had around every single one of them, even if, ultimately, you decide that not all of them need to apply.
Speaker 1:Luis any final words.
Speaker 3:Yeah, no. So just to thank you for all the appreciation of the book itself, the presentation I agree it looks amazing and it's just again a recognition of what consultants who have done a big part of the editing. And also to highlight again that, yes, we've talked a lot about the FHIR side of the moisture and durability sections, because there's also a lot of good stuff there not directly related to fire, but it's also challenges that are very relevant and very current for these type of buildings.
Speaker 1:Fantastic. Yeah, as I said, we're not just designing buildings to withstand fires, but they have. The roles, and considerations for durability and moisture, especially in timber buildings, are very important, and they also, to some extent, will influence the fire performance of the building due to the choice of solutions to address them. So, unfortunately, everything that works well with moisture is combustible for some reason. I need a non-combustible moisture-working material. Please give me one, because the world is becoming annoying. Everywhere I have to put plastic nowadays. Anyway, that's the subject for another podcast. That perhaps an introduction to that. Thank you, guys for joining me today in the first show and all the best rounds. Thank you, thank you and that's it.
Speaker 1:Not much to add to this besides, uh, linking you to the commercial timber guidebook. You have to see it for yourself open. Open it up, read it up a bit and see for yourself what does it cover. I think it's a very useful thing, very, very useful thing.
Speaker 1:I wrote guidance in the past on my own and it's a hard job to write a guidance and my guidance was definitely not a consensus guidance. I just wrote it myself the best I can do. You know, I took the risk that Danny didn't want to take. So Danny said they didn't want it to be the OFR guide to Mass Timber. They wanted to merge many points of view. In my case, I wrote a guidance on JetFan systems and it was very my opinion on how to do them.
Speaker 1:It's a way to approach it. I know it was challenging. I see huge benefits in the way how they approached it. So, from the perspective of someone who writes these types of documents, I appreciate how they did it and I also appreciate what they put inside. So it's very useful. It's very actionable really.
Speaker 1:It doesn't tell you that, okay, if you have a building of this height, put sprinklers in, no, no, but it tells you what to consider, like what are the pain points in mass timber and how to address them. And if you address them sufficiently, you will know if you need sprinklers in your building or not. That's the point. They're not giving you prescriptive list of solutions. They're giving you those design considerations that are important in case of mass timber. So you have a complete, fine-set engineering overview of the problems, issues or challenges that mass timber will bring to your building, and I think that's a really great approach. Perhaps in the future we'll get an easier way, we'll get this shopping list approach that will tell us exactly what to do and how, but for now this is the best we got and it, in my opinion, it's.
Speaker 1:It's a very well crafted piece of work and also just the way how they build it. This is absolutely outstanding, absolutely outstanding. Again, congratulations to the authors of the book. Anyway, that would be it for Fire Science Show, episode 199. And well, next week, episode 200. And what else? It's still Fire Science Show and it's still going to deliver you more fire science and engineering, and I'm excited to meet you there next Wednesday for this little milestone. So thanks for being here. You next wednesday cheers. Bye, bye.