Fire Science Show

184 - Cost-benefit analysis in structural fire safety with Thomas Gernay and Chenzi Ma

• Wojciech Węgrzyński

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This episode delves into the financial aspects of fire safety in building design, highlighting the balance between cost and effectiveness. My guests - prof. Thomas Gernay and Chenzi Ma from Johns Hopkins University share insights from their NIST-sponsored research project on cost-benefit analysis and loss estimation for structural fire safety. In the discussion, we explore the differences between prescriptive and performance-based approaches, discussing insights from a comprehensive analysis of over 130 structures and how to better allocate resources for passive fire protection measures.

In this episode, we cover:
• Understanding fire safety costs in construction 
• Insights on prescriptive vs. performance-based design 
• The importance of maintenance and lifecycle cost assessments 
• Analyzing fragility functions for predicting fire damage 
• Cost dynamics across different building occupancy types 
• Future developments for implementing this analytical framework in practice

Please find here useful links about the project:

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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.

Wojciech Węgrzyński:

Hello everybody, welcome to the Fire Science Show. Today we're talking about money Money in fire safety, or rather how much fire safety costs. From my guests today I've learned that the cost of fire safety in a building could be up to 12% of the building costs, and that actually is in line with a small survey that we've done many years ago asking some fellow directors of construction companies who said it was like bulk 10% of their buildings. So in fact, fire safety costs a lot. Everyone knows that we don't save on fire safety. That's what a lot of people tell me but in the end everyone has a finite amount of resources. It's not possible or feasible to do everything you want in a building. If we don't save on safety, then why, in Poland, is so hard for me to get sprinkles in my buildings? In fact, in some cases we are saving on safety. We're just not saving on things that are very difficult to go around or require a ridiculously long process to approve. Now in today's episode, my guests Professor Thomas Gernay and his third-year PhD student Chenzi Ma from Johns Hopkins University. They've tried to answer the question how much fire safety costs. They are looking into passive fire safety, into structural fire safety of composite concrete floors, which means they're looking into things like spray motors and intumescent paints and overall savings on your structure, but also looking into structural stability. So perhaps you can, instead of applying a sprayars for two hours, maybe you can increase the reinforcement in your concrete floor and provide the same value in terms of fire safety. They look into monetary value of those works, including a lot of interesting elements such as maintenance of that structure, such as lifecycle, cost, sustainability, workload, etc. You learned about that in the episode, but in the end, what you get is some extent, let's say, unbiased it's always biased, but this one is really clean image of how much do we spend on providing this particular aspect of fire safety, which is structural fire safety, and I love it. I love it because it allows you to look on your code. If you take their framework, it allows you to look on your code. If you take their framework, it allows you to look on your code and say how costly is your country and what can you do better? And it's something that they absolutely have to do for my country, because I feel that we've reached a point where we really could spend our money better. What Chenzi developed in here is a brilliant simulator available online that allows them to compare hundreds of buildings and have some higher level view on the stuff. So, even if you don't try to apply this in your country, I hope this discussion is valuable for you and, in general, it allows us to reflect on how much do we spend on safety. So please let me welcome Professor Thomas Gernay and Chenzi Ma from Johns Hopkins University. Let's spin the intro and jump into the episode.

Wojciech Węgrzyński:

Welcome to the Fire Science Show. My name is Wojciech Wegrzynski and I will be your host. This podcast is published in partnership with OFR, a multi-award-winning independent consultancy dedicated to addressing fire safety challenges. Established in the UK in 2016 as a startup business of two highly experienced fire engineering consultants, the business has grown phenomenally to eight offices across the country, from Edinburgh to Bath. Colleagues are on a mission to continually explore the challenges that fire creates for clients and society, applying the best research, experience and diligence for effective, tailored solution. In 2025, there will be new opportunities to work with OFR. Ofr will grow its team once more and is keen to hear from industry professionals who would like to collaborate fire safety safety features this year. Get in touch at ofrconsultants. com. Hello everybody, I'm here today with two guests from Johns Hopkins University Professor Thomas Gernay hey, thomas, good to have you back in the podcast.

Thomas Gernay:

Hello, wojcic, thank you very much for having me.

Wojciech Węgrzyński:

Great to have you, as always, and Chenzi Ma from the same university. Hey, chen, good to have you on the show. Hi, wojcic, thanks for the invitation.

Wojciech Węgrzyński:

It's my great pleasure to be here, and the subject of today's discussion is fire protection costs in general, because you've performed a really outstanding cost-benefit analysis of various fire designs. It's something we wouldn't really do that much in the fire safety. I have this experience in Poland like no one saves on fire safety. We spend whatever money is to be spent on fire safety, but actually when you start thinking about what benefits different aspects of fire safety bring you to the building, no one really knows like how much $1 of spends, how much fire safety that gives you. And here comes your paper. I assume this is part of a bigger project, so perhaps, thomas, you would like to introduce where does this come from and what inspired you to do this type of really complicated study?

Thomas Gernay:

Yes, absolutely. So it's really based on two realizations it's, on the one hand, that as a society we are actually investing a lot in passive fire protection, in protecting our built environment from fire. So if you are spending a lot of money, it's good to know if that money is well spent and if we could do things better. And the other aspect is that in the community fire engineering community, structural fire engineering community we have been working for a long time to develop the tools to conduct performance-based designs to model the response of structures in fire, and yet these approaches are still rarely used. In practice. We see that they are not embraced.

Thomas Gernay:

Most people or most buildings are still built using prescriptive designs. So the motivation behind this project was to assess the comparative performance of a prescriptive design versus a performance-based design and compare these not only on technical merits but also on cost benefits. So the project is supported by the NIST. It's called Economic Impact of Performance-Based Fire Design of Composite Steel Frame Structures, because we also leverage and we take advantage of great data that the NIST has been generating over the last few years at the National Fire Research Laboratory, conducting full-scale experiments on composite structures in fire. So these experiments provide us the data to build on this economic analysis.

Wojciech Węgrzyński:

Can you define composite steel frame structure, because a lot of listeners of Fire Science Show wouldn't be structural engineers, so perhaps we need to be aware of defining stuff for people.

Thomas Gernay:

Yes, here we are looking at buildings that use steel framing. So you have steel columns and steel beams with composite steel concrete flooring, so you have a steel deck and then the concrete is poured on top of the steel deck, so the concrete and steel work together. This is a very efficient structural system that's commonly used in multi-story buildings. For example, if you think about a 10-story office building in a downtown area, that would be a very typical construction method in the US.

Wojciech Węgrzyński:

And Chenzi, what brought you to the project? How did you start your journey with this cost-benefit analysis in here?

Chenzi Ma:

I did some research on the us uh fire statistic. I noted that the fire is very costly. So in the us alone the annual cost of fire safety matter is around 57 billion us dollars, which is amazing. Besides the construction cost in the fire safety measures and fire is also very frequent in this Every year there is around 575. This is my main motivation to this project. The fire is very cost, it's very frequent. We have to identify how our design performs, how much it can save me.

Wojciech Węgrzyński:

Good, good, good. One thing that I could start with. It's an interesting question when you start thinking about it. But if we spend money on passive fire protection, what really is the purpose of that? Is this just to prevent the structural collapse of a building? Is this the sole and only goal? Or are we looking for preventing that in a very specific time, like for an hour, it doesn't collapse? Or are there further like have you looked into that? Because you have to. If you go PBD, performance-based design, you have to have some goal in mind. What the goals would be in, let's say, performance-based design and traditional prescriptive design.

Thomas Gernay:

You're right, the goal should go beyond safety. So obviously, safety of occupants and firefighters is a prime objective. But with these type of approaches because it's in a performance-based design method, as you were saying you lay out objectives for the building, so you can also look at buildings that survive the fire, how long it takes to recover and to be reused. So this is something we looked at. We developed fragility functions under different natural fire scenarios, which is a way of quantifying the probability of being in different damage states after an event and then from there, we evaluate how long it would need to be repaired and to recover. And, chengyi, maybe you can talk more about the work you did on indirect losses and recovery.

Chenzi Ma:

Yeah. So right now we use the same safety target on the performance-based design, pre-security design. Let's take the NIST test as an example. The target is to resist to our standard fire. So what's the difference between PPD and prescriptive? It's the post-fire recovery. For the prescriptive design, when the fire happened the fire may spread to adjacent compartment or even the whole building. But for the performance speed design, the probability of fire spread might be much lower and correspondingly the fire cost. Building closure time, the duration for PDBD could be much lower than the prescriptive design and accordingly the corresponding extra losses due to the building closure, due to the building shutting down, would be much less for the PVD compared to prescriptive design From my experience in here, we of course have a prescriptive system for structural fire design and all we work with is fire resistance as the vehicle to get there.

Wojciech Węgrzyński:

But I wouldn't say that fire resistance is strongly connected with any sort of a goal. I would rather say it's more like you know historical context, like we had one hour for office buildings and it was sufficient. Or perhaps two hours in high-rise or four hours or whatever. We have four hours in super tall office buildings, which I don't understand really what that gives you, but it's just a requirement.

Wojciech Węgrzyński:

And it becomes very interesting when you are not able to meet those goals because of some technological reasons or cost perhaps, and you want to apply for derogation. And then you have to prove why you want to derogate and what you're giving as a trade for having a lower fire resistance, for example. And when I look at your studies, this is the most perfect thing I could use in those procedures, because I could literally show that investing more and more money in this gives me less and less return on the investment, and that's why I really love this type of analysis. Anyway, let's perhaps talk about framework, because it's not that you just took one building and analyzed it, you've literally analyzed more than 100, and you have an entire framework put out for that. So perhaps let's discuss the main points of the framework that you've developed for this project.

Thomas Gernay:

Indeed. So the objective is to compare the lifetime cost of different designs. So we consider a building prototype. The engineer has several options in how they would approach the fire design. It could go prescriptive or performance-based, and within performance-based, lots of options, and the objective was to assess the lifetime cost. So to do that we had to compare or consider the investment cost, the construction, the cost of materials and labor originally, and then also consider avoided losses or fire damage in case the fire occurred over the lifetime of the building. And in addition we had a number of co-benefits that we also looked at, such as does one design lead to a faster construction, for example, so that you get the benefit of the building earlier? If you can omit some of the fire protection in a large building, it may mean that you get earlier delivery of the building, so you get some rental revenues right. We also looked at some of the sustainability aspects.

Wojciech Węgrzyński:

Did you look into the lifetime of the protection, because lifetime of a fire protection versus the lifetime of the building, how often it will have to be repaired, replaced.

Chenzi Ma:

Yeah, actually the project, we focus on the lifetime cost of the fire protection. So, as you mentioned, regarding the hot oven, it will be replaced. We introduced the lifetime maintenance cost. So right now we use a simplified method. We take the annual maintenance cost as a constant percentage of the construction cost, for example, uh, three percent of the construction cost, this is annual maintenance fee and and did you go into like a whole life cycle, like also demolishing, utilizing afterwards or not yet there?

Thomas Gernay:

so we did that for the fire damage losses part. So we did the fine analysis of the damage state after fire and we studied different natural fire scenarios and, based on this damage state, chenji looked at a number of factors on the time to recovery and repair. So it's not only the demolition and material cost but also availability of contractors and time to perform the work etc.

Thomas Gernay:

So that is, you tune or you adjust the design method at the beginning. You would then get very different outcomes in terms of how long it takes and how costly it is to repair after a fire.

Wojciech Węgrzyński:

Chance you may want to add on how the fire damage was established. Actually, that's an interesting aspect.

Chenzi Ma:

Yeah. So the fire damage estimation is established based on the construction cost database. So we build a construction cost database with 130 prototypes. So for each prototype we have detailed component costs. It's very detailed. It's such as one column costs how much, the flow system costs, how much the fan protection, the furniture, the stairwell. It contains a lot of construction components. So based on this detailed cost we can easily specify when the fire happened what kind of components we need to replace for different damage status.

Chenzi Ma:

So in the damage analysis we use the idea of the Fragility curve. Fragility curve provides the relationship between the hazard intensity and the distribution of different damage states. So we have four different damage states Damage state one, which represents the least severe damage. Damage state four, which is the least severe damage. Damage state four, which is most severe damage. So for different damage states we define different sets of structure components that is damaged and then we split the cost into construction cost, because we may need to reconstruct this component, and we also consider the demolished cost because, for example, if the floor system is totally destroyed we have to hire some laborer to remove the debris right. So in a damage analysis we consider some sort of the demolished cost, the reconstruction cost, as well as some human injuries.

Wojciech Węgrzyński:

So maybe we can go through the parts of the framework. So where does one start with such an analysis and how does one proceed through the framework?

Thomas Gernay:

Yes, so the framework entails different components. You have to evaluate the initial construction cost of your design so that can be facilitated by the database that Changejs built for the different prototypes. So either your building is very similar to one of the prototypes, so you will get all the cost, or, if it is a different design, we have actually a software tool that Changejs built that interpolates within this database, so that would provide once again the cost of your fire protection design for your entire building of the composite construction type.

Wojciech Węgrzyński:

So in your case you specify I want a 10-story 1,000 square feet floor plan office building, and it just takes market costs. I guess some averages. Where do you take the numbers from? Actually, that's quite interesting.

Chenzi Ma:

We build this database from the IceMins. The IceMins are a very popular construction cost database, I think mainly in the US. They provide a square footage estimation. You can specify the building occupancy type, the aspect ratio, the floor area etc. A lot of building parameters.

Wojciech Węgrzyński:

Okay, and the cost of fire protection is also specified in those databases as per feet or per square meter.

Thomas Gernay:

Yes, it is. The cost of fire protection is also taken from the database and the cost is adjusted based on the fire rating. So we also took into account the thickness that would apply based on prescriptive fire rating and adjusted the cost to be refined there in terms of, if you want a two-hour rated building or three-hour rated building. The project is, as I mentioned, so funded by the NIST and it's also a collaboration with an industry partner, alia Shafi and Jenny Sideri at Tonton Tomasetti. So we worked with industry also to guide us and corroborate some of those cost inputs.

Wojciech Węgrzyński:

Brilliant. So here I see the first difference between the DPBD and prescriptive. You said the cost scales with the fire protection rating, so here performance-based design comes into play. Right, because you can optimize.

Thomas Gernay:

That's right. So for the same building, the user can run first an estimate based on prescriptive design. It would refer to a rating and then modify the design according to a performance-based approach. One optimization that would be one trade-off I should say that would be typical in a PBD would be to remove some of the passive fire protection on some of the steel work and instead harden the structure. So in the performance-based design you really want to achieve a good fire performance and a high safety level based on the embedded structural fire resistance.

Thomas Gernay:

In practice, for all buildings that means more steel reinforcement in the floors embedded in the concrete of the composite floors. That is what the NIST has shown, also through their experiments. So now it's a good time to talk just a little bit about those experiments that were conducted at the NIST starting in 2019. So one thing that was really unique the NIST they tested at full scale this floor system. So this is a bay of six meter by nine meter and they also built the adjacent bay. So you even have the restraint.

Thomas Gernay:

And what is really nice is that they repeated the full scale experiments for three variations of design.

Thomas Gernay:

So we have direct comparison of performance from the same lab in the same conditions of the prescriptive design and two variations of performance-based design and they showed experimentally that the prescriptive design and two variations of performance-based design. And they showed experimentally that the prescriptive design rated for two hours, actually didn't really achieve two hours of integrity at full scale because the amount of steel reinforcement in the composite floor is insufficient when you look at that large scale and you have the large deflection, so they had crack openings and flame pass-through and in comparison, the performance-based design. So where you remove the passive protection on the steel build but you add reinforcement was much more robust and maintained integrity. So this is really what we want to show, that it's not just about saving costs, removing insulation. Rather, that is a trade-off. You remove some of the passive fire protection but you harden the structure and the performance is better. And so you can quantify that. First you can quantify the initial savings in the construction cost, but then you can also quantify the avoided losses, the better performance.

Wojciech Węgrzyński:

But here the NIST experiment 6.9,. I assume that must be a natural fire.

Thomas Gernay:

It's actually. But actually they have the capability to run a standard fire resistant test, so with a 20 megawatt hood and a huge furnace. So they ran the ASTM E109 for two hours on that experiment. So it's quite a unique lab there.

Wojciech Węgrzyński:

They have a great tool, good, good, good, interesting. So investment costs also means like what type of fire protection was applied, how it was applied, the workload costs.

Chenzi Ma:

Yeah, yeah, yeah. So we consider the material cost and the labor cost regarding the fire protection, and in our database we also incorporate two different fire protection materials, including both the spread fire SFRM and the Intium Scent, and on average, the Intium Scent costs around five times higher than the SFRM.

Wojciech Węgrzyński:

Okay, and where do those come from? Just the cost of the solution. I wonder how universal is that? Because the industry is listening, so I guess people will have opinions on that.

Thomas Gernay:

So I think this is indeed, as you say, a specificity of the US market, that the solution that is typically applied is on-site sprayed fire-resistive material sprayed on the steelwork. It's rare to have shop painting or even intumescent painting applied, but this is something that the industry is increasingly looking at. So you know, the prescriptive spread fire-resistive material solution has been employed for many decades, but as those performance-based design approaches are getting more and more known and people are thinking about how structures are protecting against fire, the industry is also looking overseas and the UK and other countries. Shop painting is more common. It can speed up the the erection process on site. I mean, there are potential benefits, especially if you don't need to protect the entire structure. So this is I think this is evolving, but but right now the painting solution is seen as much more expensive here in the us but that's the cost component.

Wojciech Węgrzyński:

What about the safety component, like if you have one hour of, let's say, fireboard versus one hour of spray paint? Do you find them in your methodology, are they equivalent safety, or you go in-depth into the properties of those materials?

Thomas Gernay:

So to evaluate the safety or the fire performance of the different design solutions, we don't have data, like we do for construction costs, because fire is rare, fortunately do for construction costs, because fire is rare, fortunately. So we relied on simulation and modeling, and we used finite element modeling with Saphir and lots of models that we've been developing over the years to simulate the response of the natural fires and on the range of different fire scenarios. So there we model each design and each material with their properties and we again simulate the anticipated performance.

Thomas Gernay:

So if an engineer has specific data on a specific insulation product of gypsum boards or others, you would then see the difference that would be captured by the method in terms of different performance, damages for GT functions and, eventually, costs.

Wojciech Węgrzyński:

And to close on investment costs. I want to move to avoided losses and to close on investment costs. I want to move to avoided losses but to close on investment costs. You mentioned some sustainability aspects. What did you mean by that? Did you calculate CO2 emissions? What was the sustainability aspect?

Chenzi Ma:

We calculated the CO2 emissions. So for a specific fire protection material we can extract the environmental product report from the internet. So from that report we can get the relationship between the weight of that material with the weight of CO2 emission and from our cost database we can get the total cost of the fire protection material. We can get the total cost of the fire protection material and we can get the total weight of the fire protection material, which provides us a relationship between the cost and the CO2 emission. So we captured the CO2 emission based on its total cost.

Chenzi Ma:

One thing, referring to what you just said if you capture the weight, do you also optimize the structure for the weight of passive protection, or this is too far Right now? We didn't consider the optimization of the total weight of the construction.

Wojciech Węgrzyński:

We had that on one project. We had to consider fire protection versus weight because the location of the project above a metro line was so sensitive to the weight of the building and the way how the building was constructed. So we don't affect the metro line underneath too much. Very interesting discussion. Anyway, let's move perhaps to the avoided losses. So, as we talked about the costs and everything you said, to me that's quite reasonable. You summarize whatever comes in. You basically distilled it into atoms, like all the aspects that go in. You have hundreds of variants. You drop the cost on them and you have the finite number of that. But now avoided losses, that's an interesting part. First, you mentioned the fragility curves, but how do you put those avoided losses in the lifetime of a building? Do you have an expected loss from a fire?

Thomas Gernay:

Yes, you're right. So then we come into the world of uncertainty. As you very properly said, we can calculate the construction cost, but we can just estimate the probability of an expected loss. So we don't have data. There are not, fortunately, not many fires. So we use simulation, we use our modeling tools that, again, have been developing research committee for many years. So we run lots of simulations, finite element simulations of the structural response under a range of fire, and we apply uncertainty in the fire development. We use natural fire curves in the thermal response and in the structural response.

Thomas Gernay:

One thing we were very happy with this project is that we had again this unique data from the NIST experiments and the test run by Lisa Cho, and we thank Matt Huller and Matt Bundy and so on for the great data that we had so we could validate our models at full scale, at least under one fire, the standard fire in that case. But then, yeah, we run lots of simulations. We built fragility functions in order to make this research also more generally applicable. So you can compare the performance of prescriptive and performance-based design against any intensity of the fire and with all this probabilistic framework we get to different probabilities of being in different damage states and then the next step is to evaluate the losses and repair costs associated with those different damage states we have.

Thomas Gernay:

Also, there are uncertainty, but we analyze it component by component in terms of demolition, reconstruction, time for unavailability and so on. I should also add that youition reconstruction time for unavailability and so on. I should also add that you know, again, we built on what we've been working on before, and a very important project was a project funded by the NFPA with a great friend and colleague, ruben Van Coyle from University of Ghent, who was leading that project, and we were working with Shunani and Andrea Luccherini as well. And in that project by the NFPA already we were looking at economic impact of fire and we had done some work to quantify also injuries and lives lost etc. So there's a very low probability of these, fortunately, but very high cost. So again, with a probabilistic approach, we account also for these and I'll just briefly thank Amanda Kimball and Birgit Messerschmidt also for the support a few years ago on that which we are still building on.

Wojciech Węgrzyński:

The damage assessment for a specific fire. How do you proceed with that? You choose a probability of a fire. Let's say there will be a one megawatt fire in the building. You simulate that fire in the building and and have some outcomes. And then you proceed to another one, another one. You know probabilities of each of them and then you come up with the final curve.

Chenzi Ma:

No, actually so. For the first we we identified the criteria of to define different damage status. So here we use residue deflection, so we have three different thresholds of the deflection. So once the residue deflection exceeds the threshold we assign a distinct damage state for this simulation. So because we consider the uncertainty in the fire, because here we consider the oxygen content, we consider uncertainty in the fire protection material, such as conductivity, the density etc. We also consider the uncertainty in the mechanical property of the rebar. So we consider five, five randomly in these materials, in these fires, and we run simulations.

Chenzi Ma:

For a distinct simulation we can get a specific outcome, for example, such as the displacement, radio displacement, and we run 10 different simulations. We can get 10 different radio deflections and then we compare this response with our threshold. If this response is higher than the threshold, we assign a specific damage state to this run. So at a specific file load we can get a distribution of different response and then we can convert them to the distribution of different damage states and then we go through from low fire load to the high fire load. Then we can create the fertility curve.

Wojciech Węgrzyński:

But the damage states are connected to the architecture of the building. I know the height, presence of sprinklers, stuff like that.

Thomas Gernay:

So the damage states are structural damage states. First of all there is integrity failure. So if really we have the simulation shows under a specific fire that the structure, the floor would fail, then usually the simulation stops because nonlinear fire intimate simulation and we assume then the fire propagates and that would be a very severe damage state. And then we have intermediate damage where we define them based on the residual deflections in the structure which are correlated to the repair needs and whether you can reuse the structure after work. So this depends on the span and the base size, but it doesn't really depend. I mean, as we work only with steel concrete, you know steel framing, composite floor structures, we have similar definition of damage states across the spectrum of buildings we are looking at.

Wojciech Węgrzyński:

And now those damage states. How do you like, is there an expected occurrence of those fires in the lifetime of a building? How do you transfer from this into a tangible number of avoided losses?

Thomas Gernay:

Yes, you're right, that's how we do is expected numbers of fire frequency. So one component is to build this library of structural fire response. That's what we explained. This library of structural fire response that's what we explained. It's based on running lots of simulations under a range of fires with uncertainties. But then we still have to evaluate the probability to have a fire over the lifetime of the building. So this we do based on fire statistics in the US. So looking at the numbers of actual fire occurrences in similar typologies of buildings commercial, you know, multi-story office buildings, for example. So if we have a lifetime of 50 years for a building, we know it's probably that the fire would occur. We also need an assumption on the probable or the expected severity of that fire which we correlate to the expected fuel load.

Thomas Gernay:

We know it's not perfect, but it's a way of doing that. So if it's an office building, and either the authority or the engineer assumes a fuel load distribution in that type of building. We correlate that to the expected fire severity. So priority of fire occurrence, expected fire severity and then expected damage states based on all our simulations. And from those expected damage states, which is a distribution, we have then the economic loss assessment with repairs, demolition labor and also time of unavailability of the building.

Wojciech Węgrzyński:

But that's a loss and you use avoided loss. So where does avoided come from?

Thomas Gernay:

I see. So when I talk about avoided loss, you should understand that it's comparative.

Thomas Gernay:

So here, the whole framework is aimed at comparing design options. So we would evaluate losses for the prescriptive design and we would also evaluate losses for the alternative, performance-based design, and the difference would be the avoided loss. So what we are showing for this the case study specifically is that by trading fire protection on secondary beams and instead adding more reinforcement in the composite floor, not only there is a possibility to save in initial cost a little bit, but also you saved in those avoided losses, because the losses of the performance based design are expected to be much smaller because the system is more robust.

Wojciech Węgrzyński:

Very interesting and in your analysis you must eventually clash those numbers like the investment costs and avoided losses. Is this like a dollar per dollar basis? Are there weights on that? How do you compare? Like the investment costs, which is obvious, right, it's money spent upfront versus a loss. It could happen in the lifetime of a building. It could not happen in the lifetime of the building. You cannot say it's not the same value In this methodology. Is it dollar by dollar or there's a method to that?

Thomas Gernay:

Yeah, very good question. So there are two aspects to it. I would say first, it's a present net value approach. So obviously dollar in the future is weighted by the inflation rate and so on. So that's a way of comparing things that do not happen at the same time. But what you refer to is more of an uncertainty component, right? So I know how much I'm going to. So it's a very good point. We have lots of discussion also in the industry on that. I would even add one more thing is that with the performance-based design, a big hurdle is the uncertainty that the design will be accepted. So the owner wants the building made and the engineer has to deliver. And if they go the prescriptive route, for sure it's going to be signed off. But if they want to do an alternative design, there is uncertainty, you know, will it be accepted or not? That's really hard to weigh in in that approach.

Wojciech Węgrzyński:

It's very difficult. Perhaps you've been in those discussions with investors, but you know, saving $1 today to avoid the loss of $1 in the future is not such a great deal, to be honest.

Thomas Gernay:

Yeah, so the thing is that here we are building on. So for several years I think the committee has shown the technical benefits of the performance-based design right. You have more freedom, you can optimize, you can have maybe better resilience, et cetera, and here we want to show the economic benefits. But in some cases what we are showing is that you can have both. Not always, but in some cases you can save now because the construction might be cheaper, because again you remove some of the fire protection, you have less on-site work, you may have completed the building a little bit earlier because it goes faster to increase the diameter of pre-bars in slab than to spray material on all the beams.

Thomas Gernay:

You may have a saving now plus more avoided losses, so plus a better performance. But of course it's not always the case and also there are these uncertain components that I was referring to. Will it be accepted? There is also additional cost of engineering, which may be very variable. So it's not all clear cut, but we think that we are providing here data to show that there is an economic case in addition to the technical case and in many markets because we also look at different costs of labor depending on the location and so on In many markets you might save now plus save in the future.

Wojciech Węgrzyński:

I think, from my perspective, I'm doing this podcast selfishly to teach myself and apply stuff and, by the way, there's hundreds of people listening along me, but I appreciate learning from the world's best. You know, in my case I see an immediate benefit of having some benchmark losses that would be associated with the standardized solution. And then, technically, I could run an optimization study where I would just I would like this number to not grow, you know, and see like what kind of elements I can remove or switch, like to get the lowest investment costs while maintaining the same loss. That would be a good optimization front. I think that could actually work. And then it's interesting that your method actually allows for that. Did you try something like that, chenzi, or wasn't that part?

Chenzi Ma:

Actually no, we didn't try this aspect. But I would like to argue a little bit about what you said saving $1 and avoid $1 loss in the future. I mean, with time goes by, everything is becoming more and more expensive. Today we repair the floor system we can't cost $100, but in the future probably we need to cost $200. So if we convert all the future value in current value perhaps it is always $1 loss. So the saving, the avoid losses, I don't think it will ever change significantly with the time.

Wojciech Węgrzyński:

Interesting and perhaps let's go to the outcomes of the research, because so far we've spent like 40 minutes discussing this framework and it's really a big framework, like we're talking about it, like it's an easy task, but it's years of research, from what I see in the paper, and it's like most impressive, to be honest. But you've created this database of 130 buildings, You've pre-designed them, you've chosen some sort of fire protection measures for them and you've run this analysis. What are the main outcomes that listeners can take home from this analysis and perhaps then we can go to more detailed outcomes.

Chenzi Ma:

So we built the construction cost database. We analyzed 130 different building prototypes. So from this aspect we do find something. We found that for the fire safety measure cost, it accounts for 4% to 12% of the total construction cost. All fire safety measures yes, all fire, including the sprinkler, the fire pump, all the detectors, all the fire safety measures. If we zoom into the passive fire protection on the steel work, it ranges from 0% to 1.2%.

Wojciech Węgrzyński:

And for context, what would be the cost of steel and concrete in a building? Like a rough number.

Chenzi Ma:

It is around 20% of the total construction cost.

Wojciech Węgrzyński:

So it would be like 5% of the cost of the structure itself. Right Interesting. And how did it vary between the solutions that you've looked into?

Thomas Gernay:

So yes, we find in. So the numbers that Chenji just gave are for composite multi-story building in the US with prescriptive fire design. Okay, so with the performance-based fire design there is an opportunity to shave off some of that cost, because we can omit some of the fire protection. So maybe you get from 1.2% of the cost of the building to maybe 0.6% of the cost of the building to maybe 0.6%. But one thing that's important to mention is that the prescriptive design in the US uses very little steel reinforcement in the composite floors. It uses 60 square millimeters per meter.

Thomas Gernay:

So maybe listeners from Europe who know about structural design of composite buildings would find that to be very, very small.

Thomas Gernay:

It's a welded wire mesh that's there for construction reasons but it's not really aimed to carrying forces because they rely on the steel deck. So the reason I'm mentioning that is that in order to activate tensile membrane action and robust behavior in our performance-based design in fire, we need to increase quite a bit this amount of steel in the floors. So in the US you have to pay more if you want tensile membrane action, whereas in Europe, for example, they already start from a higher value. So they often find that with PBD they remove fire protection, they don't necessarily need to pay much more elsewhere. Right, they would need to pay attention to continuity and overlap and so on, but not that much more material. We found that we can save maybe 0.6% of the cost of the building value, but we almost put the same amount back in the steel in the floor. The details vary, but it will not be very, very different in one way or another in terms of initial construction costs.

Wojciech Węgrzyński:

But there will be differences in avoided losses.

Thomas Gernay:

Very much so. Yes, and that's backed up by the data from the NIST. So it's not just our simulations, but already the NIST showed in their experiments that the minimum amount of steel in the floor it was not sufficient. It led to integrity failure. So there is really a question there in whether we should. You know that it would be recommended to put more steel anywhere in the composite floors Because once you look at full scale, you know beyond. You know the just small standard fire furnace. You really need more reinforcement to maintain integrity in that case for the two-hour rating. So we showed that also with the simulations on the natural fire. The performance enhanced, the avoided losses much better with the performance-based design in terms of priority of failure, of maintaining integrity for the entire fire.

Wojciech Węgrzyński:

And for those losses. If you compared a solution with one, two, three hours of fire resistance, was the effect really as like? Was two hours twice better than one hour fire protection, you know? Or there was a diminishing return. There must be because you have natural fires.

Thomas Gernay:

Yeah, it's a great question and that's something that the method can do. So, which is, I would say, the answer depends on the expected fire severity for your building, which, again, you may correlate to the occupancy and the fuel load. So with the method it's actually a way to optimize the recommendations or the code guidelines for different types of occupancies and important consequent classes and so on. Right, because it's not a linear relationship. As you correctly said. It's not like we had twice better performance if it's two or versus one, or it's more, that you will have a certain investment in fire protection and the amount that makes sense depends on how much fuel you have in that building and how important, how valuable a failure is. If it's a small building everybody's out and it's not a big deal to rebuild maybe we can accept a complete failure after evacuation. But if it's a large building, you don't want to. So what is the right amount of prescriptive fire rating to get to that outcome is something we can evaluate.

Wojciech Węgrzyński:

You've investigated 130 buildings, which were different types of buildings. So what types of buildings have you looked at, and is there any distinct differences between them? That perhaps surprised you, or they were all the same.

Chenzi Ma:

Yeah, actually we consider four occupancy and eight different building types, we split them as high-rise thrust and mid-rise thrust and we consider office building, apartment, hospital and hotel. So the five design of this prototype are based on the international building code. So for some of the mid-rise buildings fire protection is not mandatory, so the fire protection cost can be as low as zero. And the one thing is a little bit surprised is that for the hospital the outcome is slightly different from to other occupants. It's because so a lot of cost in hospital originated from the facility, so which results in the total fire protection cost, especially cost multiplayer, for hospital is much lower than other building occupancy. It is around 4% to 6%. But for other occupancy, for example the office maximum, can be 12%.

Wojciech Węgrzyński:

But it's still the same dollars. It doesn't mean it's cheaper to fire protect the hospital, it's just a smaller part of the entire cost. And between those buildings did you notice some sort of regimes in which the PBD starts to make more and more sense? Was it something your methodology could indicate when it starts to really pay off to play with PBD and when you just go with traditional standardized systems and you're good?

Chenzi Ma:

Yeah, absolutely so, for at least the inner Uruko. Different occupancy has different fire load distribution. So for the hospital the fire load distribution is much lower than the dwelling so it can be reflected in our damage analysis. So for the low fire load zone we noticed that a performance-based design may have a little bit higher direct damage losses because the secondary beam is left unprotected. It gets heated up very fast and even in the low fire load it can get significant deflection.

Chenzi Ma:

But for the performance-based, but for the prescriptive design in the low fire load, because the secondary beam is protected, the heating process is relatively low and the deflection is not that significant as performance-based design. So in this aspect, from the aspect of the direct damage at low fire load occupancy, such as hospital, the prescriptive design might be a little bit better. But when we incorporate all the cost components, such as where we consider the savings of performance-based design during the construction overall the life cycle cost of performance-based design may still overcome the prescriptive method. And for the high fire load occupancy, just as dwelling, the fire load is relatively higher than the hospital. We noticed that the performance-based design has relatively lower damage losses, which is around 50% of the prescriptive design in our case study. So at this occupancy the performance-based design can save in both damage losses as well as during the construction phase. So from our framework we can identify for different occupancy which design must be economic optimal, different occupancy of which design must be economic optimum.

Wojciech Węgrzyński:

If I could just comment, you can reverse, saying that if you look into those losses for performance-based design and your traditional design, it's obvious that performance-based design has to better respond to that fire, because that's the part you're investigating. You're optimizing for that, whether the traditional one is just one point in a cloud of solutions and it's just at one point and by chance it's either closer or further. What you're showing here is like how far the reality is from the safety delivered from the traditional one. I would assume the performance base always will be closer, because that's what you're looking for. The traditional will deliver you some sort of safety in all types of buildings. Two-hour fire rating is two-hour fire rating. That's only true for the furnace, but in every building it's going to deliver different type of safety. In some buildings that's going to be just enough or perfect combination. In some buildings it's going to be way too much or way too less. Anyway, thomas, you wanted to add something. Sorry, but this is just a thought I had.

Thomas Gernay:

No, no, absolutely. Yeah, you're correct. With the performance-based design you can tailor the design to the specific building, including the expected fire severity, as well as to your objective. So if it's very important for that building to be reopened soon after a fire event, because it is commercial real estate or I don't know which is valued a lot, you can do that. I just wanted to rebound on what Chengyi was saying. So that's right, we can find the better design for each occupancy and we find different outcomes.

Thomas Gernay:

As a general rule, the performance-based design I'm talking about the US market makes more sense when the expected fire severity increases. So if you are in an occupancy with higher fuel load or risk of casualties, then it made more sense because you had a lower likelihood of integrity failure and fire spread. It also worked better or was even more beneficial when you had high labor costs. So we compared New York City versus a city in the Midwest and because you don't need to spray all the beams, and also in terms of the repair. So we have those nuances and I would refer the interested listener to our papers. But we discuss, depending on typologies and markets, et cetera, the optimum. Yes.

Wojciech Węgrzyński:

But this also brilliantly goes back to what you said at the beginning, that you could have a shop spray paint like delivered already, fire-protected, and other things where you could like in New York City. You could import steel that's already protected and you get away with this labor cost of spraying, for example. That's another aspect of optimization that could go in Very very good, and where do you go forward with this?

Wojciech Węgrzyński:

Like, what's the next step for this methodology? Is it going towards a practical tool for cost assessors, or is it something for governments to use, or is it just a funny tidbit of knowledge that engineers can use? Where do you sit, I think?

Thomas Gernay:

there are two main aspects. So one is really in this specific project which we looked at composite building and we get all those data. So we want to turn that into an actionable tool, and Changey has been building a web-based tool that users can go and interact with, where you will get our database of cost, you will get the fragility functions and so you can tune, you know again, the inputs of the building, the size, et cetera, the location, and you will get a clear answer of whether prescriptive or performance-based is less costly over the lifetime. So that's really for the composite buildings. Again, there is the website and that will be delivered.

Thomas Gernay:

And then the other aspect is, I think, this cost-benefit methodology to evaluate our designs and our safety investments. That, again, we've been working on with Ribbon Van Kool, with NFPA and now with NIST. I think it's really applicable to any problem of resilience of the built environment. So even if we look at the wildfires that are unfortunately unfolding in LA, there would be questions about how to rebuild, and so should we use other types of construction materials or should we, you know, harden our communities differently against wildfires? We can weigh in investments and avoid losses based on this type of methodology. So I think that's a very important next step in terms of trying to have positive impact on community resilience I really like with your project.

Wojciech Węgrzyński:

I see there's a generic use of the framework you create because basically you compare this with IBC and the reality of US in terms of costs, the fuel load distributions and some sort of requirements or expectations that are in the US. But each country will have their own building code frameworks and it's a generic project you could literally do in every country in the world. Take your code requirements, calculate the investment and avoided losses cost as a benchmark and then see what type of performance-based design could be performed in your country and see the cost-benefit analysis. This is a project that you could apply in Poland, in France, in Germany, in the UK, wherever in the world. So every listener is welcome to apply for funds in their own countries and run studies like that, because we usually don't have them and 5% goes to Chenzi from that project as the author's cost.

Wojciech Węgrzyński:

I mean, I think it's a brilliant methodology. In Poland I could run this investigating sprinkler effect. You know sprinklers versus pacifier protection In US. I assume you just had sprinklers in your buildings, that's a part of your, or have you looked into removing them, for example, as a part of your study?

Thomas Gernay:

Well, first of all, thanks for the cameras, and you're right them, for example, as a part of your study. Well, first of all, thanks for the cameras, and you're right, we think it's very generally applicable. We hope to personally keep working on that, but also happy to collaborate with anyone, so please reach out if you're interested in learning more in working with that methodology. I would even add that Changey is getting to the end of his PhD, so he's going to be on the market.

Chenzi Ma:

So you can even hire him. There you go, so you can even hire him.

Thomas Gernay:

There you go, you get all the knowledge. So take advantage of that. But to answer your question, we didn't look into sprinklers or active fire protection in the NIST project that you've been discussing, but in the previous NFPA project with Ruben Van Correl, andré Lecun, ishunani, david Dunobe I should also cite we did look at sprinklers. For example, in the US there is a requirement to install sprinklers even in individual houses and only a couple of states have picked up or have adopted that code. Maryland is one of them and we looked at whether it was. I would say it made sense on an economic basis. There is some safety consideration, but trying to quantify also the cost-bene benefit of that. So yes, similar approaches can be applied to active fire protection. We haven't done that in details for commercial buildings, but that can be done. Yeah, james, you want to add on that.

Chenzi Ma:

Yeah, I totally agree with what Thomas said. So this framework can be used in any field. For the sprinkler, it can affect the severe fire occurrence rate significantly, so we can quantify its cost benefit. By comparing with buildings without sprinkler, the severe fire occurrence rate is different and then we can get a distinct value for each design. We can directly compare the benefit of these two, the benefits of these two, the cost of these two designs, which can inform stakeholders more straightforward. I think it's a good thing.

Wojciech Węgrzyński:

Yeah, I like it. I like all of it. I like the approach, the complete view on the lifetime of the building. I like inclusion of the maintenance and and repairs. I like the sustainability aspect. I really like having two separate values for investment and avoided losses, because it's really like if you constrain one and look at the other. It allows you to really look at your solutions from different perspectives, not just like the money put up front, because that would be often the the main thing you'd optimize for. I like it a lot.

Wojciech Węgrzyński:

It's a little difficult to implement in practice. So high hopes for this web tool and simplifying it. Chenzi, advice from older colleagues like you need to make it so people can use it, because it's a really big piece of work and turning this into a useful tool will tremendously increase the success rate of people using this tool. Thomas knows something about designing user-friendly software and improving that over the course of years, so you're in good hands. But wow, this was very good, very interesting, and I wish you all the best. Any final thoughts for the future users of this methodology or future horizons? Thomas, you may want to start.

Thomas Gernay:

Well, first of all, thanks a lot, swazil, for having us and the great conversation. Yeah, future thoughts, I mean. You know we are, as a community, working to try to make the built environment safer against fire, more resilient. We've been working a lot on simulation capabilities, modeling tools and data and we think here it's yes, it's a very important complement because it's more tied to showing the benefits to the outsiders, to other engineers who are not structural fire engineers or fire safety engineers, but also having a tool to go and show to building owners authorities. Right, that's why we are doing everything we are doing. You can optimize, have better buildings and also save on future losses of a more resident built environment.

Wojciech Węgrzyński:

So that's what we are working towards. Fantastic and Chenzi. I guess next on your plate is defending the PhD from this. Yeah, and the web interface. That's a lot on your plate, yeah and also try to get a job.

Wojciech Węgrzyński:

Well, perhaps an offer will come after this interview, and I also would like to highlight that there's a GitHub repository with stuff from this project. Is it okay to share the GitHub? Yeah, sure, sure, no problem. So there's a GitHub repository with a lot of stuff that has been discussed today, and I will also link your papers in the show notes. So if people are interested in the details of that, I would highly refer them to reading. So, yep, that would be it. Thank you guys. Thank you so much. Thank you so much, and that's it. Thank you for listening. That is a lot.

Wojciech Węgrzyński:

I know that, and it also took me a while to get through their framework. It was definitely easier when listening to them explaining it to me rather than figuring out on my own, but indeed this is a huge piece of work. It's an entire PhD cramped into a few papers. It's an entire previous project that's grown into something new and much bigger. Really impressive, impressive stuff out there, and if you want to fully, fully benefit from the work that was presented in here, you really probably should read the papers, which I will link in the show notes. They're available online. There is also the GitHub repository with all the code used for this project so you can take a look in how it works and perhaps play with it a little bit. If you know a bit of Python, there will also be a website. They've said there is a website, but it's, I believe, in production right now, and once the website tool is available publicly, I will be sure to update the show notes and send it your way so you can once again try it out, perhaps in a more friendly interface than just the Python script.

Wojciech Węgrzyński:

Anyway, I think it's very worthwhile to dig into this methodology because it can be twisted and applied to so many things in fire safety, to so many aspects of fire safety where you would like to compare some solutions based on the upfront cost, the maintenance cost, and then versus the possible losses. This is really good and I believe there's so many utility for the framework presented in this podcast episode. Anyway, that would be it for today's episode. I hope you've enjoyed this little difficult discussion on the cost of structural fire protection. I hope it was worthwhile. I've promised you to deliver you the best fire science and yep, this is it. This is a very good fire science, very recent and very useful, so that's what I'm bringing to you. Thanks for being here with me. See you here next Wednesday for another piece of good fire science. Cheers bye, thank you.