120 - How we have designed a fire safe green wall

I would not say they are the most important technology in having sustainable build environment but they definitely look good on images . So if you have been following me for a while , you probably noticed that I do a lot of research on green facades . We publish a lot on that .

We put a lot of blog posts on LinkedIn about green facades and it created quite a turmoil in the industry .

We've been showing the challenges and dangers perhaps related to green facades based on our full-scale experiments , but I have never really told the story about how we have started research on this type of building features , and I don't think I've ever shared you how we've designed a green wall that we felt quite fire safe with and what I went into this solution and

how we reached that through , of course , full-scale experiments and a lot of fire safety engineering . This is something I want to share with you in this episode . I don't think I need to convince you anymore . If you are still here with me , I guess let's play the music and start talking about fire safe green walls . Welcome to the Firesize Show .

My name is Vojci Wimczynski and I will be your host . Firesize Show podcast is produced in partnership with OFR Consultants , a multi-award winning independent consultancy dedicated to addressing fire safety challenges .

Ofr has been once again ranked on Best Company's top 50 list as the best medium-sized company to work for in the UK , and also ranked in top 5 of the best consultancy companies to work for in the UK . That's an amazing future . Congratulations , ofr , and it seems that your employees are quite happy with your work . Please , ofr is not just winning awards .

They're also participating in giving awards . They're proud sponsors of the 2023 Structural Timber Award , where they are sponsoring the client of the year accolade . That's great to hear and I'm looking forward who's gonna win this award ?

And , of course , ofr is giving back , not only in this space , but also our proud sponsors of Firesize Show , for which I am more than grateful . Thank you , ofr , and if you would like to learn more about their dinks , get in touch at OFRConsultantscom and welcome back and let's do the Firesafe Green Fassade . I promised you a story how it all started .

So it actually started in two different ways on , which kind of happened in the same week . I was quite a coincidence . First , I have a PhD student , jakub , who has a ton of great ideas .

He's in that part of his scientific career where he is discovering things all the time , comes up with new ideas , and my ungrateful job is to hold him back and tell him why he should focus on his PhD .

But sometimes his ideas are really , really interesting and that was the case when he came to me and told me Wojciech , we've done a lot of research on facades . You've done research with Matthew Bonner on Kresnik Database where we kind of investigated 200 something different facades in terms of how they burn in a Polish method .

We've also done some full-scale research on a secret project with Imperial , and Jakub was we've never burned these green facades and I start to see them popping everywhere and I was like , yeah , that's kind of interesting . I mean , we've burned some really bad combinations of materials , but we've never tried a facade with a living material on it .

So I was one of the initial triggers for this research , this discussion I had with Jakub . So instantly the same week we had a commercial client approaches who said that they are doing an office in a very high prestige , high-rise tower in Warsaw and their client wants a jungle in it .

Literally that's what they said they want a jungle , they want a wall that was perhaps 100 square meters large and that wall is going to be totally filled with vegetation . And this is going to happen at like 30th or the fourth-year floor of the building . So really not a great place if you want to have a huge fire in it .

And they were unhappy because their fire expert was not very supportive of the idea of placing a combustible jungle in this office . My first initial thought was , yeah , perhaps the fire expert is kind of right and maybe you should not pursue putting two tons of combustible material into this office space .

But after some discussions and seeing Jakub's dark urge to burn a vegetated wall , I saw an opportunity . Maybe let's try and see how this feels like and what where we can get with it . Our plan was to do full-scale experiments with the Polish method that we know the best .

It's a fairly simple test where we take 2.5 meter tall , 1.8 meter wide sample of a facade in a configuration as it will be delivered on the building . We put a small wood crib in front of that . The wood crib is designed so it gives something like 250-ish kilowatts of heat release rate when it burns .

And of course the conditions for the Polish tests are related to temperature and fire spread along the facade .

For our case , because it was a custom test , we have designed our own conditions , like we wanted to see how much of the facade will be involved in fire , what will be the maximum temperatures on that facade , how quickly will the fire spread from the initial source .

And we have also asked for a second bunch of samples of that facade to run SBI single burning item tests in the SBI room at the lab so we could estimate the heat release rates and we could estimate the smoke production from these samples .

So of course the green wall is not placed in the vacuum In here we're again talking about something that goes into the building . So immediately we recognize it's not going to be exposed to wind , and wind is an inherent part of the Polish standard . So it kind of made no sense to test it with the wind .

So we chose to not use wind in this particular test , but instead we chose to make the crib a little bigger . So we've expected north of 500 kW from that initial fire source . That's actually quite big If you think about sources of ignition in commercial buildings .

That's litter bin on fire or a small electronic device on fire , or perhaps almost a scooter on fire . That's the size of the crib that we've designed . The second thing was that this green wall is going to be attached to a wall of the building . Of course you're not putting plants directly on a concrete wall . You need to have a system .

So let's talk about how the system looked like In this particular case . The wall was built with felt pouches . So there was this textile material . It looked like felt . It was some sort of fire-retarded material .

It was built into pouches and in those pouches they've put some grounds , some organic material in which the plants grow and the plants themselves , these layers of felt . In the back they had some other materials that helped spread the moisture and gave structural integrity to the felt layer in the front .

And all of this all together was attached to rigid polyvinyl boards . Now , looking at the details of the materials , we had plastic materials that were quite flame-retarded . If I'm not wrong , the felt pouches were Euroclass B , which I would say is quite nice the PVC was Euroclass C if I'm not wrong . Perhaps it was even Class B .

It was really good material , like if you wanted to ignite it with lighter , you would not be able to ignite it with a small flame . And now , because how this system works I mean you're not having living plants in it you will have a constant application of water into that system . You'll have a lot of moisture in that system .

You don't want to put it directly on the concrete , so the whole thing was built on a rack and the rack was kind of moved away from a facade , creating a ventilation cavity behind it . You see where this is going . We have created a system where we have combustible okay , fire-retarded , but combustible materials , a ventilation cavity .

It's not looking pretty and that was our first worry about the system once we understood how it's built , when we took the samples into the laboratory . First we've run SBI tests and it was not pretty .

Eventually , five , six minutes into the test , we have started observing flames on the back of PVC and once that went into the cavity it was quite a large fire with really , really insane smoke production . It was really bad when the fire started in the cavity . So that was confirmation of our first worry . Plastics and cavity not a great combination .

We as a society should have perhaps learned that a long time before . The plants were not even that important . Ground in the test was not that important . The moisture of the felt pouches was not that important . To be honest , it all broke once the fire met the back side of the PVC panel and the cavity . In the full scale it was very similar .

However , in full scale we had a better chance to observe what's happening from very close . We saw that , first of all , the felt of the pouches is degrading , thermally degrading . You could see it kind of melting away , being damaged in a way . You could see those felt pouches break and the ground with plants fall out of those pouches .

That was something that was happening quite rapidly into the experiment . One thing that I have not mentioned is how the samples were delivered to us . So the client of course brought us the green walls , but they brought walls with very young plants in them , so the plants were not very big . It was not fully covered in vegetation .

Actually I would say there was more exposed felt pouches than vegetation on the wall . The client also made sure to improve their chances for the fire test by absolutely soaking the felt pouches with water . I think they had as much water as they can hold for , so definitely they were not able to be tested in the first one , two days after being delivered .

We had to wait until this goes away . This is another example of how people trying to kind of game the fire safety system . Thankfully in here we were doing fire engineering , so , yeah , we had the liberty to wait a few days .

Anyway , coming back to the amount of plants we had , and we immediately recognized that , but there was not much we could do about it because this was the system that was about to be delivered to the building in question , so we couldn't tell the client to wait a half year until the plants grow .

It was something that we later picked up in the scientific research that I'm gonna talk in the end of the episode . So the plants were not a big part of the combustible mixture on the wall . The felt pouches were breaking out and falling out from the facade , so also not a very significant contributor to a fire . But the boards were still there .

So once we had the fire reach some sort of connection between two PVC boards and in some ways spread to the backside of the wall . You can imagine what happened Fire in the cavity , plastics , huge flames , a lot of smoke , very bad outcome of the fire test .

This meant that the solution as proposed was kind of dangerous and we wouldn't like to have this type of solution in the building .

But having in mind what we've researched with Matt Boner and during our post-Kresnik follow-up , we actually discussed that in the podcast I think it was episode four , very early episode in the show where we've discussed these experiments .

In those experiments we had some really bad material combinations like combustible boards on combustible insulation , ones that you would really not like on your building . But we've built them in ways that we had no ventilation cavities .

We quite tightly fit them all together and the resulting fire performance of those systems was not really bad , like perhaps not ideal , you would have a fire of that facade , but it was not as dangerous as the ventilated facade fires .

So , having that in mind , I thought , okay , what makes this green facade that we have this combination of plants , felt pouches , pvc and a cavity ? What makes this dangerous ? So at this point we kind of knew that the pouches not a big deal . They probably meld and collapse sooner than they start burning and creating a big fire hazard Plants .

Okay , at that point we had no idea what the plants will bring , but we've estimated that the mass of plants on the facade is not going to be very huge .

We've also discussed it with the supplier of the Greenwell system that perhaps they should change some of the initial ideas about how the wall will look to reduce the amount of organic combustible material in them . So we've kind of optimized that by reducing the amount of organic content in the wall as well .

This left us with the main suspect , which was the combustible boards , which provided the structural rigidity of the solution and of course , the ventilation cavity between this and the wall of the building .

So looking at how the course of the fire looked like in both the full scale and the small scale , we thought that the fire goes really crazy the moment that it kind of spreads into the PVC and through PVC to the ventilation cavity .

If we somehow could separate the PVC boards from the flames , from the fire that's happening on the external side of the facade , for long enough for that fire to be either controlled or gone , or perhaps people from the office have already escaped . So we're talking about 15-30-ish minutes of time delay in having this part of facade contributed to the fire .

If we can provide that , the system could be considered as fairly safe .

Now , to understand how you can separate it , you must understand how things ignite . For this I can send you back to episodes with Rory Haddon where we've discussed a lot about ignition of fuels of different type solids as well .

You can either have a self-ignition while you heat up material to specific temperature and it just ignites , or you can have a piloted ignition , where the energy density of your trigger is much higher . You have a pilot flame that is capable of igniting the heated up surface of a material . When we had the initial fire test , we saw flames touching PVC .

We saw flames going into the joints between boards . We saw this being the trigger of the further fire growth of this facade . So we thought , okay , if we can insulate the boards from the flames so there is no direct flame contact , we're at least moving from the piloted ignition regime into self-ignition regime , which is at much higher temperatures .

You would need a much bigger initial fire to trigger ignition in this way .

So we've used some kind of silicate cloth , the one that you would see in fire blankets , and we've asked them to put layers of this material on the boards between the felt and all the other textile materials and the PVC boards , as a layer that separates the exterior , that's going to be moist , that's going to be plant-based , and the rigid PVC boards that were

the support for the whole structure . We've placed this solution in SBI . It looked much better because we have not seen the spread to the back of that facade and we've put that into tests in the full scale .

Now , this test was quite interesting , to be honest , because we've observed , in terms of damage to the external layer , if I may , where you had felt pockets , the plants and everything . It was very similar to the Festes .

So the pockets were melting , the ground was falling out , you could see continuous damage happening to those pouches and then you would see this membrane of silicate cloth material exposed . It would be the outermost layer and you would see flames touching that and you would not see that much smoke coming from the PVC behind like very low amounts of smoke .

So it looked quite good . Now an issue was with the amount of overlap the client did for the cloth .

Eventually some vents were present in this silicate cloth , which exposed a tiny fragment of PVC in the facade very near the primary source of ignition and , as you can imagine , what happened is that flame went into that little hole , burned out through the PVC and we have a huge fire once again . So at this point we were sure that the direction is good .

We asked them for a different design of these non-combustible layers between the layers of that green wall and in the third try , third time , the charm it actually passed the test . I mean , of course , there was external damage to that wall . Almost all pouches were eventually collapsed or damaged in a way .

The plants burned down , but the fire did not spread into the back of the wall . We had no fire in the cavity and , in general , if you compare the amount of heat and smoke produced in the experiment , it was quite manageable . It looked like quite a good solution .

Now , with this result at hand , we start to think is this something that we are okay placing in the building ? And now we go into false trees and ideas of what can happen in the building in reality . So , first of all , the building was protected with a water mist system .

We assumed that if there is a fire of this size that we placed against this wall , this fire would be sufficient to trigger the water mist system and we could expect suppression in that area where the wall is . So if there is suppression the threat is significantly lower .

So we thought , okay , if water mist is there , that's a first and most important layer there is . Then we could have this cloth introduced in between the combustible layers of our sandwich of green facade , which really reduces the chance that the fire can propagate to the ventilated cavity and will not be a very huge fire .

So that's a big win because we've reduced one potential propagation way . But okay , let's be honest , it's the sample for the laboratory is perfect made . We have no control over how well the thing is built on the building , how well it's managed . What will happen if someone takes away part of that wall and replaces it with the new part ?

Will they keep the overlaps and everything ? And we saw how this tiny detail of the overlap between the fire proof cloth , how big difference it made when it broke and the fire could spread . So we thought we need one more layer of protection in there and we thought , okay , the cavity is dangerous .

We know that cavities kind of promote large fires in ventilated facade systems , so let's break the ventilation in there . We forced them to introduce cavity barriers .

So 20 centimeters of mineral wool every , if I'm not wrong , one and a half meter into the head green wall inside , and this was meant to halt the chimney effect , to stop the fire propagation through the cavity , which should kind of slow down the growth and limit the maximum potential fire you could have in that system .

So all things together , we came up with a system that had actually multiple layers of protection on top of it . Of course this is for fires that start near the wall and propagate into the wall , and then the wall is the secondary item ignited .

If you have a very large fire in the office and , let's say , a flash over the fire and the wall will inevitably contribute because it's combustible material . But also , you know , given the challenge , it's an office building protected with what we thought it was .

If there's a fully grown fire , the influence of this green wall will be simply an increased fire load density of the room , which was kind of accounted for in the general fire strategy for the compartment . So all in all , we were happy with how far we got so far .

Our last concern , which I've mentioned in the beginning , was with the plants , because we had no knowledge about what the plants will add to this , how bad the presence of plants will be . We only learned it recently when we were doing the full-scale experiments with our green walls in the lab .

At that point what we did was an engineering analysis of what can happen . So we saw that plants , when they are wet , when they are moist , they are not spreading the fire . They have to be dried by the flames . Then they ignite . But it's not like the whole facade ignites , it's parts of the facade that participates in fire in terms of the vegetation .

So we understood that if the plants are well maintained , moist , it's unlikely they're very dangerous in the case of a fire and they're probably the initial fire triggered . The initial fire present against the wall would be perhaps more dangerous than the fire of the wall itself . So if the plants are well maintained , that's okay .

If the plants are not maintained , which means they die off and they dry out , that's a whole different story , because now suddenly you have dry vegetation that is very well known to spread fire very

quickly .

But we thought , okay , but in this case we still have the layer of the water mist system in the compartment , so it should be capable of at least reducing the consequences of a fire of this vegetation very quickly , because if the fire is very big , the water mist will trigger instantaneously in the large part of the building and then perhaps take down the

radiation and heat and reduce the amount of smoke produced in that compartment very quickly In a way that the fire will not be immediately dangerous to the people . If the water mist fails and we have neglected plants , okay , that would perhaps be a quite bad outcome and we at that point had no idea what it will mean to the facade .

But we also considered that probably indicates a case of very bad negligence in the building , or at least for this particular tenant .

And if someone is not maintaining the water mist system , if someone is not maintaining their very expensive and beautiful green wall that is in the very middle of their office , it probably means they are kind of out of business and there should not be that many humans in there .

And okay , if you have neglected building , broken water mist systems , dried out wall , we're talking about some apocalyptic scenario in which the fire safety is perhaps not in our focal point .

So we figured out it's very unlikely that we will have at the same time both negligence in terms of broken water mist system or non-operational water mist system and negligence at the wall itself .

Later on , when doing experiments this year , we tested the scenario in which we had a neglected wall , a large wall that was a five meter tall sample of a green wall . And this case it was not with pouches , it was with modular pots , modular plastic pots with a large amount of plants .

This time the wall was really a green wall which we kept dried out for 90 days . All the plants were dead and completely dry and we've put it on a five meter tall facade . We've set a hundred kilowatt fire underneath that wall and we've ignited it . And boy , this one went fast . It was probably the fastest spreading fire I've seen in my life .

Really , the five meters of the facade ignited in something like nine seconds . It was absolutely crazy . But the amount of vegetation , even though visually it was a lot , was not really that much and it burned out within a minute .

And we have in that test , where we had plastic pots , we had dried out ground with a lot of organic content in it no separation layer between the plants and the potting system . In that scenario we have not observed fire spread from the plants to the potting system .

What happened a few minutes later is a different story because our initial fire source was not removed from the facade and it kind of ignited the potting . The flames went into the cavity between the potting and the wall and again we had a massive , massive fire in the cavity quickly spreading very large fire , one of the biggest I've seen in my life .

And in terms of facade fires , I've really seen some bad solutions like polyethylene , acp , uncombustible insulation with the cavity , and that was a very similar experience , to be honest , something I would not like to witness in reality in large-scale building , but that's the subject of the different podcast episode . Let's talk about solutions that work .

So from our full-scale experiments we have built confidence that the spread from the plants to the potting system , to the underlying structure of the green facade is perhaps not that huge risk . Of course we're talking here about one facade system , one solution for one building .

I cannot guarantee you that this will work everywhere and for every solution , but it gave us like confidence that that what we've designed back then on that building , for that office , for that beautiful jungle , then they wanted , we were quite confident that that it was a good solution

. Now , to wrap it up , we have this new emerging trend in civil engineering green walls , green facades . Post a child of sustainability . Google sustainable building and you will see a green facade , that this is one of the dreams of the future , and they , of course , look beautiful , but they bring us completely new set of challenges .

Well , it's actually not the complete a new set of challenges . I actually I should rephrase that they bring back some challenges that we thought we are kind of done with right . When I have approached this scientifically , I hope for an extremely interesting research on flammability of plants and you know Vegetation far spread on plants .

I was really fascinating for me to learn about and what we ended up was plastics and cavities again and again . So Some old issues coming back in a new wrapping , something that we need to be aware of . One thing that you should also understand from this episode we had the wall system that was placed inside the building .

This means , first , the system is Maintained throughout the year With no real Deathly cycle of the plants . It's engineered to be evergreen . If you have facade outside , there's a good chance that , at least in European climate , the plants for the winter will die out .

It's very unlikely you will have a full green facade for winter , which means that their moisture content will naturally drop when they're dead or when they are in in the winter mode . What a vehicle plants going into winter . So you will have outside . You will have natural cycle of plants going dry and moist and also they will follow what's happening outside .

So if you have a long streak of very hot days , very dry , arid weather , you may end up with a very dry facade whether you like it or not , and Of course , the fire safety challenges for facade that is dried out are significantly greater than when you have Moist , well maintained facade is something we definitely seen in our Experiments .

Another thing is the impact of wind on facade . When we had our our green wall inside , as I mentioned before , we have not considered the wind there , because you're not having a wind in middle of your office .

Outside is a different story , especially if you have tall building , there will always be wind and when doing our experiments for both dry and moist facades , we have observed significant differences when you have introduced wind .

We think that these differences Accelerated fires of the facades when wind is present are connected to how convective Heating changes the drying process of the plants , how it accelerates the drying process of the plants and also how the flames are simply pushed Into the porous layer of the leaves or the vegetation itself , leading to a much greater fire .

So in our experiments we have seen tremendously different outcomes for tests with wind and without wind . So that is another thing to consider when you're having systems outside . Next one the presence of suppression systems . In our office we had what the mist system . Outside you probably won't have sprinklers .

Perhaps you would like to design some sort of drencher system or sprinklers that could be used for that facade . That could be quite an interesting Solution to actually increase the fire safety of the wall outside .

And also cavity barriers , something that we have introduced in our system for this particular office project , but something that should be definitely installed in any external application of wind facades . In our experiments will also observe some effects that inside that they were not that interesting , but perhaps when you have building facade outside they would be .

That's first the firebrand production . This fires produced a lot of firebrands like . Difficult for me to quantify how much a lot is , but it truly was a lot . Not very huge firebrands at least not the ones in our experiments but suddenly the amount was impressive .

The second thing is that these Pouches and in the later experiments , the plastic potting , they were breaking down and the contents were falling down . So you would have a pile build up with the ground , plastic , organic material in it that would be burning small ring .

The pile would be growing as more and more of the facade is the damaged and more and more of that falls down . And In case of the office that we were considering , it was not that Impactful . But if you have 10 , 20 meters of of sides outside , the pile could be actually quite large and Perhaps quite difficult to take down .

So at the building scale , this could be something you should perhaps consider . And one thing that we were really thinking about and we had long discussions with the client it cannot we just replace the combustible parts with non combustible ones .

We are looking into materials that could be used and unfortunately most of the materials that would immediately come to your mind , like gypsum or silicate balls , they want to work with this moist green wall which is constantly wet , it's it's not gonna work .

Well , if you think about concrete , perhaps some some concrete balls could work , but I think the biological has is related to that . Having moisture , concrete , porous material , I don't think it would work very well .

Cement fiber boards this perhaps could work , and that was one thing that we have gave a serious consideration , but the client was unable to design that because of the wave and they would wait too much and they would have to redesign the completely the structural design of these Wall system to the level that perhaps it would be not possible to build it the same

for Ceramic pots instead of the felt pouches or the plastic pots . It's also not simple to replace them . An interesting solution is to use metal pots , and I've seen a solution like that , where you would have aluminum trays instead of the plastic pots or felt pouches , which is quite interesting .

I think this could work quite well Because it's it's still life-weight , but it's completely non combustible . So here you would have only the challenges related to the vegetation and the challenges related to the organic substrate Burning and perhaps to the structural fire resistance of this system . But yeah , some something to consider .

So material considerations are not so easy . To replace the system with non combustible variant Perhaps possible in some scenarios , but in ours we gave it a good consideration , but it was simply not possible . So that would be it about the interesting case study we had with our first green wall inside of a building .

Since then we've done a lot of tests on plastic pot systems like modular green walls , where you stack multiple pots together and with that you create a wall that is filled then with ground and vegetation . We've burned those with fresh plants , we've burned those with dry plants . We've burned those on the Polish test method walls . We've burned a 5 meter sample .

We've done SPIs . This is all in the paper that I am advertising for a long time and it is still not here the moment I am recording this episode . It's still in the final phase of review . The last time I saw it we had a minor review , so we are almost there with the paper .

As soon as it is published , I am definitely gonna tell you about it and because we're very proud of that paper , we hope that it will be useful for people . So that paper contains a ton of data from our experiments . That's also why I am not using this podcast episode to just go through the data , because it's gonna .

All of it will be in the paper and a case study is perhaps more interesting to hear about . So that's coming . We also , with the paper , wrote a paper to Fire Protection Engineering Magazine . I think it is gonna go in the fourth quarter , so looking forward to that piece that also summarizes some challenges for external green facades .

We're also going to conferences with this . Jakub gave some webinars to some SFB chapters . He was at SFB Berlin . We're going to present it in IFSS in Japan and then later in the year some more practical considerations at the workshop held at Frisbee in Slovenia . So a lot of conference coverage of this subject for sure .

And if you would like to immediately learn more about this subject from a different source , you can read the Great Peace by Professor Ed Gallia and his team about UK context and challenges legislative challenges related to walls , pointing out the need for a better testing regime . Very interesting piece .

Any architect or anyone dealing with green facades in build environment and fire safety should read that paper . They're gonna be in the show notes . I'll try to update the show notes as the new materials come out , so I'll try to keep you up to date with the most current knowledge in the green facades . So that would be it .

Thank you very much for spending this short time with me . I hope you enjoyed the case study we've done . I wonder what are your thoughts . We were quite happy with the design and we had this feeling that we really did a lot to improve the initial concept and the end product was something that we were fine . Writing off and accepting this as the final solution .

Wonder what your thoughts are . Perhaps you would approach this in a different way . Let me know if you have ideas how to deal with such challenging design . And yeah , that's it for today . Thanks , and see you here again next Wednesday . Cheers , bye .