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March 2, 2022

040 - Resilient road tunnel infrastructure with Ingo Reiss

040 - Resilient road tunnel infrastructure with Ingo Reiss

This week I've invited a guest, that I was looking to talk to for a good while... Dr Ingo Riess from Riess Ingenieur-GmbH is someone I look up to in the field of tunnel fire safety, in which I am very active in the last few years. In this chat, we had the chance to go through the concept of tunnel resiliency and calculate the risk related to the whole road network, rather than just a tunnel on its own. This is such a refreshing concept, in which the goal - maximizing public safety - is well defined, and thanks to that, smart decisions can be made. And these decisions are not always to make the tunnel a bit safer - in some cases, it may be just better to invest in other safety infrastructure. This holistic view opens new pathways and possibilities and makes investments in fire safety really reasonable. I absolutely love it, and it is something I wish we can implement in my own country.  Outside resilience, we also had a good chance to discuss the ventilation and modelling, design fires and some tough choices the engineers have to make when refurbishing tunnels. If you have anything to do with tunnels, this episode is definitely for you. And if you do not, still can be inspiring, as the world of tunnels is one the forefront of applying risk-based concepts in performance-based engineering. Something, that the rest of the world must eventually catch up.

Make sure to check Ingo's ResearchGate, where he stores all the magnificent reports we have talked about (and many more we did not).
https://www.researchgate.net/profile/Ingo-Riess

Also, give a chance to the Graz  Tunnel Safety and Ventilation conference, which always delivers the best content related to the fire safety of tunnels:
https://www.tunnel-graz.at/

Transcript
Wojciech Wegrzynski:

Hello, everybody. Welcome to the fire science show episode 40. It's kind of difficult to record this in the cheerful manner when. There is a war next doors, like literally in the country. Next to mine and. we've been called paranoid. About Russia. We Polish people. now you see what we were afraid of. Anyway. Let's hope for the best. I can only tell you that the Polish nation is extremely supportive to the Ukrainians. both in terms of supporting their military efforts. And at the same time, supporting those who escape. From Ukraine and the. And this mainly women and children and. I must tell you. observation. It's really surprised me. There is hundreds of thousands of young ukrainian males who are working in Poland, who are on their way to the Ukraine to fight. If that's not being a hero, then I don't know what is. Anyway. Let's not make the spotless political, let's go back to fire science and, I hope. to some of you hardest to this will at least let you. Escape the Realty for some brief time, Today I have a guest today when we wanted to invite to the podcast for a long time. Dr Ingo Riess. Ingo is an engineer working with our roads tunnels. And tunnels in general. And to me, he's one of the biggest authorities in terms of engineering tunnels he's not a researcher, but he surely acts like one. I love that. He's experienced with designing tunnels performing risk analysis. One dimensional, um, ventilation analysis and just being a part Often efforts to design some of the Europe's biggest tunnels. He's experienced this immense and I was looking forward to the talk because I'm myself, I'm a total engineer lately and we've been involved in many, many road tunnels in Poland. So this episode was as much for me as for. For you. And I've truly learned a lot from that. it's a good one. You want to listen to, to the end? So that's not prolong this anymore that's been the intro and jump into the episode Hello everybody. I'm here today with Dr Ingo Riess from Riess Engineur GmbH.. Hello, Ingo and great to have you here.

Ingo Riess:

Hello. Thank you for having me.

Wojciech Wegrzynski:

I wanted this for a long time. I mean, you're a fellow tunnel engineer, which is probably the closest part to my heart now in the fire engineering world. And. I must say the resources you provide in your papers and the repos that you participate are priceless to me. So I loved the opportunity to talk to you, like face to face. Thanks for coming.

Ingo Riess:

thank you.

Wojciech Wegrzynski:

Okay. Recently I, uh, came a report that you've participated on the resiliency of tunnels that was done for PIARC And, I saw you doing a lot of work around the topic of resiliency of tunnels. And actually I would love to start with that because that gives us a better impression of why we should design safety in tunnels and how to design it. So maybe let's start with. Defining what's resiliency in the world of tunnels

Ingo Riess:

that's a rather difficult question. We

Wojciech Wegrzynski:

know.

Ingo Riess:

I'm in a broken group of PIARC In the initial meetings, uh, we try to find a definition, a common definition of resilience, and this was really difficult and it had to be revised several times. For a for tunnels of for the traffic network it's about keeping traffic moving. And if there is a disturbance to the system to get back online as quickly as possible. So the resilience is the measure of, the possibility of keep the network or the connect traffic connection open from any adverse impact. And if there's, the connection is broken to get it open as fast as possible.

Wojciech Wegrzynski:

Like the ability to restart, doing normal operation. As quickly and as little cost as possible. Right.

Ingo Riess:

and there's always the aspect of safety. If the tunnel is broken, you can always open it. If you accept any level of safety or unsafety.

Wojciech Wegrzynski:

I like the goal of the tunnels to get the traffic moving. And, yeah, we, we build them now in Poland. For example, Poland is not a very mountainous country. We have mountains in the south of Poland, but it's not a part of huge, conurbations or something. We have their connections with our neighbors, but now I'm mostly involved or are highly involved in tunnels being built in cities, in large cities as a part of like giving the city back to the citizens. And that's a trend that's been here for ages. If I. remember correctly, there was this huge, fire safety program, Memorial tunnel, and that was connected to a large project like that. I think it was in Boston, the USA, where they tried to move, uh,

Ingo Riess:

Central.

Wojciech Wegrzynski:

Yeah. And, that was like 30 or 40 years ago. And the trend is now in here. And we start digging under the cities. We start building this huge tunnels for large volumes of vehicles. And this approach is not going anywhere because it seems to be, a successful and w with this growing demand for tunnels growing, Traffic volumes in this tunnels and the modern view on, safety, which is unfortunately triggered by huge tunnel fires we've had in the past. This project seemed to be increasingly challenging, at least for us in here, like the expectations are higher and higher. Not necessarily saying that the targets are higher because the target was always for the tunnel to be safe, but the solutions to provide that safety are increasing. Is that something you observe as well in you're designing tunnels for quite a while, I guess.

Ingo Riess:

and my impression is that there's, it's a pendulum. So after the, the large tunnel fires we had. Demand for safety. And, the government put up a lot of money to increase, tunnel safety. And right now it's swinging back a little bit. in, in central Europe, we've got these design codes, so everything is pretty much defined and it wouldn't decrease much above that. On the other hand, there are tendencies to. Except the higher level of risk, for reduced cost. So at the moment, it's more like, possibly going away from these prescriptive codes to risk analysis. And in that way to accept more risk for particular tunnels or infrastructure or.

Wojciech Wegrzynski:

But the thing you can really compensate that in the risk. The bottom line is that if you allow for heavy vehicle traffic in the tunnel, any heavy vehicle traffic, you will eventually have a scenario. There is a large fire in the tunnel, like very large fire. Even like for me, cutting probability by half or one-third, it doesn't really make such a big difference because still you have this scenario. I know it may go from like a 10 to the minus five to the 10 to the minus of six, but, is this a big enough change in probability or risk that to, to allow significant cost reductions

Ingo Riess:

the argument in Switzerland is that, you could save money in your tunnel and you could spend it elsewhere for road safety.

Wojciech Wegrzynski:

uh,

Ingo Riess:

So the tunnels are inherently more safe than the open road in average. So accepting more risk in a tunnel, set, gives you additional. to solve accident points risky points on the open road network. That's the argument and the truck fire or the dangerous goods fire in a tunnel. You have to weigh it against a dangerous goods event on the open road. So we have this discussion again in another country, another project where we discuss dangerous goods in the. And then the argument was what happens if the accident is not in the tunnel, but in the residential area above ground. So in the end, it always should be about risk, but the problem with risk is then you are in performance-based design. And then it's a question. How do you prove that you meet the requirements and how do you prove that you are on the safe.

Wojciech Wegrzynski:

I like the two cases that you've made. One is that the whole road system is a, is one body. And the, you can holistically approach it, especially that in most countries, I would say. there is some governmental authority that manages all of it. It's not like a bunch of private tunnels of combating gas companies. It's, it's mostly, uh, uh, one network in the country. And if in fact, you do, free funds in one project to improve safety in another project. That's fantastic. And the second thing you've mentioned about the, fire or the catastrophic event happening. If there was just the road, not the tunnel and you're right. It's a, from my experience also is it's usually would be worse than in a tunnel, at least for the people around that, location. And this is a very difficult thing to convey to the, communities that needed tunnels.

Ingo Riess:

Yeah. It's well, it's the European approach that the whole network is operated by the government, but there are numerous countries where especially tunnels are built and operated by private. We'd have contracts with the road network operator. And this makes the concept of resilience rather complicated because the operator looks at his object is a piece of infrastructure he's tunnel or bridge or whatever. And he wants his, piece of road of the road network as resilient as possible. While the network operator may not be in. In that resilience, especially for an urban town. When you, you mentioned the urban tunnels in Poland, when you have the urban road network around that, if the tunnel has closed, the traffic capacity will be drastically reduced, but the connection will not be closed. So it's not such a big issue as for a tunnel like Mount Blanc, or that's really connecting. and would require a detour of hundred kilometers. it's a different perspective. Are your network operator, are you a tunnel operator or are you the driver just wanting to get from.

Wojciech Wegrzynski:

And. From your experience for this, private projects is this, capacity to, to restart the tunnel, this resiliency. Reflected in the design, because, for us, as you mentioned in European, we have standardization and codes and the good practices that we usually follow. And we're usually limited to that. So is this resiliency, a design factor that you would design for you? Would you spend more money on the tunnel systems, to improve that? Which like install, uh, I know sprinklers in the tunnel just for this.

Ingo Riess:

Resilience is a rather new concept when it comes to tunnels or Road networks. Let's, let's stick to road networks, it's a new concept. And so far, I think there aren't too many examples where really improvements have been made for resilience. but, the effects are already noticed in, 2016 and 2017, there were rather similar fires in a road tunnel in Germany and in the road tunnel in Austria. And the German tunnel was equipped with a foam fire suppression system. The Austrian tunnel was not. So the Austrian tunnel had a fully developed fire and the tunnel was closed for, I think just about two months. And the German tunnel was closed for about seven or eight hours. So that's resilience, but then you have to consider how much money is the other two months worth. is it reasonable to install such a system to maintain it and test it and operate it? Just to get these two months of operation every 20 years and lots of discussion. Only starting right now. I think that's, in most existing tunnels, this has not been investigated.

Wojciech Wegrzynski:

for us, this is in a way problematic because in our law system, which is very prescriptive, like it gives you this. Certain requirements. You'd your total must pass to be allowed to be built. There is almost no ways to include, benefits from like extinguishing systems. You, you cannot. Install a system and decrease the fire resistance. If your walls or don't do a spalling protection on your walls, you cannot lower the capacity of your exhaust system. You cannot change the design fire scenario. Maybe you can, but it takes a lot of efforts to do that. So you are not required to install it and you want to install it. You know, the benefits are there, but it's difficult for you to benefit your design that would allow you to, loosen some other requirements.

Ingo Riess:

I don't necessarily agree with that. As an example in Switzerland, we currently design. Started to construct the second tube of the Gotthard road tunnel. And this is in principle, a resilience measure because it increases the safety because we've got uni director and the traffic in both tunnels in the end. But first we have to close the existing road tunnel for a couple of years, month. And there has been a study made on what to do, uh, while the tunnel is refurbished. And, there were several options investigated, like, temporarily using the old rail tunnel, like using the detour across some Bernardino, which would mean several hundred kilometers of detour. and the study calculated the societal. So it was not investment against investment, but costs societal costs, including environmental impact, including, increasing accidents on the open roads. so all of this was investigated and in the end, the government decided, well it's well worth building a second cube to increase safety and, to reduce the impact of the tunnel closure. So this was a cost benefit analysis covering the 30 years, 50 years of tunnel operation. And the government decided, that it's worth including these societal costs, that's public money. That's private money. It's not money. The government saves directly. So if, if you have a more global view on your infrastructure, it may be well-worth for the government as a road network operator to increase resilience.

Wojciech Wegrzynski:

I think it's a discussion we need to open in Poland with our road operator. They seem to be open for discussions in fields like that. And I think the points are very strong that you have to look beyond. Just a, the most basic costs of your system. And that is it. We wouldn't have not even mentioned life safety yet in this discussion because it's self-evident that if you install sprinkler system or some other technical means you will also improve the life safety and operational capacities of the fire brigade, at the same time. But this is something that is, is fundamental.

Ingo Riess:

it's, it's a standardized approach in Switzerland. You have to do this type of it's a defined procedure, this cost benefit analysis, and you have to do it for every project, every new tunnel, every refurbishment project, and the Gotthard is not the only example. There's the Belchen tunnel, which is. Along on one of the main traffic arteries in Switzerland, which is now getting a third tube for the refurbishment of the existing two ones. And there will never be all three cubes open to traffic. It's just a temporary measure for the refurbishment to have another tunnel tube. And it's, the cost benefit analysis shows it's worth to do that. It's better than closing the tunnel for a couple of.

Wojciech Wegrzynski:

That is astonishing.

Ingo Riess:

it's really the question. how do you value the time spent for the, the driver needs on a detour? How do you deviate the traffic? What's the impact there? And in the end, the cost benefit is.

Wojciech Wegrzynski:

that is astonishing. I wanted to drive the discussion towards refurbishment because, I also know that in the Western Europe, like in Germany, or I assume in Austria and Switzerland as well. The tunnel network is actually quite old. You guys have been digging these things for, hundreds of years almost. I think the, the median age of a railway tunnel in Germany is above hundred. So that's quite a challenge. I wonder. How you approach, like you've mentioned now that the third tube, which is for me exotic and amazing concept to, to build for resiliency, but how you approach like developing safety and resiliency. When you get into a tunnel that's a hundred years old and you have to work with what you have there.

Ingo Riess:

There's no general approach at first, you have to that's. These are the most interesting projects for the design. Of course, first you have to see what is what's there and what can you do with it? And is it possible to upgrade it to current standards or do you have to deviate from that because of the stuff you have. we have ventilation systems conversion from transverse fully transfers concept to longitudinal concept or longetudinally with local smoke extraction. Then you get different pressure forces on the false ceilings. So do you have to strengthen the false ceiling or do you have to reduce the flow rates or do you have to change the concept? Change your fans from fixed blade to variable pitch. There are so many options what you can do, but you have to analyze each project.

Wojciech Wegrzynski:

this intriguing guy you've said transversal into longitudinal

Ingo Riess:

there are a couple of tunnels where we remove the false ceiling and use the full cross-section for longitudinal ventilation. When it's unidirectional. there are projects where part of the full ceiling has been removed to make room for jet fans and other parts are sturdy used as a cable tunnel or cable duct. it's the kind of work where you as a designer can become really.

Wojciech Wegrzynski:

I'm asking that because in here we have. this assumption, and I'm not sure where it came from that transversal system is, universally better than longitudinal system. And, I have worked with transpersonal systems and, I'm not necessarily. Convinced that is the case probably when you have by direction, a little tunnel, that's the only way you can go, to have, safe conditions, both sides. But if the traffic is unidirectional, it really don't feel that improvement.

Ingo Riess:

transversal. I mean, distributed, fresh air and distributed exhaust there. I mean, we've got the, we've got the local smoke extraction with the dampers and this is still, this is used in new tunnels in new bi-directional towns. Have a certain. but, uh, we found after the large fires in Europe, that the distributed exhausts doesn't really work. you have to have local extraction in half. You have to have airflow control in the tunnel using jet fans to control the flow velocity.

Wojciech Wegrzynski:

yeah.

Ingo Riess:

and this control algorithms are still challenging.

Wojciech Wegrzynski:

I know

Ingo Riess:

They asked that used in Switzerland, in Austria for a long time now. And they work pretty well, but still the requirements, in my opinion, the requirements are not Very well-defined. We know where we want to go. We want to have symmetric flow or we want to have a reduced flow velocity. If there's no smoke extraction, we don't go for critical analysis.

Wojciech Wegrzynski:

I love you.

Ingo Riess:

But it's, currently these control algorithms are defined as you have. You have to get to that target and you have to get there within say five minutes after fire detecion But I think that that's not enough because sometimes it's better to approach to do it slowly and not use all the jet fans in the tunnel. And today there are jet fans of their tunnels where when the tires detected all the jet fans thought, and these designers, I think, forgot that. The reason why you want to achieve that target of maybe 1.5 meter per second, you want to maintain smoke stratification. And if you spin on all the jet fans in the tunnel, you don't have any smoke stratification. So the measure defeats the objective

Wojciech Wegrzynski:

Exactly. I love how you segwayed me into the next question I wanted to ask you. You you've mentioned symmetric, conditions at ends of the smoke controls, zone and, some assumptions behind the flow management, like starting all the jet-fans at the same, or, or controlling that in a better way. A lot of that comes to this unrealistic assumptions or ideas that we go when we modeled tunnels. if you, Go into, um, project with the download and you simulate it or you check out the simulations. the there's usually no traffic because it's, it's a hell of a problem to model traffic along CFD. Or even if you did, it's, not really reliable because. Small change in traffic will result in large change in the simulation outcomes. So you would have to run a, some Monte Carlo probably to get it right, and that you cannot afford that. you usually start with the initial conditions like zero, uh, zero velocity and no movement static field. Then you start your fire, which is a beautiful, buoynt plume that touches your ceiling flows both directions. Then you start your fans and they disturb it. You don't usually consider metrology like the weather conditions outside and not even touch the mistakes people doing the simulations with the grid size or. Or a bunch of conditions but this initial image is so different than what you would see in a tunnel where you're in one we have a tunnel with it, with a bus stop in the middle of it in Warsaw. So if you go there, there is definitely a movement in there. Uh, not to mention that noise is unbearable but the air movement is always there. And, it doesn't like magically disappear when you have a fire. So your initial field yes, it's already, you need directional air movement. That will make a lot of funny things to the smoke. And I'm doing this simulations and I'm doing it like everyone is doing because otherwise I would not be able to explain to the stakeholders why I'd done it differently in why it's better. Maybe I should try one day. We'll see. I think it did go well, but you know, there is something with this that we, we put so much focus into super detailed analysis where the initial conditions are just plain wrong and I feel I'm doing it wrong. Are you doing it wrong as well?

Ingo Riess:

I think I never had to do a CFD design safety of a simulations for a tunnel design.

Wojciech Wegrzynski:

Really?

Ingo Riess:

I think for a few projects, we had to deliver it, but this was more about jet fan debt, impingement on traffic and things like that. But I didn't never did a fire simulation. I always avoided that. And today when I'm working on a project, I have someone else do it. I'm not really interested in this. When I see the fire life safety report for these performance based design. Project, they do it, as you say, they use FDS and they use standard boundary conditions, still air as an initial condition, no traffic movement. And they have an egress model showing that everyone gets to the nearest door And well, you have the two scenarios. You have the unidirectional traffic, which is boring because the result is always. And you have the bi-directional tunnel where things get really messy.

Wojciech Wegrzynski:

and reasonably is always complicated.

Ingo Riess:

what I would like to do at least in the initial, I mean, it's, it's really, a scientific level of CFD. If you start with moving vehicles and moving boundary conditions and dynamic flow conditions, that's not standard stuff you would expect in a design. But what you can do is you can combine the findings from this kind of steady state CFT, 3d modeling with a dynamic 1-D model. So you combine how realistic you can prove show how realistic or unreal realistic are the boundary conditions. And then you have to make an interpretation, which is. Difficult for the client because he wants to see the numbers and the pictures. What does the smoke do? But I think that would be the right way to.

Wojciech Wegrzynski:

You think that in this field? 1-D modeling or the traffic, sorry. The network, a modeling of tunnels would be a superior to CFD because of this capacity to model multiple scenarios versus a nice three dimensional flow field in a, in a

Ingo Riess:

the thing about 1D is when I do a tunnel model and simulate a fire, I have about seven seconds simulation. For a scenario.

Wojciech Wegrzynski:

that's

Ingo Riess:

So there are quite a lot of scenarios I can look at and find the critical ones and understand how the system works. If it's a steep gradient tunnel that the behavior will show me a pattern. And if I interpret this pattern, right, I can develop the optimized ventilation solution A single CFD simulation 3d will not help me to see.

Wojciech Wegrzynski:

that's really that's powerful. I, our experience is, opposite. We would, do CFD for this projects. Mainly, well, we're usually having jet fans and stuff like that. And you would like to see is the placement of jet fence, correct? did they interfere with each other? But frankly, the reality is the main goal is, is to present the authorities with, proof of compliance that, the conditions are maintained for like seven minutes. And they're good. And. From this perspective, the CFDs is necessary as. We as engineers, we benefit from it partially by investigating some of the aspects. But as you said, it's not possible to, it's not realistic. I mean, it is possible. It's just not realistic or economically viable to do, to run into this complex simulations. So with, multiple variables in, in included in them and. In that case, this is 1-D modeling or network modeling seems like an interesting approach. We also deal with some very complex tunnel system. That have junctions connections, multiple levels, not necessarily in road tunnels. In road tunnels. The world is a little simpler, but in railway tunnels, when you have a rail network with stations and stations have multiple levels, we felt that CFD was the only way we could truly track where the air will go once it enters the station. If it has seven possible outlets.

Ingo Riess:

I mean the state railway station, an underground railway station is a classic example where you need CFD that's not one dimensional. That's highly three-dimensional.

Wojciech Wegrzynski:

exactly. so you would also have these experiences switching from tool to tool in this manner.

Ingo Riess:

well, I, I've done very little CFD in my, Past work.

Wojciech Wegrzynski:

Uh,

Ingo Riess:

it's usually, uh, we have specialists for that. I don't do it myself, but I can, set the, define the boundary conditions. I can discuss the results. I can understand the flow, the mechanics of the software, I leave that to.

Wojciech Wegrzynski:

I actually highly respect that because I think this approach should be more widespread in the world and we would have much less issues with the systems as we do today. I wanted to ask for another, interesting feedback loop that it's obvious, but it's in the way missing. Impact of the airflow velocity and the growth of a fire or in general, our design fire assumptions for tunnels. we've as a humanity, we've been lucky enough to have some full-scale controlled tunnel fire experiments. Like the Memorial tunnel that has been mentioned, the Eureka Upton, there was Runehammar a fire tests that, or that was the part of Eureka. I always confuse them.

Ingo Riess:

I think that was part of Eureka

Wojciech Wegrzynski:

there, there was the Metro project in Sweden, probably many more, fire experiments in the tunnels. There's a tunnel testing facility in, in Spain, in Applus I think it's called the laboratory. so we, we have this data points, and they show you the causes of, large vehicle fires and we just go and employ them in. Design, but now when you think about fires in tunnels, there are factors that will for sure change the way, how the fire goes first, being the velocity of the air. So you may have. Something near the critical velocity where you just push the smoke, but not necessarily grow the fire, but if you blow 10 meters per second on the fire, I mean, you don't have to be a fire engineer to understand that increases the severity of the fire and the same with. cross section of the tunnel, the, the hammer was like 47 square meters in cross section. There was a tiny tunnel and the huge fire in it. So the radiation from the walls is completely different than you would have, in the tunnel that was drilled with 12 meter diameter TBM machine. so I wonder to what extent. It makes sense to use these design fires as the ultimate basis for our design and other in other way. I don't think we have another choice though.

Ingo Riess:

I didn't look too much into that because the fire dynamics, that's not really my field of expertise. an interesting, interesting aspect was brought up in the paper in Gratz in 2020, the. Geometry of the fire, is it usually we assume it's a point, a mathematical point in the tunnel but if it's a rail wagon on fire or a rail train, which really, if you have the large fires, it can't be a point. It must have some longitudinal extension and the physics change. If your fire is five meter long, or if it's 50 meters long and the critical velocity will change. the smoke spreading will change the oxygen supply towards the fire will change. I don't think this has been investigated in any depth.

Wojciech Wegrzynski:

the, the fire is also. It pumps air. If you take cold air you heat it up, you pump it upward and it goes away. So it needs a lot of air for a hundred megawatts fire. And if you do a CFD, you can see a local velocities of like five, 10 meters per second near the fire, just because the fire exists. And it's so, so powerful in there. And, I don't think we take this into account, you know, that that's such things w we'll we'll have around the fire. You've also investigated a lot about the throttling effect of fires and how this influences the, the ventilation system in the tunnel.

Ingo Riess:

well, that's a, that was an interesting project. There was a lot of discussion about the fire trotting effect in since well, I learned about it in 2006, from a paper from conference paper. And, in 20 17, 18, 19, I had a research project funded by the Swiss, road administration to do a CFD analysis on this. and I had some very interesting findings, which contradicted a lot of the papers that were published before. the report was well received. and, but still, to me, this is a CFD study and I did the CFD, myself, so I'd like to mistrust my own results and I would really love, any confirmation or any opposition against those results provided by. Or if possible, even large-scale fire test to validate the results because without, without large-scale fire tests, the value of these results is a bit limited. The current status is that a PhD student has confirmed via the fire throttling effect as found in, in my study in an independent analysis, using different. But still, that's just a verification. That's not a validation.

Wojciech Wegrzynski:

Mm.

Ingo Riess:

And, currently I'm hoping for funds for a research project where we can actually measure the throttling effect in this Spanish, test facility. But that's rather expensive doing full, size fire tests.

Wojciech Wegrzynski:

Yes. Uh, so this effect how does it work? Like the fire is a resistance to the flow, and you try to measure how big this resistance

Ingo Riess:

there are several effects going on. One effect is that the expansion of the heated air in the fire, which causes a local press of drop because of the acceleration that's been newly more or less or momentum balance. And then you have increased friction downstream because of the higher volume you push through the tunnel. And there's another effect downstream from the fire when you have temperature stratification and the flow profile resembles the temperature profile. So it's not the fully developed tube flow. You, you know, from the cold. Yeah. And the, the resistance along the tunnel of this, oddly shaped flow profile is apparently higher than the normal tunnel flow. And this is significant. this fire throttling effect. If this temperature stratification remains stable, that would be relevant for ventilation.

Wojciech Wegrzynski:

I've read your report. And I loved it. And I immediately struck me that again, in the like when we commissioned the tunnel when we do hot smoke testing in it with, 2, 3, 5 megawatts source in it, and we base our opinion on the observations in that moment of time. And you have, Investigated this, I assume, with the relation to the ventilation systems and how it could impact the ventilation system in a negative way. Like it's a high resistance that you would have to push against for us. It was interesting opposite way. Like the wind effects on, on the tunnel fire. If the wind is acting on the tunnel, let's say against us. And there is this increased resistance that comes from large fire being there, mainly the thermal expansion and this heat pump that I talked. Briefly before then maybe the wind effort would have less severity because it will also act against this local and throttle making the whole equation so complex, probably unsolvable because suddenly you have so many forces that act on each other and influence each other. But the main point is we pace our opinion on thing that is happening in this brief moment. When we do the hotsmoke test. Unfortunately not possible with a hundred megawatts or not really welcomed owners have the talent to do that with a hundred megawatts. And, in a way, you know, understanding that in reality, it's going to be different because there's going to be different forces acting than we have now.

Ingo Riess:

the smoke test. They convey a level of safety. That's not really there. it's very good. For public opinion. You can have a nice movie. You ask you get the smoke. Stratification is also an effect I don't think there was too many real fires where we had a stable smokes layer because usually vehicles are moving in the smoke. there's the fire brigades are, is run rushing in and every movement, like that will disturb the smoke layer. It might not stop the temperature stratification, but the visibility.

Wojciech Wegrzynski:

Yeah.

Ingo Riess:

And, all these fire tests show very stable smoke stratification So it's, it's again, it's the test and what you see there is it conveys a level of safety that might not be there.

Wojciech Wegrzynski:

Well, my experience is that the bigger the fire, the better the stratification though. And, uh,

Ingo Riess:

Froude number. Yeah, the stronger, the temperature stratification, the strong number, the better the stability of the smoke layers.

Wojciech Wegrzynski:

but in reality, I also think that in the hot smoke test, when you immediately set on fire five megawatts pans of diesel and, gasoline, like people did that Austrian style. I love that. I there's also an unrealistic representation of the growth of the fire, which, which will be growing, which will be, uh, hopefully slower in a way, and may not have this buoyancy or will be spread out, at the larger fire source. Not necessarily a point source, like, like a panel would be a point source.

Ingo Riess:

and there's also the traffic behavior. there, there were so many, especially in tunnels that got an emergency breakdown. We don't have that in Switzerland. Most tunnels don't have that, but if you have that, the likelihood that a fire occurs on that breakdown lane is probably the highest in the tunnel cross section, which leaves two lanes of traffic free for the vehicles. So maybe the vehicles will not stop in front of the fire as we assume in our safety analysis, but they will continue to go through, they will see close to nothing, but still what they will continue to put. That's how people act.

Wojciech Wegrzynski:

and, at the phone for the end we've discussed so many interesting aspects of the tunnel, fire safety and ventilation, and. How much research you see about this particular aspects? Because, and I mean, in, in like peer reviewed papers, because I see very little, the only places where I really see this research, as a great source of knowledge is you've mentioned Graz conference and that's a place where. You can learn a lot. There's a PIARC conferences, but in peer reviewed research, I have this odd feeling. It's all about critical velocities and backlayering, scale models of tunnels I'm really let down by, by the fact how disconnected or disjoint from the engineering that is.

Ingo Riess:

yes. I mean the, the engineers don't read peer reviewed papers. They are too expensive. And usually you don't come across them. Most engineers are not directly connected to a university, so they don't, they simply don't have access to these papers. The only thing they have access to is conferences where the community meets and, the same, the research for these project is done by engineering companies and not at universal. So there's research done in Germany. It's funded by BAST in Switzerland. It's funded by ASTRA, in Austria. And they've got their research program. It's done by engineering companies. And in the past couple of years, there has been some work done on human behavior with a sprinkler systems. And what do people actually do? And we've got due to the European directive we've got by now consider data from real events. This was another change in the last 20 years. Now we really know we get the report. We see what happened, how people behaved,

Wojciech Wegrzynski:

We also get the measurements and that's, that's something

Ingo Riess:

and we've got more equipment in the tunnel that gives us more date day.

Wojciech Wegrzynski:

But I still, I would put the case in the reverse order. The scientists are also the engineers and they are. Rarely have practical experience designing or solving technical issues in tunnels and, there's a level of. Problems that you only learn when you face them. And when you match them on, on a real project and that are not evident in a small-scale tunnel in your laboratory, and you can run into this loophole off of critical velocity or back layer in distance, which is very interesting to research. I would say it's, fairly easy to research in, your scale models because they are very convenient for that. But. You've already said you don't use critical velocity. And that does not either. I do not really care that much about that concept.

Ingo Riess:

well, I think the critical velocity is a design requirement. It defines the capacity of the system and. I like the Swiss approach to this. They, the Swiss design code for old tunnel ventilation just says we want three meter per second. They don't, they don't talk about critical velocity at all. We want three meters per second, and I think that's a very sound approach.

Wojciech Wegrzynski:

and so much easier then the page long equation to solve for the fourth, significant digits in the

Ingo Riess:

And with every new edition of NFPA it changes.

Wojciech Wegrzynski:

Yeah. So there we've seen the papers that, that actually, and I'm happy with that. They started questioning the new values that there are the, they started to be unreasonably high, like unrealistically high end, without really sound proof of why we need as high numbers, because they translate into costs. Operational costs, construction costs and, and, they just make it more difficult to design the system, which probably has worked even with the previous versions.

Ingo Riess:

and this may be an another program. Why we, we don't research these things enough. there are two, we've got these design codes in Europe. Which are pretty well fixed. And, there are too many energy engineering companies, where people think we already know everything. So they don't do research anymore. if you get, go to the conferences and you see the work that's presented, there it's so much today. There's so much more about projects we did and then no longer questions. And, it goes more into marketing and less into research, which is a pity, because I think there's still a lot of work to do.

Wojciech Wegrzynski:

Thank you. Thank you for that. I'm happy to finally have an engineer in the podcast and well, you're, you're a scientist to me. And, was a great pleasure to discuss with you the challenges of resiliency of safety in tunnels, and then eventually ventilation. I think a beneficial thing would be to advertise a bit. this conferences are the places where the engineering mixes with research and for me, such places is Tunnel Safety Ventilation Conference in Graz. And I hope to be there this, this year. It's, um, it's in may my ninth to 10th, in GRAZ in Austria. And, I'll link to that conference in the bottom. You have your favorite conference outside of.

Ingo Riess:

well, actually in the, in the past couple of years, I only went to Graz there is The HR conferences, British hydraulic research Institute, which I left 20 years ago. but I didn't have the opportunity to go. They were very innovative and very technical, the ones on ton of fire and ventilation. but I don't know how they develop the past 10 to 15 years.

Wojciech Wegrzynski:

there's also PIARC conference in Granada that's happening in October, I think. And I hope to be there

Ingo Riess:

Yeah, the PIARC conferences, they are more strategic and a state of the art. They are less scientific. it's a different they're different topics. This.

Wojciech Wegrzynski:

And I would also like to highlight that, the materials from the technical conferences in Graz are available online usually. And you, you can find them, I just see your paper on trotting ethics. So it's there. That's great that this is being shared outside of the conference to be used. So I'll link to this resources and also rulings. Research that, that you have been doing. Ingo thank you very much for coming here and being a part of the podcast was a, it was a huge pleasure to have you in here and, see you soon on some tunneling project in Europe.

Ingo Riess:

thank you for having me. I hope to meet you in God's.

Wojciech Wegrzynski:

Looking forward to that. See you soon. And that's it. What a great talk with Ingo. I'm really happy to. Having discussed with him, especially the risk aspects And he know this whole concept of resiliency and how we could actually build the third. Tunnel nodes just to have the tunnel operational for, for the time of refurbishment that's, that's is something very new for me and very intriguing. And it makes a lot of sense. When you think about the economical impact that tunnels have in. here that he doesn't like to do CFD. it doesn't feel secure about it. Please don't trust him. He literally writes his own one dimensional coats for tunnel ventilation and everything. So I am. Way more confident in his capabilities then. He is. And I've read his report on throttling ethics, which is linked in the show notes and it is purely excellent. One of the best pieces I've read. In a long time. Uh, so for the end, I think the resources are there. You should follow Ingo and researchgate. He posts all his reports. That's actually the best place to go, I assume. we also advertise hard the Graz conference, because it is really good. It's a really great conference for everyone. Dealing with tunnels. it's full of great people, full of grades. Research is a great place to be if you're engineering funnels and I hope to be there. And I hope to see you there. And that's it for the episode. Thank you very much. And cross fingers for Ukraine and the safety of Ukrainian people, please. And let's stop the madmen from blowing up the world. Thank you and, uh, see you here next week. Cheers.