180 - Fire Fundamentals pt. 12 - Pressurization systems

Transcript

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Hello and welcome to the Fire Science Show, session 180 and the 12th episode of the Fire Science Fundamentals.

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We've not had the Fire Science Fundamentals for a while, so I thought it's a good idea to create a new episode for this series and since I'm here alone, I'm going to be talking about stuff that, let's say, I am somewhat knowledgeable of, and that is building systems, automation and smoke control.

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In this episode we'll be covering pressurization systems, so that's a very interesting subject to a lot of people.

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A lot of people believe they do not work and they have their reasons for that that I will try to debunk in this episode.

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A lot of people are a little bit clueless in how to apply those systems and they're making quite a big career, at least in here in Poland.

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They are very, very important part of our life, safety strategies for buildings, especially high rise, and we've learned to deal with them quite well, to be honest, and we've learned to trust them, which is perhaps the most shocking for many of our colleagues outside of Poland.

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So in this episode I'm going to try to give you some of that mine or ours experience with the pressurization systems as a part of a fire safety strategy, but more from a perspective of the scientific understanding of what the system is supposed to be delivering.

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How does it operate?

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What are the physical phenomena related to the operation of the system is supposed to be delivering?

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How does it operate?

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What are the physical phenomena related to the operation of the system, and how exactly is this system keeping smoke away from our staircases, vestibules and spaces in which we do not want to have smoke?

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I believe that once you learn the fundamentals, once you understand the physical conditions in which this system really thrives, you'll very quickly understand the principles of design of the systems and will be able to apply successful pressurization systems in your projects as well.

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And this episode can be also quite valuable to other people dealing with fire science, compartment fire experiments, especially because, of course, pressurization pressure effects on openings and flow paths that establish in the building are highly relevant to any type of building fire strategy.

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Now I wonder if I made a good job doing this introduction.

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I hope I made the pressurization attractive enough for you to stay with me and listen to this podcast episode.

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These systems are definitely attractive enough for me to talk about them, so let's spin the intro and let's try it out.

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Welcome to the Firesize Show.

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My name is Wojciech Wigrzynski and I will be your host.

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This podcast is brought to you in collaboration with OFR Consultants.

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Ofr is the UK's leading fire risk consultancy.

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Its globally established team has developed a reputation for preeminent fire engineering expertise, with colleagues working across the world to help protect people, property and environment.

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Established in the UK in 2016 as a startup business of two highly experienced fire engineering consultants, the business has grown phenomenally in just seven years, with offices across the country in seven locations, from Edinburgh to Bath, and now employing more than a hundred professionals.

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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 fire safety solutions.

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In 2024, OFR will grow its team once more and is always keen to hear from industry professionals who would like to collaborate on fire safety futures.

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This year, get in touch at OFRconsultantscom and welcome back.

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Let's learn about the pressurization systems.

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Actually, you've just heard the OFR intro, the sponsors of this and I had an interesting story with OFR and pressurization because in the past, one of the founders of OFR, Simon, had very strong opinions on pressurization systems in the UK and he even wrote a paper that pressurization systems do not work and pose a threat to life.

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That was quite an interesting read actually.

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In many regards it stays actual for the type of systems that he had to deal with and I've tried to convince him that actually they do work and they are not a threat to life.

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And eventually I've invited him to Poland.

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I've shown him the lab, I've taken him to some high-rise buildings in Poland, We've shown him the factories of the vendors who are producing those systems and I think Simon was quite convinced and I believe he changed his opinion in that regard.

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Anyway, my best wishes to Simon and I hope that I can change mind on pressurization systems for many others through this podcast episode.

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So why do we want pressurization in our buildings?

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The principle is super simple you want to keep smoke away from spaces in which you'll have some vulnerable people or some other things that you wish to protect from smoke.

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There are two ways you can keep smoke away you can extract it or you can prevent the smoke from coming to that space, and pressurization, of course, acts on this second layer, which means it prevents smoke from accessing a particular volume or a compartment in your building.

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That compartment could be usually a lobby or a vestibule, whatever you call them.

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You could do it for an elevator, lift or any shaft in your building.

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Sometimes it could be a corridor, but technically it can be any any space that you want in your building to be protected against smoke.

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It's one of the tools in our toolbox that allows us to split our building in compartments and just make sure that within that compartment we're not going to have anything, Just like your fire doors, just like your walls, just like any other dampers In this case they just operate on air, of course.

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Like any other dampers In this case they just operate on air, of course.

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So this idea has been attractive for a long time, especially when you think about protecting staircases.

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Because what's a staircase?

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A staircase is a natural chimney in your building and if you have some sort of a high-rise development and a fire breaks out in any compartment, some sort of a flow path will establish between that compartment and the exterior of the building.

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The flow path may occur at the window, Of course.

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It's going to occur at the window.

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As the fire breaks out the windows, the smoke is going to start flowing outside the compartment through that opening and kind of ventilate itself to some extent.

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But you also have doors.

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You have doors to your compartments which will be opened by people escaping, which can be opened by firefighters entering the compartment, which can be destroyed by the fire, providing a new pathway for the smoke to go.

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And in this case the smoke ventilates itself to spaces which you would like to have secure.

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It ventilates to corridors and from those corridors it can penetrate the staircase.

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And that becomes an issue when it does that, because a staircase, as a vertical space, is a perfect place for smoke to rise, so it acts as a natural chimney.

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And you could, actually, if you have an opening at the top of a staircase and you often do because of the smoke control strategy you don't want the smoke to accumulate in the staircase in case it entered there, so you would ventilate the staircase.

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You can create a very, very efficient chimney, even more efficient than just ventilating flames and smoke through your windows, which would mean that your smoke goes from your compartment to your corridor to your staircase and just continues to do so throughout the fire.

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That obviously is quite a risky thing that you do not want to have, so you have to break it.

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Now, if you think about modern buildings for a second, because I put this image into your head that windows will break.

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But if you think about modern buildings with multi-layered glass and very, very strong windows that act as the facade of the building, the chances that the window is going to break very early in the fire are not that high, to be honest.

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I mean, we don't even know what they would be.

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I had an episode with Yi Wang on modern glass some episodes ago and it's very challenging to actually predict the breakage of glass, especially at the early stages of the fire.

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Today Ruben Van Coyle, in his ERC grant, is battling with the same problem.

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So we don't know if the windows will break.

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If the windows do not break, then literally the only flow path the smoke has is through your corridors and your staircases, which means in those buildings in which the fallout of the window or breakage of the window is not very likely, an early phase of fire you will have smoke in your corridor, you will have smoke in your staircase and you really don't want to have that.

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So now the idea comes up let's perhaps create pressure difference between the staircase and the spaces surrounding it, in a way that the pressure in the staircase is higher staircase and the spaces surrounding it in a way that the pressure in the staircase is higher than in the spaces surrounding it.

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That's a brilliant, simple idea.

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What creates a flow of air?

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The pressure difference creates a flow of air.

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The air flows from space which is at a higher pressure to a space that is at the lower pressure.

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That's a very simple physical principle that you cannot break.

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The air will always fly in the direction from higher pressure to lower pressure.

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So if your staircase is at a higher pressure and the smoke is a fluid, it cannot ignore this principle and it cannot enter the staircase.

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Simple as that.

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If a pressure difference is present, the staircase seems safe, and here I need to put this in.

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That's a theoretical thing.

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However, in practice, the staircase is not at uniform, one single pressure value and it's not one unified space.

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It's a volume.

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The fluid inside is continuous, but there's a lot of things happening in the staircase.

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So if you not design it correctly, you'll not have this effect, because parts of the staircase may be at different pressure and may not provide the safety you want.

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And that's probably one of the reasons why those systems were deemed not fit in the early days, because the way how the pressurization was executed was through some steady state volumetric flow pushed into the staircase with some, perhaps mechanical dampers that would release too much of the pressure, the excess pressure, and those systems would sometimes fail.

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They would fail due to weather, due to static effect.

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They would fail due to their mechanical or electrical reliability.

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They would fail due to failures of establishing good fire safety strategy.

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They could fail because too many doors were opened, and that's a common thing when the firefighters enter the scene, they have to open some doors to take their hoses through it and there's a dynamic process of evacuation and rescue happening in the building.

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You cannot expect that people will seal down the staircase because the mighty pressurization has to work.

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So there are reasons for those systems to fail and, what's interesting, the new developments that we have in the space of pressurization systems.

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So we have the fundamentals sorted.

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We want the pressure difference between space A versus space B.

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We understand how to create this pressure difference.

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We understand the flows through the openings.

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Now we are developing systems that reduce those downsides, that reduce the risk of the over-pressurization or the risk of not having sufficient amount of air in the staircase, that allow us to combat the stack effect, that allow us to control what's happening in the staircase when there's five-heightest movement inside.

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These are the new generation, I would call them, of systems that we employ, and the better those systems get, the more trust to using them in our projects we have.

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Actually, I have a lot of trust to those systems in my projects, but that goes back to me being a fire testing laboratory which actually tests their systems, and I've tested a lot of them and, yeah, I've built my confidence, which I will be sharing with you shortly Now.

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I briefly mentioned the types of the system, so the old systems and the new systems.

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So let me put a maybe more precise distinction between what I would consider the previous generation of systems and what I would consider the new generation of systems.

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So the old type of systems is basically a fan that's plugged into your staircase, a mechanical fan that blows a lot of air into your staircase.

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The amount of air depends on how many doors you would like to have open when the pressurization system operates.

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So you have some sort of idea about how much air you need to push through all the open doors in the staircase so that the smoke doesn't go in through open doors when people evacuate, when firefighters respond.

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This gives you the base idea of the volumetric flow that you need for this project.

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Now, because the system also has to operate when the doors are closed.

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The system has no idea whether the doors are open or closed.

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It will pump the same amount of air when the doors are closed.

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Now, in this scenario, the only flow path through the staircase is through its leakages.

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Every building has leakages, every compartment has leakages, staircases have leakages, and a lot of them actually.

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But the flows through those leakages will be significantly lower than the flows that you will have through your doors, the one that you designed for.

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So in this case, you're pumping the staircase with tremendous amount of air.

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That leads to increase of the pressure that could increase technically close to the operating pressure point of your fan, which is a lot, usually probably hundreds and hundreds of pascals.

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So that's way, way, way too much for a staircase.

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Why you cannot have that?

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Because the pressure will also act on every surface in that staircase.

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That includes the leaves of the doors.

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So if you have a few hundred pascals acting on the leaf of a door and you press the door handle, two things can happen.

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If the door opens outwards, you will be hit with a tremendous force by the leaf of the door, and if the door opens inwards, you will be hit with a tremendous force by the leaf of the door, and if the door opens inwards you will simply not be able to open it at all.

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So we want people to be able to access the staircase and we don't want people to be hurt by the staircase itself.

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You cannot go too crazy with the pressure, because then you create situations in which the staircase is useless, Because then you create situations in which the staircase is useless.

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There is a sweet point at which the system must operate, which is enough to keep the smoke away, but not enough to create harm at the doors by exerting static pressure on them.

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So to control that state we actually put another device in the staircase.

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We put a relief damper.

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A relief damper in this case is basically a hatch on some sort of spring and it's mounted in such a way that if there is a pressure exceeding, let's say, 30, 50, 80 pascal whatever you set the value to, the hatch is going to open and it's going to release the excess air from the staircase.

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And when the pressure goes down again below some specific threshold value, then the hatch will close and you will keep the high pressure in your staircase.

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And this hatch, this relief valve, will help regulate the pressure inside the staircase.

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This relief valve will help regulate the pressure inside the staircase.

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Now this sounds, let's say, to some extent reliable or smart, but this brings a lot of challenges into the design, Because if you have a very tall building, the pressure at the hatch and the pressure at your doors 10 floors lower will be completely different pressures due to the hydrostatic pressure, due to stack effect, whatever else.

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There is a lot of phenomena that affect it.

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So the fact that you have 30, 50, 80 Pascal at your valve does not guarantee you that you will have this value of pressure along your staircase, and this makes the design very challenging.

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This is why, in many countries, you would have to cut the staircase into multiple smaller staircases that connect to each other at some transition floors to not exceed a specific height, because you simply cannot maintain correct pressure when you have just one relief and one inlet to your staircase.

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Now the other system, the new generation of the systems, as I would call them, are systems which are controlled through some sort of fire automation.

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In this case, you would have a fan that supplies air to the staircase again, but you would not usually have relief damper.

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Well, okay, in many modern systems you actually have the relief dampers, but that's for different reasons.

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In many modern systems you actually have the relief dampers, but that's for different reasons.

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Anyway, you would have the fan that can blow enough air to your staircase to make sure that the flow through your openings is established.

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But also, at different levels of your building you will measure the pressure difference between your staircase and the space that you are protecting.

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Now, why do we measure pressure?

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If you design the system to maintain, let's say, 50 pascal, 80 pascal pressure difference and you know that the fire is at the 17th floor, you tap into the measurement system of the 17th floor and you know that at this particular time the pressure is, let's say, 20 Pascal.

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So the fan ramps up until it reaches a value of 50, let's say that's your design value and at this level the flow is cut off, it's blocked.

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So you only deliver this much air to provide 50 Pascal at this particular part of your building.

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That's the beauty of the system it knows where it's delivering the air, it knows where the pressure difference is required and delivers this much air that is needed for that part of the building to be at correct pressure.

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Now someone opens the door to the staircase, releases the air from the staircase into another space, which means the pressure dramatically drops down.

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You release the air, so you release the pressure as well, and the pressure sensor again picks this up, that there's a drop in the pressure, which means the fan is ramped up, usually to its maximum power, at which the fan achieves some sort of flow condition at the doors and stays at that, that providing that flow through the doors.

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Then the doors close, pressure starts to ramp up again in your staircase and when it reaches, let's say, those 50 pascals, another signal is issued to the fan to lower the flow and establish new baseline conditions in the staircase.

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And this happens continuously every time someone opens the door, any time a pressure changes in the building and it.

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This happens continuously every time someone opens the door, any time a pressure changes in the building, and it happens in quite a dynamic manner.

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So this type of system actually responds to the state at which the doors and the staircase is in your building and provides the optimum parameters of the pressure and flow for that particular point of time.

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So I've promised you some fundamental physics that will help you design those systems and understand those systems better.

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So let's talk about what physics says about those parameters of pressure and flow that are the optimum for the different points in time that the system has to operate.

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The most fundamental thing is that you have two states of operation One, when the staircase is to some extent sealed, when most of the doors or all of the doors are closed and you have this maximum pressure difference that you can create in that space.

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And the state number two when the doors to the compartment where the fire is present are open.

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So there's a potentially direct flow path from the compartment to your staircase, and in this case you obviously cannot do 50 Pascal difference.

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You have to do some difference and you create this difference through exerting the flow through that opening.

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Two most fundamental states for the pressurization systems that we need to understand and pretty much the same physical phenomenon that drives them.

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That is again the pressure difference between the staircase or space that's pressurized versus space that is non-pressurized.

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But why does that make sense?

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So, first of all, when there's an orifice, an opening in a wall between two spaces, at different pressures, a flow will establish through that orifice and that flow is directly related to the pressure difference.

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So we have those two types of pressures that we talk about in fluid dynamics the static pressure, which is basically the force that the fluid exerts on the surfaces, and a dynamic pressure, that's the pressure related to the flow.

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You could simplify it to how much force there is within the flow itself.

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So when there's an opening, the pressure, the force that was acting on the wall is now acting on the opening and creating a flow with the force that you would act on your wall, flow with the force that you would act on your wall.

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Pretty much the formula is very easy.

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So the dynamic pressure is half of the density times the velocity squared.

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So that's a very easy formula.

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You can memorize it and it's very useful.

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And if you want to know the velocity, that's the square root of two pressures divided by the density.

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Very easy formula again.

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And this relation between static and dynamic pressure at an orifice, at an opening, is what tells you how fast the fluid will flow through an opening.

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So how does this relate to the state of doors closed and states of doors open?

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In one you have no opening.

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In the other you have opening, but in fact, in both cases you have openings.

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It's just that when the doors are closed your openings are extremely small.

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That are all of your leakages.

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The leakages can be through narrow gaps at fitting the doors.

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They can be at imperfections in the structure of the staircase.

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They can even be through porous medium.

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Most of the building materials are porous to some extent, even concrete.

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So you would have some losses not very much losses, but some losses through those spaces.

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And when you have something like a gap between the doors and the floor, you'll have a flow that's got quite significant velocity in that gap.

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That comes out of this pressure difference that you have in the staircase.

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So no matter if your doors are closed or opened, the same phenomena are playing a role.

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It's just at different times the scale of that flow is different.

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When you have doors open, that's obviously a completely different flow than when you have a small orifice or a small gap in the joint between the doors and the staircase.

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Now, that's the the staircase side.

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Let's discuss the compartment side, because you have to have the pressure difference between the staircase and the compartment.

00:23:15.605 --> 00:23:29.413
So let's brainstorm how much the pressure can rise in the compartment, and that's's a different story If you have a very airtight building and that was a trend at least in European Union some years ago.

00:23:29.413 --> 00:23:36.222
Now I think we're also working with passive housing with some heat exchangers that actually seals the building quite well.

00:23:36.222 --> 00:23:44.510
So you could expect in a very tight building you could expect a very significant pressure rise during a fire.

00:23:44.510 --> 00:23:50.472
I think my colleagues from VTT in Finland measured even 1800 pascal difference.

00:23:50.472 --> 00:23:58.814
I think they came to a number I cannot cross-reference it from my head right now, but I remember a really absurdly high number.

00:23:58.814 --> 00:24:03.028
But that's a very, very sealed compartment.

00:24:03.028 --> 00:24:11.273
If you open your doors to your corridor you've created some leakages and obviously this value will be much lower.

00:24:11.273 --> 00:24:17.292
Anyway, if you have a tight compartment you can expect the pressure rise to be quite high.

00:24:17.800 --> 00:24:25.458
I would say 20-25 Pascal in a fire would be something you could actually expect between compartments in normal conditions.

00:24:25.458 --> 00:24:36.887
If your windows fall off, if the fire is fully developed probably that's the value you could also be looking at from just the temperature expansion of gases, but perhaps not much higher than that.

00:24:36.887 --> 00:24:43.973
So 20, 25 pascal, that's the overpressure you could expect in your compartment.

00:24:43.973 --> 00:24:46.368
Of course there could be additional effects to that.

00:24:46.368 --> 00:25:01.471
You could have wind acting on the facade at which your compartment is, and then some of the dynamic pressure from the wind will transition into flows inside of your building and that could add to the pressure increase of the fire.

00:25:01.471 --> 00:25:03.207
So that's a challenging aspect for sure.

00:25:03.207 --> 00:25:08.932
But in general you're looking at a few dozens of pascals maximum on the fire side.

00:25:08.932 --> 00:25:18.734
So on the staircase side you probably would design for values that would be somewhere between 20 and 80 pascal.

00:25:18.734 --> 00:25:21.468
Depends on which standard, depends on which approach you go.

00:25:21.468 --> 00:25:22.854
The sweet number some time ago in Europe was the 50 pascal.

00:25:22.854 --> 00:25:24.097
Depends on which standard, depends on which approach you go.

00:25:24.097 --> 00:25:26.807
The sweet number some time ago in europe was the 50 pascal.

00:25:26.807 --> 00:25:48.810
I personally prefer systems that are designed for 30 pascal because that lowers some of the dynamic effects, but anything between 20 and 80 usually would be sufficient to provide you safety for your space, given you of course have a way to establish the flow path from your air supply, which is another thing we'll be talking in a second.

00:25:49.432 --> 00:26:05.034
One more thing that I wanted to cover is that when you understand how static pressure and dynamic pressure interact, you start to understand that flow and pressure on your opening are pretty much the same thing.

00:26:05.034 --> 00:26:16.209
One is so directly linked to another that it's just a measure of a phenomenon and they're kind of inter-exchangeable and that creates a very interesting dynamic.

00:26:16.209 --> 00:26:32.872
So if you open your doors and you have one meter per second flow in that door, that pressure difference is definitely less than a pascal, perhaps two pascal, because then when you have those flows through large openings you will also have some effects of the aerodynamic discharge coefficients.

00:26:32.872 --> 00:26:36.686
So it's not a direct correlation but roughly few pascals.

00:26:36.686 --> 00:26:42.664
If the flow is 10 meters per second it means that there's more than 50 pascal at the other side of the door.

00:26:42.664 --> 00:26:47.512
So the flow and pressure are interchangeable things.

00:26:47.653 --> 00:26:50.644
And sometime ago we had this funny thing in a European standard.

00:26:50.644 --> 00:27:04.865
You had the requirement that you provide two meters per second at your doors, which roughly corresponds to something like two and a half Pascal, maybe five at best if you include all the orifice effects into that.

00:27:04.865 --> 00:27:09.781
And at the same time you were supposed to maintain 10 pascal in the staircase.

00:27:09.781 --> 00:27:17.953
So how ridiculous is that you're being told to maintain two meters per second and 10 pascal at the same time, which is technically impossible.

00:27:17.953 --> 00:27:20.323
You cannot have two meters per second at 10 pascal.

00:27:20.323 --> 00:27:24.105
10 pas Pascal will give you so much more velocity in your doorway.

00:27:24.105 --> 00:27:29.885
That was a funny thing and it just shown that someone did not completely understand physics.

00:27:29.885 --> 00:27:32.154
They had some good reasons to provide that.

00:27:32.154 --> 00:27:37.929
They wanted to have some residual pressure difference at the staircase to protect it at different levels.

00:27:37.929 --> 00:27:47.409
But they created the requirement that that's physically impossible to meet, to have two meters per second and 10 Pascal at the same time.

00:27:47.940 --> 00:27:50.650
Now one more thing about flow establishing through doorway.

00:27:50.650 --> 00:28:02.512
If you have a very small pressure difference between the both sides of the doors, let's say a few Pascal, it's very hard to make the doors act as a uniform, let's say boundary condition.

00:28:02.512 --> 00:28:07.813
It's very hard to create a uniform flow through such a big opening, especially at low velocities.

00:28:07.813 --> 00:28:22.152
So it is technically possible that you have a higher pressure on the left side of the door ceiling, the ceiling jet.

00:28:22.152 --> 00:28:28.057
You can realize that in a ceiling jet, locally the pressure can be a little bit higher because of the velocity of the ceiling jet.

00:28:28.057 --> 00:28:51.936
Again, that's a dynamic pressure, right, the velocity of the jet on the doorway, which means that even though on averages you have more pressure on the staircase side and less pressure on the compartment side in the ceiling jet where you have smoke, you could technically penetrate that staircase and introduce smoke to the staircase.

00:28:51.936 --> 00:28:56.930
It's quite challenging, and this is why controlling the flow path is critical.

00:28:56.930 --> 00:28:58.799
So, yeah, maybe let's move to that.

00:28:59.240 --> 00:29:01.364
What do I mean by controlling the flow path?

00:29:01.364 --> 00:29:23.402
So if you supply air to your staircase and you expect that air to flow from the fan to your staircase, then through the doors, into some sort of corridor, and you want to be 100% certain that this is the direction of flow on every single opening along the way, what happens with the air at the end?

00:29:23.402 --> 00:29:24.708
Where does it go?

00:29:24.708 --> 00:29:28.521
You cannot just pump it indefinitely, because you're just going to increase the pressure.

00:29:28.521 --> 00:29:30.826
If you pump it, it has to go somewhere.

00:29:30.826 --> 00:29:53.970
And if there's no relief, if there's no opening at the end, if I am pumping this air to a completely airtight volume in which a fire is actually happening, what I'm ending up is over-pressurizing that space, creating even pressure between the staircase and the compartment that I'm trying to protect, and I don't have any pressure difference anymore.

00:29:53.970 --> 00:29:55.019
I don't have any protection anymore.

00:29:55.019 --> 00:30:12.682
So I need to be sure, absolutely sure, that when the air goes into the final place where I want it to be, which is usually the corridor, it has a way out, and we establish that through smoke extraction in that space.

00:30:12.682 --> 00:30:16.871
You can establish that through some relief openings in that space.

00:30:16.871 --> 00:30:30.276
You can establish it and that's perhaps the least reliable but still works through opening windows in that space, maybe even windows in compartments that are in fire, just to enforce a specific pathway that you have.

00:30:30.920 --> 00:30:41.789
The best strategy from my point of view is to have the pressurization be designed as a part of the smoke control solution in your compartment.

00:30:41.789 --> 00:30:57.083
So you have a corridor, you have extraction from that corridor, you extract, let's say, five cubic meters per second of air from that volume and you would want some amount of that smoke that you extract to come from your pressurization system.

00:30:57.083 --> 00:31:05.640
So you can build additional sets of dampers that will transfer the air from the staircase to the corridor when your doors are closed.

00:31:05.640 --> 00:31:28.642
There are some even very fancy solutions that automatically will decide where the air goes Does it go to the staircase, Does it go to the compartment, and what relation goes where, to maintain the correct pressure difference and to make sure that sufficient amount of air is getting into your smoke control system, because your smoke control system also relies on the fact that you have air supply.

00:31:28.642 --> 00:31:38.395
If you don't have sufficient air supply, you're going to under-pressurize the compartment and create an even larger pressure difference between the staircase and your corridor, which is not good either.

00:31:38.395 --> 00:31:45.278
So you need to design the system as a part of the complete smoke control strategy in your building.

00:31:45.278 --> 00:31:46.301
That's the only way.

00:31:46.869 --> 00:32:08.211
I actually have a book chapter in a handbook of autonomous system by Nasser, Like four years ago we've published that and in that book chapter we go in depth into those strategies that allow you establishing this flow path accurately, that make sure that you have control over where the air is going and how those different solutions play.

00:32:08.211 --> 00:32:12.720
So that's a very detailed description of how those systems operate.

00:32:12.720 --> 00:32:26.455
I'm going to drop the link in the show notes and if you have challenges accessing that, drop me an email and I'll send you my authoscopy and you can read about that, because that's a little bit higher level considerations than this podcast episode.

00:32:26.455 --> 00:32:34.321
I want this podcast episode to be a baseline for everyone and if you want to know more, there are more detailed resources than you can access to.

00:32:34.321 --> 00:32:51.579
But basically, the important thing is when you supply air to your staircase, where you supply air to some part of your building, you need to know where that air will go and you need to assure that this air will be extracted at the space, because only then you can establish a flow path.

00:32:51.579 --> 00:32:59.483
And if you establish a flow path, a beautiful thing happens you will not have smoke even come remotely close to your staircase.

00:32:59.483 --> 00:33:05.002
Maybe some smoke, but definitely not a ceiling jet that could even penetrate the staircase.

00:33:05.002 --> 00:33:15.659
You are creating a very robust, resilient strategy for your building by establishing a flow path that makes sure that the danger is far away from spaces that you want to protect.

00:33:15.659 --> 00:33:22.930
That's much more value than just creating a pressure difference between the staircase and the space that is under fire.

00:33:23.490 --> 00:33:37.973
Now there is one more thing, and that's perhaps the secret about why systems in Poland work so well and why a lot of systems around the world are deemed not working and perhaps a threat to life.

00:33:37.973 --> 00:33:39.478
So the pressure is rising.

00:33:39.478 --> 00:33:40.160
What's the secret?

00:33:40.160 --> 00:33:40.740
What's the secret?

00:33:40.740 --> 00:33:42.653
Is it some sort of Polish magic?

00:33:42.653 --> 00:33:44.777
No, it's the lobby.

00:33:44.777 --> 00:33:52.395
The lobby is the secret Lobby or vestibule or whatever you call the small room that connects your staircase to your corridors.

00:33:52.395 --> 00:33:55.903
If you pressurize that little space, you win.

00:33:55.903 --> 00:34:12.121
So you can create a robust strategy that relies purely on pressurizing the staircase, creating a flow path to your corridor, extracting smoke from your corridor yes, that can work, and that can work actually quite well.

00:34:12.121 --> 00:34:28.704
But if you add an additional element to this strategy, which is an additional small space between your staircase and your corridor, the lobby, and you pressurize this space with a separate system, you create such a resilient machine.

00:34:29.570 --> 00:34:33.161
It's unbelievable how difficult it is to break that system.

00:34:33.161 --> 00:34:37.581
So many things would have to go wrong to have smoke penetrate your staircase.

00:34:37.581 --> 00:34:38.889
It's almost impossible.

00:34:38.889 --> 00:34:45.503
You'd have to have a massive, massive, total failure of the automation systems in your buildings to fail this resilient strategy for the automation systems in your buildings to fail this resilient strategy.

00:34:46.610 --> 00:34:47.231
And what's best?

00:34:47.231 --> 00:34:54.264
When you pressurize the lobby, the scale of the system that is required because you have a very tiny space.

00:34:54.264 --> 00:34:57.619
In Poland that would be 1.4 meters squared.

00:34:57.619 --> 00:34:59.315
That's not a very big space.

00:34:59.315 --> 00:35:01.217
It's barely enough to open the doors inside.

00:35:01.217 --> 00:35:10.019
So you need a very little amount of air to create overpressure in that space and you can design it for, let's say, one meter per second on your doors.

00:35:10.019 --> 00:35:15.463
So in the end you're pushing maybe two and a half cubic meters of air into that space.

00:35:15.463 --> 00:35:17.577
It requires a very small shaft.

00:35:18.250 --> 00:35:41.445
Okay, there are some challenges with the transfer of the air, but you can create that lobby in a way that it acts as your main air inlet for your smoke extraction system and you have all pieces of your smoke control strategy in place in such a way that the smoke is extracted from your corridor and the staircase is absolutely protected from any hazard.

00:35:41.445 --> 00:35:50.336
I've done studies and simulations in which we would even turn off the staircase pressurization system and just rely on the lobby, and it worked.

00:35:50.336 --> 00:35:52.001
That's how resilient it is.

00:35:52.001 --> 00:35:56.940
So if you want to win, you add the lobby to your system and it becomes beautiful.

00:35:56.940 --> 00:36:03.206
Of course, you need to have a gradual pressure difference between your staircase, lobby and the corridor.

00:36:03.206 --> 00:36:19.208
We would usually design it such that in the staircase I have 50 pascal overpressure, in my lobby I have 45, and then there's the compartment to which we blow the air and from which we extract the smoke, which is the corridor, and that's like, let's say, zero.

00:36:19.208 --> 00:36:23.442
Because we're talking about the pressure differences between the corridor, lobby and the staircase.

00:36:23.730 --> 00:36:25.860
It also requires you some more automation.

00:36:25.860 --> 00:36:31.358
You need to measure the pressure difference between the lobby and the corridor, between the lobby and the staircase.

00:36:31.358 --> 00:36:38.929
It also requires quite a spectacular active system to control the amount of air you push into the lobby.

00:36:38.929 --> 00:36:44.530
It's such a small space, it responds almost immediately to any air that goes into that space.

00:36:44.530 --> 00:36:51.818
So you have to have a system that can control the amount of air versus the pressure gain extremely fast.

00:36:51.818 --> 00:36:57.795
Actually, in the standards that we test for that response has to be shorter than three seconds.

00:36:57.795 --> 00:37:02.472
It's really almost immediate response to opening or closing the doors to your lobby.

00:37:02.472 --> 00:37:05.057
But there are systems that have that.

00:37:05.057 --> 00:37:14.443
There are systems that exist that provide this capability and create this beautiful, super safe strategy for your pressurization systems.

00:37:15.090 --> 00:37:20.282
So I have many more things on my list, so let's briefly talk about the stack effect.

00:37:20.282 --> 00:37:25.601
So one thing that we've always battled with pressurization systems is the stack effect.

00:37:25.601 --> 00:37:30.795
Always battled with with pressurization systems is the stack effect.

00:37:30.795 --> 00:37:34.804
That stack effect is basically you have this hydrostatic pressure in any body fluid, which is the atmosphere of the earth.

00:37:34.804 --> 00:37:42.032
So with every meter you have additional kilograms of air that put pressure on the surface at the bottom.

00:37:42.032 --> 00:37:48.014
The higher the stack, the more the pressure you have, which also means the higher you get, the less pressure you have.

00:37:48.876 --> 00:37:51.922
Now the pressure is also dependent on the temperature.

00:37:51.922 --> 00:38:06.364
So if you have minus 20 degrees outside and plus 20 degrees Celsius inside, there is actually quite a significant density difference between the exterior of the building, the air outside of your building and the air inside of your building the gravity is the same.

00:38:06.364 --> 00:38:08.974
The height of the building, the air outside of your building and the air inside of your building the gravity is the same.

00:38:08.974 --> 00:38:28.003
The height is the same because it's building height, but the densities are completely different, which means in winter the air outside would weigh more than the air inside of the compartment, which means the hot air inside, when you establish a flow flow path, will fly up like a hot balloon.

00:38:28.003 --> 00:38:30.597
In the summer, that would be reversed.

00:38:30.597 --> 00:38:36.282
However, it's usually more profound in the winter and in countries in which the winter is strong, such as Poland.

00:38:36.282 --> 00:38:40.701
So this stack effect can be actually overwhelmingly powerful.

00:38:40.701 --> 00:38:44.159
It can create hundreds of pascal of pressure on its own.

00:38:44.159 --> 00:38:45.976
So we have to combat it.

00:38:45.976 --> 00:38:46.592
Now.

00:38:46.652 --> 00:39:01.324
The way, how you can battle it and this is something that was invented in Poland, and I had an episode with Grzegorz Sypek on this before in the podcast is that you can create an extraction point at the end of your staircase.

00:39:01.324 --> 00:39:09.134
So your system is not only mechanically supporting air, but it's also mechanically extracting air from your staircase.

00:39:09.134 --> 00:39:11.384
You can release it with natural means.

00:39:11.384 --> 00:39:13.893
You can release it with pressure relief dampers as well.

00:39:13.893 --> 00:39:22.681
The point is that you release air so that this additional pressure increase that would come from the stack effect is neutralized.

00:39:22.681 --> 00:39:37.802
The technical, the scientific explanation for that is that it's compensated by the resistance of your staircase acting as a duct, so you basically create a flow that counter affects the stack and it actually works brilliantly.

00:39:38.224 --> 00:39:46.672
We have measurements from 200 meter tall buildings in Poland with continuous staircases which show that this stack effect could be countermeasured with this solution.

00:39:46.672 --> 00:40:11.356
I've myself done CFD for the tallest skyscraper in European Union, the Varso Tower in here, which had, I believe, 240 meters of continuous staircase, something like that, with six independent systems for pressurization at that staircase, working at unison to provide the pressurization of that monstrous, at unison to provide the pressurization of that monstrous, monstrous staircase, and we succeeded.

00:40:11.356 --> 00:40:13.742
Yeah, it's quite a successful system.

00:40:13.742 --> 00:40:14.242
It works.

00:40:14.242 --> 00:40:18.559
It worked brilliantly in the simulations and we've commissioned it.

00:40:18.559 --> 00:40:21.112
It worked brilliantly on the building as well.

00:40:21.112 --> 00:40:23.918
So it's not that I only based this on cfd.

00:40:23.918 --> 00:40:33.101
We we also measured that on a real building afterwards and we've done that for I don't know a dozen skyscrapers in Poland from 100 to 200 meters tall.

00:40:33.101 --> 00:40:41.114
In each of them we've managed to countermeasure the stack effect and have a really well-working solution provided for those buildings.

00:40:41.114 --> 00:40:46.090
Again, stack effect is a little bit higher complexity than this podcast episode.

00:40:46.090 --> 00:40:55.682
If you want to learn more, there's the episode with Grzegorz Supek and there's the book chapter that I wrote where I go much more in-depth into the problem and the solution.

00:40:56.170 --> 00:41:00.829
The final thing that I wanted to talk about in this podcast episode is the assurance.

00:41:00.829 --> 00:41:03.760
I just had an episode with Abishek on assurance.

00:41:03.760 --> 00:41:08.961
So how are we sure that the systems delivered to the buildings are the ones that we expect them to be?

00:41:08.961 --> 00:41:12.699
And for pressurization we have standards in Europe.

00:41:12.699 --> 00:41:15.818
That's EN 12101, Part 6 and 13.

00:41:15.818 --> 00:41:26.130
Part 6 defines how do we test the systems and since that was a project many, many years ago, we've built a rig following the project of that standard.

00:41:26.130 --> 00:41:31.902
And yeah, we've tested at least 10 different pressurization systems in my laboratory.

00:41:31.902 --> 00:41:37.900
I was personally involved in doing those tests, so I'm pretty sure that the systems work.

00:41:37.900 --> 00:41:42.161
I give you my guarantee by the means of the technical reports I've issued.

00:41:42.610 --> 00:41:48.362
Anyway, the test rig is a 100 cubic meter volume that's connected with a smaller volume.

00:41:48.362 --> 00:41:54.880
Between them we have some fast dampers that open and the big room simulates the staircase.

00:41:54.880 --> 00:41:57.239
The smaller room simulates the corridor.

00:41:57.239 --> 00:42:02.342
We open and close a fast damper between them to simulate the door openings.

00:42:02.342 --> 00:42:06.742
So basically we run the system as it would operate on a building.

00:42:06.742 --> 00:42:12.523
We very quickly open the damper so the system has to establish this flow path, establish high volume.

00:42:12.523 --> 00:42:16.780
Then we rapidly close the damper so the system has to go back to 50 pascal.

00:42:16.780 --> 00:42:19.978
We call that a dynamic behavior cycle, DBC.

00:42:19.978 --> 00:42:24.300
That's one test six seconds of maintained pressure.

00:42:24.300 --> 00:42:28.492
Then we open the damper, six seconds of flow, then we close the damper.

00:42:28.492 --> 00:42:38.452
Then that's one dBc cycle and within those cycles we measure how quick the system responds to the change, to the change in the state of the damper, which has to be faster than three seconds.

00:42:38.452 --> 00:42:42.802
We also repeat this test 10,000 times.

00:42:42.802 --> 00:42:46.976
10,000 times that's 44 hours of continuous operation of the rig.

00:42:47.639 --> 00:42:50.355
This is the reliability test and durability test.

00:42:50.355 --> 00:42:55.751
You need to make sure that the system can operate and operate and operate and will not break.

00:42:55.751 --> 00:42:58.318
So that's what's being tested at the rig.

00:42:58.318 --> 00:43:00.422
We also test oscillatory behavior.

00:43:00.422 --> 00:43:05.197
So we open the damper in consecutive open-close, open-close cycles.

00:43:05.197 --> 00:43:10.704
Sometimes some systems with faulty automatic will die on this test.

00:43:10.704 --> 00:43:19.936
So we make sure the system doesn't get into oscillations and we do this test for the largest for the smallest pressurization system offered by a vendor.

00:43:20.329 --> 00:43:24.001
We tie it up to a specific set of automatics.

00:43:24.001 --> 00:43:32.097
So we tie it to a specific frequency inverter that they use the specific steering panel, specific pressure sensors.

00:43:32.097 --> 00:43:42.032
Those things have to be sourced from reliable sources and during the certification phase and factory inspections this is checked out to give them a certificate.

00:43:42.032 --> 00:43:50.300
So we know where the pieces come from and we know that the parts that are used in real buildings are exactly the same as from, and we know that the parts that are used in real buildings are exactly the same as the ones that we've tested.

00:43:50.300 --> 00:44:00.081
And, what's also interesting, we also do electromagnetic compatibility and environmental resilience tests for the electronics of the system.

00:44:00.081 --> 00:44:05.061
So the control panel, cabinets, the pressure sensor, this goes through electromagnetic tests.

00:44:05.061 --> 00:44:12.534
Maybe I should do an episode on electromagnetic compliance that could be interesting for you, because that's another of my personalities.

00:44:12.534 --> 00:44:16.030
We also have an electromagnetic lab under my supervision.

00:44:16.030 --> 00:44:20.621
So in this lab we test how the pieces of electronic work together.

00:44:20.621 --> 00:44:28.655
Do they break in specific electrical scenarios such as the surges in the electrical input line, electrostatic discharges and such on.

00:44:28.655 --> 00:44:35.076
And the environmental reliability means that you can put this on the roof of your building and it's not going to break pretty much.

00:44:35.076 --> 00:44:46.221
So it goes a very, very specific and robust set of tests before it is approved to the market and, as I said, we are doing that since 2015.

00:44:46.992 --> 00:44:50.592
I know there are only two rigs in laboratories in europe.

00:44:50.592 --> 00:44:52.456
Maybe there's more, but there's only two.

00:44:52.456 --> 00:44:55.402
I know about mine and one more in germany.

00:44:55.402 --> 00:44:59.625
I think we've done more tests, if that's that's something to brag on.

00:44:59.625 --> 00:45:12.800
I know some manufacturers would have their own rigs, but you cannot certify products on that, so there's not that many sources where you can get certified and assured products from and you can usually tie them back to my lab.

00:45:13.289 --> 00:45:15.679
We do not have accreditation for the new standard for this.

00:45:15.679 --> 00:45:21.358
This is a question I have to answer a lot because at the final end of the standard they made differences to the standard.

00:45:21.358 --> 00:45:25.621
That means my rig is not 100% compliant with the standard.

00:45:25.621 --> 00:45:32.079
They basically changed the frequency of the data sampling from 10 to 20 hertz and I have a 10 hertz system.

00:45:32.079 --> 00:45:35.496
That's the difference and it annoys the hell out of me, but it's a problem.

00:45:35.496 --> 00:45:48.322
We'll probably fix it in the future, but so far, we are providing reliable testing for our business partners, based on the Polish path to implement the things on the market through national assessment.

00:45:48.322 --> 00:45:52.340
If you are interested in that, send me an email.

00:45:52.429 --> 00:45:54.478
That's definitely not the subject for the podcast.

00:45:54.478 --> 00:46:01.596
This goes way too far into the assurance regimes, which are quite interesting, as you've learned from the previous episode with Abishek.

00:46:01.596 --> 00:46:04.880
Anyway, for this short episode, that would be it.

00:46:04.880 --> 00:46:11.802
I didn't cover everything that I wanted and I certainly did not speak in depth on many aspects of the pressurization systems.

00:46:11.802 --> 00:46:15.425
But thankfully there's another episode with Grzegorz Sypek a long time ago.

00:46:15.425 --> 00:46:30.869
Many of you have not heard about that episode so I would send you there, because Grzegorz talks more about the technicalities, about how they discovered the countermeasures for stack effect, about how to design the systems properly, about how they operate from the technical perspective.

00:46:30.869 --> 00:46:33.679
I talked more about fundamental principles in physics.

00:46:33.679 --> 00:46:36.318
Grzegorz talks more about technicalities.

00:46:36.318 --> 00:46:40.021
So it's a good companion to this podcast episode to go there.

00:46:40.471 --> 00:46:43.380
I believe that was episode 46 or 47, somewhere around there.

00:46:43.380 --> 00:46:45.378
I'll double check and put that in the show notes.

00:46:45.378 --> 00:46:48.496
And there's also the papers from myself that you can read.

00:46:48.496 --> 00:46:54.777
Send me an email if you cannot access them, because there's much more technical, specific knowledge in that paper.

00:46:54.777 --> 00:46:59.217
That will answer many of the questions you may have after this podcast episode.

00:46:59.818 --> 00:47:03.451
I hope I've empowered you to design good pressurization systems.

00:47:03.451 --> 00:47:08.603
I hope I convinced you that we can design good pressurization systems.

00:47:08.603 --> 00:47:40.534
Fundamentally, it's a brilliant strategy to provide smoke-free spaces in your buildings, and if you execute it properly, if you use good technology, if you understand what you are doing, if you understand the fundamental principles behind the system, if you create a robust, resilient air path and you add additional measures to your system that increase the resiliency of it, such as the lobby with independent pressurization, you are going to have a very safe building with very good pressurization system in it.

00:47:40.534 --> 00:47:48.967
So that would be it for today's podcast episode, and I am looking forward to meet you up here again next Wednesday.

00:47:48.967 --> 00:47:52.150
Another great 5-Centure content going your way.

00:47:52.150 --> 00:48:20.139
Cheers Bye, Thank you.

180 - Fire Fundamentals pt. 12 - Pressurization systems

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