192 - Fire Fundamentals pt. 14 - Jet fan systems for car parks

Jet-fan systems effectively control smoke in car parks by creating directed airflows that transport smoke from one point to another, similar to how longitudinal ventilation works in tunnels. These systems offer cost-effectiveness and simplicity by eliminating ductwork while providing powerful smoke management capabilities when properly designed and understood.

• Jet Fans create momentum transfer through air entrainment rather than directly moving smoke
• Two distinct operational modes exist: smoke clearance (reducing thermal stress) and smoke control (maintaining clear firefighter access)
• Systems require careful balancing of extraction capacity with Jet Fan thrust force
• Optimal design typically requires CFD modeling followed by hot smoke testing for verification
• Jet Fan activation timing presents challenges for evacuation - usually delayed until occupants exit
• Systems excel in tunnel-like geometries but struggle with complex layouts (the "Tetris rule")
• Particularly effective against heavier-than-air gases like LPG or EV battery fire emissions
• European standards now available through EN 12101 family for design guidance

If you need design assistance with Jet Fan systems for your projects, email me directly at w.wegrzynski@itb.pl. 

Further reading:

- Jet-Fan Systems in Car Parks Design Methods: an Overview and Assessment of Performance

- Our in-depth multiparametric study on car park ventilation

- A. Król and M. Król, Study on numerical modeling of jet fans

- Thunderhead's guide to modelling jet-fans in FDS

Thank you to the SFPE for recognizing me with the 2025 SFPE Fire Safety Engineering Award! Huge thanks to YOU for being a part of this, and big thanks to the OFR for supporting me over the years.

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The Fire Science Show is produced by the Fire Science Media in collaboration with OFR Consultants. Thank you to the podcast sponsor for their continuous support towards our mission.

Chapters

• 1:50 Introduction to JetFan Systems
• 4:08 What is a JetFan System?
• 9:27 Clearance vs. Smoke Control
• 13:15 System Components and Operation
• 20:28 Velocity Requirements and Space Impact
• 27:22 Design Challenges and Evacuation Considerations
• 34:26 CFD Modeling and Testing
• 37:53 Design Factors and Final Remarks

Transcript

Wojciech: 0:56

Hello everybody, welcome to the Fire Science Show. You know that I love exposing engineers to fire science and I like to do it otherwise as well. I love to expose my fellow fire scientists to some solid fire safety engineering concepts that go probably a little bit deeper than what's mostly thought at different universities. And some time ago I've published an episode on pressurization systems in stairwells. It was well received. A lot of people commented. It made me organize like 20 different private meetings with people, so a lot of you have enjoyed that episode.

Wojciech: 1:28

I thought let's share another piece of technology that I think in Poland is way, way, way more popular than in other parts of the world and that is the Jetfan systems in car parks. I like car parks, I like Jetfan systems. They are a big part of my professional career, even before I have became a fire scientist. First I was an engineer designing them, later I became a scientist studying them. So yeah, I've seen some car parks and I would love to share with you the experience that I've gained over the years. Jetfan systems they have mixed opinions. Some people swear by them that it's the best ventilation system you can have in a car park. I believe they are a very good solution. If you understand what you want to achieve and if you're realistic about the goals that you want to achieve and you're very mindful about what is the expected outcome of the system operation, you can have a very, very good system for very, very good money. And those who don't believe in them well, they simply don't believe in them. I don't think engineering systems are stuff that you either believe or not believe in. I think it should be discussed on engineering grounds, and this is what we're going to do in this podcast episode. So stay with me. Let's spin the intro and jump into the episode.

Wojciech: 2:46

Welcome to the Firesize Show. My name is Wojciech Wigrzyński and I will be your host. This podcast is brought to you in collaboration with Ofar Consultants, a multi-award-winning independent consultancy dedicated to addressing fire safety challenges. Established in the UK in 2016 as a startup business of two highly experienced fire engineering consultants, the business has grown phenomenally to eight offices across the country, from Edinburgh to Bath. Colleagues are on a mission to continually explore the challenges that fire creates for clients and society, applying the best research experience and diligence for effective, tailored solution. In 2025, there will be new opportunities to work with OFR. Ofr will grow its team once more and is keen to hear from industry professionals who would like to collaborate on fire safety features this year. Get in touch at ofrconsultantscom. Okay, let's go.

Wojciech: 3:51

So first question what the hell is a JetFan system? Well, it's a system that employs JetFans. Jetfan is an axial ventilator, not a very large one, that you put underneath the ceiling of your car park and it simply blows air forward. They're like those tubes that you see on the cover of the episode that you install underneath your car park ceiling to transport air through your car park and with that air you transport smoke through your car park. It's a very interesting way of operation, very similar to the operation of longitudinal systems in road tunnels. Actually, from what I've learned, the jet fans were introduced by a company, novenco, in 1990s, and one of the directors in that company, rudvan Beke, is a good friend of mine and I've spent more than a decade working with him, and I've been told a story that they just thought that perhaps the same idea of operation as you would have in a road tunnel could be actually employed in a car park. If we could blow the smoke through the car park in a way like you blow away candles on your birthday cake. Perhaps that would work. They've tried and actually it worked. They developed a solution for that called the jetfan Carpark jetfan and this has been since then a common solution used in the Netherlands.

Wojciech: 5:11

It's a very common solution in Poland. I know that those systems are used all around the world. I said mixed opinions and also legislations show that mixed opinions. In some countries it's possible to use them. In some countries it is not possible to use them. But in general, instead of extracting your smoke upwards through a layer of ducts, you simply blow smoke from one point to another and happily extract it at the end of the pathway where you are blowing at it. It's a very simple concept of operation.

Wojciech: 5:41

Now, I said those systems are popular in Poland. There's also a story behind that and it's kind of funny, like how a wrong legislation builds a market for you. So in Poland, before 2009, I believe, we had a law that said that in a car park of a specific size, you are required to have extraction point every 10 meters. This was made for duct systems. You need an extraction point every 10 meters and because jet fan systems obviously do not have ducts, you don't have extraction points. So whenever someone came and wanted to make a ductless system. They were called the ductless systems back then, the jet fan systems. You actually had to apply for a national derogation from that and to get that you had to run some CFD simulations to prove that your concept is actually working on par with the traditional system. And boy, that has built the industry in Poland. And my institute, itb, also participated in that early Russia for CFD simulations in compact systems. And well, that's kind of how we got answers fluent for our simulations.

Wojciech: 6:47

If anyone wondered how we can afford that, it was the golden era of Jetfan systems that enabled us to do that. But anyway, the Jetfan systems stoned Poland because at that time it was very expensive to build the duct systems. There were not that many approved systems, they were in general very expensive and for jet fun systems you did not need any ducts. Therefore you saved a ton of money in your buildings and usually the savings on the jet fun were sufficient to pay for the CFD, additional engineering, all the hassle, and you would still save some.

Wojciech: 7:25

Since then it has changed. The duct system also evolved. There are so many new solutions that you can use in your car products. I'm not sure if this economic argument still holds, but there are still benefits, other than economic, for use of jetfan systems. Now, as we're talking about jetfan systems, it's necessary to put it straight, like what they can do, what they cannot do, and I think this is the most fundamental problem people have with jetfans they don't understand what you can do with the system and sometimes they have wrong expectations.

Wojciech: 7:54

So in our book on designing jetfan systems in for polish market 2015, we've defined two ways of operation of the jet fan system. One we call the clearance it's inspired by the British nomenclature and one we call the smoke control. In a clearance system, what you want to achieve with your jet fan system is to remove the majority of hot gases from your car park and significantly reduce the thermal stress you impose on the structure and on the people in the car park by blowing air through the fire, through the smoke layer and removing the smoke with the air and, first and foremost, mixing all of that together. And in this clearance system, you would not care about the visibility of the fire source, so you would expect that there could be a whole smoke control compartment full with smoke. So basically, you're focused on reducing the hazards coming from the heat and after the fire, when, when the fire is extinguished, this system will will very quickly manage to clear the car park from the smoke. Hence the name smoke clearance.

Wojciech: 8:59

In smoke control it's different. It's more like longitudinal ventilation in the tunnels. So you would like to have a sharp boundary between the space in which there is smoke and space in which there is no smoke. So you'd really want to stop the smoke at the level where the fire is Like. You would create a wall of air that's impenetrable for the smoke. So always coming from the fresh air side, you would see the fire. You would create a wall of air that's impenetrable for the smoke. So always coming from the fresh air side, you would see the fire. You would, you would be able to reach it. In fact, there are some criteria defined in the new ian standard. I was also very pleased to participate in that standard writing.

Wojciech: 9:34

Shout out to the previous episode on the committees. Perhaps that made the link in my brain to do the jet fan episode, because the jet fan committee is the one I've spent the most time in. Anyway, you want to have a wall of air that's clear. The smoke is stopped, literally at a line almost, and you have an access to the fire. There are more ways you can distinguish those systems. Some of them should include for human evacuation. This is very challenging in jet fun systems and we'll come back to that in this podcast episode. Some of them are meant just as a tool to assist firefighting. Some of them are just meant as a tool to clear the car park after the fire from the smoke.

Wojciech: 10:12

So there are many ways to cut this cake and it's important that your expectations are set beforehand, especially in regards of the clearance and control, because that's going to have large differences. Now where do those differences would come? How does the smoke clearance system differ from the smoke control system? The main thing comes down to the volumetric capacity of your extraction shafts. Pretty much, I would say that's the defining factor. So how much air in the end you're capable of extracting from the car park?

Wojciech: 10:45

Obviously, for smoke control you need more air than for smoke clearance, because you care about moving all the smoke, not just most of the smoke, and the differences in velocities that you need to achieve in a car park are quite significant. Usually, for smoke control in a car park of a height of, let's say, three meters, what you would be aiming for is approximately 0.9, maybe one meter per second. That usually would be sufficient. If you have average velocity like that in the cross-section of your car park, you should be able to achieve the smoke control operation really, and that's very low velocities. If you look at tunnels, we're talking about two and a half, three and a half meter per second. Here just around one meter per second would be sufficient for smoke clearance. This velocity would be perhaps lower, maybe as low as 0.5, 0.6 meter per second. Those numbers sounds very low, but if you multiply them by the cross section of your car park, you have one meter per second. Your car park is 32 meters wide. You have three meters of height. Suddenly you have 96 cubic meters per second to remove.

Wojciech: 11:49

If you want to have an average of one meter per second in that car park, 100 cubic meters per second, that's quite a big system already. That means you need at least 10 square meters of extraction shaft in your building. You will need 10 square meters of your inlet shaft in your building. This means you just lost 20 square meters of leasable area on every floor of your building. So yeah, that's where expenses come in in the safety systems. People often think that the expensive part of your systems are the systems that you're designing, but no, really the expensive part is the space they take and the cables that you need to plug them in. Anyway, those differences in velocities going up from 0.6 to 1 meter. What will happen is that you will start removing more and more air, you will start clearing more and more of your car park and eventually you will reach that point where you have a wall of air that prevents any backfiring of the smoke, that prevents the movement of the smoke back upwind and will protect your car park a low, free path of entry.

Wojciech: 12:50

Now there's also one thing about jet systems that made them so popular in here is that in poland we had a lot of lpg powered vehicles and that's a very popular alternative fuel used in Poland for decades. And LPG is a nasty thing because if it spills in your car park from your vehicle, it's heavier than air, so it would spill along your floor. So the normal duct systems were not that effective on removing that. You would have to have separate grills closer to your floor to remove that Very challenging remove that very challenging design, very expensive design, and with jetfan systems you just mix the air through the entire cross-section of your car park. So you're very effectively. We can remove hazards like like lpg and perhaps in the age of electric vehicles we also see there are clouds forming with gases that are obviously heavier than air because they are spilling along the floor. So I would assume the operation of jet fan system would also be quite good against those, especially if you design the smoke control mode where your people would not be exposed to any smoke from the electric vehicle. Anyway, you don't need fire to benefit from that.

Wojciech: 13:57

Car parks means vehicles operating in them. That means a lot of fumes, that means a lot of gases already in the car park. So they are also great for sanitary mode operations. Very cheap, very comfortable. You need perhaps 0.2, 0.3 meter per second and you're good with those operations. So sometimes they would be run on a low energy setting just to clear the car park from the fumes from the cars.

Wojciech: 14:20

Next thing about JetVent systems that you can have different systems. You could have a system in a completely open car park like imagine hundreds of meters of car park without any walls, without any boundaries, just a set of columns and a massive building above them. We've done car parks like that. Or you could have car parks that are literally a collection of smaller compartments, few hundred square meters each, and from one compartment you go to another, to another, to another. That's a popular way to design the car parks in Belgium, for example, and in that case in a very large car park you would like to have most of the car park empty, free of smoke.

Wojciech: 14:54

With your JetFan system we would usually design the smoke control compartments with a size of up to two and a half thousand meter square, perhaps up to five thousand square meter if it's really really challenging project with a massive car park. But that comes with additional cost. So that would be our usual design for compartments in those large car parks. You'd also like to have the system reversible so it can go both directions. So you always extract to the shaft closer to the fire.

Wojciech: 15:22

And if it's really really large car park and you have to separate it into multiple smoke compartments, not always you have to put physical boundaries between them. Sometimes it's possible to create those invisible walls with just the jet fan system operation. But again that's another challenge. For smaller compartments there is a strategy where you would just transport the smoke from one compartment to another with the JetVan system. So it's also like an interesting way of operation not very popular in here.

Wojciech: 15:47

And finally, a lot will depend on your inlets and outlets. The easiest is if you have open facades and you have, like, unlimited source of air on one facade. You have unlimited extraction space on your external facade. Then you can make a really efficient, really cheap jet vent system that will beat any other smoke control way really, and they can also beat the wind quite easily. Actually, I've had an episode about open car parks with wind a year ago and we've noted that if you just have an open car park, in some wind scenarios you get very bad conditions inside the car park in fire. With JetFan systems in such an open car park I would assume 95% of scenarios you would easily beat the wind. It's something that we are currently researching so I can just tell you work-in, work in progress results, but it's looking very promising.

Wojciech: 16:36

Jetfan systems are really good enhancement for open car parks. For wind conditions in particular. If you have an enclosed car park, you need an extraction shaft. You need an air inlet shaft because you need to supply the air that you're extracting and this is when it becomes challenging. The inlets and outlets can become quite large if you need large quantities of air and you also cannot really supply air with too high velocity. So every time you think about it, if you supply air with high velocity, the air has some kinetic energy in it. Inevitably. If you supply air with 5 meters per second 10 meters per second that's a lot of kinetic energy the air will fly very, very far. And in jet-fed system we need to direct air through a very specific pathway to clear the car park from the smoke. If I have a very strong stream of air, I need to use a lot of force to push that jet stream in the place where I want it to be, and in most cases it's even impossible if you have more than five meters per second inlet. So the inlet strategy in the JetFan system will be as important as your extraction strategy.

Wojciech: 17:44

Okay, now let's go to some technicalities of JetFan systems and shortly after we'll go into scenarios, because that's perhaps the most controversial part of a jet fan system design. So for components you would have your inlet and extraction fans, that those would be a very large, usually axial fans that operate for even hundreds of cubic meters per second that provide you the air supply and extraction from your car park. They obviously need to be fire rated. It's best if they're reversible, so you can have two directions of operation of your JetFan system. In that way they are the most useful. And other way to define the JetFan systems, whether they are one directional or reversible you also need JetFans obviously. Jetfans would also be axial fans. They will also be fire rated and they are usually in Europe. They're tested according to EN 12101, part three, a very important standards that actually includes.

Wojciech: 18:39

For jet fans, they are tested within furnaces like normal fans would be. Well, not exactly like normal fans. Normal fans would have an installation connected to the furnace. You would extract this hot gases from your furnace, transfer them through your fan and that's how you would expose it to temperature. For jet fans, we simply hang them inside the furnace, we set the temperature on the oven to 400 degrees and they operate 15 minutes later, shut them down two minutes, wait, turn them on again and let's go. They have to survive the remaining time for the specific class that they are exposed to. Very nice experiment that I'm very used to. I used to be doing a lot of those now. One thing that actually I I took off my table very few of those is is the the component testing. I'm not doing those that much anymore.

Wojciech: 19:29

Um, and there will be auxiliary components in the jet fan system. Sometimes you would use some smoke curtains. They could be a part of your smoke control strategy. You of course, need to supply power to your jet fans, so you need some sort of cabinets, smoke control panels to steer the jet fans, to trigger the correct jet fans at the correct time. You would need smoke detection. Some people ask me how the hell the jet fan knows that there's a fire in the car park and it has to have a smoke detection system. You need to trigger it with something, preferably automatically. So there needs to be smoke detection. There needs to be some redundant power source, usually there, and that would be pretty much it. Those are fairly simple systems in the end.

Wojciech: 20:11

The jet fans themselves they are characterized not by flow, like normally you would think about a ventilator. You would like to quantify the ventilator by the flow that it has. In case of a jet fan, we use a different property In jet fan systems. We talk about the thrust of the jet fan. So you can calculate the thrust if you multiply the air density by the velocity in the jet fan by the volumetric capacity of the jet fan. That's an approximation of the thrust of the jet fan and for car park systems we would normally get jet fans that would be 35 newton to perhaps 55 newton for axial fans. And there are also those centrifugal fans that could have like 100, 110 newton thrust force. In comparison, jet fans used in road tunnels those would have, like I'm using, 950 newton to 1,600 newton, but I've seen on the market that there would be jet fans with 2,800 newton thrusts. And if you want a really interesting comparison, the engine of Boeing Dreamliner. There's this massive turbojet engine that powers the airplane. That one has like 100,000 newton thrust. So that's pretty far away from our little jet fans, but the same family nevertheless. Anyway, why thrust?

Wojciech: 21:29

Thrust is a very good measure because it allows you to calculate how much force you can pass to the air. In your carport, a rule of thumb you have 100 square meters of cross-section. You want to express one pascal dynamic pressure on that. You need 100 newtons. Of course that's an extreme simplification. You cannot really do engineering calculations like that, but it gives you an idea of how much force you need. There will be losses, there will be inefficiencies in how the momentum is transferred to the air.

Wojciech: 22:00

Another thing about jet fans is how do they act. A lot of people would have the misconception that the jet fan sucks the smoke at one end and releases the smoke on the other end, therefore pushing the smoke further away, and this, like it could look like that when they operate. But this is not really the fundamental principle on which they operate. The jet fans are more like your hair dryer, hand dryer or those annoying leaf blowers. The idea is that you want to push a stream of air at very high velocity into the car park that, through entrainment, exchanges momentum with the surrounding air, with air that surrounds it, and eventually you have a much bigger mass of air but a much lower velocity. So you kind of transfer the momentum from the blades in your jet fan into the air, into the jet fan, and that high velocity stream released from the jet fan transfers the momentum through the surrounding air. Now it takes a lot of space for this momentum transfer to happen. It would take, I would say, 20, 30 meters of space in front of your jet fan for this momentum to fully, fully happen. And this means that the jet, if you have a fire at one location in a car park, the jet van that really is acting on that location is not the one above the fire but the one 30 meters before the fire. That's the jet van that will create the uniform velocity distribution that you are looking for. So the jet vans operate much further than they are.

Wojciech: 23:35

It's a very wrong misconception that they operate at the location where they are hanged. You would space them so you cover most of the car park with the low velocity flow that you're creating by their operation. So they would be horizontally spaced by 8 to 12 meters. In the direction of the operation they would be spaced by 32 to 48 meters. From my experience, those are the optimal distances and if you can make a nice grid of jet fans in your rectangular car park like this, you're going to have a very good system.

Wojciech: 24:11

Well, there obviously are challenges if the geometry of your car park is complicated, especially if you have a central core of the building inside the car park. So this is a common way to design buildings. You would have a square cut in the ground and you would have a central core. So you have a square car park and those are very challenging to ventilate. With JetFan systems it takes a lot very challenging to ventilate with jet fan systems. It takes a lot of work to optimize them. Still possible, though. Now another common question that I ask, like how strong they are? How big jet fans do I need to ventilate my car park? And actually it's a design decision. You need to get those jet fans to an operational point where it's optimal for your car park. We've done those studies in the past. I'll link them in the show notes.

Wojciech: 24:56

If you actually have too many jet fans, you will observe a very interesting phenomenon you move more air than you're capable of extracting and because there's kinetic energy in that air, it has to go somewhere. So we often see that if you use too many jet fans, the air will kind of bounce back, or the smoke will kind of bounce back from the walls and will return to the place which you wanted to protect from the smoke. So actually, so not enough and too much are both very bad in jet design. If you end up like this, with air crawling back to the location of your inlets, for example, you will eventually end up with a car park that's completely overfilled with smoke. Again, if you are designing smoke clearance system, perhaps that's acceptable. If you're designing smoke control system and you really want a clear path of entry for firefighters. This is definitely not acceptable.

Wojciech: 25:45

It's a very difficult art of balancing the extraction rate and the jet fin locations, placement and numbers of jet fans that operate. That truly is something I would call an engineer's art and it's something that makes designing jet fan systems good jet fan systems really, really challenging. That's the design difference between a good and bad jet fan system One that balances the number of jet fans, the thrust with the extraction and inlet capabilities, one that balanced the number of jet fans, the thrust with the extraction and inlet capabilities. And the other one would just randomly pick a number of extraction inlet, drop some jet fans. That's usually not a good design. Now let's move to the scenario of operation, because that's the source of some controversy around the jet fan systems.

Wojciech: 26:28

As I told at the beginning of the episode, you can have them to help you with evacuation, you can have them to help you with firefighting and boy, this is a challenging thing. So if you operate jet fans, they will transfer the air through the entire cross section of your car park. That's how they work. That's how they are supposed to work. That's the effect that you are looking for. Actually, that's the reason why you are designing your ventilators in the car park you want to transport the gases and air through the entire cross-section of your car park. Now, if you do that, inevitably the smoke will fill the entire height of the car park, from the very bottom of the car park to the very ceiling of the car park. You will be transporting smoke through the entirety of the cross-section of your car car park. That's how you wanted it to be.

Wojciech: 27:15

If you have people in that layer, they will lose visibility and it will be very challenging for them to evacuate. They would probably not be exposed to high temperatures, which would be lethal, um, for toxic gas concentrations. Uh, depends on the source, really, but visibility is something you will 99% lose. There's almost no way to maintain visibility in a layer of smoke behind the source of the fire in the jet fan system. Therefore, if you want to evacuate people from the car park, usually you'd need to delay the operation of the jet fans for the time it takes people to evacuate.

Wojciech: 27:53

Luckily, car parks are fairly easy to evacuate. They're usually because of the way, the reason we build car parks they have to be convenient to leave your vehicle and go away. They have ample exit spaces usually and the evacuation there would not be that many people inside the car park. They would hopefully not be sleeping, so there's good chances. The evacuation can be fairly swift in the car park. They would hopefully not be sleeping, so there's good chances. The evacuation can be fairly swift in the car park and from my experience it usually ends within four or five minutes. That's pretty much the max we get in most of the car parks, but for that time you probably should not operate your jet fans. And that's the controversy, that there's a safety system that you want to remain silent, not operating in the early phase of fire.

Wojciech: 28:39

What does happen with the smoke then? Well, it forms a buoyant layer underneath the ceiling of your car park and it spreads around. Is it bad? Depends on the height of the car park. If your car park is high enough, you have enough volume in your smoke reservoir in that car park for the smoke to spread for even minutes. The biggest car park we've ever done had like 10,000 square meters compartment and we were releasing smoke for like seven, eight minutes into that car park and you could see a hundred meters away the buoyant layer of the smoke. So it's real, it's not imaginary. The buoyant layer. You see that in CFD. You see that in hot smoke tests it really works like that.

Wojciech: 29:22

It is possible to delay operation of jet fans and provide for this evacuation. Not in all cases this is the most optimal. There may be cases in which it's actually better to operate the jet fans early and risk exposing people to smoke. This is a difficult design decision and it has to be taken in accordance with your local country jurisdiction. Usually the country and the fire department will dictate to you whether you can delay them or not.

Wojciech: 29:50

Another controversy is whether they should operate before sprinklers, after sprinklers. That's really a challenge and a pain. Sometimes we have to delay the operation of jet fans based on the sprinkler operation to not interfere with the sprinklers. However, I've done a part of the research a few years ago where I was looking into how much jet fans disturb the sprinkler operation and unless you have sprinklers directly in the airstream of the jet fan, they were not influenced that much actually. So if you coordinate the designs very well, you don't put sprinklers in the literally axis of your jet fan operations. There should not be that much negative interference between the devices, so sprinklers should not affect the jet fans. Jet fans should not affect the sprinklers. Um, if you cannot delay them, jet fans should not affect the sprinklers.

Wojciech: 30:37

If you cannot delay them that much, what can you do? There are some intermediate solutions so, for example, you can start your inlets and extraction shafts without starting the jet fans. This should give a very gentle push to the air in the car park. So you will start moving the air a little bit, perhaps not with the full velocity that you want. But also, we dimensioned the system for a full-size vehicle fire. We've discussed them with Zahir a few weeks ago. That would be multiple megawatts. In the early phase you will have just hundreds of kilowatts of the fire. So perhaps you don't need that much air to obtain the effects that you're looking for. Therefore, enabling the extraction and inlets for a very low velocity may be very beneficial. Another thing that you can do and we all sometimes observe this in car parks when you start the Jetfire systems, you immediately lose the visibility, like in split second in the entire car park, and to lessen that effect, you can start them sequentially, like from the furthest to the closest, and just add some delay between the time you operate the the next group of jet fans and for your inlets and extraction funds. You can put a long ramp up functions on your control panels so you can say the fan should start from zero to maximum capacity gently for like two minutes, and this usually really softens the blow and prolongs this evacuation time, improves the conditions. It's a very good operational strategy for the jet fans and of course there will be I've said that before with the square car parks.

Wojciech: 32:12

There are some challenging configurations of buildings in which designing the car park is with jet fan system is really hard. The easiest is when the car park reassembles a tunnel. If it's narrow, if it's long, it's perfect for jet fans. The more complicated the geometry is, then you probably will have a harder time designing jet fan systems. If you have like a labyrinth of compartments, it's going to be very, very difficult or almost impossible to time designing jet fan systems. If you have a labyrinth of compartments, it's going to be very, very difficult or almost impossible to design a jet fan system. I like the simple rule of thumb. I've invented the Tetris rule. If you can define the shape of the car park with a Tetris block from the original game, you're pretty okay. If not, then it's going to be challenging, and I also use that for shopping malls. I think I mentioned it in the podcast. So, yeah, there will be challenging configurations in which providing a JetFan system will be very, very challenging. I've already spoken that you use CFD to design them and that's a big part of the JetFan system design.

Wojciech: 33:15

No two car parks are the same, even though they reassemble each other. Even though every car park is to store cars, they have similar highs. They would have similar areas. They look very similar, but they're not. From the perspective of designing JetFan system or ventilation system overall in car parks, every car park is different and it's those little things like location of your inlets that can make or break your system. That can be a tremendous difference between two systems in a building One that works, one that doesn't. You have to take it into account. So there are no easy pathways to design efficient jet fun systems On a piece of paper.

Wojciech: 33:53

You need to do some good engineering and for that you need some engineering tools, and the tool of choice is CFD modeling. I remember 10 years ago there was this little bit of drama in the industry because with some changes to a fire dynamic simulator, fds, it lost the ability to model jet fans. It did not simulate this momentum exchange between the stream of air to the surroundings and this created some really big issues in the industry because so many people were using fds to model jetfens systems. It was fixed like one or two years later. Today's today's fds is very capable of modeling jetfens systems. It's just a little difficult when you want to put them on angle because it's cartesian mesh, of course. But you can simulate JetFence with FDS. There are guidelines on how to do it. On Thunderhead Engineering we are using ANSYS. For ANSYS there are a lot of ways you can simulate JetFence and my good friend Gosia Krul has written a paper on the ways to model JetFence. I'll link that in the show notes. So if you are not an FDS user but you use Ansys, fluent or perhaps OpenFOAM, you can find some inspiration in there on how to model them correctly.

Wojciech: 35:04

And in general, I find CFD a brilliant tool of choice to really let me study Jetfens. I've done CFDs for I don't know 200 car parks, maybe even more, and every time I do a car park I find something new and interesting in them. So yeah, it's a tool that is absolutely necessary to do and another tool that I find quite necessary are hot smoke tests. So I really find huge value in performing hot smoke tests in JetFan systems in car parks because this allows you to visualize the flow of air in your car park. After the car park is built, the system is fitted in your building and you can really look into where that air goes through, does it follow your strategy? And because we're working on low-velocity systems and fairly low fire powers, the hot smoke test is quite a good representation of a real fire in the car park. There is not that huge difference in buoyancy between a growing vehicle fire and a hot smoke test really. So it really is the most brilliant tool you can use, and we recommend running hot smoke tests in every single car park that we design, because this just allows you to fiddle with the system on site and perhaps change the things that you've missed in your CFD. The real building and the model those are two different things, and sometimes in the real building you will find things that you have not expected with CFD. Can you fix them? Yes, from our experience, you can do a lot of fiddling with the JetFan system on the side. You can turn JetFans on off. You can change the capacities of your inlets, outlets, lower them. Sometimes you can combine some smoke compartments together. You can choose a different set of jet vents. You can revert their operation if they're reversible. There's a lot of ways you can fiddle with jet vent system on site at hot smoke tests and this really is like this fine tuning moment of the system where you get the most of its performance, fine-tuning moment of the system where you get the most of its performance. And finally, as we finish the episode, some remarks on the design properties.

Wojciech: 37:02

So when I would be approaching a project with JetFan system, a factor would be the height of the car park. So if it's less than 2.7 meters I would not even do the JetFan system at all. I just find it almost impossible to provide any evacuation and tentability into the car parks With JetFan system. With normal systems I just find it almost impossible to provide any evacuation and tentability into the car parks With jet fin system. With normal systems I just don't do car parks that low. For me they're dangerous If they're tall enough, like three meters and higher. I'm very comfortable with the jet fin systems and for most of the car parks we would go with one.

Wojciech: 37:28

The second thing is the width and the shape of the car park, so I need to look into how big and wide it is. The more narrowed and more reassembling the tunnel, the easier it is to design the jet fan system. For more complex car parks, you would need multiple inlet extraction points so you can drive the air a little better. I would look into where are the narrow passages in my car park. When the air will accelerate, I would look into potential locations for smoke curtains if I want to limit the spread in some direction. I would look into where the extractions are on the roofs. That's an important thing. I don't want the extraction to be too close to my inlet point on the roof, for example, so it's also something that we take into account.

Wojciech: 38:11

Another thing that most people would worry with is the design fire. For us, it's not a worry. In our book in 2015, we've used the TNO design curves and we stay with that, and that's something that we normally ordinarily use. A big discussion on design fires for car parks has been done with Zahir in some episodes ago, so please look into that if you're looking for inspiration for your design fire.

Wojciech: 38:37

And while designing, I would start with some capacity. I usually design the systems for smoke controls, I would look if I am able to provide this smoke-free access to the fire brigade with starting capacity. My usual starting capacity would be 180,000 cubic meters per hour for the smaller car parks, 300,000 cubic meters per hour for larger car parks. That's what I would start with and I look at the outcomes. If they're good, I could possibly optimize that further. If it looks to them lacking some more, I would increase that by, let's say, 30,000 cubic meters per hour until I reach my capacity that I am comfortable with and something that the designers can actually fit into the building. That is another thing. So those would be the factors that I would go through when designing a JetFan system for a car park from the scratch.

Wojciech: 39:27

So to summarize, jetfan systems could be a very efficient way to provide smoke control in your car parks fairly cheap way, easy, easy. Like I like simplicity, and the jet fan system is a very simple system. You blow air in one direction and you expect the smoke to follow. You extract it at the end of the pathway. You are good. For me, that's a very, very simple idea of operation with not that many points of possible failure. A lot of challenges underway, a lot of things to consider it. It's not an easy system by any means in terms of complications that you can see in the design process. But as you work with them, as you build your experience with them, you will gain more comfort designing those systems and you will start seeing and understanding more about them, more about them.

Wojciech: 40:15

If you need some design help, you can always ask us. We have tremendous experience with JetFan systems. I also have the book written about them in Polish that perhaps Google Translate can do a sufficiently good job in translating that. So if you want that, just point me an email and I'll try to organize something for you. Other than that, just point me an email and I'll try to organize something for you. Other than that, there is new European standard on jet fin systems in the EN 1211 family and that drives you towards high level smoke control systems meant for firefighting. I think it's a very good design principle.

Wojciech: 40:54

There are some guidelines coming from the UK. I think it's a very good design principle. There are some guidelines coming from the UK. There are guidelines coming from the Netherlands, belgium, so there's a lot of design choices you can have. There's a paper, a short paper by myself in the SFP Europe magazine, which tells you about the JetFan design. I'll link it in the show notes as well. So if you want a quick read to look into our research into the JetFan systems, you're very welcome to do so and you perhaps will find a lot of interesting information about the systems, operation in them.

Wojciech: 41:26

And that would be it for today's episode, a little shorter than usual, but I hope it still carried enough value to justify listening to this episode. I hope you've enjoyed it and I wonder what are your opinions about the JetFan systems? I remember an episode with Mike Woodrow and he was telling me the story of how an engineer designed a really good JetFan system in Russia, I believe and since then I thought, yeah, perhaps we should talk about JetFan systems in the car parks, because I really believe that they could be a good solution. That's it for today. Follow up Fire Science Show for more fire science and engineering, useful knowledge for you, fellow fire engineers, and I'm also open to learn from you. What would you like to hear about in Fire Science Show? What are the topics that we have missed so far? What should I introduce in here? Who should I invite? What should we talk about? I'm doing this podcast for you and I am very open to any feedback you can provide me. Thanks for today. See you here next Wednesday. Cheers Bye, thank you.