203 - The lessons from repeating Jin's experiment on visibility in smoke

WEBVTT

00:00:00.462 --> 00:00:02.508
<v Wojciech Wegrzynski>Hello everybody, welcome to the Fire Science Show.

00:00:02.508 --> 00:00:09.233
<v Wojciech Wegrzynski>Today we are talking visibility in smoke and if you follow the podcast, you know that this topic is very dear to my heart.

00:00:09.233 --> 00:00:19.969
<v Wojciech Wegrzynski>It is something that I research on my own and that has been a very important part of my scientific career thus far and probably will be for ongoing years.

00:00:19.969 --> 00:00:25.524
<v Wojciech Wegrzynski>Many years ago I've done an episode with Lucas Arnold about visibility prediction framework.

00:00:25.524 --> 00:00:36.896
<v Wojciech Wegrzynski>Our new back then grant that we were just starting at that point that we hope that will allow us to revolutionize the way how visibility is assessed in fire safety engineering.

00:00:36.896 --> 00:00:44.173
<v Wojciech Wegrzynski>This project is actually ongoing, but I finally have some findings that I can share with you and that makes me super happy.

00:00:44.173 --> 00:00:47.506
<v Wojciech Wegrzynski>Have some findings that I can share with you and that makes me super happy.

00:00:47.527 --> 00:01:12.887
<v Wojciech Wegrzynski>A year ago I have recorded an episode in the series I've called the experiments that changed fire science and in that episode I've covered experiments by Japanese scientist Jin, which are the basis of this model, and I said back then that Jin's model needs urgent repeat, that we really need to do it, and I knew we were going to repeat it because we've built the rig to do it, but shortly after that episode was published a very happy thing to me happened.

00:01:12.887 --> 00:01:28.605
<v Wojciech Wegrzynski>I got a student from Hong Kong, Wai-Kit Wilson-Chung, from Hong Kong Polytechnic University, from Xinyan Huang's  Wai-Kit, stayed with me for six months and he was really focused on doing those experiments.

00:01:28.605 --> 00:01:31.861
<v Wojciech Wegrzynski>So, together with Waikid, we've actually redone the Jin's experiments.

00:01:31.861 --> 00:01:58.135
<v Wojciech Wegrzynski>We've redone them, we've processed the data and today I am happy to show you some findings, because while I think I understood the Jin experiment and you can listen to that in the episode about Gene's experiments, why I think I knew what Gene done actually repeating those experiments, you know, doing that research on your own really opens your eyes on what is important in those experiments.

00:01:58.135 --> 00:02:03.668
<v Wojciech Wegrzynski>And this is a broader reflection the papers don't tell you the full story.

00:02:03.668 --> 00:02:05.507
<v Wojciech Wegrzynski>You need to talk to the scientists to tell you the full story.

00:02:05.507 --> 00:02:20.344
<v Wojciech Wegrzynski>You need to talk to the scientist to really learn the full story what was hard, what was easy, where the challenges were, and I think we've narrowed down where the challenges of the visibility smoke model lie really, and this is what's gonna be said in this episode.

00:02:20.344 --> 00:02:24.112
<v Wojciech Wegrzynski>I've presented this at the sfp, edinburgh.

00:02:24.112 --> 00:02:25.515
<v Wojciech Wegrzynski>So finally, a time.

00:02:25.915 --> 00:02:28.764
<v Wojciech Wegrzynski>This reaches also my dear fire science show audience.

00:02:28.764 --> 00:02:32.539
<v Wojciech Wegrzynski>So let's spin the intro and jump into the episode.

00:02:32.539 --> 00:02:38.584
<v Wojciech Wegrzynski>Welcome to the fire science show.

00:02:38.584 --> 00:02:42.026
<v Wojciech Wegrzynski>My name is vojtěj věkřínski and I will be your host.

00:02:42.026 --> 00:03:11.561
<v Wojciech Wegrzynski>The FireSense show is into its third year of continued support from its sponsor of our Consultants, who are an independent, multi-award winning fire engineering consultancy with a reputation for delivering innovative safety-driven solutions.

00:03:11.561 --> 00:03:25.300
<v Wojciech Wegrzynski>As the UK leading independent fire risk consultancy, ofar's globally established team have developed a reputation for preeminent fire engineering expertise, with colleagues working across the world to help protect people, property and the planet.

00:03:25.300 --> 00:03:41.409
<v Wojciech Wegrzynski>Established in the UK in 2016 as a startup business by two highly experienced fire engineering consultants, the business continues to grow at a phenomenal rate, with offices across the country in eight locations, from Edinburgh to Bath, and plans for future expansions.

00:03:41.409 --> 00:03:49.968
<v Wojciech Wegrzynski>If you're keen to find out more or join OFR Consultants during this exciting period of growth, visit their website at ofrconsultantscom.

00:03:49.968 --> 00:03:52.074
<v Wojciech Wegrzynski>And now back to the episode.

00:03:53.040 --> 00:04:02.481
<v Wojciech Wegrzynski>So when I talk about visibility in smoke and recently I have a lot of chances to talk about this model I like to start with very difficult questions.

00:04:02.481 --> 00:04:04.622
<v Wojciech Wegrzynski>Easy questions are always the most difficult to answer.

00:04:04.622 --> 00:04:07.865
<v Wojciech Wegrzynski>What is visibility in smoke Like?

00:04:07.865 --> 00:04:09.945
<v Wojciech Wegrzynski>What are we really talking about?

00:04:09.945 --> 00:04:19.591
<v Wojciech Wegrzynski>Because, on one hand, you could consider it being a measure of a distance at which something can be observed.

00:04:19.591 --> 00:04:26.173
<v Wojciech Wegrzynski>I think that would be the simplest, easiest definition of what visibility in smoke is.

00:04:26.173 --> 00:04:34.997
<v Wojciech Wegrzynski>And this definition probably is right, but it has a lot of details in it, like what does it mean you can see something?

00:04:34.997 --> 00:04:39.588
<v Wojciech Wegrzynski>Is it enough that you see a glimpse of light?

00:04:39.588 --> 00:04:41.680
<v Wojciech Wegrzynski>Is it enough that you see a shape, a blurred out shape?

00:04:41.680 --> 00:04:47.723
<v Wojciech Wegrzynski>Or you have to be able to process data that's shown on the thing that you're observing.

00:04:47.723 --> 00:04:57.050
<v Wojciech Wegrzynski>How certain you have to be that the thing you observe is the thing that you observe, and those things change when the visibility changes.

00:04:57.692 --> 00:05:02.725
<v Wojciech Wegrzynski>If you're a physicist, then perhaps this is ill-defined for you.

00:05:02.725 --> 00:05:07.595
<v Wojciech Wegrzynski>Perhaps it's a distance at which the light can still pass through obscuring medium.

00:05:07.595 --> 00:05:21.629
<v Wojciech Wegrzynski>So if you point a ray of light through smoke, fog, whatever aerosol that disturbs it, the light will start to decay, it will scatter to the sides, it will be absorbed by the particles.

00:05:21.629 --> 00:05:32.642
<v Wojciech Wegrzynski>So with every meter you will have less and less light passing through, and if you capture the point at which the light has decayed completely, that's the point where you cannot see the light anymore.

00:05:32.642 --> 00:05:37.153
<v Wojciech Wegrzynski>So perhaps this distance is visibility in smoke In some way.

00:05:37.153 --> 00:05:38.983
<v Wojciech Wegrzynski>This is how we measure it.

00:05:38.983 --> 00:05:39.946
<v Wojciech Wegrzynski>This is how we measure it.

00:05:39.946 --> 00:05:52.233
<v Wojciech Wegrzynski>In laboratories we have densitometer, optical densitometers which emit light, which measure light, and they measure how much light is lost in between the emitter and the target.

00:05:52.233 --> 00:05:56.170
<v Wojciech Wegrzynski>So a physicist could define visibility as such a distance.

00:05:56.701 --> 00:06:11.567
<v Wojciech Wegrzynski>If you think about genes experiments the ones that brought us the visibility in smoke model that we use in fire science, visibility was actually the initial condition or actually the assumption of the study, the distance itself, the meters.

00:06:11.567 --> 00:06:25.158
<v Wojciech Wegrzynski>So Jin built his facility in such a way that you could observe the science from either 5, 10, or 15 meters and in all honesty, we still have not found how he measured the 10 meter distance.

00:06:25.158 --> 00:06:32.458
<v Wojciech Wegrzynski>But anyway, the rig is reported to be able to measure at 5, 10 and 15 meter distance.

00:06:32.458 --> 00:06:36.687
<v Wojciech Wegrzynski>So it's discrete points in space rather than continuous spectrum.

00:06:36.687 --> 00:06:41.723
<v Wojciech Wegrzynski>And in Gene's experiment the participant was placed at this distance.

00:06:41.723 --> 00:07:03.245
<v Wojciech Wegrzynski>They were observing a light source through a smoke and they had a little widget that they could turn around and this widget would make the light dimmer and dimmer and they would just find the dimmest light they could see through the smoke and then Jin would save that data and use that in the further research.

00:07:03.245 --> 00:07:08.074
<v Wojciech Wegrzynski>So in Jin's research the visibility is actually a fixed number.

00:07:08.074 --> 00:07:09.867
<v Wojciech Wegrzynski>It's either 5, 10, or 15.

00:07:09.867 --> 00:07:12.569
<v Wojciech Wegrzynski>There's no intermediate values for that.

00:07:12.569 --> 00:07:14.187
<v Wojciech Wegrzynski>It's quite interesting when you think about it.

00:07:14.187 --> 00:07:25.329
<v Wojciech Wegrzynski>If you're a firefighter, the visibility range would be something that's very natural to you, because that's the distance you can see in your fires, how far into the building, how far into the field you can see.

00:07:25.329 --> 00:07:37.531
<v Wojciech Wegrzynski>So, perhaps closest to the first, most simple definition that I've brought up and allegedly, the observations of firefighters the distances they were saying are 10 meters is probably enough.

00:07:37.531 --> 00:07:44.923
<v Wojciech Wegrzynski>Those were the background for creating the discrete values of visibility that we use today for engineering.

00:07:44.923 --> 00:07:47.964
<v Wojciech Wegrzynski>But it does not mean the same thing for an engineer.

00:07:48.427 --> 00:07:55.387
<v Wojciech Wegrzynski>If you're practicing fire safety engineering, you are not really assessing the ability to observe things through smoke.

00:07:55.387 --> 00:08:05.351
<v Wojciech Wegrzynski>You're not assessing light decay in smoke and you're definitely not assessing the critical brightness of a widget that you can observe through smoke.

00:08:05.351 --> 00:08:10.307
<v Wojciech Wegrzynski>No, you are applying a very simple mathematical correlation.

00:08:10.307 --> 00:08:14.641
<v Wojciech Wegrzynski>In one part of the correlation you put smoke density in.

00:08:14.641 --> 00:08:17.588
<v Wojciech Wegrzynski>How much smoke do you have in your space?

00:08:17.588 --> 00:08:22.461
<v Wojciech Wegrzynski>And this is something you know from your CFD analysis, from your zone model analysis.

00:08:22.461 --> 00:08:24.021
<v Wojciech Wegrzynski>You know your soot yields.

00:08:24.021 --> 00:08:25.483
<v Wojciech Wegrzynski>You know your yields of combustion.

00:08:25.483 --> 00:08:29.464
<v Wojciech Wegrzynski>You can calculate how much soot gets emitted to your room.

00:08:29.464 --> 00:08:41.932
<v Wojciech Wegrzynski>You know the flows in your room, you can calculate how much smoke is there in any given part of my building while performing fire safety engineering.

00:08:42.812 --> 00:08:52.256
<v Wojciech Wegrzynski>And when you do this fire safety engineering, you have to show those results to someone and you usually choose to present them as visibility in smoke.

00:08:52.256 --> 00:08:54.798
<v Wojciech Wegrzynski>So I'll just give a quick recap.

00:08:54.798 --> 00:08:58.868
<v Wojciech Wegrzynski>How does the smoke density turn into visibility in our modeling?

00:08:58.868 --> 00:09:00.592
<v Wojciech Wegrzynski>Because it's a very simple correlation.

00:09:00.592 --> 00:09:23.243
<v Wojciech Wegrzynski>You basically have a factor we call it large K usually and it takes values of 3 for light reflecting signs, 8 for light emitting signs I'll come back to this at the end of the episode and you basically subdivide it by your smoke density multiplied by specific extinction coefficient of smoke.

00:09:23.243 --> 00:09:30.410
<v Wojciech Wegrzynski>The extinction coefficient is something we know from experimental work from Mulholland's and I'll also come back to this at the end of the episode.

00:09:31.059 --> 00:09:37.909
<v Wojciech Wegrzynski>The logmock density you know from your CFD, and so you have all the things that you need to calculate visibility.

00:09:37.909 --> 00:09:45.446
<v Wojciech Wegrzynski>Well, does this mean that you will be able to see for 10 meters in your building if you've calculated 10 meters visibility?

00:09:45.446 --> 00:09:46.470
<v Wojciech Wegrzynski>Of course not.

00:09:46.470 --> 00:10:00.590
<v Wojciech Wegrzynski>It just means that if an entire space was filled with a smoke of density, like you have in this one point of space that you've just measured, then probably in the whole room you would have visibility distance of something like 10 meters.

00:10:00.590 --> 00:10:06.842
<v Wojciech Wegrzynski>That's pretty much what it says, but it doesn't tell you anything about what you can see, what you cannot see.

00:10:06.842 --> 00:10:17.600
<v Wojciech Wegrzynski>It doesn't tell you anything about where the light will stop in your room and it definitely does not tell you at what kind of brightness you can observe things in your compartment.

00:10:17.600 --> 00:10:27.985
<v Wojciech Wegrzynski>It just allows you to translate value that's perhaps a little less understandable the density of smoke into a value that people can understand visibility.

00:10:27.985 --> 00:10:38.113
<v Wojciech Wegrzynski>That's the trick that has been used as the backbone of fire safety engineering for five decades now, I guess, and I cannot say we've been pretty successful with it.

00:10:38.113 --> 00:10:50.293
<v Wojciech Wegrzynski>It's just that it's so profound, so impactful in our engineering that I really find it not great that we have such a coarse approximation that we use for very significant engineering decisions every day.

00:10:50.895 --> 00:10:57.472
<v Wojciech Wegrzynski>So now let's talk a little bit about the story of repeating genes experiments, because it was a very interesting story.

00:10:57.472 --> 00:11:04.043
<v Wojciech Wegrzynski>First we've done I thought I'm clever, you know I'm not gonna, you know use a widget to control the brightness.

00:11:04.043 --> 00:11:06.210
<v Wojciech Wegrzynski>That just gives me one point of data.

00:11:06.210 --> 00:11:13.374
<v Wojciech Wegrzynski>I am a clever scientist and I figured out a way how I can get much more data from the same experiment.

00:11:13.374 --> 00:11:20.688
<v Wojciech Wegrzynski>So in my experiment, contrary to Jin's, I have a huge LED screens at the back of my experiment.

00:11:20.688 --> 00:11:35.201
<v Wojciech Wegrzynski>Jin certainly did not have those in 1970s and instead of projecting one sign, I can project as many as I want and I can make them dimmer and dimmer, and dimmer and control this through my software.

00:11:35.201 --> 00:11:45.765
<v Wojciech Wegrzynski>So when Gene was able to project one sign on his frosted glass, I am capable of projecting however much the hell I want.

00:11:45.765 --> 00:11:47.270
<v Wojciech Wegrzynski>So I definitely did that.

00:11:47.311 --> 00:11:55.456
<v Wojciech Wegrzynski>I did that with my student Pavel, and we were trying to do those signs emitted on a screen of TV and replicate Gene's experiment.

00:11:55.456 --> 00:12:04.043
<v Wojciech Wegrzynski>And in Gene's experiment there is this one way he's presenting results and it's called the dimensionless brightness.

00:12:04.043 --> 00:12:08.360
<v Wojciech Wegrzynski>It's not very useful but it's kind of relevant, so I'll talk you through.

00:12:08.360 --> 00:12:14.466
<v Wojciech Wegrzynski>So dimensionless brightness is that Gene took the brightness of the sign that he was projecting.

00:12:14.466 --> 00:12:25.508
<v Wojciech Wegrzynski>He was measuring that with pretty complicated optical measurements that I cover in the previous podcast episode and he was subdividing that by the brightness of the background.

00:12:25.508 --> 00:12:30.586
<v Wojciech Wegrzynski>So if the dimensionless brightness is above one, that means the sign was brighter than the background.

00:12:30.586 --> 00:12:39.726
<v Wojciech Wegrzynski>If the dimensionless brightness is less than one, it means that the sign was darker than the background and the higher the value, the brighter the sign right.

00:12:39.726 --> 00:12:55.606
<v Wojciech Wegrzynski>So with Paavo we start to calculating dimensionless brightness for our results and we very quickly see that we're nowhere close to Gene's results, like we are nowhere close to the range of dimensionless brightness that Gene's used.

00:12:55.875 --> 00:13:05.256
<v Wojciech Wegrzynski>Our TV is not bright enough, and that was the first shocker because I felt the TVs, the setup that we've built, was imitating the building conditions fairly well.

00:13:05.256 --> 00:13:06.921
<v Wojciech Wegrzynski>I've been in a lot of buildings.

00:13:06.921 --> 00:13:12.080
<v Wojciech Wegrzynski>I've been in a lot of buildings in fires, actually, because we're doing those fire tests in them.

00:13:12.080 --> 00:13:19.605
<v Wojciech Wegrzynski>So I know how evacuation routes in a building in emergency lighting in your evacuation conditions should look like.

00:13:19.605 --> 00:13:31.004
<v Wojciech Wegrzynski>I have a pretty good idea of that and I thought my tvs are fairly well representative of that environment, whereas now we see that we're nowhere close to jeans results.

00:13:31.004 --> 00:13:33.509
<v Wojciech Wegrzynski>That was quite a shocker to us.

00:13:33.811 --> 00:13:46.054
<v Wojciech Wegrzynski>And then wiki chunk came and the first job I gave gave to Wilson was to build me a light emitting source that could match gins and boy, that was a journey.

00:13:46.054 --> 00:13:52.227
<v Wojciech Wegrzynski>We've 3D printed the box and the box was lined up with light reflecting foil.

00:13:52.227 --> 00:13:58.826
<v Wojciech Wegrzynski>Then we've put a bunch of LEDs into the box, like it took us like five iterations of adding more and more and more and more and more LEDs into the box.

00:13:58.826 --> 00:14:04.503
<v Wojciech Wegrzynski>Like it took us like five iterations of adding more and more and more and more and more LEDs to the box until we've reached the box.

00:14:04.503 --> 00:14:13.442
<v Wojciech Wegrzynski>That's like literally, you know, a lighthouse lantern you cannot look straight into the box because it blinds you for like 30 seconds.

00:14:13.442 --> 00:14:14.899
<v Wojciech Wegrzynski>That's how bright it is.

00:14:14.899 --> 00:14:16.441
<v Wojciech Wegrzynski>And now we match Jin's.

00:14:16.441 --> 00:14:20.524
<v Wojciech Wegrzynski>And now we match the Jin's frosted glass brightness.

00:14:21.235 --> 00:14:24.326
<v Wojciech Wegrzynski>And this was like a shocker, but also an eye-opener.

00:14:24.326 --> 00:14:37.006
<v Wojciech Wegrzynski>Like Jin has used extremely bright sources in their experiments, extremely bright sources, and therefore he could observe those signs through very, very dense smoke.

00:14:37.006 --> 00:14:46.144
<v Wojciech Wegrzynski>If you look at Jin's experiments closely, you'll notice that the ranges of extinction coefficients that Jin is working with they're reaching up to two.

00:14:46.144 --> 00:14:48.724
<v Wojciech Wegrzynski>This is unbelievably dense smoke.

00:14:48.724 --> 00:14:54.664
<v Wojciech Wegrzynski>This is a smoke at which you will not see your hand if you stretch it in front of you.

00:14:54.664 --> 00:14:58.586
<v Wojciech Wegrzynski>You probably will not even see your elbow in smoke of this density.

00:14:58.586 --> 00:15:05.835
<v Wojciech Wegrzynski>It's unbelievably dense smoke and he was carrying observations and calculating those models in such dense smoke conditions.

00:15:05.835 --> 00:15:15.501
<v Wojciech Wegrzynski>So, ah, this is already something that moves Jin's experiments away from the space of real buildings, real engineering.

00:15:15.501 --> 00:15:18.263
<v Wojciech Wegrzynski>The sources are too bright, the smoke is too dense.

00:15:18.263 --> 00:15:25.636
<v Wojciech Wegrzynski>It's not something that we commonly work as fire safety engineers and again, you can read the paper as many times as you like.

00:15:25.697 --> 00:15:41.220
<v Wojciech Wegrzynski>You can, you know, spend ages on studying what has been done in Japan in 1970s, but it really took us to repeat the experiment to very quickly realize what we are dealing with with those light sources.

00:15:41.220 --> 00:15:53.506
<v Wojciech Wegrzynski>Very interesting, and therefore I find this podcast episode of real value, because previously I was speaking about what I think the problems with genes experiments are.

00:15:53.506 --> 00:15:56.224
<v Wojciech Wegrzynski>Now I know what they are because I've run into them.

00:15:56.224 --> 00:16:00.505
<v Wojciech Wegrzynski>But that's not everything that we've realized while repeating Jin's experiments.

00:16:00.505 --> 00:16:05.923
<v Wojciech Wegrzynski>Actually, we've learned a lot more with Wilson, so let's try digesting that.

00:16:07.296 --> 00:16:42.605
<v Wojciech Wegrzynski>When Jin was doing his experiments, the profound finding in his study and I think that's the biggest discovery of Jin really was that the relationship between the extinction coefficient and the distance at which you can observe the sign is fairly constant across a range of sign sizes, distances, background brightness and just the brightness of the sign, which meant that he could collapse a lot of results into straight lines and just find a linear correlation between the variables, therefore creating the model that we are currently using.

00:16:42.605 --> 00:16:44.100
<v Wojciech Wegrzynski>I'm not sure he was creating a model.

00:16:44.100 --> 00:16:51.822
<v Wojciech Wegrzynski>Actually I think he was just looking for a relationship that allows his engineering to be done, whereas we turned it into the model.

00:16:51.822 --> 00:16:58.086
<v Wojciech Wegrzynski>We, as a collective fire safety engineering community, we've started using this as a model to predict visibility.

00:16:58.086 --> 00:17:06.837
<v Wojciech Wegrzynski>He was just representing the outcomes, I think, but anyway, in his experiments he was doing them with different range of lights with different sizes.

00:17:06.837 --> 00:17:23.184
<v Wojciech Wegrzynski>As I said, he was also using dimensionless brightness of a sign to reduce the number of variables in the studies and he was able to actually collapse those results into one very elegant line and I think you can see this plot in sfp handbook.

00:17:23.184 --> 00:17:28.461
<v Wojciech Wegrzynski>We'll see if it's there in the next edition of handbook which is released just in a few days.

00:17:28.461 --> 00:17:31.406
<v Wojciech Wegrzynski>But he was basically able to simplify this a lot.

00:17:31.907 --> 00:17:34.721
<v Wojciech Wegrzynski>Now we've repeated this experiment as closely as we could.

00:17:34.721 --> 00:17:53.957
<v Wojciech Wegrzynski>We really paid a lot of attention to repeat these experiments as closely, as accurately as we could, following whatever is being said in Jun's papers and our results, while they do keep this linear relationship between brightness and extinction coefficient at which you can observe the sign.

00:17:53.957 --> 00:17:59.954
<v Wojciech Wegrzynski>So in some way we confirm that there is this close linear relationship.

00:17:59.954 --> 00:18:01.280
<v Wojciech Wegrzynski>That's the basis of the model.

00:18:01.280 --> 00:18:04.144
<v Wojciech Wegrzynski>That's, I think, a very good finding that we confirmed that.

00:18:04.144 --> 00:18:10.628
<v Wojciech Wegrzynski>Besides that we have not been able to collapse them this elegantly as Jin did.

00:18:10.628 --> 00:18:14.105
<v Wojciech Wegrzynski>So our results just do not collapse that easy.

00:18:14.105 --> 00:18:17.965
<v Wojciech Wegrzynski>They do not collapse that perfectly, and we were looking into why would they not collapse that perfectly?

00:18:17.965 --> 00:18:18.589
<v Wojciech Wegrzynski>And we were looking into why.

00:18:18.589 --> 00:18:20.196
<v Wojciech Wegrzynski>Why would they not collapse that perfectly?

00:18:20.196 --> 00:18:28.157
<v Wojciech Wegrzynski>And we started thinking it could be related to the background conditions, to the background brightness.

00:18:28.157 --> 00:18:43.281
<v Wojciech Wegrzynski>We've used led strips in the in the room so we had a very nice uniform brightness across the room, jim using incandescent lights which he was turning on and off, so he definitely had non-uniform light distribution.

00:18:43.281 --> 00:18:57.722
<v Wojciech Wegrzynski>But as we were looking into that, we realized that perhaps there's a bigger story to be told about the brightness which is not told by Jin and which I think the fire safety community needs to know and understand.

00:18:57.722 --> 00:18:59.787
<v Wojciech Wegrzynski>So what I mean by that?

00:19:00.048 --> 00:19:13.288
<v Wojciech Wegrzynski>If you look at the perhaps most influential graph of all of them in Gene's papers, there's a graph that shows you on the y-axis, the dimensionless number which is smoke density multiplied by visibility.

00:19:13.288 --> 00:19:17.319
<v Wojciech Wegrzynski>On the x-axis, the dimensionless brightness of your sign.

00:19:17.319 --> 00:19:27.144
<v Wojciech Wegrzynski>And in this plot this plot basically, is the basis for the values of k3 and 8, really, that's the original of those values.

00:19:27.144 --> 00:19:30.055
<v Wojciech Wegrzynski>And why it's important?

00:19:30.055 --> 00:19:37.506
<v Wojciech Wegrzynski>Because we've noticed that in the top left-hand of the plot there's a note external light 180 lux.

00:19:37.506 --> 00:19:42.666
<v Wojciech Wegrzynski>Gene has carried his experiments in extremely bright conditions.

00:19:42.666 --> 00:19:50.808
<v Wojciech Wegrzynski>180 lux is not something you normally have in your buildings in the evacuation phase.

00:19:50.808 --> 00:19:59.327
<v Wojciech Wegrzynski>In Poland the minimum is one lux, of course, but in normal buildings like 100 is already a lot, really really a lot.

00:19:59.327 --> 00:20:07.086
<v Wojciech Wegrzynski>180 is a very, very, very bright room and you normally do not evacuate through spaces with such an immense brightness.

00:20:07.086 --> 00:20:10.884
<v Wojciech Wegrzynski>And why I say there's a story to be told about brightness.

00:20:11.476 --> 00:20:38.107
<v Wojciech Wegrzynski>As soon as you go into the laboratory, as soon as you start repeating those experiments, as soon as you start playing with that, you immediately notice how impactful the background brightness is, how important is the brightness of the environment in which the evacuation takes place and how quickly it changes the ability to see or not see the evacuation signage.

00:20:38.107 --> 00:20:48.344
<v Wojciech Wegrzynski>We had experiments in which you would set a brightness of a sign and at some external brightness you would not see even a glimpse of the sign.

00:20:48.344 --> 00:20:52.561
<v Wojciech Wegrzynski>And if you tune the brightness down, you would see the sign perfectly.

00:20:52.561 --> 00:20:56.561
<v Wojciech Wegrzynski>The same smoke, the same sign, just changing the background conditions.

00:20:56.561 --> 00:21:04.144
<v Wojciech Wegrzynski>This is how big impact the brightness of the environment can have on visibility and actually it makes sense.

00:21:04.144 --> 00:21:05.226
<v Wojciech Wegrzynski>It makes perfect sense.

00:21:05.226 --> 00:21:12.708
<v Wojciech Wegrzynski>So if you have a scattering medium in your space, like smoke is, you can think about it.

00:21:12.708 --> 00:21:16.479
<v Wojciech Wegrzynski>It's an averaging filter of light that's going through the room.

00:21:16.479 --> 00:21:23.328
<v Wojciech Wegrzynski>Basically, all the light that passes through that scattering medium bounces off particles, let's say mixes.

00:21:23.328 --> 00:21:35.521
<v Wojciech Wegrzynski>I'm not sure if it's a good word to be used about physics of light, but let's say that the light from different sources mixes and that's why your eyes cannot tell those lights apart, because they're mixed.

00:21:36.143 --> 00:21:39.827
<v Wojciech Wegrzynski>Now you will also see the brighter thing.

00:21:39.827 --> 00:21:46.546
<v Wojciech Wegrzynski>If you have a very bright point next to not such a bright point, you of course see the brighter point first.

00:21:46.546 --> 00:21:58.506
<v Wojciech Wegrzynski>So the sign has to be more bright than the background, and the bigger the difference between the background and the sign is, the easier it's going to be to observe the sign.

00:21:58.506 --> 00:22:00.277
<v Wojciech Wegrzynski>I think that that's quite reasonable.

00:22:00.277 --> 00:22:05.407
<v Wojciech Wegrzynski>Now your signs have a very specific light intensity that they emit.

00:22:05.407 --> 00:22:06.876
<v Wojciech Wegrzynski>It's in their characteristic.

00:22:06.876 --> 00:22:13.698
<v Wojciech Wegrzynski>Therefore, if your background is too bright, you cannot increase the brightness of your signs anymore.

00:22:13.698 --> 00:22:16.522
<v Wojciech Wegrzynski>You will start losing visibility of those signs.

00:22:16.522 --> 00:22:19.728
<v Wojciech Wegrzynski>And, trust me, if you go into the experiment.

00:22:19.728 --> 00:22:28.224
<v Wojciech Wegrzynski>If you go into the laboratory, if you start observing those signs through the glass, and if you're ever in Warsaw, you're very welcome to come to my laboratory.

00:22:28.224 --> 00:22:35.105
<v Wojciech Wegrzynski>I'll show it to you you will notice that the change in the background brightness perhaps has the most profound impact on the outcomes of the study.

00:22:35.595 --> 00:22:41.904
<v Wojciech Wegrzynski>And now, why it's important for fire safety engineering is because of that assumption of Gin's model 180 lux.

00:22:41.904 --> 00:22:44.131
<v Wojciech Wegrzynski>We're not really having 180 lux.

00:22:44.131 --> 00:23:14.501
<v Wojciech Wegrzynski>So therefore, with Wilson, we've tried to create this collapse of results for lower brightnesses to see, because Gin doesn't present a graph like that We've tried to collapse the results for different brightness conditions and for a brightness level of 22 lux or 1 lux I think very reasonable for normal evacuation conditions, we go with K values up to 11.

00:23:14.501 --> 00:23:20.576
<v Wojciech Wegrzynski>That's much higher than Jin did and we generally observe very high k values for those conditions.

00:23:20.576 --> 00:23:29.917
<v Wojciech Wegrzynski>Therefore, reassuring me, in my everyday practice I simply use this k value of 8 as the baseline in my engineering.

00:23:29.917 --> 00:23:32.563
<v Wojciech Wegrzynski>I very rarely engineer for k value of 3.

00:23:32.563 --> 00:23:41.674
<v Wojciech Wegrzynski>And I reassured myself that using high k values is actually more representative of built environment and that's one finding.

00:23:41.674 --> 00:24:00.161
<v Wojciech Wegrzynski>Probably, if you do engineering on that and you go into third party audit, you probably should not quote a podcast on that, but I promise you there's a paper to be submitted very soon and as soon as the paper is published I'll put the link in the show notes and then you will have a peer-reviewed, credible source to quote.

00:24:00.161 --> 00:24:07.042
<v Wojciech Wegrzynski>So I hope I give it to you, my fellow FISA engineer, so you have less troubles in your work.

00:24:07.042 --> 00:24:09.502
<v Wojciech Wegrzynski>But anyway, to summarize, the brightness.

00:24:09.502 --> 00:24:21.780
<v Wojciech Wegrzynski>Brightness is extremely impactful and it seems that higher K values correspond to brightness levels in buildings which are more in line of what we observe in everyday life.

00:24:21.780 --> 00:24:25.750
<v Wojciech Wegrzynski>So that's one reassuring thing and really wow.

00:24:25.750 --> 00:24:32.955
<v Wojciech Wegrzynski>We need to study it more because it's really interesting how much the background brightness changes the outcomes of the experiment.

00:24:32.955 --> 00:24:40.970
<v Wojciech Wegrzynski>But this is not the only obvious thing that we knew about Jin's experiment that we did not put enough emphasis on previously.

00:24:41.476 --> 00:24:43.904
<v Wojciech Wegrzynski>The next one is the sign sizing.

00:24:43.904 --> 00:24:55.467
<v Wojciech Wegrzynski>I've mentioned it already in the Jin's experiment podcast episode and I've actually re-listened to the episode and I found ah, I've talked about it but I did not really recognize the impact of that the sign signage.

00:24:55.467 --> 00:25:07.247
<v Wojciech Wegrzynski>So, as I told you, Gene was observing signs from 5, 10, or 15 meters, but he somehow did not want the sign's size to influence the results of the study.

00:25:07.247 --> 00:25:11.000
<v Wojciech Wegrzynski>Therefore he also used signs of different sizes.

00:25:11.000 --> 00:25:18.301
<v Wojciech Wegrzynski>So when he was observing sign from 5 meters, the sign dimension was 5 centimeters.

00:25:18.301 --> 00:25:21.618
<v Wojciech Wegrzynski>When he was observing it from 10 meters, it was 10 centimeters.

00:25:21.618 --> 00:25:24.527
<v Wojciech Wegrzynski>When he was observing it from 15 meters, it was 15 centimeters.

00:25:24.527 --> 00:25:34.039
<v Wojciech Wegrzynski>So the further he was, the bigger the sign was and now, as you can imagine, it has profound impact on the outcomes.

00:25:34.240 --> 00:25:42.099
<v Wojciech Wegrzynski>Profound, of course, in real building, if you are further away from the thing, you observe, the thing looks smaller.

00:25:42.099 --> 00:25:46.856
<v Wojciech Wegrzynski>The smaller it is, the harder it is to observe it through obscuring mediums such as smoke.

00:25:46.856 --> 00:25:52.256
<v Wojciech Wegrzynski>In jinn's experiment the signs were always the same size no matter what distance you observe them.

00:25:52.256 --> 00:26:04.310
<v Wojciech Wegrzynski>So he was really looking into ability to see the light from the source and not really observe a real evacuation signage in a real evacuation scenario.

00:26:04.310 --> 00:26:10.627
<v Wojciech Wegrzynski>And as soon as you go into the lab and you start observing those signs, you immediately see that.

00:26:10.627 --> 00:26:12.722
<v Wojciech Wegrzynski>So our setup has multiple mirrors.

00:26:12.722 --> 00:26:16.806
<v Wojciech Wegrzynski>You can observe the signs from different distances at the same time, really.

00:26:16.806 --> 00:26:22.126
<v Wojciech Wegrzynski>So you can really narrow the time at which you see the sign at 10 meters.

00:26:22.126 --> 00:26:25.874
<v Wojciech Wegrzynski>You see the sign at 5 meters, you cannot see it at 15.

00:26:25.874 --> 00:26:26.960
<v Wojciech Wegrzynski>Or, even better.

00:26:26.960 --> 00:26:29.943
<v Wojciech Wegrzynski>You see it perfectly in 5 meters.

00:26:29.943 --> 00:26:35.781
<v Wojciech Wegrzynski>You almost lose the visibility of it at 10 meters and you cannot see it at all at 15.

00:26:35.781 --> 00:26:37.681
<v Wojciech Wegrzynski>That's probably a better description.

00:26:37.681 --> 00:26:53.484
<v Wojciech Wegrzynski>So yeah, in our case we're able to see those differences and we've took the measurements and it's going to be another paper that's in production with Wilson, which is how much does the size of the sign change the outcomes of the experiment?

00:26:53.484 --> 00:27:03.825
<v Wojciech Wegrzynski>But it's just important to know that in Gene's experiment that was constrained and I think this has really considerable impact on our ability to engineer.

00:27:03.825 --> 00:27:06.229
<v Wojciech Wegrzynski>I think this has really considerable impact on our ability to engineer.

00:27:06.249 --> 00:27:11.638
<v Wojciech Wegrzynski>I always felt it a lackluster that I cannot do any engineering with my science.

00:27:11.638 --> 00:27:21.711
<v Wojciech Wegrzynski>Like, I go into a building, I do my CFD simulations, I do some smoke, I measure the visibility, of course, and I find the reason of visibility.

00:27:21.711 --> 00:27:23.075
<v Wojciech Wegrzynski>Let's say, 9 meters.

00:27:23.075 --> 00:27:32.948
<v Wojciech Wegrzynski>That's the outcome and my HAJ is very unhappy because it was supposed to be above 10 meters and I don't meet my tenability criterion.

00:27:32.948 --> 00:27:49.957
<v Wojciech Wegrzynski>So I have to put a lot of extraction in that room to increase the my capability of removing smoke, to decrease the smoke density, to improve the visibility conditions, and then my building is considered safe because I finally have more than 10 meters visibility.

00:27:50.444 --> 00:27:58.955
<v Wojciech Wegrzynski>But if, instead of placing another fan, I could just put twice the size evacuation signage, would that help In real engineering scenario?

00:27:58.955 --> 00:27:59.861
<v Wojciech Wegrzynski>It definitely would help.

00:27:59.861 --> 00:28:02.536
<v Wojciech Wegrzynski>It would be a difference in fire safety engineering if I could just use a larger signs in my experiments.

00:28:02.536 --> 00:28:07.010
<v Wojciech Wegrzynski>It would be a difference in fire safety engineering if I could just use a larger science in my experiments.

00:28:07.010 --> 00:28:09.035
<v Wojciech Wegrzynski>It would make a big, big difference.

00:28:09.656 --> 00:28:12.589
<v Wojciech Wegrzynski>But with Jin's model it does not recognize the size of the sign.

00:28:12.589 --> 00:28:24.880
<v Wojciech Wegrzynski>Therefore it's impossible to use that, as you know, your design variable and unfortunately I do not think there is an easy way how this could be implemented in Jin's method.

00:28:24.880 --> 00:28:30.184
<v Wojciech Wegrzynski>The reason is that the results collapse into a line because the size is constrained.

00:28:30.184 --> 00:28:36.679
<v Wojciech Wegrzynski>As soon as you remove the size constraint from those relationships, they do not collapse into a line anymore.

00:28:36.679 --> 00:28:41.176
<v Wojciech Wegrzynski>And if there is an empirical relationship, it's going to be very complicated.

00:28:41.176 --> 00:28:48.858
<v Wojciech Wegrzynski>So it's going to be extreme challenge for us to have a model that would include for the sign size in it.

00:28:48.858 --> 00:28:59.204
<v Wojciech Wegrzynski>I'm not saying we're not trying, but it's very hard and I think it's a flow of genes model that we probably will not be able to go over.

00:28:59.806 --> 00:29:31.119
<v Wojciech Wegrzynski>However, what I want to say is that I think in many documents in which fire engineer has ability to use their knowledge for their benefits, it's fairly fair to say in my building, in order to improve the evacuation conditions, I have doubled the size of the evacuation signage, therefore making them more observable from larger distances, therefore making them more observable from larger distances, and just put a claim that the existing visibility in smoke model does not account for size of the signage.

00:29:31.119 --> 00:29:35.382
<v Wojciech Wegrzynski>Therefore, using larger signage is conservative versus the normal approach.

00:29:35.382 --> 00:29:38.123
<v Wojciech Wegrzynski>I think that that's highly justifiable.

00:29:38.123 --> 00:29:48.877
<v Wojciech Wegrzynski>Even though you cannot quantitatively tell how big the difference is, it's obvious that the larger size will be easier visible from larger distances.

00:29:48.877 --> 00:30:00.748
<v Wojciech Wegrzynski>And actually, the second thing is that if you ever use Jin's model to assess visibility from distances higher than, let's say, 10-15 meters, I would say 15 is already questionable.

00:30:00.748 --> 00:30:02.010
<v Wojciech Wegrzynski>I would not use it.

00:30:02.010 --> 00:30:06.759
<v Wojciech Wegrzynski>Like tenability distance 10 meters, yeah, okay, fine, we can use it.

00:30:06.759 --> 00:30:32.036
<v Wojciech Wegrzynski>But if you are interested in visibilities of 30, 50, 100 meters, let's say you're designing a runway for an airport or you're designing a traffic system or something else, perhaps using larger values of visibility that are far away from Jin's experiment, that would mean that the signs observed are absurdly large, it makes no sense and I would not extrapolate into distance for sure.

00:30:32.384 --> 00:30:41.194
<v Wojciech Wegrzynski>And the third very challenging thing that we found about Jin's experiments and this is something I do not fully understand yet is how he has considered the light reflecting signs.

00:30:41.194 --> 00:30:53.826
<v Wojciech Wegrzynski>So, as I mentioned before, you have this dimensionless brightness how much brighter or dimmer the sign is than your background and now you have your light reflecting signs.

00:30:53.826 --> 00:31:06.942
<v Wojciech Wegrzynski>For light reflecting signs, by definition, your value cannot be larger than one, Like your sign cannot reflect more light than the background.

00:31:06.942 --> 00:31:13.634
<v Wojciech Wegrzynski>And the dimensionless brightness, in my opinion, will be reflectance of the sign.

00:31:13.634 --> 00:31:14.826
<v Wojciech Wegrzynski>That's it Like.

00:31:14.826 --> 00:31:21.071
<v Wojciech Wegrzynski>It's impossible for the signage to have a higher value than the reflectance In smoke.

00:31:21.071 --> 00:31:29.657
<v Wojciech Wegrzynski>It could even have a lower value because the light has to reach the sign and it's already obscured on its way from the background to the sign to be reflected.

00:31:29.657 --> 00:31:33.532
<v Wojciech Wegrzynski>Therefore, this will be probably even lower than the reflectance.

00:31:33.532 --> 00:31:50.717
<v Wojciech Wegrzynski>But in general you cannot have value larger than one and indeed in Gene's model he does not show any results for value higher than one, but it doesn't stop the line to cross that point, you know, and there are like extrapolations for values between one and two.

00:31:51.626 --> 00:31:55.717
<v Wojciech Wegrzynski>The second thing is, when you have those light reflecting signs.

00:31:55.717 --> 00:32:09.192
<v Wojciech Wegrzynski>You really do start losing the ability to see them very quickly and this is something that we start having a little bit different results than gin, extremely scattered results, I would say.

00:32:09.192 --> 00:32:18.537
<v Wojciech Wegrzynski>It's space in which, especially in darker conditions, it's really challenging to observe those light-reflecting signs.

00:32:18.537 --> 00:32:28.898
<v Wojciech Wegrzynski>And we're also looking into photoluminescent signs, which are of interest to us because it's a common technology used in my country for almost all of your evacuation signage.

00:32:28.898 --> 00:32:32.134
<v Wojciech Wegrzynski>So we start to see different results.

00:32:32.134 --> 00:32:48.974
<v Wojciech Wegrzynski>Perhaps we also get results that could match Jin's observations, but in this case we had five observers, so it was us the researchers, but five different people, and the differences between us are profound in this regime.

00:32:48.974 --> 00:32:55.178
<v Wojciech Wegrzynski>So it's very, very hard to create a good universal model for that.

00:32:55.178 --> 00:33:00.738
<v Wojciech Wegrzynski>For the light-emitting science, for the very bright science, we found good agreement between us.

00:33:00.738 --> 00:33:06.377
<v Wojciech Wegrzynski>It was actually much more reasonable to approximate among the population.

00:33:06.904 --> 00:33:12.738
<v Wojciech Wegrzynski>But for light reflecting science, this is like way, way, way more difficult than I thought it's going to be.

00:33:12.738 --> 00:33:16.895
<v Wojciech Wegrzynski>It's a part of the paper that we really struggled to write.

00:33:16.895 --> 00:33:21.010
<v Wojciech Wegrzynski>And also the ability to see those signs.

00:33:21.010 --> 00:33:30.856
<v Wojciech Wegrzynski>You lose it at very low obscuration densities of your smoke and also you lose them at very low background lighting.

00:33:30.856 --> 00:33:35.596
<v Wojciech Wegrzynski>There are background conditions that you don't even need smoke and you still cannot see the signs.

00:33:35.596 --> 00:33:48.036
<v Wojciech Wegrzynski>So definitely this part of the model is probably way more complicated than a simple relationship brought by Jin and probably very difficult to use in real-world engineering.

00:33:48.424 --> 00:34:00.251
<v Wojciech Wegrzynski>What, for me, is even more challenging is that Jin has made a claim that you could use this approach to distinguish the presence of solid boundaries like walls, columns, doors etc.

00:34:00.251 --> 00:34:07.090
<v Wojciech Wegrzynski>And many engineers practice it like that, and for me this is very questionable because the size will matter a lot.

00:34:07.090 --> 00:34:19.152
<v Wojciech Wegrzynski>Like I mentioned before, the size of the sign will really influence the outcomes of the observation, and if we're talking about a column or a door, they are enormous compared to a little placard of an evacuation sign.

00:34:19.152 --> 00:34:26.753
<v Wojciech Wegrzynski>Therefore, I struggle to say that you can use the same rule applied to both of those and have the same results as your outcome.

00:34:26.753 --> 00:34:34.856
<v Wojciech Wegrzynski>The other thing is the brightness of the background plays a lot of role and in this case, the brighter the background, the better the visibility of the signage.

00:34:34.856 --> 00:34:39.456
<v Wojciech Wegrzynski>So you can see we come into some sort of competing objective.

00:34:39.965 --> 00:34:54.648
<v Wojciech Wegrzynski>If you want your backlit evacuation signs to be best visible, you would like to have as dark environment as possible, because that allows you to see the backlit, the self-illuminated signs in the best way.

00:34:54.648 --> 00:35:03.170
<v Wojciech Wegrzynski>If you want your reflecting signs to be visible, you probably want the brighter environment, as bright as possible.

00:35:03.170 --> 00:35:06.617
<v Wojciech Wegrzynski>Only the brightest environment will allow you to see those.

00:35:06.617 --> 00:35:13.817
<v Wojciech Wegrzynski>And if you want to look at your photoluminescence signs, you probably want as dark as possible, because any light will overshadow them.

00:35:13.817 --> 00:35:19.297
<v Wojciech Wegrzynski>So it's a challenging engineering environment in which you have to make choices.

00:35:19.297 --> 00:35:25.005
<v Wojciech Wegrzynski>Should my evacuation emergency lighting conditions be very bright or should they be dim?

00:35:25.005 --> 00:35:30.260
<v Wojciech Wegrzynski>Is there the perfect point at which you get the most of both worlds?

00:35:30.260 --> 00:35:30.902
<v Wojciech Wegrzynski>I'm not sure.

00:35:30.902 --> 00:35:32.166
<v Wojciech Wegrzynski>Probably there is.

00:35:32.166 --> 00:35:34.614
<v Wojciech Wegrzynski>Maybe between 30 and 60 looks.

00:35:34.614 --> 00:35:47.309
<v Wojciech Wegrzynski>Probably somewhere around there you get the perfect point where you still have a great visibility of your emergency lighting and still sufficient visibility of your obstacles and reflecting signs.

00:35:47.550 --> 00:35:49.132
<v Wojciech Wegrzynski>Again, don't quote me on that.

00:35:49.132 --> 00:35:58.425
<v Wojciech Wegrzynski>I still have to write this into a peer-reviewed paper and if it comes out of a journal, then you're very welcome to quote me on that.

00:35:58.425 --> 00:36:05.119
<v Wojciech Wegrzynski>But it's just my feelings and it's really funny that you study a thing for so many years.

00:36:05.119 --> 00:36:08.153
<v Wojciech Wegrzynski>I studied visibility for at least 10 years.

00:36:08.153 --> 00:36:08.414
<v Wojciech Wegrzynski>Now.

00:36:08.414 --> 00:36:27.306
<v Wojciech Wegrzynski>I think I've started studying visibility in 2015, which would make it 10 years of research and I've read Jin's papers countless number of times and yet it took me to repeat the experiments with Wilson to really understand the challenges in that model.

00:36:27.306 --> 00:36:37.240
<v Wojciech Wegrzynski>So to recap that, because I'm babbling for a long time already and I'm not sure if you're getting any value out of that, recap Brightness, background by brightness.

00:36:37.382 --> 00:36:41.652
<v Wojciech Wegrzynski>This is a critical condition in assessing visibility in your buildings.

00:36:41.652 --> 00:37:00.735
<v Wojciech Wegrzynski>Gin, the relationship that you know and that you use in your engineering, assumed 180 lux in the background, which is enormously high, and usually in your building you would have less and that also means that the K factors in darker buildings are larger.

00:37:00.735 --> 00:37:07.135
<v Wojciech Wegrzynski>So you probably are on the safe side if you're already engineering for K values around 8.

00:37:07.135 --> 00:37:20.677
<v Wojciech Wegrzynski>You probably could even increase that number if you know your background conditions and we are working very hard to provide you a quotable item on how much you can increase that and what space you can play with.

00:37:20.677 --> 00:37:31.577
<v Wojciech Wegrzynski>But it seems reasonable that our buildings are a little darker than Jin's experiments and the visibility in those buildings should be a little better than what's predicted.

00:37:31.577 --> 00:37:32.398
<v Wojciech Wegrzynski>That's good news.

00:37:32.398 --> 00:37:43.577
<v Wojciech Wegrzynski>Second news is that the sign size was constrained in Jin's model, which makes the model not as directly useful as we hope it to be.

00:37:43.577 --> 00:37:57.880
<v Wojciech Wegrzynski>We are looking for a solution, which I do not have right now, but I think it's highly justifiable to use larger signs in your fire safety engineering as a measure to increase safety in your buildings.

00:37:57.880 --> 00:38:04.757
<v Wojciech Wegrzynski>I am 100% convinced that if you use larger evacuation signage, you improve safety of your buildings.

00:38:05.304 --> 00:38:10.918
<v Wojciech Wegrzynski>The third thing is the reflectance of the light reflecting signs.

00:38:10.918 --> 00:38:20.532
<v Wojciech Wegrzynski>This is something that's going to dictate their performance and the performance is lost very quickly in almost any smoke, probably even worse than in Jin's model.

00:38:20.532 --> 00:38:36.376
<v Wojciech Wegrzynski>So beware, those signs in smoke will not really work well and you, if you have conditions in which you have smoke on your evacuation routes, you really should use the backlit signs, because those are the ones that will be visible in smoke conditions.

00:38:36.376 --> 00:38:42.552
<v Wojciech Wegrzynski>I've also mentioned Mulholland's specific smoke extinction coefficient.

00:38:42.552 --> 00:39:01.614
<v Wojciech Wegrzynski>There's a default value of 8.7 square meters per gram, I believe, and this value is being default used in FDS and my colleagues from Germany, the ones that I'm doing project with Christine Berger, professor Lukas Arnold, alexander Belt and Christoph Gnendiga and Tolsten Schutze.

00:39:01.614 --> 00:39:07.217
<v Wojciech Wegrzynski>Together they found some new ways to measure extinction coefficients from aerosols that are very interesting.

00:39:07.217 --> 00:39:08.985
<v Wojciech Wegrzynski>I'll link the paper in the show notes.

00:39:08.985 --> 00:39:15.413
<v Wojciech Wegrzynski>They show largely different values than the ones reported by Mulholland, so it's also something we need to take in mind.

00:39:16.144 --> 00:39:20.036
<v Wojciech Wegrzynski>So where do we go ahead with this in fire safety engineering?

00:39:20.036 --> 00:39:34.114
<v Wojciech Wegrzynski>One thing that is obvious is that the existing model whether it's wrong or not, it definitely allowed us to engineer buildings that would be considered safe, and I do not question that I've been asked.

00:39:34.114 --> 00:39:35.369
<v Wojciech Wegrzynski>So what do we do now?

00:39:35.369 --> 00:39:37.132
<v Wojciech Wegrzynski>Do we cancel the visibility in smoke model?

00:39:37.132 --> 00:39:38.891
<v Wojciech Wegrzynski>No, we cannot cancel it.

00:39:38.891 --> 00:39:43.793
<v Wojciech Wegrzynski>We use it in like 93% of our projects as the tenability criterion.

00:39:43.793 --> 00:39:45.893
<v Wojciech Wegrzynski>It's too impactful to be canceled.

00:39:45.893 --> 00:39:50.215
<v Wojciech Wegrzynski>We need to use it, but we need to find a smart way to use it better.

00:39:50.215 --> 00:39:55.527
<v Wojciech Wegrzynski>Therefore, I still think it's a useful tool In my engineering.

00:39:55.586 --> 00:40:13.405
<v Wojciech Wegrzynski>A long time ago, I've moved away from visibility in smoke and I started using smoke density as the measure of my tenability using smoke density as the measure of my tenability, and I like this approach much better because it just works on raw data from CFD that I get smoke densities what I do get from my CFD.

00:40:13.405 --> 00:40:16.291
<v Wojciech Wegrzynski>Therefore, I like to work with smoke density directly.

00:40:16.291 --> 00:40:31.496
<v Wojciech Wegrzynski>But I think at this point the model while I feel it's a bit wrong in the spaces that I've described in this episode it plays an important role in modern engineering and still can be used.

00:40:31.496 --> 00:40:35.190
<v Wojciech Wegrzynski>I'm really looking into possibility to modify it.

00:40:35.190 --> 00:40:42.588
<v Wojciech Wegrzynski>Perhaps due to the sign problem it's not not possible to just simply, you know, find a new k value and be done with it.

00:40:42.588 --> 00:40:47.318
<v Wojciech Wegrzynski>Perhaps there is more engineering to be done to have the model work.

00:40:47.318 --> 00:40:49.954
<v Wojciech Wegrzynski>But if there is a way we will find one.

00:40:49.954 --> 00:40:54.637
<v Wojciech Wegrzynski>And we're also working on a new generation of visibility in smoke models.

00:40:54.637 --> 00:41:02.873
<v Wojciech Wegrzynski>Our friends at Wuppertal are having great progress in numerical modeling smoke and optical properties of smoke.

00:41:02.873 --> 00:41:18.947
<v Wojciech Wegrzynski>I'm super excited for the work from Lucas Arnold's group on this and we're working together to find new relationships, new models and new ways to engineer fire safe buildings with visibility in mind, and visibility understood as ability to see objects through smoke.

00:41:18.947 --> 00:41:21.012
<v Wojciech Wegrzynski>So that's for the future.

00:41:22.074 --> 00:41:23.235
<v Wojciech Wegrzynski>Think I will stop here.

00:41:23.235 --> 00:41:26.067
<v Wojciech Wegrzynski>That would be it for today's fire science show episode.

00:41:26.067 --> 00:41:31.184
<v Wojciech Wegrzynski>Thank you for being here with me again listening to my rambling about visibility in smoke.

00:41:31.184 --> 00:41:38.929
<v Wojciech Wegrzynski>I hope this time I've made it remotely useful to you and brought you some opinions of my own that will help you guide your engineering.

00:41:38.929 --> 00:41:47.295
<v Wojciech Wegrzynski>Let's call them design considerations I love how FSRI calls their recommendations to firefighters and the considerations.

00:41:47.295 --> 00:41:56.114
<v Wojciech Wegrzynski>So I gave you some visibility in smoke considerations that, whatever you do with them, it's yours, but I hope they're useful in your engineering.

00:41:56.114 --> 00:42:01.994
<v Wojciech Wegrzynski>Thanks for being here with me in the Fast Science Show and I'm looking forward to see you here next Wednesday.

00:42:01.994 --> 00:42:02.945
<v Wojciech Wegrzynski>Cheers, bye, bye.