So the light is coming in, but we’re also able to see out of it.So it’s reflecting and transmitting at the same time.And then after that, we have our camera.

In this US Government lab, they study air flow to solve crimes, using mirrors, lights and lasers to illuminate the tiniest differences in air temperature and density, and track how drug powder settles in the rooms of a house, determine which person fired a gun, or spot particles escaping from a sealed package.

However, it turns out nature has already provided us with the best chemical detector - the dog’s nose. To demonstrate this, they used a 3D-printed, anatomically-correct model of a female Labrador Retriever named Bubbles. Dogs can sniff very faint scents and from far away, but they don’t do it just by breathing in. They breathe out and in rapidly around five times a second - creating a turbulent air jet that comes out of each nostril. This allows them to detect scents from far away and push air back, pulling air from ahead of them.

To further demonstrate this phenomenon, they used Schlieren imaging to show the dog’s breath. This was done using an automotive headlamp, condenser lens, mirror, and camera. The light beams were used to detect something of a different refractive index, such as the heat from a hand, or a different density, such as a gas of a different density. By making the vapor detectors sniff like a real dog, they were able to improve the detection capabilities by roughly a factor of 16 to 18. And this is a really powerful tool to be able to visualize what is happening in the air.

Light can travel through a mirror, but when it comes back, it turns 90 degrees. To block certain beams of light, a razor blade is positioned exactly at the focal point of the mirror. By moving the knife edge in and out, turbulence in the air can be seen. A Shadowgraph system is a similar but less sensitive tool than a Schlieren system, which requires a flashlight and a white wall to cast a shadow of a plume on the wall. When a gun is fired, the hot gases released expand outwards and create a shockwave, which can be observed in the Shadowgraph. The darkness of the shockwave indicates the loudness of the gun. A laser sheet can also be used to visualize flow, which illuminates fine particles such as gun powder residue when a gun is fired. This is a powerful tool to understand gunshot residue. We’re looking at the plume of gunshot residue generated after a firing event, which can’t be seen with the naked eye. We’re trying to differentiate between something that’s been done by the shooter and something done by a bystander. We use laser lights and high speed cameras to help illustrate what’s happening, and this is related to trace contraband detection. We’re all constantly shedding skin cells, and this is an important principle in forensic science called Locard’s Exchange Principle. We’re also doing experiments to simulate illicit drug manufacturing, and we use lasers to help us see the plume that’s generated, which we wouldn’t otherwise be able to see. And so what it does is it takes the video that’s coming out of this camera, and it’s basically doing a pixel-by-pixel analysis of the particles that are in the air.

Let’s do a little experiment where I take illegal substance A and pour it into substance B. I’ll just watch when I take the lid off of this. (tense music) Take it from here. There is a little bit coming off, yeah. A little bit? Oh yeah. It’s still going. So just imagine, you’re in a basement, and you’re building stuff like this, and you don’t realize that there’s all this contamination spreading and landing on other surfaces in your room. And I can’t talk about the numbers, but they’re pretty startling. Like there’s a lot. There’s a lot. It spreads everywhere. There’s a lot, yeah. (tense music) This thing’s going to be full of smoke in here. You ready? Yep. (tense music)

What I really love about the laser sheet technique is it allows you to visualize the turbulence that’s in the air. [Matt] So this is a way we can see how the air flow in the room is actually being tracked. Oh, that’s nice. [Matt] Yep. If you look at the graph and the top right, that is actually real-time counts of the particles that are being generated around this person. So that plot represents basically inhalation exposure of the materials that he’s working with. That’s crazy, if you think about, ‘cause if that’s fentanyl, and that person doesn’t have a mask on, they’re gone.

We add fluorescent powder to this kind of stuff, so we can actually visualize where the contamination goes. The other cool part of this is that we can use a quantitative method of sampling surfaces in the house. We basically use swabbing. And it’s the same idea when you go to the airport. Have you ever gone there and they ask for your hands? Yeah. Right? And they take a little swab and they wipe your hands. What they’re doing is they’re looking for these trace amounts of explosive particles that could be on you if you were involved in the manufacture of an explosive device.

But that’s a drone. That’s looking at a drone. And the question is, ‘cause you know, you get this cool prop wash, and these four propellers that are are all interacting with each other. So the question is, can we use the fluid dynamics of a drone to do the sampling for us? And here’s what I mean by that. If there is a suspected, you know, manufacturing facility of something, say it’s a methamphetamine or fentanyl, you know, it’s very, very expensive to get Hazmat crews involved. Have them come, they have to gown up, they have to go in, to a potential really dangerous situation. What if we had a drone? We just flew the drone in, right? It buzzes around and it’s got some special kind of collector on the belly of the drone and we’re using the prop wash of the drone to stir up particles off of a surface, and then somehow inhale them, collect them. The drone comes back to base, you run your chemical analysis, you say, okay, the house is clean, or no, we found stuff. Okay, now it’s time to pull out the Hazmat crew. You know?

So the big-picture idea that I want you to keep in the back of your head the whole time is this idea of public safety and security. So that’s really what happens in this lab. But underneath that kind of umbrella term, think mask research. So when the Covid pandemic hit, we kind of switched gears in here to try to address some of the issues related to masks. This thing will actually breathe as a human does, that human happens to be me. So I measured my own kind of breathing rate, and then built a system, kinda engineered a pneumatic system that replicates that, but it also has a fog machine, a fog generator. So this thing basically just looks like it took a drag off of a cigarette and exhaled.

What’s kind of cool with this is it looks like there’s nothing coming through, right? But there is millions and millions of particles trying to make it through. Some do, ‘cause it’s not 100%. So I wrote an image-processing code. And so what it does is it takes the video that’s coming out of this camera, and it’s basically doing a pixel-by-pixel analysis of the particles that are in the air. So you take this information, plug it into a code, and it analyzes, based on pixels and it’s counting white pixels, and sure enough, if you use an N95, you put an N95 on here, you run it through an image processing code, guess what percentage of pixels light up white? - 5%. Now I just want you to breathe naturally. When you’re inhaling, it gets dark, and when you’re exhaling, it gets lighter, because the air is being warmed by your lungs and then coming back out. It’s interesting how fast you can see the effect of the breathing in, like just makes it go dark so quickly. But that shows me that, like this now doesn’t change color at all, so this is being used to seal versus filter. I notice the color change is a lot more dramatic with a thinner mask.

The thing with masks, right, is like, initially they were like, masks don’t work, don’t wear a mask. And then they were like, masks do work, like, and wear a cloth mask, and then they were like, no, no cloth masks don’t work, like, I don’t know, there was a lot of confusion around masks. What we learned early on was that the communication of, you know, mask effectiveness could have been improved, right? And so that’s kind of why I did what we did with the Schlieren. The truth is, the average American is not gonna sit down and read a scientific journal article. But they will sit down and watch a 90-second video of me coughing with a mask on and off. And that’s what we did. It’s kind of a unique relationship we have with other federal agencies here. So you have a three-letter agency that has a specific need for something, right? In the security arena. What they’ll often do is they’ll come here to NIST, and they’ll say, hey, we’re really interested in sampling people’s shoes for explosives for whatever reason, right? So what we do here, and in this lab in particular, is we figure out what are some good ways to sample shoes for explosives? What are some not so good ways, right? What do the measurements need to look like to evaluate a shoe-sampling system that doesn’t even exist yet? And then what do the standards need to look like that support those measurements, right? And so we figure all this stuff out in the lab, package it up nice and neat, give it back to the sponsoring agency, and then they take it to industry. And industry already has a leg up on the development of these kinds of systems, because we did a lot of the heavy lifting here in the lab.

Because with the success of, you know, doing the Covid-related visualization, we’re realizing now that the application space for this kind of technology is huge. Indoor air quality. You can imagine a bigger mirror where we could look at two people interacting with each other, and what that transfer looks like from one person to the other. The take-home message is flow visualization is a critical tool that we use here at NIST to really help understand what’s happening, right? It’s one thing to do quantitative analysis on various surfaces, but now we can see, we can actually see what’s happening, and where these particles are generated.

Thanks to Lutron for sponsoring this portion of this video. Perfect lighting isn’t just important for visualizing air flow, it’s also essential for making your house feel welcoming, cozy and safe. And with the sponsor of this video, Caseta by Lutron, you can easily set up your own perfect lighting. You know, Caseta provides premium smart lighting control, including switches, remotes and plug-in smart dimmers, which allow you to customize your home lighting from anywhere in the house. What I love about smart switches is that one switch can control many regular bulbs. Replacing your switch with Caseta’s Smart Switch is an easy way to make all your bulbs smart. Installation is easy: turn off power to the switch, disconnect the existing wires, and connect them to the Smart Switch. In addition, they provide help with just a click or a call away. With the Smart Hub, you can control your lights with your phone, or with Alexa or Google Assistant. Caseta works with more smart home brands than any other smart lighting control system, and their switches don’t rely on Wi-Fi, so you always have control. I personally like setting timers in my house, for example the lights in my office turn on by themselves in the evening, giving me peace of mind that my family will always come home to a well-lit house. Even when I’m already in bed, I can check which lights are still on and turn them off without having to run around the house. To learn more about Caseta, visit casetawireless.com/veritasium. Thanks to Lutron for sponsoring that part of my video.