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Lynn Hildemann: What’s lurking inside our homes and offices?

An expert on air quality talks about the hidden dangers of indoor pollutants and offers tips to reduce our exposure.

A disproportionate amount of attention has been paid to pollutants and emissions inside. | Stocksy/Aleksandar Novoselski

A disproportionate amount of attention has been paid to pollutants and emissions inside. | Stocksy/Aleksandar Novoselski

We all know about the decades-long battle to improve air quality outdoors, but Stanford environmental engineer Lynn Hildemann says that while much progress has been made in that regard, it may have caused us to look past the pollutants in our own homes.

Hildemann, who studies air pollution and its effects inside and outside the home, says that chemicals and microparticles from cooking, furniture, carpets, cleaning products and good-old household dust represent the latest air quality battleground. She says it’s such a big concern because most Americans spend some 90 percent of their lives indoors.

Hildemann offers a few small steps we can all take to improve air quality at home. Using the ventilation hood when cooking is a great first step. Opening the windows whenever possible is another. And, opting for easily cleanable hardwood floors over carpet can help, too.

You can listen to The Future of Everything on Sirius XM Insight Channel 121iTunesGoogle PlaySoundCloudSpotifyStitcher or via Stanford Engineering Magazine.

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Russ Altman: Today on The Future of Everything, the future of air pollution. Now, I grew up in Brooklyn, New York in the 1960s, and during my childhood, pretty much through kindergarten, we lived in an apartment in Brighton Beach, near Coney Island in Brooklyn, with, on the 18th floor of a building that gave us a spectacular view of the New York City skyline, and I actually remember, and, as an aside, I remember watching the World Trade Center Twin Towers being built during my childhood. I watched them rise up during the construction, but what I remember even more vividly is a layer of brown smog that enshrouded all the buildings in Manhattan. It kind of started about halfway up the buildings, and it ended somewhere above them, and it was unmistakable. It was brown, and even as a 5- or 6-year-old child, I remember thinking, “That can’t be good,” and I’m not ever sure that I connected that observation with the fact that I had pretty bad childhood asthma, but there may have actually been a connection there.

Unfortunately, the other — I had a wonderful childhood — but the other not so great memory I have is sitting in that same apartment with relatives playing cards and smoking, and I remember it was fun to see the patterns of smoke, you know, as they, as it got blown out of their mouth, and it formed these little clouds of smoke in the apartment, and the sun came through from the window and illuminated the smoke, and it was all very entertaining as I watched them, basically, exhale cigarette smoke into the room.

Fast forward 50 years. We have a much better understanding, I think, of the health consequences of the pollution that I saw in the New York City skyline, of the potential impacts on my health of that smoke from my relatives. We know about particulate matter counts, and how they are affected by different factors, cars, aerosols, mold, and others. In the West Coast of the United States, we see the effects of fire on air quality. We’ve had some, couple tough years with big fires, and in developing nations, we see a struggle to keep air clean, while ramping up industrial capacity.

So how are we doing with our air? Are things better now than they were in the 60s, both locally and globally?

Professor Lynn Hildemann is a professor of civil and environmental engineering at Stanford University, and an expert at human exposure to particulate matter, air pollution, is what I call it. We’ll find out if that’s the right term. Lynn, people may think that the issues of air quality are a problem chiefly in the developing world, and that with smoking rules, and car emission standards, things are under control in the United States. Well, how are we doing?

Lynn Hildemann: I would say we’re doing better than we use to do for the outdoors. Cars are so much cleaner now, but it’s a constant battle between having more population, more congestion, and trying to have less and less emissions from things like cars. Where things have not gotten so much attention are indoors. We spend, depressingly, in California, 90% of our time indoors, and we’re breathing while we’re indoors.

Russ Altman: And we think of ourselves as an outdoorsy type state.

Lynn Hildemann: Yes we do.

Russ Altman: Maybe not so true.

Lynn Hildemann: A lot of what someone breathes every day is in the indoor environment, and there hasn’t been nearly as much attention paid to emissions and pollutants indoors that you would be breathing while you’re spending time indoors.

Russ Altman: Things are better on the outside, but we need to focus. Tell me about the inside because, so now, a common thing that we’ll do at my home is, we’ll open all the windows if it’s a nice evening, to let the air in. Is that a good idea, a bad idea? Do we even know? What are the sources of trouble in the internal, kind of built environment?

Lynn Hildemann: So when you look at air pollution indoors, you’ve gotta think about, does it come from indoors, or come from outdoors? If you and I were living in Beijing, the last thing we’d want to do is open our air, our windows, and let in the really bad air pollution from outdoors, but someplace like the Bay Area, opening windows is a very good idea because the outdoor air pollution here is very low. I tell students in my class it’s boring. Just not much going on, most of the time.

Russ Altman: Is that a change from 40, 50 years ago, or has it always been pretty good around here?

Lynn Hildemann: Around here, it’s always been pretty good. We’re lucky with the meteorology. Nice winds, kind of carrying everything away. So around here, though, what we really worry about are indoor sources of air pollutants, and as you say, if you, if you don’t have those windows open then they tend more to build up in the indoor environment, and you’re exposed to higher levels.

Russ Altman: So what are the primary sources? Like right now, nobody in my home is smoking. We don’t turn the car on in the house. Where is, where are the bad stuff coming from?

Lynn Hildemann: So, you worry about —

Russ Altman: Or is it bad? I mean, I guess, is the question.

Lynn Hildemann: It varies from home to home. You worry about cooking. So many people don’t like to use their hood above their stove, so all those emissions are going into the home. You worry a lot about dust that can be re-suspended into the air. Dust on your carpet, dust on your furniture. That dust contains all sorts of things, including allergens, for example.

Russ Altman: What about, I know you’ve written a little bit about plastics, new car smell, furniture that you bring into the house. Do we need to worry about this, or is, or have, kind of, regulatory agencies in the United States, at least, keeping an eye on the quality of the air produced by new furnishings, and rugs, and drapes, and stuff like that?

Lynn Hildemann: I think we’ve got a long way to go in doing a better job of regulating, or looking at what’s emitted, and that’s true not only of furniture, but home cleaning products. It’s so easy for people to think, “Oh, this has a certain symbol on the package. It must be natural, organic, good for me,” but analyses have shown there’s still a lot of very not good, organic chemicals in those that are ending up in your air indoors when you use them.

Russ Altman: Now, how, so this is really important. How well do we understand the health impacts of these indoor particulate matters? Is it, is it a vague sense that this can’t be good? Or is there now starting to be evidence that no, no, no, we can show adverse outcomes based on these exposures?

Lynn Hildemann: I find the evidence strong, but honestly, it’s not as structured as some people would like. You can’t take a group of people and say, “Hey, we’re gonna set you inside this room with this smelly stuff.”

Russ Altman: It’s unethical to like, expose people on purpose.

Lynn Hildemann: Yes, let me know. So you end up looking at big, urban areas, and saying, “Oh, okay the pollution was really high during this time period. What health effects did we see?” But the, for particulate matter, it’s pretty well understood that some of those particles deposit in your lungs.

Russ Altman: Yes.

Lynn Hildemann: And can cause irritation, and can take weeks or even months to clear back out.

Russ Altman: This is The Future of Everything. I’m Russ Altman. I’m speaking with Dr. Lynn Hidelbrand, Hildemann, excuse me, about particulate matter in the air, and air pollution.

So you, I looked at some of your papers, and one of the things I love about your work is that you’ve done a lot of what I would say, kind of, almost experiential research. One example is, you wrote a paper about the exposures that some, that I think 70 people had while driving in a car to a restaurant. So can you tell me about that study? Why would you do that, and what did we learn from it?

Lynn Hildemann: Yeah, the interest is, of course, we also spend a fairly significant amount of time in our car, driving around. You would think of indoor sources like that new car smell, if you’re lucky enough to have an indoor, a new car, and then there’s —

Russ Altman: Many of our Sirius listeners will have a new car since Sirius often comes with your new car.

Lynn Hildemann: Okay, well, there you go.

Russ Altman: So, hi out there, and hope you’re enjoying your new cars, but listen to what she’s about to say.

Lynn Hildemann: But then you also worry about, when you go inside the restaurant, how good is their ventilation system? What type of cooking are they doing? Is it actually polluted indoors, while you’re in the restaurant?

Russ Altman: So going out to the restaurant, there’s the indoor phase of being in the car, and then there’s the indoor phase of being in the restaurant. So what did you find when you looked at these? Was that about 70 people, or so, that you followed?

Lynn Hildemann: It was, yeah, it was about 70 different restaurant visits, and it was, most of the time, it’s pretty safe. Once in awhile, it’s much more interesting, and the much more interesting tended to be in just a few of the restaurants, that we didn’t look in great detail into why, but the levels of airborne particles were a lot higher than what we would’ve expected, based on outdoor levels.

Russ Altman: And I would guess that you, it’s very difficult for a person who’s concerned about this to get any information about the likely exposure at their favorite restaurant?

Lynn Hildemann: No. I mean, they can go by smell, if it smells smoky indoors, but otherwise, it’s not much information available at all.

Russ Altman: And what is the experience in the new cars like? Was that alarming, or not so much?

Lynn Hildemann: We were not measuring for new car smell.

Russ Altman: Okay.

Lynn Hildemann: But what we were measuring for would’ve been mainly pollutants coming from the roadway, and then entering into the vehicle, and the main pollutants to worry about besides the airborne particles, the smoke from the tailpipe is carbon monoxide, and the good news there is CO emissions from motor vehicles have dropped way down, so that part was, felt very safe. For the particulate matter, once in awhile, we’d get behind a car or a truck that was not well tuned, and was emitting a lot of smoke.

Russ Altman: We’ve all seen those, with the black puffs.

Lynn Hildemann: And yes, indeed, it does make it inside your car.

Russ Altman: That’s interesting. So yeah, so the intake valves, the intake inlets from the car will just suck up that black smoke and blow it in your face, basically.

Lynn Hildemann: Yeah, I mean, cars have somewhat of a filter, but not a really great one, and certainly, if you have your windows down a little, then that negates any filtration protection you get.

Russ Altman: So since we’re talking about that, another really fascinating series of studies that you’ve done has looked at particulate matter levels in people who are near roadways, either because they’re at a bus stop, I believe, there was one paper, or because they live. So can you summarize? Is it risky to live near a highway, or a major thoroughfare? And what did you find in that work?

Lynn Hildemann: I mean, that’s part of a broader interest I’ve had in, what if you’re close to where the emissions are happening? And we call it the proximity effect, being close to the source, and you worry about this indoors, as well as for outdoors, if you’re near roadways, or near a major industry, and so yes, we were particularly interested in that study, and these extra, extra, teeny tiny particles that are generated sometimes, and we did see elevated exposures at times. For example, people sitting at bus stops.

Russ Altman: And tell me about these small ones. Are these a particularly worrisome, or are they just a new phenomenon that people don’t know what to make of?

Lynn Hildemann: They’re a new phenomenon. People aren’t sure what to make of them. There is concern that the smaller the particle is —

Russ Altman: And how big are we talking, for when you say teeny tiny?

Lynn Hildemann: Teeny tiny is less than, say, a tenth of a micron, and to give context, a typical human hair is about 100 microns, so it’s much, much tinier than that.

Russ Altman: And then I think a red blood cell is five or six microns, so this is much smaller than a single cell in your body.

Lynn Hildemann: Right, and the thought is it’s, alas, maybe easier for it to pass into the bloodstream from your lungs when it’s that small.

Russ Altman: And so people sitting at bus stops were getting more of these?

Lynn Hildemann: Yes.

Russ Altman: And that, those bus stops are, those are not long exposures, so that’s pretty concerning, because if you sit there for 10, 15 minutes every day, twice a day, there could be an accumulated exposure that’s quite significant.

Lynn Hildemann: Yeah, but it wouldn’t just be true for bus stops, Russ. It would be true if you, if you like to walk along a busy roadway, if you’re a jogger, and you like, your jogging route includes some busier roadways, so it is a broader concern than just for bus riders.

Russ Altman: Again, going down the list of what I found to be fascinating studies, you participated heavily in the secondhand smoke research and science, in particular. I saw that you wrote some papers about casinos, and so what were, what are the issues? And anybody who’s been in a casino, well, people who’ve been to casinos know two things. One is that 15 years ago, they were probably the most smoky, difficult areas to be in if you were not a cigarette smoker, and that there’s been a miraculous change, at least like, in places like Las Vegas, with smoke-free, so I guess there’s both a technical story, and then a political/social story about how we went from casinos where you walked in and started coughing, to casinos where you really don’t even smell smoke anymore, so tell us about that.

Lynn Hildemann: Sure, sure. We got interested in casinos in California because it is pretty much the only public place in California where smoking is still allowed.

Russ Altman: And is that true today?

Lynn Hildemann: Oh, yeah. It’s because these casinos are run by Native American tribes, and so they do not have to follow California laws.

Russ Altman: Gotcha.

Lynn Hildemann: We, what was exciting about this study is we did it covertly. We did not let the casinos know we were coming because past experiences involving a colleague of mine who did some measurements in Las Vegas is, if they know you’re coming, they turn the ventilation system way, way up, and so we went in and did measurements. We did measurements of people sitting and playing slots, and also of people kind of just walking around, to try to get a feel for the whole casino. We measured non-smoking areas, ranging from the magic line on the floor.

Russ Altman: Yeah I love those.

Lynn Hildemann: That says, “This side is non-smoking,” and “The other side is smoking.”

Russ Altman: Those of us old enough to remember the non-smoking section of airplanes, where there was this magic line, and there was, everybody was smoking, and it was kind of ridiculous, but that’s how they did it.

Lynn Hildemann: Yes. So the magic line doesn’t work so well, shocker, but the problem casinos have is, for the non-smoking areas, they want them to look inviting, and so even if they have doors that they can close to kind of seal them off well, they tend to leave them open, so that they’ll look more inviting, so you actually still see higher levels of smoke in there than what you would experience outdoors. Now, the other really interesting thing with that study is, we also measured in restaurants.

Russ Altman: Yes.

Lynn Hildemann: And in a lot of the —

Russ Altman: Affiliated with the casinos?

Lynn Hildemann: Yeah, in a lot of the bigger casinos, there’s restaurants that overlook the gambling area, and even though children aren’t allowed on the gambling floor, they’re allowed in the restaurants, and a lot of those restaurants were also being impacted by the cigarette smoke from the gambling area.

Russ Altman: This is The Future of Everything. I’m Russ Altman. I’m speaking with Lynn Hildemann about her work in casinos, and at bus stops, and so the message really is coming clear that these indoor environments are really showing some worrisome trends.

One of the things you’ve also written about, I’ve just gotta ask about this last one, is dryer lint, so I was amused and stunned to see that I had a colleague who was writing. So what is the issue with dryer lint, and particulate matter in the indoor environment?

Lynn Hildemann: That was certainly a small study. It’s not something that—

Russ Altman: You still get credit for it.

Lynn Hildemann: Comes up on everyone’s mind, but anyone who’s used a dryer knows that you then reach in and pull out all the lint.

Russ Altman: Of course, it’s one of my favorite obsessive compulsive things to do.

Lynn Hildemann: You can see this kind of puff come out, as you do so, and so the question was simply, “How bad is it? How much is being released?” And the somewhat good news is yes, you know, your eyes aren’t deceiving you, but the fact that you’re able to see those dust particles means that they’re fairly large, and if you breathe them in, they’ll be immediately captured by your nose or throat. They won’t be penetrating deep into your lungs, where they can stay for weeks or months.

Russ Altman: So, yeah, so that’s a great lesson, which is, it’s not just the amount of particulate matter, but it’s the size, and you talked about those super small ones, and in the case of the lint, it’s kind of macroscopic. It’s bigger, and your normal physiology of your lungs and trachea might be able to clear it without too much of a problem.

Lynn Hildemann: Exactly. You blow your nose and it’s gone.

Russ Altman: This is, and with that, this is The Future of Everything. I’m Russ Altman. More with Dr. Lynn Hildemann about particulate matter in the air next on Sirius XM Insight 121.

Welcome back to The Future of Everything. I’m Russ Altman. I’m speaking with Lynn Hildemann about particulate matter, both indoor and outdoor, and one of the things I want to think about is the home, and one of the big things that happens in the home is cooking. What are the concerns? You mentioned people don’t like to use their hoods, and therefore, things accumulate. Are we worried about the smoke from the cooked food? Or are we worried about things that are coming off the cookware, the Teflon, or whatever? What are the main issues there, and sources that we should keep an eye on?

Lynn Hildemann: The answer to your question is yes, both of them. It’s, certainly everyone’s seen, you know, when their cooking gets a little smoky the — what you’re seeing are teeny tiny particles being generated that can persist in the home for hours.

Russ Altman: And so those are not like the dust lint, which is big, and not so worry. Those are worrisome because of the size.

Lynn Hildemann: Those are worrisome because it, they’re much smaller in size, but the other interesting thing is, even your cookware itself and your cooktops can give off pollutants when you start heating them, and you may have actually seen this once in awhile, that you’re heating something up, and even though there’s no food in it yet, there’s some, and what that is, there’s a little bit of residue left over from either cleaning or having it sit around for a few weeks and that’s also being released into the air. What’s extra interesting about that, Russ, is that those are those teeny tiny particles.

Russ Altman: Yeah.

Lynn Hildemann: Those little ones that you worry about passing into your bloodstream.

Russ Altman: Okay, so it sounds like just from common sense, I know that common sense can sometimes mislead us, but using the hood, and keeping the windows open in the kitchen if you can tolerate it with respect to the temperature outside and other things, those are not bad ideas.

Lynn Hildemann: Those are definitely good ideas.

Russ Altman: Okay. Now, what about new home construction? Have any of these lessons that you and your colleagues have been learning, has that begun to affect any ways in which new homes are being constructed for safety, and to help with these issues?

Lynn Hildemann: So for new homes, it’s a bit of a tug of war. They’re trying to make the homes more energy efficient, and that means they’re sealing them up more, and that means if you have the windows closed, then the pollutants, any pollutants released indoors are gonna stay indoors longer, and build up more. Where I see some good news is more culturally. People are starting to turn away from loving carpet so much, and going back to things like hardwood floors. Those are so much more cleanable than carpets, that you don’t need to worry about having this reservoir of dust that keeps getting re-suspended every time you walk over it.

Russ Altman: My wife and I, who have been happily married for 35 years, as of last week, the one argument that has continued for about 35 years is because of my allergies, I’ve asked that we don’t have rugs or drapes, but it means that our windows, you can see right into our house, and then our feet are always cold because we don’t have rugs, so this has been a big issue, and I will use this part of our conversation to get a little bit of an upper hand, but I can assure you this will not end the conversation. So, any other construction tips?

Lynn Hildemann: So —

Russ Altman: You said the hardwood floors are easier to maintain and clean, windows that open, I guess, would be better, even though there’s a potential energy cost to that.

Lynn Hildemann: So the other thing to think about is the furnishings, and what, the paint you put on your walls, and things like that that, depending on its composition, it can, everyone knows new paint smell.

Russ Altman: Right.

Lynn Hildemann: With water-based paints, all the paint, when it dries, it’s mostly giving off water, so there isn’t much of a smell associated with it. Some of the other paints have all these organic materials.

Russ Altman: The oil-based for bathrooms and stuff because they’re more waterproof.

Lynn Hildemann: Yes.

Russ Altman: So those might be a little bit more concerning because of those organic solvents that are coming out.

Lynn Hildemann: And the one other comment I would make is that to think about the glues that are used to either glue down carpeting in some places, or tiles. The ones that you actually squirt out on the floor and mix together, again, there’s a lot of organics associated with that.

Russ Altman: So in, this is The Future of Everything. I’m Russ Altman. I’m speaking with Lynn Hildemann about indoor air interventions to help improve the quality of the air in your home. There are these apps, well, two things I wanted to ask you about. Maybe we’ll get to the apps in a second.

I know that one important area that you focused on is gender differences, and exposure, and risk. So can you tell me about that work? It sounds like a great topic. It sounds like, kind of obvious that there might be differences based on gender and exposures, and it wouldn’t be surprising to me if they’ve been ignored to the detriment of certain groups. So what have you found?

Lynn Hildemann: The goal of that study was to compare developed countries with developing countries in terms of whether there were, or to what extent there were gender differences. The no big surprise part of it is in developing countries, where it is almost always the female doing the cooking, while the male isn’t even in the household often.

Russ Altman: Not always ventilated, I’m sure.

Lynn Hildemann: Yeah, poorly ventilated. Their exposures can be much worse. What was a little more surprising was that even in the United States, looking at gender differences from a survey, and where people spend their time, that even there, we could spot places where the woman was exposed to more pollutants, but also for you men, the exciting place to be if you really want to get exposed to a lot of pollutants is your garage or workshop.

Russ Altman: Yeah, it’s my favorite room in the house.

Lynn Hildemann: Yeah, yeah, there’s a lot going on there, right? Yeah.

Russ Altman: You’re killing me.

Lynn Hildemann: I’m sorry.

Russ Altman: But it is true. It’s filled with oils, and paints, and dust from wood, and, but this is not good.

Lynn Hildemann: So that’s where, to be kind of gender stereotypical, whoever’s spending more time in the workshop is getting exposed to more of those kinds of chemicals.

Russ Altman: Now, and it’s mostly, so you said from these, from this study, you, the risk to, the women were mostly in the kitchen, and it was the kinds of things we were discussing before, those different dust sources.

Lynn Hildemann: Yeah, and also to a lesser extent, whoever cleans the house is going to be exposed to both the cleaning products, and the dust getting kicked back up.

Russ Altman: So this is fascinating, because it really does suggest that there’s been a shift of concern from the outside environment. My little story about New York, and the smog, and the, to really —

Lynn Hildemann: You were looking at this from your apartment.

Russ Altman: Yes.

Lynn Hildemann: You were inside the apartment while you were looking at it.

Russ Altman: And then there was all the smoke from my relatives that was in the apartment, and that’s where the efforts are, and that’s what I want to get, now I wanted to talk about these apps because there are now, and maybe these are now not so relevant, because it’s come to my attention that there are these apps where you can get air quality measurements from various stations, but these are, as far as I can tell, these are almost all on the outside. So they say, “This is the San Francisco particulate matter count,” or, the ”Beijing, China.” They’re not telling me how things are looking in my garage, or my kitchen.

Lynn Hildemann: That’s correct.

Russ Altman: So what’s your take on these apps? Is this too much information? Is this a distraction? Is it serving a purpose? What, as an expert, how do you look at these?

Lynn Hildemann: I still think it’s very valuable in terms of having you decide what activities you are, or are not going to do on a given day. Russ was referring to the Camp Fire that we had last November, which was, caused very high pollution levels, and friends of mine who were like, “Well, I don’t know how bad it is.” I would show them some of these Bay Area air quality management district maps, where they literally had to create a whole new color to show the —

Russ Altman: For the high end?

Lynn Hildemann: For the high end, and explain to them that purple was very, very bad.

Russ Altman: And we had a lot of purple.

Lynn Hildemann: Yeah, and it was to convince them that no, maybe they really shouldn’t work out.

Russ Altman: And I would guess that those fires are creating particles all along the spectrum of size, but it includes the bad stuff?

Lynn Hildemann: Mainly fine. Whenever it’s a burning type process, it’s mainly the fine particles that end up deep in your lungs.

Russ Altman: So that’s kind of bad news.

Lynn Hildemann: Yes.

Russ Altman: So is there any, are there technologies for measuring indoor air quality that people who are concerned can access? Or is that a future, coming attraction?

Lynn Hildemann: That’s a developing area. It’s exciting. What I would say right now is that some of these monitors available are much better than others. Some of them are probably not worth spending money on.

Russ Altman: So we’re in the Wild West?

Lynn Hildemann: We’re in the Wild West.

Russ Altman: I take it it’s not well regulated yet?

Lynn Hildemann: Well, it’s not. Some of these devices, they haven’t done much testing to see whether they’re really accurate or not, but I’m, I am very optimistic that within maybe, four or five years, there’s gonna be some really good devices for measuring air particles.

Russ Altman: Is there federal agency that, kind of charged with oversight of these kinds of devices?

Lynn Hildemann: No there are not.

Russ Altman: Should there be?

Lynn Hildemann: Well, I mean, the EPA regulates the outdoor air. I joke that they imagine everyone is a porch potato. That is, they spend all 60, 70, 80 years of their life sitting on the porch.

Russ Altman: And that’s not true.

Lynn Hildemann: And so, yeah. So they focus on outdoors only.

Russ Altman: Very interesting. Thank you for listening to The Future of Everything. I’m Russ Altman. If you missed any of this episode, listen anytime on demand with the Sirius XM app.


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