This was in The Guardian today. “Alpine”, “Rockies”, same difference.
Source: The Guardian
Category: Analysis
Anything that I have tested empirically, or explain with detailed calculations, or just generally bother to get all the facts straight.
Post #618: Blue skies, a followup
My wife found the definitive article in the Washington Post. I’m not crazy, the air is significantly cleaner now, thanks to lockdown.
That article also has links to research suggesting that long-term exposure to “PM2.5”-type air pollution (fine particulates) explains much of the variation in coronavirus death rates across the country.
As I noted in an earlier post, Italian research points vaguely in that same direction. Wuhan had notoriously bad air pollution, as did the hardest-hit region of Italy (the Po Valley). And air quality in New York is not so good. And, to be honest, that doesn’t bode well for DC.
So the sky really is better-looking these days. And if the Italian analysis is right, the reduction in particulates helps slow the spread of disease. But our long-term exposure to particulates likely increases the mortality rate among those who fall ill.
Post #614: The sky is blue
Source: Clipart-library.com
No, really. Stick with me here. What I mean is, have you noticed that the sky is unnaturally blue.
This is Virginia, for crying out loud. The spring/summer sky should be, at best, pale blue, edging toward fish-belly white. But day after day, it’s like we’re living at high altitude in the Rockies. Perfect beautiful blue sky.
Did you know that if we shut down all industrial activity and fossil-fuel use, the impact would be to raise the earth’s temperature significantly? In the short run. And only in the short run. True fact. That’s because we release both C02 and particulates/aerosols. C02 warms the earth, but aerosols cool it. The C02 is very stable, remains in the air for a enormously long time. Most particulates and aerosols would rain out/fall out in a matter of weeks to months.
Basically, the longer the shutdown, the better the sky should look.
But apparently this is perception of better air in the DC area is purely in my head. Because empirically, somehow, the air quality index for DC is … no different than it normally is. Per this web page.
So I’m a little perplexed. You’d think, from the traffic reduction alone, you’d see better air quality. But … no. I think I’ll keep looking around to see if anyone can explain this. Or maybe the Air Quality Index doesn’t quite measure what I think it measures.
Post #612: Election confusion on two fronts
First, it looks like the Governor is trying to get all May elections postponed until November. I think that’s the correct thing to do, all things considered.
Second, there still seems to be considerable confusion in Town over campaign finance laws. Twice in the past two days I’ve seen or hear of things that lead me to believe that many people in Town still either don’t understand what the law is, or are deliberately misrepresenting what the law is.
I heard that, sometime in the past couple of days, somebody claimed that a sign was illegal because it had some candidates names, but no “Paid by …” line noting the source of funding. That’s wrong. And we all know that’s wrong, because we’ve never had “paid by” lines on the yard signs before. And I also see that, this year, one candidate actually does have a “paid by” line on her signs. That’s also wrong, if she’s trying to convince people she’s complying with the CFDA. But as long as we all recognize that’s just a bit of let’s-pretend, I think that’s harmless.
If you actually want to comply with the CFDA, you have to have duly-constituted and registered Virginia Political Action Committee. I know because I did that last year, to make sure I understood the process. And detailed what the CFDA does and does not do, on this website.
Looks like it’s time for a refresher course on the Virginia CFDA.
In a nutshell, no campaign finance disclosure laws apply to Town of Vienna elections. That’s the way it has always been, ever since Virginia pass the Campaign Finance Disclosure Act. (CFDA). The only change this year is that they’ve added a clause that says, if you spend $25,000 or more, as a candidate, in a Town election, then yeah, in that case, you have to obey the CFDA.
So, briefly, with citations as to source:
Campaign finance law for Virginia Towns with under 25,000 population.
There are none. So let’s start with the basics. No campaign finance laws apply to Town of Vienna elections. I wish they did (Post #272, from May of last year.) Not unless the Town Council slipped in a piece of last-minute legislation. Or a candidate is planning to spend more than $25 grand, which I think is way beyond unlikely.
So if somebody tells you that (e.g.) some sign is illegal because it doesn’t comply with Virginia law, they just haven’t read the law. Or they are trying to pull a fast one on you. If somebody puts a “paid for” line on their signs, they’re either trying to convince you of something that’s not so, or they’re planning to shell out more than $25,000 in their election bid.
But that last one is easy enough to check. If somebody’s complying the the CFDA, and that “paid by” line has any legal meaning, they have to have a Virginia PAC. No PAC? Then a “paid for” line is just an additional bit of election-year nonsense. It’s easy enough to search all the active Virginia-registered PACs, right at this link. Have a look for yourself, if you care.
It’s a simple test. Got a PAC? No? Then any “paid for” line you see is the politician’s variant on “guaranteed not to turn pink in the can“.
So let’s all go read the law, because boy am I tired of having to explain this. And, interestingly, it changed since the last time I looked at it:
This is § 24.2-945. Elections to which chapter applicable; chapter exclusive.
The provisions of this chapter shall apply to all elections held in Virginia, ... except nominations and elections for ... (iii) town office in a town with a population of less than 25,000, ....
Emphasis mine. But they’ve added a new exception since last year. If you spend in excess of $25,000 on the election, you’ve got to abide by the CFDA:
The provisions of this chapter shall be applicable to a candidate for a town office in a town with a population of less than 25,000 if (a) such candidate accepts contributions or makes expenditures in excess of $25,000 within the candidate's election cycle
And then it goes on to say, or if the Town votes to put itself under the CFDA. Herndon actually did that about 7 years ago. But not, to my knowledge, the Town of Vienna. Last time my wife brought this up at a Town Council meeting (Post #507). That was met with roughly the same reaction as a fart in an elevator: Dead silence and dirty looks.
Why do I know the law? Because I bothered to go through all the steps to form a legally-registered Virginia PAC (Post #272). I needed to know, first hand, exactly how burdensome it was, before I suggested that the Town vote to put itself under the CFDA. I even wrote up a guide to doing all the steps required to form a legally-registered Virginia PAC. I offered to make that guide freely available to anyone who wanted it if the Town ever voted to put itself under the CFDA,. My wife got up in (one, several, I forget) Town Council meetings and pleaded with the Town to put itself, for reals, under the CFDA.
Which is also why I find people who don’t know the law, but throw it around to intimidate people, or mimic it to impress the gullible, I find that irksome.
Actually complying with the CDFA requires some significant effort. There are a lot of legally-required reports that must be filed, for example. I went through that, myself, forming a PAC, because I did not want to recommend that the Town put itself under the CFDA if that process was impossible to comply with.
But the short and simple answer is, the CFDA simply does not apply to Town of Vienna elections. This year. Just the same as it didn’t apply in any prior Town election.
Unless you plan to spend $25,000 or more. That’s the only change for this year.
Post #606: US Census: If you’ve gotten “the postcard”, you’re being unhelpful
Look familiar? If so, you’re being a bad person.
We have all gotten our notices in the mail by now requesting that we get on-line and fill in the US Census. I’ve neglected mine. Which is kind of horrifying, considering that I’ve actually done a bit of survey work professionally. And used the Census data professionally.
When I finally got “the postcard”, I knew I was being a bad actor. Assuming that Census does this in a standard manner, getting “the postcard” is a mark of shame. So it was time to fill in the Census. Which I have now done.
I timed it. It took me 10 minutes, for the four people in my household. Which is typical. But I messed something up, so I thought I might mention that.
The plain language of the Census form says to count all individuals who were staying in your house on April 1. But that’s not correct. If you have a child who was supposed to be away at college on April 1, you are NOT supposed to report them as living in your household in April 1. Even though they were. They will be counted as they usually are, in their respective college towns.
Here’s a link go the US Census page on that.
Unsurprisingly, the last question specifically addresses that. Census gives you the opportunity to flag that college student, so that Census can (somehow) identify them based on some college reporting them. Presumably, because Census will find a person with my daughter’s exact name and date of birth, at some college near to my home, they’ll take her off of the count for my household, and retain it on the count for the college.
Now let me explain the postcard of shame. I’m assuming Census uses standard survey protocols. Typically, in a mail survey, you’ll get a first notice in the form of a full letter. If you don’t fill it in, there will be a followup in the form of a short letter, saying, in effect, please read the prior letter.
But only the truly uncooperative get the postcard. The postcard is typically used for the second followup. The practical reason for using a postcard for second followup is that, by that time, you’re not worth the price of a first-class stamp. If you’ve been enough of a jerk as to ignore the first and second notices to do what you are legally obligated to do, chances are you aren’t going to cooperate no matter what.
In other words, by the time you get to second followup, the likely yield is so low that you’re practically just not worth bothering with. But it’s still cheaper than having to send out the paper-copy Census form.
And vastly cheaper than having in-person followup, which I’m not even sure they are going to be able to do this time. Census taker was always a somewhat hazardous occupation. Now, it’s not even clear they are or should send people door-to-door, to deal with the least-cooperative people among us.
The upshot is that the US Census is among the many things that COVID-19 has scrambled. It’s a pretty good guess that a lot of people are not going to be counted. Do your part to fix that. Get on line and fill out your Census form today.
Getting our fair share of Federal, state, and local government money — not to mention our seats in the U.S. House of Representatives — all depend on that Census count. The information they ask for is minimal. Name, date of birth, sex and race/national origin for every person in the household. And do you own or rent the place where you live. That’s it. Get it done.
Post #594: Expedient masks, part 2: What can you buy
Source: Amazon.com
As our Federal government stumbles toward a public mask policy at a glacial pace and with off-the-cuff advice, let’s see if we, the people, can get ahead of the game on this one.
The just-prior post already established that a reasonable home-made mask will do just fine for protecting others. This next series of posts is about protecting yourself.
And this post is about what you can buy, right now. Its about expedient masks, meaning anything you can buy or make to serve as a face mask, that would (we hope) never be used by health care workers. Anything other than real medical masks — either N95 (or equivalent hardware-store P95) or proper, certified surgical masks — such as might be used in a hospital.
Upshot:
If you want to buy a plausibly-effective sanitary mask, right now, for wearing in public, it looks like your sole option is disposable “surgical” masks bought through Ebay. As discussed below, these are not actually proper certified surgical masks, and some of them are in fact simple “single-use” masks, as described in my just-prior post. You can order the same thing through Amazon, but typical wait times are about a month. I list out the features you want to see in those masks, if you buy them, below.
Caveat emptor: I just looked at Ebay, and there are clearly a lot of unscrupulous sellers, and a general air of on-line panic shopping. If you absolutely have a need for these, consider it. But be aware that you may well be wasting your money.
In addition, anybody who is in the business of throwing away N95 or P95 masks (respirators) should read this analysis of how long an N95 may be re-used. The answer is, putting aside the issue of sterilization, a long, long time. Which is good, because (e.g.) the screeners at Dulles Airport have been asked to re-use their masks on a permanent basis. So, even if you don’t re-use them now, it’s probably time to start separating them from the rest of the waste stream and retaining them.
What’s off-limits, what’s available on Amazon
This post is about masks that you can buy, right now. And, separately, how you might modify them to improve their filtration capabilities. I’m not going to spend a lot of time on this, because I suspect that when CDC issues guidance that Americans should wear masks when in public, anything for sale will disappear from the shelves.
I am sticking with Amazon, for the time being, because they appear to be doing things responsibly, as discussed below. As I read it, right now, if you see it for sale to the general public on Amazon, that’s because it’s not needed by the US health care system. That is not uniformly true of places like Ebay. So I’m only going to look at items that are for sale on Amazon. I may check availability of those same items on Ebay. Clear enough?
I spent some time explaining the technical jargon in the last post, so I am going to feel free to use those terms around here without explanation. Just refer the last post.
But this is not about protecting yourself, at the expense of the health-care workers. In my last post, I explained why hospital workers need N95 masks and you don’t, under the section on aerosol transmission of disease. So let me list not just the things you can buy, but the things you shouldn’t buy.
N95, P95, P99, P100: NO.
Source: Wikipedia
If you stumble across anything rated N95 or P95 or better, just leave it alone, unless you plan to purchase it for donation to your local hospital or fire and rescue unit. You should not be able to find these for sale now, but that’s only because responsible companies have withdrawn them. (See Home Depot in just-prior post. I don’t think the Federal government has taken any action to make the sale of these (to other than medical/fire/rescue providers) illegal. This class includes not only classic N95 “masks” as above, but (e.g.) anything like the P100 paint respirator pictured at the very top of this posting.
Again, you don’t need it. Health care workers and fire and rescue units are going to need them. See my prior post on why health care workers need them, and you don’t.
Surgical masks certified for medical use: NO.
Source: Wikipedia.
I’m not sure if you can find proper certified surgical masks for sale or not, but ditto the remarks above on N95s. Leave them for health care workers. Please see the prior post for a discussion of the difference between single-use masks and surgical masks, and the filtration standards.
Note that several large-scale controlled clinical trials show that surgical masks are just as good as N95 respirators at preventing flu infection among hospital workers. An excellent summary is here, at Smart Air. So, in a pinch, you bet hospital workers would use those if N95 respirators are not available.
Read my just-prior post for the difference between certified surgical masks, and “single-use” masks, which you can buy, and which are not critical to the US health care system right now.
Things that look like surgical masks but are not certified for medical use, available on Amazon, and are probably “single-use masks”, not surgical masks (defined below): I would say, yeah, for now, probably YES.
Wait times are long (typically one month) on Amazon, but this same sort of produce appears widely available (for now) on Ebay with short delivery times promised.
Source: Amazon
What makes me say that? Amazon is one of the responsible vendors who have pulled all masks that can be used by medical personnel and first responders. Anything like that, their pages now have this wording:
Available only for hospitals and government agencies directly responding to COVID-19
For example, Amazon has withdrawn not only N95 respirators, but high-quality nuisance dust masks as well. They have withdrawn surgical masks that appear to be certified for medical use. (Note that those masks list their actual filtration rates, whereas the ones that remain for sale do not.) To me, that suggests that they really have gone through their inventory and pulled out anything that would be useful to medical providers or first responders.
I have to infer, then, that if Amazon doesn’t say that, then there has been some professional judgment that the item in question is not needed by health care workers. I am not 100% sure about that, but at some point, I have to believe that Amazon knows its business, and has done the right thing, and has stopped sale of all items that would be useful to health care workers (as Home Depot has done.)
An incredibly helpful and succinct discussion of single-use masks, surgical masks, and N95 respirators, along with considerable other helpful information (e.g., can you wash disposable masks) can be found at Smart Air. If you want to get up to speed on what’s what, for actual medical supplies, that’s the place to start.
So, provisionally, I’m going to say, despite some misgivings, these are probably OK to buy. I’m guessing that most of them are, in fact, “single-use masks” and not surgical masks. If (note, if) those were manufactured to any standard, it would be a Chinese standard, and they would be able to filter out 95% of large aerosol droplets (3 microns), but would not filter something the size of a virus. Proper surgical masks, by contrast, will filter out virus-sized particles. Again, see Smart Air for a discussion of mask standards.
Even though these are not certified, and some appear to be poorly made, many of them do appear to have the right construction:
- Three-ply construction, with
- A layer of melt-blown fabric, and
- A metal strip at the bridge of the nose.
To the extent that these are fairly good at filtering the air, that’s due to the melt-blown fabric and the nose piece. See prior post for “melt-blown fabric”. (You don’t know the quality/specs on the melt-blown fabric, but at least it has some, suggesting that it has filtering ability above-and-beyond what you’d get from just paper.) The nose piece is required to seal up what would otherwise be the largest air leak for the mask, right at the bridge of the nose.
Finally, multiple large-scale controlled clinical trials have shown that proper, certified surgical masks (not single-use masks) work just as well as N95 respirators at keeping hospital workers from catching the flu. (Cite Smart Air). Whether or not whatever-these-are on Amazon — single-use masks or possibly uncertified surgical masks — would work as well as certified surgical masks is a complete unknown. For sure, single-layer single-use masks, even if they were built to the Chinese standard, have no ability to filter virus-sized particles. They would not have the filtration capacity of a certified surgical mask.
Check the delivery time before you buy. The main catch here is delivery time. That nice-looking white mask above? I searched “face mask”, sorted by descending customer rating, and checked the earliest promised delivery time for the first 20 entries. Median earliest promised delivery date was 26 days. Three entries promised delivery within six days. Two of those were of such low quality (by description and customer comments) that I doubt they would work. The third was priced at about three times the going rate for masks.
The upshot on delivery is that a) for the typical product, it’s going to take a month, and b) anything promised for near-term delivery is either too poor to be useful, or (in one case) priced at several multiples of the going rate.
I re-sorted by descending price, and spot checked. Even for very large orders (e.g., 1000 masks) first promised delivery dates were about a month away.
To summarize: It appears that Amazon has stopped selling anything that has been judged useful to the medical or first-response sectors. The only safe thing is to assume that whatever you are seeing on Amazon, at best, meets the Chinese standard for filtration for single-use masks. If so, those would provide significant filtration against droplets, but limited filtration against aerosols and virus particles. (I.e., they aren’t as good as real surgical masks). Some of the disposable masks appear to have proper construction, per bullet points above. If so, you could reasonably assume that wearing them would offer you some protection, but that is just an assumption. The best of these have melt-blown fabric (the “filter” portion of a certified surgical mask), but you have no way of knowing what type of melt-blown fabric it is (i.e., how well it would filter air). Even with that, you should expect about a one-month wait time for anything that looks worth buying, or feed the occasional price gouger who is promising an earlier delivery time.
Can you get them now, on Ebay? Yes, that appears to be true. If you go that route, look for three-ply construction, metal nosepiece, melt-blown fabric, and some claim as to bacterial filtration. You have no idea whether the claim is right or not, but so be it. A fair price appears to be in the range of $0.70/mask or so, in large lots.
Fabric sports masks: YES, if you are wiling to modify it. What you can routinely get does not appear very effective as a protective mask, because these are designed to “breathe”. If you can sew, you can add a lining. If not, you can try to add a paper lining. You will definitely want to add a wire nosepiece to provide a tight fit across the bridge of the nose.
Source: Amazon
At present, everybody says that any type of fabric mask is OK. Masks like that are frequently sold as pollen/pollution masks for outdoor exercise. Amazon has a wide range of them. Most (perhaps all) are really not adequate for this task, consisting of a single layer of cloth. Because these are exercise masks, they are made to “breathe”, which is what you don’t want, right now.
At the minimum, you’d have to line these with something. Practically speaking, I think you’d have to resort to lining these with paper towels. That provides some protection, but not much (see prior post, last section). You would also want to take a bit of wire and either duct-tape it to the mask, or thread it through the mask, to provide a metal nosepiece for sealing the mask to your face at the bridge of your nose.
And, as with the disposable masks above, most have one-to-two-month shipping times. I saw a handful with promised delivery times of a couple of weeks. Weirdly, I did not find these on Ebay. Maybe I just didn’t have the right search terms.
I’m not going to pursue these any further.
“PM2.5 masks”: Eh, I’m not even sure what this means.
Source: Amazon
There is a huge range of masks — some hard-surfaced, as the one above, some fabric, some hybrid — that are sold as anti-air-pollution masks. That is, they claim to filter out particulate matter of 2.5 microns in size (PM 2.5).
Near as I can tell, as discussed in my prior post, there are no standards and there is no testing of these masks. Some probably work. Some probably don’t. I have no way to tell. I’m not going to discuss these further. The few that I checked appeared to have delivery days 6 weeks away or so.
Caveat emptor.
Various loose-fitting masks and bandanas. These protect others, a bit, but the lack of any seal means they provide very limited protection to you.
Source: Amazon
And, of course, even these have promised delivery dates 6 weeks out. These are single-layer loose-fitting cloth mouth coverings. Better than nothing, but probably not as good as just pulling your t-shirt up so it covers you nose and mouth. I don’t see value here.
Etsy hand-sewn cloth masks.
I did not pursue this option, but I would assume that some are available.
My next posts will discuss making masks.
Post #593: Expedient masks, part 1, background.
Source: Amazon.com
The bottom line of this posting is that, yes, home made masks work to block much of your potential for transmitting disease to others. Wear a real medical mask if you own one. Buy (and potentially improve) a non-medical one if you don’t. Or make one from scratch. Even paper towels have some efficacy in filtering the air.
This post is really just background. If you already know that you need to wear a mask, there is no need to read this. Next post will be about what you can still buy, for now. Final post will be on making them.
Background
The drumbeat in favor of universal mask use outside the home is getting louder. Some people figured this out sooner than others. I finally wised up less than a week ago, and did my 3/27/2020 grocery shopping masked. And every time I enter a public place from now on, I’m wearing a mask.
That said, you can see a summary of the achingly slow progress on this front in this Washington Post article.
So, unless spectacular stupidity triumphs, you will soon have official guidance from the CDC that you ought to wear a mask in public. I’ve already written down what I would use as the official rules, FWIW (Post #589). I’ve now posted a comment on the Whole Foods Facebook page, asking them to consider some form of “no mask, no service” policy.
Everybody who is smart, ethical, or both is withholding N95 respirators from the general public. AKA, the best masks. Those need to be kept for health care providers. Here’s Home Depot’s policy.
Executed a "Stop-Sale" on all N95 masks in stores and HomeDepot.com and redirected all shipments to be donated to hospitals, healthcare providers and first responders around the country
I highlight Home Depot because that’s the first place I detected panic buying/hoarding behavior, back in Post #535. Even if they were too late to stop that, they have had the good sense not to restock.
My point is that mask use is coming. You can’t buy the ones that protect you with some security (if they are properly fitted). What can you do? What are your options for an expedient mask? What is your best expedient mask choice? Adapt what you have? Buy? Buy and modify? Make from scratch?
From the standpoint of not infecting others, it’s all good, pretty much. Any mask beats no mask, hands down. When you talk, and even to a small extent when you breath, you emit tiny droplets (discussed at length in Post #573, Post #585). Droplet transmission of disease is believed to be the primary way in which the infection is spread. Any sort of substantial cloth barrier over your face will reduce the spread of those droplets significantly, both by catching some, and by reducing the velocity/range of others, as the mask slows the velocity of your breath. (See wet finger whistle test in Post #589 to prove this to yourself.)
See this reference for a scholarly look at the ability of home-made masks to stop spread of disease. But please note that they used the wrong cloth (cotton t-shirts) — nobody recommends that. They concluded that homemade masks aren’t as good as surgical masks, but they are much better than nothing. I’ll get into that paper in detail, at the end of this posting.
So the only thing to discuss, really, is how you can get some sort of mask, and then, how well can you expect that mask to protect you. This assumes you are smart enough to do everything the CDC already says, and in addition, minimize your trips to enclosed public spaces, and the time you spend there, on those trips.
While you can buy some type of (e.g.) cloth face mask now, well, by this time we all know the drill. The supply chain is set up to deliver product only at the rate at which it is used. As soon as the CDC says “wear a mask of any sort”, it’s a fair bet that what’s currently for sale will get hoovered up.
So, for most of you who don’t have a mask, I’m afraid this is going to turn into a DIY project. Or, having your neighbors make one for you.
So I thought that what I might do is offer a kind of mask tutorial. This is mostly by way of helping me get my thoughts together on whether or not I could build a high-quality expedient mask from available materials. Anybody can make a mask. The question is, can I make a good mask, in quantity.
This is part 1: Background. Part 2 will be, what can you buy (for now) and modify. Part 3 will be, what can you make from scratch.
Step1: What are we talking about? Definition of N95, PM2.5, MERV, HEPA, and so on.
I’m kind of tired of writing, at this point, so this will largely be done without citation as to sources. I’m just summarizing things here that I have duly cited in earlier posts, mostly. New information will be cited as needed.
Aerosol versus droplet transmission
Micron (micrometer): One millionth of a meter. 1000 nanometers. Droplets from a sneeze range from under about one micron to hundreds of microns.
Nanometer: One billionth of a meter. The diameter of an individual coronavirus particle is around 120 nanometers (Wikipedia). An obsolete term for it is “millimicron” or “millimicrometer”.
Aerosol versus droplet transmission. Here’s a key distinction. Conventionally, anything under 5 microns is an “aerosol”, meaning, it will stay suspended in the air and float around on air currents. See Post #585. Particles that size are far too small to be seen. When professionals talk about “airborne transmission”, then mean transmission of the disease in this fashion. If you inhale enough of them, from an infected person, and they land in the right place in your respiratory tract, you get infected.
Studies of influenza showed that aerosol particles were quite potent at spreading lower respiratory tract infections. It takes less total volume of virus to cause an inflection of you aerosolize it, versus leaving it in larger droplets. The reason is that if you inhale these tiny droplets, they have the ability to penetrate far into the lungs. (This same ability is what makes very fine particulates from (say) diesel exhaust particularly harmful air pollution). And, for SARS (currently SARS-CoV-2 aka COVID-19), that’s where this virus wants to be. So aerosols put the virus directly into its most favorable habitat within the human body.
Sneezing and coughing produce some aerosol-sized droplets. But, surprising, just breathing produces a few. Talking produces them at a rate somewhat less than coughing (but you talk a lot more than you cough, so total production can easily be the same, when integrated over time). The louder you talk, the more aerosols you produce. And singing is easily the equivalent of coughing, in terms of the rate of aerosol production.
One fact you need to know is that, for aerosols, some people are “superemitters”. They produce orders-of-magnitude more aerosol than the average person. And it’s not really all that rare, but I’m not going to stop and look that up right now. My recollection is that in any group of 100, you are more than likely to find a few.
And so, likely that event that I wrote about — 45 persons of a 60 person choir got COVID-19, after a single carefully-done practice — it’s a very good guess that this was the result of aerosol transmission of disease by an infected superemitter.
That said, I need to be clear here, because this is now a hot topic: As far as anyone knows, aerosol transmission of this disease is rare outside the hospital setting. How do they know? Well, they think they know that because of what they think they know of the epidemiology of it. If aerosol transmission were common, you probably wouldn’t be able to trace cases back and figure out how they got infected. Because they think they can do that tracing, and they find that most transmission (that they can trace) appears to occur when people are symptomatic (i.e., coughing), they infer that most transmission is, in fact, droplet transmission, not aerosol.
Let us each now solemnly pray to our respective God or Gods that they are correct, and not just kidding themselves.
The situation in a hospital is different, though. There, you can get instances where the concentration of aerosol particles is high enough, and exposure times are long enough, that people can get sick literally by simply breathing the same air as the patient. You’ve got a combination of a very sick patient (so, high virus shedding rate), in a small room (so that person can build up high density of aerosol per cubic foot), and you have health care personnel who spend considerable time in that tainted air.
The non-negligible potential for aerosol transmission in that setting is one of the reasons that health care practitioners need N95 masks. I’ll get to the definition of N95 below.
By contrast, health professionals use the term “droplets” to mean drops larger than 5 microns. To a greater or lesser degree, these settle out of the atmosphere fairly quickly. (Or, at least, that’s the conventional wisdom). But, if you inhale them, or they land on you in the right place (in your mouth, eyes, nose), or they land on a surface that you touch and then touch your face (mouth, eyes, nose), they can infect you.
You produce droplets by sneezing or coughing, but you also produce them by talking. (And, because we talk a lot more than we cough, arguably, at small droplet sizes, we’re producing more in total by talking. Which is among the reasons I called for us all to shut up in public spaces.)
The fact that droplets settle pretty quickly is the basis for the 6-foot social distancing rule. In theory, if somebody coughs from six feet away, the droplets produced won’t hit you.
But social distancing alone is not good enough for the Chinese. They use masks, both to absorb some of the droplets, and to slow down the velocity with which they are projected away from the source. And they are absolutely right in doing that. Which is why US policy is about to change.
Filtration standards and such.
An incredibly helpful and succinct discussion of single-use masks, surgical masks, and N95 respirators, along with considerable other helpful information (e.g., can you wash disposable masks) can be found at Smart Air. If you want to get up to speed on what’s what, for actual medical supplies, that’s the place to start.
A different guide to the different types of “surgical” masks can be found at Crosstex (.pdf). The takeaway from both of these is that just because it looks like a surgical mask does not mean that it filters viruses and droplets like surgical mask. It may or may not. And if it were certified to filter like a surgical mask, it would probably not be on sale to the general public.
N95: A filtration standard meaning that, when new and carefully tested, a mask will stop 95% of very tiny (0.3 micron or 300 nanometer) particles. Source: FDA. Note that, in real life, you don’t actually achieve that because air leaks around the edge of the mask. That’s why, for protecting the mask user, a properly-fitted mask is important. For the mask maker, that means you need to construct it so it seals well.
But that’s the primary reason that health care professionals need N95s. They really need to be able to stop everything, all the droplet sizes, and stop particles down the size of a few viruses stuck together. That’s why they need those masks more than we do.
N99, P95, P99: Additional mask standards. First one filters 99% of particles that size. The Ps have the indicated filtration, but are good for oily particles as well, where the Ns aren’t (I think of it as P as in paint).
How in the heck do you filter out something that small, and still be able to breathe through the mask? Mainly, through the miracle of Melt-blown cloth. This is a nonwoven cloth made from small-diameter plastic fibers fused together. It is the heart of most common medical masks, including both N95 and true surgical masks. This is the element in the mask that filters out fine particles. And, of course, many different types are made, so you can’t just buy melt-blown cloth and assume it’s good enough for a mask.
PM2.5 (particulate matter 2.5 microns) refers to air pollution particles of around 2.5 microns in size. In essence, PM2.5 is shorthand for all the common air pollutants that are aerosols, i.e., can stay suspended in the air. Note that, by definition, an N95 mask filters out at least 95% of PM2.5.
PM2.5 mask. Near as I can tell, this is not a standard. This just means that the manufacturer claims that the mask was designed to filter out PM2.5. It’s a mask that claims to filter out (some, all, most?) particles of that size. Near as I have been able to tell, a) nobody tests those claims, b) a lot of PM2.5 masks and respirators don’t do what they claim (but some do), and c) near as I can tell, these are not approved for use by health care personnel.
Mask versus respirator. Near as I can tell, anything that is truly designed to seal up against your face, so that air doesn’t leak around the device, is technically a respirator. By contrast, if it’s designed that air likely leaks around the edges and/or the principal purpose of it is to stop fluids, that’s a mask.
That’s why you’ll hear the terms N95 respirator and N95 mask used interchangeably. Even though the thing looks like a mask, it’s supposed to function like a respirator. You are supposed to fit the thing to your face so that air leaks are minimized. Otherwise, really, what’s the point?
Edit: Single-use mask versus surgical mask. I didn’t even realize there were standards here, but see this page at Smart Air for a very helpful discussion. Single-use face masks are typical single-layer thin masks. If manufactured to the Chinese standard, these will stop large droplets (3 micron) fairly well, but not viruses. The US does not have a standard for these. The US only had standards for surgical masks:
Surgical mask standards: BFE and PFE. An excellent summary of the difference between single-use masks, surgical masks, and respirators can be found at Smart Air Filters. They explain it much better than I do.
Edit: CORRECTION. I have now located a proper description of surgical mask standards, from Primed, which I am going to crib here.
1. BFE (Bacterial Filtration Efficiency): BFE measures how well a surgical mask mask filters out an aerosol consisting of 3 micron droplets containing staph. In order to be certified as a surgical mask, the cloth has to filter out 95% of those droplets. Better grades of mask (mderate and high protection masks) must filter out at least 98% of those droplets.
2. PFE (Particulate Filtration Efficiency): PFE measures how well a mask filters out virus-sized particles. They are supposed to be tested with particles of 0.1 micron size (about the size of coronavirus). The higher the percentage, the better the mask filtration. Apparently, some masks are tested with somewhat larger particles, and can show a misleadingly high PPE.
Note that the actual performance of a surgical mask, in use, will not be as good as these filtration rates suggest, because the mask does not seal up against the face. (See Mask versus Respirator). Air leakage around the edges of the mask compromises the overall filtration. The standards above show the filtering ability of the cloth, not the overall mask assembly as a whole.
Edit: WRONG. Note that surgical masks are NOT tested for their ability to stop penetration by bacteria in the air. They ARE tested against penetration by fluids, and penetration by bacteria and such in fluids. They are designed for health care workers who need to avoid being infected by fluid-borne bacteria and viruses. As far as I can tell, that’s why a proper surgical mask, tested and certified for health care use, has some ability to filter particles. Most (some?) are made with three-ply construction, the middle ply of which is some form of melt-blown cloth.
And, helpfully, melt-blown cloth is also used in some (but by no means all) home furnace filters ( (see this manufacturer’s page). Which gives me the segue to comparing the standards above to two that homeowners are familiar with: MERV and HEPA. And here, I assume you all know I am not talking about standard fiberglass, very-open-weave filters. I’m talking about the ones that look like a sheet of fuzzy cloth.
MERV: Minimum Efficiency Reporting Value. From Wikipedia.
The scale is designed to represent the worst-case performance of a filter when dealing with particles in the range of 0.3 to 10 micrometers. The MERV value is from 1 to 16. Higher MERV values correspond to a greater percentage of particles captured on each pass, with a MERV 16 filter capturing more than 95% of particles over the full range. (That little factoid will be important for tomorrow’s post.)
Do two MERV 8s make a 16? No, absolutely not. The MERV rating is like a pore size. As you go up the scale, in groups of four, they start filtering smaller particles. The 8s simply have larger pores, in effect, and let the smallest particles pass through. That’s clear from this full explanation of MERV ASHRAE chart. (But, if I’m reading that right, two MERV 14s, in sequence, come very close to achieving the same filtration as a MERV 16. And two MERV 15s in sequence exceed that).
HEPA: High-efficiency particulate arresting. Again, from Wikipedia:
“Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least .. 99.97% (ASME, U.S. DOE)[5][6] of particles whose diameter is equal to 0.3 μm; with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm.[7]
The little μm thing is microns (micrometers).
MPR: Microparticle Performance Rating. This is a propriety rating system developed by 3M. It reflects the ability of a filter to capture the smallest airborne particles—from 0.3 to 1 µm in size (Wikipedia). So you have to get the detailed 3M literature, if you want to look at Filtrete electrostatic filters: https://multimedia.3m.com/mws/media/1740587O/filtrete-merv-vs-mpr.pdf
Filtrete (r) filters differ from MERV-rated filters in that all varieties of Filtrete capture some small particles. If you look at E1s (the smallest particles, down to 0.3 micron), it appears that you need two layers of MPR 2800 Filtrete to achieve 95% or more of filtration of E1 particles. Although, for particles one micron and up, one layer of MPR 2800 or one layer of MPR 2500 would achieve 95% capture of those particles in a single pass.
I am uncertain as to how that Filtrete electrostatic material behaves under adverse conditions, such as when damp.
Filtration properties of common household materials.
This is where the rubber hits the road. Start with this article, where they actually tested cloth and made masks.
Here’s one key table, below
This is a pretty good setup, because they literally aerosolized the bacterium and virus, then tested what happened when they pushed that aerosol through a cloth panel at about the rate you would if you were breathing. These particles are certainly on a par with the size of the coronavirus itself, and presumably the aerosol droplets are about the best proxy you are going to find for … well, aerosol droplets.
First, note the similarity of the first two columns, despite the differing size of the bacterium and the virus. That’s because, by and large, the masks are catching the droplets, not the individual bacteria and viruses themselves. The standard here is the surgical mask, circled in red. I note that a vacuum cleaner bag (not stated as to type, likely not HEPA, because I’m pretty sure they are talking about cloth bags) was just about as good as a surgical mask — I put a red line there. And a tea towel, doubled over, was just about as good. But in the right-hand column, that’s the back-pressure you would face, in breathing through those materials. The vacuum-cleaner bag and the doubled-over tea towel were 2 to 2.5 times harder to breathe through than the surgical mask material.
Source: Testing the efficacy of homemade masks: would they protect in an influenza pandemic? Davies A1, Thompson KA, Giri K, Kafatos G, Walker J, Bennett A. Disaster Med Public Health Prep. 2013 Aug;7(4):413-8. doi: 10.1017/dmp.2013.43.
This is important, because the harder the material is to breathe through, the more air will leak around the mask, rather than through it, and reduce the overall filtration efficiency.
So, to be clear, yeah, you can find stuff around the home that will give as much filtration efficiency as a good surgical mask (but not an N95 mask). But it’s going to be somewhat hard to breathe through.
And, if you care, read the section of that paper on fitting the mask. All of the home-made masks were much leakier than a good-quality surgical mask. That’s important, and that’s what you need to focus on if you make a mask.
Finally, how much better is it to wear a home-made mask, made out of a cotton t-shirt, than to have no mask at all, in terms of containing the spread of disease (from people coughing, in this case). Well, they tested that empirically: Literally had people cough, through a mask, into a sterile box, and counted the crap that came out.
Source: Same as prior table.
Do home-made masks help prevent the spread of contagion? Heck yes. Look at the bottom line: No mask, 200, homemade mask, 43, proper surgical mask, 30. That’s the count of bacterial “colony-forming units” that they observed. Do the math, and a home-made mask gets you (200-43/200-30) = 92% of the reduction that you would get from a standard high-quality surgical mask.
Now in case you’re surprised by that, my reading of it is that anything that stops droplets from flying is good. You aren’t literally trying to filter out tiny little viruses. You are trying to filter droplets, most of which you can catch with cloth, some of which fly right through.
Filtering ability of paper towels. I didn’t find a scholarly article (and got tired of looking), but these people seem to have their act together. It’s one of those great articles that just gets to the point. And the short answer is that common household paper towels, do, in fact, have some measurable ability to filter out particles in the size range we are talking about.
For very tiny (0.3 micron) particles, “A single layer of kitchen paper captured just 23% particles. Adding an extra layer only increased particle capture to 33%.”
But for aerosol-sized particles (smaller than “droplets”): “For larger 2.5 micron particles, paper towel performed better. The single layer of kitchen paper captured 52% of these larger particles”.
(From that, I would infer that two layers would get 75% or so.)
Those same folks provide a nice graphic re-write of the article on home-made masks, at this location.
Near as I can tell, nobody has done the one I want to see, which is a coffee filter. I use(d) those as a pre-filter when purifying raw water when camping, and I think that’s a pretty common use. I did test that you could breathe through one (possible, but a lot of resistance). I will keep looking for that one.
Bottom line: Wear ’em if you’ve got ’em. If not, buy one and modify it. If not, make one from scratch. Any mask is better than no mask. Even paper towels have some filtering efficiency.
Next post is about buying and modifying masks.
Final post will be about making masks. But you can just go on Amazon and get a free Kindle download on that.
Post #527: W&OD bridge?
Two of the W&OD road crossings in the Town of Vienna will be updated, based on suggestions in the Town’s Maple Avenue Multimodal etc. study. The W&OD road crossings at Park Street and Church Street will get raised crosswalks, turning them more-or-less into speed humps. And they’ll get new signs.
It’s tough to say why, of all the things in that study, the Town decided that those two W&OD road crossings were a priority. For sure, there was no formal cost-benefit or risk analysis done. I think they just sort of liked the idea, and it was cheap to do. So they’re going to do that, and that’ll be the tangible outcome of that study, along with filling in a right-turn lane where Mill and Church intersect.
This seems to have stirred up some interest in a W&OD bridge for the Mape Avenue/W&OD crossing in the Town of Vienna. To be clear, we’re not getting a bridge there, and nobody is talking about paying for a bridge. And in this post, I’m briefly going to explain why that is — why this was ignored in the Town’s Multimodal study, and will it will likely remain a low-priority issue. My conclusion is that the stoplight we have now for the W&OD Maple Avenue crossing is probably good enough, given the size and cost of a bridge.
But other crossings have bridges …
Sure, but those crossings tended to be ones with significant problems and traffic, often where a new traffic light would not work, or where there are problems, despite a light, due to heavy traffic.
The closest large dedicated bridge on the W&OD is the Citizens’ Bridge in the People’s Republic of Falls Church. This is where the W&OD trail crosses Route 7/Broad Street. This bridge dates to 1992 or so. Falls Church citizens agitated for a bridge because bicyclists and pedestrians were crossing Broad Street there, rather than walk/bike to the stoplight-controlled intersection at West Street.
That bridge is an object lesson in the nature of bicycle and pedestrian traffic. At the time, the bridge was lauded as an example of effective small-town government. But one could just as easily say it’s there because various bicyclist and pedestrian scofflaws routinely jaywalked rather than walk an extra 200 feet to cross with the light (while getting their exercise along the W&OD trail.)
More recently, the influx of new tax and toll monies means that all kinds of marginal and low-value projects are now being funded, as long as they plausibly help people get around without a car. This includes a spate of new bridges for the W&OD. These tend to be for intersections where the road crossings were an annoyance to bicyclists and/or motor vehicles, though not particularly dangerous (at least in my opinion).
There’s a bridge going up for the Route 29 crossing just east of Falls Church, and a bridge is planned for where the W&OD crosses Wiehle Avenue in Reston. Neither of these is a particularly difficult crossing now, although Weihle is awkward because it’s so close to a stoplight with no place to stop in the median. Both of these crossings, though, apparently have fairly high automobile accident rates, as cars stopping for bicyclists get rear-ended with some frequency.
Above: Route 29 W&OD crossing just east of Falls Church, and Weihle Road crossing in Reston.
In essence, right now, these are just crosswalks used by a lot of bikes. Not unlike the W&OD crossings in Vienna. But soon those simple crosswalks will be replaced by some fairly large and obtrusive bridge structures. Here’s a “before and after” view of Weihle Avenue where it crosses the W&OD trail.
Above: Wiehle Road crossing now, and Wiehle Road showing artist’s conception of bridge. (Orient by trees in background). Source for Weihle bridge: FCDOT via restonnow.com
So why not Maple Avenue in Vienna?
It boils down to need, cost, and size. And all of these argue against a similar structure at the W&OD crossing on Maple Avenue.
First, the existing light-controlled crossing works well. We have the occasional bicycle scofflaw crossing against the light. But in my experience, those are few and far between. And that’s because that current path is in fact the shortest distance. So we do not have the problem that Falls Church had, with a constant stream of jaywalkers who were unwilling to walk to the nearest light-controlled intersection.
Second, a bridge there would necessarily be fairly large. And it’s not that you need a massive structure to move the bicycles. It’s that VDOT requires a minimum 17.5′ clearance (I just looked that up), and bike paths are never supposed to have more than a 5% slope if that can be avoided. When you combine those two (17.5′ tall, 5′ slope) you realize the bridge would have to span Maple Avenue and 350′ on either side of Maple.
The upshot is that the entire bridge structure (including earthworks at either end) would have to span about 750′ (350′ + 350′ plus the width of Maple). No coincidence, this is roughly the length of the Citizens’ Bridge in Falls Church. So, if you look at that (above), that’s more-or-less the minimum size of structure that you can get away with. Not due to the load of the bicycles, but due to the combination of clearance and slope limits on the structure.
So the very smallest it could be, built to those standards, would be a span from almost Church Street at one end, to almost the end of the Whole Foods market at the other. This would cut Maple Street off from the trail and make trail access difficult. (In fact, some of the opposition to the Falls Church Citizens’ Bridge came from local merchants who saw the bridge as discouraging bicyclists from stopping (and spending money) in Falls Church. See the newspaper article cited above.)
It will also cost somewhere in the neighborhood of $6M to $12M. Or so.
A internet search shows the cost of steel pedestrian bridges runs about $2000/linear foot for a prefab steel footbridge such as the Falls Church one. Of the 700′ length, the Falls Church Citizen’s Bridge is roughly 400′ of steel bridge, and the rest earthworks. At that price, the steel bridge alone would cost about $8M. So call it $10M or so, based on that.
A second data point comes from the bridge slated for Weihle Avenue in Reston, which has a preliminary cost estimate of $11.4M, per the newspaper article cited above.
A third data point is a reported cost of about $6M for what looks like a roughly-similarly-sized intersection (W&OD crossing four lanes of traffic).
Caveat: The reported cost of the Falls Church Citizens’ Bridge, just under $1M, is vastly less than $10M after accounting for inflation. Adjusting that circa-1992 cost for the Consumer Price Index change to 2020 yields about $2M in today’s money. On the other hand, that initial cost estimate may have been in error, as the $11.4M Weihle Avenue bridge was originally supposed to cost under $3M.
So, maybe not exactly $10M, but somewhere in that ballpark seems likely.
In summary: The current Maple Avenue W&OD crossing appears safe, appears to have relatively few bicyclist scofflaws, and in general provides easy on/off access to the W&OD in the heart of Vienna. Any bridge there would necessarily be large and fairly expensive. It’s easy enough to see why other intersections have gotten bridges before anyone would think of funding a bridge for the Maple Avenue W&OD crossing.
Post #521: The cost of sidewalks
Source: Google maps.
The point of this post is pretty simple: The cost of installing new concrete sidewalks various enormously. And the cost of the sidewalk itself — i.e., the 5′-wide ribbon of concrete — is the least of it. The bulk of the cost is in everything else that has to be done — curb, gutter, curb cuts, ramps, and, most importantly, drainage including storm sewers.
To make this point, I identified four sidewalk projects in the Town of Vienna, and estimated cost per linear foot. (Detail given below. This is a “sample of convenience”, being the first four projects I ran across.) The costs were $100, $150, $445, and $666 per linear foot of sidewalk. Presumably, if I’d looked at a larger sample of projects, I would have seen even more variation.
In the Town of Vienna, a) there’s really no meaningful “typical” cost for putting in sidewalks and b) in any given situation, the cost might be a lot more than you’d think.
The high costs of sidewalks — and the fact that literally “the sidewalk” is typically the smallest part of the cost — has some important implications for a couple of items that I’ve mentioned recently.
Robinson bequest for sidewalks. At the last Transportation Safety Commission (TSC) meeting, I found out that the Robinson estate bequest for sidewalks in the Town of Vienna was being interpreted as literally that: payment for the concrete sidewalk, period (Post #518). Depending on the project, then, the Town would have to pay for everything else to make that sidewalk possible. That’s certainly going to tilt the use of those funds toward simple projects where (e.g.) there is already curb and gutter in place, with no need for extensive modifications for site drainage.
Sidewalks versus road closure for the neighborhoods behind Sunrise/444 Maple West. At the last Town Council meeting, citizens offered some things the Town could do to address pedestrian safety and traffic in the neighborhoods adjacent to the proposed Sunrise facility (Post #517). Among those was the idea of putting in sidewalks on (among other) Glen Avenue. But Councilman Potter suggested that simply closing Wade Hampton at Glen would be a less costly solution. And based on these per-foot costs, that seems like a plausible statement. Based on those four costs per foot, 1400′ of sidewalk for Glen Avenue (pictured above) might cost anywhere from $140,000 to more than $900,000.
Post #519: The tear-down boom and increased residential share of Town property assessments
This is just a quick back-of-the-envelope spurred by a presentation made by the Town’s Director of Finance at the 1/27/2020 Town Council meeting.
One statistic that caught my eye is that the residential share of total property assessments in town rose over the last decade, from 77.5% in 2011 to 81.0% in 2019 (Page 9 of this document (.pdf)). The Director of Finance suggested that this was one possible justification for hiring the new business development officer for the Town of Vienna. That is, to help bolster Vienna business and hence assessments. Conversely, Councilman Majdi suggested that the tear-down boom might account for it, with small houses being torn down to make way for much larger ones.
So, that’s the question here: Does the increase in residential share of total property assessments mean that commercial real estate in Vienna showed poor price appreciation, compared to residential? Or is that plausibly just a consequence of the tear-down boom, with small, lower-cost houses in Vienna being systematically replaced by larger, higher-cost houses?
Here, in the crudest way possible, I want to test that. Can the tear-down boom plausibly account for this change? In keeping with the idea of a round-numbers calculation, I’m going to do a crude cut at this. Basically, is the impact of the tear-down boom anywhere near large enough.
So: My recollection is that, of late, the Town has averaged about 100 tear-downs per year, based on building permit data. Further, based on a couple of observations, property value for a tear down typically increases by about a million dollars (in 2019 terms), from (say) $0.7M for a small house, to $1.7M for the typical mansion that replaces it.
So, 9 years x 100 houses per year x $1M/house = $900M in additional residential property values, in 2019 dollars, from the cumulative effect of the tear-down boom from 2011 to 2019. Roughly speaking then, if I net out the crude impact of the tear-downs, I get this table:
| Crude impact of tear-down boom on Vienna assessed real estate values | |||
| Residential | Total | Residential % | |
| Actual 2019 | 4,251,761,320 | 5,204,854,490 | 81.7% |
| Less tear-down impact | 900,000,000 | 900,000,000 | |
| 2019 less tear-down | 3,351,761,320 | 4,304,854,490 | 77.9% |
And the answer is that the (crude estimate of the) impact of the tear down boom is more-or-less the right size to explain the shift in assessment share in the Town of Vienna. The difference between the two red numbers, in the table above, is roughly as large as the difference between the two red numbers in the opening paragraph.
In other words, this shift in assessed values in the Town of Vienna doesn’t show any particular problem with our commercial real estate. Plausibly, it just shows the impact of the replacement of small, lower-cost houses with much larger ones.
This is consistent, I think, with repeated mentions of high rental rates for commercial property along Maple (e.g., in the new Town economic development officer’s “listening tour”). The complaint is that high rental rates are driving businesses out of Vienna. But if so, that’s just an indication that business is good along Maple. Nobody likes paying rent, but if property owners along Maple think they can get (e.g.) $60/square foot/year, that means they expect that business opportunities are such that some business can afford to locate on Maple and pay that kind of rent.