Two years ago, in Vienna Town Council elections, supporters for the two pro-development candidates reminded voters that they didn’t have to vote for three Town Council members. They could vote for just two.
This year, the non-incumbent candidate is reminding voters that they don’t have to vote for three Town Council members. They can vote for just one.
Every year, in Town Council elections, the vote total is less than three times the number of voters. Even though every voter may select up to three candidates on the ballot.
The Canning Lid Shortage of 2021 may be over. For now, at least.
I heard a rumor, via my wife, that canning supplies were back in stock in the southern Maryland town where a friend of hers lives. The local hardware store there hung a big banner in the window to advertise that they had canning jars in stock again.
And so, in 2021, Texan F150 hybrid owners are finding out what Prius owners have known since at least 2005: A hybrid car makes an excellent backup generator. In this post, I’ll lay out the simplest approach to using your Prius (or similar full hybrid) as an emergency generator. Continue reading Post #1020: PriUPS
I posted something yesterday, chiding people for wearing cheap face masks, and in particular for wearing them poorly. Apparently I hit a nerve with more than a few people, and I’ve been challenged to offer some practical advice.
What you are going to get next on this website is a series of posts on masks. Solely from the standpoint of protecting yourself, not from the public health standpoint of protecting others. Starting with some straight-up “buy this” practical advice, before I go off on a deep dive on the whys and wherefores.
But because most people don’t grasp the basic math of masks, I have to do the math first. And that’s because mask ratings and mask performance tests hide the true relative risk of various types of masks.
If you just want to get to the quick advice, just skip to the next section. But you really ought to try to answer the question below.
Mask ratings hide the true relative risk of poor masks versus good masks.
Here’s a simple question. Even if you think you really, truly understand masks, take 15 seconds to see if you can get the correct answer.
Question: An N95 respirator (mask) filters out 95% of airborne particles. A procedure mask with ear loops filters out about 30% of airborne particles. Let me loosely call that an “N30” mask. Roughly speaking, how much better is an N95 mask, compared to an N30 ear-loop procedure mask?
A) Obviously, it’s about three times better, because 30 x 3 = 90, which is close to 95.
B) Obviously, it’s about 14 times better, because (100 -30)/(100 – 95) = 70 / 5 = 14.
C) Obviously, this must be a trick question.
The answer is B, it’s 14 times better. Why? The mask rating (N30, N95) shows you what the mask keeps out. But the viral load you inhale isn’t about what the mask keeps out. It’s about what the mask lets through. It’s about 1-minus-the-mask-rating. And in any given situation, the ear-loop surgical mask will let through and expose you to 14 times as much viral load as the 95 mask. Because 70% of what’s in the air is 14x as much as 5% of what’s in the air.
In case you still don’t quite get it, let me do the math the other way. How much better is that N30 ear-loop surgical mask, compared to wearing no mask at all?
Question 2: Assume that you need to inhale 100 copies of COVID-19, at a sitting, in order to get infected. Assume that you are going to inhale one cubic meter of air, at a sitting. How dense can the COVID-19 particles in the air be, before you inhale enough to get infected, based on wearing:
No mask.
N30 mask (ear-loop surgical mask, worn loosely)
N95 respirator.
Answer:
Edit 1/15/2021: Question 2, same math, but rephrased. Suppose there’s a room filled with COVID-19 aerosol. Suppose that, without a mask, you can sit in that room for no more than 10 minutes before you get infected.How much more time does your cheap, blue ear-loop surgical mask buy you? That is, how long could you sit in that room and remain uninfected, wearing an ear-loop procedure mask? And then, how long wearing an N95 respirator?
Yep, that cheap blue mask buys you a whopping four additional minutes of time, before you get infected. Which not only makes my point, but which shows you why you want to stay away from close, crowded situations, mask or no mask.
Sure, a loosely-fitting ear-loop surgical mask is better than no mask at all. But not by a whole lot, in the overall scheme of things.
I hope you now get why I’m so persnickety about masks. To the point of making my own, so I can be sure of what I’m putting on my face (Post #807, Post #780), and trying to test them (Post #790). And why I continue to be irked about the inability of citizens to purchase true N95 respirators. The difference between a good mask and a poor mask isn’t a little bit. It’s a lot. It’s an order-of-magnitude difference in performance.
Edit: And I’ll go you one better. In at least one hospital here in Northern Virginia, the nurses serving the COVID-19 ward wear half-face N100/P100 respirators. Like the one below. Because if you’re really heavily exposed, allowing even 5% of viral particles past your respirator just won’t cut it.
If you just want some quick advice on a reasonably good mask to wear.
I’m not going to go even one inch into all the details. Fact is, there is a mask, that you can buy, that is easy to wear, and that did very well in a realistic test, by real scientists, published in the Journal of the American Medical Association. In terms of some quick advice, on what to wear, that’s about as bulletproof as it gets.
The recent test of masks published in the Journal of the American Medical Association found that two-layer nylon masks filtered out about 80% of airborne particles, once the masks had been washed (Post #924, or you can try to pull up the tables in the JAMA article itself).
Because this was actual scientific research, they specified the mask fully as: “(1) a 2-layer woven nylon mask (54% recycled nylon, 43% nylon, 3% spandex) with ear loops (Easy Masks LLC) tested with an optional aluminum nose bridge and nonwoven filter insert in place.”
I honestly don’t think there is anything unique about those masks, within that specification. Except that they are made correctly. If you go to the website, you will see that they are generously cut, and cover the face from throat to eyes, ear-to-ear. And that they make them in different sizes, and they tell you how to measure your face, to choose the right mask. And they make small ones for kids.
If I had to bet, I’d say that this particular North Carolina firm’s masks were chosen because the principal author and all of his colleagues are from North Carolina. And because the manufacturer seems to do everything more-or-less correctly.
At some point, I’ll belabor exactly why this is a reasonable choice. But for now:
The upshot is, based on their cheapest mask, for under $20 (including shipping), you can get two copies of the mask tested in that JAMA article. It’s roughly an N80 after washing. You can reduce your exposure to airborne virus 3.5-fold, compared to a standard ear-loop surgical mask.
With no fear of counterfeits. With an actual legit test of that exact mask, on the books. Easy-on, easy-off. I’m sure if you did your homework, you could find well-fitting two-layer nylon masks for less. But at some point, it’s not a lot of money, given what’s at stake.
Is this the best mask you could possibly use? No. You can see where this sits on the scale of risk, in the graph below (redone from above). At least you can see the difference without using a ruler to measure the bar. But is this a substantial upgrade, if you’re still using disposable ear-loop surgical masks? Yes, the odds are overwhelming that it substantially out-performs a blue disposable ear-loop mask.
Be sure to wash these before you wear them. Filtration improves greatly after washing.
And if you insist on using up that pack of blue masks that you bought, look into the tied-and-tucked method for improving the fit and filtration of those masks, in this YouTube video.
A recent article in the Journal of the American Medical Association (JAMA) performed a sophisticated test of several face masks. The results had a few surprises. I thought I might take the opportunity to repeat a few key results, and then, in a separate posting, maybe compile all the presumably legitimate masks tests that have been published. You don’t want to make too much out of any one test, but this one appears to be about as realistic and accurate as you are likely to find. Continue reading Post #924: Mask test published in JAMA
If you look for graphic images of clotheslines, you inevitably get a page of crap like the image to the left. Clothes lines are stereotyped as old-fashioned, or hicksville, or as the case of the one at the left, both. With a side-order of sexism.
Warning: This is just the background. I don’t get around to making these until the next post on this topic, which will occur after I’ve gathered the needed materials. To see the wood DIY version of these, look at the just-prior Post #886.
Edit 2/24/2024: The actual construction is shown in Post #927. To see that properly-configured cardboard is more than strong enough for this use, see Post #891.
My last post presented plans for a practical way to allow wheelchair users to transition easily from from floor to chair and vice-versa. The key insight — from a wheelchair-using friend — was that all you need is a broad, shallow set of steps, and a couple of “push up bar” handles (like these, say). Portable handles vastly simplify the construction, relative to a device with built-in hand-holds or railings.
My friend reports that this combination of stairs-plus-portable-handles has increased her mobility. Which, apparently, is high praise indeed.
For many people, constructing that set of stairs may not be possible. While the carpentry wasn’t complicated, it required space and tools adequate for cutting up a full sheet of plywood. The final result was nice, but what good does that do you if you can’t obtain one?
Today’s post goes in the opposite direction: Volkssteppe. The people’s stairs. I’m going to work out how to create the same functionality using tools and materials that almost anyone can easily obtain and use. It may not look as nice or last as long. But it will work just as well as the original.
In this post, I use this as an opportunity to present some systematic analysis of this particular construction problem at hand. I’m not actually going to produce a working set of stairs using this new approach until the next post on this topic. The reason is that I need time to gather the materials and work out exactly what I’m going to do.
Corrugated Cardboard
After looking over the options, the obvious choice of material for this project is corrugated cardboard.
When I say “cardboard furniture”, I’m guessing that many people immediately dismiss the concept. They’re thinking in terms of a cardboard box with a tablecloth spread over it, or some sort of spindly little table.
You might be thinking that cardboard can’t possibly be strong enough for this use, right? If so, think again.
My point is that if manufacturers routinely make cardboard pallets capable of supporting a ton or more, you can probably make a small set of cardboard stairs capable of supporting 300 pounds.
If you still don’t get it, just Google “corrugated cardboard furniture” and look at the examples.
Source: Google images.
Or maybe watch this guy jumping up and down on his cardboard chair, at 3:50 into this YouTube video:
So, with a bit of planning, there’s no doubt that the average person can build a set of cardboard stairs strong enough to support an adult.
Now let me briefly list the advantages of corrugated cardboard, relative to almost any other alternative.
Available everywhere.
Cheap, typically free.
Easily worked with knife or shears.
Easily joined with common wood glue or carton-sealing tape.
Relatively lightweight if used well.
Too many choices for method of construction.
For these stairs, I am sticking to the basic footprint and form outlined in my just-prior post.
Each step will be 12″ x 30″, to accommodate both the user and the handles.
The top step will be 18″ above the ground.
A four-step staircase will be 4 feet long, with 4.5″ risers.
A three-step staircase will be 3 feet long, with 6″ risers.
I am also sticking to the “carcass and skin” approach of the prior model. That is, I’m going to build an ugly, functional structure (the carcass), then add a nicer-looking surface on top of that (the skin). This lets me be as crude as I want to make the functional parts of the structure as strong as needed. In this case, the “skin” will be large sheets of blank cardboard, covering up the internal details of the construction.
Beyond that, there are any number of ways to build a completely functional set of steps. There are simply too many choices.
And there is surprisingly little systematic guidance on the engineering of cardboard structures. For a material that is everywhere, and used for packing just about everything, I could find no systematic engineering guidelines for using it in construction. No rules-of-thumb as to how much weight a piece of corrugated cardboard would support. And so on.
And after examining a few boxes, I think that part of the reason is that corrugated comes in a wide range of thicknesses and weights. There is no one standard corrugated cardboard to use as a reference. Hence, there’s little standard guidance on using it.
That said, I’m basing everything below on a medium-sized carton from Amazon, which turned out to have walls that were 1/8″ thick, and weigh in at just about 1.6 ounces per square foot of cardboard. Or, conveniently enough, one pound for every ten square feet.
A nosology of cardboard furniture construction
Even if I can’t find a good engineering guide, I can at least try to categorize the various techniques used to make strong cardboard furniture.
With this method, you build a solid block of cardboard, in the desired shape, by stacking up cardboard sheets cut to shape. For strength, the sheets would be vertical, with the corrugations (channels) running vertically.
This approach clearly could generate a set of stairs strong enough to support a person. If in doubt, review the YouTube video cited above.
The main problem with simple stacked sheets, for this project, is the sheer amount and weight of cardboard required.Assuming zero waste, and not accounting for the weight of any glue used, for the shallow 4-step stairs described above, if I simply made a solid set of steps, it would require:
720 square feet of cardboard.
Equal to about 45 “medium” moving cartons.
Weighing about 72 pounds.
Glue could easily add another 13 pounds, even if used sparingly.
Calculation: Titebond is a commonly-used high-quality wood glue and would be suitable for this purpose. Titebond says that, for wood applications, the maximum spread rate for their glue is 250 square feet per gallon. At that rate, if you thoroughly glued this together, you’d end up using (720/250 =) almost three gallons of glue. Titebond (same source) weighs 9 lbs/gallon, half of which is solids, so that would add maybe (3*9*0.5=) 13 pounds.
The total weight of the stairs could easily approach 100 pounds. And, once you figure in the wastage, would easily require gathering more than 1000 square feet of cardboard, or the equivalent of 60 to 70 “medium” moving cartons. There would also be a considerable amount of waste left over, after cutting out the required shapes.
In short, if used as a brute-force approach, it would simply be too much. Too much material, too much weight, too much glue.
That said, one obvious alternative is to make the structure hollow. Laminate up a series of broad “U”s. Each broad “U”, upside-down, would be a step. They would be laminated from strips cut from cardboard. Would that work?
If I make each step 4.5″ thick (from tread surface to underside of tread surface), that would still use abut 450 square feet of cardboard, amounting to maybe 27 “medium” moving boxes, and weighing in at over 50 pounds.
So that’s better, and results in less waste. But it’s still not what what I would call a sterling candidate. The only way to reduce it further would be to make the step cross-section thinner than 4.5″. That would certainly require experimenting to see how thin I could make it and still have it be sturdy enough to sit on.
Tentatively, I’m going to dismiss this one. I see almost no modern commercial cardboard furniture made this way, and I think that’s probably sending a signal that this is not very practical.
2 Strength from geometry: Folded beams and triangulated surfaces.
This approach typically gets billed as “origami-like”. That’s because, at first glance, the strength of the furniture derives from the carefully folded cardboard.
At root, this is about creating horizontal load-bearing elements that act like structural beams. That is, single pieces of cardboard folded so that you would have to stretch or rip the cardboard along the bottom edge of the beam, in order to make the beam deflect downwards. These constructed horizontal beams are then married to inherently strong vertical members such a thick cardboard, or thick cardboard folded into geometrically stable shapes such as triangles.
That said, the one thing I notice about most of these is that they are NOT made of recycled cardboard and NOT made out of standard 1/8″ thick carton cardboard. Instead, all or nearly all of these origami-like pieces seem purpose-built of virgin materials, and most seem to use corrugated that is substantially thicker and stronger than what you find in garden-variety cartons.
Upon reflection, I think that goes hand-in-hand with this approach. My guess is that if you start piecing together materials and using a variety of thin, waste cardboard, you compromise the structural integrity.
I judge that this approach, by and large, isn’t going to be practical for a set of instructions focused on using whatever-is-available scrap cardboard. This is great for commercial product or piece of artwork, but it looks inherently risky when translated to a set of D-I-Y instructions using scrap materials.
3 Structural grid (or grid-plus-envelope) method.
The hallmark of this method is criss-crossed strips of cardboard, oriented vertically. This comes in two varieties that look similar, but work in completely different ways.
The first variety is more-or-less an air-filled version of the stacked sheet method. This translates a load vertically, to the floor, via vertical sheets of cardboard. You can tell these by the presence of closely-spaced cardboard strips held in a vertical orientation, as in the seat portion of the chair pictured above. Mechanically, this is really not very different from the solid stacked sheets, it just uses less cardboard, and uses the criss-cross pattern to keep the sheets in the proper orientation.
If you were then to place a sheet of cardboard over the seat of this chair, you’d have “structural grid plus envelope”, per this website. You still have a structural grid of vertical cardboard sheets transmitting load to the ground. they are just hidden beneath a cardboard envelope.
But the second variety of structural grid is a classic beam. These elements take a downward stress, and carry that stress horizontally over to some load-bearing element. In effect, these are horizontal elements built just like a hollow-core door: Continuous skins on top and bottom, glued tightly to a central (mostly air-filled) core that holds those skins a fixed distance apart.
In the picture above, the horizontal bookshelves are just slabs of very thick corrugated cardboard. The wide spacing between the top and bottom paper layers gives them enough strength to hold up the weight of the books.
So these elements work like an I-beam. In order to flex this downward, you have to compress the top skin, stretch or break the bottom skin, or both. The significant distance between top and bottom skins — maintained by the core — makes it quite difficult to do either. And hence, you get reasonable load-bearing capability with relatively light weight.
I doubt that I could make a properly functioning beam of this sort from scrap cardboard. The problem is that the two skins need to be held rigidly apart. I doubt that I could cut scrap cardboard accurately enough to create that tight, non-moving bond between upper and lower skin.
But at this point, it seems pretty clear that the first type of structural-grid-plus-envelope — cross-crossed strips of vertically-oriented cardboard — is the most promising technique so far. All I want to do is translate the force of someone sitting on these steps, down to the ground. It looks like I could do that, with used cardboard, with a structural grid approach. So that’s where I’m headed.
This post is completely irrelevant for most readers. If it doesn’t apply to you, just move along. I’m posting this for a very specific target audience who would not otherwise be reading this blog.
This post is a brief description of a how to build a sturdy, cheap, relatively light-weight system to allow paraplegic wheelchair users to go from floor to chair and vice-versa, within their homes. In a nutshell, this is a set of broad, shallow, lightweight carpeted steps, coupled with a pair of standard “pushup bar” padded handles to allow the paraplegic user to mount those steps.
Making this set of steps requires power tools and a place to use them. But the design is simple enough that any halfway competent D-I-Y carpenter can make them.
Source: Immunogenicity and protective efficacy of influenza vaccination
Claude Hannouna, Francoise Megas, James Piercy, Virus Research 103 (2004) 133–138.
The importance of this graph will be clear about five paragraphs down.
At this point, with the Phase III trials of coronavirus vaccines well underway, even if they don’t have enough “statistical power” to do the formal statistical test, our public health bureaucracy ought to have a fairly good indication of how things are shaping up.
I’ve been waiting for any US public health leader to start leaking information on the likely effectiveness of the coronavirus vaccines. Informally tossing some numbers out there, to get us prepped for the eventual formal announcement.
This post is prompted by 
I posted something yesterday, chiding people for wearing cheap face masks, and in particular for wearing them poorly. Apparently I hit a nerve with more than a few people, and I’ve been challenged to offer some practical advice.
If you look for graphic images of clotheslines, you inevitably get a page of crap like the image to the left. Clothes lines are stereotyped as old-fashioned, or hicksville, or as the case of the one at the left, both. With a side-order of sexism.
