Tag Archives: safety

Deadly screw sizes, avoid odd numbers and UNF.

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The glory of American screws and bolts is their low cost ubiquity, especially in our coarse thread (UNC = United National Coarse) sizes. Between 1/4 inch and 5/8″, they are sized in 1/16″ steps, and after that in 1/8″ steps. Below 3/16″, they are sized by wire gauges, and generally they have unique pitch sizes. All US screws and bolts are measured by their diameter and threads per inch. Thus, the 3/8-16 (UNC) has an outer diameter (major diameter) of 3/8″ with 16 threads per inch (tpi). 16 tpi is an ideal thread number for overall hold strength. No other bolt has 16 threads per inch so it is impossible to use the wrong bolt in a hole tapped for 3/8-16. The same is true for basically every course thread with a very few exceptions, mainly found between 3/16″ and 1/4″ where the wire gauges transition to fractional sizes. Because of this, if you stick to UTC you are unlikely to screw up, as it were. You are also less-likely to cross-thread.

I own one of these. It’s a tread pitch gauge.

US fine threads come in a variety of standards, most notably UNF = United National Fine. No version of fine thread is as strong as coarse because while there are more threads per inch, each root is considerably weaker. The advantage of fine treads is for use with very thin material, or where vibration is a serious concern. The problem is that screwups are far more likely and this diminishes the strength even further. Consider the 7/16″ – 24 (UNF). This bolt will fit into a nut or flange tapped for 1/2″- 24. The fit will be a little loose, but you might not notice. You will be able to wrench it down so everything looks solid, but only the ends of the threads are holding. This is a accident waiting to happen. To prevent such mistakes you can try to never allow a 7/6″-24 bolt into your shop, but this is uncomfortably difficult. If you ever let a 7/6″-24 bolt in, some day someone will grab it and use it, in all likelihood with a 1/2″ -24 nut or flange, since these are super-common. Under stress, the connection will fail in the worst possible moment.

Other UNF bolts and nuts present the same screwup risk. For example, between the 3/8″-24 and 5/16″-24 (UNF), or the #10-32 (UNF) and also with the 3/16″- 32, and the latter with the #8-32 (UNC). There is also a French metric with 0.9mm — this turns out to be identical to -32 pitch. The problem appears with any bolt pair where with identical pitch and the major diameter of the smaller bolt has a larger outer diameter (major diameter) than the inner diameter (minor diameter) of the larger bolt. If these are matched, the bolts will seem to hold when tightened, but they will fail in use. You well sometimes have to use these sizes because they match with some purchased flange. If you have to use them, be careful to use the largest bolt diameter that will fit into the threaded hole.

Where I have the option, my preference is to stick to UNC as much as possible, even where vibration is an issue. In vibration situations, I prefer to add a lock nut or sometimes, an anti-vibration glue, locktite, available in different release temperatures. Locktite is also helpful to prevent gas leaks. In our hydrogen purifiers, I use lock washers on the ground connection from the power cord, for example.

I try to avoid metric, by the way. They less readily available in the US, and more expensive. The other problem with metric is that there are two varieties (Standard and French — God love the French engineering) and there are so many sizes and pitches that screwups are common. Metric bolts come in every mm diameter, and often fractional mm too. There is a 2mm, a 2.3mm, a 2.5mm, and a 2.6mm, often with overlapping pitches. The pitch of metric screws and bolts is measured by their spacing, by the way, so a 1mm metric pitch means there is 1mm between threads, the the equivalent of a 24.5 pitch in the US, and a 0.9mm pitch = US-32. Thread confusion possibilities are endless. A M6x1 (6mm OD x 1mm pitch) is easily confused with a M5x1 or a M7x1, and the latter with the M7.5×1. A M8x1.25 is easily confused with a M9x1.25, and a M14x2 with an M16x2. And then there is confusion with US bolts: a 2.5mm metric pitch is nearly identical to a US 10tpi pitch. I can not rid myself of US threads, so I avoid metric where I can. As above, problems arise if you use a smaller diameter bolt in a larger diameter nut.

For those who have to use metric, I suggest you always use the largest bolt that will fit (assuming you can find it). I try to avoid bringing odd-size bolts into their shop, that is, stick to M6, M8, M10. It’s not always possible, but it’s a suggestion. I get equipment with odd-size metric bolts too. My preference is to stick to UNC and to avoid odd numbers.

Robert Buxbaum, January 23, 2024. Note: I’ve only really discussed bolt sizes between about #4 and 1″, and I didn’t consider UNRC or UNJF or other, odd options. You can figure these issues out yourself from the above, I think.

Ladder on table, safe till it’s not.

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via GIFER

Two years ago I wrote about how to climb a ladder safely without fear. This fellow has no fear and has done the opposite. This fellow has chosen to put a ladder on a table to reach higher than he could otherwise. That table is on another table. At first things are going pretty well, but somewhere about ten steps up the ladder there is disaster. A ladder that held steadily, slips to the edge of the table, and then the table tips over. It’s just physics: the higher he climbs on the ladder the more the horizontal force. Eventually, the force is enough to move the table. He could have got up safely if he moved the tables closer to the wall or if he moved the ladder bottom further to the right on the top table. Either activity would have decreased the slip force, and thus the tendency for the table to tip.

Perhaps the following analysis will help. Lets assume that the ladder is 12.5′ long and sits against a ten foot ledge, with a base 7.5′ away from the wall. Now lets consider the torque and force balance at the bottom of the ladder. Torque is measured in foot-pounds, that is by the rotational product of force and distance. As the fellow climbs the ladder, his weight moves further to the right. This would increase the tendency for the ladder to rotate, but any rotation tendency is matched by force from the ledge. The force of the ledge gets higher the further up the ladder he goes. Let’s assume the ladder weighs 60 lbs and the fellow weighs 240 pounds. When the fellow has gone up ten feet up, he has moved over to the right by 7.5 feet, as the diagram shows. The weight of the man and the ladder produces a rotation torque on the bottom of 60 x 3.75 + 240 x 7.5 = 1925 foot pounds. This torque is combatted by a force of 1926 foot pounds provided by the ledge. Since the ladder is 12.5 feet long the force of the ledge is 1925/12.5 = 154 pounds, normal to the ladder. The effect of this 154 lbs of normal force is to push the ladder to the left by 123.2 lbs and to lift the ladder by 92.4lbs. It is this 123.2 pounds of sideways push force that will cause the ladder to slip.

The slip resistance at the bottom of the ladder equals the net weight times a coefficient of friction. The net weight here equals 60+240-92.4 = 217.6 lbs. Now lets assume that the coefficient of friction is 0.5. We’d find that the maximum friction force, the force available to stop a slip is 217.6 x 0.5 = 108.8 lbs. This is not equal to the horizontal push to prevent rotation, 123.2 lbs. The net result, depending on how you loot at things, is either that the ladder rotates to the right, or that the ladder slips to the left. It keeps slipping till, somewhere near the end of the table, the table tips over.

Force balance of man on ladder. Based on this, I will go through the slippage math in gruesome detail.

I occasionally do this sort of detailed physics; you might as well understand what you see in enough detail to be able to calculate what will happen. One take home from here is that it pays to have a ladder with rubber feet (my ladders do). That adds to the coefficient of friction at the bottom.

Robert Buxbaum, November 6, 2019.

bicycle helmets kill

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There is rarely a silver lining that does not come with a cloud, and often the cloud is bigger than the lining. A fine example is bicycle helmets. They provide such an obvious good that, at first glance, you’d think everyone would wear one, even without a law mandating it. Why would anyone risk their skull in a bicycle accident if injury were prevented by merely wearing a particular hat? Yet half the people ride without, even when there are laws and fines. There are some down-side to helmets, but they are so small that even mentioning them seems small. Helmets are inconvenient, and this causes people to ride a little less, so what?

hospital admissions for bicycle related head injuries, red, left; and bicycle related, non-head injuries, blue, right. Victoria Australia.

Hospital admissions for bicycle-related, head injuries, red, left scale, and bicycle-related, non-head injuries, blue, right scale. The ratio is 1:2 before and after the helmet law suggesting that helmet law did nothing but reduce ridership.

As to turns out, helmets hardly stop accidental injury, yet cause people to ride a lot less, and this lack of exercise causes all sorts of problems — far more than the benefits. In virtually every city where it was studied, bicycle ridership dropped by 30-40% when helmets were required, and as often as not, those who still rode, rode unhelmeted. There was a 30-40% decrease in head-trauma injuries, but it appears that this was just the result of 30-40% less ridership. You’d expect a larger decrease if the helmet helped, as such.

Take the experience of Victoria, Australia; head and non-head bicycle injury data plotted above. Victoria required bicycle helmets in January 1990. Before then, in the peak summer months, hospital records show some 50 bicycle-related head injuries per month, and 100 bicycle-related, non-head injuries — a 1:2 proportion. Later, after the law went into effect, each summer month saw about 35 bicycle-related, head injuries, and 70 bicycle-related, non head injuries. This proportion, 1:2, remained the same suggesting the only effect of the helmet law was to reduce ridership, with no increase in safety. The same 30% decrease was seen by direct count of riders on major streets, though now a greater proportion of those still riding were flaunting the law, and not wearing helmets.

One reason that helmets don’t help much is that the skull is already a very good helmet. As things stand, the main injury in a bicycle flip does not come from your skull cracking, it comes from your brain hitting the inside of your skull, and a second helmet doesn’t help stop that. There’s no increase in safety, and perhaps a decrease as the helmet appears to decrease vision. In a study of bicycle-injury-related highway deaths, Piet de Jong found that countries with the highest helmet use had the highest highway death rates. The country with the highest helmet use (the USA, 38% helmeted) had the highest cyclist death rate, 44 deaths per 1,000,000,000 km. By comparison, the nation with the least helmet use (Holland, 1% helmeted) had among the lowest death rates, only 10.7 deaths per 1,000,000,000 km. There are many explanations for this finding, one sense is that the helmets hurt vision making all types of injury and death more likely.

An hour or three of exercise per week adds years to your life -- especially among the middle aged.

From the national cancer institute. An hour or three of exercise per week adds years to your life — especially among the middle aged. Note these are healthy weight individuals. 

Worse than the effect on visibility, may be the effect on exercise. Exercise is tremendously beneficial, especially for middle-aged people in a sedentary population like the US. The lack of exercise is a lot more deadly, it turns out, than any likelihood of flying over the handlebars. How do I know? From studies like the National Cancer institute, shown at right. To calculate the cost/benefit of a little riding, less say you ride 3 hours per week at 10 mph (slow roll). The chart at right suggests a middle-aged person will add 3.4 years to your life, or about 10% life extension. Now consider the risks. This person will ride 30 miles per week, or 2400 km per year. Over 35 years the chance of death is only 0.36%. In order to get a 10% chance of death, you’d have to ride, over 2.3 million km, or 1000 years. Clearly the life extension benefit far outweighs the risk from fatal accident.

But life extension isn’t the total benefit of exercise. Exercise is shown to improve metal health, reducing depression and ADD in children, and likely in adults. Exercise also helps with weight loss, and that is another big health benefit (the chart above was for healthy body weight riders). So my first suggestion is get rid of bicycle helmet laws. I would not go so far as to ban helmets, but see clear disadvantages to the current laws.

The other suggestion: invent a better helmet. While most helmets are vented, and reasonably cool while you ride. They become uncomfortably hot when you stop. And they look funny in a store or restaurant. You can’t easily take them off, either: Restaurants no longer have hat racks, and stores never had them. What’s needed is a lighter, cooler helmet. Without that, and with helmet laws in place, people in the US tend to drive rather than ride a bicycle — and the lack of exercise is killing them.

Robert Buxbaum, January 19, 2017. One of my favorite writing subjects is the counter-intuitiveness of health science. See, eg. on radiation, or e-cigarettes, or sunshine, or health food. Here is a general overview of how to do science; I picked all the quotes from Sherlock Holmes.

The Hindenburg: mainly the skin burnt

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The 1937 Hindenburg disaster is often mentioned as proof that hydrogen is too flammable and dangerous for commercial use. Well hydrogen is flammable, and while the Hindenburg was full of hydrogen when it started burning, but a look at a color photograph of the fire ( below), or at the B+W  Newsreel film of the fire, suggests that it is not the hydrogen burning, but the skin of the zeppelin and the fuel. Note the red color of the majority flame, and note the black smoke. Hydrogen fires are typically invisible or very light blue, and hydrogen fires produce no smoke.

Closeup of the Hindenburg burning. It is the skin that burns, not the gaseous hydrogen

Closeup of the Hindenburg burning. It is the skin and gasoline that burns, not the gaseous hydrogen.

The Hindenburg was not a simple hydrogen balloon either. It was a 15 story tall airship with state-rooms, a dining room and an observation deck. It carried 95 or so passengers and crew. There was plenty of stuff to burn besides hydrogen. Nor could you say that a simple spark had set things off. The Hindenburg crossed the ocean often: every 2 1/2 days. Lightning strikes were common, as were “Saint Elmo’s fire,” and static electricity discharges. And passengers smoked onboard. Holes and leaks in the skin were also common, both on the Hindenburg and on earlier airships. The hydrogen-filled, Graf Zeppelin logged over 1 million flight miles and over 500 trips with no fires. And it’s not like helium-filled zeppelins and blimps are much safer. The photo below shows the fire and crash of a helium-filled Goodyear blimp, “Spirit of Safety”, June, 2011. Hydrogen has such a very high thermal conductivity that it is nearly as hard to light as helium. I recently made this video where I insert a lit cigar into a balloon filled with hydrogen. There is no fire, but the cigar goes out.  In technical terms, hydrogen is said to have a low upper combustion limit.

Helium-filled goodyear blimp catches fire and burns to destruction.

Helium-filled goodyear blimp “spirit of safety” catches fire and burns before crashing. It’s not the helium burning.

The particular problem with the Hindenburg seems to have been its paint, skin and fuel, the same problems as caused the fire aboard the “Spirit of Safety.” The skin of the Hindenburg was cotton, coated with a resin-dope paint that contained particles of aluminum and iron-oxide to help conduct static electricity. This combination is very flammable, essentially rocket fuel, and the German paint company went on to make rocket fuel of a similar composition for the V2 rockets. And the fuel was flammable too: gasoline. The pictures of the Hindenburg disaster suggest (to me) that it is the paint and the underlying cotton skin that burned, or perhaps the fuel. A similar cause seems to have beset the “Spirit of Safety.” For the Hindenburg’s replacement, The Graf II, the paint composition was changed to replace the aluminum powder with graphite – bronze, a far less flammable mixture, and more electrically conductive. Sorry to say, there was no reasonably alternative to gasoline. To this day, much of sport ballooning is done with hydrogen; statistically it appears no more dangerous than hot air ballooning.

It is possible that the start of the fire was a splash of gasoline when the Hindenburg made a bumpy contact with the ground. Another possibility is sabotage, the cause in a popular movie (see here), or perhaps an electric spark. According to Aviation Week, gasoline spoiled on a hot surface was the cause of the “Spirit of Safety fire,” and the Hindenburg disaster looks suspiciously similar. If that’s the case, of course, the lesson of the Hindenburg disaster is reversed. For safety, use hydrogen, and avoid gasoline.

Dr. Robert E. Buxbaum, January 8, 2016. My company, REB Research, makes hydrogen generators, and other hydrogen equipment. If you need hydrogen for weather balloons, or sport ballooning, or for fuel cells, give us a call.

Seniors are not bad drivers.

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Seniors cause accidents, but need to get places too

Seniors are often made fun of for confusion and speeding, but it’s not clear they speed, and it is clear they need to get places. Would reduced speed limits help them arrive alive?

Seniors have more accidents per-mile traveled than middle age drivers. As shown on the chart below, older Canadians, 75+, get into seven times more fatal accidents per mile than 35 to 55 year olds. At first glance, this would suggest they are bad drivers who should be kept from the road, or at least made to drive slower. But I’m not so sure they are bad drivers, and am pretty certain that lower speed limits should not be generally imposed. I suspect that a lot of the problem comes from the a per-mile basis comparison with folks who drive long distances on the same superhighways instead of longer, leisurely drives on country roads. I suspect that, on a per-hour basis, the seniors would look a lot safer, and on a per highway-mile basis they might look identical to younger drivers.

Canadian Vehicle Survey, 2001, Statistics Canada, includes drivers of light duty vehicles.

Deaths per billion km. Canadian Vehicle Survey, 2001, Statistics Canada, includes light duty vehicles.

Another source of misunderstanding, I find, is that comparisons tend to overlook how very low the accident rates are. The fatal accent rate for 75+ year old drivers sounds high when you report it as 20 deaths per billion km. But that’s 50,000,000 km between fatalities, or roughly one fatality for each 1300 drives around the earth. In absolute terms it’s nothing to worry about. Old folks driving provides far fewer deaths per km than 12-29 year olds walking, and fewer deaths per km than for 16-19 year olds driving.

When starting to research this essay, I thought I’d find that the high death rates were the result of bad reaction times for the elderly. I half expected to find that reduced speed limits for them helped. I’ve not found any data directly related to reduced speeds, but now think that lowered speed limits would not help them any more than anyone else. I note that seniors drive for pleasure more than younger folks and do a lot more short errand drives too — to the stores, for example. These are places where accidents are more common. By contrast, 40 to 70 year olds drive more miles on roads that are relatively safe.

Don't walk, especially if you're old.

Don’t walk, especially if you’re old. Netherlands data, 2001-2005 fatalities per billion km.

The Netherlands data above suggest that any proposed solution should not involve getting seniors out of their cars. Not only do seniors find walking difficult, statistics suggest walking is 8 to 10 times more dangerous than driving, and bicycling is little better. A far better solution, I suspect, is reduced speeds for everyone on rural roads. If you’re zipping along a one-lane road at the posted 40, 55, or 60 mph and someone backs out of a driveway, you’re toast. The high posted speeds on these roads pose a particular danger to bicyclists and motorcyclists of all ages – and these are folks who I suspect drive a lot on the rural roads. I suspect that a 5 mph reduction would do quite a lot.

For automobiles on super-highways, it may be worthwhile to increase the speed limits. As things are now, the accident fatality rates are near zero, and the main problem may be the time wasted behind the wheel – driving from place to place. I suspect that an automobile speed limit raise to 80 mph would make sense on most US and Canadian superhighways; it’s already higher on the Autobahn in Germany.

Robert Buxbaum, November 24, 2014. Expect an essay about death on tax-day, coming soon. I’ve also written about marijuana, and about ADHD.

Hormesis, Sunshine and Radioactivity

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It is often the case that something is good for you in small amounts, but bad in large amounts. As expressed by Paracelsus, an early 16th century doctor, “There is no difference between a poison and a cure: everything depends on dose.”

Aereolis Bombastus von Hoenheim (Paracelcus)

Phillipus Aureolus Theophrastus Bombastus von Hoenheim (Dr. Paracelsus).

Some obvious examples involve foods: an apple a day may keep the doctor away. Fifteen will cause deep physical problems. Alcohol, something bad in high doses, and once banned in the US, tends to promote longevity and health when consumed in moderation, 1/2-2 glasses per day. This is called “hormesis”, where the dose vs benefit curve looks like an upside down U. While it may not apply to all foods, poisons, and insults, a view called “mitridatism,” it has been shown to apply to exercise, chocolate, coffee and (most recently) sunlight.

Up until recently, the advice was to avoid direct sun because of the risk of cancer. More recent studies show that the benefits of small amounts of sunlight outweigh the risks. Health is improved by lowering blood pressure and exciting the immune system, perhaps through release of nitric oxide. At low doses, these benefits far outweigh the small chance of skin cancer. Here’s a New York Times article reviewing the health benefits of 2-6 cups of coffee per day.

A hotly debated issue is whether radiation too has a hormetic dose range. In a previous post, I noted that thyroid cancer rates down-wind of the Chernobyl disaster are lower than in the US as a whole. I thought this was a curious statistical fluke, but apparently it is not. According to a review by The Harvard Medical School, apparent health improvements have been seen among the cleanup workers at Chernobyl, and among those exposed to low levels of radiation from the atomic bombs dropped on Hiroshima and Nagasaki. The health   improvements relative to the general population could be a fluke, but after a while several flukes become a pattern.

Among the comments on my post, came this link to this scholarly summary article of several studies showing that long-term exposure to nuclear radiation below 1 Sv appears to be beneficial. One study involved an incident where a highly radioactive, Co-60 source was accidentally melted into a batch of steel that was subsequently used in the construction of apartments in Taiwan. The mistake was not discovered for over a decade, and by then the tenants had received between 0.4 and 6 Sv (far more than US law would allow). On average, they were healthier than the norm and had significantly lower cancer death rates. Supporting this is the finding, in the US, that lung cancer death rates are 35% lower in the states with the highest average radon radiation levels (Colorado, North Dakota, and Iowa) than in those with the lowest levels (Delaware, Louisiana, and California). Note: SHORT-TERM exposure to 1 Sv is NOT good for you; it will give radiation sickness, and short-term exposure to 4.5 Sv is the 50% death level

Most people in the irradiated Taiwan apartments got .2 Sv/year or less, but the same health benefit has also been shown for people living on radioactive sites in China and India where the levels were as high as .6 Sv/year (normal US background radiation is .0024 Sv/year). Similarly, virtually all animal and plant studies show that radiation appears to improve life expectancy and fecundity (fruit production, number of offspring) at dose rates as high as 1 Sv/month.

I’m not recommending 1 Sv/month for healthy people, it’s a cancer treatment dose, and will make healthy people feel sick. A possible reason it works for plants and some animals is that the radiation may kill proto- cancer, harmful bacteria, and viruses — organisms that lack the repair mechanisms of larger, more sophisticated organisms. Alternately, it could kill non-productive, benign growths allowing the more-healthy growths to do their thing. This explanation is similar to that for the benefits farmers produce by pinching off unwanted leaves and pruning unwanted branches.

It is not conclusive radiation improved human health in any of these studies. It is possible that exposed people happened to choose healthier life-styles than non-exposed people, choosing to smoke less, do more exercise, or eat fewer cheeseburgers (that, more-or-less, was my original explanation). Or it may be purely psychological: people who think they have only a few years to live, live healthier. Then again, it’s possible that radiation is healthy in small doses and maybe cheeseburgers and cigarettes are too?! Here’s a scene from “Sleeper” a 1973, science fiction, comedy movie where Woody Allan, asleep for 200 years, finds that deep fat, chocolate, and cigarettes are the best things for your health. You may not want a cigarette or a radium necklace quite yet, but based on these studies, I’m inclined to reconsider the risk/ benefit balance in favor of nuclear power.

Note: my company, REB Research makes (among other things), hydrogen getters (used to reduce the risks of radioactive waste transportation) and hydrogen separation filters (useful for cleanup of tritium from radioactive water, for fusion reactors, and to reduce the likelihood of explosions in nuclear facilities.

by Dr. Robert E. Buxbaum June 9, 2013

Link

Some 2-3 years ago I did an interview where I stood inside one of our hydrogen generator shacks (with the generator running) and poked a balloon filled with hydrogen with a lit cigar — twice. No fire, no explosion, either time. It’s not a super hit, but it’s gotten over 5000 views so far. Here it is

Nuclear Power: the elephant of clean energy

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As someone who heads a hydrogen energy company, REB Research, I regularly have to tip toe about nuclear power, a rather large elephant among the clean energy options. While hydrogen energy looks better than battery energy in terms of cost and energy density, neither are really energy sources; they are ways to transport energy or store it. Among non-fossil sources (sources where you don’t pollute the air massively) there is solar and wind: basically non-reliable, low density, high cost and quite polluting when you include the damage done making the devices.

Compared to these, I’m happy to report that the methanol used to make hydrogen in our membrane reactors can come from trees (anti-polluting), even tree farming isn’t all that energy dense. And then there’s uranium: plentiful, cheap and incredibly energy dense. I try to ignore how energy dense uranium is, but the cartoon below shows how hard that is to do sometimes. Nuclear power is reliable too, and energy dense; a small plant will produce between 500 and 1000 MW of power; your home uses perhaps 2 kW. You need logarithmic graph paper just to compare nuclear power to most anything else (including hydrogen):

log_scale

A tiny amount of uranium-oxide, the size of a pencil will provide as much power as hundreds of train cars full of coal. After transportation, the coal sells for about $80/ton; the sells for about $25/lb: far cheaper than the train loads of coal (there are 100-110 tons of coal to a train-car load). What’s more, while essentially all of the coal in a train car ends up in the air after it’s burnt, the waste uranium generally does not go into the air we breathe. The coal fumes are toxic, containing carcinogens, carbon monoxide, mercury, vanadium and arsenic; they are often radioactive too. All this is avoided with nuclear power unless there is a bad accident, and bad accidents are far rarer with nuclear power than, for example, with natural gas. Since Germany started shutting nuclear plants and replacing them with coal, it appears they are making all of Europe sicker).

It is true that the cost to build a nuclear plant is higher than to build a coal or gas plant, but it does not have to be: it wasn’t that way in the early days of nuclear power, nor is this true of military reactors that power our (USA) submarines and major warships. Commercial nuclear reactors cost a lot largely because of the time-cost for neighborhood approval (and they don’t always get approval). Batteries used for battery power get no safety review generally though there were two battery explosions on the Dreamliner alone, and natural gas has been known to level towns. Nuclear reactors can blow up too, as Chernobyl showed (and to a lesser extent Fukushima), but almost any design is better than Chernobyl.

The biggest worry people have with nuclear, and the biggest objection it seems to me, is escaped radiation. In a future post, I plan to go into the reality of the risk in more detail, but the worry is far worse than the reality, or far worse than the reality of other dangers (we all die of something eventually). The predicted death rate from the three-mile island accident is basically nil; Fukushima has provided little health damage (not that it’s a big comfort). Further, bizarre as this seems the thyroid cancer rate in Belarus in the wind-path of the Chernobyl plant is actually slightly lower than in the US (7 per 100,000 in Belarus compared to over 9 per 100,000 in the USA). This is clearly a statistical fluke; it’s caused, I believe, by the tendency for Russians to die of other things before they can get thyroid cancer, but it suggests that the health risks of even the worst nuclear accidents are not as bad as you might think. (BTW, Our company makes hydrogen extractors that make accidents less likely)

The biggest real radiation worry (in my opinion) is where to put the waste. Ever since President Carter closed off the option of reprocessing used fuel for re-use there has been no way to permanently get rid of waste. Further, ever since President Obama closed the Yucca Mountain burial repository there have been no satisfactory place to put the radioactive waste. Having waste sitting around above ground all over the US is a really bad option because the stuff is quite toxic. Just as the energy content of nuclear fuel is higher than most fuels, the energy content of the waste is higher. Burying it deep below a mountain in an area were no-one is likely to live seems like a good solution: sort of like putting the uranium back where it came from. And reprocessing for re-use seems like an even better solution since this gets rid of the waste permanently.

I should mention that nuclear power-derived electricity is a wonderful way to generate electricity or hydrogen for clean transportation. Further, the heat of hot springs comes from nuclear power. The healing waters that people flock to for their health is laced with isotopes (and it’s still healthy). For now, though I’ll stay in the hydrogen generator business and will ignore the clean elephant in the room. Fortunately there’s hardly any elephant poop, only lots and lots of coal and solar poop.

 

Why the Boeing Dreamliner’s batteries burst into flames

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Boeing’s Dreamliner is currently grounded due to two of their Li-Ion batteries having burst into flames, one in flight, and another on the ground. Two accidents of the same type in a small fleet is no little matter as an airplane fire can be deadly on the ground or at 50,000 feet.

The fires are particularly bad on the Dreamliner because these lithium batteries control virtually everything that goes on aboard the plane. Even without a fire, when they go out so does virtually every control and sensor. So why did they burn and what has Boeing done to take care of it? The simple reason for the fires is that management chose to use Li-Cobalt oxide batteries, the same Li-battery design that every laptop computer maker had already rejected ten years earlier when laptops using them started busting into flames. This is the battery design that caused Dell and HP to recall every computer with it. Boeing decided that they should use a massive version to control everything on their flagship airplane because it has the highest energy density see graphic below. They figured that operational management would insure safety even without the need to install any cooling or sufficient shielding.

All lithium batteries have a negative electrode (anode) that is mostly lithium. The usual chemistry is lithium metal in a graphite matrix. Lithium metal is light and readily gives off electrons; the graphite makes is somewhat less reactive. The positive electrode (cathode) is typically an oxide of some sort, and here there are options. Most current cell-phone and laptop batteries use some version of manganese nickel oxide as the anode. Lithium atoms in the anode give off electrons, become lithium ions and then travel across to the oxide making a mixed ion oxide that absorbs the electron. The process provides about 4 volts of energy differential per electron transferred. With cobalt oxide, the cathode reaction is more or less CoO2 + Li+ + e– —> LiCoO2. Sorry to say this chemistry is very unstable; the oxide itself is unstable, more unstable than MnNi or iron oxide, especially when it is fully charged, and especially when it is warm (40 degrees or warmer) 2CoO2 –> Co2O3 +1/2O2. Boeing’s safety idea was to control the charge rate in a way that overheating was not supposed to occur.

Despite the controls, it didn’t work for the two Boeing batteries that burst into flames. Perhaps it would have helped to add cooling to reduce the temperature — that’s what’s done in lap-tops and plug-in automobiles — but even with cooling the batteries might have self-destructed due to local heating effects. These batteries were massive, and there is plenty of room for one spot to get hotter than the rest; this seems to have happened in both fires, either as a cause or result. Once the cobalt oxide gets hot and oxygen is released a lithium-oxygen fire can spread to the whole battery, even if the majority is held at a low temperature. If local heating were the cause, no amount of external cooling would have helped.

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Something that would have helped was a polymer interlayer separator to keep the unstable cobalt oxide from fueling the fire; there was none. Another option is to use a more-stable cathode like iron phosphate or lithium manganese nickel. As shown in the graphic above, these stable oxides do not have the high power density of Li-cobalt oxide. When the unstable cobalt oxide decomposed there was oxygen, lithium, and heat in one space and none of the fire extinguishers on the planes could put out the fires.

The solution that Boeing has proposed and that Washington is reviewing is to leave the batteries unchanged, but to shield them in a massive titanium shield with the vapors formed on burning vented outside the airplane. The claim is that this shield will protect the passengers from the fire, if not from the loss of electricity. This does not appear to be the best solution. Airbus had planned to use the same batteries on their newest planes, but has now gone retro and plans to use Ni-Cad batteries. I don’t think that’s the best solution either. Better options, I think, are nickel metal hydride or the very stable Lithium Iron Phosphate batteries that Segway uses. Better yet would be to use fuel cells, an option that appears to be better than even the best batteries. Fuel cells are what the navy uses on submarines and what NASA uses in space. They are both more energy dense and safer than batteries. As a disclaimer, REB Research makes hydrogen generators and purifiers that are used with fuel-cell power.

More on the chemistry of Boeing’s batteries and their problems can be found on Wikipedia. You can also read an interview with the head of Tesla motors regarding his suggestions and offer of help.

 

Purifying the Hydrogen from Browns gas, HHO, etc.

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Perhaps the simplest way to make hydrogen is to stick two electrodes into water and to apply electricity. The gas that is produced is mostly hydrogen, and is sometimes suitable for welding or for addition to an automobile engine to increase the mileage. Depending on the electrodes and whether salt is added to the water, the gas that is produced can be Browns gas, HHO,  town gas, or some relative of the three. We are sometimes asked if we can purify the product of this electrolysis, and my answer is typically: “maybe,” or “it depends.”

If the electrode was made of stainless steel and the water contained only KOH or baking soda, the gas that results will be mostly hydrogen and you will be able to purify it somewhat with a polymer membrane if you wish. The gas isn’t very explosive generally, since most of the oxygen that results from the electrolysis will go into rusting out the electrodes. The reaction is thus, H2O + Fe –> H2 + FeO. To see if this is what you’ve got, you can use determine the ratio of gas production with a simple version of the Hoffman apparatus made from (for example) two overturned glass jars, or by separating the electrodes with a paper towel. You can also determine the H2 to O2 ratio (if you know a bit more physics) from a measure of the amperage and the rate of gas production. The hydrogen you form with steel plates will always contain some oxygen though, as well as some nitrogen and water vapor. While a polymer membrane will remove most of the oxygen and nitrogen in this gas, it won’t remove all, and it will not generally remove any of the water. With this gas, I suspect that you would be better off just using it as it is. This is particularly so if the fraction of oxygen is more than a few percent: hydrogen with more oxygen than this becomes quite explosive.

Since this gas will contain water, you probably don’t want to store it, and you probably don’t want to purify it over a metal, either, There are two reasons for this: the water can condense out during storage, and will tend to rust whatever metal it contacts (it’s often alkaline). What’s more, the small amount of oxygen in the hydrogen is likely to react over a hydrogen storage metal to form water and heat. This may give rise to the explosion you were trying to avoid. This is clearly the quick a dirty approach to making hydrogen.

Another version of electrolysis gas, one that’s even quicker and dirtier than the above involves the use of table salt instead of KOH or baking soda. The hydrogen that results will contain chlorine as an impurity, and will be quite toxic, but it will be somewhat less explosive.The hydrogen will smell like bleach and the water you use will turn slightly greenish and quite alkaline. Both the liquid and gas are definitely bad news unless your aim was to make chlorine and alkali; this is called the chlor-alkali process for a reason. On a personal note, as a 12 year old I tried this and was confused about why I got equal volumes of gas on the cathode and anode. The reason was that I was making Cl2, and not O2: the chemistry is 2 H2O + 2 NaCl –> H2 + Cl2 + 2 NaOH. I then I used the bromide version reaction to make a nice sample of bromine liquid. That is, I used KBr instead of table salt. Bromine is brown, oily, and only sparingly soluble in water.

Another version of this electrolysis process involves the use of graphite electrodes. If you are lucky, this will give you a mix of CO and hydrogen and not H2 and O2. This mix is a called “town gas.” It’s a very good welding gas since it is not explosive. It is, however, quite toxic. If you begin to get a headache using this gas stop immediately: you’re experiencing CO poisoning. The reaction here is H2O + C –> H2 + CO. CO headaches just get worse and worse until you die. If you are not lucky here you can get HHO instead of town gas, and this is quite explosive: H2O –> H2 + 1/2 O2. The volume ratio will be a key clue as to which you are making; another clue is to put a small volume in a paper bag and light it. If the bag explodes with a terrific bang, you’ve made the wrong gas. Stop!

With all of these gases I would recommend that you add a polymer of paper membrane in the water between the electrodes. Filter paper will work fine for this as will ceramic paper; the classic membrane for this was asbestos. If you keep the two product gas streams separate as soon as they are formed, you’ll avoid most of your explosion-safety issues. Few people take this advice, I’ve found; they think there must be some simpler way. Trust me: this is the classic, safe way to make electrolysis hydrogen.

A balloon filled with pure hydrogen will not ignite. To show you, here is a 2.5 min long video where I poke a lit cigar into a mylar balloon filled with hydrogen from my membrane reactor generators. Note that this hydrogen does not even burn in the balloon because it is oxygen free. As a safety check try this with your hydrogen, but only on a much-smaller scale. Pure hydrogen will not go boom, impure hydrogen will. My advice: keep safe and healthy. You’ll feel better that way, and your heirs will be less inclined to sue me.

In case you are wondering how electrolysis hydrogen can add to the gas mileage, the simple answer is that it increases the combustion speed and the water vapor decreases the parasitic loss due to vacuum. I’ve got some more information on this here. I hope this advice helps with your car project or any other electrolysis option. In my opinion, one should use a membrane in the water to separate the components at formation in all but the smallest experiments and with the smallest amperage sources. Even these should be done only in a well-ventilated room or on a car that is parked outside of the house. Many of the great chemists of the 1800s died doing experiments like these; learn from their mistakes and stay among the living.