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#91
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Inflatable helmet, really
Tom Sherman °_° wrote:
On 9/9/2010 10:51 PM, Frank Krygowski wrote: On Sep 9, 8:37 pm, "MikeWhy" wrote: Phil W Lee wrote: Utter bull****. If cycle helmets met the same standards, don't you think some motorcyclists would be wearing them? Not bull****. Look it up if you can figure out Google. Motorcycle helmets have additional criteria not specified for bicycle helmets, including coverage area and involving the chin bar when present. Retention criteria are also more stringent. Impact loads and survivability, however, are essentially the same. A funny thing happens when one actually looks up what MikeWhy claims. Specifically, they find that MikeWhy is either mistaken or lying. Here's an article that discusses motorcycle helmet testing standards in detail. (I've got it bookmarked.) http://www.motorcyclistonline.com/ge...iew/index.html or http://tinyurl.com/zglbq What it says? "The killer—the hardest Snell test for a motorcycle helmet to meet—is a two-strike test onto a hemispherical chunk of stainless steel about the size of an orange. The first hit is at an energy of 150 joules, which translates to dropping a 5-kilo weight about 10 feet—an extremely high-energy impact. The next hit, on the same spot, is set at 110 joules, or about an 8-foot drop. To pass, the helmet is not allowed to transmit more than 300 Gs to the headform in either hit." Later, it says: "Where the Snell standard limits peak linear acceleration to 300 G, the DOT effectively limits peak Gs to 250. Softer impacts, lower G tolerance. In short, a kinder, gentler standard." I'm not sure about that "effectively." According to http://www.smf.org/articles/mcomp2.html DOT limits acceleration to 400 gs, but from a drop height (for a large helmet) of about 7.35 feet, or 2.25 meters, which corresponds to 110 Joules for a 5 kg headform mass. By contrast, the CPSC bicycle helmet standard calls for just a two meter drop. It allows 300 gs acceleration of the same headform. The standards are NOT the same. Furthermore, the motorcycle helmet standard has much more rigid penetration tests. This is what drives the design of their heavy, hard shells. And this is pertinent, because a heavy, hard shell is less likely to get traction with the road during a tangential impact, and is more likely to have significant rotational inertia, to aid in reducing the brain's rotational acceleration. This might be considered an accidental benefit, because penetration of any helmet is rare, but rotational brain accelerations are now commonly recognized as being more likely than linear ones to cause serious brain injury. (Still, NO helmet standard tests for them!) What's even more enlightening is that article's discussion of the effect of various acclerations: "Newman is quoted in the COST study on the impact levels likely to cause certain levels of injury. Back in the '80s he stated that, as a rough guideline, a peak linear impact— the kind we're measuring here&151of 200 to 250 Gs generally corresponds to a head injury of AIS 4, or severe; that a 250 G to 300 G impact corresponds to AIS 5, or critical; and that anything over 300 Gs corresponds to AIS 6. That is, unsurvivable." Bike helmets are designed to attenuate the acceleration of a decapitated human head - no body attached - to 300 gs in a 14 mph impact. 300 gs is the borderline between critical and unsurvivable, according to that estimate. And that doesn't take into account rotational acceleration, which is worse in its effect, and which helmets may exacerbate (by their larger diameter and higher friction compared to a bare head). So leave the cyclist's head attached to his body, subject him to a head impact greater than 14 mph, include a slight tangential component to the impact, and you've blown away the "protection" of a bike helmet. Is it any wonder they haven't been shown to reduce serious head injuries? Dear Frank, Please stop confusing the Liddites™ with facts - it only makes them angry that their religious belief in the Magic Foam Bicycle Hat™ is challenged. Actually, it's the facts that make you, not me, cringe, run, hide, and blow smoke. The only agenda *I* have is to counter the misinformation spewed here about helmet ineffectiveness. There are factual errors and errors of logic in Frank's post above. I won't address them individually. To do so would be to spend the rest of eternity talking at insensate and unlearning furniture. The facts of the matter are these: The impact load applied in helmet testing is equivalent to a forceful blow from a 12 pound sledge hammer applied to the helmeted head. You split the hair if you like between 105 joules, the Snell Memorial Foundation test specification, and 102 joules, the energy resulting from the CPSC test specification. To understand what 100 joules looks, sounds, and feels like, drop a 12 lb bowling ball from eye level to the floor. This is equivalent to the CPSC impact test on a flat anvil. Choose for yourself whether the small difference between eyebrow height and a few inches higher is a meaningful difference. Decide here, this moment, if further discussion is at all necessary or meaningful. You can work through the rest of it yourself, given this proper picture of what the impact test really entails. Bearing in mind that a helmet worn on the head does nothing for the neck or its attachment to the head, just what does it mean to substitute the full body mass, as Frank suggests, for the head mass in the test? I intended that as gently rhetorical, but it would be interesting to hear further defense of his oddly blind suggestions. |
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#92
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Inflatable helmet, really
On 9/10/10 1:46 AM, MikeWhy wrote:
The impact load applied in helmet testing is equivalent to a forceful blow from a 12 pound sledge hammer applied to the helmeted head. Which is actually less than a typical 'header' bicycle accident, and really, really far below the impact of a header from getting hit by a car. In any event, if i were wearing a lid, i would definitely NOT let you hit me on the head with a 12-pound sledge on the head on a dare, but get enough beer in me, and I'd take the dare wearing a motorcycle lid. Maybe. Would take a lot of beer. |
#93
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Inflatable helmet, really
On Sep 10, 4:46*pm, "MikeWhy" wrote:
Tom Sherman °_° wrote: On 9/9/2010 10:51 PM, Frank Krygowski wrote: On Sep 9, 8:37 pm, "MikeWhy" wrote: Phil W Lee wrote: Utter bull****. If cycle helmets met the same standards, don't you think some motorcyclists would be wearing them? Not bull****. Look it up if you can figure out Google. Motorcycle helmets have additional criteria not specified for bicycle helmets, including coverage area and involving the chin bar when present. Retention criteria are also more stringent. Impact loads and survivability, however, are essentially the same. A funny thing happens when one actually looks up what MikeWhy claims. Specifically, they find that MikeWhy is either mistaken or lying. Here's an article that discusses motorcycle helmet testing standards in detail. *(I've got it bookmarked.) http://www.motorcyclistonline.com/ge...lmet_review/in.... *orhttp://tinyurl.com/zglbq What it says? "The killer—the hardest Snell test for a motorcycle helmet to meet—is a two-strike test onto a hemispherical chunk of stainless steel about the size of an orange. The first hit is at an energy of 150 joules, which translates to dropping a 5-kilo weight about 10 feet—an extremely high-energy impact. The next hit, on the same spot, is set at 110 joules, or about an 8-foot drop. To pass, the helmet is not allowed to transmit more than 300 Gs to the headform in either hit." Later, it says: *"Where the Snell standard limits peak linear acceleration to 300 G, the DOT effectively limits peak Gs to 250. Softer impacts, lower G tolerance. In short, a kinder, gentler standard." I'm not sure about that "effectively." *According to http://www.smf.org/articles/mcomp2.html DOT limits acceleration to 400 gs, but from a drop height (for a large helmet) of about 7.35 feet, or 2.25 meters, which corresponds to 110 Joules for a 5 kg headform mass. By contrast, the CPSC bicycle helmet standard calls for just a two meter drop. *It allows 300 gs acceleration of the same headform. *The standards are NOT the same. Furthermore, the motorcycle helmet standard has much more rigid penetration tests. *This is what drives the design of their heavy, hard shells. *And this is pertinent, because a heavy, hard shell is less likely to get traction with the road during a tangential impact, and is more likely to have significant rotational inertia, to aid in reducing the brain's rotational acceleration. *This might be considered an accidental benefit, because penetration of any helmet is rare, but rotational brain accelerations are now commonly recognized as being more likely than linear ones to cause serious brain injury. (Still, NO helmet standard tests for them!) What's even more enlightening is that article's discussion of the effect of various acclerations: *"Newman is quoted in the COST study on the impact levels likely to cause certain levels of injury. Back in the '80s he stated that, as a rough guideline, a peak linear impact— the kind we're measuring here&151of 200 to 250 Gs generally corresponds to a head injury of AIS 4, or severe; that a 250 G to 300 G impact corresponds to AIS 5, or critical; and that anything over 300 Gs corresponds to AIS 6. That is, unsurvivable." Bike helmets are designed to attenuate the acceleration of a decapitated human head - no body attached - to 300 gs in a 14 mph impact. *300 gs is the borderline between critical and unsurvivable, according to that estimate. *And that doesn't take into account rotational acceleration, which is worse in its effect, and which helmets may exacerbate (by their larger diameter and higher friction compared to a bare head). So leave the cyclist's head attached to his body, subject him to a head impact greater than 14 mph, include a slight tangential component to the impact, and you've blown away the "protection" of a bike helmet. Is it any wonder they haven't been shown to reduce serious head injuries? Dear Frank, Please stop confusing the Liddites™ with facts - it only makes them angry that their religious belief in the Magic Foam Bicycle Hat™ is challenged. Actually, it's the facts that make you, not me, cringe, run, hide, and blow smoke. The only agenda *I* have is to counter the misinformation spewed here about helmet ineffectiveness. There are factual errors and errors of logic in Frank's post above. I won't address them individually. To do so would be to spend the rest of eternity talking at insensate and unlearning furniture. The facts of the matter are these: The impact load applied in helmet testing is equivalent to a forceful blow from a 12 pound sledge hammer applied to the helmeted head. You split the hair if you like between 105 joules, the Snell Memorial Foundation test specification, and 102 joules, the energy resulting from the CPSC test specification. To understand what 100 joules looks, sounds, and feels like, drop a 12 lb bowling ball from eye level to the floor. This is equivalent to the CPSC impact test on a flat anvil. Choose for yourself whether the small difference between eyebrow height and a few inches higher is a meaningful difference. Decide here, this moment, if further discussion is at all necessary or meaningful. You can work through the rest of it yourself, given this proper picture of what the impact test really entails. Bearing in mind that a helmet worn on the head does nothing for the neck or its attachment to the head, just what does it mean to substitute the full body mass, as Frank suggests, for the head mass in the test? I intended that as gently rhetorical, but it would be interesting to hear further defense of his oddly blind suggestions. I would have thought that even the illogic of the Unlidded (can I ™ that?) would have noticed that a motorcyclist impact velocity is likely to be somewhat higher than that of a cyclist, requiring more energy to be absorbed and a slightly more arduous test condition for the safety helmet. Also, has anyone actually dabbed their head on the ground while traveling along, to try to gauge the applied torque produced comparing a bare head to a bicycle helmeted one? What is the coefficient of dynamic friction of scalp compared to helmet? http://www.bhsi.org/hodgstud.pdf JS |
#94
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Inflatable helmet, really
James wrote:
On Sep 10, 4:46 pm, "MikeWhy" wrote: Tom Sherman °_° wrote: On 9/9/2010 10:51 PM, Frank Krygowski wrote: On Sep 9, 8:37 pm, "MikeWhy" wrote: Phil W Lee wrote: Utter bull****. If cycle helmets met the same standards, don't you think some motorcyclists would be wearing them? Not bull****. Look it up if you can figure out Google. Motorcycle helmets have additional criteria not specified for bicycle helmets, including coverage area and involving the chin bar when present. Retention criteria are also more stringent. Impact loads and survivability, however, are essentially the same. A funny thing happens when one actually looks up what MikeWhy claims. Specifically, they find that MikeWhy is either mistaken or lying. Here's an article that discusses motorcycle helmet testing standards in detail. (I've got it bookmarked.) http://www.motorcyclistonline.com/ge...lmet_review/in... orhttp://tinyurl.com/zglbq What it says? "The killer—the hardest Snell test for a motorcycle helmet to meet—is a two-strike test onto a hemispherical chunk of stainless steel about the size of an orange. The first hit is at an energy of 150 joules, which translates to dropping a 5-kilo weight about 10 feet—an extremely high-energy impact. The next hit, on the same spot, is set at 110 joules, or about an 8-foot drop. To pass, the helmet is not allowed to transmit more than 300 Gs to the headform in either hit." Later, it says: "Where the Snell standard limits peak linear acceleration to 300 G, the DOT effectively limits peak Gs to 250. Softer impacts, lower G tolerance. In short, a kinder, gentler standard." I'm not sure about that "effectively." According to http://www.smf.org/articles/mcomp2.html DOT limits acceleration to 400 gs, but from a drop height (for a large helmet) of about 7.35 feet, or 2.25 meters, which corresponds to 110 Joules for a 5 kg headform mass. By contrast, the CPSC bicycle helmet standard calls for just a two meter drop. It allows 300 gs acceleration of the same headform. The standards are NOT the same. Furthermore, the motorcycle helmet standard has much more rigid penetration tests. This is what drives the design of their heavy, hard shells. And this is pertinent, because a heavy, hard shell is less likely to get traction with the road during a tangential impact, and is more likely to have significant rotational inertia, to aid in reducing the brain's rotational acceleration. This might be considered an accidental benefit, because penetration of any helmet is rare, but rotational brain accelerations are now commonly recognized as being more likely than linear ones to cause serious brain injury. (Still, NO helmet standard tests for them!) What's even more enlightening is that article's discussion of the effect of various acclerations: "Newman is quoted in the COST study on the impact levels likely to cause certain levels of injury. Back in the '80s he stated that, as a rough guideline, a peak linear impact— the kind we're measuring here&151of 200 to 250 Gs generally corresponds to a head injury of AIS 4, or severe; that a 250 G to 300 G impact corresponds to AIS 5, or critical; and that anything over 300 Gs corresponds to AIS 6. That is, unsurvivable." Bike helmets are designed to attenuate the acceleration of a decapitated human head - no body attached - to 300 gs in a 14 mph impact. 300 gs is the borderline between critical and unsurvivable, according to that estimate. And that doesn't take into account rotational acceleration, which is worse in its effect, and which helmets may exacerbate (by their larger diameter and higher friction compared to a bare head). So leave the cyclist's head attached to his body, subject him to a head impact greater than 14 mph, include a slight tangential component to the impact, and you've blown away the "protection" of a bike helmet. Is it any wonder they haven't been shown to reduce serious head injuries? Dear Frank, Please stop confusing the Liddites™ with facts - it only makes them angry that their religious belief in the Magic Foam Bicycle Hat™ is challenged. Actually, it's the facts that make you, not me, cringe, run, hide, and blow smoke. The only agenda *I* have is to counter the misinformation spewed here about helmet ineffectiveness. There are factual errors and errors of logic in Frank's post above. I won't address them individually. To do so would be to spend the rest of eternity talking at insensate and unlearning furniture. The facts of the matter are these: The impact load applied in helmet testing is equivalent to a forceful blow from a 12 pound sledge hammer applied to the helmeted head. You split the hair if you like between 105 joules, the Snell Memorial Foundation test specification, and 102 joules, the energy resulting from the CPSC test specification. To understand what 100 joules looks, sounds, and feels like, drop a 12 lb bowling ball from eye level to the floor. This is equivalent to the CPSC impact test on a flat anvil. Choose for yourself whether the small difference between eyebrow height and a few inches higher is a meaningful difference. Decide here, this moment, if further discussion is at all necessary or meaningful. You can work through the rest of it yourself, given this proper picture of what the impact test really entails. Bearing in mind that a helmet worn on the head does nothing for the neck or its attachment to the head, just what does it mean to substitute the full body mass, as Frank suggests, for the head mass in the test? I intended that as gently rhetorical, but it would be interesting to hear further defense of his oddly blind suggestions. I would have thought that even the illogic of the Unlidded (can I ™ that?) would have noticed that a motorcyclist impact velocity is likely to be somewhat higher than that of a cyclist, requiring more energy to be absorbed and a slightly more arduous test condition for the safety helmet. Also, has anyone actually dabbed their head on the ground while traveling along, to try to gauge the applied torque produced comparing a bare head to a bicycle helmeted one? What is the coefficient of dynamic friction of scalp compared to helmet? http://www.bhsi.org/hodgstud.pdf JS Jeezus! I didn't bother to read it. Yet. All I needed was Fig. 2. |
#95
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INFLATABLE HELMET STUCK ON YOUR HEAD ? WE HAVE THE ANSWER ...
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#96
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Inflatable helmet, really
On Sep 10, 3:07*am, James wrote:
I would have thought that even the illogic of the Unlidded (can I ™ that?) would have noticed that a motorcyclist impact velocity is likely to be somewhat higher than that of a cyclist, requiring more energy to be absorbed and a slightly more arduous test condition for the safety helmet. I would have thought that those arguing in favor of bicycle helmets would have realized that, therefore, the test standards are NOT the same, and would not have claimed that they were. In fact, that they'd realize that some MC helmet impact standards (e.g. Snell) are vastly different than those of bicycle helmets. I'd also have thought they'd realize that the extreme differences in penetration standards - which necessitate very hard shells on MC helmets - might effect performance of the helmets in other ways that I mentioned. Also, has anyone actually dabbed their head on the ground while traveling along, to try to gauge the applied torque produced comparing a bare head to a bicycle helmeted one? I don't know of a test for the effective friction coefficient of a bare human head subjected to a tangential force from an asphalt surface. I suspect, though, that the coefficient is much lower than that of a helmet in the same situation. The scalp is free to move laterally a certain distance over the surface of the skull, and it tears relatively easily (and bleeds messily) if stressed too highly in that direction. I assume this is an evolutionary (and/or God given, if you prefer) adaptation to protect the brain from angular accelerations. Angular accelerations are the kind of motion that's most likely to result in diffuse brain injury, yet the kind which no helmet standard even bothers to measure. - Frank Krygowski |
#97
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Inflatable helmet, really
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#98
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From Dean Swift to the Waterfall Trail
On Thu, 9 Sep 2010 10:30:45 -0700 (PDT), in rec.bicycles.tech Andre
Jute wrote: [...] A "full Irish breakfast" is a delete-option multiple choice. You tell the landlady, "Leave off the bangers and the black and white puddings, poach the eggs and crisp the bacon," and then you get a breakfast that is palatable, looks good on the plate with the mushroom and grilled tomato, and leaves space for lunch. The "pudding", which I have only tasted in guest houses, actually tastes good if cooked right. We eat cereal or toast for breakfast at home, or rarely barley oats porridge and kippers, so I don't know how to prepare black pudding right, but suspect it is fried in lethal amounts of fat; not for people our age, if you won't think me impertinent. Well, my government is printing money like it's toilet paper; therefore, everything we did was very expensive based on our country's currency. We really couldn't afford to have someone cook for us, so we used our little butane burner extensively. Sorry we couldn't spend more money, but we spent all we had! If you're close to broke, then porridge on the beach starts looking a lot better! We found a nice beach south of Cork and set in there a few nights. We went into Cork twice by bus. We came due south from the Galway area, so we didn't get over your way, although, I wanted to do so. The wife wanted to allocate our time in Waterford and I don't regret it. It was a nice town in which to walk... but we missed... what is it? ... the "Ring of Cork"??? (That doesn't sound right.) OTOH, I now have a Waterford Crystal marble for my marble collection... which was all we could afford. I like your pics -- you've found some places down the road from me that I didn't even know existed -- but I'm surprised you didn't see more sunshine. August, which is about as far back as I remember, was so hot, I had to take my rides before dawn for a couple of weeks. No doubt you noticed how small the Emerald Isle is, so that wherever you go you're never far from water. We did see some sun... a little, anyway. I see all of *that* I need at home; the clouds and rain worked for me, thank you! "so hot..."??? gimme a break! I got 114 (F) degrees in the shade and 3% humidity! I'm quite happy to get rained on a little bit! more silly pictures in the desert http://picasaweb.google.com/ra15932556/BikeTrip# /more silly pictures in the desert FYI, "Ajo" is Spanish for "garlic". OK, so post *your* pictures, asshole! Jones |
#99
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Inflatable helmet, really
On Thu, 9 Sep 2010 20:56:50 -0700 (PDT), in rec.bicycles.tech Frank
Krygowski wrote: You're boring me, Frank. I don't care, Jones. I'm not typing for the entertainment of a troll. I'm merely using you as an excuse to get logic and information out to others who may be interested. Are you calling me a "troll", Frank? I'm offended! Not really. But, hey! Exactly how many people do you think are hanging on our every word? OK!!! ALL OF YOU PEOPLE OUT THERE, SIGN IN AND REPLY *NOW*! You know, Frank... nobody gives a rat's ass what you think. Nobody gives a rat's ass what *I* think, either; the difference is that I know it! Well... you do, I suppose. It's too bad we're not queer, Frank... don't you think we'd make a beautiful couple? Jones |
#100
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Inflatable helmet, really
On Sep 11, 1:35*am, Frank Krygowski wrote:
On Sep 10, 3:07*am, James wrote: Also, has anyone actually dabbed their head on the ground while traveling along, to try to gauge the applied torque produced comparing a bare head to a bicycle helmeted one? I don't know of a test for the effective friction coefficient of a bare human head subjected to a tangential force from an asphalt surface. *I suspect, though, that the coefficient is much lower than that of a helmet in the same situation. Maybe your Unliddedness has let your eyesight degrade. I posted a link. MikeWhy found it. Strangely you overlooked it. Maybe, like so much else you didn't like the message it brought and chose to sweep it under the carpet and respond with more rubbish. JS JS. |
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