Helmets: why cycling, skiing, skateboarding helmets don’t workPosted: August 15, 2012 Filed under: Cycling, Skiing / Snow Boarding | Tags: Bicycle helmet, Bike Helmet, biking, CPSC, Cycling, Cycling Helmet, helmet, Helmets, skiing, UIAA 3 Comments
Thanks to Brad Waldron at Kali Protectives for giving me the visual to explain this.
A helmet needs to absorb energy to work. The more energy a helmet absorbs the more protection a helmet provides. If you look at the inside of your helmet
what is there to absorb energy?
A helmet does not work by being a hard surface to protect your head from head injuries. Hard surfaces protect your head from pointed objects. Think Knights of the Round Table and spears and arrows. If you are riding a bike or skiing and someone is shooting arrows at you, you need a hard helmet.
Hitting the ground is different. Your brain bounces around inside your skill causing damage; a concussion. You need something to absorb the impact and soften the blow or extend the time the impact (force) is being applied to your head, which softens the blow. Helmets as they are currently used, do not do that.
Think about the issue this way. If you drop a weight on an egg, say 11 pounds from 4 feet the egg is going to smash. If you put a book on top of the egg and drop the 11-pound weight the egg is still going to smash. The amount of energy transmitted to the egg maybe reduced by the book; however, the energy reduction is not enough to protect the egg.
A Bicycle or ski helmet is the same way. There is some energy absorption, but not enough to protect your brain.
If you want to know why I picked 11 pounds from 4 feet that is the test for helmets. Watch Video of cycling helmet testing. No one is testing the force on the head, if the helmet absorbs any of the force, or if the impact broke your neck.
On top of that, always remember the helmet is tested with the impact landing in the center top of the helmet. When you fall to make sure you drive your head into the ground hitting the helmet in the center on top of your head to receive the maximum protection.
See for yourself. This is the UIAA (European) Test for Helmets.
This test is for climbing and some European ski helmets. In the US, a bike helmet and ski helmets are not tested for lateral force, slippage or chin strap strength.
There are some organizations that test the helmets to greater extremes such as Consumer Reports, but all they are doing is testing the helmet. They are not looking at whether the helmet protects your head. See Consumer Reports Bike Helmet Testing.
We are not testing whether a helmet looks good after an impact. We are testing whether the helmet protects your head from an impact and the drop test does not test that sufficiently, if at all.
If you want to test this yourself, figure a way to stick an egg under a helmet and drop a weight on the helmet. The egg is still going to crack or break.
Yes, your head is not an egg. It is just easier to see the results with an egg. The helmet did not decrease the pressure enough to protect the egg. The injury still occurred. If you could take the time to measure the breaking strength of an egg and then start below that number and drop weights on the helmet you would see a difference eventually which would be the amount of protections the helmet provides. However, that number would be small and probably no different from what a plastic bowl would do.
If you really want to test this, go buy two eggs. Drop one from 15 feet and see what happens to the egg. Tape the other one in your helmet and drop it from the same height. The egg will crack (and make a real mess in your helmet).
Want more laughs about this? Watch this video where a cardboard helmet does a better job of protecting your head, by absorbing more force, than a bicycle helmet. See Kranium helmet Crash Test
Yes, your head is not an egg. Yes, a helmet will protect you from minor hits. Yes, a helmet is probably better than not using a helmet, unless the process stops you from riding a bike or skiing. The health benefits of activity out weight the risk of a head injury.
If that is the case, then why not wear a helmet when you drive, shower or work in the kitchen. All three have a far greater risk of head injuries then cycling.
However, we have not looked at whether using helmets deters activities. See TEDxCopenhagen – Mikael Colville-Andersen – Why We Shouldn’t Bike with a Helmet. I love the fact the in the video Mr. Colville-Andersen lets you know that the helmet tests were designed for pedestrians wearing helmets. Also he points out that helmet laws do not reduce head injuries. They reduce the total number of people riding bikes, which results in a reduction of head injuries.
Nor have we looked at the issue of the advertised protection versus the real protection afforded by a helmet.
Finally, we have not looked at whether wearing a helmet makes you react in a way to protect other parts of your body rather than your head. If you fall you natural protect your head. Your arms go out to keep your head form hitting the ground and then your cradle your head from being hit or hitting the ground. This accounts for tons of videos and statements when people hold up their battered helmet and say my helmet saved my life.
However, a helmet will not save your life. If you want to be cool and have a helmet that might protect your head watch this video: Hövding krocktest
But without bike and ski helmets where would we mount our video cameras?
Gourley, Jim, Bicycle Times August 1, 2011, Pull Your Head Out of Your…Helmet
Kim Gorgens: Protecting the brain against concussion
A.J. Jacobs: How healthy living nearly killed me
TEDxCopenhagen – Mikael Colville-Andersen – Why We Shouldn’t Bike with a Helmet
Other Articles on Helmets:
A father of a deceased skier pushing for a helmet law in New Jersey.
A helmet manufacture understands the issues(Uvex, Mouthguards)
A new idea that makes sense in helmets: the Bern Hard Hat
California bill to require helmets on skiers and boarders under age 18 dies lacking governor’s signature.
Does being safe make us stupid? Studies say yes.
Great article on why helmet laws are stupid
Great editorial questioning why we need laws to “protect” us from ourselves.
Helmet death ignited by misconception and famous personalities
Helmets do not increase risk of a neck injury when skiing
I could not make my son wear a helmet so I’m going to make you wear one
I once thought you had to take an IQ test to run to be a state legislator. You could run only if you flunk the test
Mixed emotions, but a lot of I told you so.
More information over the debate about ski helmets: Ski Helmets ineffective crashes were the wear is going faster than 12 miles per hour
National Sporting Goods Association reports that Helmet use at US Ski Areas increased during the 2009-10 ski season
OSHA Officially recommending helmets for ski area employees
Other Voice on the Helmet Debate
Recent UK poll shows that 10% of cyclists would quite biking if there was a compulsory helmet law.
Skiing/Boarding Helmets and what is the correct message
Survey of UK physicians shows them against mandatory bicycle helmet laws.
What do you think? Leave a comment.
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I do agree a helmet needs to dissipate the impact energy as opposed to just provide a barrier, but isn’t that exactly what the styrofoam does?
I think your EGG example is FLAWED. Comparing apples and oranges. I suspect the force/energy needed to break an egg is far lower than what can cause a head injury. I expect hemet design is optimized to absorb higher energy impacts that could cause a head injury and therefore may not be effective for protecting an egg. If the helmet could absorb these lower impacts, then I suspect it would be less effective at absorbing injury causing impacts.
I’d like to help clarify some clear misunderstandings about how current bicycle helmets are designed to work and how they are tested. As written, key aspects of this article are inaccurate and misleading.
Cycling, and skiing helmets DO work for what they were designed to do, which is to reduce acceleration to the head due to impact and help prevent catastrophic head injuries like skull fractures and lacerations or contusions to the brain. These are severe injuries that have a high probability of causing death or significant disability. The article is correct in that current helmets are not designed to prevent concussions, which are a less severe type of head injury.
If you look at a helmet, you’ll see a hard outer shell on the outside and expanded polystyrene (EPS) foam on the inside. The hard outer shell serves several purposes. Primarily, the shell protects the inner foam layer and allows the helmet to slide in an impact by providing low friction. The shell also provides protection from scrapes and cuts and helps distribute the impact force over a larger area.
It is the EPS foam that absorbs energy in an impact, by permanently deforming like the crumple zone of a car. This reduces the peak energy of an impact and helps decelerate your head slower. Since the foam crushes, the helmet needs to be replaced after a big crash.
Because of the risk of injury, helmets can not be tested with real people. Instead, manufacturers and researchers perform drop tests and compare these results to injury thresholds determined from cadaver tests. To do these impact tests, a helmet is attached to a surrogate head and dropped from a certain height onto a fixed steel anvil. The surrogate head, or headform, has a similar size and mass to a real head. An accelerometer mounted within the headform measures the acceleration of the head during impact. The goal of a helmet is to reduce the peak accelerations and forces below the levels that caused skull fracture when cadavers were tested in a similar manner.
There are standards that describe how these drop tests are to be performed. By law, since 1999, all cycling helmets manufactured and sold in the United States must satisfy the Consumer Product Safety Commision safety standard (http://www.cpsc.gov//PageFiles/86318/10mr98r.pdf). This standard specifies that each model and size of helmet be tested at several different temperatures, at least four different locations (not just the top) and on different shaped surfaces. A 5.0kg (11lb) headform is dropped from heights of 1.2m (~4ft) onto hemispherical and curbstone anvils and from 2.0m (~6.5ft) onto a flat anvil. If the acceleration exceeds 300g for any test, the helmet fails. The European standard (EN 1078) uses a height of 1.5m and a threshold of 250g. A detailed comparison of the different standards can be found here: http://helmets.org/stdcomp.htm
The UIAA Test for Helmets referenced in the article is a standard for mountaineering helmets. It also specifies that helmets be tested in several different locations, as depicted in the top middle panel.
Instead of an egg, a better food analogy would be to use a melon, like this 9 year old did as a science fair project:: http://www.youtube.com/watch?v=h7g723Rhuyk. A cycling helmet does not do a good job of protecting an egg, because an egg has a much lower injury tolerance than a human head and a much lower mass. At a drop height of 2m (6.5ft), the 5kg (11lb) headform obtains about 100 Joules (~74 Ft-lb) of kinetic energy. A 70g (2.5oz) egg dropped from the same height only has ~1 Joule (0.7 Ft-lb) of kinetic energy.
If you wanted to design a helmet for an egg, you would have to use a material that compresses easier, like a cleaning sponge in order to keep the force on the egg below the ~25N (5.5lbf) required to break an egg. Unfortunately, using the same material to try and slow down a much larger human head at the same impact speed wouldn’t work very well. The sponge would only absorb ~1% of the energy before “bottoming-out”, i.e. compressing completely, causing the force to suddenly rise as if the head hit the ground directly.
These helmets DO work for what they are currently designed for and tested against, which is preventing skull fracture (and a good chance of death) in a serious crash.
The real problem is that the CPSC standard and all other current standards are based solely on linear acceleration. Research dating back over 30 years has shown a link between concussion and rotational acceleration. Unfortunately, concussion is much more difficult to study than fracture. While some researchers and companies are developing helmet designs to address this, there is little motivation for manufacturers to make these new helmets unless the standards change.
Thanks, Jim. I appreciate your willingness to offer an alternate perspective.