Comments on: Going Down Hard: A Bicycle Helmet’s Perspective http://blog.charleskiyanda.com/2008/05/08/going-down-hard-a-bicycle-helmets-perspective/ Open Source Culture and Science Wed, 29 Oct 2008 17:34:15 +0000 hourly 1 http://wordpress.org/?v=3.0 By: Charles Kiyanda http://blog.charleskiyanda.com/2008/05/08/going-down-hard-a-bicycle-helmets-perspective/comment-page-1/#comment-464 Charles Kiyanda Fri, 09 May 2008 16:29:29 +0000 http://blog.charleskiyanda.com/?p=38#comment-464 Richard, I just saw the second document is 173 pages, so it might end up being tomorrow. :) Just before I keep going in this discussion, let me point out that I've seen your site (I had been there and read a lot of the material some time ago as well). I agree with you that there are other factors that play an even bigger role than helmet in bicycle safety. Learning how to ride a bicycle safely probably leads in a greater reduction of cycling injuries than simply wearing a helmet. I'm a strong advocate of teaching kids how to ride a bicycle safely. I would also advocate teaching safe riding practices to children in a formal teaching environment (i.e. not at home, but in a place which makes the child conscious that this is something important to remember). Safe riding practices are number 1. We agree on this. The questions I'm posing here are: 1-Can modern bycicle helmet actually help your head in a crash and to what point? 2-Are typical crash conditions which involve your head within the design bounds of bicycle helmets or do they occur at a point where it would make no difference? Just trying to clarify the scope of what I'm discussing here. It also seems like the documents you suggested in your comment deal with that point. Richard,
I just saw the second document is 173 pages, so it might end up being tomorrow. :)
Just before I keep going in this discussion, let me point out that I’ve seen your site (I had been there and read a lot of the material some time ago as well). I agree with you that there are other factors that play an even bigger role than helmet in bicycle safety. Learning how to ride a bicycle safely probably leads in a greater reduction of cycling injuries than simply wearing a helmet. I’m a strong advocate of teaching kids how to ride a bicycle safely. I would also advocate teaching safe riding practices to children in a formal teaching environment (i.e. not at home, but in a place which makes the child conscious that this is something important to remember). Safe riding practices are number 1. We agree on this.

The questions I’m posing here are:
1-Can modern bycicle helmet actually help your head in a crash and to what point?
2-Are typical crash conditions which involve your head within the design bounds of bicycle helmets or do they occur at a point where it would make no difference?

Just trying to clarify the scope of what I’m discussing here. It also seems like the documents you suggested in your comment deal with that point.

]]> By: Charles Kiyanda http://blog.charleskiyanda.com/2008/05/08/going-down-hard-a-bicycle-helmets-perspective/comment-page-1/#comment-463 Charles Kiyanda Fri, 09 May 2008 16:14:06 +0000 http://blog.charleskiyanda.com/?p=38#comment-463 Richard, thank you for leaving this comment. I've just finished reading the first document at: http://www.cpsc.gov/LIBRARY/FOIA/FOIA98/PUBCOM/34C7A89B.PDF Basically, engineer Sundahi argues against the use of a heavier test mass (5kg was proposed for the standard instead of about 3kg) for infant helmets. The justification is that helmets need to decelerate the head at impact respecting a certain maximum acceleration. To do so, the helmet crushes. (Sundahi says that energy absorption is not the critical factor, but acceleration/time is the critical parameter to watch. While it may be through, most materials used to decelerate impacts do so via crushing which absorbs impact energy, so really the helmet does both, it decelarates the head and absorbs energy as crushed materials don't tend to rebound very hard, but nonetheless, that's not the point.) The analysis engineer Sundahi goes through shows that a helmet designed with a 5kg test mass would end up being stiffer (the liner material is made more dense) and a lighter head would not allow the liner to crush, but really just to rebound. So the helmet would decelarate the head, but make it reaccelarate the other way. The analysis also shows such a helmet in such a condition would also produce more acceleration than it was designed for. It's quite interesting, but this letter doesn't tell me whether this has caused actual head trauma in children wearing helmets designed for heavier heads. Also, this document is from 1998. I haven't looked but is the standard still at 5kg for infant head proxy? I'm not saying the Sundahi letter is useless, I'm just wondering if there's more information on this particular issue. From the analysis in there, it sounds like something to be investigated further. Could it be that in the end, maximum acceleration isn't the critical factor in head damage in children? This is an interesting discussion (and I think an important one). I haven't read the second document you sent, but let me do so today and comment back here. Richard, thank you for leaving this comment. I’ve just finished reading the first document at:

http://www.cpsc.gov/LIBRARY/FOIA/FOIA98/PUBCOM/34C7A89B.PDF

Basically, engineer Sundahi argues against the use of a heavier test mass (5kg was proposed for the standard instead of about 3kg) for infant helmets. The justification is that helmets need to decelerate the head at impact respecting a certain maximum acceleration. To do so, the helmet crushes. (Sundahi says that energy absorption is not the critical factor, but acceleration/time is the critical parameter to watch. While it may be through, most materials used to decelerate impacts do so via crushing which absorbs impact energy, so really the helmet does both, it decelarates the head and absorbs energy as crushed materials don’t tend to rebound very hard, but nonetheless, that’s not the point.) The analysis engineer Sundahi goes through shows that a helmet designed with a 5kg test mass would end up being stiffer (the liner material is made more dense) and a lighter head would not allow the liner to crush, but really just to rebound. So the helmet would decelarate the head, but make it reaccelarate the other way. The analysis also shows such a helmet in such a condition would also produce more acceleration than it was designed for.

It’s quite interesting, but this letter doesn’t tell me whether this has caused actual head trauma in children wearing helmets designed for heavier heads. Also, this document is from 1998. I haven’t looked but is the standard still at 5kg for infant head proxy?

I’m not saying the Sundahi letter is useless, I’m just wondering if there’s more information on this particular issue. From the analysis in there, it sounds like something to be investigated further. Could it be that in the end, maximum acceleration isn’t the critical factor in head damage in children? This is an interesting discussion (and I think an important one).

I haven’t read the second document you sent, but let me do so today and comment back here.

]]> By: Richard Keatinge http://blog.charleskiyanda.com/2008/05/08/going-down-hard-a-bicycle-helmets-perspective/comment-page-1/#comment-462 Richard Keatinge Fri, 09 May 2008 11:18:40 +0000 http://blog.charleskiyanda.com/?p=38#comment-462 The main problem is that in real accidents helmets don't seem to work as designed at any speed. See the senior engineer of Bell at http://www.cpsc.gov/LIBRARY/FOIA/FOIA98/PUBCOM/34C7A89B.PDF and the Australian Federal Bureau of Transport at http://www.atsb.gov.au/publications/1987/Mcycle_Helm_1.aspx The main problem is that in real accidents helmets don’t seem to work as designed at any speed. See the senior engineer of Bell at
http://www.cpsc.gov/LIBRARY/FOIA/FOIA98/PUBCOM/34C7A89B.PDF
and the Australian Federal Bureau of Transport at
http://www.atsb.gov.au/publications/1987/Mcycle_Helm_1.aspx

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