May-June 1998 Newsletter
Helmet Testing at USCby Ken Hoff
Remember the time when you had your first bicycle accident? Or perhaps you know of someone who crashed and bounced his or her head off the road? I had a buddy that did and to this day, he claims to have ho affects of drain bamage. Eventually, most of us who love to ride our bikes will fall. If you are fortunate, only your ego will get bruised. It you are less fortunate, well, let us hope that you are wearing a good helmet and can heal quickly.
All of us in the club wear a helmet and I bet your loved ones wear one too. Sadly, 96% of all bicycle riders do not own a helmet let alone strap it to their melon. If you know of someone in this group, give them this article. Then take them to the local bike and help them pick out one.
Last month, while attending classes at the University of Southern California, I visited the USC Head Protection Research Laboratory and its Director, Dr. David R. Thom. Dave is an avid cyclist and the kind of guy who really loves his work. After spending about an hour visiting with Dave and watching him conduct a couple of tests, it became clear as to the ramifications of not wearing a good helmet. Let me tell you about the Head Protection Research Lab and what the good doctor does.
This facility does primarily two things. First, evaluate damaged helmets from the “Returns Program” sponsored by several of the leading bicycle helmet manufacnrers in the United States. (So this is where my Bell Helmet went when I sent it back.) Second, replicate helmet damages using the new helmets provided by the manufactures. This involved recreating or replicating the damage documented on the impacted helmet using an identical helmet supplied by the manufacturer. All testing was done in accordance with ANSI and Snell standards and strict scientific testing practices.
The drop apparatus used for these tests consisted of a twin-wire guided free-fall apparatus fined with an appropriate size ISO headform. In order to monitor headform accelerations, an accelerometer was located at the center of gravity of the headform assembly and fed into a dedicated charge amplifier, which in turn was input into a PC-based data acquisition system. An infrared beam velocimeter system was used to monitor impact velocity immediately prior to impact. Does reading this make your head hurt? It not, read on.
The helmet and headform are oriented in such a way to replicate the direction of impact and was raised to an approximate height that the typical cyclist head sits while riding. This is about five feet for the average rider or five and a half feet if you were a former Club President.
The helmet is then released into free-fall, and immediately prior to impact, the computer began digitizing the accelerometer signal at a rate of 10000 Hz. Upon completion of the impact, the digitized signal was then filtered and calibrated to determine peak headform acceleration and plotted the acceleration-time curve. The data collected by this laboratory over the past 12 years using approximately 800 helmets shows that most helmet impacts occur at the forward left half of your helmet. And when you hit the ground, expect the average impact to be near 180 G’s. This of course is the Reader’s Digest version of a very detailed and much complicated testing program. The variances found in accident investigations reveal that riders have sustained impacts between 20 and 300 G’s without hurting their protected heads. Remember, this high force can only be absorbed over a very short period of time, measured in milliseconds. Any falling force longer than a tenth of a second, and your brain will be like the proverbial melon that was dropped on the sidewalk.
Dr. David Thom has seen vast improvements in helmet design over the past four years. One of the most notable improvements is the incorporation of improved crushable material that makes up the body of the helmet. The addition of the aft helmet stabilizing system which prevent the helmet from shifting up and aft will significantly reduce the forward blunt trauma.
When asked about the helmet visors that are popular among mountain bicyclists, he commented that he sees this as a safety improvement, however no testing methodology has been developed to verify their safety value.
Dr. Dave declined to comment on what brand of helmet he preferred; however he did warn against choosing any helmet on gimmick criteria. Even the best helmet manufacturers have marketing departments that do not have our safety as a primary interest. It is difficult to summarize this experience without sounding preachy. The choice to wear a helmet is yours and yours alone. Falling and sustaining injury can happen to anyone whether you are the local Cat II racer sprinting to the finish line or just out for a spin to the neighbor’s house. Knowing what can happen will allow you to make the right choice.
Copyright ©1998 Louisville Wheelmen. All rights reserved.
Web posted: 27 April 1998
last updated: 29 April 1998
by Duc M. Do