It is a question of physics. Of kinetic energies and Newtons 'Laws of Motion'. The equivalent speed of the fastest impact a DOT compliant helmet has to survive is 13.4 MPH That is the speed a helmet reaches in free fall from a height of six feet. That is the speed only of the helmet dropping in a "guided" free fall, without any additional energy associated with the fall. If you factor in even a relatively low horizontal speed, impact speeds can rise dramatically. NHTSAs own independently contracted testing facilities have shown that from 1980 to 2008 over 61% of manufacturer certified DOT compliant helmets failed to passed testing.
Newton's First Law states; "An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force." This is what happens inside your head (whether you are wearing a helmet or not) when your head impacts an object. Your skull will at the least, experience a rapid deceleration, or possibly a deflection to a different direction. However like all else following Newtons First Law, everything inside your skull will continue moving in the same direction and speed it had been traveling. Until it collides with the inside of your skull. Where it will then be compressed under the inertial effect, until Newtons Third Law forces your brain and other soft tissues to recoil back. This continues until the kinetic energy of the impact has been absorbed. In even simple impacts some G Forces can exceed 600 units of Gravity (G's). That is 600 times the force of gravity on a stationary object. With such forces, soft tissue, blood vessels, and brain matter can easily tear and be destroyed . Whether you are wearing a helmet or not. Motorcycle helmets can help to dampen the effects. But they cannot nullify the laws of physics. It is true, that helmets have been shown to have a statistically significant effect on head injuries. There are however, other effects of motorcycle helmets that should be considered.
The study by Dr.'s Cooter and David of the Australian Craniofacial Unit of the Royal Adelaide Hospital, "Motorcyclist Craniofacial Injury Patterns" found that "objects worn at impact on the craniofacial region (skull) may influence significantly the final fracture pattern, and this may be detrimental for some motorcyclists wearing full-face helmets." It seems that motorcyclists wearing some of the popular full face helmets while involved in crashes have, as a result of their design, "sustained fatal skull base fracturing in the absence of significant facial trauma". The helmets did their job, and protected the face and frontal lobes of the brain. But they did so at the cost of causing fatal basal fractures of the skull, and traumatically severing the pons from the medulla. Both conditions in and of themselves fatal.
These same helmets are DOT compliant, and meet the FMVSS-218 standard. However, their use exposes the rider to a significantly higher risk of fatal injuries do to anterior impacts in a crash. These helmets, which are among those mandated by the legislature to be worn by motorcyclists in Washington State, have no warning about the possible fatal consequences that accompany the use of these helmets. The States mandated use of these helmets could actually lead to fatalities in otherwise survivable crashes. Without knowledge of the risk involved; how many motorcyclists purchased these helmets, then died because of the helmet they were forced to wear to protect them?
Imagine the injuries to a person that has just been hanged, and had the knot of the noose positioned below the jawbone. The injuries are almost identical to those suffered by a significant number of motorcyclists involved in fatal crashes wearing rigid full face helmets. The real tragic irony as shown by the Cooter Study, is that those wearing more flexible full face helmets, and even open face helmets, while suffering severe facial fracturing, had a much higher rate of surviving, and a lower rate of fatal skull fractures and brain damage.
The Goldstein Study, many in the effort to eliminate the mandatory helmet law seem to take at least an initial dim view of because of its findings that helmets do afford a signifcant effect on the severity of head injury. However, if one looks closer, the study goes further and acknowledges other risks that wearing helmets in a crash have an increased effect of. One of which is; that above an average speed of 13 mph (the highest speed used in impact tests to meet FMVSS-218...coincidental?), "helmet use has a statistically significant effect which increases the severity of neck injuries." So at impacts beyond 13 mph, helmets have been shown to "exacerbate neck injuries."
Since the impact speed of 13 mph is the speed the helmet reaches falling from six feet, it is obviously a low speed impact. Roughly the same as a six foot tall man falling down and hitting his head as he walks down the sidewalk. Yet the thought of mandating helmets be worn by pedestrians is ludicrous to even be suggested. Yet to mandate the use by motorcyclists traveling at a much greater speed to wear a helmet that has only been certified by the manufacturer to be able to withstand an impact of 13.4 mph seems just as ridiculous. Especially when one realizes that the two leading causes of fatality on motorcycles, are the riders speed (kinetic energy), and blood alcohol level.
Again from the Goldstein Study; "an increase in the crash speed from 40 to 60 mph increases the probability of death from 7.1% to 36.3%." Even factoring in glancing blows to the head at those speeds, the impacts are still going to be greater than 13.4 mph, which is all the helmet is designed to withstand.
Even Professor Harry Hurt, author of the famous "Hurt Report" on traffic safety stated in an interview with KABC TV that; "As impact speeds reach 25-30 mph, no helmet in the world is going to save you." It is simply a question of physics. Given enough kinetic energy, a helmet isn't going to save your brain from being damaged due to the extreme inertial and gravimetric forces at play. Man may be able to violate mans law, but we cannot violate the laws of physics.
As a final point a NHTSA study showed that between 2000 and 2002; of all fatal motorcycle accidents, only 19% suffered fatal injuries to the head, while 81% suffered no fatal head injuries.
Now, tell me why Washington State does not allow motorcyclists to take responsibility for our own safety choices. If for example; some types of "DOT compliant" helmets put the motorcyclist at a higher risk of fatal skull and brain injuries, and if the leading cause of fatality on motorcycles is excess speed, with over 61% of "DOT compliant" helmets tested failing, then why are we even forced to wear a motorcycle helmet that is only suppose to protect us from the impact speed of a man falling to the ground from a standing position?
Catch ya on the road sometime...