The adverse effect of this aerodynamic shape is that the wedge at the back of the helmet tends to deflect and rotate the helmet on the head when impact occurs there. Any impact at the front or sides of the streamlined helmet is no different from other helmet shapes, but any impact on the rear wedge tends to rotate the helmet on the head, probably deflecting the helmet to expose the bare head to impact, and at worst ejecting the helmet completely from the head. Actually, everybody who has tested these streamlined helmets over the past years has encountered the problem of these helmets being displaced during impact testing at the rear wedge. Usually additional tape was required to maintain the helmet in place during rear impact tests; usually the basic retention system alone could not keep the helmet in place during impact testing on the rear of the helmet.
Unfortunately, the implication of helmet displacement and possible ejection in an actual accident impact did not register as a real hazard in previous years of testing, but now there are accident cases appearing that show this to be a genuine hazard for bicycle riders wearing these streamlined helmets. Accident impacts at the rear of these streamlined helmets can cause the helmet to rotate away and expose the head to injury, or eject the helmet completely. The forces generated from the wedge effect can stretch the chinstraps very easily, and even break the [occipital--Prof. Hurt used a trademarked name] retention devices.
We request that F08.53 committee study this problem and develop advisory information for both manufacturers of these streamlined helmets and consumer bicyclists who now own and wear such helmets. There is a definite hazard for displacement or ejection from impact on the rear wedge of these helmets, and bicyclists should be warned of this danger by an authority such as ASTM.
