Choosing the right helmet can be a daunting task. Over the past decade, an unprecedented variety of helmets has been introduced differing in style, price point, compliance with standards, and manufacturer’s claims of improved protection.
Selecting the best helmet is further complicated by the scarcity of test data that provide evidence-based guidance. This article provides guidance on three aspects critical for selection of helmets that deliver superior head protection, namely brain protection, lateral protection (Type II), and helmet retention.
BRAIN PROTECTION
Brain protection has been the blind-spot in helmet design. The September 2023 lead article in Occupational Health & Safety, titled “Addressing an Overlooked Danger”, stated that current helmet standards must be updated to account for rotational motion, which is the key cause of concussions on construction jobsites. There are two different types of head injuries, namely skull fracture and brain injury. Fracture of the hard but brittle skull is caused by a straight impact, similar to the straight impact one would induce to crack a brittle egg shell. A rigid helmet shell combined with an impact-absorbing liner or suspension greatly reduces the skull fracture risk by decreasing the force of a straight impact to the skull.
Conversely, brain injury is mainly caused by head rotation in response to an impact. Head impacts typically cause a short but forceful head spin that twists the brain and shears the soft brain tissue. Similar to severing nerves of the spinal cord, shearing of brain tissue causes irreversible damage that may lead to life-long suffering with staggering financial implications. Brain injuries can range from a mild concussion to severe traumatic brain injuries, whereby the cost associated with a single work-related traumatic brain injury typically exceeds $1 million. This staggering human and financial cost of brain injury is often caused by rather simple and frequent events.
Over 60% of work-related brain injuries are caused by simple slips, trips, and same level falls. Most interestingly, over 90% of such brain injuries occur in absence of a skull fracture, which further confirms that the soft brain is injured by a different mechanism than the hard skull.
Michael Bottlang
However, this critical vulnerability of brain to rotational forces is neither considered in standardized helmet tests nor accounted for in traditional helmet designs. Sports helmets have recently adopted technologies to shield the brain from rotational force. One technology, called MIPS, is a plastic sheet that seeks to reduce transmission of rotational force by slipping during impact.
These MIPS slip liners can be retrofitted into existing helmet designs and are available in a wide range of bike and snow helmets. In contrast to this 2-dimensional slip sheet, WaveCel technology employs a dome formed of a spatial cellular structure that was specifically designed to fold, crush, and glide during impact. Compared to standard helmets, it has shown to reduce transmission of rotational forces by up to 73%, and was able to reduce the predicted risk of sustaining a concussion by 54-97%. WaveCel is located in Oregon and has sold millions of bicycle and snow helmets to date. In 2022, WaveCel expanded their cellular dome technology into a completely new safety helmet design. This helmet can provide vastly more protection from rotational forces than modern safety helmets with an EPS foam core. Since over 50,000 work-related brain injuries are admitted to hospitals in the US each year, selecting helmets that have rotation-damping technology should be a primary consideration when selecting a new helmet.
LATERAL PROTECTION
The strap suspension of traditional helmets is a directional design. It is designed to absorb crown impacts, but it was found “practically useless against side, front and rear impacts” in a 1987 helmet test study. The authors of that study properly concluded that a redesign is necessary, since the majority of impacts are lateral while only 15% of impact occur to the helmet crown. The US ANSI standard Z89.1 properly recognized this shortcoming and added a Type II designation, whereby Type II certified helmets are tested for their ability to absorb lateral impacts. A recent publication document that most helmets from leading brands still only delivered Type I “crown only” protection. This shortcoming was noted for hard hat style helmets as well as for “climbing-style” safety helmet. While many safety helmets employ a foam liner in addition or in place of a strap suspension, this liner might be too thin or might not extend far enough to the sides to pass Type II testing. Selecting an ANSI Type II helmet is therefore important to provide protection for the most frequent lateral impacts.
HELMET RETENTION
A helmet can only provide protection if it stays on the head during a fall. Chin straps can readily prevent a helmet from falling off the head. The US standard ANSI Z89.1 does not require chin straps, but requires retention testing of chins straps if they are supplied with the helmet. In contrast, the European standard EN 12492, titled “Helmets for Mountaineers” requires chin straps. This standard is often used for “climbing style” safety helmets, since it requires chins straps as well as lateral impact testing. However, lateral impact testing is far less stringent in EN 12492 than in the US standard ANSI Z89.1 since it utilizes a 20% lower impact energy, a flat rather than a focal impactor, and since the test area does not extend as far down to the brim as in the US standard. For best head protection, helmets with chin straps should be selected. While an EN 12492 certification will ensure the presence of a chin strap, this standard is no substitute for meeting ANSI Z89.1 Type II performance.
CONCLUSION
When choosing a helmet based on available evidence of performance, the following three aspects should be considered:
- Choose a helmet with a rotation-mitigating technology to reduce the risk of brain injury. Since rotational forces can readily be measure in tests, manufacturers should provide data on the relative benefit of their technology compared to standard helmets.
- Choose a helmet that is ANSI Type II rated to provide protection from lateral impacts which occur far more often than crown impacts.
- Choose a helmet with chin straps to ensure the helmet remains on the head during impact.
In addition to these impact performance criteria, factors pertaining to user satisfaction are equally important for helmet adoption, such as comfort, weight, heat and style. In regard to style, the industry-led promotion of presumably safer “climbing-style” safety helmets over traditional hard hats is not supported by data. Helmets should be selected based on performance, independent of a particular helmet style.
Written by Michael Bottlang the founder and director of the Legacy Biomechanics Laboratory in Portland, Oregon. His research has been funded by the National Institute of Health and he has published over 80 peer-reviewed papers. Dr. Bottlang is also a founder of WaveCel LLC, a helmet company dedicated to reduce the incidence and severity of brain injury.
This article published with permission from Wavecel. View our other blog posts related to Head Protection.