Helmets: My Two Cents

Earlier this summer a question on the Great Outdoors StackExchange site led me to look further into the standards for climbing helmets.  The question itself, a basic “can I use my bicycle helmet for climbing”, was fairly simple and has been asked many times in many places.  The development of lightweight foam climbing helmets has also caused some confusion in this area, with even experienced people confused as to where these new designs sit on the spectrum from traditional hard-shell climbing helmets and ultra-ventilated bicycling helmets.

For example, one person wrote: “there are helmets sold as climbing helmets which are basically one-hit-wonders. Those are constructed similar to bike helmets that are meant to crack as they absorb the force of an impact. Once they are so compromised they are pretty much useless. A proper mountaineering helmet would be one built with high impact plastics and other shock absorbing features that allows them to absorb multiple impacts and keep on ticking.

My immediate thought was this writer has rather unrealistic expectations about both types of helmets.  As you’ll see at the end of this post, the relevant climbing (and cycling) helmet standards call for each test helmet to receive impacts in a few different spots (e.g. two on the crown, one on each side, etc.).  Contrary to many expectations, the bicycle helmet standards seem to have just as much emphasis on these “multiple impacts” as do the climbing helmet standards!  Additionally, most “hardshells” currently on the market are actually single-impact hybrid designs.  So, let’s dig into this a bit more…

To start with, the purpose of all helmets is to resist penetration and act as a shock absorber to slow an impact and thus reduce the peak force.  This is done by either compressing or stretching of an impact-absorbing material.  Spreading out the impact over a wider area is largely incidental to this, as is energy dissipated by the helmet cracking.

Traditional hard shell helmets use an internal cradle of nylon webbing to suspend a hard plastic shell above the wearer’s head.  (An example includes the discontinued Petzl Ecrin Roc, which had a thick polycarbonate shell.)  Impacts are absorbed by the elastic properties of the webbing.  A hard shell that’s not suspended may offer some penetration protection, but will happily pass nearly all the force of the impact through to your skull.  This is also why they offer little protection from impacts that don’t come from overhead.

Foam helmets have a thin polycarbonate shell enclosing a thick layer of foam, commonly expanded polystyrene (EPS).  (Examples include the Black Diamond Vector and Petzl Meteor.)  The foam is engineered to crush when impacted with sufficient force; this crushing absorbs the energy and slows the impact.  This provides excellent impact protection for both top and side impacts, and adequate penetration protection.  Unfortunately, once crushed EPS foam has little ability to absorb further impacts.  Some models (e.g. Petzl’s Sirocco) use an expanded polypropylene (EPP) foam, a multi-impact foam which is much more durable than EPS and is also able to recover much of its shape and impact resistance after a hit.

Many helmets currently thought of as hard shells rely on a foam lining rather than a suspension cradle, and would technically be considered hybrid designs.  (Examples include the Black Diamond Half Dome and Petzl Elios, which use ABS plastic for the hard shell rather than polycarbonate.  ABS has about half the impact strength of polycarbonate, but is less expensive.)  Often in hybrids this lining only covers the crown of the helmet, meaning there is little to no protection against side impacts.  This also means that these helmets are subject to the same multiple impact problems as the foam models.

Regardless of type, each helmet is tested to the same standards, either the EN 12492 standard or the slightly stricter UIAA 106, so the significant questions are whether one type provides better coverage than the other, and whether one type handles multiple impacts better than the other.  To answer the latter would require a third party to do some exhaustive testing.  Mark Taylor, of Leeds University, has been doing a good deal of work in this area, but it appears to be not widely available.  His suggestion back in 2002 was to use a foam model for general cragging or ski mountaineering, and a traditional suspension hardshell for alpine or ice climbing.

In the link above, the author observed an informal test that gave initial results of about 4.1 kN for the Ecrin Roc, 6.9 kN for the Meteor, and 7.9 kN for the Elios.  For most of the helmets tested, a second drop test gave results that would not pass the standards (e.g. 10.5 kN for the Meteor, and 11.5 kN for the Elios).  This seems in line with my expectations regarding the lack of significant difference between the hybrid and foam models.  I am also reminded of an anecdote posted by Dane Burns of ColdThistle, in which he mentions his Meteor shrugging off a hard impact while his partner’s Elios cracked when a dinner plate of ice hit it.

Searching for additional examples of fragility online brings up plenty of cases of people who assume the foam designs would not be anywhere near as durable, along with a few favorable comments from those who have actually used them.  Yes, there are those who have cracked their foam helmets while sitting on them or packing them, and those who have placed their “hardshells” through much abuse and are glad they are still going strong.  It’s the latter case that’s dangerous; putting a hybrid helmet through abuse that would damage a foam helmet could very easily result in similar damage to the actual impact-absorbing components of the hybrid.  Would I want to climb with such a helmet?  Not particularly!

My personal thinking on helmets is that the current hybrid models benefit from a mythology built on their full-suspension predecessors, but I see little to indicate that holds true today.  I feel the lower weight and improved protection against lateral impacts currently favors the foam models.  That said, if severe rockfall is expected, perhaps an older Ecrin Roc or HB Dyneema might be called for.

*The one exception I can think of is the HB Dyneema, which was claimed to withstand 10 runs of the UIAA impact tests.

My original StackExchange answer:

The main standards to focus on for bicycle helmets are probably the CPSC standard in the US, and the EN 1078 standard in Europe. The climbing helmet UIAA 106 standard is based on the EN 12492 standard. Unfortunately the EU standards do not appear publicly available due to copyright issues.

Bike helmets:

CPSC: Helmet is attached to a 5kg headform and dropped: 2 meters onto a flat anvil, 1.2 meters onto hemispheric and curbstone anvils. The test is performed on helmets conditioned for at least 4 hours at ambient temperature, sub-freezing temperatures, high temperatures, and immersed in water. Peak acceleration must not exceed 300 gravities for any impact. Each helmet receives a test of the retention system (chinstrap) and 5 impacts: two each from the flat and hemispheric anvils followed by one from the curbstone anvil. [ed. I believe the curbstone impacts are performed on a second test helmet.]

EN 1078: The EN standard appears to call for two impacts from 1.5 meters; one onto a flat anvil, the other onto a curbstone anvil, with a 250 gravities limit. Helmets are conditioned by temperature and UV aging.

Climbing helmets:

EN 12492: Helmet is placed on a headform and a 5kg striker is dropped onto the helmet. Front, side, and back impacts are done by tilting the headform 60°. A hemispherical striker is dropped 2 meters for the top impact, and the flat striker is dropped from 50 cm for the front, back, and sides. A penetration test is done using a 3kg conical striker dropped from 1 meter. Finally, there is a retention system test. To pass, none of the impacts must transmit more than 10kN of force to the headform.

UIAA 106: Identical to EN 12492, except the transmitted impact force must not exceed 8kN.

Comparing the two:

One item immediately apparent is the use of acceleration in the cycling helmet standards vs. kilonewtons (a unit of force) in the climbing helmet standards. (I suspect this is because for a cycling helmet the total force is known; it’s a person’s head falling from a bike to the pavement. Thus, the goal is to manage the deceleration.) If we assume a 5kg headform is experiencing 250g’s from the bike helmet test, the classic F=ma equation gives us: 5.0 kg * 250 g * 9.80665 m/s-2/g = 12.3 kN. (Hopefully someone will speak up if I’m completely off-track here!)

Combined with the types of tests performed, one might conclude that a climbing helmet of the expanded foam sort, should have a better chance of passing the cycling helmet tests than the other way around. A well-known example is the Petzl Meteor III+, but others, such as the Kong Scarab, also exist. I would point out that these meet the European cycling standard, but have not been certified against the American standard. This may be due to the high cost of certification, but it may also be due to the stricter CPSC requirements. Hard-shell climbing helmets are likely to have trouble with the side impact cycling helmet tests. Personally I would not use a cycling helmet to climb with, but I have used a foam climbing helmet on my bike.

References:

On a related note, there’s an excellent article about the overall effectiveness of helmets in reducing brain injury at bicycling.com. The takeaway is that most helmets are not designed or tested to offer protection against concussion or similar traumatic brain injuries; only against direct physical impact: http://www.bicycling.com/senseless/index.html

Leave a Reply

Your email address will not be published. Required fields are marked *