Improved Helmets

Improved Helmets: Thinking about modelling the brain

So I’m doing some more thought exercises on this project. Yes, been a long time since I posted anything and I only just got around to having a look at the report into Phillip Hughes’ death.

In this case, the ball managed to strike a vertebral artery. There are typically two of these, and they flow to the basilar artery which feeds the brain stem. The other major route is via the carotid arteries . Both of these sets branch out into much finer blood vessels within the brain.

That, to my mind would have triggered a sharp impulse in the blood pressure in those arteries. The arteries are somewhat elastic, but they probably don’t appreciate that level of abuse: they have pretty thin walls in that part of the body and are quite small in diameter as they branch out from the brain stem. In the report, they talk about “traumatic basal subarachnoid haemorrhage“.

According to Wikipedia, that means blood is leaking out of vessels and into the protective layers that surround the brain. We often joke about the smoke escaping from an electronic component when we put too much current through it.

This would seem to be the blood vessel equivalent: a minor artery or three went “pop”.

It would appear that this is definitely one mode of failure in the brain that should be considered when designing protective gear. It’s particularly an issue for soldiers with IEDs. In their case, the helmet can work “perfectly”, but it’s the pressure wave hitting the body causing pressure up the blood vessels in the neck that do damage, as well as pressure waves in the cerebral fluid itself.

The other mode of failure seems to be in the neurons and their connections.

Thinking about this latter point, we know that the brain is a very delicate organ when taken out of its casing. It is described as having the consistency of tofu in some articles.

This makes me wonder whether the brain should be considered a solid at all. To my way of thinking, perhaps a very dense mesh of interconnected nodes is a more accurate representation of what’s going on.

As the head moves through space (which is what seems to do much of the damage), Newton’s First Law does its worst. If you consider a single node in this mesh travelling through a linear path, the node experiences a tension force from each connection to its neighbours.

These connections have a limit to the amount of tension they can withstand. When they break, that’s when brain damage takes place.

Now, under constant velocity, or at rest, these tension forces are within tolerance, nothing bad happens. However, when a sudden blow is experienced, it is this additional tension as individual nodes get jostled around from their own inertia and the transferred tensional forces from neighbouring nodes that may trigger these connections to break.

Modelling both of these situations is an interesting problem. The latter could be done with strain gauges, but they’d have to be sensitive ones. How sensitive? Not sure. 2AM isn’t a great hour to be answering such questions.

As for the vessels, perhaps piezo transducers at differing locations might give some insight into how much pressure is in different parts.

It may also be possible to have a tree-structure of tubes representing the arteries, and measure how much they expand as the pressure wave hits by measuring how much light is blocked between a LED and a photo diode with the “artery” running in the path: the fatter it is the less light hits the diode.

More food for thought I guess. 🙂

Improved Helmets: Case Study: Phillip Hughes

It appears that Cricket Australia might release the findings of a safety review into the death of Phillip Hughes. This could be an interesting report to read when it comes out, in that it hints at what parts of the head are particularly vulnerable to hits from hard objects.

If you consider a cricket helmet for a moment, and contrast that to the coverage area of a bicycle helmet. Both are designed with the assumption of a collision with an object coming from in front, and so the back of the neck was not an area given much thought.

Motorcycle helmets do a lot better here in almost all cases except the “half helmets”: tick-a-box helmets if ever I saw one! More recent designs come down much lower on the head. Interestingly, professional cricket did originally start with motorcycle helmets, but found them too heavy.

Within the construction of even a motorcycle helmet however, it’s interesting to note where the foam exists: and it’s thickest around the top of the head. The sides where one’s ears would be, the foam gets thinner. Possibly a compromise for acoustic reasons, but is it significant?

Bicycle helmets however, with the exception of MTB type ones, don’t seem to cover this very well from what I’ve seen. Perhaps the back and sides needs a bit more attention. I guess I’ll have to have a gander at the report when it is released.

Improved Helmets: Project background

Well, looks like this project is very much thrust into the spotlight having been covered in Hacklet 105 . Mine’s probably the least technical of the lot, it’s definitely worth having a look at what the others are doing, as there’s some really innovative ideas there. Many thanks to @Mike Szczys and @Adam Fabio for the shout-out. 🙂

One thing I haven’t done with this project yet, is to actually post the background of why I’ve started this. A big part of this was I wanted to get permission from the family of a work colleague of mine so that I could mention him by name, but at this stage, permission has not been given, so I have to keep things anonymous.

On the 12th of February, a colleague of mine was cycling to work over the Go Between Bridge here in Brisbane when he lost control on a bend as the bridge joins the Bicentennial Bikeway. This is an off-road, dedicated cycleway, so no cars, and supposedly no pedestrians, however many seem to not understand what a sign with a bicycle symbol and the letters O, N, L, Y mean. (I usually ride past and comment: “Funny bike you’re riding!”. Since this accident though, I intend to be a lot more assertive.)

(Above: the crash scene. That blood smear is still visible on the path today.)

I’m no crash investigator, but I did study physics, and I cycle as my sole means of transport myself, having no driver’s license. (And no interest in getting one either.) I’m familiar with what that bridge is like to cycle over, having done it many times shortly after it opened when I worked at West End.

Looking at the scene though, it was apparent to me that my colleague was going much faster than was sensible for that stretch of road, and something caused him to lose control just prior to the bend.

The resulting impact with the railing was devastating: in addition to a few broken bones elsewhere in the body, he suffered skull fractures, and what I understand now to be a Coup-Contrecoup injury to the brain.

I remember that morning arriving at work early (we both were early birds, and had he not crashed, he would have beaten me that morning), sitting down at my desk and preparing to do battle with U-Boot and an industrial PC, when at 6:34AM, the office phone rings. It was then I learned that my colleague was in a serious condition in hospital, and I then found myself frantically looking for contact details for his wife. (Which were nowhere to be found.)

We later learned he’d never regain consciousness, having lost all executive function in the brain. The only bits that worked, were the bits responsible for low-level muscle control. From bright mind, to persistent vegetative state. He passed away about a fortnight after his accident.

During his brief time in ICU, we were told by one of the people there that these sorts of injuries were common in bicycle and motorcycle accidents. That worried me.

That tells me that perhaps, something is wrong with these blocks of foam we insist on strapping to our heads, and that we’ve missed something. This is one of the first goals I’d like to pinpoint, but so far, has been the most difficult: trying to get hold of data that would statistically prove or disprove how “common” these injuries are.

There’s no point in protecting the skull itself if the brain is to get shaken around to the point that the person winds up with total mental incapacitation.

Research seems to suggest that helmets have had a big hand in reducing the incidents of these injuries, but the fact that it’s still “common”, seems to suggest there’s lots more work to be done.

The standards are focussed on linear acceleration, and single impacts at no more than about 20km/hr. Is that sufficient? I regularly find myself doing 40, and I’m no speed demon. (Hell, I’ve accidentally found myself doing 71km/hr once!) I think it’s time the standards were revised. The question is: how?

My colleague was a key member of our team, and one of the brighter minds I know. While he shouldn’t have taken that bend at such speed and expect to get away with it, he did not deserve to die. I can’t save him, but perhaps I can help save someone else. That’s what this project is about.

Improved Helmets: ICD-10 codes

A couple of people have suggested I have a look at the ICD-10-AM codes, as this is how a lot of stats are actually recorded.

The trouble was getting hold of a copy of ICD-10-AM to look at in order to determine what is of interest. It’s a very heavily guarded secret apparently. They’re derived from the ICD-10 standard codes.

As it turns out, there’s a site that provides the ICD-10-CM codes .

The codes appear to be similar for things like head injury, so perhaps this will be “close enough”? For privacy reasons, I might not get deep enough for the differences to be significant, but this is a starting point and will at least get us most of the way there.

The ones that appear to be of interest seem to be the following:

Code Description Reasoning
S12 Neck Fractures (vertebrae) Too-heavy protective gear may be a factor in whiplash injury, need to ensure we don’t make other problems worse.
S14 Nerve injuries in Neck Again, related to whiplash and other neck-related injuries.
S16 Tendons/muscles in neck Once again, whiplash and similar conditions
S02 Skull fractures This is the area helmets are supposed to protect!
S06 Brain injuries Again, what helmets are supposed to protect!

I haven’t gone to the deeper levels for two reasons:

  • There may be privacy issues going too much deeper
  • The stuff I’ll be looking at will be according to the ICD-10-AM system, which may have slightly different designators at the lower levels.

Improved Helmets: Senseless article

Doing a bit more searching, previously I had stumbled across one article by Bike Magazine Australia entitled “Lifting The Lid”.

I did try to get in touch with the author via the email link on the website, but heard nothing. However, it appears, that article is a reprint of this article , which was published by Bicycling magazine in June 2013. I thought it might’ve been older than that.

There’s also a furious rebuttal by the Bicycle Helmet Safety Institute. Well lets face it, being provocative helps magazines sell sometimes, although it pays to not be too provocative.

However, I feel the author has a point, even if he gets some details wrong.

It appears that the AIM system mentioned in the article is still in its prototype stage. I doubt this one is royalty free, but for sure it’ll be one to watch, owing to its safety features, and the fact that it’s a very different construction, should make for a cooler helmet to wear in summer.

Improved Helmets: Catalyst: Motorcycle Clothing

My father just spotted this television program segment regarding the safety of motorcycle clothing, in relation to thermal management .

They tested two factors, one was how well the clothing managed the wearer’s temperature, and also how well they protected the wearer. Interestingly, there is no Australian Standard regarding protective gear other than the helmet. Gear sold here typically comes with tags citing the CE standard.

Apparently, a lot of gear out there is not fit for purpose, with the more popular clothing being totally inappropriate in our hotter climate, and materials like “ballistic nylon do very poorly for abrasion protection (leather and denim do better). The poor thermal management contributes to heat stress, and the poor design decisions sometimes leave the wearer with a false sense of security.

I suppose it’s worth pointing out what I look like when I go out on the road. This is me wheeling the bike out one afternoon to head home from work.

That’s a cheapo $60 motorcycle helmet (I have never trusted bicycle helmets), and fairly lightweight overalls. Not what you want to try out at 60km/hr on a bitumen road, but I feel is a reasonable balance between thermal management, visibility and protectiveness on a bicycle. A MAMIL I am not!

My commute is about an hour, and involves two biggish hills. Yes, I sweat a bit, particularly my head, but when going long distances, I often take short breaks for a minute.

Riding from my home at The Gap in Brisbane’s north west, to Rochedale in the far South East, a journey of about 40km, I’ll typically stop once when I get to South Bank for a drink, then again near Holland Park, then I reach my destination. I’ve done this in the summer heat without issue. Then again, I’ll be riding at maybe 20km/hr most of the time, which requires less concentration. I find I’m still able to think clearly much of the time.

A loss of concentration on a motorcycle could be fatal due to the higher speeds typically involved. Reaction times are crucial there.

Helmets are typically made from expanded polystyrene foam, the same material used in eskys. In the former case, it is chosen because it crushes. In the latter, it’s for its thermal insulation properties. The head radiates the most heat in humans, and so is a prime candidate for thermal management.

It’s factors like this that make me wonder what came of that AIM prototype helmet design mentioned in the ” Lifting the Lid ” article. Being an aluminium honeycomb would make it more like wearing a heat-sink, an interesting concept that ought to make it cooler. Could this be adapted for motorcycles? I guess we’ll have to find out.

Improved Helmets: Digging into existing reports

Well, after my last couple of emails, I’ve been pointed to some rather interesting reports that peek into the area of interest.

Robin Guda at the Australian Institute of Health and Welfare was able to point me to ” Trends in serious injury due to road vehicle traffic crashes, Australia: 2001 to 2010 ” which sheds a light on serious injuries (requiring hospitalisation) from road accidents, where the patient survived. She was also able to provide a link to where I can request further information . There’s a fee involved in the latter case, but I do not mind paying a smallish amount of money for such information, alternatively, crowd-funding might be an option.

Both of these are a big help, and that article is raising some interesting questions.

One thing that stuck out was this passage (page 8):

Rates of life-threatening cases involving motorcycle riders and pedal cycle riders rose significantly over this period, with average annual increases of 5.2% and 7.5% respectively. Rates of cases involving passengers of motor vehicles and pedestrians fell, with average annual decreases of 1.2% and 1.0% respectively.

Injuries per registered motorcycle did not change much from 2001 to 2010, suggesting that the rise in population-based rates is largely due to growth in the number of motorcycles in use.

Now, due to the fact we do not have bicycle registration here in Australia, we cannot come up with a hard equivalent statistic for bicycles. Two groups I might be able to approach to get some sort of approximate figure though:

  • Peak bicycle bodies, e.g. Bicycle Queensland — who may be able to give me rough figures on the trends in membership over that period.
  • Australian Bureau of Statistics, who do the national census. One of the questions they ask is “how did you get to work that day”, so there’d be a figure there for the number of people cycling to work.

Another prospect might be to see if I can get similar stats out of China. They have a big population, many of whom ride bicycles/motorcycles, and even their bicycles are registered.

Meanwhile, Angela Watson was in touch from CARRS-Q, and was able to shed some light also. One article she posted through was ” Fatal Road Traffic Accidents, Study of Distribution, Nature and Type of Injury “.

This, in contrast to the above AIHW report, looks at accidents where the victim died within 21 days of the accident, for accidents that took place in India between December 2003 and November 2004. India have somewhat different road and safety standards to Australia, and a much bigger population. Table 6 on page 3 gives the stats for avulsion injury (that is, things getting torn off) to contre-coup injuries, cyclists and motorcyclists made up about 7% of cases there in total, with pedestrians ruling the roost.

They note there in the introduction that a big factor here is poor pedestrian infrastructure in India. If we take pedestrians out, the number rises to 7 out of 24 cases, or 29%. Probably a big portion of those were not wearing helmets, but that is pure speculation on my part.

Two other articles Angela sent through, which I’m yet to study in depth are ” Mechanisms of Head and Neck Injuries Sustainedby Helmeted Motorcyclists in Fatal Real-World Crashes:Analysis of 47 In-Depth Cases ” and ” Bicycle helmets are highly effective at preventing head injury during head impact: Head-form accelerations and injury criteria for helmeted and unhelmeted impacts “.

I will certainly have a look at these.

A very valid point was raised though regarding the availability of raw data. Much of the medical type data is heavily guarded for privacy and ethical reasons, and so getting near it may prove to be difficult. In addition, there appears to be no linkage between the stats on road accidents, and the stats on injuries.

Traffic bodies like the Queensland Department of Main Roads are mostly not concerned with details like injuries sustained, and groups like Queensland Health are mostly not concerned about whether the person was wearing a particular model helmet or whether they hit a car bonnet or a bridge railing.

A sub-area of research for me will be to get to understand the classifications for these injury types, which are covered by the ICD-10-AM standard. This is no freebie however, unlike the Australian Standards, which SAI Global sell for about $50 a piece (and I got for free when I was studying at QUT), I haven’t been able to get pricing on the ICD-10-AM standard. I guess we’ll create an account there, and ask the silly question.

The ideal situation for me would be to borrow a copy for a short period and make a note of the relevant codes. I don’t need a permanent copy. Russel suggested a couple of them in a comment a few days ago, so that’s a starting point.

In short, the road ahead is becoming a little clearer, and it’s going to be a long one. Good thing I’m not gunning for the 2016 Hackaday prize, as I’ll almost certainly not have it done by the due date.

Improved Helmets: Looking for answers in textbooks

As mentioned earlier, I’ve been doing a little “light” reading. Light reading being in the form of a 1500-page physics textbook which was purchased in my first year of engineering.

I’ve just been reading through it revising the material. Not doing the actual problems but just refreshing my memory, I figure I’ll go back and do selected problems once I’ve gone over everything.

I figured I’d see something that would perhaps jog my memory, or inspire me in one form or another.

One area was Hooke’s law, which relates the force exerted on a spring to its amount of displacement. I figure as a model of the brain, this might be one way to model it, not as a single mass, but as a series of “marbles”, if you will, connected by springs, as an analogy to the concept of neurons and their interconnections. The thought that, perhaps brains are not solid, but are a very dense mesh.

I’ll have to ponder this a bit more I guess. It’s basically a finite-element analysis approach to modelling the brain and what goes on inside. It’d be interesting to try a physical modelling of that mathematical model. Lead sinkers and strain gauges perhaps? I don’t know there.

The other was in relation to my test apparatus that I described earlier. In flicking through the problems, I found this:

Now, there are obvious differences, but really the headform moves the centre of mass closer to the end. If we can find the details of the centre of mass, we can derive what the headform is doing. Moreover, it might be useful to model the mass of the cyclist’s body in the form of mass in that rod, perhaps a bulk mass towards one end.

In short though, the equations needed to answer the above question are undoubtedly in that book, and moreover, I do have a worked copy of that example, but we won’t look at that just yet, that would be cheating.

Improved Helmets: Further leads on statistics

Today I had a reply back from the statistics branch of Queensland Health . QUT run the Centre for Accident and Road Safety, Qld (CARRS-Q) who do a lot of research into this field already. They’re based at QUT’s Kelvin Grove campus, fairly easy for me to get to if needed.

It would appear they likely have access to the sorts of statistical data I’m chasing, and will also have the statisticians on hand to make sense of it all. They already publish much of their data online. In short, they’ll be a good mob to talk to.

Their article, Monograph 5 – Bicycle Helmet Research , appears to have a lot of information, I’m yet to study it fully but I’ve had a brief look.

I was also referred to the Australian Institute of Health and Welfare who were the authors of the article that Nick Rushworth (Brain Injury Australia) pointed me to. Specifically, their article Trends in serious injury due to land transport accidents .

There’s lots to go through in that collection alone. Thankfully, there’s an extra long weekend due to Good Friday and Easter Monday coming up, so plenty to keep me occupied, and a few good leads to chase up.

Improved Helmets: Re-analysing the AS/NZS 2063:2008 test case

This afternoon, I managed to stumble on one of my old text books from my first years studying Electrical Engineering at university. In the first year, we future engineers are all one big happy family, with civil, electronics and other groups, all lumped together. So we study the same things, including physics.

For me, studying at QUT in 2004, the text book we were told to read was Physics for Scientists and Engineers with Modern Physics , Serway and Jewett, 6th Edition (International student edition, ISBN 0-534-40949-0 ). In reading this, I realised I had made an error in my earlier analysis of this test case.

So we make the same assumptions as before. That doesn’t change. We fix our earlier incorrect equation, and re-calculate based on that. If someone does happen to notice something amiss, feel free to let me know. If you’re not a user, I can be contacted a number of ways.

Another difference is that the CPSC tests use a headform mounted to a carriage that runs along a single rail, whereas Australian Standards testing appear to use the dual-guide-wire technique judging from the videos, one of which is here (Sorry guys, I’d link to the page, but then 1999 called asking for their proprietary Flash Player plug-in back).

Thus, without further ado, I present my re-analysis.

First, a diagram of the test set-up.

So y increases with distance from the anvil mounted on the floor. The guide wires are assumed to present negligible resistance, and we’ll ignore wind resistance.

Annoyingly, I can’t copy and paste the table from earlier, so please refer to my previous post on this for the assumed values.

Taking the correct equation for the height over time, and trying to solve for when the helmet meets the anvil, the impact time, we get the following equation:

0={1 \over 2}(-9.8)(t_I)^2 + 0t_I + 1.5 which re-arranged, gives:

t_I = \sqrt {-1.5 \over {({1 \over 2}) \times -9.8}} = \sqrt {-1.5 \over -4.9} = 0.553283

So a flight time of 553.283 milliseconds. In that time, it accelerates by -9.8m/s every second, so we can work out the impact velocity.

v_I=at_I=-9.8 \times 0.553283 = -5.422 We can work out the momentum at that the time of impact.

p_I = mv_I = -27.111 Our worst case is an elastic collision, so we can describe the momentum after impact as being the momentum at impact, in the opposite direction:

p_A=-p_I=27.110 This gives us a change in momentum as follows:

\Delta p = p_A - p_I = 27.110 - (-27.110) = 54.222 We can’t model an instantaneous change, so let’s assume it happened all in a millisecond. That gives us the following force after impact:

F_A={\Delta p \over \Delta t} = {54.222 \over {10^{-3}}} = 54221.767 Given the headform/helmet mass, that gives us an upward acceleration of:

a_A={F_A \over m}=10844.353 = 1106.567 g If the other scenario didn’t kill our cyclist, this definitely would.