Lots of people have asked me about the kind of forces involved in producing injuries similar to those Michael has suffered. It’s an interesting question, and after doing some calculations, it’s emphasised to me something that I think must be done relatively urgently. More of this later.
Let’s make a few assumptions as to baseline conditions. This means any results are at best approximations of the real world, but they allow us to “ballpark” the forces in question, and to perhaps compare with other mechanisms. And while I’m on the qualifiers, I’m SO not a physicist!
I’m assuming that the mechanism of injury is a near vertical fall onto the head, after Michael was “launched” by contact with a rock. I’ll assume his head was at 2.5 meters, not unreasonable for this kind of mechanism (and only slightly higher than one’s own height), that there was only a vertical component to his movement, and that he weighs 70 kg. This results in an energy of 1715 joules. Never mind the units for the moment – we’ll just generate some more energy data and then compare.
How about Felipe Massa’s accident? We know the spring weighed 800 gm (0.8 kg), and that Felipe was moving at 260 km/h (the spring is considered to have no horizontal velocity). This gives an energy of 2085 joules.
The same kind of calculation shows us that the bullet from a Kalashnikov (7.9 gm, muzzle velocity of 715 m/s, thanks Wikipedia!) has . . . 2019 joules!
To compare some other energies, let’s look at a soccer player heading the ball. Just to simplify, I’ll assume the player has no vertical speed when he heads the ball, and that the ball is falling from, say, 20 meters. This gives a “measly” 86 joules. Nothing, eh? (The actual value will be higher because of the player’s vertical momentum, and also if the ball falls from higher). Well how about this: there is a direct correlation between a the number of heads a soccer player has in his career and his cognitive function. So even this relatively tiny force, repeated many times, will likely damage a brain!
What about American football, where we read every day about cases of chronic traumatic encephalopathy (the damage done by years of hits)? Again, a few assumptions. Defensive lineman, 100 kg. Offensive lineman, 150 kg. Speed of each at impact? 1.2 meters/sec. What does this give? This gives us 180 joules combined. Again, doesn’t sound like much, but repeated over a career from high school, through college, to the pros, it seems often to result in very significant damage to the brain.
But back to the object of our concern. What explains the dramatic difference in outcomes between Michael and Felipe?
The obvious first (and perhaps only significant) answer is their helmets. Felipe was wearing the latest spec full face carbon kevlar racing helmet. Michael was wearing a . . . ski helmet.
Remember that force is not the only factor – we have to consider the area over which the force is spread. When a 70 kg man steps on your foot with his loafers, it hurts, but nowhere NEAR as much as when a 70 kg woman does the same with a stiletto heel. In one case, the force is spread over a much larger AREA, giving a lower pressure. And it’s pressure that actually does the damage. One of a helmet’s main roles is to distribute a force over a (much) larger area, dramatically reducing the pressures generated.
Now, the FIA Institute has done remarkable applied research in helmet design, and the helmet Felipe was wearing reflects that research. This helmet was designed specifically with very demanding requirements for impacts with objects having rounded edges as well as those having sharp edges, and equally for penetration resistance. These requirements were based on known mechanisms of injury in the sport concerned, and the levels of energy seen.
Ski helmets, on the other hand, are designed and homologated (WHEN they’re homologated) almost solely to prevent skull fractures. While this provides an easy method of evaluation in testing labs, we know that this has VERY little (if anything) to do with the actual mechanisms of brain injury. And unfortunately, Michael is a living demonstration of this.
Therefore, I’d like to throw a few ideas out there:
- the Federations responsible for skiing, from recreational to competitive, should convene a working group of experts to look at the epidemiology of head injury in the sport
- conclusions should be drawn about the kind of head protection likely to mitigate the injuries ACTUALLY SEEN
- Jean Todt should offer the full resources of the FIA Institute (data, expertise, etc) to help design this helmet, to make it affordable, and to make sure it is used as widely as possible.
Michael’s injury is no more tragic than those of every patient who suffers severe head trauma. If, however, his public persona spurs action that goes on to significantly improve the safety of skiing, it will be another of his many remarkable accomplishments!