F**king Helmets, How Do They Work?

So, this blog post has come across my Facebook feed a couple of times and at first I didn't bother to read it, thinking it would be the same inane blather that usually occurs. Anecdotes, not forcing people to wear helmets at knife-point = telling people not to wear helmets, THINK OF THE CHILDREN!!!!!!!!!!!!!!!!!!!, the Parellis are money-grubbers, blah blah blah.

Then I read it and came across this passage (no emphasis added):

I’m writing this calmly but inside I am screaming: If Linda Parelli had been wearing a helmet [when she fell off Remmer] she may not have been knocked out (read- concussion) and under her horse’s feet when he got up.  A helmet may have saved her from a concussion and it may also have saved her from bruises and 4 broken ribs. I wonder if that was extreme enough for Linda Parelli. I wonder what she considers a safe horse.

Oh, for crying out loud.

No. No, Ms. Fox, we can't say that at all. People get concussions while wearing helmets. People get knocked out while wearing helmets. People die while wearing helmets.

I come across this sort of thinking all the time, people seeming to think that helmets are magic, a force-field of protection against any and all head injuries, and, by proxy, any and all other injuries. Because people never break bones or anything like that unless they sustain head injuries. F**king magic. Like magnets or something.

Then, I got to thinking ("A dangerous idea" "I know"). Maybe I'm being too critical of Ms. Fox. Maybe she has never taken a physics course and has no idea how the basic principles of force work. Maybe she has about the same level of expertise regarding the principle of helmets as I do about how the internet works: absolutely no idea. For all I know, fairies bring websites from one computer to the other, and that's how websites get overloaded and shut down: not enough fairies. Perhaps Ms. Fox believes fairies reside in helmets and generate protective fields as the ground looms ever closer. So, in order to help Ms. Fox and anyone who didn't take (or failed) physics, I shall now destroy the magic and attempt to explain the basic principle behind helmets.

The main guiding principle behind helmets are among the most basic is physics: f = ma. Breaking down the equation, we have f as the force an object experiences, usually measured in Newtons. m is the mass of the objects. a is acceleration or the rate of change in the velocity of the object (usually we use acceleration to mean increasing the velocity, but in physics acceleration means either speeding up or slowing down). So, the force of the impact is directly related to both the mass of the object and the rate of change in the velocity of object. The saying "The bigger they are, the harder they fall" is actually true from a physics standpoint. But (and this is where helmets come in) it is also true that the faster they are, the harder they fall.

Your brain is a very soft and squishy thing that is surround by solid hard bone. A concussion is caused not by injuring to the skull bones, but by your brain bouncing around inside your skull cavity. Your brain starts bouncing around in your skull when you hit the ground, and that is where the equation f = ma comes in. In order to reduce the likelihood of head injury (and thereby brain injury), you have to reduce the force sustained by your head when you hit the ground. There are two ways to do that: reduce the mass, which is not possible, or reduce the rate of the change in velocity, which is where helmets come in. A helmet is composed of a hard shell enclosing lots of padding, usually some kind of foam. When a helmet contacts the ground, the inner foam starts to compress and crumble. This decreases the rate of deceleration and therefore the force of the impact, and hopefully bring the total force experience by your head below the threshold of injury. Or, watch what happens when the Mythbusters go to town with beer bottles.

So, there it is: slow the rate of change in velocity, reduce the force experience by the head and brain, hopefully reduce or eliminate injury to the head. Simple and elegant, but not magic. No fairies, no shields, no guarantees. Helmets have limits. Sometimes the force of the impact is still large enough to send the brain bouncing around the skull and cause a concussion, even a fairly severe one. Or loss of consciousness. In addition, helmets only have one shot, so to speak. Once that lining is crushed, it's done. It's already done its deed, thrown itself on the grenade, and it can do no more. So if, after a fall on your head, you hit your head on something else (like a fence or your horse's hoof), the protective properties are greatly reduced, and you may get a concussion or broken skull anyway. Also, helmets do not prevent general shock, and your reflexes may not be as sharp after a fall and not able to get out of the way of your horse's hooves.

Most helmets come with an ASTM/SEI certification, which entails hitting the helmet against an anvil designed to simulate a horse's hoof and measuring the forces experienced by various parts of the helmet. They do not, however, strap the helmet to a crash test dummy and torture it, a la Mythbusters, by dropping it from ridiculous heights to see if any other body parts get injured.

Pictured: not an approved method of testing helmets

There is not a helmet manufacturer in the world stupid enough to claim that their helmets will completely prevent any and all head injuries or injuries to any other body parts. Because they would get sued for false claims, and they would lose. There is absolutely NO DATA showing that helmets are magical panaceas, or that they even have a chance of preventing injury to any area of your body that is NOT your head.

Should Linda have been wearing a helmet? Probably. Would a helmet have prevented her concussion? Maybe. Would a helmet have left her faculties intact and/or thereby prevented the broken ribs and bruises? There's absolutely no reason to think that could have been the case.

You want more people to wear helmets, Ms. Fox? A good start would be if you stopped lying about them. Stop trying to pretend more than they are. Treating your audience like a bunch of idiots who can't read the news and see lots of cases where people are injured or killed while wearing helmets is not going to get you very far at all.

You want to know why people don't wear helmets? Maybe you could ask them why not. I would be very surprised if "Pat and Linda Parelli don't wear helmets" cracks the top ten reasons. So maybe get off your high unicorn and join the rest of us in the real world. It's surprisingly nice here.