What happens to our bodies in a car crash? Obviously, nothing good. Cars are, after all, hulking metal containers and we are mere flesh capsules. But are you aware of the actual impact a high-speed car accident can have on your body, and how their sometimes-fatal transfer of energy actually works, science-wise?
We asked Dr. David Logan, Senior Research Fellow from Melbourne’s Monash University Accident Research Centre (MUARC), to break down what exactly happens to our bods – and our bowels – in the “200 milliseconds” of a crash; how advanced car engineering seeks to protect us, weirdly, by “deforming” the car upon impact; and how we can keep ourselves safe, even in the most dangerous-seeming scenarios. Given the 252 lives lost on the roads in 2015, this information could help bring the number for 2016 towards zero.
Kinetic energy. Sounds cool. Hurts heaps in a crash.
“When you’re driving along in a car, you have kinetic energy, and that’s the energy you possess by moving along,” Dr. Logan explained to Student Edge.
“Normally, when you want to stop a car, you have to get rid of that kinetic energy again, and so what you do to get rid of that kinetic energy is put the brakes on, and it dissipates as heat into the brakes."
In a crash, you don't usually have that luxury.
“The whole purpose of a modern car is to absorb as much of the energy in the structure of the car by deforming the structure of the car and preventing that from going into your body,” he said.
“But, in higher speed crashes – and for some cars, and some kinds of crashes – it’s inevitable that you will have to absorb some energy in your body.”
Think of it like a punch to the chest, which, it should be noted, would hurt a lot less than a crash.
“I can punch you in the chest, and you won’t be injured up to a point, because you’re absorbing energy from my fist into your chest,” he said.
“But beyond a certain threshold, your body can’t absorb a sufficient amount of energy and it will be injured.”
What actually breaks (and bursts) in the body during a crash?
First, depending on the impact of the crash, you can probably expect a broken collar bone.
“[From] the seatbelt alone, you tend to get a fracture in most frontal crashes; you’ll get a fracture in your right collar bone, if you’re a driver, or the left collar bone, if you’re a passenger,” Dr. Logan said.
“In a higher speed impact, you start to break ribs. The more energy you’re absorbing on the ribs, the more ribs you’ll break,” he added.
“Once you’ve broken enough ribs, the chest loses its structure and you start to impact upon the lungs.”
This is where things get disgusting.
“If you puncture the space between the lungs and the ribcage, then your chest will expand as normal but your lungs won’t go with it, and that’s called a pneumothorax; that’s when you have air in the space between the lungs and ribcage. That’s one of the first injuries that happens in a high-speed frontal crash.”
Sometimes even the misuse of a seatbelt can cause violent injuries.
“If you’re wearing a seatbelt incorrectly (very short people and very large people may have trouble having that seatbelt sit over that large part of their pelvis) and you have the lap-part of the seatbelt going over your stomach or your abdominal region, there’s no structure in there to absorb the energy,” he explained.
“So, the seatbelt loads up directly on the abdominal contents and there’s obviously a lot of organs in there that are quite delicate; you’ve got the spleen and the liver and the stomach itself, and the seatbelt will just carve into those.”
“Think of it like a slab of butter – a seatbelt is going to just drag through it,” he added, evocatively.
“There’s a lot of organs in there that, if you rupture them, you can get stomach acid sploshing around the rest of your body. If the bowel gets ruptured, which sometimes happens, you’ve got waste products slushing around the inside of the body where they’re not meant to be, and the outcome is much worse.”
That’s just in a frontal crash. What about side-swipes?
“In a frontal-crash, you have the benefit of the whole front of the car to absorb the energy,” Dr. Logan said, noting that the front is built to “deform in a controlled manner”. (That is, unless you’re in a van.)
“In a side-impact crash, all you’ve got protecting you is the door, which is maybe 10cm or 15cm thick,” he said.
“Your body’s just being crushed from the side. With a side-impact we see much more severe injuries to the thorax and upper-body; you get a lot more rib fractures; a lot more damage to the lungs and internal organs because of the side-impact. You also get pelvic fractures as well, because it’s the height of the bumper bar of the car that hits you.”
Seatbelts: they break your collar-bones, but can also save your life. “The first line of defence in a frontal crash is a seatbelt,” Dr Logan clarified.
“If the steering wheel is hopefully no closer than 30cm in front of you, as the car starts to decelerate – and it’s doing that very quickly - your body starts to move forward and the seatbelt is designed to support you and your chest, and stop you from contacting the steering wheel.
“The seatbelt is simply holding you by the chest and the pelvis which are fairly strong. You’re transferring energy to the strong parts of your body, rather than the stomach or your head.”
That's why you shouldn't be too upset if you walk away from a car accident with just a broken collar bone. That means the seatbelt basically did its job. However, it’s not just the ‘where’ that matters when absorbing injuries from a crash, but also the time it takes to do so.
“The longer your body can be given to absorb the energy, the better it will respond,” he said.
“If you were unbelted for example, as the car starts to slow down, your body will continue to move forward at the speed the car was travelling. So the car could slow down in the first 30 milliseconds from 60km to 50km, as it runs into the wall or the other car that it’s hitting. "But your body – if not connected to the car via the seatbelt – will continue to move forward at 60km an hour until it contacts something, and the first thing it will contact if you’re unbelted is the steering wheel with your chest, and your head on the windscreen.”
Here’s what airbags do (and why they don’t always deploy).
“Once the sensors in the car detect that the crash is more severe than the seatbelt alone will be able to protect you, the airbag deploys as well,” Dr. Logan said.
“The airbag is inflated with nitrogen [and] inflates very quickly. There are two holes in the back of the airbag. As you load the airbag with the body, it pushes the air back out through these holes in the back, allowing it to collapse in a controlled way, and that again dissipates the energy.”
(Dr. Logan confirms the movie Bad Neighbours depicts the force of a deploying frontal airbag in "a reasonable (and entertaining!)" manner, though it probably wouldn't go off without "the appropriate activation signals from the electronic control unit." Still, funny.)
“Cars generally have multiple airbags, but the frontal airbags will only deploy in a frontal crash,” he said.
“Most cars these days have a curtain airbag, and that airbag is really across the whole top of the car across the side window, and when the sensors in the car detect sufficient deceleration, the airbag deploys downward.”
The reason? As the Wu-Tang Clan once opined, it’s to protect ya neck, and the noggin sitting atop it.
“The head is the one thing we have to protect,” Dr. Logan stresses.
“You can live with injuries to most other parts of your body, but you can’t live with injuries to your head. It’s the one that causes the greatest damage to your quality of life in the longer term.”
Here’s how to stay safe – by using science!
Dr. Logan says slight increases or decreases in speed can have serious impact on the extent of your injuries.
“The energy [in a crash] is proportional to the square of the speed. So doubling your speed from 50km an hour to 100km an hour increases the energy that has to be dissipated by a factor of four,” he explained.
“Tripling the speed means nine times the energy.”
You don’t need to know advanced calculus to guess the results.
“If you just increase the speed of your car from 70km by 10 per cent to 77km, the energy absorbed goes up by 20 per cent. So the injuries aren’t just 10 per cent worse – they could be 20 per cent worse,” he said.
“If you decrease your speed by 10 per cent, your injuries don’t decrease by 10 per cent – they decrease by 20 per cent.
“Small changes in speed have a big effect on the outcome, both positively and negatively.”
Our bodies, as smart and well-designed as they are, can only withstand a certain force. Automotive engineering miracles aside, being cautious of your speed is still instrumental in saving lives.
“That’s why I find myself driving very well; within the speed limit all the time,” Dr. Logan said with a laugh, but not at all jokingly.
