#253 How does G-force kill people?

I learned this today. Sustained G-force of 6 G are generally considered to be fatal because they squash our organs and starve our brains of oxygen.

Gs is the shortened form of G-force, which is in itself a shortened form of the gravitational force equivalent. G-force can be caused by rapid acceleration or rapid deacceleration. The G in G-force is gravity and 1 G is the force that is pulling all of us down towards Earth all the time. If you experience 2 G, it means that you are experiencing two times the force of gravity. So, me, an 80 kg person, would weigh 160 kg. If I were to experience 10 G, I would be experiencing ten times the force of gravity, so I would weigh 800 kg.

G-force is a force that is caused when someone is accelerated or decelerated. It doesn’t just mean the weight of gravity pressing down on you because it can obviously be horizontal as well. It means the force acting upon you is x times the force of gravity. To calculate G-force you have to divide the object’s acceleration in m/s² by the force of gravity, which is 9.8 m/s².

A car accelerating from 0 to 100 km/h in 2.3 seconds would pull 1.2 G. 100 km/h is 28 m/s. 28 m/s divided by 9.8 is 1.2 G. This G-force is perfectly survivable, and you would just feel as though you were being pulled back in your seat. However, the reverse is probably not survivable. A car decelerating from 100 kph to 0 (i.e. crashing) experiences a lot more G. If a car hits a concrete wall at 100 km/h it decelerates in 2.9 milliseconds, which is well over 100 G. That would be the equivalent of me weighing 8 tons.

This is the reason why cars have crumple zones, airbags, and seatbelts. If that 2.9 milliseconds can be extended out, the G-force starts to come down. The idea behind crumple zones, airbags, and seatbelts is the same as the way you would catch a baseball thrown hard at you. If you catch it with a stiff arm, you’re going to hurt your hand. You move your hand with the ball to slow down its momentum before you catch it. The crumple zones, the seatbelts, and the airbags in the car do the same thing for the person inside. They try to extend the amount of time it takes for the car to come to a stop and reduce the G-force. The seatbelt is designed to stretch a little. If I undergo the same crash while wearing a seatbelt, I only experience 70 G. That’s still probably fatal, but the airbags and crumple zones could bring that number down even lower.

So, how much G-force can we survive? Well, it depends on the person, the level of fitness, the amount of training they have had, what they are wearing, and how long they undergo the G-force for. The world record for G-force experienced is 46.2 Gs by an Air Force officer called John Stapp. He was riding a rocket sled to test harnesses for fighter jets. He believed that humans could survive even higher Gs if they were properly harnessed in.

Fighter pilots are trained to stay conscious during higher G-forces than most people can. They are trained to use breathing and muscle-tensing techniques to keep the blood in their brain. They also wear suits that use air bladders to keep the blood from sinking into their lower body. The biggest problem for fighter pilots is that if they lose consciousness, they might crash.

So, why do high Gs kill people? There are two things that they do to us. The first is that because our organs are all loose inside of us, when we experience significant G-forces, the organs can get squashed against each other and crushed. Due to their different densities, the organs experience different amounts of G-force, and they can get torn. If the G-forces are high enough, bones can be broken, and joints dislocated.

The second way that they kill us is through asphyxiation of the brain. Our hearts have evolved to pump blood to our brains in an atmosphere of 1 G. If the G-force starts to get higher, it gets harder for the heart to pump blood to the brain and the blood starts to pool in the extremities. If there is no fresh blood going through the lungs and heart to the brain, there is no oxygen arriving in the brain. It won’t take more than a few seconds for someone to lose consciousness under high G-force and if the G-force isn’t lifted, their brain will suffocate. Pilots are trained to keep as much blood in their brains as they can, so that they remain conscious until the G-force has dropped.

A Lithuanian artist called Julijonas Urbonas came up with something he called the “Euthanasia Coaster”. It is a roller coaster that euthanizes the riders by exposing them to 10 G for over a minute. The G-force for such a length of time would kill the riders because their brains would suffocate.

So, G-force kills people by crushing their internal organs and by starving their brains of oxygen. And this is what I learned today.

Photo by Pixabay: https://www.pexels.com/photo/aerobatics-air-air-force-aircraft-264416/

Sources:

https://en.wikipedia.org/wiki/G-force

https://www.sciencefocus.com/science/whats-the-maximum-speed-a-human-can-withstand/

https://www.medicaldaily.com/breaking-point-whats-strongest-g-force-humans-can-tolerate-369246

https://hypertextbook.com/facts/2004/YuriyRafailov.shtml