Science Buddies: "Ask an Expert"

I was wondering at what velocity would kill a human? When I am reseaching it I just get tons on deaths realted to it. I am working on a project where we are to find a velocity and then tell if it would have killed them.

Thanks a Bunch!
Laura

Let me put on my Trauma doctor hat and stethoscope here for a minute...

It's a complicated question. It's not the velocity that's the issue, it's the deceleration. Astronauts go at 25,000 mph, and slow down 0 when they hit the water, and nothing happens to them. But going from 30mph to 0 by hitting a brick wall, and you may not do so well. And different parts of the body are more susceptible to injury than others. It's probably not very relevant to survival statistics if your hand undergoes a 100g deceleration. Your brain and parts of your vascular tree have other ideas on what constitutes a bad day.

Do a google or ask.com, etc... search on: deceleration injuries, closed head injury, thoracic aortic injuries, collision severity, for a start. There might also be some information available from the people at the Indy Racing League, or CART (and since Dale Earnhardt's death, NASCAR, but they are years behind the others in research.) This is a design issue that racing teams face every day. A hint - it is not accidental that Indy cars disintegrate into very many pieces when the hit the wall at 220mph, but the drivers survive, but NASCARs and for that matter your car at home look pretty good after an impact, but the drivers may not survive the impacts.

You will come across a number of stories of persons that have fallen/jumped out of planes, had their parachutes fail, and walked away from the impact. Why that is possible will give you a tremendous insight into collision severity and survivability of collisions.

I know that's a lot of information, but I hope it will get your research rolling and therefore starting to find what should be a lot of great information on this topic.

This subject needs a lot of assumptions and the result depends largely on these assumptions. For example: which part of the human body (as we know the head is more sensitive), what kind of object hits the human body, in what way (directions...)

To be honest this not a simple project, the difficult part is to define the problem correctly and 'cleanly'

reehlgirl wrote:I was wondering at what velocity would kill a human? When I am reseaching it I just get tons on deaths realted to it. I am working on a project where we are to find a velocity and then tell if it would have killed them.

Thanks a Bunch!
Laura

Hi, Laura!

This is a very interesting topic! As has been previously posted, it is also a very broad one with many variables. Your best bet for doing a project on this topic is to narrow the scope down to where you have a much smaller number of variables.

If you really are interested in velocity, for example, you could narrow the scope of your project by studying the percentage of fatalities in automobile accidents based on the speed of the vehicle at the time of the accident.

A previous post from zzzzdoc mentions another way to look at this problem. You could do a study of how the Apollo astronauts survive the decelleration of a splashdown in the ocean, or how the crew of the Space Shuttle is able to survive the acceleration of a lift off. Quite a bit of research and design as well as an understanding of human physiology has gone into making those events safe for humans.

This triggered another idea that's related - how do air bags in cars reduce the effects of crash decceleration on the human body?

I hope this gives you some idea of the VAST areas of investigation related to your topic. It sounds fascinating to me!

Laura:

You know its a good general topic when you have all the experts intrigued by it.

Here's another interesting reference to look at:

http://en.wikipedia.org/wiki/Free_fall

They discuss 3 airmen and a flight attendant (in separate episodes) who fell out of airplanes, had parachute failure, reached terminal velocity, and survived the collisions. So these were presumably approximately 120mph survived collisions.

Also, a link on that page to the Free Fall Research Page, is interesting and likely informative for you:

http://www.greenharbor.com/fffolder/ffresearch.html

The reason I am bringing up free fall, is that it is a classic example of reaching a high velocity, and rapidly decelerating to zero velocity. As they say, "It's not the fall that kills you, it's the messy landing."

As OneBriiguy, and franklinduan, have already mentioned, it is EXTREMELY important to narrow down this topic. Once you have formulated a research question, there are a huge number of resources on the web to help you with your research. And you have the experts here as well to help guide you.

Clearly, being able to survive severe automobile accidents is a big priority with many, many scientists, engineers, and physicians around the world. All of these people publish work.

It seems the MDs have covered this pretty well. All I can add are a couple of appropriate quotes from the author Douglas Adams.

"All it takes to fly is to hurl yourself at the ground... and miss."
"It is not the fall that kills you. It's the sudden stop at the end."