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Does body weight affect falls differently?

Doug Myette, P.Eng.
Profile Picture of Doug Myette, P.Eng.

Graduated 1992, Bachelor of Engineering, Mechanical Engineer.

Experienced in engineering design, manufacturing and project management in a variety of industries since graduating. Including mechanical automation systems design, modular interior spaces development, high-speed metal packaging manufacturing, and heavy drilling equipment manufacturing.

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Q:Does body weight affect falls differently?
A:

Calvin: That brings up a very interesting topic. So, I’m around 220 lbs. I’m soaking wet, so how does my fall compare to someone who is say 150 lbs? Of course, this with no tools on. I probably have tools and all the actual PPE on which weighs us down. How does a heavier person’s fall compare to a lighter person’s fall?



Doug: Well, as far as fall speed and the distance you are falling in a certain amount of time…



Calvin: Let’s talk about all of it.



Doug: It’s exactly the same.



Calvin: Okay.



Doug: Everything falls at the same rate. Everything. Gravity affects everything equally. Where the difference comes in is the weight of the person. So, a lighter person will have lower impact force than a heavier person. The old saying, ‘it’s not the fall that kills you, it’s the sudden stop at the bottom’.



Calvin: Yeah.



Doug: Well, in the case of a falling worker, a heavier worker will generate more fall energy which needs to be dissipated to stop that worker from falling. So, conversely, a lighter worker will have less fall energy over the same amount of distance, so it depends. And this is why a fall protection equipment is designed for heavy workers. They have a set rate, you know, a 140-kg or 310-lb worker is what most fall protection equipment is rated for. You can get heavier rating equipment but the typical equipment you just go and you buy from your safety supplier will be rated for 140 kg or 310 lb worker, which is well above your weight with this equipment and everything else. So, you’re good there. And these devices are designed to perform a certain way based on the weight of the worker.

So within that range, your typical – you know, you’re quite tall guy, so your weight is on average with a person of your size. It’s very common that you will use a particular energy absorber, and it will perform in a certain way and it would decelerate to catch you and stop your fall. But it takes distance to do it, because it took distance to generate your fall energy.

And fall energy, in foot pounds or kilonewton meters is simply that – your weight times the distance you fall is your fall energy, and fall energy needs to be dissipated by a force and a distance. So, if you have a higher force, you can do it in shorter distance. And, the other way around. Less force, higher distance. We only have so much room that we can fall. And if you don’t want to fall for 30 feet, 40 feet, you want to fall as short as possible. So, we get into particulars of equipment and how they behave is much more complicated. It’s a much more complicated discussion.


Calvin: Yes, anyway, we’ll talk about it later.



Doug: Yes


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