Adding to the site because yesterday I was asked a question by a newbie and I realized (after I had answered with something stupid, that actually sounded REALLY stupid) I had completely forgotten and had to ask someone else.
So I’m actually writing it down, because otherwise I’ll forget. And what’s a website for, if not writing things down so you don’t forget, and sharing it with others?
A kilonewton is a measurement of force. When an item is rated, it usually measures what amount of force can be safely applied to that item.
This is important in suspension, because we use gear to suspend people (rigging plates, carabiners, rope, etc) and it’s preferable to use gear that is rated.
(Fun fact: natural fibre rope is almost never rated.)
The easy conversion of kilonewtons to kilograms = x 100, divide by 10 for safety.
So 1 kilonewton = roughly 100 kg of mass you can suspend without equipment breaking- if it’s holding still, and there are no other factors involved, which never happens.
The measurement of kilonewtons is sort of mass (kg) x the earth’s gravity. Kilonewtons are the sum of the force involved in that equation.
A carabiner rated at 25 kilonewtons is able to support 250 kg of mass reasonably reliably, because it’s actually capable of supporting 2,500 kilonewtons. So the original weight vs gravity plus a hell of a lot of leeway for whatever other forces might be placed on it (swinging, falling, etc.)
As an example, when you use a carabiner as a pulley, or to pull something up, you’re exerting more force. So your 90 kg person by themselves requires about 1 kilonewton, and then you have whatever forces (being pulled up, swung around, whatever) are ALSO exerted on the item. That’s difficult to measure, so yeah, let’s have lots of extra kilonewtons on there. If you just went with a few kilonewtons, you’re considered way to close to the failure point to use that equipment safely; your safety margin isn’t big enough.
Fuck it’s embarrassing how easy it is forget basic shit like this. Good reminder to go back and look it up though.
In general, when using a piece of gear, you want to have it rated at over 20 kilonewtons, (Kn) and you want it used correctly. E.g. carabiners are better used lengthwise than sideways, because they can support more force that way.
I enjoyed this post. But wouldn’t 25 Kn = 2,500 kg?
Actually, yes. I missed some bits in the post, which is what I get for scrawling down ideas at 4.30 in the morning and not proof reading
And updated for more clarification
“As an example, when you use a carabiner as a pulley, or to pull something up, you’re exerting more force. So your 90 kg person by themselves requires about 1 kilonewton, and then you have whatever forces (being pulled up, swung around, whatever) are ALSO exerted on the item”
When lifting someone of approx 90kg using a carabiner as the “pulley” you will effectively double their weight during the lift as you need to add equal or greater weight to the other side to even begin the lift.This is only accurate if the lift is done at 0 degrees from the “pulley” (i.e if you were to pull straight down towards the floor.) This is the biggest reason why we use a safety factor of 10 rather than 5 (Standard) when working out or safe working load. So your SWL of 250kg gets pushed pretty close when lifting someone. While you might think you have lots of extra wiggle room up your sleeve it can vanish very quickly. The best way to avoid pushing past your SWL is to use more carabiners in your lift. Create your own mechanical advantage by adding a “pulley” to the bottom of the lift so you dont need to exert as much force during the lift and therefore reducing the amount of force on any one single carabiner.
Keeping in mind that our natural rope isnt rated if you dont take care in how to set up and plan your lift your rope is going to be the first thing the breaks not your other rated gear.
In conclusion, think before you rig, every time. Even if its a suspension you have done a hundred times. Its better to be safe than sorry. Also get someone to teach you about this stuff before attempting it on your own. This is how people get seriously injured.
That’s some very specific information, which makes it a great contribution to the post! Thanks very much for your contribution 🙂
I will add simple reason why natural hemp isn’t rated (and forbidden for climbing, by the way). It is because of way it breaks. It just give way totally and immediately. Synthetic PA, PP, and similar materials break gradually, you can see individual strands of sheath “crawl” the rope and yet rope will hold still quite a lot stress. Hemp will just break, when overstressed, or too old, without warning.
Still, hemp is just nicer to look at and work with, so it is used a lot. My advice is to use relatively new ropes for suspension and change them regulary.