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.