Force of a 250mm fall

[daltontrees]

8 hours ago, Justme said:

Did you not see the word static? 

That calc works for you.

Using static over dynamic doubles the impact force.

I was commenting on all 3 of your posts, just saying rock and tree climbing are on different bases. Fall factors are a rating for ropes, not anchors or climbers. I suppose another key difference is that  in tree work the rope length can never be more than twice the height above last anchor, whereas in rock climbing you can be way way above last anchor. So far sometimes tha teh amout of rope out i a good deal more than the distance to the groundI remember a climb in Skye where I was a full 50 metres out, my last runner had pulled out as I passed it and I was 40 metres above my last runner. I was having kittens. Just made the belay ledge.

[Justme]

7 minutes ago, daltontrees said:

I was commenting on all 3 of your posts, just saying rock and tree climbing are on different bases. Fall factors are a rating for ropes, not anchors or climbers. I suppose another key difference is that  in tree work the rope length can never be more than twice the height above last anchor, whereas in rock climbing you can be way way above last anchor. So far sometimes tha teh amout of rope out i a good deal more than the distance to the groundI remember a climb in Skye where I was a full 50 metres out, my last runner had pulled out as I passed it and I was 40 metres above my last runner. I was having kittens. Just made the belay ledge.

Fall factors would still be important.

They define how many kn is felt by your & your gear.

Lower the factor the less impact you / gear feels.

You can never have a factor greater than two. But longer fall distances adds impact power.

 

One thing I always remember is that you can climb above a nylon sling & get a factor 2 fall & it will be ok but do the same on a dynema (sp) type sling & it can snap.

 

Tree climbing is not my thing but I assumed you would have your main anchor point & then intermediates / redirects nearer where you are working. I guess that would end up with the tree festooned like tinsel on a christmas tree.

 

Sounds like a bit of an epic. Far to many come to a fast stop on the ground.

 

I have seen belayers jump off a ledge to take slack up & save the leader. Other times its give slack so they drop past the high impact slam zone.

 

Interesting stuff looking at falls & forces.

 

[Paddy1000111]

I don't think fall factors can actually apply to this industry in a realistic, useful way. Fall factors are only really applicable for a fall from above an anchor which is never (unless you're doing something profoundly dumb) something we come across. Our maximum fall is 0.5m which means that our fall factor is always tiny and it's not something we can actively change. Considering we never climb above anchors our worst fall can only really ever be the length of the rope or a fall factor of 1. That being said, if you fall from an anchor point 0.5m and stop then you fall 10m and stop, both fall factors are the same but you're ****************ed after a 10m drop onto static line

 

You are also able to have a fall factor of over 2 in rock climbing. If a climber is say 3m above the belayer who is anchored on a ledge and falls, the belayer could panic and pull rope in. The climber then falls past the belayer which means he's fallen 5.5m on 2.5 meters of rope giving a fall factor of 2.2. Unrelated but still... 

 

Only reason I say this is because it's all well and good to know about fall factors but when using climbing kit the loading matters not the fall factor as we have no springs in our systems like dynamic rope so a 14ft fall is a lot more brutal than a 3 foot fall as we don't gain a 14ft spring to help us. 

 

Lets take a bad day example= A treemotion harness can handle 150kg maximum weight (good effort getting in the tree but for example sake)

 

if they both climbed 250mm above their anchor then they would both get a fall factor of two

 

The guy on a dynamic rope would experience 33.75kN and the guy on dynamic would experience 16.87kN

 

Same factor fall, big difference in factor ouch. 

 

Edited February 21, 2021 by Paddy1000111

[Justme]

12 minutes ago, Paddy1000111 said:

I don't think fall factors can actually apply to this industry in a realistic, useful way. Fall factors are only really applicable for a fall from above an anchor which is never (unless you're doing something profoundly dumb) something we come across. Our maximum fall is 0.5m which means that our fall factor is always tiny and it's not something we can actively change. Considering we never climb above anchors our worst fall can only really ever be the length of the rope or a fall factor of 1. That being said, if you fall from an anchor point 0.5m and stop then you fall 10m and stop, both fall factors are the same but you're ****************ed after a 10m drop onto static line

 

You are also able to have a fall factor of over 2 in rock climbing. If a climber is say 3m above the belayer who is anchored on a ledge and falls, the belayer could panic and pull rope in. The climber then falls past the belayer which means he's fallen 5.5m on 2.5 meters of rope giving a fall factor of 2.2. Unrelated but still... 

 

Only reason I say this is because it's all well and good to know about fall factors but when using climbing kit the loading matters not the fall factor as we have no springs in our systems like dynamic rope so a 14ft fall is a lot more brutal than a 3 foot fall as we don't gain a 14ft spring to help us. 

 

Lets take a bad day example= A treemotion harness can handle 150kg maximum weight (good effort getting in the tree but for example sake)

 

if they both climbed 250mm above their anchor then they would both get a fall factor of two

 

The guy on a dynamic rope would experience 33.75kN and the guy on dynamic would experience 16.87kN

 

Same factor fall, big difference in factor ouch. 

 

Yes but understanding fall factors helps you manage risk by for instance not climbing past the anchor.

 

Did some googling (dangerous I know) on the max kn a body can take.

 

 

This value comes from military studies on paratroopers: the human body can withstand a maximum deceleration of about 15 G, or 12 kN for an 80 kg mass.

 

Whilst HSE say 6kn limit. A deceleration of 12G is considered survivable in a parachute harness, i.e. a harness with torso enclosing straps and shoulder straps. For such harnesses the NASA/AGARD researches indicate a 5% injury risk at 12.1G, but the differing posture, physical fitness levels, harness attachment location, 'wearer comfort' and other factors have influenced the advisability of 6G as a maximum for users of industrial harnesses. https://www.hse.gov.uk/research/hsl_pdf/2003/hsl03-09.pdf 

 

[Paddy1000111]

11 minutes ago, Justme said:

Yes but understanding fall factors helps you manage risk by for instance not climbing past the anchor.

This is what I'm saying though, a fall from 250mm above your anchor on 250mm of rope (A fall of 500mm) is a fall factor of 2 although the guy would come to a stop from 3.13m/s. A fall of 40M on a static line is supposedly a fall factor of 1 although the guy would be doing 28m/s when he comes to a stop. 

 

Static lines aren't like hitting a pavement but they sure as hell aren't like hitting a mattress. If fall factors worked for this industry then a 40M fall would be half as bad as the 500mm fall?  

 

 

Edited February 21, 2021 by Paddy1000111

[Justme]

2 minutes ago, Paddy1000111 said:

This is what I'm saying though, a fall from 250mm above your anchor on 250mm of rope (A fall of 500mm) is a fall factor of 2 although the guy would come to a stop from 3.13m/s. A fall of 40M on a static line is supposedly a fall factor of 1 although the guy would be doing 28m/s when he comes to a stop. 

 

Static lines aren't like hitting a pavement but they sure as hell aren't like hitting a mattress. If fall factors worked for this industry then a 40M fall would be half as bad as the 500mm fall?  

 

 

Been a while since I looked at rope spec but from memory dynamic will stretch about 25-40% & static (or more accurately semi static) only stretches about 10% ish. I think true static is sub 6% at a % of its rated capacity.

So in your 40m example he would decelerate over 4m. Still very very harsh compared to dynamic over up to 12m.

 

Either way dont fall on static kit.

 

Its not for that.

 

If you are going to have fall potential use dynamic links or have an arrestor of some sort.

Down side is in a tree falling further will let you hit the tree.

So back to dont fall

 

 

[Dbikeguy]

Whilst I agree with the rescue issue, when doing the cs38 rescue portion the training was (at least in my case) based on the climbers gear being cut/unsafe so you would transition the casualty into your gear by a bridge to bridge and tying an alpine butterfly into the static side of your ddrt or using a prussic to do the same then clipping them into that so you can take the casualty weight up on your gear  and disconnecting the casualty from their kit completely or in reality cut it away so it shouldn't make too much difference? 

Same training, say your climber cuts rope one and falls onto his asap tether pops. To get him down you would have to go up to him as the device is now 8ft from him. Do you want to cut a second climb line or have the knowledge to release it and save the kit?

If doing a rescue does everyone carry a knife? I know as climbers we normally have a silky but would you remember to put it on when rushing to gear up to rescue climb?

To me an asap type device seems the most logical for two rope working especially if climbing SRT.

[Paddy1000111]

10 hours ago, Dbikeguy said:

 

Same training, say your climber cuts rope one and falls onto his asap tether pops. To get him down you would have to go up to him as the device is now 8ft from him. Do you want to cut a second climb line or have the knowledge to release it and save the kit?

If doing a rescue does everyone carry a knife? I know as climbers we normally have a silky but would you remember to put it on when rushing to gear up to rescue climb?

To me an asap type device seems the most logical for two rope working especially if climbing SRT.

 

Yea I 100% agree for the device, I think it would work a treat, especially if climbing srt like you say. If he has fallen and the arrest tether has popped then the tether is for the bin anyway. Cutting the strap isn't going to effect anything. You can still re-use the ASAP (although I'm not sure what the manual says about re-using gear that's experienced a fall) just have to buy a new strap which you would have to do anyway as once their popped, in the words of Bridgerton- "She's all loose and ruined".

 

I'd be curious how you would rescue a climber by climbing the 8ft above them and releasing the ASAP that is loaded with their weight whilst simultaneously having a bridge to bridge and supporting them on your climb line? IMO you would either cut the strap or just undo the carabiner from the harness? I wouldn't cut the rope that the asap is on especially as I would have to climb past the ASAP to do it. 

 

If you're assigned rescuer or even climbing anyway I think you would be mad not to carry a knife, I have a petzl spatha next to the first aid kit on my treemotion. If a crotch breaks on a rigging line and it gets caught on your leg or wrapped around you I would much rather cut it free with a knife in a second than trying to hack at it with a silky. 

[htb]

1 hour ago, Paddy1000111 said:

If a crotch breaks on a rigging line and it gets caught on your leg or wrapped around you I would much rather cut it free with a knife in a second than trying to hack at it with a silky. 

Sod using a knife or silky for that, if its that big it would get a touch with 200T or whatever saw I'm using.

[Paddy1000111]

2 minutes ago, htb said:

Sod using a knife or silky for that, if its that big it would get a touch with 200T or whatever saw I'm using.

Well, That's the preference. I'm on about the point where the saw is off, the branch is free and falling and it's hooped around you or something. I know for sure I would drop the saw on the lanyard. I can easily reach back and grab the knife which is held on with a carab on a cheapo cable tie so I can pull it off when needed. Rather have it than not