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Old 03-14-2012
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Shock absorbing tethers. Food for thought.

These are commonly used on via ferrata climbing routes. Like a double arm sailing tether, there are 2 locking biners (the ones shown here are competely equivalent to the Kong Tangos used on WMs tethers). One arm would need to be 6 feet, instead of arm length. A third carabiner would need to be added, or a snap shackle, if that is the preference.

The advantage is that these have built in shock abporption that limits impact load to ~ 600 pounds, something you ribs can survive when you're thrown across the cockpit. Shock absorption is generally less important on jacklines, as the jackline stretches and absorbes impact.

Black Diamond Easy Rider Via Ferrata Set :: CampSaver.com

Since some tether makers have started with impact indicators, wht not finish the job and add impact absorption? They would not need as much as these offer, though the triggering force should be less (a chest harness cannot safely manage the force a seat harness can manage).

Thoughts? No, I don't think this is the product, but it points toward a line of development.
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Old 03-14-2012
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Re: Shock absorbing tethers. Food for thought.

Looks good. I like the basic concept. Sometimes I wonder whether or not some our current safety equipment is likely to do more damage than good.
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Old 03-15-2012
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Re: Shock absorbing tethers. Food for thought.

What about some compact device similar to a rubber anchor snubber?
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Re: Shock absorbing tethers. Food for thought.

Quote:
Originally Posted by Barquito View Post
What about some compact device similar to a rubber anchor snubber?
One rational in favor of the via ferrata type system (tearable bartacks) is that it has been used by climbers for 25 years and OSHA for 20 years. It is a very well proven way to absorb impact loads in a predictable manner. Many other systems have been used and discarded.

One rational against using a rubber snubber is that it makes the system stretchy even at low loads. Since many sailors lean against lanyards this is unacceptable. It would also require ~ 2 x as much stretch acheive the same impact absorption (linear rate vs fixed rate).

In practice, though these are single-use once triggered, they doen't trigger often, the climber/construction worker/sailor is generally glad to replace it after a bad fall, and they are still full-strength and useable after triggering (useable until replaced).
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Re: Shock absorbing tethers. Food for thought.

I think that's the biggest problem. They are single fall/use tethers. It is a better/safer option, but people don't want to buy a new tether after they're caught by it. Seat belts in cars can cause injury and frequently do, but they save a lot more lives.

And honestly, most people don't go flying off of boats or free fall even 6' and catch. They're usually sliding off the deck with a much lower impact/load.
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Re: Shock absorbing tethers. Food for thought.

"I think that's the biggest problem. They are single fall/use tethers. It is a better/safer option, but people don't want to buy a new tether after they're caught by it."

I disagree. First, the new "fall indicator" tethers trip at the same force, so both would be replaced after the same fall. Second, very few rock climbers ever trip these. It actually takes a VERY hard fall.

It would be nice to have a design where the carabiners fould not need to be replaced (they should be fine in this sort of impact). The webbing part should only cost ~$30.

"Seat belts in cars can cause injury and frequently do, but they save a lot more lives."

I don't understand this annalogy. The shock absorption feature reduces injuries.

"And honestly, most people don't go flying off of boats or free fall even 6' and catch. They're usually sliding off the deck with a much lower impact/load."

Check your math. If you fall 6 feet you are going about 12 feet per second or something like 8 knots. That is NOT a difficult speed to achieve with a stumble and a wave strike. (acceleration due to gravity = 32 feet per second for about 0.4 seconds in this example). It is a worst-case, but not very unrealistic.

---------------

I see safety eqipment as rather important, and I want safety equipment that won't hurt me. As a very expereinced climber, I think I have a good idea what that takes. OSHA banned chest harnesses many years ago because of numerous fatalities.
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Re: Shock absorbing tethers. Food for thought.

Quote:
I see safety eqipment as rather important, and I want safety equipment that won't hurt me.
I agree. However, I am OK with a trade-off. If there is a small or moderate chance of injury in a fall that otherwise would have killed me, that seems like a good deal. Would be better if there was almost no chance of injury from the safety device, but, then there are other factors (cost, comfort, etc).
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Old 03-16-2012
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Re: Shock absorbing tethers. Food for thought.

Quote:
Originally Posted by pdqaltair View Post
I disagree. First, the new "fall indicator" tethers trip at the same force, so both would be replaced after the same fall. Second, very few rock climbers ever trip these. It actually takes a VERY hard fall.
Nope. Both SHOULD be replaced at the same time. But they won't. I'm not arguing that these aren't safer tethers. They are safer.

Quote:
The webbing part should only cost ~$30.
and how much does it cost to get the new webbing sewn in with the break away threads and certified safe? That's not a DIY project. Most sewing machines can't put out that kind of consistancy.

Quote:
"Seat belts in cars can cause injury and frequently do, but they save a lot more lives."
I don't understand this annalogy. The shock absorption feature reduces injuries.
Again, I'm not dissagreeing with you. But it's accepted that seat belts (like a standard tether) can injure you. No one seems to be outfitting millions of cars with break away threads to indicate straining. I just think this is more than what's needed.

Quote:
"And honestly, most people don't go flying off of boats or free fall even 6' and catch. They're usually sliding off the deck with a much lower impact/load."
Check your math. If you fall 6 feet you are going about 12 feet per second or something like 8 knots. That is NOT a difficult speed to achieve with a stumble and a wave strike. (acceleration due to gravity = 32 feet per second for about 0.4 seconds in this example). It is a worst-case, but not very unrealistic.
Check your math. What does a body experience in a 50mph car wreck with a stationary object? I'm willing to bet it's slightly higher than free falling 6'. And seat belts don't have break away threads. Or if you really want to see high loads, look at racing harnesses and crashing into something at well over 100mph. Loads are much higher and no break away threads. Not to mention the harness is strapped to the roll cage, as apposed to a jackline, which will absorb a huge amount of that shock load.

Yet again, I'm not saying that these aren't a better mousetrap, they are. But no reason for people to think they're going to break ribs or do serious bodily harm by having a standard tether.

Quote:
OSHA banned chest harnesses many years ago because of numerous fatalities.
And what was the distance of those falls? Source?
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Re: Shock absorbing tethers. Food for thought.

I've been in the climbing gear manufacturing business, so I'm not guessing. 6-sigma quality control and all.

"Nope. Both SHOULD be replaced at the same time. But they won't."

This is not clear. If the tether has not ripped ALL of the bar tacks, the biners have not seen a load over 600 pounds. Additionally, in climbing and industrial use it is common practice for the webbing to be damaged or abraded long before the biners are damaged. User inspection is always vital.

"and how much does it cost to get the new webbing sewn in with the break away threads and certified safe? "

I was not suggesting DIY. The webbing by itself could be sold as an assembly for that cost. Yates 'Screamers' sell for $18.00 and are similar. By far, most of the cost is in the biners.

"But it's accepted that seat belts (like a standard tether) can injure you. No one seems to be outfitting millions of cars with break away threads to indicate straining. I just think this is more than what's needed."

Not a good comparison. Seatbelts hold the body in a different manner. If they stretch significantly you strike the dash. A loosening fit could be very dangerous, as the contact points would become dangerous (stomach and neck). Cars are designed with crumple zones to limit g-force. No, not a good comparison. I think.

Maybe it is more than what's needed; it's a forum, so this is just for fun and to make us think. Otherwise, nothing changes.

"And what was the distance of those falls? Source?"

I'm sorry, but this is common knowledge and common sense. OSHA flatly forbids the use of a chest harness where fall potential exists. Ask any construction worker or any rock climber to take a 2-foot fall in a chest harness against a static anchor (not a stretch rope) and they will explain to you how much that will hurt. Don't try it; you will be injured. You will find little discussion of this on the net, because climbers learned chest harnesses where nuts 60 years ago. Thus, up-loaded modern data is lacking.

Chest harness are not acceptable where fall potential exists (like off the deck). Only positioning. Fall Protection. They give big tickets for that.

Energy absorbing lanyards are required at 6 feet.

------------

To learn about fall energy and shock absorption, rock climbing classes and engineering course work are useful. I have taken short falls (2 feet) against non-stretch anchors in a seat harness, and the impact is truly bone jarring. Climbers have broken 5,000-pound test gear in 3- to 4-foot falls. Ask the climbing instructor; this also is well known and is the reason Yates makes 'screamers.' (Yates invented these for climbers long before OSHA figured it out. Notice that 'Sceamers' are sewn the opposite direction from OSHA tethers; climbers know the bar tacks cause high frequency vibration when tearing that can rattle rock climbing gear and cause biner gates to flutter open, which weakens them. Lots of on-the-cliff fall testing.)
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Old 03-17-2012
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Re: Shock absorbing tethers. Food for thought.

Interesting UK study on falls, survivable tether impact loads, and energy absorption.

http://www.hse.gov.uk/research/hsl_p...3/hsl03-09.pdf

IF the subject is well secured in a body harness it concludes g-forces over 10 Gs have significant injury potential and forces over 20 Gs are generally fatal. Since 20 Gs ~ 3500 pounds, it seems clear that the sailor will be dead before the harness breaks (cutting over sharp edges excluded) and probably seriously injured at 1,000 pounds, since he is only wearing a chest harness. Much depends on geometry, but the general conclusion is unarguable.

I found the discussion of variable arresting force depending on a persons weight (page 14-15) interesting. To me, this also suggests a sailing tether should have a lower arresting force. A lesser total energy absorption capacity is needed, perhaps 40%, so the required extension will not be excessive, perhaps 2 feet, based upon a comparison of industry figures and potential wave impact/falls on a boat (they are looking at a 12-foot fall, we are considering the wave force plus boat free board).

-----------

I should add that these are not just numbers on a table to me. I've taken thousands of roped falls rock climbing--most top-roping, but other sorts as well--and have a pretty well tuned gut feel for the issue. I have a strong feeling also, that non-climbers have no respect for how dangerous a fall on a chest harness, without shock absorption, really is.
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