 Poster: A snowHead
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A chair carrying three skiers on the Ruthie's Express lift at Aspen (Colorado) broke on Saturday 14 April, resulting in a skier falling 10 feet. He was reportedly uninjured and skied away. His friends managed to hang on until the rescue services arrived...
The incident was reportedly put down to "metal fatigue" by a spokesman for the lift company.
Reports from EarthTimes.org and The Denver Channel.
I can't personally recall an earlier example of metal fatigue on a chairlift causing this type of failure. Does anyone know which manufacturer built the lift concerned?
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Unless it's been replaced since, Ruthie's Lift was installed by Poma in 1997, and is a 600HP Double Detachable Chair.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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Hmmmmm.. I have some engineering friends who spend ages looking at the machine work of the big lifts. They will be shocked at this 'fatigue' after just 10 years...if that is the new build timescale. So am I.
Glad the exposure was just 10 feet
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The key points from the Earth Times report seem to be:
| Quote: |
The break was reportedly caused over time by stress from loading and takeoff vibration, said Aspen Skiing Co. spokesman Jeff Hanle.
He said an inspection showed the fracture did not occur at a piece of the metal that was welded. |
On the surface this is really quite something. If there were three skiers on there (assuming it's a quad) then it wasn't even fully loaded, unless the skiers were grossly overweight ... but the tolerances these chairs are designed to presumably allow for loading way in excess of anything actually anticipated.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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Ruthie's is a High Speed detachable Double. The carriers on Ruthie's are actually triple chairs, but Aspen Mountain only allows two people to load each carrier.
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Amazing - that's the first I've ever heard of a regulation like that. What's your source for that, veeeight?
If that's the case, then the chair was obviously overloaded by 50%, but the news reports don't mention this.
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| veeeight wrote: |
| Ruthie's is a High Speed detachable Double. The carriers on Ruthie's are actually triple chairs, but Aspen Mountain only allows two people to load each carrier. |
In that case, I wonder if the lift company was aware of an installation/design problem - which they hoped to overcome by running below designed capacity.
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I am sure there are metallogists and structural engineers among the snowheads who could tell us more.
It is noteworthy to point out that a metal if subjected to a stress reversal, from being pulled in tension and then immediately changed to being pushed into compression, then there is a final number of cycles before material will breaks due to "metal fatigue".
It is also noteworthy to point out that the number of stress reversals is primarily dependent on the magnitude of the stress. If a materal is used in a working state close to its structural capacity it will have a fatique life much shorter than one that operates comfortably at a lower working stress level.
To quote the chairlift fails due to metal fatique can mean the design has not been "generous".
Snowheads can be assured that there is good engineering practice and design standards that the chairlifts design must comply and a minimum safety factor must be provided. For example it is common to expect a cable is have a minimu safety factor of 5 to 10.
I always take an interest, by spending time to look in deatils while travelling, at the chairlifts I ride on and can confirm in general the modern designs in European resorts are quite generous with several lines of defence, as borne out by the current incident, that a failure of one component should not bring about a catastrophic situation. The chairlift in question has tilted but the passengers and the structure reamined safely suspended and completed the transfer.
Structural design nowaday is based on statistics known as limit state. In it there is a population of components expected to fail in practice! In British standard the common allowance is 5% for building structures. Therefore if a bolt snaps in a lift system in a line of 100 chairs (say) after operating 10 years it is totally normal to an engineer.
Although it is possible but pretty rare for a competent engineer to skim the safety factor hoping the system would be OK because it would not be used at full capacity all the time, as by default he must use the full capacity as the working condition. This is because the structural calculations will have to be prepared, checked, submitted to acredited agency for approval and the person and his company are legally accountable for any negligence. It is unusal for a designer to be subjected to commercial pressure to trim everying to the bare minimum.
Last edited by After all it is free  on Mon 16-04-07 11:23; edited 1 time in total
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You'll get to see more forums and be part of the best ski club on the net.
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achilles,
I thought that....
Quite an odd situation for the load though.... what is the point of a 3 chair lift with a load for 2..?
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Isn't 10 feet a bit close to the ground for a chair lift seat?
add 2 feet for the foot rest and that leaves a ground clearance of only 8ft. Easily reachable with a ski pole, a bit dangerous surely?
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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Maybe it happened close to the base station or top station. Luckily it didn't happen when he was 30ft above a rock.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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| boredsurfin wrote: |
Isn't 10 feet a bit close to the ground for a chair lift seat?
add 2 feet for the foot rest and that leaves a ground clearance of only 8ft. Easily reachable with a ski pole, a bit dangerous surely? |
That will vary wth the snow depth they had to dig a channel to allow the chairs to clear the top of the col du vent in serre chevalier a few years ago, the normal snow level is 15-20 feet below.
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pistemeister, Good point! 
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You know it makes sense.
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boredsurfin, Hard to get on the lift when it's higher than that though.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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| JT wrote: |
achilles,
I thought that....
Quite an odd situation for the load though.... what is the point of a 3 chair lift with a load for 2..? |
It's so the big McDonalds butts can fit - each passenger is allowed one and a half seats.
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Poster: A snowHead
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As a matter of interest does any  know how often safety checks are done on ski lifts and gondolas? I'd imagine it's costly and time consuming to check the structural integrity of cables etc.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| JT wrote: |
achilles,
I thought that....
Quite an odd situation for the load though.... what is the point of a 3 chair lift with a load for 2..? |
A while since I delved in this sort of stuff - but in general, I think that an increase in sustained load, superimposed on the fluctuating load which causes fatigue, will affect the fatigue life. So, if I am right, reducing the sustained load (by reducing the number of passengers permitted per chair) would increase the fatigue lives of crucial elements in the chairlift system.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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I think we have to be careful about the facts on this.
veeeight has made a point above, and Aspen Mountain are highly unlikely to know of this thread. The point of fact -about only two skiers allowed on a triple chair - needs corroboration.
Or does anyone else know this lift?
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You need to Login to know who's really who.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| boredsurfin wrote: |
Isn't 10 feet a bit close to the ground for a chair lift seat?
add 2 feet for the foot rest and that leaves a ground clearance of only 8ft. Easily reachable with a ski pole, a bit dangerous surely? |
Why do you find that dangerous?
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| abc wrote: |
| boredsurfin wrote: |
Isn't 10 feet a bit close to the ground for a chair lift seat?
add 2 feet for the foot rest and that leaves a ground clearance of only 8ft. Easily reachable with a ski pole, a bit dangerous surely? |
Why do you find that dangerous? |
Only reachable with a ski pole if you lie on the seat, rest your shoulder on the foot rest and stick your arm and pole out.....
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If that genuinely is a fatigue failure, they will now have to replace every single one of those components on that lift, because they will all (by definition) fail in the next few years in the same way.
I would imagine the design is substantial enough to give a virtually infinite fatigue life. I suspect this failure is due to a manufacturing error, damage or corrosion. I wouldn't want to be in the designer's shoes if it turns out to be a fatigue failure!
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I wouldn't think Lift companies have a choice when they review and test load their kit. It will be stipulated that they must carry out checks per year, etc.a dnall sorts of certificates will be required. How well those checks are carried out by some countries is another thing. I wouldn't expect the U.S to be shoddy here, unlike some other countries ...............
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Metal fatigue on lifts happens all the time. They are inspected annually for this reason. Detachables, especially, tend to suffer from more fatigue than do traditional fixed-grip chairs.
No one is "at fault" here. In fact, the "victim" obviously isn't concerned, so why should anyone else be? Seems like another episode of the "blame game" that's completely inappropriate. Stuff happens. Life isn't perfect, and neither are devices or materials. Yeah, I'm an engineer. Perhaps that's why I find this so silly. Regardless, it's not the least bit surprising that out of the millions of chairlifts that were loaded this season that one or two or even a few dozen have experienced some issues. Most of the time, the lift maintenance team catches them before anything happens. And that's a good thing.
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| JT wrote: |
| I wouldn't expect the U.S to be shoddy here, unlike some other countries ............... |
In the US, this is a State responsibility, and in Colorado, annual inspections are required. All resorts I know do continual inspections, with annual thorough inspections of every chair done as a matter of course.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| ssh wrote: |
| ........the "victim" obviously isn't concerned, so why should anyone else be?........... |
Cos we don't want to fall off ourselves. 
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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ssh, as a former aviation maintenance engineer, I am apalled by your attitude to safety. In the aviation world, we accept there is a risk in flying. Even so, when there is an accident, there is an enquiry, so that lessons may be learned. And (though I note that you say no one was at fault in this case, based on what evidence I do not know) if there is blame is found in the aviation world, disciplinary action is considered.
The risks I choose to take as a skier are up to me. I take it for granted that I will arrive safely to my destination on a lift system. I regard lift systems as safe, because I expect high standards of design, installation, and maintenance. And because if an incident does occur, I take it for granted that there will be an enquiry to determine what went wrong, so that preventative measures can be taken in future. You may be content to put up with spilling milk continually, I do not like the idea of chairs falling off around the mountains. Nor, to be fair to them, will the lift company, I suspect.
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You know it makes sense.
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I read this thread earlier on and its certainly one of those I'm not sure I wished to have read - the trouble was ignoring the title!!
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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| Quote: |
| A man fell 10 feet when a chairlift on Aspen Mountain broke after he tilted the chair toward the ground because of metal fatigue, but was not hurt. |
AP apparently don't read Eats Shoots and Leaves threads.
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Poster: A snowHead
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ssh, what sort of engineer are you? What do you mean "metal fatigue on lifts happens all the time"?? Do you mean corrosion or stress related fatigue failure? Two very different things. Fatigue failure implies that the design safety factor was too low. Highly unlikely. Corrosion implies inadequate maintenance and inspection.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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I have suferred a total lift failure, along with my fellow snowhead II
Sounds funny but many could have been killed......................................if we hadn't been the only ones on the T bar when the cable snapped
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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uktrailmonster, my engineering degree is in electrical engineering, but my studies have ranged wider than those topics.
Fatigue failure that I have seen and discussed with lift maintenance personnel has been stress-related, not corrosion. Some were in complex mechanical components, especially the grip subsystems on detachable lifts. I just recently read a report of a similar discovery at a different Colorado ski resort that was found by an experienced lift maintenance supervisor before it became a problem. There are other issues that are also quite routine (such as stresses on the conveyor chain and master links on the verge of failure). Lifts are huge machines comprising many intricate yet massive components. It's more of a shock that they work at all rather than that there are occasional failures.
Frosty the Snowman, frightening!  I'm glad you're OK...
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ssh, well my degree is in mechanical engineering, which is a lot more relevant to this discussion. Stress related fatigue failures are down to poor design or failure to replace limited life components at the correct service interval. I work in F1 where we walk a very thin line when it comes to fatigue life of safety critical components.
If, as reported, this metal support simply broke due to the stress of normal loading over time, they have a serious problem on their hands. It would mean that all the chairs are due to fail in exactly the same way from the same fatigue loading. It just doesn't make any sense, unless the failure was due to something else or someone seriously messed up the design. They're asking for trouble putting out a statement like that!
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| Quote: |
I work in F1 where we walk a very thin line when it comes to fatigue life of safety critical components
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And yet I have seen numerous examples of "lash together" jobs in F1 too! 
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I can corroborate Veeeight's statements; I remember quite clearly, the last time I skied at Ajax (around 2002), thinking "these chairs are wide enough for three, yet they're loading this lift as a double".
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uktrailmonster, I figured that you'd be an ME and call me to task for my EE. Regardless, I stand by my comments given my experience in ski resorts.
It is a result of normal stress over time. This is why they do complete inspections at the intervals that they do. The components do wear and stress and will fail if they are not repaired or replaced as they age. As I understand it, they do not replace every component on a regular interval but rather rely on the inspections. I assume (but haven't asked so don't know) that they have a maximum lifetime at which they will replace the components.
Do you mean to imply that the components should work flawlessly for an indeterminate period? (I know you don't mean that!) If not, though, it makes sense that there will be failure at some point if the components are not repaired/replaced. Some of the components, of course, will fail before the MTBF and perhaps before the expected time range.
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Does anyone know what actually broke? How was the part made? Any chance it could have been a faulty part (i.e. if it was a cast part then mayhaps it hadn't been cast too well)?
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You'll get to see more forums and be part of the best ski club on the net.
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Why did the chair have 3 people on it whenAspen limits the number to 2?
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Frosty the Snowman,
Weren't we behind you at that time...?? I felt the tremours....!!!! 
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