Tech Tip: Answered SWL, WLL, MBS - ratings of Rapides and Climbing Gear

Question - Can someone explain the difference between safe working load and fall impact load? Or are they the same?

A good place to start is this post by Richard Delany at Rope Test Lab: Carabiner Specifications

--- which covers the subject of carabiner specs and what they mean in detail and very clearly.

WLL and SWL (working load limit and Safe Working Load) are two systems for rating hardware (and software) for industrial use. They apply to Rapid Links. It is a claim that under specific normal industrial lifting conditions, this item can be used (in a specific manner) for lifting a load up to the rated weight. If the WLL is 750 kg, and you need to lift your Lotus Europa Special (mass=740kg) out of the display case with a crane, you can use this item in the chain. IF your crane operator is a real crane operator and not your cousin Vinny who saw how to do it on YouTube.

Climbing gear is rated using an entirely different system. Manufacturers provide a Minimum Breaking Strength (MBS) which is the load that you can apply to the device without it breaking - though the load needs to be applied in exactly the way the item was tested.

For any specific item, the MBS can be calculated from the WLL or SWL by multiplying by the Safety Factor. The Safety factor takes account of what kind of loads are created on the item in reality when you lift your aged sportscar using a crane. But you would have to know the Safety Factor used for that specific item, which can vary. The lowest I have seen is 5X, and I am told some items might use 10X. The rapid links we were talking about use 5X, so they are 5 times stronger than the WLL stamped on the side.

The Fall Impact Load is the force generated by an object falling and then being caught by a rope, cable, lanyard, etc. More rigorously, we state a single number which is the highest force generated in the catch. This is a very difficult number to calculate, ... no, impossible is a better term. It is a hard number to measure, but it can be measured with proper equipment. If you are taking a fall of significant length, you want to be falling on a dynamic climbing rope, which has a carefully engineered stretch to it so that the Impact Load is minimized. Which helps things not break. Climbing rope designs are tested for the Impact Load they generate in a standardized test fall (a UIAA fall), which is about the worst fall one would expect (to survive) in the field.Thus when you buy a climbing rope, there is a number in its specifications that tell you what the rated Impact Force is on this rope, under extremely specific conditions, when new.

But in the real world, Fall Impact loads are difficult to get a handle on. There are calculators available to estimate the Impact Load, but you have to enter numbers into the calculator which you probably don't know. If I say the catch was made in 0.1m, I get one answer, but if I say 0.2m, the answer I get is probably half that. If it is a human being caught, the squishiness of the human is not accounted for. The human is modeled as a collection of steel weights... and some of us might have the delusion that that models us well, but I don't. The squishiness in short falls probably reduces the Impact load by 50%. (Avoiding defining what a short fall is).

If your fall impact load exceeds the MBS of the carabiner, it is likely to break. If your fall impact load exceeds 5X the WLL of the rapide, it is likely to break.

Tom

Been slow lately. This came up on another forum; thought folks might want to arm wrestle over it here:

Rapid Links

What you are looking for are Rapid Links (aka Rapides, Quick Links, Maillon Rapide, Links). Available in many styles and sizes. The cheap ones, as above, are junk, meaning, they have no brand name on them, and their quality varies widely... and they are not really made for life-safety applications. These no-brand rapides are often referred to as "Pacific Rim", and are available at Home Deport, Harbor Freight, etc... I recommend against using non-brand-name hardware for life safety applications.

Kelsey used RL/QL, so he uses the fancy kind that are both Rapid and Quick, at the same time!!!

I sell Rapides made by a French company with excellent quality control called Maillon Rapide. They come in many sizes, and the 7mm seems to be a good balance of weight vs. strength and working size. Some people use the 6mm (especially for explorations), but they are small enough that the fattest ropes people might take into canyons might get stuck in the pull. The 8mm size is good for high-use canyons, but they are heavy. Larger rapides are not only quite heavy, but also may be big enough to let a biner block slip through.

Galvanized Steel (carbon steel with a zinc coating) are what is normally used, and they normally last a long time. Canyons that have noxious chemicals in the water might destroy these quickly, but this is not too common. Quality stainless steel rapides are also available, but they cost about 5X as much.

It is good to carry two or three rapides as a standard part of your kit to replace worn rapides you find on anchors.

Very few canyoners include a torque wrench in their kit, though some bring a 6" adjustable wrench... well, okay, ONly me and a few former cavers. Rapides do not have "extra threads" so when they unscrew a bit (for instance when the rope is pulled through) they become very much weaker, and can open under load. This is especially true of the junky Pacific Rim links that may have bad machining in the first place, where 1 turn of the gate can un-close the threads.

The best way to avoid this problem is to inspect the rapides you come to on anchors and make sure they are closed, with zero threads showing. Replace if necessary, that is why you brought some along.

Maillon Rapides are available at climbing stores or online at my CayoneeringUSA store.

There are EVEN BETTER rapid links available, sold by climbing companies like Metolius and Camp, that are CE certified for PPE (life-safety) applications. My opinion is, these are the same rapid links I sell, but with additional quality control and you get a booklet explaining how to use them in 13 languages. They cost about twice as much.

Other shapes are available for specific applications, including for caving harnesses and paragliding. If you find these rigged in the field, get RID of them. Biner blocks can fall through them.

Aluminum rapides are available in limited sizes. They are 1/3 the weight, 3X the cost, and if used for rappelling anchors will wear out quickly. Not advised.

Hope this helps. TOM

As Tom stated, calculating maximum tension during a fall is almost an impossibility. We've done a lot of drop tests and found an old equation that has been used and passed on numerous times, then tweaked it slightly since the accepted equation is heavily weighted to fall factor. The equation is relying on the modulus of elasticity to be in the same ratio regardless of increased kinetic energy on longer falls. In other words they are saying: 1) that the extra fall distance also adds extra elasticity, and 2) that this addition of elasticity is relative to the additional kinetic force (thus cancelling each other out). While the first part of that statement is true, the second part is not - as empirical data proves when you actually start dropping stuff and measuring it.

So, through empirical data (with various static ropes, not dynamic) and slight equation tweaking this equation now matches realistic results better (You can download the calculator here: https://randallsadventure.com/sites/default/files/tension-calculator.xlsx.zip It's in a zip file but it is safe to download. There are still some issues with this one but it’s close. So, if it spits out 1800 pounds in force, your actual test may show that it ranges from 1500-1600 pounds. I’ve also found that two exact same ropes, both new from the factory, will have different elongation rates and this difference is enough to skew the results. Also, if you do not allow your test ropes time to relax after a test drop, that can skew the results in the same manner if you are doing a haul under tension and allow slack, then a drop, then that may alter the results compared to actual. So, the bottom line is there is no way to accurately calculate fall tensions based on manufacturer’s specs, or expect it to duplicate between two exact same ropes. Thus the reason no good equation exists I suppose. With that said, this calculator gets you close and while it’s not meant to be a tool used in the field, it can be used to teach rope systems and consequences of a screw-up.

Thanks Jeff...

Does this calculate the force generated by a solid steel weight falling H amount? or of a live human body falling H amount?

Tom

Solely using test weights and rescue dummies, which in itself skews the data from an actual live fall. With that said, the calculator is designed to be an estimation of forces to teach rope rescue students the consequence of a drop should an accident occur, such as a high directional failure or other “potentials” that could cause an increase of forces in a live system. So, shorter drops that produce a potentially high impact on both the rescuer (or patient), anchors and other components in the system. In the end, it’s almost impossible to predict the dynamic elongation of any rope with any absolute accuracy, or predict the absorption of energy of other components in the system (including the human body), thus making it impossible to predict the maximum tension in a system when a drop or fall occurs, but you can get a decent estimate.

You state the caveats well. Thank you.

Did you do tests with fully static ropes like my Imlay ropes? If you need samples, I can provide.

Tom

Yes, fully static ropes since that's what we use in rescue. Imlay rope continues to be used in both testing and the field applications, as well as Sterling HTP. These are the two main ropes I've been using to do drop testing. Also, it needs to be noted that most all of my tests are short drops up to fall factor 2 with no more than 8 feet of rope in play. Pretty amazing how fast that force goes up on very short drops on static rope.

The QLs (which isn't that many-I still prefer lighter hardware for seldom trotted canyons) I have were bought in climbing shops and rated to 2200 lbs. I don't remember the brand.

I do wonder though, how much is enough?

Has there even been a rapid link failure in a canyon or on a climb? I have never heard of one.

Of course we must be safe and not lax, but even though I know where where my rapid links came from, does anyone here actually check this on ever single canyoneering or climbing anchor that was placed by someone else? I admit that I do not. Does anyone do this? Maybe Tom does. Anyone else? Does anyone actually replace ever single one that you come across if you don't know where it came from? Please be honest.

I would assume that most high quality RL have at least a stamp on them, which is good to look for.

Although I look at the QL, most of the time when I inspect and anchor, I am more concerned with the sling material and chockstone/deadman than I am the QL.

Your standard for what constitutes "high quality" is a bit different than mine.

I think the point, Scott, is that it takes but a little effort and a small amount of treasure to carry reliable hardware into the canyon, rather than junk.

I agree and I got my RLs from a reputable climbing shop (rated 2600 lbs.).

I'm not asking about which RLs to buy or carry, but what I'm asking about is how people check the hardware left by others that is already in the canyon. How many people check the RLs and what do you look for? I'd assume any made specifically for climbing should at least have a stamp on it (with the manufacture)?

That's what I was asking.

I like the stainless Péguet Maillon Rapides that are built to the EN12275 standards and marked as such, but there are also others that are just as good.

To your point, Scott, there are a lot of hardware pieces being used around here that have no markings and some even appear homemade. When we find these we usually try to replace them. In fact, we are headed out this week to place a couple of new bolts at the request of a park manager, as well as replace a couple of bolts soon in a cave that are in pitiful shape and still being used.

I think it’s important that all of us always try to think of the next person coming through and make it as safe as possible for those who just take for granted that the anchor or gear is ok to use.

My apologies Scott, I thought my lecture on rapide markings was included in this thread. This one:

If I take a large paper clip and my micro-pen and write 2700 lbs on the Paper Clip, is it now a rated piece?

Of course not. This is pretty much what some manufacturers do, so buyer beware.

Stamping or laser-etching some numbers and letters onto an object does not make it a rated object. When you buy rapid links at Home Depot (or Harbor Freight) they may or may not have numbers and letter stamped on them; but they are unlikely to be certified to a standard or even have a manufacturers brand on them. Which means someone put some numbers on those rapides - and that is all it means.

Much of the life-safety equipment we use in canyoneering is certified to a standard and carries the CE mark (Conformité Européenne). This means that the design has met specific, rational strength and function criteria, and that it is manufactured in a facility that has a certified quality control process in place. You want stuff that your life depends on to meet this strict standard. But it is expensive, and not always necessary. (Certified rapid links are available in a couple of sizes, and available at some climbing stores under brand names Camp and Metolius (etc.)).

The next level of Quality is to buy a reputable brand name that has a certified quality system in place. The Rapides I sell are manufactured by Péguet Maillon Rapide made on the same machines and with the same materials as the Certified links they sell. My Imlay Canyon Gear ropes are not certified, but they are made in an ISO 9001 factory (a quality control certification). For my business, certifying my ropes would be expensive without adding value for the consumer - although it might open up selling to SAR operations that require certifications... but it is unclear that selling to those SAR groups would be either effective or a good idea.

The lowest level of Quality is "other". Low-quality rapid links may or may not have anything stamped on them, are unlikely to have a brand name, they might have a country of origin. Some even have "CE" stamped on them, which does not mean they conform to a European Standard - they SAY it means "China Export", wink wink nudge nudge... When these break, your survivors will be trying to sue China. Good luck with that.

Then again, Home Depot rapid links are made of steel, and steel is an easy to work with, strong material. And 8mm rapides from Home Depot are most likely just fine. Because even without good QC, they are likely to hold enough for our meager rappelling loads.

Story: I used to buy Rapides at Bolt and Nut Supply in Salt Lake City. Your basic "other" rapides. Using small ropes, we could use the 6mm size. I bought them there for a year or so, and was getting well-machined units. Then the next box I bought were real junk. The sleeve and body threads barely joined. We tested some and they were half the strength of the other 6mm rapides I was buying. I switched to buying from Peguet.

My own choices are as follows:
1. I SELL non-CE rapides from Peguet. The price is reasonable, the quality is excellent.
2. I purchase (from myself) the same, and use those in the field.
3. I inspect in-situ rapid links and generally use the ones in place unless they are jacked. The ones out there in the field are rarely Peguet ones, usually are "other" rapides, but also usually fairly large. If they are corroded or poorly functioning I remove and replace.

A large point of this thread is to provide information so canyoneers can make intelligent informed choices.

Tom

Just saying your RLs are rated 2600 lbs does not tell me much. Could you expand on that? What size are you buying, what brand, and what rating specifically WLL, MBS, just a number?

And: https://en.wikipedia.org/wiki/CE_marking

I'd have to check, but I'm in North Africa right now so can't check them.

I bought them at Gearheads in Moab if if my memory is right they were 2600 lbs WLL and 13,000 MBS. I'd have to check on the brand. I believe they were 1/2 inch, but I'd have to check. At least 3/8 for sure. I bought them to replace old RLs in high traffic canyons; in canyons that see almost no traffic, I'm still using my supply of Omega Pacific thick rap rings. I still have at least 100 of those left, but I don't use them in high traffic canyons.

I'm not really worried about either of those though. I'm more concerned with checking the QLs left by others in the canyons or on climbs. In places like the last rap of Mystery Canyon I remember a bunch of RL's chained together and and they could have been put there by multiple parties.

Sometime it's obvious when a QL needs to be replaced. Sometimes they are rusty and of a small diameter. Some of them are new and shiny though and those are harder to tell of what quality they are.

Sounds like you are using 10mm rapides, which can be had certified. It is possible to leave on anchors rapid links that are too big, through which biner blocks CAN pull. Please do not do this.

Tom

bump

bump