Minimum Breaking Strength - am I the only one who is confused?

[ARLO]

The regs say that ropes used for life support must have a minimum breaking strength of 5,400 lbs. So, what exactly does that mean? The International Cordage Institute Testing Standards say that MBS is equal to 2 standard deviations less than the mean. On page 30 in "On Rope" they say that MBS is equal to 3 standard deviations less than the mean. And some manufacturers (e.g., Samson) only report MBS figures for spliced ropes, whereas others apparently report figures for unspliced ropes. And almost none of the arborist suppliers provide MBS values for the ropes they sell. They just provide estimates of average breaking strengths (ABS).

So, my question is, if manufacturers don't use the same test procedures and vendors don't report MBS values for ropes, how is an arborist supposed to know if a particular hitch cord or climbing rope meets the regs? If there are any experts on this topic on Treebuzz, I would love to hear from you.

 

[JeffGu]

Using a 10:1 safety factor, are you concerned that any of the ropes sold as climbing lines aren't going to hold you? That's a huge margin of safety. I can't imagine any rope on the market, sold as an arborist climb line, wouldn't meet the minimum MBS. I look at all the rating figures that I can find for the rope, and apply a 10:1 and a 15:1 safety factor to them, and look at the numbers. If any of them are under 250 lbs. I look for a different rope. I have no plans to put two people on a rope, but the numbers always seem to come out good enough to do that, in a pinch. Remember, the 15:1 numbers are ridiculously conservative.

I understand being confused about how the OEM arrived at their numbers, and why they don't test and publish the information in a standardized format that they all use, but I'm just saying that it's not likely there would be any surprises if they did. Their own insurance rates are incentive enough to make sure all of their rope products meet the requirements, but sometimes the marketing guys just can't get it through their thick skulls that customers who buy this stuff really do like to see the details, the technical info, the certifications and ratings... I wish the certification requirements also required that all of this info had to be in the product details description. That would make it real easy for those of us that love the fine print and details to pretend we're going strictly by the technical advantages instead of the cool color scheme.

I've never spent much time trying to figure out why they all publish the information differently, but I bet somebody on here has! I won't actually mention any names, but his initials are @monkeylove.

 

[monkeylove]

Lol, thanks @JeffGu . Any manufacturer is certainly welcome to explain it or disagree with me but....It simple terms they have no idea what to do with us. There are to many standards, to many countries and to many trades to have one governing body. The rock guys have a standard the deals with falls and impact and so on and usually climb on Dynamic rope. Now don't confuse their Dynamic with our Dynamic because that is whole other problem. We prefer ropes that generally have a whole lot less stretch no matter what the manufacturer calls them. Now to make life more interesting most trades that use ropes for humans, don't climb on them. They use them as backup in case you fall, and most require a fall arrest of some sort so the sudden stop that saved you from hitting the ground doesn't kill you with the shock load of suddenly stopping mid air. Damn it Jeff you got me ranting again. I'm stopping here.

I have to agree with Jeff, buy from a good manufacturer and trust they know what they are doing. In all honesty tree work has so many variables in gear alone that you could never make a standard that would cover every possible thing that could be done. The only almost certainty is that after it passed the break test, no one will ever use it the way the test was designed.

 

[ARLO]

I have to agree with Jeff, buy from a good manufacturer and trust they know what they are doing. In all honesty tree work has so many variables in gear alone that you could never make a standard that would cover every possible thing that could be done. The only almost certainty is that after it passed the break test, no one will ever use it the way the test was designed.[/QUOTE]

Thanks for reinforcing my frustration. I am not at all concerned about ropes breaking because I think the ropes that we get from our reputable suppliers are very safe. My frustration is over a standard that is evaluated differently by different manufacturers and that is rarely provided in supplier catalogs. This makes it pretty useless. All you can do is buy a good rope with an average breaking strength greater than 5,400 lbs and ASSUME that it meets the MBS safety standard as well.