Recovery 101 including acronyms and definitions

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Originally Posted by mools

SF - Safety Factor

I dare not attempt a definition.

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SF is a magic number that is used to divide the MBS to get SWL. ;)

There may or may not be a "standard" SF for certain types of gear in certain situations, but there is generally no standard SF for all of the pieces involved in a load chain, for example in a winch recovery the SF for the tree sling, shackle, pulley, cable, winch, winch bar, bolts used to attach the winch bar will almost certainly all be different.

Some manufacturers do not tell you what the SF on a specific piece of gear is, whilst others do (either by exposing the SF or MBS).

Per previous post the SF for applications with people in, on or under the load are generally double what you might see for applications where people are not in direct contact / near the load chain.

Knowing the SWL but not the SF / MBS is interesting, but not helpful if you want to really know how safe the whole load chain is.

Any time gear is used for life support / older / degraded / not used in the manner intended the SF should be increased accordingly (reducing the effective SWL), as failing to do this risks breaking the gear well under the SWL printed on the tin.

Flame suit on! :twisted:

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Originally Posted by Tank

Quote: "MBL Minimum Breaking Load
is the minimum load required to make the piece of equipoment fail

GBS Guaranteed Braking Strain
Is this the same as MBL?".

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The difference is CYA ;)

I suspect they are calculated the same, but the manufacturers who use MBL are removing any doubt or claim that they are guaranteeing the quoted number is right, as "guarantee" is a very specifically defined legal term... :angel:

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Originally Posted by weeds

we will see how this rolls as recovery topics can get a bit heated......

this thread will kinda be like wikipedia where i will update post one once there is a concensus i.e. the number of thanks on each post

we need to keep it in laymans terms so that it is easy to read, understand and apply

we might start with acronyms

SWL - Safe Working Load
is the load that a piece of lifting equipment, lifting device or accessory can safely lift, suspend, or lower without fear of breaking. This should be mark on the equipment by the manufacturer. The SWL is calculated using a safety factor For example, 5:1 (5 to 1, or 1/5). An example of this would be a chain that has a MBL of 2000 lbs would have a SWL or WLL of 400 lbs if a safety factor of 5 (5 to 1) is used

WLL - Working Load Limit
which is the maximum working load designed by the manufacturer. The load represents a mass or force that is much less than that required to make the lifting equipment fail or yield, also known as the MBL The SWL is calculated using a safety factor For example, 5:1 (5 to 1, or 1/5). An example of this would be a chain that has a MBL of 2000 lbs would have a SWL or WLL of 400 lbs if a safety factor of 5 (5 to 1) is used

MBL Minimum Breaking Load
is the minimum load required to make the piece of equipoment fail

GBS Guaranteed Braking Strain
Is this the same as MBL?

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from the texts Im using

MBL can also be the Manufactured Breaking Load and its worked out off of a batch of items that are tested to destruction and the MBL is whatever the lowest failure point was. This is the number that you should be using to calculate out your SWL/WLL.

GBS is the highest of the same batch.

dont forget, on paper, when calculating WLL/SWL as soon as you have people in or on the gear being lifted/moved you are supposed to double the safety factor

Is there a difference between SWL and WLL? Yes.

The WLL is the maximum load that can be put onto and Item BEFORE the SWL is caculated and includes the Safety Factor.

Now to make it confusing......

Some companies have their gear marked with an SWL which is then fed through rigger maths to give you the WLL. Other companies will give you a WLL which is fed through rigger maths to give you an SWL. You can also use the provided SWL/WLL and come up with the Caclulated SWL/WLL

Better is some (most now) companies will give you a tag on the bit of kit that shows you all the permissible ways of using the bit of kit AND what the end result of the rigger maths is.

The current trend however is to have the WLL as the number that you use in rigger math to get to the Calculated WLL or SWL.

Hypothetical.

I have a Single leg sling that is 20 feet long and has a MBS (I prefer to use the MBS rather than the GBS) of 20000Kg. The standard safety factor for THIS particular type of sling is 5:1 this gives me a WLL of 4000KG. Basically this means that EYE to EYE on the sling I can safely put 4000KG of load

Now if I take that same sling and double it over then use it to lift up a round object I get a SWL of 8000KG

If I loop the sling back over itself to form a hitch I have to apply about a 25% reduction to the WLL to get the SWL so Im down to 3000kg

end hypothetical...

Heres a generic sling chart from a manufacturer that calculates out what you can do with various version of their slings
https://www.aulro.com/afvb/images/im...013/05/866.jpg

The WLL would be the vertical application and the SWL would be all the ones to the right of it. For a straight pull WLL=SWL

heres a sample of the kind of tag that would be on the sling itself
http://www.unirope.com/syntheticslin...ling_tag_c.jpg

This is usually what you find on a single leg chain or extension
https://www.aulro.com/afvb/images/im...013/05/867.jpg

in this case the WLL of the sling this is attached to needs to be used to calculate the SWL.

And this is whats usually on a premade chain sling.
https://www.aulro.com/afvb/images/im...013/05/868.jpg
all the gonkulating is done for you.

and heres a link to a page with piccy's that does a pretty good job of explaining it.

Rigging With Slings: Basic hitches, Working Load Limits, Sling angle, Reach

If the item you're using is something like a winch or a crane in effect the WLL and SWL are interchangable because they are the same value and what you name that value comes down to local legislation/manufactures preference and the whimsy of the local OH+S nut.

http://www.dotengineering.com.au/p7l..._Gantry_fs.jpghttps://www.aulro.com/afvb/images/im...013/05/869.jpg

other things you might see are
Maximum load (ML)
Capacity (CAP)
Rated To
Limit
Test load
Proof load


good luck.

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Originally Posted by Tank

So why don't they put 2 weights on recovery/rigging gear, SWL is the weight at which the item is subjected to Safely. Your statement makes out that something being dragged along the ground is half as heavy or that you can't be injured by an object on the ground.
Look go here
http://www.workcover.nsw.gov.au/formspublications/publications/Documents/rigging_guide_2005_005.pdf
and show me the item that backs up your statement, a shackle or a sling with SWL stamped on it doesn't know whether it's lifting something off the ground or not, it's all related to HOW much load is applied, Regards Frank.

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I'm just going by years of experience handed down since the Military started pulling stuff of Battlefields.
REME came up with the formulas for the use of Terminal Tackle, RAEME adopted it, I just worked with it and taught people how to use it in the recovery role and the lifting role.
Have a look here, page 52, right at the bottom. And have a look at the table, you will see that for recovery the SWL is X 2.

REME Recovery Manual not trying to be a smart ass, but that's how it is.

Interesting read, particularly the bit about recovery gear having a WLL but not a SWL. Thanks for the link.

The 2 x factor removal makes sense if the WLL was calculated with people in / on / under the load, and you are in a static load recovery situation where the only downside of breaking gear is broken gear.

Personally if people or property damage will result directly from recovery gear failure (and by that I mean cars rolling of cliffs and other such nastiness) I add another 2x or more to the stated factors.

Dynamic loading / recoveries is a whole other ball game...

That's why the rule of thumb is 45 Degrees being the cutoff point when the TPR, (Total Pull Required), is calculated out.

Seems Hymie and I learnt in the same place but we still used the recl on all recovery jobs regardless of the gradient. I do remember though that the gradient reistance formula changed to full cas. weight above 45 degrees.

I agree that gear has, but not necessarily should have, a different SF for different applications. The same risks apply weather gear is carrying people or just materials. Should it fall the variables are how far [and so quantity of damage], direction of fall and associated spread of materials, subsequent potential of damage to other objects and structures and potential for injury/death. SF should assume worst case scenario, that would result in potential for death or injury. The flip side is that it would result [pending everyone following the rules] in requiring recovery gear that would be massively oversized.

Which is why for an un-suspended load I think there is room for an alteration of the safety factor. But there should be no such thing as a safety factor of 1. This would just result in people self assessing a non need for safety and using devices at the limit of their strength. Similar to what I've seen when the safety factor is displayed and what it is known. If the device is rated to 2000kg and 5:1, the device is simply treated as a 10,000kg object.

Devices should be marked at their factored rated stength. Documentation should note detail such as MBS, SF etc but this info should not be marked on the gear, those that would use stuff to it's absolute limit are probably most likely not to read the book either.


Acronym.
AFD: Absolute ****in Dickhead; Someone who uses [insert name of recover gear here] in a way that I don't like and cannot justfy reasonably why.

I.E. If Tank or Hymee were to do something I didn't like they'd [and fairly and reasonably] explain why and I would probably defer to them [especially if made sense] but I'd hope that there would be two way communication and I could give & ask opinion and feedback on my thoughts of doing it differently.

Try doing this with (and generalising here) Toyota, Nissan etc but especially Rodeo/Hilux drivers. Jeeps seem to be ok.

My point is that as the GBS/MBS/???, changes downward (diminshes) from the first use, so it is impossible to know what the GBS etc. is after say 3 months hard use, is it now 1/2 of what it was or has it only lost 5% of it's capacity, only way to tell is break it in a Lab test.
That's why SF's are used for different work situations and onlySWL/WLL's should be used as the max. weight lifted or pulled, no other method is safe, Regards Frank.

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Originally Posted by clubagreenie

Acronym.
AFD: Absolute ****in Dickhead; Someone who uses [insert name of recover gear here] in a way that I don't like and cannot justfy reasonably why.

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lol nice catch.

One of my pet hates is people standing way too close to recoveries / winching, or being in the "line of fire" if something lets go.

Particularly when you watch spectators at comps on a certain 4wd tv show :angel: