breaking away
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Chain Saw Lanyard Safety
Kevin Schieck
ISA Certified Arborist
ON-1362A
October 2010
For the lanyard shown the SWL of the weakest point is the swivel dog leash snap at 50 lbs.
For the lanyard shown the MBS of the weakest point is the swivel dog leash snap at 500 lbs.
The numbers clearly show that the SWL of the lanyard is well under the 200 lbs. threshold for a breaking point. So it seems like a safe choice. However the SWL is just a recommended safety guide line to follow. The weakest MBS is actually the weakest point in the lanyard.
As this paper shows easily, commonly, cheap made lanyard can exceed the 200 lbs. threshold.
*Note:
Some dog leash snaps have varying SWL depending on the manufactures safety factors but they are often based off the same MBS.
For example the Vermeer swivel dog leash snap has a 10:1 safety factor. Vermeer’s has a 500 lbs. MBS and a 50 lbs. SWL. So the SWL is 1/10th of the snaps MBS.
Compared to a similar swivel dog leash snap from a local hardware store has a 150 lbs. SWL. Still having a 500 lbs. MBS it makes it a 3:1 safety factor. So the snap is 1/3rd of the snaps MBS.
*Definitions:
SWL (Safe Working Load)
MBS (Maximum Breaking Strength)
W.W. Grainger Inc. 1994 - 2010. www.Grainger.com, Accessed October 18th 2010.
1/4” yellow polypropylene, twisted, 3- strand, SWL 113 lbs., MBS 1250 lbs.
3/8” yellow polypropylene, twisted, 3- strand, SWL 244 lbs., MBS 2440 lbs.
1/2” yellow polypropylene, twisted, 3- strand, SWL 420 lbs., MBS 3780 lbs.
All 3 above ropes conform to cordage institute standards.
Vermeer, Sherrill Tree, 2010 Arborist Supply Master Catalogue.
Swivel dog leash snap, bronze, MBS 500 lbs., SWL 50 lbs. (Pg. 65)
A spliced rope termination retains around 90% of a ropes strength. (Pg. 8)
90% of 1/4” yellow polypropylene, twisted, 3- strand,
SWL 101.7 lbs, (113 x 0.9= 101.7), MBS 1125 lbs. (1250 x 0.9= 1125)
90% of 3/8” yellow polypropylene, twisted, 3- strand,
SWL 219.6 lbs. (244 x 0.9 = 219.6), MBS 2196 lbs. (2440 x 0.9= 2196)
90% of 1/2” yellow polypropylene, twisted, 3- strand,
SWL 378 lbs. (420 x 0.9= 378), MBS 3402 lbs (3780 x 0.9= 3402)
Chain Saw Lanyard Safety
Kevin Schieck
ISA Certified Arborist
ON-1362A
October 2010
For the lanyard shown the SWL of the weakest point is the swivel dog leash snap at 50 lbs.
For the lanyard shown the MBS of the weakest point is the swivel dog leash snap at 500 lbs.
The numbers clearly show that the SWL of the lanyard is well under the 200 lbs. threshold for a breaking point. So it seems like a safe choice. However the SWL is just a recommended safety guide line to follow. The weakest MBS is actually the weakest point in the lanyard.
As this paper shows easily, commonly, cheap made lanyard can exceed the 200 lbs. threshold.
*Note:
Some dog leash snaps have varying SWL depending on the manufactures safety factors but they are often based off the same MBS.
For example the Vermeer swivel dog leash snap has a 10:1 safety factor. Vermeer’s has a 500 lbs. MBS and a 50 lbs. SWL. So the SWL is 1/10th of the snaps MBS.
Compared to a similar swivel dog leash snap from a local hardware store has a 150 lbs. SWL. Still having a 500 lbs. MBS it makes it a 3:1 safety factor. So the snap is 1/3rd of the snaps MBS.
*Definitions:
SWL (Safe Working Load)
MBS (Maximum Breaking Strength)
W.W. Grainger Inc. 1994 - 2010. www.Grainger.com, Accessed October 18th 2010.
1/4” yellow polypropylene, twisted, 3- strand, SWL 113 lbs., MBS 1250 lbs.
3/8” yellow polypropylene, twisted, 3- strand, SWL 244 lbs., MBS 2440 lbs.
1/2” yellow polypropylene, twisted, 3- strand, SWL 420 lbs., MBS 3780 lbs.
All 3 above ropes conform to cordage institute standards.
Vermeer, Sherrill Tree, 2010 Arborist Supply Master Catalogue.
Swivel dog leash snap, bronze, MBS 500 lbs., SWL 50 lbs. (Pg. 65)
A spliced rope termination retains around 90% of a ropes strength. (Pg. 8)
90% of 1/4” yellow polypropylene, twisted, 3- strand,
SWL 101.7 lbs, (113 x 0.9= 101.7), MBS 1125 lbs. (1250 x 0.9= 1125)
90% of 3/8” yellow polypropylene, twisted, 3- strand,
SWL 219.6 lbs. (244 x 0.9 = 219.6), MBS 2196 lbs. (2440 x 0.9= 2196)
90% of 1/2” yellow polypropylene, twisted, 3- strand,
SWL 378 lbs. (420 x 0.9= 378), MBS 3402 lbs (3780 x 0.9= 3402)
Ok the results are in:
As i thought the break of the system was low due to the SWL on the snap , which was rated at 150lbs. the snap failed at 700 and 640 lbs. We then removed the broken snap and broke just the rope and its splice which broke at 2650 and 2500. the rope failed at the splice. The rope had a little stretch as it was pulled
Thanks to Todd for the testing
As i thought the break of the system was low due to the SWL on the snap , which was rated at 150lbs. the snap failed at 700 and 640 lbs. We then removed the broken snap and broke just the rope and its splice which broke at 2650 and 2500. the rope failed at the splice. The rope had a little stretch as it was pulled
Thanks to Todd for the testing
