Since Michael brought up one of the "sacred cow rules" (no metal on metal connections) that are frequently accepted without question by many people, what are some of the other "rules" you all have come across that make you wonder why?
How about this "rule" as an example?
If a piece of hardware is dropped more that 3 feet onto a hard surface it must be immediately taken out of service. I suspect this "rule" has been pushed heavily over the years by instructors who just so happen to sell rescue gear.
Garin Wallace Director of Manufacturing at Seattle Manufacturing Corporation (SMC) did a series of drop tests on aluminum carabiners and presented the results at the 2000 International Technical Rescue Symposium (ITRS). The goal of the testing was to determine what effect dropping a carabiner has on its long axis breaking strength.
He dropped 115 carabiners 27 feet and 54 feet onto asphalt and concrete. All the carabiners would have failed a visual inspection because of deep impact marks, gate tabs spread and blown out locking sleeves. When tested in the factory on the pull test machine the carabiners were found to have no significant loss of major axis strength!
The 6 control carabiners (not dropped) had an average breaking strength of 6242 lbs. The 30 carabiners dropped 27feet onto asphalt had an average breaking strength of 6579 lbs (yep, you read it right....they got stronger). The 29 carabiners dropped 27 feet onto concrete had an average breaking strength of 6587 lbs (again, stronger than the control group). The 29 carabiners dropped 54 feet onto asphalt had an average breaking strength of 6515 lbs and the 27 carabiners dropped 54 feet onto concrete had an average breaking strength of 6489 lbs.
The conclusion: Their carabiners were a lot stronger than they ever gave them credit for. They obviously do not recommend dropping any carabiner 54 feet onto concrete and keeping it in service. Their advice was to inspect any piece of hardware dropped from height. If it passes visual inspection (no sign of damage) then it MIGHT be ok to keep in service. The old "rule" here is....if in doubt, throw it out.
Now, let's hear some more "rules" and see if we can't debunk some myths and learn from the process. If any of you want to further your rope rescue knowledge I strongly urge you to attend the ITRS symposiums. They are absolutely eye opening.
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04-30-2013, 02:14 PM #1
- Join Date
- Oct 2002
- Port Allen, LA
05-02-2013, 03:03 PM #2
How about a system safety factor (SSF) of 15:1
05-03-2013, 10:50 AM #3
- Join Date
- Oct 2002
- Port Allen, LA
The 15:1 ratio may be an ideal number but it will seldom be achieved in real life. If you use the old information for 1 and 2-person loads of 300 and 600 lbs then a 1-person rope must have a minimum breaking strength of 4500 lbs and a 2-person rope must have a minimum breaking strength of 9000 lbs. Note: These weights have changed in the ANSI Fall Protection Standard (which is a user document) to the following definition: The capacity of a one-person rescue system shall range from 130 to 310 pounds (59 to 140 kg). The capacity of a two-person rescue system shall range from 130 to 620 ponds (59 to 280 kg). The maximum and minimum rated working loads for each system component shall encompass the capacity range of the assembled system.
If you tie a knot in a rope it reduces the strength (how much is another "rule" for discussion) of the rope. If the rope is wet it loses strength depending on the material of construction (yet another "rule" for later discussion). If the rope is new or used, clean or dirty, natural fiber or synthetic fiber, a slow steady pull or a shock load, it all affects the breaking strength of the rope.
But the rope is just one component of the rescue system. We also have to look at our anchor straps, connectors, progress capture devices, lowering devices, raising systems, patient packaging equipment, rescue harnesses, litter bridles, etc., etc., etc. Many time our system safety factor is much closer to 10:1 rather than 15:1 until we look at litter strengths. A stainless steel basket litter, from many manufacturers, have a rated strength of 2500 lbs which meets the 1-person load but not the 2-person load, although I think it would be a real challenge to try to pack a 630 lb patient in one. Some OPS litters (OPS = orange plastic stretcher) have a rated strength of only 600 lbs.
Ultimately, it will come down to the authority having jurisdiction (AHJ). I know many rescue teams that use a 10:1 SSF. I also know many mountain rescue teams that are comfortable with a 4:1 SSF and work safely with that. OSHA, in part of its fall protection standard accepts a 2:1 SSF under some conditions. In general, a higher SSF = heavier gear. How far do you have to transport all the gear you need to the rescue location? Can you transport all that weight by vehicle or will you have to pack it in a few miles on your back? All of this must be considered when determining what an acceptable SSF is for your particular team.
I'd be interested in hearing others thoughts.
05-04-2013, 07:31 PM #4
- Join Date
- Oct 2006
I have never heard of the no metal on metal connection "rule". Could you clarify? It can't mean what I think it means.
EDIT: Disregard. Got my answer when I found the thread "Metal on Metal".
Last edited by DFDMAXX; 05-04-2013 at 07:39 PM.We do not rise to the occasion. We fall back to our level of training.
05-05-2013, 11:18 AM #5
USAR TF Rescue Specialist
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