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sbruel
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Cable Strength for Horizontal Lifeline

04/02/2012 11:58 PM

I want to use 3/8 inch steel cable (specs in link) to span between 2-3 roof anchors for me and my roofers: the average roof is about 38-45 feet long. I will be creating a horizontal lifeline by which my guys harness in and then clip onto the horizontal steel cable with safety ropes for construction available from Homedepot (link for safety rope). Say the farthest span for the average roof is 16-18 feet from the eave to the ridge (top to bottom). So if the heaviest guy is 250 pounds, which is me, how much force would me falling 18 feet put on the cable, and could the cable handle it? What is the most amount of people I could put on said cable safely imagining a worst case scenario of everyone falling the max distance simultaneously.

I was watching some competitors shoveling the roof next to us last year with this system and I thought this is the best way to get the most mobility because you are often constrained by having a fixed anchor point instead of a span: I looked online didn't really like what I saw and thought wow cable in a horizontal lifeline, measuring 60 feet, in a 5 gallon bucket for $650 sounds like a rip off.

Thanks for your help,

Joe Roofer aka Sam

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Sapper
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#1

Re: Cable Strength for Horizontal Lifeline

04/03/2012 12:38 AM

Sam,

I wouldn't take shortcuts with the static line if I was you.

The cable used for static lines is made and batch tested to meet certain loading conditions. The cheap stuff you are looking at probably doesn't meet those conditions.

I'm not sure of US regs, but in general no more that two (2) should be on the same static line at any given time, is there is a fall you would over load it and it would fail.

Also spans should not be any longer that 5meters or 15 feet.

I would also check the post ratings as well.

Regards,
Sapper

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durtieduck
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#2

Re: Cable Strength for Horizontal Lifeline

04/03/2012 1:40 AM

you're motive as to changing the safety lines seems self-severing at best. consider safety first then modify the system to suit your needs.
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SolarEagle
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#3

Re: Cable Strength for Horizontal Lifeline

04/03/2012 1:32 PM

Sounds good as far as it goes...I wouldn't worry about the 3/8" stainless line, and the amount of weight support will be dependent on your anchoring, generally speaking 3 anchors for 4 guys....The only other thing is the wear of the sliding parts and line...I've had this problem in the past and used rollers, but I don't know about regulations for this application...

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passingtongreen
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#4

Re: Cable Strength for Horizontal Lifeline

04/03/2012 7:12 PM

There is a question in my mind, does Joe Roofer want something that may or may not work, but looks like it would work, or does he want to be OSHA compliant. The difficulty is that he has opened the door, he has shown that he is aware of the need, and, should there be an accident, and should the assembly be less than OSHA compliant at the time, a ton of bricks could fall on Joe Roofer.

Scroll down to 1926.502(d) at

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10758

You can eyeball a system, but you are not likely to end up with a compliant system. Little things get in the way, for example, snaphooks and Dee-rings proofed to 3600lbs as required by:

1926.502(d)(4)Dee-rings and snaphooks shall be proof-tested to a minimum tensile load of 3,600 pounds (16 kN) without cracking, breaking, or taking permanent deformation.

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Sapper
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#5
In reply to #4

Re: Cable Strength for Horizontal Lifeline

04/03/2012 9:37 PM

GA...

Being Down Under, I wasn't sure of the local standards, so I had to be generalistic with my response.

He needs to ensure the system installed is compliant and that the equipmentent he uses with it is compliant.

If not and there is an incident or accident, he would deserve any bricks falling his way, however, anyone he takes with him would take him (or whats left) to the cleaners.

Either do it safe and right....or Don't do it!!

Regards,
Sapper.

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passingtongreen
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#6
In reply to #5

Re: Cable Strength for Horizontal Lifeline

04/03/2012 9:49 PM

Thanks, something I learned in this life, don't ask questions unless you are prepared for expensive answers.

I wonder whenever I see you post, I did my two for the queen as a sapper in the Royal Engineers so I wonder if you might also have been one.

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Sapper
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#7
In reply to #6

Re: Cable Strength for Horizontal Lifeline

04/03/2012 10:16 PM

Yes... Was a sapper in Royal Australian Engineers (5CER) for 6 Years as a reservist.

Good Fun, Great Experience.

Regards,
Sapper

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leveles
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#8

Re: Cable Strength for Horizontal Lifeline

04/04/2012 12:00 AM

You are almost wrong, asking here. What you need is specialized mountain rock climber techniques and equipment. One thing for sure: the rope used have to have plenty of yield. A nonyielding steel cable snaps a falling man's back.

Go to the real professionals for help.
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Sapper
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#9
In reply to #8

Re: Cable Strength for Horizontal Lifeline

04/04/2012 1:03 AM

Yes & No...

While Height Safety equipment has it origins in Climbing equipment there are many differences between climbing and building environments.

OH&S compliant equipment has to meet different standards and capabilities to those applicable to climbing.

The Steal line the OP is refering to is the Static line or anchor line to which he would attach the fall arrest device, this is what would decelerate the person that may fall.

You are correct that if he use a steal cable to attach to the achor point or static line the shock at the end of the fall would be nearly as devistating as hitting the ground.

Regards,
Sapper

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Gene Hayes
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#10

Re: Cable Strength for Horizontal Lifeline

04/04/2012 2:59 AM

I spend many hours in a fall arrest harness working from the bucket on a hydraulic boom. My safety line is 5 feet long and will stretch to almost 8 feet if I should fall. Even with this margin of safety, I am warned by the manual of the chance of severe injury.

The maximum SAFE WORKING LOAD is 10% of breaking strength. So, let's do a quick and dirty analysis of your situation: If your static line is 45 feet long and your 250 pounds deflects(without even falling) the center of the static line , say 2.25 feet, the tension on the static line is already 1250 pounds which exceeds 10% of 12000 pounds (breaking strength of your 3/8" stainless steel cable). I honestly doubt the cable would break even if you did fall 18 feet, but I doubt that your roof anchors would hold under those conditions. The roof anchors are designed for a load perpendicular to your static line and they will already be stressed in the wrong direction by the tension you put on your static line to keep it straight. So, what I picture is your spine and probably your neck as well snapping as you reach the end of your safety line, severe impact damage as you hit the ground when the anchors give way, and finally, all the cabling and anchor hardware piling on.

If you do decide to go through with this, please set-up a camera to document the action for the benefit of the next guy who lacks respect for proper safety.
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SolarEagle
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#11
In reply to #10

Re: Cable Strength for Horizontal Lifeline

04/04/2012 8:11 AM

The system cited is OSHA compliant...

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passingtongreen
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#12
In reply to #11

Re: Cable Strength for Horizontal Lifeline

04/04/2012 11:13 AM

Negative. The linked vertical assembly is compliant, but Joe wants to rig a horizontal wire and only picks out a wire, nothing on the anchors for said wire. If that wire is taut and someone falls perpendicular to it , the force in it can go very high.

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SolarEagle
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#15
In reply to #12

Re: Cable Strength for Horizontal Lifeline

04/04/2012 6:09 PM

The horizontal line is anchored at both ends and in between with pass thru supports ideally, the number of supports have to do with the roof length and weight of workers...but the basic setup is how it's done...and the harness and safety line is OSHA compliant...at least that is my understanding...

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K_Fry
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#16
In reply to #15

Re: Cable Strength for Horizontal Lifeline

04/05/2012 11:57 AM

The part that Joe Roofer seems to be wanting to avoid is the approved horizontal line -- which he describes as being $650. The link he provided shows the harness and individual fall arrest line, which are about $100 per person. The number and spacing of the intermediate supports can have a huge effect on the stresses at the ends. The anchoring system is not something that should be quasi-engineered in an online forum.

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Elroy
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#13

Re: Cable Strength for Horizontal Lifeline

04/04/2012 12:45 PM

In industry the maximum allowable drop allowed is I believe 6 feet. The 18 feet you talk about will likely injure you at least or possibly be fatal. The answer seems to be a device that works similar to a seatbelt retraction system in that at slow speed it allows payout but locks up at higher speeds. The attached website may have the information you require.

http://www.caisafety.com/applications/roof_hll.php

Good luck and stay safe. Elroy

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K_Fry
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#14

Re: Cable Strength for Horizontal Lifeline

04/04/2012 4:51 PM

The tension of a taut horizontal line with perpendicular pull can get extremely high - high enough to rip out whatever you are using to anchor the ends of the line. If you are using anything but the anchor that comes with the kit, you are putting yourself at risk for injury, liability, etc. You will need a PE to sign off on your installation, and should review it with local OSHA.

Use the anchor supplied with the kit in the way it was intended to be used.

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durtieduck (1); Elroy (1); Gene Hayes (1); K_Fry (2); leveles (1); passingtongreen (3); Sapper (4); SolarEagle (3)

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