Horizontal (with sag) lifeline

[dylansdad]

I have been asked to review an in-place fall arrest system. It consists of a cable wrapped around a beam (at each end) and secured to itself. From end of cable to end of cable is approx. 200 feet. Notice there is an underdetermined sag (see pic.) as the cable makes its way parallel to the pipes and across the pipe rack beams. This is a pipe rack system undergoing demolition, where the workers (only 1 in this case) will be moving along the top of the pipe with the tie-off below his feet. Folks, I just don't feel right about this, with so many unknowns, and would appreciate any and all comments.

 

[rb1957]

what is the length of the cable ? is any more cable going to pay out if someone falls ? call that length L.

the point of the cable is to stop someone hitting the ground.

i'd model/analyze the problem as though the cable was two straight lines, from an anchor point to the person's attach point. there's another variable, the worker will be tethered to the cable with a sliding loop, yes? so if they fell they wouldn't start fixed to their starting point, but would slide "down-hill" along the cable (tending towards the middle of the cable), yes?

so you might work out how far they could fall, two straight lines L/2 from the anchor points. this sounds like it'll be the worst case, but see how far they'd fall if they were at a 1/4 point ... one line L/4, the other 3L/4.

then there are bunch of other things ... would they hit anything (other piping ?) in their fall ? how fast will they decelerate ? i'd expect the load in the cable to be less of a problem, but still something else to check.

 

[dylansdad]

Thank you rb for your reply. The overall cable length is unknown (could be determined). Workers attach to the cable with a body harness hook and "slide" along the cable, as they work on top of the pipe. My concern is that they might impact one of those pipe rack beams, being that the tie off is below their feet, before the fall arrest system is engaged. Does this not violate one the the OSHA requirements?

 

[rb1957]

i don't know OSHA but it sounds like a problem.

i guess the key issue is would they hurt themself ? (if they fell onto the rack beam)

is there an option ? is this the best that can be reasonably done ??

 

[ishvaaag]

Since there are transverse supports, maybe some clips joining cable and transverse beams, or creating some sort of handrail cable through clipped upwards supports, may reduce the hanging span. The idea of the main cable slipping in friction over all supports to arrest a fall is quite disgusting.

 

[dicksewerrat]

If there is more than one worker, they will hit each other as they slide along the cable. Call OSHA and/or the insurance carrier.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[dylansdad]

Thanks to all for your comments.
rb: I was told by the site safety professional that a similar system was used when the pipe was installed (I know don't make it right), and yes I have a concern with impacting the cross beams before any type of fall is arrested. I envision a type of beam clamp with (tall) stanchion with a lifeline height near the chest of the worker as he stands atop the pipe.

ishvaag: I am with you, quite disgusting.

dicksewerrat: I agree with the OSHA involvement.
Again, thanks all.

 

[SteveGregory]

You could load test it with a W12x50 beam 6' long (300 lbs) with a lug near the midspan. Set it on a stand about 4 feet above the beams (or the normal walkway elevation) and let it fall. This would get everyone's attention!

Is there a potential for a worker to fall and then swing and hit the structure below or would the worker fall straight down and just hang there until rescued?

 

[geoffdale]

You'll also need to check the horizontal load component as I expect it will be large.

 

[paddingtongreen]

A falling man could hit the cross beam, yes; but with that much slack, he could hit the floor if he misses or slides off the cross beam.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[berkshire]

dylansdad,
I do not think what you have is adequate, it would appear that there is too great a risk of hitting the framing underneath in a fall.
can rou raise the cable?
Here is a link about the osha reg, it is a little vague about a situation like that.

http://www.osha.gov/doc/outreachtraining/htmlfiles/subpartm.html

B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[dylansdad]

Thank you all for all the good comments. We are looking at other options. Thanks again.

 

[umrce]

I worked for a contractor before moving over to the consulting side to use my structural degree as I intended. I can tell you OSHA does have regulations that require the lifeline to be above the individual's waistline. If it cannot be done feasibly I believe you can put it at there feet though.

The photo overall looks like its not the best situation with everything below if they did fall. OSHA also has required safety factors and anchorage requirements for a lifeline system of this nature. I don't know what the scope of your work is, I briefly skimmed most of the posts above, but if I had been asked by a contractor verify the safety of the fall protection system I would reference OSHA for the safety factors but in my letter to the contractor very explicitly say that I did not review the fall protection system to be in accordance with OSHA requirements. Safety is the responsibility of the contractor not the structural engineer.

 

[MiketheEngineer]

There are a couple of very good companies that specialize in this stuff and sell off-the self kits.

Miller and Web-devicesUSA come to mind. They will help you all the way down the line...

 

[ToadJones]

If you add up the height from the D ring on the workers back to lifeline + the fall arrest distance of the lanyard, you'll likely be over 10-12 ft.
Funny how many places I've been in and used life lines that if I were to fall with a typical lanyard (in place of the proper retractable) you would fall 10-12' and land on equipment or worse, chemical baths.

 

[dylansdad]

Again, thanks to all viewing and replying. We are reviewing other options.

 

[MiketheEngineer]

OSAh really doesn't want you to fall more than 6'; - that is why overhead life lines are generally above your head!!