Fall Protection 1

[BSVBD]

I've reviewed the 2014 Eng-Tips post entitled "OSHA Fall Arrest System".

There is apparent debate, indecision and, unless I do not understand, no apparent credible conclusion regarding what load must be applied to the structure supporting Fall Protection "Systems".

Lanyards... 5,000 LBS.
Self-retracting lifelines and lanyards... 3,000 LBS.
D-rings, snaphooks and carabiners... 5,000 LBS proof tested at 3,600 LBS.
Anchorages... 5,000 LBS.
Travel Restraint Lines... 5,000 LBS.
(MAF) Maximum Arresting Force on employee = 1,800 LBS.
Initial Arresting Force... 2,000 LBS.
Subsequent Arresting Force... 1,000 LBS.

The arresting forces seem to be the (reasonable) relevant load(s) to apply to the structure.

All of our time is valuable. I will contact OSHA and local and state reviewers when and if permissible. Until then, has anyone contacted any legal authority for such conclusion or advice?

Other thoughts?

Thank you!

 

[jayrod12]

No, you design the building for the anchorage force. 5000lbs.

 

[TehMightyEngineer]

Agreed, design to 5,000 lbs unless you have very careful control over the types of fall protection equipment used.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL, CO) Structural Engineer (IL, HI)

 

[JStephen]

OSHA has updated their standards since 2014, so first thing is to go visit the OSHA website and look up the current rules.

 

[dhengr]

BSVBD:
Actually read the OSHA regs. They can be found on the internet. Often, it is kinda tough reading, pretty convoluted and it often seems difficult to follow and kinda contradictory. But, it gives you a pretty good foundation/understanding of the situation from their perspective. Then, contact the local OSHA office and talk with them about what they want (will accept) w.r.t. your various details. After all, it all depends upon their interpretation of the regs., so you might just as well know what their thinking is. There just isn’t real much sense in getting too far into your design and detailing until you have a fairly good idea what they consider acceptable, and it is much easier to come to some meeting of the minds at a prelim. design (planning) stage than when they disagree and it is already cast in place. For the most part, they have become more helpful to engineers and designers when approached at the early stages of the design. This approach to how they interact has come down from above and is working pretty well So, find one you can talk to, in that office, and have a little discussion about the various details. What’s good, what’s not so good, their suggested improvements, loads, etc.

You will find that the 5000lbs. is a catch-all minimum, for any/all connections which are not engineered and designed as safety connections. I believe that’s an ultimate strength and that connection can fail at 5001lbs. Be careful for all of the possible directions of loading, etc. But, as mentioned above you should probably design for that when you don’t have much control over how it will be used or what safety equipment will be used and connected to it. The lower loads are with different FoS, at different locations in the whole system, and for different types of safety equipment, nearer the worker, which absorb a good deal of the fall energy, etc. They do allow well engineered connections and systems lower than 5000lbs. when supporting data and some control over their use justify same. Note that a wire rope btwn. two 5000lb. connections, and supporting a perpendicular load at mid span can exert more than 5000lbs. on the connections.

 

[BSVBD]

dhengr...

I did read OSHA 1910.140. That's how I came up the criteria in the OP, despite the corresponding similarities with the 2014 Eng-tips post.

Yes, it IS a challenge to follow, and, yes, it IS more guidance and helpful than not.

Thank you!

 

[darthsoilsguy2]

I would bet that in the market there are a bunch of OSHA field inspectors who do not understand the nuance beyond 5000 lbs. When i've rated anchor points on existing structure, it started with a routine OSHA inspection of a manufacturing facility. The facility manager can argue the finer points on their own time, but i don't want to get in the middle of it unless i can rate 5-kips and walk away.

 

[JLNJ]

A 5000# service load is nice if you can get it, but is probably unnecessary. It will kill a lot of structures and cost your clients $$.

I read OSHA such that I start with a service load of 1800# with a load factor of 2.

 

[JoshH726]

ASCE 7-16 now has a fall arrest live load of 3,100 (ASD). Or 3,100 x 1.6 = 5,000 lbs (SD).

 

[human909]

A 5000# service load is nice if you can get it, but is probably unnecessary.

I'm not sure I like that attitude. Are you somebody who regularly works at heights or just somebody who says near enough is good enough for somebody's safety? Oh and we aren't talking about service loads when we are talking about 5000lb ratings.

It will kill a lot of structures and cost your clients $$.

Surely the bigger concern is killing a user of the equipment.

I'm not abreast with USA OHSA requirements here but they aren't too dissimilar across the world. Generally minimum breaking strengths are in the order of 22kn (5000lb). And energy absorbtion devices for personell often AIM to limit forces to 6kn-10kN depending on jurisdiction and circumstances. (~1300lb-2200lb)

But remember theses figures SHOULD NOT BE used to guide anchor strengths. These are design requirements for fall arrest systems if used in the correct manner. It is simple to exert much higher numbers on your anchorage points.


MAF) Maximum Arresting Force on employee = 1,800 LBS.
Initial Arresting Force... 2,000 LBS.
Subsequent Arresting Force... 1,000 LBS.
ALL THESE FIGURES SHOULD NOT BE USED FOR CALCULATING LOADS ON STRUCTURES. Their purpose is to have limits to prevent harm to the user, NOT as upper limits of potential forces on a structure.

 

[Lomarandil]

My understanding (having both designed and worked from several fall protection systems) matches Dhengr's post.

OSHA prescribed anchorage loads (5000#, or 2xMAF if the FP system is designed by an engineer) are described as ultimate loads. Interpretations of that vary, but I've commonly seen that interpreted as an already factored load, so either compared to the LRFD capacity (phi*Rn) or compared to the nominal capacity (Rn) without additional factors of safety (phi or omega).

JLNJ is correct that defaulting to 5000# can introduce a lot of cost. Some contractors I worked with specifically invested in fall protection with MAF of 900# (with the training and enforcement behind it), which made the cost savings of an engineered system pretty substantial. When a competent engineering professional is involved, I disagree with Human909's last point. Arresting force is not anchorage force, but can be a reasonable basis for calculating the anchorage force based on FP system response characteristics, intended use, and geometry.

For the sake of being complete, geometry makes horizontal life lines a different animal, and 5000# should not be considered a default anchorage load in those systems.





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just call me Lo.

 

[CANPRO]

Designing the system for 2xMAF is appropriate. Note that the anchorage force might actually be higher than 2xMAF or 5000lbs depending on the type of fall protection (horizontal life line for example).

Most personal fall arrest gear limits the MAF to 900 lbs. If a human body was subject to an arrest force of 1800 lbs they would be in very rough shape, although you can get gear with an MAF of 1800 lbs.

With that said, I only design to 2xMAF if I have some control over the system - i.e. I'm not just designing the anchor point, but providing a drawing/specifications on the entire system, including personal fall protection gear. If it is a one-off anchor that I have no control over, I design for failure load of 5000lbs. Typical roof anchors are often used for other purposes such as swing-stage tie-backs, which I think still require the 5000lbs design force.

 

[WinelandV]

For the sake of being complete, geometry makes horizontal life lines a different animal, and 5000# should not be considered a default anchorage load in those systems.

And that's why I don't like referring to the OSHA 5000# as the anchorage load. I always refer to it as just the load, and then follow the load path back into the building - if the tie-off point is in the middle of a beam, those beam shear connections don't need to be designed for 5 kips (though, it's not much load at that point and you'll probably get over 10 kips of shear capacity in a steel to steel connection anyway). But ESPECIALLY on horizontal life-lines, the end forces on the cable are HUGE, requiring ANCHORING forces much much greater than 5 kips.

 

[Lomarandil]

I suppose that depends on what you define as the anchorage point. (E.g. where the transition from fall protection system to structure occurs.)

----
just call me Lo.

 

[joshsgamb93]

@CANPRO and @human909 I understand how, for horizontal lifelines, the force translated to the anchor can be greater than 5000lbs due to the geometry; however, in a simple fall arrest system (full body harness, 6' energy absorbing lanyard with an average arresting force of 900lbs, I-beam clamp), I don't understand how the forces translated to the anchor can be greater than 5000lbs. How can the force on the anchor be greater (in this situationI stated above) be greater than the forces imposed stated by the equipment being used?

If OSHA states an MAF of 1800lbs, then why not use a safety factor of two (as a Qualified Person) as a design load for an anchor?

 

[CANPRO]

joshsgamb93, there is nothing wrong with designing a fall arrest anchor for 2xMAF as I stated above. My personal preference is to only do that if I have reasonable control over the entire fall protection system, i.e. I’m providing a usage drawing that shows how to use the system and what fall arrest gear is appropriate.

If the anchors are for a typical roof, they’ll likely be used for swing stage tie backs at some point, which need to be designed for 5000 lbs (where I practice anyway). Remember, you might design a “one-off” fall arrest anchor for a certain project, but once you leave, it just becomes an “anchor”....and most people will assume it is good for 5000 lbs.

 

[joshsgamb93]

CANPRO, I agree. Fall protection anchors that receive an impact load should be reanalyzed, while the rest of the fall protection equipment (harness, lanyard, connectors, etc...) shall be taken out of service.