Design for fall protection
Design for fall protection
(OP)
I am designing a fall protection system for an existing (1960's) truck loading station at a chemical plant (see attached sketch). A person will be walking ontop of a tanker truck attached to an overhead monorail system. I am designing this for the OSHA 5000# requirement as a static force. Using ASD the existing rafter, bracing, column and anchor bolts are all overstressed.
I feel like I am too conservative on the design approach because the 5000# force is only going to be present for a short time, and after the fall you will just have the weight of the person plus any tools.
Has anyone else been involved with dsigning for fall protection? How have you considered the 5000# load?
I feel like I am too conservative on the design approach because the 5000# force is only going to be present for a short time, and after the fall you will just have the weight of the person plus any tools.
Has anyone else been involved with dsigning for fall protection? How have you considered the 5000# load?






RE: Design for fall protection
RE: Design for fall protection
RE: Design for fall protection
RE: Design for fall protection
RE: Design for fall protection
RE: Design for fall protection
Also, you can use lanyards that limit the force and design for that force rather than design for the 5,000 lbs- should be addressed in OSHA as well.
RE: Design for fall protection
RE: Design for fall protection
As far as members are concerned, OSHA does not say 5000#. So, I would design the members for the load recommended by the Lanyard Vendor - if I remember, it was something like 1900#.
I would like to see others respond, as to how they do it.
RE: Design for fall protection
Make sure that only one worker will be fastened to the monorail at a time.
BA
RE: Design for fall protection
RE: Design for fall protection
Many states reference the National OSHA which requires either the 5,000# requirement (without certification) or a factor of safety of 2.0 (with certification).
In the past, I have used the factor of safety of 2.0 requirement that is in OSHA and ANSI requirements. Per OSHA, the maximum arresting force (MAF) can not be larger than 900# when using a body belt or 1,800# when using a full-body harness. The MAF is the maximum force that will be imparted to both the user and the anchorage or lifeline.
With that information in mind, I typically design for 1,800# (assume full-body harness) with a factor of safety of 2.0. With the 2005 AISC spec, the factor of safety against yield for ASD is the omega factor. It maybe sound a bit convoluted, but I use the actual MAF and then determine what the maximum capacity ratio of the steel can be, assuming a factor of safety of 2.0, since the omega factor in flexure is typically 1.67.
In my opinion, you can either place the factor of safety on the load or the resisting elements, but I feel it is overly conservative to use a "breaking strength" load as JSA2 stated with an additional factor of safety per AISC or the governing design criteria.
Sorry for the lengthy rant, but I have had many discussions with other engineers in the past about this and I always marvel at how everyone has a different take on the design. I do wish that OSHA would rewrite these requirements to better clarify the intent of the regulation.
JWB
RE: Design for fall protection
Thanks for the contribution. Just for clarification, when I used the 5,000# load there was no safety factor associated with it. It truly was a breaking strength. In other words, the first element in the support system load path will physically break at 5,000#. I would even consider strain hardening of a ductile steel element to get to justify this 5,000# number.
RE: Design for fall protection
RE: Design for fall protection
For an engineered system use twice the MAF. MAFs vary based on the safety equipment being used and can be as low as 600 lbf
RE: Design for fall protection
I forgot about Ellis' book, which really helped me when I was first learning about fall protection. You are correct that MAFs do vary from vendor to vendor, I have seen 900# in many applications. In the end, MAF times 2.0 is much more efficient for design than using 5,000#. It is great to have other engineers sharing the same approach that I have been using.
JWB
RE: Design for fall protection
I just obtained a copy of the book from our construction department. Chapter 7 covers anchorages. Thanks for the tip.