Fall Protection Monorail

[abuchman]

thread507-447086

I'm designing a monorail that will be used as a fall protection device over a train car. The owner wants the system to be designed for an occupancy of 2 people.

My understanding from reading OSHA is that each anchor point needs to be designed for 2 times the MAF, which for a full body harness would be 1,800 lbs. To me, this means that the factored load is 3,600 lbs (i.e. no other load factors applied).

My question is in regards to multiple occupancy. OSHA does not seem to land firmly on this issue. Should a system with 2 occupants assume that both occupants fall simultaneously (applied load of 7,200 lbs)? Or should it be a single occupant (applied load of 3,600 lbs) Or should the assumption be that one person has fallen and another is falling (3600 lbs + a static load)? 7,200 lbs seems excessive, but a single load of 3,600 lbs doesn't seem correct either. I'm looking for something like a multiple presence factor that exists in bridge design and I can't find it.

Also, the system will be need to be load tested. Should it be load tested to 2 times the MAF, or to the standard 125% of the MAF - 2,250 lbs. Similarly, should it be for 2 occupants at 2,250 lbs or one static load of 250 lbs and one load of 2,250 lbs.

Any input would be appreciated. Thanks!

 

[CANPRO]

In the CSA (Canadian) standards for a flexible horizontal lifelines, it says that it is statistically unlikely that you'll get the MAF from both users at the same time (after all, the MAF is only applied for a fraction of a second) , and does not need to be considered in design - EXCEPT if the circumstances make that scenario likely, i.e. workers are on a suspended platform that if failed, both would fall simultaneously.

 

[R Naples]

abuchman,

I can't pull up the passage at the moment, but all the HLL systems on the market have test data that shows that for multiple occupants, the system needs to be designed for 2 simultaneous falls + the additional dead loads from the occupants. In the case you describe, we would require harnesses and yoyo's or shock packs to bring the FAL to 900-lbs per occupant (or a design force of 1800 lbs per occupant). Then you should still apply standard load factors to the live loads.

For testing, in the past we had the contractor drop a 300# mass off the side of the building connected with a shockpack. If you are going to do a static test, then I agree that you should support the design force as a dead load - so 1800 lbs masses.

Good Luck!

 

[GC_Hopi]

I think the horizontal lifeline is left to engineering judgement see II.B.4 Link

Here is the quote from OSHA.

 

[BMart006]

In my opinion (and what I was taught) is that the static load of one user (usually 310 lbs in US) should be combined with the 1800 lbs MAF so that should one person fall, the system has sufficient reserve strength for the remaining user. It is possible that the rescue/recovery operation will partially involve the non-fallen user, so their safety needs to be protected even after the first fall. Of course then use a safety factor of two per OSHA. With that being said, if the fall of one user is likely to cause the fall of the other, simultaneous falls should be a design consideration. This is common in flexible HLLs since the displacement of the line during a fall will carry with it significant load (enough to knock over the other worker).
Finally and equally important, be sure to consider the rescue of the fallen worker be it additional strength in the monorail or a separate anchorage.

 

[abuchman]

Thanks for the input - all very helpful!