Rope Grabs

The strength, purpose and performance of rope grabs differ depending on the user and situations with which the actual unit is being used in. Many times we see strength ratings such as 2,500 lbs/11.5 kN, 5,400 lbs/24.5 kN or even 7,500 lbs/34 kN; yet the rope damage may actually occur as low as 2,000 lbs/9 kN. Are we measuring the strength of the grab itself or the unit capacity to carry a load? What is this load and is it a static pull or a dynamic catch? Grabs are not marked with a minimum breaking standard; there is no suitable test method for determining a valid or usable breaking strength.

Yes, rope grabs are strong… and there are many to choose from. Ascender/Back up types range from Gibbs Ascender, Petzl Shunt or Micro/Macro and the Rescucender, or PMI Progressor to the Mobile Fall Arrest type that includes the MIO, PMI Arrestor or the Yates/ISC Rocker. The latter type is also considered the self trailing style.

As mentioned earlier, the question of strength is not nearly as important as how the unit is used on the rope, the design of the over all system (with which the unit is being employed) and the type of load seen by the unit (impact force).

ANSI Z359.1 dictates that rope grabs must hold 11 kN/2,472 lbs without permanent damage to the rope (is there really such thing as non permanent damage?) There is no real standard for rope grabs being used for haul systems (though one could assume that holding a load without damage, could be applied to haul systems of like load). The technician must understand force vectors and what the rope grab is actually seeing (as the load travels the rope, through the raising system into the unit itself). Question is… do we normally do this?

The other question that could be asked is… is it fair to rate one unit equally well for multiple uses? I don’t know. Is one ANSI standard good enough to include uses for ascending, fall arrest/protection and hauling? I think the answer is no… For one, the self-trailing aspect of a grab is very important in the fall arrest/protection arena; not so in the complicated world of haul systems. Always bear in mind, rope diameter also plays a significant roll in the success of any rope grab.

When contemplating the use of any rope grab, consider the above situations, take a good look at the situations you’ll be using the unit in and think about possible failure points (within the system). Deem your system fallible; what part of this failure will the rope grab play? Single person rope access use, is quite different from that of a double person load… or is it? For more OSHA / ANSI information see this page.

Be educated about the gear you use and how you’re going to use it. Give us a call any time. 888-600-9116 or Contact US. We would love to help out and make sure you have the right gear for the job.