The Problem with eyenuts as Anchor Points

Eye Nuts

There are 4 standards specifically written to cover fall protection anchor devices for working at height.

BS EN 795:2012; TS16451:2013; BS 8610:2017 and BS 7883:2019

BS EN 795:2012 replaces SANS 50795:1996 which is totally out of date and due to be replaced with the 2012 version at the SABS.   When eyenuts are used for fall protection they must comply with the relevant testing loads and procedures contained in the various standards.

Persons that select, install and test eyenuts and structural anchors must be competent to perform that work. Suitable training programmes are recognised by the Institute for Work at Height (IWH)   

Do other forms of training or registration make a person competent?  The short answer is NO.

  • Rope Access level 3 technicians (aka Rope Access Supervisors) are not competent to select, install and test anchor points if their qualification is only that of a level 3 Rope Access technician.  
  • Persons that have received training, even from the manufacturers, for the installation of anchor bolts, chemical anchors or expansion anchors are not competent to select, install and test anchor points for fall protection.
  • Registration with the SACPCMP as a Construction Health and Safety Officers does not confer competence to select install and test anchor points.
  • ECSA registered Lifting Machinery Inspectors (LMI) are not competent to select install and test anchor points.

All of these categories of persons, although properly trained for their respective activities can only be deemed competent in anchor point selection if they receive proper anchor point training which addresses at least the following topics:

  • Reaction loads and direction of applied loads
  • Test loads as per the standards
  • In-service loads
  • Resultant forces
  • Combined Shear and Tensile forces and limitations
  • Bending moments and bending stress
  • Allowable stress in anchor bolts / size/ mechanical grade.
  • Supporting structures /substrates/
  • Load testing vs pull-out testing
  • Minimum anchor size and embedded depth
  • Minimum edge distances and anchor spacings

The training programmes recognised by the IWH covers anchor points for fall prevention and fall arrest for use by one person only.

Any requirement or installation of anchors that exceed the criteria of type “A” anchor devices shall only be done after the design of such systems have been undertaken / approved by competent engineering professionals.

Safety issues with cast eyenuts for fall protection.

All anchor points (also known as “hangers”) need to be pulled up tight against a hard, load bearing surface such as normal concrete. Plaster covering (aka “rendering”) over a concrete surface is not hard nor is it load bearing. An anchor point fitted up against such plaster will cause the bolt to bend during a fall arrest situation. So, the correct installation requires that all the “soft” materials (plaster and non-load bearing waterproofing) be removed between the contact surface of the eyenut and the concrete.

Of critical importance is the correct orientation of the eyenut to ensure that it is not subjected to what is known as “cross-loading” or “lateral loading”. Eyenuts can only take their full rated load in a direction that is in line with the anchor bolt i.e. pure axial loading.

A reduced load can be applied along the perimeter of the ring but only in a direction that is in-line with the shape of the ring of the eyenut. If the eyenut is positioned so that the ring is in a vertical orientation, then the load on the eyenut needs to also be in that vertical direction.

The reduction in the safe working load is significant. The allowable load at right-angles (90 degrees) to the direction of the anchor bolt is only half of the safe working load stamped on the eyenut.    

“Cross loading” or “Lateral loading” is a situation where the load is not applied radially along the curvature of the ring part of the eyenut. This load is applied onto the side of the ring and is not permitted by the manufacturers.  

Figure 1. Eye nut loading limitations. Lateral loads are prohibited

Why is this load direction important?  

Once an anchor is chemically set into the concrete structure it can no longer be turned  and when the eyenut is then tightened onto the threads of the anchor, the chances of the orientation of the eyenut lining up in exactly the right direction of the applied load is almost nil. Imagine the face of an old-fashioned clock with the numbers 12 on top and the 6 at the bottom. Now assume that the applied load has to go vertically up from the 6   over the 12.   

When you tighten the eyenut, the ring must end up exactly in that direction! What are the chances of that happening? And if you then unwind the eyenut to get the orientation right, then the nut is loose and does not press tightly against the concrete. The anchor bolt can now bend under fall arrest loads and the nut might work itself completely loose with fatal results in a fall arrest or fall prevention situation.

Fitting normal sized flat washers between the eyenut and the concrete structure is also not the best solution as the outer diameter of standard washers is smaller than the diameter of the base of the eyenut thus leaving the anchor bolt unsupported and exposed to bending forces.    

The vast majority of existing eyenut installations use M12 anchor bolts. Look at the working loads for the top-of-the-range, high quality DIN standard eyenuts as listed in Figure 1 above. An M12 DIN 582 eyenut is limited to 340kG axial load. All fall arrest anchor devices should have a minimum working load capacity of 600kg so M12 eyenuts cannot be safely specified for fall arrest use!  

IMPORTANT NOTE:

The use of anchors set into brick walls, precast concrete block walls or materials other than in-situ cast concrete is beyond to scope of competency envisaged in the above-mentioned course and must be avoided. South African face bricks are not cast as solid units and have holes through them which makes them unsuitable as structural substrates (base materials) for fall arrest anchors.

In all cases where the base material is anything other than grade C20/25 in-situ cast concrete, you should refer the matter to a professional engineer that has experience in this field.

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