Testing of Energy Absorbing Coil Fall-Arrest Safety Devices

Testing of Energy Absorbing Coil Fall-Arrest Safety Devices

Case Study

The Test House was contacted by Safety Squared to assist with dynamic and static tests of energy absorbing coil fall-arrest safety devices. These safety devices are designed to take the impact from a fall and absorb the energy so as to protect people from the damage that would be sustained from a simple safety line.

Testing Parameters

Five dynamic tests were carried out on prototype coil absorbers of different designs, materials and at different ambient conditions. These dynamic tests included one with a temperature of 54°C with a relative humidity of 85%, one at a sub-ambient temperature of -40°C and one on an energy absorber that had been subjected to accelerated corrosion conditioning using the Natural Salt Spray method. Three static tests were also conducted to failure from the deployed coil energy absorbers following the dynamic tests.

For the dynamic tests, a bracket assembly was manufactured and installed on an overhead crane beam, which included a 128kg drop weight, a quick release mechanism and a calibrated load cell to measure the dynamic force during the tests (Fig. 2).

All of the tests were performed to ANSI/ASSE Z359.13-2013 and EN 364:1992 standards, while the load cell was calibrated to ISO 376 and ASTM E74. The drop distance was 4 metres with the weight being attached to the coil energy absorber via a 10mm diameter wire rope of 6 X 36 stainless steel construction.

Dynamic Testing

Figure 1. Notched untested test piece

Figures 2 and 3. Dynamic Testing Assembly Tested Notched Piece

Figures 4 and 5. Dynamic test piece prior and during static testing

Each of the dynamic tests was measured for the output of force versus the time taken. This showed the peak force exerted on each of the test pieces, with this data then recorded and filtered at 60 and 100Hz before plotting on a graph showing the differences between the filtered and unfiltered results. This created four graphs for each test:

As recorded data at 2KHz (2000 measurements per second)
Data filtered at 60Hz
Data filtered at 100Hz
Over plot of 60 and 100Hz data

As well as measuring the peak force, the post-deployment length of each coil was measured for each test.

Static Testing

A tensile testing machine was used to test three of the coils from the dynamic tests to destruction. The static tests were conducted on two 304 stainless steel and one 316 stainless steel notched coil, with the load cell from the dynamic tests being transferred to the tensile testing machine to determine the force, while an additional LVDT was used to measure the displacement of each test piece. The failure load and displacement for each test was then recorded as each test was taken to complete failure.

Conclusions

The eight dynamic tests were conducted at ambient and preconditioned states as requested by Safety Squared, with three of these tests then being taken forward to destruction through static tensile testing. The data from these tests was collected and analysed to produce graphs showing the performance of each test piece.

The dynamic tests showed a pre and post-deployment length, the net deployment, and the peak force when unfiltered and also when filtered at 60 and 100Hz. The static tests demonstrated the failure load (in KN) and the length of displacement for the three chosen test coils. As a result of these tests Safety Squared were able to determine the performance characteristics of the coil energy absorbers.

About Safety Squared

Safety Squared is an independent consultancy that specialises in fall protection and safety at height, including a variety of engineered protective measures to facilitate safe access and prevent falls. These measures include fall-restraint, fall-arrest, work positioning, rescue, emergency descent and powered climb assist. Operating since 1995, Safety Squared has served clients around the world, advising manufacturers, installers, users and specifiers of fall protection equipment and systems, while also providing technical support to enforcement agencies. As a member of various safety groups, Safety Squared also participates in scientific and technical research and the generation of standards.

For more information, please contact us.