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HSE ALERT - Zig-Zag failure


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HSE ALERT – High Potential

Equipment Failure / Fall From Height

10 December 2019

 

Summary of the accident

 

A Tree Surgeon employed by contractor was carrying out tree works to a tree located at Lille Barracks in Aldershot. The IP was located at approximately 7.5m from the ground in a 10m tree when his Petzl ZigZag mechanical prusik mark 3 failed causing the IP to free fall for approximately 2.4m. Fortunately the IP hit a branch stopping the IP but resulted in a tooth becoming dislodged, no other injuries were sustained. The IP reported the incident and the contractor has stopped all works involving this device on site pending investigation.

 

ZigZag Cam

 

Area of failure to the Cam

 

Initial Actions:

 
  • All works stopped on site.
  • All Petzl ZigZag mechanical prusik mark 3 have been quarantined.
  • Manufacturer notified of equipment failure.
  • Investigation commenced.
  • ll tree climbers have revert back to an alternative rope on rope prusik system.
 

 

 


 

Underlying Causes:

 
  • Initial findings have identified that the cam which can be seen in photo has a spring within it to hold it in the up position, this locks the cam against the rope but the internal spring appears to have failed so the cam does not spring up and can now be moved freely with no resistance which resulted in the rope passing through the cam and the IP free falling.
 

 

 


 

Follow Up Actions:

 
  • Still to be determined, however it appear to be equipment failure.
  • Petzl ZigZag mechanical prusik mark 3 (Serial number 18d0132220825) sent to the manufacturer for testing and examination to establish why the equipment failed.
 

 

 

 

 

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27 minutes ago, Steve Bullman said:

I wasn't aware there were springs in those cams?

There isn’t only the top link which aids the device to engage, can only assume this is what they meant. I find it hard to imagine a free fall scenario from a failed spring.

Edited by Marc
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1 minute ago, Steve Bullman said:

Thats what I thought. I think they need to clarify exactly what they mean by this spring.

 

It concerns me that a report such as this written so poorly...

In the first pic it appear clear that the top link is not sprung as it appears collapsed against the top cam/friction bar.

 

Again find it hard to imagine a free fall from this. Wouldn’t of happened with SRT!

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7 minutes ago, Marc said:

It concerns me that a report such as this written so poorly...

In the first pic it appear clear that the top link is not sprung as it appears collapsed against the top cam/friction bar.

 

Again find it hard to imagine a free fall from this. Wouldn’t of happened with SRT!

No doubt the HSE will be using this to support their demand for 2 rope working

 

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