Is chain shot a problem with Mechanised Arb ?

The simple answer is yes.

Under the Provision and Use of Work Equipment Regulations 1998 (PUWER), protection from flying or ejected objects is legally mandated. The regulations handle this risk under Regulation 12 (Protection against specified hazards), which explicitly addresses dangers caused by things being thrown from or produced by machinery.

What is chain shot ?

Chain shot is where a chain breaks causing the end of the chain to whip round usually striking the saw box. In some cases a link of the chain may detach and travel through the air at near ballistic speed. This is obviously bad news for anyone in it's path.

What can we do about it ?

Generally speaking there are two routes you can take.

1. Set up an exclusion zone which is usually up to 90m and place the machine operator in a suitably guarded machine.

2. Ensure that chain shot cannot be produced in the first place.

Where as option 1 is a workable solution in a forestry environment it is not very practicable in a mechanised arb / urban environment.

As employers / business owners we have a duty of care to protect staff and the wider public. In this case it means that any equipment we purchase and put into use needs to be suitable and compliant.

Manufactures of grapple saws are required to state whether or not their attachments are capable of producing chain shot. Many of them simply state an excessive risk zone in order to cover their backsides, others have gone through testing.

ISO. 11837 covers chain shot testing in intimate detail. To the best of my knowledge only one manufacturer has confirmed that their grapple saws meet this standard and have performed the tests.

In my honest opinion chain shot in a mechanised arb environment is very unlikely, the power and speed of a grapplesaw is much lower than a harvesting head. However this subject is actually covered by a piece of legislation which enables the HSE to proactively shut you down and prosecute. This is a very different thing to the usual "investigation after the event and prosecute" occurrence.