Huntley Hinge

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Manual Chainsaw Felling  - Musculoskeletal injuries and getting support with The Huntly Hinge

Felling trees manually is hard work and it can also take its toll on the body. Looking at the typical pattern of work from tree preparation, felling, de-limbing and crosscutting, through to stacking - it’s actually the processing of the branches in the snedding or de-limbing that absorbs most of the time. Husqvarna’s Organised Felling manual sets out the approximate proportions:

  • 12%    Felling
  • 49%    Snedding
  • 4%    Marking    
  • 6%    Crosscutting
  • 23%    Dragging
  • 6%    Other

Quite rightly we have a major focus on the immediate and catastrophic type of injury within our risk assessment process, but it is important to remember the health part in the Health & Safety at Work Act 1974. These longer-term issues are also covered within the Management Regs (Management of Health & Safety at Work regulations 1999).

Musculoskeletal injuries are a significant cause of time off work and the HSE has a substantial amount of data on the causes and possible remedies via a range of guidance on manual handling. FISA also gives guidance via the FISA guide on Chainsaw Cross-Cutting and Manual Handling - however this is fairly basic and does not offer a lot of advice other than to use ‘best practice” when manual handling, although there are some safety bulletins that give more specific advice around moving on commercial mechanized harvesting sites

So why can this work be bad for us?

It is a combination things including repetitive, one sided work at low height with high loads. Another good reason is lack of rehabilitative or corrective practices.

It makes sense to do this method of processing at a comfortable height, typically around waist height. This saves excessive bending and allows the 6 snedding positions to work as they should. It also means that brash can drop away more easily – forming a protective mat and limiting ground damage where extraction machinery might otherwise cause compaction or erosion. Supported trees can also be rolled, lifted, dragged and then crosscut as a group saving effort and as shown above, a lot of time.

So how can arrange our felled trees to be at a comfortable height?

There are a few options:

  • Fell onto a natural feature, such as a mound of earth or across a hollow - but beware of likely reactions and make sure escape routes are thoroughly prepared and used!
  • Fell onto a brash pile
  • Create an artificial support – there are a few ways to do this. It could be a log pile or a stake tied to an adjacent tree at an angle; note that a tree felled high at 90 degrees to the main felling direction is ideal.

Some trees may well provide suitable support but many would either split or the hinge would fail, making the support short lived. That’s why the Huntly Hinge is ideal to give a more robust structure. It is established by creating a mortice & tennon like joint by constructing the felling cut in the following way:

  • Sink – cut at around waist height, keep small and open up angles at bottom.
  • Mortice/Tennon vertical cuts – starting at the front, cut these from the intended hinge position to at least the diameter of the tree.
  • Mortice base – bore in joining the side cuts.
  • Felling cuts – from either side up to the position of the tennon, insert a lever after the first one is complete.
  • Finally sever the hinge and allow the tennon to drop down securely into the slot.

 

There is little reference of this technique but Demonstration of the Huntly Hinge tree felling

shows a set of the original photographs courtesy of Tom Dunn, Forestry Commission Operations Supervisor based at Huntly.

 

During our chainsaw and climbing courses I do talk about muscular skeletal issues. A few of the key points that I find myself mentioning consistently are –

  • Mix your work – young climbers often say I want to climb every day. This isn’t recommended and a mixed workload is likely to be better over a career than one task day in day out.
  • Look at output or productivity over a career, not in terms of speed round one tree. Again this can be a challenging concept, but time off due to injury or accident is not very productive.
  • Find positive ways to look after your body, such as Yoga, Pilates or Tai Chi. Be proactive rather than reactive.