In one of American Mountain Guides Association Single Guide InstructorBy discussing ongoing training programs, we discussed the power of trees. An SPI provider noted that he tested a tree by breaking a load cell and found that the tree was worth 17 kN.

17kN is a decent amount. One kilowatt (kN) is worth approximately 5 225. And most carbines and slings have a degree of 21-24kN. 17kN is not high enough for an independent anchor, but high enough for a rappel or anchor component.

How good is that tree in the gap?

As soon as the presenter spoke, several people challenged him. “This rank was only good for that tree at that point,” said one. “It’s all about the root system,” says another. “You can’t say anything with an experiment,” said a third.

All three who challenged the presenter were right. An experiment on a tree in an area really does not give you any real information. You need more …

I participated in it a few weeks later International Technical Rescue SymposiumThis symposium brings together some of the best rope-saving minds. Many participants in this event provide research and articles. At this special symposium, John Morton, a rescue technician from Everett Mountain Rescue and the Snohomish Helicopter Rescue Team, presented an article on the KN value of trees.

Morton began valuing trees a few years ago with Mark Miller, a mountain guide and rescue instructor who was tragically killed in an accident. After Mark’s death, Morton continued to work on the project.

In essence, he approached the problem in a new way. He looked at the trees as anchors that had already been tested … by the wind.

When a windstorm occurs, the trees are under severe pressure. In fact, they are tested just like any other rescue or mountaineering equipment. They act almost like a sail and take a lot of wind. If they do not fall, they are tested at a certain level of KN.

Morton did this and developed a formula based on a combination of tree species characteristics and how wind storms affected those trees. In the process, he modified his formula for placing trees on the left side of hills. And when he was done … he had a tool to actively rank every tree everywhere kN.

Click to enlarge

The previous cases show the environment of several trees in the Pacific Northwest and their degree kN based on Morton’s formula.

For a Rappel anchor, we probably want something with a minimum value of at least 8kN. The leader fall is often given an approximate value of 7.5 kN, so while Rappel should not make such an impact, we must be prepared for it.

For a mountaineering anchor, we want something with at least 20kN. And for a rescue anchor, we should probably have at least 30kN.

With these figures, any tree in PNW that is at least 22 inches in circumference is suitable for a mountaineering anchor. And any tree that is at least 25 inches in size is suitable for a rescue anchor.

For SAR personnel, Morton recommends that you have a field guide so that you can look specifically at specific tree species and determine how small you can go.

This is really cool work. To view Morton’s full article, please log in search for John Morton, “What if trees have a rating in kN? Tree anchor rating based on wind load.”

-Jason Di Martin

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