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Hazard trees, borderline trees, tree limit, line clearance, assessment of hazards... Trees are not only of good - they can actually present serious risks for people and property! Regular, preventive risk assessment and utility vegetation maintenance is necessary to reduce the safety risks involved. Falling trees are one of the most common causes for electricity breakdowns, and especially so when the weather makes it tough to handle service interruptions. Hard wind and heavy rains, ice and snow are all typical reasons to why trees fall over.

The definition for Hazard trees according to http://na.fs.fed.us/fhp/hazard_tree/geninfo/definitions.shtm: "A potential risk from the physical presence of a woody plant. By contrast, hazardous should specifically refer to a plant with a significant flaw which, when coupled with a location in an identified public use area, makes that tree an actual risk. Thus a hazardous tree is one that, because of a recognizable mechanical flaw, poses a threat to people or property. Plants that contain toxins, irritants, or even addicting drugs should not be termed hazardous but noxious." http://na.fs.fed.us/fhp/hazard_tree/pubs/misc/nps.htm

At, for example, http://www.ferc.gov/industries/electric/indus-act/reliability/vegetation-mgt.asp you can continue reading about the potential hazards with falling trees and the damages these pose when in contact with power lines or when wires are knocked down by trees. You run the risk of being electrocuted, and fires could start. Quote from homepage: "If anything makes contact with an energized line, such as a tree, or if a broken power line falls to the ground or lands on a vehicle or fence, electricity will flow to the ground and spread out in irregular concentric circles. This is known as the Ripple Effect." 

http://www.utilityarborist.org/public/questions.aspx and http://www.forestpathology.org/hazard.html are other examples of sites where information can be found on hazard trees and what risks these can present. There are also suggestions on measures that can be taken to prevent acccidents.

There are many different names for similar functions and measurement needs. All such functions aim to prevent accidents from happening, and trees from falling over power lines, buildings and roads. Many of the advanced and specialized functions that you would normally pay extra to get - or even have to purchase a special instrument for - are incorporated as standard functions in some of Haglöf Sweden professional instrument systems.

The Hazard Tree (Tree Limit) function in our VL5 and L5 instruments has been developed, following specifications and demands from professional users. With their valued feedback, we have fine-tuned the functions and added usability. Our hazard trees function is easy to get to, and the control measurement operation is not complicated. The VL5 or L5 instrument processes data, and gives you on-hand reports on which tree is OK to keep. Easy - and money-saving!

The Tree Limit function in the VL5 and L5 instruments enables the operator to estimate the safety distance from a tree top to, for example a power line, a road or a construction site. It is always recommended to work with a security margin, given that the measurements include uncertain factors that can have effects on the results. Certain calculations will presume that the object, for example a tree, is standing straight when you measure a height. Trees that are leaning in the opposite direction from the operator’s position may be given a lower height measurement value. Other factors of uncertainty can affect the results, such as cold/warm temperature, power output in the power line, etc. If you are unsure whether the laser beam actually hit the correct spot when measuring, it is recommended to verify results with at least one more measuring operation.

The VL5 and L5 instruments incorporate several different height measuring functions. Since smaller trees often prevent free sighting to the tree to measure, and sometimes prevent supplementary tree base measuring, the HEIGHT 1P function (one measuring, aiming at the tree top) is often used. The VL5 or L5 will, in such cases, presume that the tree base is leveled with the ground. Note that, in cases where the tree base/root is lower than ground level, a larger safety and security margin is necessary, since the tree height result otherwise may be underestimated.

 

 


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