Tree Lightning Protection Systems
Lightning is one of nature’s most powerful forces and can have devastating effects on trees. Each lightning strike can reach more than five miles in length and produce temperatures greater than 50,000 degrees. The electrical charge in a lightning strike can range from 10,000 to 30,000 amperes or more at 10 to 100 million volts, and can travel at a speed of 450,000ft per second. When a tree is struck by lightning, water within the tree is instantaneously vaporized. Steam is created usually in the outer sapwood and cambium, resulting in an explosion which tears grooves and strips off bark from the tree.
As current flows down a tree and moves from the roots into the soil, a great difference in electrical potential exists. As the charge disperses through the soil this electrical differential is called Step voltage. People or animals standing in the area may inadvertently conduct this potentially deadly flow.
Tree lightning Protection systems help to reduce step voltage however it can still occur as current leaves the ground component of the system. Sometimes when trees are struck the electricity will travel part way down the trunk and then arc over to objects of lower resistance. This phenomenon is known as side flash, and is one of the main reasons to protect trees near homes and buildings.
(An example of how side flash occurs)
Some other reasons for installing a tree lightning protection system are the preservation of historical, rare or specimen trees.
(Trees such as this grand live oak are good cadidates for tree lightning protection systems)
Trees on golf courses or in parks or public grounds where people congregate are also good candidates. (The standard for the installation of lightning protection system, national fire protection association 2004) recommends installation of tree lightning protection systems in trees that are within 10ft of a structure, are taller than the adjacent structure or with limbs over hanging the structure.
The concepts and components of these systems are relatively simple. It should be noted however that no two systems are ever exactly the same. Each system must be designed with each tree’s individual limb structure in mind. Larger trees for instance (generally greater than 36 inches in diameter), may require the use of two primary grounding cables, and two grounding rods. These should be installed 180 degrees from each other, and tied together to promote even dispersal of electrical flow. Installing these protection systems, can therefore sometimes be time consuming depending on tree height, overall canopy spread and number of secondary connections needed to ensure optimal protection.
(It is also a good idea to protect larger trees next to buildings and houses)
Once the main and secondary conducting cables are installed in a given tree, they are connected at the tops of all the main limbs or leaders to solid metal conductor points called (air terminals). These should be of solid copper or copper bronze.
(An air terminal typical of tree lightning protection systems)
As the main conductor descends down the trunk of the tree to the ground, it is buried and attached to a solid ground rod that is hammered into the ground just beyond the drip line (outer most spread of the tree canopy). This is done to minimize or prevent root damage that can result from extreme electrical shock.
(An illustrated example of step voltage)
All though the working life of a lightning protection system can be from 50 to 100 years, periodic inspection and maintenance are critical for the system to remain in proper working order. Inspection should be done annually on fast growing trees, and every 2 to 3 years on slower growing trees. Properly installed tree lightning protection systems are relatively inconspicuous non injurious to the tree and very reliable. These protection systems are a risk management tool that can minimize or prevent tree damage, reduce collateral damage around the tree and provide a preferred path for electrical charges to the ground. These systems do not prevent or reduce the risk of lightning striking a tree, and are not designed to protect people or animals from lightning strikes or step voltage. Therefore they should never be viewed as making a protected tree a safe haven during an electrical storm.
A quick note on materials Aluminum conductors and components should not be used in tree lightning protection systems, as these materials are substandard and will undoubtedly shorten the life span of the system. It is important also to remember that not all trees need lightning protection systems installed.
If you would like to have lightning protection systems installed on one or more of your trees, please feel free to call us. All of our arborists are professionally trained in this specialized area of arboriculture. We can advise you on how and which trees should be protected, and can design and install the most sustainable and best possible long term system to ensure the health, safety and protection of your trees and property.
(The tree behind this house was struck by lightning the house was destroyed as a result of electrical side flash)