Tuesday, May 1, 2012

Lightning Protection for Trees

This is an example of lightning damage to a tree on our property.
           

        Lightning protection for trees is one of the fasting growing areas in lightning protection for lightning contractors. Only a trained and qualified arborist in tandem with a lightning contractor should attempt to provide lightning protection to a tree.  Once this is done correctly, these systems can be remarkably effective in protecting tall or prized trees.
             We lost an eighty year old oak tree last year to an afternoon lightning storm in August.  This is not only the loss of an historic tree, and an important focal point to the property, but quite a hazard as well.  The tree, which had been healthy with lots of branches and leaves was killed instantly, and was stripped of its bark at the lightning seemed to strike it almost in corkscrew fashion. Almost at once afterward, the tree began to rot, presenting quite a danger to anyone driving the private farm road which bisects one section of the farm.   Once we learned that trees could be protected, we were anxious to learn whether the three remaining large trees, near outbuildings, could be protected.   In 2002, The Tree Care Industry Association (TCIA) adopted the ANSI  A300 standard for installing lightning protection systems in trees.   Information on this can be obtained by calling the TCIA itself at 1.800.733-2622 .  This standard involves the use of thinner cables than would be used for the grounding of buildings.


(This picture of lightning from ehow.com, on lightning protection.)



         This is some information on how this works:

IPC Products: Grounding Options

Proper grounding is essential to the effective functioning of tree lightning protection systems. The procedure for grounding will depend upon the character of the soil and surrounding conditions
Please remember that the underground spread of the root system is usually equal in area to the spread of the branches above ground.
Extend standard conductor down trunk and out and away from base of tree in a shallow trench (approximately 6-8 inches in depth). This conductor shall terminate at a driven ground extending down to permanent moisture. A 1/2" x 10' Copper Clad Ground Rod, No. 138 and Bronze Ground Clamp, No. 50 provide effective grounding in normal soil conditions.

Fork Type Ground

The fork type ground system is often practical to use, due to soil conditions, nearness of trees to buildings, concrete sidewalks, property lines, etc. The standard down conductor is placed in a shallow trench and extended out from base of tree from 12 to 15 feet or even further. At end of this conductor a driven ground to permanent moisture is added. Standard conductors are attached to the main down conductor with No. 198 Fork Ground Connector and placed in shallow trenches forming a fork. Large trees require an additional ground.

Multiple Grounds

When it is impossible to drive ground rods to a distance of 10 feet, multiple grounds driven as deep as possible separated at least 6 feet apart are most effective (see illustration). Another alternative is copper ground plates buried in a shallow hole.Ground Interconnections
If the grounding of building protected with a lightning protection system is within 25 feet of a tree, the two systems should be interconnected. If the lightning protection ground of the tree is within 25 feet of a water pipe, sprinkler system, or a deep well casing, a bond connection should be made between them.

Trees in Groups

The major trees in a group can be protected to give ample protection for the smaller ones. If there are several trees in a row (all major trees), the grounding may be made by "common grounding" by trenching from the base of each protected tree to the depth grounds(s), as long as these depth ground locations are not more than 80 feet apart. Depth grounds shall be added as required. This avoids the practice of making independent groundings for each tree, thus reducing the cost of the lightning protection.

Grounding options were obtained from:   http://www.ipclp.com/html/aud_trees_ground.html

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It is important to realize that grounding select trees will not protect them from coming down on you from tornadic activity, wind shear, ice storm or other issues other than lightning damage.  Still, for some of us in lightning prone properties it may still be worth the trouble and expense.

 This is detailed information as to how this is done:

Step by Step Installation

1) Survey the tree
2) Design system using the following criteria:

- Species of tree
- Height of tree
- Spread from drip line to drip line
- Trunk diameter at breast height
- Number of braces or cables
- Determine if there are other nearby utility grounds or metallic water pipes
By providing IPC with the above information, we can provide you with an estimated list of material requirements for the specific installation.
Tree protection installation standards require one downlead and ground on tree with a trunk diameter under 3' 0" and two downleads and grounds on trees with trunk diameter over 3' 0".
3) Determine ground rod location or locations beyond the drip line of the tree.
4) Climber ascends the tree to the highest main trunk extension
5) Climber drops a pull-up line for attaching the main standard copper cable with air terminal attached.
6) The parts bag with miscellaneous tools and materials are sent up to the climber.
7) Climber fastens the standard main air terminal on the highest accessible main trunk extension. This air terminal is fastened with copper nails provided.
8) Climber starts down, fastening the main downlead cable with bronze fasteners ever three feet all the way down to grade.
9) The ground crew will drive the 10 foot length ground rod or ground rods in a small ground pit located outside the drip line of the tree. The ground rod is driven into the ground with a special ground rod driver similar to a fence post driver. The ground crew trenches from the ground pit back to the base of the tree.
10) If the tree requires two main air terminals and download cables, a second standard or main air terminal and downlead is located on another high branch or trunk extension of the tree and the downlead is coursed to ground 180 degrees opposite the initial download.
11) Depending on the canopy size of the tree, two to four or more additional air terminals are installed on the main upper branches in a configuration to provide perimeter protection around the entire crown of the tree. Picture this similar to an inverted umbrella so that peripheral protection is provided 360 degrees.
12) Miniature copper cable or branch conductor is attached to each miniature branch air terminal, supported every three feet with bronze drive fasteners coursing back to the main trunk and fastening to the main conductor with a double or side-by-side splicer.
13) If any braces or cabling wires are used in the tree, these need to be interconnected to the main or branch conductor to establish common ground potential.
14) If the tree requires two standard downleads and grounds, these grounds or downleads must be interconnected. This interconnection can be made within the tree or can be done below grade in a semi-circle around the base of the trunk.
15) The ground crew continues to install the downlead cables in the trench(s) or "envelope type slit" of ground surface out to the ground rod(s) and connection made with two-bolt clamp(s).
16) It is important the ground cover over the trench be replaced so the terrain is in its original condition
17) Occasionally, it is desirable to check the ground resistance. A ground ohms resistance tester is used to measure the effectiveness of the individual grounds as well as the complete grounding system.


This step by step information was obtained from:   http://www.ipclp.com/html/aud_trees_how.html


(photo: panoramio.com)




The Virginia based group who installed our lightning protection for all our buildings will be returning shortly with an arborist to complete the work of protecting our three remaining very tall trees.  I'll post some pictures when they do.






3 comments:

Ken Nicely said...

Great snapshots, did any of these trees suffer from any lightning damage? From the looks of it, no.

-Samudaworth Tree Service
Tree Service Brooklyn

JaneofVirginia said...

Ken, Prior to getting lightning protection on the trees themselves, we had at least three strikes of tall oaks. One died instantly, and the others floundered. Since placing professional lightning protection on the house and farm buildings, and then on key tall trees, there have not yet been any more tree strikes. Adding lightning arrestors to trees with arborists was expensive, but it has been worth it.

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