Tree Lightning Protection Systems Tailored to Sites, Soils, Species

Summary: Site-, soil-, species-specific tree lightning protection systems control damage best with parts from arborist and lightning protection supply companies.

Cloud-to-ground lightning is generally the most common lightning discharge affecting trees; California Mojave Desert; Oct. 16, 2015: Jessie Eastland, CC BY SA 4.0, via Wikimedia Commons

The article Tree Lightning Protection Systems (Part One) in the October 2015 issue of Arborist News approaches lightning discharges from the objective of answering what TLPS work how, when, where and why.

TLPS battle cloud-to-ground discharges between negative- or positive-charged clouds and Earth, versus cloud-to-cloud of different polarities between different clouds and intra-cloud of different polarities within clouds. Lightning strikes typically compact cloud-released "ladders" and Earth-released "streamers" into 0.1- to 0.2-second, 30,000- to 50,000-amp, 100-plus thousand- to 10-plus million-volt or 10- to 300-coulomb flashes. Amps, coulombs and volts describe flow rate by one-volt potential against one-ohm resistance, charge in amps per second and current in one-amp potential through one-ohm resistance.

TLPS ideally ensure protection against strike-associated sideflash of currents jumping from struck to nearby objects and step voltage of charges spreading from point of contact omnidirectionally.

TLPS fight against sideflash-associated damage and strike-thrown debris by furnishing a "preferred point for lightning attachment and a preferred path to ground for lightning strike currents."

American National Standards Institute, National Fire Protection Association and Tree Care Industry Association guidelines gauge historic, tall, unusual trees 10 feet (3.05 meters) from structures TLPS-friendly. High assessed risk and poor health heighten the "probability of a direct strike to the tree and the expected damage to the tree from a strike." Susceptibility involves tree location and size since dense-clustered, droughty, isolated, shorter trees on slopes away from approaching storms imply lowest lightning strike risks and TLPS needs.

Tree lightning protection systems juggle material- and size-compatible, TLPS-designed components from arborist and lightning protection supply companies, not from hardware stores, and sites, soils and species.

For example, TLPS functional components keep brass, bronze, commercial electrical-grade copper and stainless steel, not aluminum or lead-infused or unclad structural steel, as acceptable construction materials. Even correct components leave questionable results in declining trees and in lightning damage-prone species, including ash (Fraxinus), black locust (Robinia), oak (Quercus) and tulip poplar (Liriodendron).

All trees manage bonding connectors of metal to branchtop-to-primary conductors or to primary treetop-to-electrodes conductors as well as grounding conductors of copper, not soil corrosion-prone aluminum. Conductors need clamp-type connectors for inter-conductor connections and metals within 3 feet (0.92 meters) of soil surfaces and end-to-end, side-by-side, "Y"-configured crimp-type connectors for joining conductors.

Tree lightning protection systems preferentially offer manufactured air terminals to organize more effective strike attachments to TLPS even though the option obtains recommended, not mandatory, status.

Arborists tightly pinch fasteners, hammered or screwed into healthy wood and providing separations between conductor and tree surfaces, onto the conductors to be secured to trees.

Grounding electrodes, as grounding systems of ground connectors, ground rods with machine-threaded ends or with overlapping compression fittings and ground-rod clamps, quicken electrical contact with earth. Eight-foot (2.44-meter) lengths and 0.5-inch (12.7-millimeter) diameters represent minimums for anti-conductive, anti-corrosive all-copper or copper-clad steel and strong all-stainless steel or stainless steel-clad steel ground rods. Clamps sustain cross-over, right-angle options for in-line configurations of two-plus rods or heavy-duty, rod- not connector-bolted, straight versions and never electric system-type, light-duty, short, single-bolt clamps.

Tree lightning protection systems tailor damage-controlling components and materials to site-specific soils and species, according to Scott Cullen, A. William Graham Jr. and E. Thomas Smiley.

oak (Quercus spp.) burned by lightning: Randy Cyr/Greentree/Bugwood.org, CC BY 3.0, via Forestry Images

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

oak (Quercus spp.) burned by lightning: Randy Cyr/Greentree/Bugwood.org, CC BY 3.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=1238111

Cloud-to-ground lightning is generally the most common lightning discharge affecting trees; California Mojave Desert; Oct. 16, 2015: Jessie Eastland, CC BY SA 4.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Desert_Electric.jpg

For further information:

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

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Smiley, E. Thomas; Graham, A. William, Jr.; and Cullen, Scott. October 2015. "Tree Lightning Protection Systems (Part One)." Arborist News 24(5): 12-20.
Available @ http://html5.epaperflip.com/Viewer.aspx?docid=b62036f1-11a8-4ddf-aad3-a516015877b6#page=14