Saturday, December 11, 2010

Tree Electrical Safety Knowledge, Precautions, Risks and Standards


Summary: Randall H. Miller weighs tree electrical safety knowledge, electrical safety precautions and electrical safety standards against electrical safety risks.


Trees and electrical lines, a common occurrence in the modern world's electrified landscape, present potential electrical safety risks; Italian Cypress (Cupressus sempervirens) and electrical power lines near Eastern and Cottage streets, Sacramento, northern Central Valley, California: Robert Couse Baker (**RCB**), CC BY 2.0, via Flickr

Tree electrical safety knowledge arises from accepting electrical safety precautions, acknowledging electrical safety risks and acting on electrical safety standards, according to Electrical Knowledge in the December 2010 issue of Arborist News.
Author Randall H. Miller begins with a description of electrical contact with high-voltage electrical lines running through trees as "the most common fatal accident involving arborists." Electricity, like water, always claims the path of least resistance to ground, where "it dissipates in concentric 'ripples'" before the "electric charges return to their source." Voltage, from 120 for households to 765,000 for the biggest transmission lines in North America, describes the electrical potential of fully energized electrical lines for work.
Amperage expresses the measured but variable flow of an electrical current that "realizes its 'potential'" by starting to work through a conductive wire in a circuit.
Downed electrical lines, electrical lines running through trees and trees atop electrical lines furnish scenarios where tree electrical safety knowledge must translate into electrical safety precautions.
Downed lines generate threats of electrical contact by arcing and whipping around into bystanders and by energizing such conductive objects as fences, metal-sided buildings and vehicles. Occupants forced to evacuate energized vehicles have to jump clear, land "feet together" and shuffle off bounding "one foot to the ground" or hopping "feet together." Climbing, picking fruits and nuts, playing in tree houses and on tree swings, or pruning is not advisable for any trees through which electrical lines run.
Running clothes lines for outdoor-dried freshness jeopardizes people in the house and on the ground if the anchoring branch or trunk fails atop an electrical line.
Tree electrical safety knowledge keeps point of contact as the most important phrase to remember when tree-loving non-specialists and specialists seek to minimize electrical safety risks. "[S]imultaneously touching an energized object and the ground, an energized object and another conductor, grounded object" leads a person to serve as electricity's path to ground. "[M]ultiple contact with a single energized object (such as two hands, a hand and foot, or any other combination of body parts)" may open similar pathways.
A person respectively needs only 16, 20 or 100 milliamps to be unsuccessful at loosening a handhold, to experience respiratory paralysis or to suffer ventricular fibrillation. Cardiac arrest and internal organ damage occur at contact with two amps even though people survive point-of-contact surface temperatures of 1862 degrees Fahrenheit (1000 degrees Celsius).
The American National Standards Institute's ANSI Z133 and the Occupational Safety and Health Administration's OSHA 1910.269 promote tree electrical safety knowledge through U.S. electrical safety standards.
Z133 quantifies as hazardous distances under 10 feet (3 meters) to energized, 50-kV overhead conductors, with 04.-inch (92-millimeter) expansions for every kilovolt increase over 50 kV. It reveals the dangers of directly contacting power lines and of indirectly contacting conductive objects touching energized fixtures such as ground, people, telecom wires and tools. It specifies step potential as electricity jumping through someone straddling higher- and lower-voltage ground ripples and touch potential as electricity in contact with multiple energized points.
Tree electrical safety knowledge turns backyards into minimal electrical safety risks from direct, indirect, step or touch contact through electrical safety precautions and electrical safety standards.

Arbor Day 2010 campaign by Public Service of New Hampshire (PSNH) to promote tree electrical safety knowledge: PSNH, CC BY ND 2.0, via Flickr

Acknowledgment
My special thanks to:
Talented artists and photographers/concerned organizations who make their fine images available on the Internet;
Virginia Polytechnic Institute and State University for superior on-campus and on-line resources.
Image credits:
Trees and electrical lines, a common occurrence in the modern world's electrified landscape, present potential electrical safety risks; Italian Cypress (Cupressus sempervirens) and electrical power lines near Eastern and Cottage streets, Sacramento, northern Central Valley, California: Robert Couse Baker (**RCB**), CC BY 2.0, via Flickr @ https://www.flickr.com/photos/29233640@N07/2829065451/
Arbor Day 2010 campaign by Public Service of New Hampshire (PSNH) to promote tree electrical safety knowledge: PSNH, CC BY ND 2.0, via Flickr @ https://www.flickr.com/photos/psnh/4584161944/

For further information:
International Society of Arboriculture. 2005. Glossary of Arboricultural Terms. Champaign IL: International Society of Arboriculture.
Miller, Randall H. December 2010. "Electrical Knowledge." Arborist News 19(6): 12-17.


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