Felling of Trees Near Power Lines
Here at Western Area Power Administration (WAPA), our line crews are responsible for the operation and maintenance of approximately 17,000 miles of power lines within a 15-state region of the central and western U.S. Within that region are geographic areas where vegetation hazards can pose a threat to the reliability of some of our power lines. To identify these hazards, WAPA utilizes both routine aerial and ground patrols to collect and monitor vegetation data. The criteria we use to establish vegetation minimum clearance distances is based on the OSHA 29 CFR 1910.333 minimum approach distance for nonelectrical workers, rounded up to the nearest foot, plus 5 feet to account for conductor and tree movement due to wind and ice loading, or increased conductor sag as a result of thermal loading. In addition, another 5 feet is added to allow for an average tree growth of 12 inches per year and a retreatment interval of no fewer than five years.
To address situations where more rapid tree growth can be expected because of species or better than average growing conditions, a distance – either horizontal or vertical – greater than 5 feet is required. Once we’ve identified and documented vegetation hazards that are nonemergency in scope, we hire vegetation contractors to remove and/or mitigate these hazards. However, on rare occasions a WAPA patrolman on a routine patrol will identify and document a vegetation condition that may present an imminent threat to a power line. We generally define the threat as a “danger tree,” a tree located within or adjacent to the easement or permit area that presents a hazard to employees, the public or power system facilities. Characteristics used in identifying a danger tree include the following:
• Encroachment within the safe distance to the conductor as a result of the tree bending, growing, swinging or falling toward the conductor;
• Deterioration or physical damage to the root system, trunk, stem or limbs, and/or the direction and lean of the tree;
• Vertical or horizontal conductor movement and increased sag as a result of thermal, wind and/or ice loading that exceeds the facility design specifications;
• Fire risk; and
• Other threats to the electric power system facilities or worker/public safety.
Once an imminent threat to a power line is identified and requires action, the patrolman immediately reports the condition to his supervisor for resolution. The supervisor then initiates appropriate actions to alleviate or eliminate any hazards. Since most danger tree hazards need to be taken care of right away, WAPA lineworkers are typically utilized to perform this work. Each lineworker is trained and certified to perform trimming and felling of trees near power lines. Prior to performing tree removal, consideration is given to addressing safety and tree felling procedures. Our crews are required to perform a job hazard analysis, which may be verbal or written depending on the size and complexity of the job. Several requirements that WAPA employees must adhere to are addressed during the tailboard. They are:
Required Safety Equipment to Be Worn
• Full-length chaps
• Leather or ballistic gloves
• Hard hat
• Face shield or screen
• Hearing protection
• Cut-resistant footwear meeting ASTM F1818
Required Chain Saw Safety Features
• Engine equipped with spark arrester
• Anti-vibration mounting
• Gunning marks
• Dogs (both sides of chain saw if available)
Recommended Chain Saw Features
• Wraparound handlebars when available
• Semiskip chain
• A saw with at least a 24-inch bar for clearing branches
• Standardized bar nuts and bolts so only one size wrench and one size replacement nut is needed
• Standardized teeth size on every chain so only one file size is needed for all chain saws
Pre-Felling Procedure
• Study the tree to be cut.
• Determine the area where the tree will fall and walk a path if necessary to assure the area is clear.
• Visualize the path the tree will take as it falls and make sure the tree will maintain proper clearance from energized equipment as it falls.
• Determine and plan an escape route that is free of brush and other obstacles. Clear an escape path at a 45-degree angle from directly behind the tree’s direction of fall.
Felling Procedure
• During sawing, focus your attention on the top of the tree for falling limbs/debris.
• Cut at high engine speeds.
• Be aware of the push and pull motions of the chain saw. Proceed with caution with a firm grip on the handle with thumb wrapped underneath.
Post-Felling Procedure
• Leave the saw at the site; do not run with the saw.
• Do not leave tree stumps more than 8 inches high as they may cause damage to vehicles and/or other equipment.
By following these rules and procedures, tree felling near power lines is a task that can be safely performed.
About the Author: Will Schnyer is a foreman III lineman for the Rocky Mountain Region of Western Area Power Administration, a power marketing agency within the Department of Energy. He is a Certified Utility Safety Professional (CUSP) and has more than 26 years of experience working in the electric distribution and transmission field.