Inspect and Test to Prevent Wood Poles from Falling
It happens every so often – and more often than it should. A lineworker climbs a wood pole and the pole falls. With the advent of 100% fall protection, the climber is assured serious injury and often death if a pole falls while they are tied to it.
Several of these types of incidents have occurred in recent months. The first question is, why didn’t those poles get checked before anyone climbed them? The next question is, what can we do to prevent future falls?
Correct Depth is Key
First and foremost, correct depth is what keeps a pole in the air. Most companies have a specification that determines a pole’s installed depth based on its length. Another resource you can refer to is ANSI O5.1, “Wood Poles – Specifications and Dimensions.” Essentially, the taller a pole is, the deeper it needs to be buried in the ground to ensure it is stable. Across the industry, it is not uncommon for utilities to teach this rule of thumb: 10% of the pole height plus 2 feet.
Various soil types also need to be taken into consideration. Additional attention – such as tamping or a select backfill – is required when a pole is being positioned in rocky soil or a mud bog. In sandy or muddy areas, pole butts often are supplemented by a “bog shoe” or “dead man,” which is a creosote-treated pole section trenched in sideways across the pole a couple feet below ground to give the pole additional stability.
The pole brand, often referred to as a “birthmark,” includes the manufacturer’s name, date of manufacture, treatment type, length and class. Other information also may be included. For poles that meet the ANSI specifications, the brands are pressed into the wood at 10 feet, 2 inches for poles 50 feet long or less, and at 14 feet, 2 inches for poles 55 feet long or more. That is usually the first indication of the relative setting depth of the pole. Keep in mind that the pole may have been set properly at installation, but the grade could have changed over time, rendering the pole too shallow today.
Caution should be taken when making attachments to a pole because doing so can change everything. A lineman who trained me years ago as a helper on a line crew once said, “If you can’t or don’t guy the pole, you can pull anything off of it.” Many line-related incidents occur due to improper inspections of poles or changing the strain on the pole or structure without using appropriate restraints.
Three Recent Incidents
One recent industry incident I’m aware of involved a two-pole transmission H structure with two down guys on the outside leg of the structure. A contract crew had been replacing guys one at a time, but on this structure, the second guy was slacked off before the first guy was properly tensioned. The structure was in a transmission corridor with two other transmission lines and almost fell into another energized 500-kV line.
In a recent storm trouble incident, a lineman climbed a pole to cut down some conductors that needed to be spliced and re-sagged. When one of the conductors was cut down, the pole became unstable and fell, dropping the lineman to the ground some 35 feet below. The pole had not been properly inspected for depth and had insufficient guying to stabilize it.
Yet another incident transpired when a pole broke because strain was taken on by the conductors. The pole fell on the lower boom of a one-person bucket truck, causing the lineman to be ejected from the bucket. Fortunately, he was wearing a harness and using fall protection gear that prevented him from hitting the street below.
Inspection and Testing
So, what are the rules about inspecting and testing for structural stability? For wood poles and pole structures, the industry guidelines are found in Appendix D to OSHA 29 CFR 1910.269.
According to the introduction to Appendix D, “When employees are to perform work on a wood pole, it is important to determine the condition of the pole before employees climb it. The weight of the employee, the weight of equipment to be installed, and other working stresses (such as the removal or retensioning of conductors) can lead to the failure of a defective pole or a pole that is not designed to handle the additional stresses. For these reasons, it is essential that, before an employee climbs a wood pole, the employer ascertain that the pole is capable of sustaining the stresses of the work. The determination that the pole is capable of sustaining these stresses includes an inspection of the condition of the pole.
“If the employer finds the pole to be unsafe to climb or to work from, the employer must secure the pole so that it does not fail while an employee is on it. The employer can secure the pole by a line truck boom, by ropes or guys, or by lashing a new pole alongside it. If a new one is lashed alongside the defective pole, employees should work from the new one.”
The appendix then goes on to list the following conditions that qualified employees should check for when inspecting wood poles:
- General condition. Buckling at the ground line or an unusual angle with respect to the ground may indicate that the pole has rotted or is broken.
- Cracks. Horizontal cracks perpendicular to the grain of the wood may weaken the pole. Vertical cracks, although not normally considered to be a sign of a defective pole, can pose a hazard to the climber, and the employee should keep his or her gaffs away from them while climbing.
- Holes. Hollow spots and woodpecker holes can reduce the strength of a wood pole.
- Shell rot and decay. Rotting and decay are cutout hazards and possible indications of the age and internal condition of the pole.
- Knots. One large knot or several smaller ones at the same height on the pole may be evidence of a weak point on the pole.
- Depth of setting. Evidence of the existence of a former ground line substantially above the existing ground level may be an indication that the pole is no longer buried to a sufficient depth.
- Soil conditions. Soft, wet or loose soil around the base of the pole may indicate that the pole will not support any change in stress.
- Burn marks. Burning from transformer failures or conductor faults could damage the pole so that it cannot withstand changes in mechanical stress.
According to OSHA, the presence of any of these conditions is an indication that the pole may not be safe to climb or work from. The employee performing the inspection must be qualified to determine whether it is safe to perform the work without taking additional precautions.
Acceptable Testing Methods
The OSHA inspection criteria include a hammer-strike test and a screwdriver prod test below ground level to be performed by a qualified person.
Most pole falls stem from not following the Appendix D guidelines. Hammering the pole will identify shell cracks or damage and separation of the shell. Checking the pole at ground level should be done using a screwdriver with a 12-inch shank. Hammer the screwdriver 6 inches below ground level on the high side of the pole. If it is rotten, the rotting most likely will be on the side of the pole where the dirt level is highest.
To perform a rocking test, the appendix states the following: “Apply a horizontal force to the pole and attempt to rock it back and forth in a direction perpendicular to the line. Exercise caution to avoid causing power lines to swing together. Apply the force to the pole either by pushing it with a pike pole or pulling the pole with a rope. If the pole cracks during the test, it is unsafe.”
There are two final notes I want to share: First, a visual check for bird holes, knots and weather cracks usually is the easier part of the inspection, but it doesn’t always get done. Don’t be complacent – make sure to check each and every wood pole before climbing is permitted.
Also, there are companies that will conduct pole testing and leave a tag to indicate the date a pole was last inspected. I still advise you to inspect poles on your own. The primary purpose is to identify those that need immediate maintenance or to be changed out. Wood poles can be damaged at any time.
About the Author: Danny Raines, CUSP, safety consultant, distribution and transmission, retired from Georgia Power after 40 years of service and opened Raines Utility Safety Solutions LLC, providing compliance training, risk assessments and safety observation programs. He also is an affiliate instructor at Georgia Tech Research Center OSHA Outreach in Atlanta.
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