Most investigators have never heard of a wooden pole case and probably have not heard of a pole falling. Occasionally they fall, and when they do, they can cause severe injuries.
While wood poles are subject to stringent standards for treatment, inspection and replacement they still become old, their anti-rot treatment dissipates and they deteriorate. If they are not properly inspected and replaced within the proper guidelines, they will become a hazard.
· First a little about wood poles:
There are 10 grades of wood poles. A #1 pole will support the most weight, a #10 the least. The test for a #5 pole is that it must support 1900 lbs. applied two feet from the top and pulled at a horizontal angle. If it does it passes the test--but when installed in the field it is only permitted to support 475 lbs. when new. This is a required safety factor of four. The National Electrical code recognizes that over the twenty five to thirty year life of a pole it will deteriorate and loose its weight supporting capacity. The inherent strength factor will allow the pole to deteriorate up to 2/3 during its lifetime. This would still leave an adequate safety margin if the pole was properly treated and continuously maintained.
Poles are also identified by their length. A 35 foot #5 pole would be identified by 35-5 burned into the pole. Poles are different lengths because of required clearances between supported service lines. A standard pole (35-5) can carry a 7200 volt line, transformer, drop line, telephone line, and one or two cable lines. There are required distances between each of the lines, and there are required minimum distances that the lines must be supported above the ground. Different classes of roadways, drive ways and business/residential environments require different minimum clearances. Higher voltage carrier lines require greater clearance distances. All of these factors go into determining the minimum length of a pole for a specific installation.
· What are the markings on a wood pole?
What are those markings burned into the wood? Most poles now have a metal serial number tag. This number is used to inventory the pole and keep track of its inspection, treatment and age. The first marking is the date that the pole was treated. In the attached photograph that date is 6 69 or June of l969, the brand of the treatment company, next is the type of wood and treatment, SP for Southern Pipe, C for creosote, the length and strength of the pole is next, 35-5, and then the power utility for which the pole was made.
· Why is this important:
First you must know that poles fall
and hit people. If you get a case such
as this you must be able to identify the pole quickly and ascertain what caused
the pole to fall. In many cases it will
be rot. If the pole is rotten then the
fault will be with the owner of the pole.
The NEC, the Public Service Commission (in
Pieces of the rotten
pole that we collected from the scene after the power company removed the
pole and the stump in the ground.
As soon as you get the pole case... go to the scene and scrounge up as many pieces of the pole as you can find. In the event that the utility company disposes of the pole and all of the large pieces, your collected pieces will be the only evidence. These pieces of wood will give your expert something to analyze. Talk to each of the people who live and work around the accident scene. What did they see? When did it break, was it rotten? Talk to the police, the fire department, the rescue personnel. Did the news media respond, did they take photos...what about videotape? Look at the other poles in the area. How old are they? Do they show signs of rot? Do they show signs of timely inspection and maintenance.?
· What about pole inspection?
The National Electrical code, Rule 214, deals with inspection of lines and equipment, Section A....when they are in service--lines and equipment shall be inspected....Poles should be inspected and tested, records of defects shall be recorded, defects that will reasonably endanger life or property shall be corrected promptly.
The rules say that poles will be inspected as often as necessary. In cold, bug free northern climates, every eight years, ten or twelve years may be ok. The EEI (Edison Electric Institute) standard calculates the frequency of inspection on the number of frost free days in a given geographical region. In a hot, sandy, termite ridden climate such as the Southern states, every three years is not unreasonable.
Inspectors are looking for problems with the electrical services, guy wires, animal guards, damage to the pole from an outside source such as an automobile hitting it, and wood problems in the poles. The most common problem is ground rot. An inspector will dig around the pole approx 18 inches deep and take a core sample of the wood. He will determine the thickness of the outer shell in which the strength of the pole is contained.
According to James Taylor, a Wood Products expert a proper inspection would include a "Visual inspection, up and around it, from top to the ground line, look for a split top, ragged top, woodpecker hole, any cracks which are abnormal, plant life growing on the pole, green algae on the bottom. Broken guy wire, broken insulator, street light fixture hanging. The inspector would then sound the pole, bore the pole and measure the outer shell. He will take at least one boring to determine how good the treatment of the pole is, dig down 18 inches to 2 feet, scrape the pole, and look for surface decay. The inspector will then bore again to determine condition of the pole at this location. Any rotten wood he will evaluate. The inspector then writes up this pole, stating that the pole has x inches of circumference left in it, or will say it is good or bad. The inspector will then fumigate if it needs it or inject preservative"
If a pole is starting to show its age, In many areas, professional inspectors will wrap the base of a pole with preservative. This will increase the life of a wood pole. Many Utilities do not do this.
This type of inspection is not the norm. Many Utilities will just sound the pole with a hammer to see if it is hollow. They will then try and probe the pole with a screw driver, trying to drive it in the pole (through the shell). If the pole is soft it needs replacement. If the inspector cannot drive it in, it is good. An Inspector cannot always find the rot with this method and poles will many times deceive the inspectors. The only really accurate way of inspecting a pole is by the method described by James Taylor. There are private contractors such as Osmose and Asplundh that a utility can hire to do the inspections and treatments. How well a utility maintains their poles is generally an indication of how well other aspects of their business is run.
There is a difference between the requirement of a utility to properly inspect their poles and the requirements of a lineman to insure that a pole is safe to climb. In the case of a lineman, the defense will say that he has a responsibility to check a pole before he climbs it. OSHA, NEC and other standards call for the lineman to sound the pole with a hammer and probe it with a screw driver to determine if it is safe to climb. As you can suspect, this mainly applies to lineman who use ladders and spikes to climb poles. The bucket truck lineman are not as much at risk. Many of the lineman use their spikes to sound a pole. They hit the pole extra hard and listen for a hollow sound.
·
Documents
that can assist in a pole case.
1. Joint Use Agreement between each of the Utilities sharing the pole. Telephone Company, Power Company, Cable Companies.
2. Management Procedures or Polices of each of the Utilities on policy and procedures for inspection, maintenance and replacing of power poles.
3. Pole Inspection and Maintenance, REA Bulletin 161-4, October l974. Rural Electrification Administration/U.S. Department of Agriculture.
4. Methods For Inspection of Standing Wood Poles
In Overhead Lines, A report of the Transmission and Distribution Committee, Edison
Electric Institute, Pub. #59-74, Edison Electric Institute,
5. "Pole Line Maintenance," American telephone and Telegraph Co., 1966, Bell System Practical, Outside Plant Engineering, Pole Line.
6. A guideline for the Physical Inspection of Poles In Service, American Wood-Preservers' Association Standard, M13-72.
7. OSMOSE Data Sheet, Groundline
Inspection and Treating Service, l968 Osmose Wood
Preserving Co., of American, Inc.,
8. Pole Maintenance--Its Need and Its Effectiveness, James Taylor, American Wood-Preservers Association 1978.
9. National Electrical Safety Code, 214. Inspection and Tests of Lines and Equipment. (p132)
10. National electrical Safety Code, 261. Supporting Structure.
11. ANSI standard for wood products--structural glued laminated timber for utility structures, ANSI 05.2.1983.
12. ANSI standard specifications and dimensions for wood poles. C-55-03...ANSI 05.1.1979.
13. Pretreatment Decay in Poles, James A Taylor, American Wood Preservers Association. l980.
14. Pole count documents from the responsible Utility.
15. Pole inspection documents from the responsible Utility. These usually consist of maps, forms and computer print outs. The maintenance patrol will mark off sections of a road and pole map with a magic marker as they cover each area. You should have copies of these maps, the forms that they note discrepancies on, the computer print outs on the pole inventory.
16. Each worker has a responsibility to report problems as he drives through the area. Look for reports of pole problems from sources other than the Maintenance patrol.
17. Each modification to a pole or system requires a work order. Check for all of the work orders or change orders for the particular pole you are concerned with.
18. Locate the electrical service meter closest to your particular pole. The meter reader has a responsibility to check for pole and other problems as he goes from meter to meter. Was the meter so close to your problem that it should have been obvious.