What do photographic film, ping pong balls, turpentine, hockey sticks and utility poles all have in common? They are some of the more than 500 products used in everyday life that are made from trees.

As the world's population increases, so does the demand for all kids of consumer goods. One way to help the environment is to choose products that have been made from wood, a renewable resource. Goods made from other materials may consumer our natural resources than can never be replaced.

The volume of wood in Canada's productive forest increased by 35 percent over the past 20 years, due to sustainable forestry practices. Last year alone, 700 million seedlings were planted. By choosing products made from wood, you support a renewable resource.

Trees are living plants that need to breathe in order to grow. As they breathe, they removed unwanted carbon dioxide from the air – a greenhouse gas that contributes to global warming - and replace it with life-sustaining oxygen.

To grow a pound of wood, a young tree breathes in 1.47 pounds of carbon dioxide, and breathes out 1.07 pounds of oxygen. The carbon is stored in the cells of the tree. When a forest becomes old or overcrowded, trees stop growing and begin to decay. This releases the carbon. But when mature trees are harvested for wood products and utility poles, the carbon stays locked inside the wood. Replanting with young trees begins the air-cleansing process again.

Wood Poles May Last Longer Than You Think

Life-cycle cost analysis is one of the most effective methods of determining the true cost of a product. In order to accurately determine this cost it is crucial that the most important variable, expected performance life of a product, is correct.

In a recent study conducted in the U.S., most utility companies assumed a service life of 30-40 years for wood poles. Actual experience indicates that the service life is at least 75 years for a properly treated and maintained pole. Why the discrepancy between reality and perception?

When questioned on what was the limiting factor in pole service life, most respondents to the survey answered "degradation due to decay in the near ground-line zone". However, reviews of maintenance records show that when a standard maintenance program is put into place, there is no significant deterioration of the wood within the assumed 30 to 40-year life expectancy.

Other Reasons for Pole Replacement

Several factors that have contaminated life estimates of wood pole are totally unrelated to degradation. This is particularly true for distribution lines and transmission lines in cities. In order to make life-cycle cost analysis meaningful, it is important that we understand what these factors are.

Poles are often replaced due to relocation or upgrades of lines as a result of new building or road construction. As demand increases, it is often necessary to place additional equipment on an existing pole that is not capable of carrying the load, so it is replaced with a larger class pole. Such replacements usually have nothing to do with pole condition.

Poles located near major roads or in parking lots are often replaced due to abrasion and failure as a result of vehicles hitting them. While this sort of failure requires that the pole be replaced, it should not be considered a failure due to "normal" biological degradation.

Inspection Methods

Inspection data on several randomly selected transmission lines was used to evaluate actual mortality rates for wood poles. Many utilities have regularly scheduled inspection and remedial treatment of the near groundline zone, so only lines that have been maintained with such a program were included. Any improperly treated poles, poles enhanced with pretreatment and poles that are not subjected to regular groundline maintenance were excluded in order not to bias results.

If the average perceived service life of a wood pole is 33 years, as determined from the survey, one would expect more than half of the poles in lines that are older than 33 years would be replacements. The actual line inventory data do not support this. Utilities that regularly inspect their poles every 10 years are actually experiencing replacement rates of only 2-4 percent of the inspected poles. The replacement rate is consistent as long as the poles are regularly maintained.

If it is assumed that the average service life of a pole is represented by the age at which 50 percent of the poles have been replaced, the average range of service life is from 135 to 260 years for the 2 percent and 4 percent replacement rates, respectively. This range may appear to be unrealistically high, but if groundline degradation is the primary reason for pole replacement and it is being addressed with a regular remedial treatment, service life should be approaching these figures.

There are other factors that limit service life as a pole ages beyond the perceived average service life of 33 years. Pole top decay (stove piping), decay at connections, splitting a pole tops and excessive weathering are all factors that can cause failures. These types of failures are not nearly as major a factor a groundline decay and do not occur until much later in the service life of a pole. If existing inspection and maintenance programs were modified to address these other forms of pole degradation, pole service life would be extended even further.

The data from the study were not able to definitively establish the service life of a pole. They did point out that the relatively short service life of 30 to 40 years commonly used in life-cycle cost analysis by many utilities may be less than half of the actual service life and should be reviewed. Careful review of objective, uncontaminated service life experience is needed to reliably project expected service life of wood poles as well as poles made from alternate materials.

Wood Pole Life Span: What You Can Expect, A.H. Stewart, Director of Engineering, Engineering Data Management, Fort Collins, CO.