Vegetation Management
Identifying Hazard & Danger Trees Around Utility Lines

What are Danger Trees?

A danger tree is any tree, on or off the right of way, that can contact electric power lines. The ANSI 300 Part 7 provides definitions of “danger trees” as well as “hazard trees.” Both relate to the trees’ potential to come in contact with power lines. Understanding each of these situations and how to spot it can help prevent power outages, fires, and injuries.

A danger tree may be completely healthy and intact, or it may be sick or dead. Even a healthy tree could sustain damage in a severe storm and impact nearby power lines, thus the potential for “danger.” 

A hazard tree is a specific type of danger tree that poses a greater likelihood of causing problems. In this case, the tree is structurally unsound and positioned in a way that it could fall on power lines. 

Vegetation managers recognize the differences between the terms because they must be precise in recommending solutions. Any tree might break under the right conditions, therefore any tree poses some degree of risk. That means it’s important to monitor any trees near power lines to notice when they require pruning or removal.

When to Prune or Remove Danger Trees

The population of trees that live on a portion of land surrounding power lines is known as a utility forest. Vegetation management professionals mitigate the risks within the utility forest by monitoring and pruning. 

Because trees are living things, they continuously grow, shift to reach sunlight and, sometimes, contract diseases or parasites and die. Therefore, a given tree might become a danger tree or hazard tree as it goes through its life, and requires consistent monitoring. 
To identify a hazard tree, look for signs that a tree is structurally unsound. Signs may include:
  • fungal activity
  • root damage
  • weakly attached branches
  • unnatural leaning of the tree
  • deep cracks in the bark
  • leaves falling out of season 
  • insect damage (e.g. due to Emerald Ash Borer)

Sometimes other organisms live in symbiosis with a tree, like mushrooms around the roots, epiphytes among the branches, or even animals nesting in cavities. These are not necessarily reasons to believe the tree is sick or insured. Therefore, it’s important to understand the different species that live in an area and stay aware of local diseases or infestations. 

A complete picture of the tree’s health will indicate the level of risk. A resistograph can provide more objective information on the health of a tree. This device drills a small hole into the tree and then measures the density of the wood. In this way, you can monitor for unseen cracks beneath the surface.

Strict state and federal guidelines also guide how and when to maintain trees near utility lines. Power Line clearance requirements vary greatly depending on whether an electrical line is considered a transmission or distribution line. 

Storms Can Lead to Hazard Trees

It’s necessary to monitor trees for power line risks consistently, since a storm may arise and cause a problem. In parts of the country with clearly defined storm seasons, it’s always a good idea to conduct a review of potential problem areas in the utility forest before storm season starts. Large branches or whole trees often fall onto power lines during storms, interrupting power. Since fallen trees can present many hazards, it’s advisable to call for emergency storm restoration services as soon as possible. However, proper tree inspection can also help prevent the worst storm damages.

Don’t just inspect trees before storms, but also after major storms. A danger tree can become a hazard tree after sustaining damage from heavy wind, snow, or ice. A tree that didn’t contact power lines this time might do so during the next storm. 

Regular Vegetation Maintenance Reduces Risks

In commercial or residential landscaping, it’s often possible to address one or two trees at a time. However, a utility forest requires specialized, ongoing monitoring for risks. The best approach for a utility company is to follow a continuous, integrated vegetation management plan. Professional arborists can monitor for potential problems and recommend when to remove or prune trees, or manage vegetation using herbicides.

Townsend identifies and provides solutions for utility companies to keep vegetation under control near power lines and reduce the risk of outages. We formulate a plan that takes into consideration state and federal regulations, along with climate factors of your region. This helps utility companies avoid fines and better serve customers. We will monitor danger trees and hazard trees to reduce the chances that they will cause a problem.


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