Among the many changes contained within the pending ANSI Z133-2026 revision, none may prove more significant than the restructuring of Section 4, Electrical Hazards. While much attention has been given to chain saws, drop zones and climbing systems, the electrical changes represent the latest chapter in a decades-long effort to align arboricultural work practices with the hazards encountered in the field.

For all arborists, understanding these changes requires understanding how we arrived here.

Before 2017: A simple system

Before the 2017 edition, the Z133 recognized only two electrical qualifications of arborists.

Qualified line-clearance arborists operated under OSHA 29 CFR 1910.269 and maintained the minimum approach distances (MADs) contained in Table 1. Everyone else was considered electrically unqualified and was required to maintain the familiar 10-foot, up to 50 kV, separation distance contained in Table 2.

The system was straightforward. Either you were a qualified line-clearance arborist or you were not.

The challenge was that real work did not always fit neatly into those two categories.

Municipal arborists, commercial tree care companies and residential contractors increasingly found themselves working near energized conductors. Many routinely encountered service drops and lower-voltage systems, yet they were neither unqualified under other OSHA standards nor performing utility line-clearance operations under 1910.269.

As arboriculture advanced, the gap between the standard and the realities of fieldwork became increasingly apparent.

The 2017 revision: Introducing incidental line clearance

The 2017 revision attempted to bridge the gap between the traditional 10-foot rule and the realities of modern arboriculture through the introduction of incidental line clearance.

For the first time, Section 4 recognized three categories of electrical qualifications:

• Electrically unqualified arborists using Table 1.
• Incidental line-clearance arborists using Table 2.
• Qualified line-clearance arborists using Table 3.

The concept of incidental line clearance did not arise in a vacuum.

Many arborists performing residential, municipal and commercial tree work routinely encountered service drops and lower-voltage systems. These employees were already covered by OSHA’s General Industry electrical standards contained in Subpart S, which allowed qualified employees, as defined in Subpart S, to work closer to energized conductors than the traditional 10-foot rule imposed on electrically unqualified workers.

Without some form of intermediate qualification, an unusual situation existed in which arborists who were not qualified line-clearance arborists could work closer to energized conductors, per Subpart S, Table S-5, Approach Distances for Qualified Employees – Alternating Current, than qualified line-clearance arborists operating under the Z133’s Table 3. The introduction of incidental line clearance sought to address this inconsistency and provide a framework that better aligned arboricultural practice with existing OSHA requirements.

It was an important step forward, recognizing that many arborists routinely worked around electrical hazards without performing utility line-clearance arboriculture. The new table for the incidental group increased MADs to keep these workers farther from the lines than their line-clearance counterparts.

However, the three-category system also created challenges. Questions arose regarding who qualified as an incidental line-clearance arborist, what training was required, where the boundaries between the categories existed and what responsibilities the utility had. The distinction between incidental line clearance and utility line clearance was not always intuitive, and the broad range of voltages encountered throughout the industry often made a three-category system difficult to apply.

Ultimately, the industry discovered that electrical exposure could not always be adequately described by three categories alone.

Saying goodbye to “incidental line clearance”

Perhaps one of the most significant changes in the 2026 revision is not what was added, but what disappeared.

The qualification incidental line clearance has been removed entirely.

Rather than describing a type of work, the committee elected to focus on the qualifications of the arborist. This represents a subtle but important philosophical shift. The new structure recognizes that electrical hazards exist along a continuum and that qualifications should correspond to the hazards likely to be encountered.

In many respects, the standard has moved from a distance-based framework toward a competency-based framework.

Instead of asking, “What type of work is being performed?” the standard now asks, “What is this arborist qualified to do?”

The 2026 revision: Four electrical levels

The 2026 revision establishes four electrical qualification levels:

• Electrical Level 1 – Unqualified for any voltage.
• Electrical Level 2 – Qualified for voltages of 750 volts or less.
• Electrical Level 3 – Qualified for voltages up to 35 kV.
• Electrical Level 4 – Line Clearance – Qualified for all voltages.

Perhaps the most significant philosophical change is that the standard now classifies people rather than work activities.

This approach better reflects the diversity of modern arboriculture and recognizes that electrical exposure exists on a spectrum rather than within rigid categories.

Why 750 volts and 35 kV?

The voltage thresholds selected by the committee were not arbitrary.

Federal OSHA has historically distinguished low-voltage and high-voltage systems at 750 volts, although several state-plan OSHA programs use 600 volts as the dividing line.

Electrical Level 2 was intended to encompass the voltages most commonly encountered by residential and commercial arborists, particularly service drops and secondary systems.

Electrical Level 3 extends those qualifications to include much of the distribution system up to 35 kV. This recognizes that municipalities, contractors, arborists and urban foresters frequently encounter a range of voltages on distribution circuits as part of their routine operations.

Above 35 kV, the hazards, work methods and competencies become increasingly specialized. Consequently, work involving higher distribution voltages and transmission systems remains the domain of the qualified line-clearance arborist.

The significance of 35 kV

The establishment of 35 kV as the upper limit for Electrical Level 3 arborists represents another notable development.

Under the new framework, Electrical Level 3 arborists may perform work within 10 feet of electric supply lines exceeding 35 kV only when an abatement plan has been developed in coordination with the utility. In the absence of such a plan, the work falls within the scope of the Electrical Level
4 arborist.

This provision recognizes that hazards of increasing voltages are not necessarily overcome by competency alone. Instead, it acknowledges that hazards can often be effectively managed through planning, engineering controls and coordination between the employer and the utility.

At the same time, it reinforces the specialized nature of transmission and higher-voltage work, and the expertise required of qualified line-clearance arborists.

New hazards for a changing industry

Although much of the attention surrounding Section 4 has focused on electrical qualifications, the 2026 revision also acknowledges that arborists increasingly encounter hazards beyond traditional electric supply systems.

Radiofrequency (RF) hazards associated with communications infrastructure and small-cell installations are becoming more common. As a result, the standard now includes requirements for radiofrequency awareness training.

While RF hazards may be unfamiliar to many arborists, their inclusion reflects a broader trend within the Z133. As technology changes and infrastructure advances, the hazards faced by arborists do so as well.

What does all of this mean for line-clearance arborists?

Ironically, the group least affected by these changes may be qualified line-clearance arborists.
The knowledge, skills and competencies required to perform utility vegetation-management operations safely have not fundamentally changed. Line-clearance arborists remain specialists whose work demands extensive training and experience.

What has changed is the framework used to describe electrical qualifications throughout the profession.

Looking back over the history of Section 4, one can see a clear progression from two classifications to three and now to four. Each revision has attempted to better align the standard with the realities faced by arborists in the field.

Perhaps that is the greatest lesson of the 2026 revision.

Arboriculture continues to change, and our standards must continue to develop with it.

The challenge, as always, is ensuring that our standards describe not merely how we imagine the work should be performed, but how the work is actually done.

What is line-clearance arboriculture?

Line clearance may be one of the most misunderstood terms in arboriculture. Simply working near power lines does not automatically make someone a line-clearance arborist.

• Under OSHA, line-clearance tree trimming exists only when two conditions are present:
• The work is performed within a specified distance of electric supply lines or equipment.
• The work is performed for, or on behalf of, the utility or organization that owns or operates the electrical system.

Both conditions must be met.

The specified distance is not limited to the immediate vicinity of the conductors themselves. Rather, it creates a vertical plane extending from the ground to the sky, 10 feet horizontally to either side of the electric supply line or equipment. If any portion of the tree penetrates that plane, the entire tree is considered to be within the specified distance. Consequently, a tree may be considered line-clearance tree trimming even when the actual cutting occurs at ground level or on portions of the tree located some distance from the conductors.

Likewise, a tree growing directly beneath a distribution or transmission line may be considered line-clearance tree trimming, even though none of the work is performed in close proximity to the conductors. This includes herbicide work as well.

Importantly, line-clearance arboriculture is defined by the work being performed, not by who the workers are.

For example, a qualified line-clearance crew pruning a tree that lies outside the specified distance from the conductors is not performing line-clearance tree trimming. Likewise, if the same crew is working within the specified distance, but the work is being performed for a homeowner, municipality or commercial customer rather than for or on behalf of the utility, the operation is not considered line-clearance tree trimming.

Under the 2026 Z133 framework, employees performing such work would instead be classified as Electrical Level 1, 2 or 3 arborists, depending on their training, qualifications and the voltages involved.

To further complicate matters, some states maintain multiple regulatory frameworks that may apply to tree work depending on the circumstances. As a result, two crews performing nearly identical work on similar trees may find themselves operating under entirely different requirements that go beyond ANSI and OSHA safety standards.

This complexity is one of the reasons Section 4 of the ANSI Z133 has continued to change. The challenge has never been defining the hazard; electricity behaves the same everywhere. Rather, the challenge has been developing a framework that recognizes the diversity of work performed by arborists while preserving the specialized qualifications required of line-clearance arborists.

Timothy M. Walsh, CTSP, is vice president, safety & training, with The Townsend Company LLC, a dual-accredited, 48-year TCIA member company based in Muncie, Indiana. He has served as a voting member of the ASC Z133 and serves on the Utility Arborist Association as past president, and on the National Occupational Research Agenda (NORA) safety workgroup.