ANSI Z133 2017 Revision Overview

These are just a few of the revisions in the updated Z133. To fully familiarize yourself with the revisions, we recommend picking up a copy, currently available in the TCIA Shop. Non-member pricing is $20.00. TCIA members get a 25% discount and pay only $15.00.

The American National Standard for Arboricultural Operations - Safety Requirements, also known as the ANSI Z133 or just Z133, recently completed its 2017 revision. The Z133 is developed by the Accredited Standards Committee ASC Z133. This revision provides the most current and comprehensive safety guidance for arborists in the United States.

Although compliance with this standard is voluntary, Z133 carries the force of law in many instances in the U.S. When OSHA cannot find language in its own standards to guide safe work practices in a particular situation they will typically cite a section of Z133 as what the employer "should have known or done” to create a safe work environment for its employees.

The following are a small selection of changes in the 2017 revision:

Electrical hazards

One of the most notable changes is in section 4 – Electrical Hazards – specifically the expansion of the rules for working in proximity to electrical hazards to recognize three levels of qualification: the unqualified, the Incidental Line Clearance Arborist and Utility Line Clearance Arborist. This is a sizeable expansion on the topic from the previous version, and specifically details the safety requirements of each of these tree worker positions.


The following changes pertaining to climbers are relatively simple and straightforward. For example, the climber is now required to have a hand saw available while working aloft, where previously it was only a recommendation. The same now applies to aerial lift operators when pruning. The purpose of requiring a handsaw while aloft is make a strong suggestion for an alternative practice (i.e., use a hand saw) to reduce the incidents of one-handed chainsaw use..

The arborist shall be secured at all times – that part is not new, but what was added specifies that when repositioning, the arborist shall preload the new tie-in point with his/her full weight before releasing the current means of being secured. Additionally, the climber shall select a tie-in point/primary suspension point that prevents lateral movement of the climbing line.

Use of vehicles and mobile equipment

Chippers and winches received a lot of attention in the 2017 revisions. For instance, the use of chippers by arborists, mechanics and other workers includes the following clarification in the 2017 revision: If maintenance is needed, all moving parts shall come to a complete stop and keys shall be removed from the ignition and pocketed by the authorized person before proceeding.

When working with chipper winches, a winch line should not be wrapped around a load. During winching operations of loads that do not have a manufactured attachment point, the load should be secured using a sling. Winch lines must also be compatible with the winch design and shall meet manufacturer’s specifications. Additionally, when using a winch in chipper operations, the operator shall ensure that the winch line is properly stored before initiating chipper operations.

As for other equipment, the 2017 revision restates that equipment must be inspected before use, but goes further to suggest that if an inspection reveals a defect that could affect the safe operation of the equipment, the equipment shall be removed from service.

With regards to vehicles, it is noted that drivers shall know and not exceed the gross vehicle weight rating (GVWR) and/or gross combination weigh rating (GCWR) of any vehicle and towed equipment prior to moving the equipment. This essentially means that if the truck is over-loaded on a tree job, the driver is responsible.

Also important to note, the wheel chock guideline previously stated that wheel chocks need to be set before using an aerial device – the new standard specifies two wheel chocks.

General Safety

For field crews involving two or more workers at a work location, at least two workers trained in first aid/CPR shall be available, according to the 2017 revision.

Radio communications between the qualified arborist and qualified crane operator shall be used during blind picks. Radio communications shall be hands free.

When more than one worker is involved in limbing, bucking and moving debris from a tree, each shall be positioned and their duties organized so that the actions of one worker will not create a hazard for any other worker. The 2017 expansion on this requirement clarifies that only one worker shall be cutting a single tree or single tree part during the limbing and bucking process.