By Brian Wahl, DNR Urban Forestry Coordinator
Brian.Wahl@wisconsin.gov or 608-225-7943

What is the ANSI Z133, and why should you care?

The American National Standards Institute (ANSI) Z133, more affectionately known at “The Z”, is the standard that contains arboriculture safety requirements for pruning, repairing, maintaining and removing trees, cutting brush and using equipment in such operations. If you’re reading this newsletter, you, your staff or your contactors likely participate in work that falls under the purview of this standard.

According to the description on the Tree Care Association’s website, compliance with this standard is voluntary. Although, the 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 to what the employer…”should have known or done” to create a safe work environment for its employees.

The bottom line is that you should be using “the Z” to guide all arboriculture related activities you, your staff or your contractors are engaged in.

The great news is that with the release of the newest version scheduled for May 27, “the Z” will now be available for free digitally, making it easier for you and your contractors to access. Be sure to include or reference International Society of Arboriculture (ISA) Best Management Practices (BMP’s) and ANSI standards in all your contracts dealing with tree work. If you would like paper booklets of the Z133 or any of the ISA BMP’s, they are available for a cost through the ISA and other professional organizations. Tip: Check with your urban forestry coordinator or borrow a copy from your local library.

Starting May 27, 2026, the latest version of “the Z”, Z133-2026, will be available digitally in both Spanish and English versions.  Obtain your no-cost digital copy through the ISA web store. Add the free product to your webcart, check out and then access it as a digital product through your MyISA account dashboard. If you do not already have a MyISA account, you will be prompted to create one upon checkout. There is no charge for the digital version or for creating a MyISA account.

Thank you to everyone who helped to pull together this latest addition, including some Wisconsinites.

Follow the standards, be safe and do excellent tree work!