New 2017 Revision! This latest revision includes many new Z133 safety requirements. This publication establishes safety standards for tree care operations such as pruning, trimming, repairing, maintaining, and removing trees in the United States. The purpose of the Z133 standard is to provide safety criteria for workers and the public. It also is intended as an aid to federal, state and municipal authorities in drafting regulations and may be adopted in whole or in part.