Carabiners used in trimming must be?

Carabiners used in trimming must be snap close, self-locking to ensure maximum safety during operations. This type of carabiner has a mechanism that prevents accidental opening, which is crucial when working at heights or with heavy equipment. The self-locking feature ensures that the carabiner remains securely closed during use, minimizing the risk of falls or equipment failure.

Additionally, the design of a self-locking carabiner allows for ease of use and quick attachment or detachment, which is vital for efficiency in tree trimming tasks. This level of safety and reliability is essential in preventing accidents and ensuring the well-being of workers.

Other options present characteristics that do not meet the necessary safety standards. For instance, plastic carabiners lack the strength required for heavy-duty work and are not suitable for climbing or trimming. Open-ended carabiners could easily detach under load, increasing the risk of accidents. Lastly, carabiners rated for less than 3000 lbs would not only be unsafe for arborist activities, where substantial forces can occur, but also could lead to catastrophic failures under load, further emphasizing why the correct option prioritizes reliable locking mechanisms and the strength required for such tasks.