Which of the following is usually not considered a confined space?

A confined space is typically defined as an area that is large enough for a person to enter and perform work but has limited means of entry or exit and is not designed for continuous occupancy.

The choice referring to a 3 ft. trench is generally not classified as a confined space because trenches are often considered to have enough horizontal space for workers to perform their tasks, and they usually allow for easier entry and exit compared to other options. The nature of a trench, being more open and not enclosed in the same way as a storage room, boiler room, or water tank, allows workers to navigate in and out more freely, which does not meet the criteria for a confined space.

On the other hand, a storage room, boiler room, and water tank are typically more enclosed environments that pose a higher risk for workers due to restricted movement, which may also include potential hazards such as lack of ventilation or hazardous atmospheres. Thus, these spaces fit more consistently within the definition of a confined space, making the trench the most logical option for not being considered as such.