Which piece of equipment is most effective in firm soil and can be placed or removed without entering a trench?

Shoring jacks are designed to provide support to excavation walls and prevent soil collapse, making them highly effective in firm soil conditions. They can be easily placed or removed without requiring personnel to enter the trench, which is critical for maintaining safety on construction sites. This ability to operate from above ground allows workers to manage the shoring system while adhering to safety regulations.

In contrast, a trench box is primarily used to safeguard workers within trenches by creating a barrier against soil collapse, but it would typically require entry into the trench for proper placement or removal. An excavation hammer is designed for breaking up hard materials, which is not its intended purpose in trench safety contexts. Similarly, a hydraulic jack is generally used for lifting and heavy-duty applications, but it does not provide the necessary earth support that shoring jacks do within an excavation scenario. Therefore, shoring jacks stand out as the most suitable equipment for the task outlined in the question.