Trench boxes, often referred to as “Shields”, are designed to withstand the collapse forces of a failing trench wall. In addition, the shield must be rated for the type of soil and the depth for which it will be deployed. In doing so, the worker is safeguarded from injury. Having said this, those entering the trench must do their part to ensure the requirements of the manufacturer are met.
First and foremost, the worker, as well as the ladder, must remain within the shielded area. As obvious as this sounds, there have been several instances where a worker has been seriously injured or killed stepping outside the protection of the shield to either retrieve a tool or get to an improperly positioned ladder.
Secondly, and in all instances where the trench box is the sole source of protection, trench boxes are required, at minimum, to extend to the top of the trench. They may be positioned a maximum of 24″ above the floor of the trench. It’s for this reason, most manufacturers offer extendable legs for their shields.
And then finally, the manufacturer’s tabulated data will dictate the allowable spacing between the shield and the wall of the trench. In keeping this space to a minimum, the likelihood of a worker, should the shield receive an impact load, becoming crushed between the shield and what he’s working on is greatly reduced.
Trench boxes started out being big and extremely heavy; requiring large trailers and machines powerful enough to handle the weight of the shield. Not everyone requires such a robust shield. Nowadays, manufacturers like Prospan, offer extremely lightweight shields that can be brought to the dig site in the back of a pickup truck and assembled by hand; thus reducing the manpower typically required. Compliance with the OSHA requirements as well as worker safety has never been easier!