There’s a difference between an excavation and a trench. OSHA defines an excavation as any man-made cut, cavity, trench, or depression in an earth’s surface, formed by earth removal. A trench is defined as a narrow excavation (in relation to its length) made below the ground’s surface. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet. If forms or other structures are installed or constructed in excavation to reduce the dimension measured from the forms or structure to the side of the excavation to 15 feet or less (measured at the bottom of the excavation), the excavation is also considered to be a trench.
There are three ways to protect workers from a collapse when working within a trench; sloping, shielding, or shoring. Most of the soils we encounter in the New England region are classified as Type C soils. The proper sloping angle for Type C soils is 1 ½: 1 (34°). A trench shield is often called a trench box. A trench box is a structure that can withstand the forces imposed on it by a cave-in and thereby protect employees within the structure. They can be permanent structures or designed to be portable and moved along as work progresses. The last way to protect workers while working within a trench is to shore it. Shoring consists of a pump jack, timber, or an engineered shoring system.
The most common type of trench protection is the trench box. It is essential to note that it must be appropriately used to function as expected when it comes to protective equipment. Trench boxes come with Tabulated Data. Tabulated Data is a document with tables and charts approved by a registered professional engineer and used to design and construct a protective system. A trench box must always be used within the designed allowances described in the tabulated data. Setting up a trench box is critical to ensure the safety of those that will be working inside it. The trench box sides must always be backfilled to restrict lateral or other hazardous movements of the box in the event of sudden lateral loads. Access must be provided to allow no more than 25′ of lateral travel for those working inside the trench box. Any water build-up within the trench must be controlled while workers are present. To protect from material falling or rolling into the trench, the spoil piles must be at least 2′ back from the edge. The excavation of material from below the bottom of the trench box is allowed to a level not greater than 2 feet below the box.
As we enter another Trench Safety Stand Week, the goal is to refresh and reset the practices of those working in the trenches. It only takes a second for a life to change. One life is too many when it comes to a trench collapse, and every collapse is preventable. Take the time to review the basics, discuss why safety procedures are in place and remember the saying, “Stay Within the Box.”