Trench shields and trench boxes remain OSHA-approved safety measures for worker protection on the jobsite. The applications and protection that such components provide are featured in the following article, “A Life or Death Matter” by Daniel C. Brown. Part 1 of his full-feature article on the multifaceted methods of trench protection—including the advantages of trench shoring services—follows below.
A Life or Death Matter (Part 1) By Daniel C. Brown
An average of 1,000 lost-time trench collapses occurs every year, according to the National Institute of Occupational Safety and Health. In 2013, trenching hazards resulted in 30 known deaths nationwide. Authorities estimate that up to 100 fatalities may occur every year, but many are unreported.
Trench shields and trench boxes remain OSHA-approved safety measures for worker protection on the jobsite. The applications and protection that such components provide are featured in the following article, "A Life or Death Matter" by Daniel C. Brown. Part 1 of his full-feature article on the multifaceted methods of trench protection—including the advantages of trench shoring services—follows below.A Life or Death Matter (Part 1) By Daniel C. Brown
An average of 1,000 lost-time trench collapses occurs every year, according to the National Institute of Occupational Safety and Health. In 2013, trenching hazards resulted in 30 known deaths nationwide. Authorities estimate that up to 100 fatalities may occur every year, but many are unreported. [text_ad] We can do better. Trench protection is affordable, and it saves lives. OSHA endorses three basic types of trench protection: sloping, shoring, and shielding. Traditionally in the Great Lakes states, the Midwest, and the East, the prevalent method of protection has been the trench shield, or trench box. Hydraulic shores and components were developed on the West Coast, so that has driven their adoption in that region. [caption id="attachment_1815" align="alignleft" width="270"]
We can do better. Trench protection is affordable, and it saves lives. OSHA endorses three basic types of trench protection: sloping, shoring, and shielding. Traditionally in the Great Lakes states, the Midwest, and the East, the prevalent method of protection has been the trench shield, or trench box. Hydraulic shores and components were developed on the West Coast, so that has driven their adoption in that region.
Shoring is anything but a one-size-fits-all way of doing things. When it comes to sizing, flexibility is important.
“The trench shield really doesn’t have any limiting soil conditions,” says Michael Ross, national training director for Efficiency Production Inc., a manufacturer of trench protection equipment. “It is a good tool if you have moving or unstable soils, because you have the option to dig inside the box and use the box as a support as you dig down to hold the trench apart. The hydraulic shoring system does have a limitation in that the trench walls need to stand vertical long enough to install the shores. Sometimes the soil is too unstable for the use of hydraulic shoring equipment.
“Each piece of equipment has its own advantages and disadvantages,” says Ross. The most common use of trench shores in laying pipe is where utilities cross the alignment of the trench being dug. The trench shield, or box, won’t allow anything to pass through it. So if you’re in a pipe run where you have a lot of crossing utilities, that would be one reason to go with shores. That’s because the shore has natural breaks in it between the cylinders, which allows the utilities to pass through.
“Another advantage to shores is the size of the equipment,” says Ross. “A lot of utility companies will carry shores because they take up very little space, and, therefore, they can dig a hole and throw the shores in by hand. You don’t need a separate trailer to carry the box components, because they’re smaller than a trench box. For example, if you had three hydraulic shores, in say, C-60 soil, you could place those six feet apart, roughly. So you could get 12 feet of protected space in a trench. But if you need a 12-foot box, that box would take up quite a bit more space than the three hydraulic shores.”
So shores are lighter in weight and can be installed by hand. They do not require a large machine like an excavator to handle them. Manufacturers publish tabulated data that contain recommendations for the number of shores to use in various soil conditions. Ross says tabulated data for shores is not based on the depth of the trench; the data is based on the placement of the hydraulic cylinders that hold the trench walls apart.
That makes shores very flexible, not only for crossing utilities but also for different soil conditions, Ross says. You can keep collapsing and reinstalling shores, but a box is a fixed object. Shores are adaptable to changes in dimensions, but a trench shield has fixed dimensions. “But with shores, if you don’t exceed the required distance apart of the cylinders, you can arrange those cylinders in an infinite number of places as long as you don’t exceed the maximum distance that the manufacturer’s engineer allows,” says Ross.
“So you can keep shuffling your cylinders around to accommodate not only crossing utilities, but changes like the need to tap into a main or to install something in your trench,” says Ross. “A good example is if you need to find a break in a pipe and you need to dig up to a broken pipe. When you get there, and you’ve got your shores in, the break doesn’t hit the center of the excavation. With a trench box, you may have to over-dig that on both ends to reposition the box. But with shores, it’s much simpler. You can just collapse the shores and move them over. As long as you stay within the limitations set by the manufacturer, you can move them to suit your needs.
