Contruction Safety – Trench Digging

By David Ross

The beginning of construction work was digging trenches. It’s been done since Paleolithic times, and until the advent of mechanized machinery after World War II, it was done manually with pick and shovel. As trenches get dug deeper, the sides need shoring up to keep from caving in.

Following the World War, several innovations were made in backhoes, and trench digging seemed to fade away as a profession. By 1950, hydraulically actuated backhoes were developed, which make it possible to rapidly dig very deep trenches. Resulting from the innovations with backhoes, and because there were no workers inside digging the trenches, the walls no longer needed to be shored.

All types of trenches have what’s known as a stand up time. This time is the amount of time that elapses from the time the ditch is dug until the time the trench walls start to collapse. The stand up time is dependant on many factors, which include the type of soil, water content, trench depth, weather conditions, and whether or not the soil has been disturbed.

Stand-up time can be very short – zero seconds in the case of an unsafe or collapsing trench. Trenches can also last up to a year in the right soil with the right weather conditions. Before a trench is dug, soil samples must be collected, and stand up time must be estimated.

The reason for a trench is that workers will go down into it and perform some needed labor, such as laying pipe or installing telephone lines. There may be welding of pipe, or sealing valves. Supporting the trench walls is important to avoid having them collapse while people are down there; on average, nearly 150 people per year are killed in the US due to trench collapses.

The public outcry over construction accidents, and environmental impacts, means that every trench needs to be assessed by an engineer. One way to cut these risks down is through the use of a trench box.

The trench box is usually two steel plates that are put in on either side of the trench walls and cross braced to prevent collapses. It’s there to keep the earth from closing in and burying the people working in the trench, and it’s an essential piece of safety gear on a work site.

When put in, the bottom edge of the trench box sits on the bottom of the ditch. The top edge should extend over local ground levels. Workers stay within the cross braced area of the box, and the dirt stays outside their work area. As the work progresses, the trench box is pulled forward into the new work zone.

When a project calls for a large excavation such as digging the foundation for a tall building, the supporting structure for the excavated walls will be specified in the plans. The big problem with not using trench boxes occurs in cities, when water or sewer lines are being installed or repaired. The engineer doesn’t specify for the trench box in the plans, but instead leaves it up to the contractor.

If you’re working in a trench, or digging them, follow common sense. Take your time. Don’t rush. Go slowly. Particularly if you’re in an unreinforced trench, they can be deadly. Always use a trench box if you’re going to be in the trench, and if you don’t need to be in the trench, stay out. Let the machinery do the work.

David is an expert in the pressure washing business. For more informative articles on pressure washing see his site www.PressureWashingKing.com

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Tags: construction, do-it-yourself, Gardening, Home and Garden, Home Improvement, home repair, pressure washing

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