Trench Cave-Ins: A Preventable Hazard

The National Institute for Occupational Safety and Health (NIOSH) estimates that 1.2 million workers are exposed to excavating hazards and that between 75 and 100 workers are killed annually in trench cave-ins. While some states have been able to reduce the number of deaths by instituting safety programs, in Texas the number of workers dying due to cave-ins is actually increasing.

There are many causes for cave-ins.

• Soil type -- Sandy soil has little cohesive strength and tends to cave in easily if not supported.
• Moisture -- Too much water reduces the ability of soil to stick together, causing it to slide. Too little water results in drying, which can cause soil to crack and collapse.
• Temperature -- Movement from expansion and contraction of soil during freeze/thaw cycles can affect soil stability.
• Surrounding materials -- The weight of construction materials, heavy equipment, and excavated soil located near a trench can increase tension on trench walls.
• Shock and vibration -- Moving trains, highway traffic, pile driving, and blasting can cause vibrations which can loosen soil and weaken trench walls.
• Intersecting trenches -- The point formed at the intersection of two trenches has less support than other parts of a trench and is particularly vulnerable to collapse.

Just as the causes of cave-ins are well known, so are the means to prevent them. A study in 1912 made recommendations that should still be followed today. They include:

• Sloping -- When trench walls are sloped, loose soil cannot fall back into the excavation site.
• Trench shields -- These box-shaped steel structures are strong enough to withstand the force of cave-ins (but are not strong enough to prevent them).
• Shoring systems -- Wood or metal constructions that press tightly against walls also help prevent cave-ins.

Deaths from trench cave-ins are preventable. Unfortunately, the workers who are exposed to the hazard of trench cave-ins are often unskilled and have little understanding of the risks of a trench cave-in. Without our workplace safety laws, they could become the victims of construction projects where safety rules are ignored to reduce costs or meet deadlines.