An excavation is a man-made cavity in the ground and a trench is an excavation that is deeper than it is wide. Working in trenches increases the risk of injury and death and a significant number of worker injuries and fatalities are directly related to trench cave-ins. Many factors must be considered when the creation of a trench begins, including soil type, amount of moisture present, effect of vibration from equipment and nearby traffic, surcharge load (i.e. excessive weight that can put pressure on the walls of the trench), previous excavation, and weather for the area. Many methods may be used to protect against cave-ins, including the use of trench boxes. Trench boxes protect workers from cave-ins and create a safer work environment (Trenching Safety, 2010).

According to NIOSH, Bureau of Labor Statistics data from 2000 to 2009 indicate that an average of 35 workers per year died in trenching or excavation cave-ins in the United States (NIOSH, 2011). The NIOSH report also noted a study based on an analysis of OSHA data from 1997−2001 that showed 64 percent of fatalities in trenches occurred at depths of less than 10 feet (Arboleda and Abraham 2004). Another study that used OSHA inspection data showed that lack of a protective system was the leading cause of trench-related fatalities (Deatherage et al. 2004). 

OSHA has focused heavily on excavation and trenching operations over the past decade. Such operations can be dangerous past four feet deep with cave-ins causing serious injury or death. More serious incidents are likely to occur when work is performed at a depth of six to nine feet. With the average cubic yard of dirt weighing approximately one ton, a person will likely not be able to breathe due to the pressure of the dirt on his or her chest. Even if a person maintains the ability to breathe during a cave-in, it is not guaranteed that the victim will survive injuries from compression of the lungs and other organs. OSHA reviewed cases from 2004 and found they had issued over $7 million in penalties for accidents that most likely could have been avoided (Griffin, 2005).

Trench boxes are lowered into trenches to protect workers from cave-ins. Two large, typically steel, plates make up the walls of the trench box. The walls of the box are fixed and positioned to be parallel to the walls of the trench. Horizontal bars cross the structure to keep the two wall plates from compressing. The box sits along the bottom of the trench bed, while the upper edges rise above the trench opening. The walls of the box will stop dirt from collapsing on workers if the trench begins to cave in. To ensure optimal safety, the trench box is pulled through the trench as work advances (Texas A&M University, 1992).

Even with trench boxes in place, workers still need to be observant of the surroundings and exit any trenches that do not seem stable until the problem is corrected.

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NIOSH Workplace Solutions Sheet
The National Institute of Safety and Health (NIOSH) has published a series of “Workplace Solutions”, which are easy-to-understand recommendations from NIOSH research results. Related to this Construction Solution, please find more information on: Preventing Worker Deaths from Trench Cave-ins