Trenching and Excavation Safety (Part 1)

An excavation is defined as a “man-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal”

A trench is defined as “a narrow underground excavation that is deeper than it is wide, and is no wide than 15 feet”

(Definitions are from OSHA)

Trench and excavation work kills an average of 54 workers each year (these number includes only the reported numbers. Many others may be listed as having other causes of death and not officially be counted as trench related fatalities); injuries number in the hundreds. The costs associated with each trench collapse can reach into the hundreds of thousands of dollars for each incident.

Being buried alive is not a nice way to go, especially considering that most if not all of these injuries and deaths could easily have been avoided by following a few simple safety measures. According to the CDC, up to 95% of injuries and fatalities occurred in trenches where no preventative measures were taken.

Types of accidents

  1. The Spoil Pile Slide – This type of slide is where the dirt that is excavated is piled too close to the trench. When the dirt is piled too high, too close or at a critical angle it can slide back into the trench.
  2. The Shear Wall Collapse – This type of slide occurs when the shear wall breaks off, dumping a large amount of dirt and debris in the trench. This type of collapse usually occurs in clay or layered soil and is most often catastrophic.
  3. The Belly Slough – A pocket of dirt between the top and the bottom of the trench breaks off and slides into the trench
  4. The Lip Slide – Similar to the spoil pile slide, this collapse occurs when the excavated dirt is too close to the top lip of the trench causing pressure. Vibrations from excavating equipment and other machinery can cause a small chunk of dirt to collapse. Because the spoil dirt is resting on this lip, however, the amount of dirt can be much larger than just the amount of dirt from the break.

(Too see a flash animation of each of these types of slides, visit the CDC website at http://www.cdc.gov/niosh/docs/2006-133D/flash/index.html).