Excavations and Trenches

Not everyone on a given project is directly involved with trenching.  However, many people work near trenches and excavations.  Excavation safety is not just for workers in the hole.  If you observe an unsafe act, stop work and save someone’s life.  (WAC 296-155 Part N) 

Cave-ins and slough-offs are a major cause of deaths in the construction industry each year.  There have been 15 fatalities related to excavation activities in Washington State during 1998 – 2008. 

Soil collapse (cave-in) 7
Struck by machinery 4
Struck by motor vehicle 1
Struck by falling object 1
Electrocution 1
Fall 1


  • Before digging, check for services such as water, gas and electric. always treat services as live or functioning.
  • Excavations deeper than 4 feet must be supported or sloped back to prevent collapse
  • Use ladders for access and egress. Do not climb supports.
  • Those not directly involved, should keep out of the affected area-see new rules WAC 296-155-24611-1-d
  • Keep spoils piles back at least two feet from the excavation edge
  • Ensure stop blocks are fitted when dumpers are tipping into excavations and that they are guided by a signaler
  • Wear your hard hat at all times.
  • Never throw tools or materials to someone in an excavation. Always pass hand to hand or lower them on a rope if the trench is too deep.
  • Excavation inspections must be checked prior to entry at the start of a shift by a competent person

Remember, a cubic yard of earth can weigh 3000 pounds.  

Presenter tips

  • Pre-read the Toolbox Talk. Your comfort level and confidence will be higher if you know your topic.
  • Discuss related tasks, work areas or events that make the Toolbox Talk relevant to your job site.
  • Involve the workers by asking questions and input that drives discussion.

Questions for Discussion

  • What are other hazards besides cave in?
  • How does rail or freezing affect trenching activity?