Trenching and Excavation (Internal Link)

A trench is a ditch or excavation that is deeper than it is wide. A trench can be up to 15-feet wide.

Hazards of trenching and excavation

Cave-ins can cause death or serious injury. Workers can be buried in a matter of seconds when the sides of a trench collapse. A worker can die even if the soil does not cover the person’s head. Soil is so heavy that a person will not be able to breathe if the dirt surrounds their stomach and chest.

Cave-ins are most likely to happen where:

• the trench is dug in unstable soil or in soil that has been dug before; 
  
  
• there is a lot of vibration from construction equipment or traffic near the dig; 
  
  
• there is too much weight on the sides of the trench; 
  
  
• water has collected in the hole; and/or 
  
  
• there are changes in the weather like freezing, melting snow or ice, heavy rain, etc.
  
  

Other common hazards of trenching and excavation operations include:

• contact with underground utility lines; 
  
  
• being crushed or struck by equipment; and 
  
  
• air that may have not have enough oxygen or may contain toxic gases and vapors. 
  
  

Protecting workers during trenching and excavation work

Cave-ins can be prevented by taking these actions:

• Have a “competent person” in charge at the worksite who can test the soil, recognize unsafe conditions, and has the authority to stop the work. 
  
  
• Keep traffic away from the area. 
  
  
• Pile the dirt at least 2 feet from the edge of the trench. 
  
  
• Pump water out of the hole before anyone goes in. 
  
  
• Test the soil to find out it is stable or is likely to collapse. Soil is a mixture of sand, gravel, silts, clay, water and other materials. The soil must be tested to see how well it holds together (cohesiveness). The more unstable the soil, the greater the chance of a cave-in. 
  
  
• Use a protective system, such as shoring or a shield.

Shoring is made of timber, mechanical or hydraulic systems that support the sides of an excavation.  A shield, also called a trench box, protects workers if there is a cave-in. Trench boxes are a good system for laying pipe. See Figure 4. Sloping is digging at an angle as shown in Figure 5. For each foot deep, the soil is dug a foot and a half back from the edge of the trench. Benching is another method of digging that is like making stairs into the excavation. Sloping and benching are not used often because there is usually not enough space. These methods also require removing and replacing much more dirt than shoring or a trench box.

Figure 4 Figure 5

Controlling other hazards during trenching and excavation operations:

• Test the air for oxygen level, explosion and fire dangers, and toxic gases if the hole is more than 4-feet deep. 
  
  
• Contact utility companies to locate power lines before digging.

Laws to protect workers

The OSHA regulation to protect workers from the hazards of excavation and trenching work is 29 CFR 1926.650-652. A summary of the regulation, and the regulation itself, can be found in the AFSCME manual, Excavation, Trenching and Shoring Safety and the OSHA Excavation Standard.