Excavation Safety Hazards
Construction projects involving excavation and trenching are among the most dangerous work activities. An excavation is defined as any man-made cut, cavity, trench, or depression that is formed by earth removal. The term “trench” is specific to underground excavations that are deeper than they are wide, and that do not exceed 15 feet in width. The fatality rate for all types of excavation jobs is 112% higher than for general industry (US Occupational Safety and Health Administration). Given this high level of danger, it is critical that safety precautions and controls are used at all times and that extreme caution and patience be exercised when working in and around shafts and excavations.
Types of excavation risk
Cave-ins pose the greatest risk and are the most likely type of excavation-related incident to result in fatalities. Other potential hazards associated with excavation include:
• Falls in trenches or excavations
• Tripping over equipment, debris and waste
• Excavated material or other objects falling on workers
• Exposure to underground utilities or overhead lines
• Mishandled or misplaced materials
• Difficulty breathing due to noxious gases or lack of oxygen
• Toxic, irritant or explosive gases
• Vehicles and mobile equipment
Mitigate risk
The two basic methods of protecting workers from cave-ins are sloped and temporary protective structures.
Tipping involves trimming the trench wall at an angle that slopes away from the excavation work area. The appropriate slope angle depends on the soil conditions at the excavation site.
Temporary protection structures are designed to provide protection against cave-ins, collapse, sliding, or rolling stock. Examples of temporary protection structures include shoring, trench boxes, precast systems, hydraulic systems, and engineered systems.
Shoring is a system that supports the sides or walls and typically requires the use of aluminum, steel, or wood panels held in place with screws or hydraulic jacks. The shoring should be done in conjunction with the progression of the excavation. If there is any delay between excavation and shoring, no worker should enter the trench without protection. Trench boxes are often used in open areas that are far from utilities, roads, and foundations. Trench boxes can be used to protect workers in the event of a cave-in, but they are not a substitute for shoring. If the trench or excavation walls are made of rock, rock bolts or wire mesh can be used to provide additional support.
Safety tips when digging:
• Know the location of any underground utility lines
• Wear the proper PPE, including a hard hat, goggles, and shoes.
• Keep heavy equipment away from trench edges.
• Test for low level of oxygen and toxic gases.
• Inspect trenches at the start of each shift or if there has been significant rain.
• Place barriers along the outer perimeter and security signs in key locations.
• Consider consulting with a professional engineer on shoring design and installation.
• Establish a safe means of access and egress
• Know the location of water sources and what the drainage patterns will be.
• Develop an emergency response plan and include provisions for extreme weather conditions, evacuation routes, and communication plans.
What not to do:
• Do not enter an unprotected trench more than 4 feet deep.
• Do not start digging before locating and de-energizing buried utilities.
• Do not enter a trench before testing the air.
• Do not place anything less than 1 meter from the edge of the trench
• Do not rely on natural freezing to act as a soil stabilization method.
It is important to remember that cave-ins can occur without warning, regardless of depth. In fact, the vast majority of fatalities occur at shallow depths when workers do not appreciate the risks involved. All excavation projects present serious safety risks, but injuries and deaths resulting from cave-ins can be prevented with proper planning and safety precautions.