Introduction
A trench is defined by OSHA as any narrow excavation that is longer than it is deep and less than 15 ft. wide. This toolbox talk focuses primarily on Trenches and trenching shoring. For an overview on excavation safety, sloping and benching requirements see our Trench & Excavation Safety toolbox talk.
Trenching shoring is a critical aspect of construction and civil engineering, ensuring the safety of workers involved in trenching and excavation activities. Understanding the hazards and implementing proper safety measures is essential to protect workers from serious injuries and fatalities.
Understanding Trenching and Excavation Hazards
Trenching and excavation pose significant hazards, including trench collapses, falling loads, and exposure to underground utilities. Trench walls can become unstable, leading to cave-ins, which are among the greatest risks to workers. Atmospheric hazards, such as toxic gases, can also pose a threat in deep trenches. Measures must be taken to address these hazards and keep workers safe.
Protective Measures for Trench Safety
Protecting Against Cave-ins with Trenching Shoring
Trench collapse and cave-ins pose the greatest risk to workers conducting trenching operations. The Occupational Safety and Health Administration (OSHA) requires trench protection to be employed for any trenches more than 5 feet deep. The two most common forms of trench protection are:
- Sloping & Benching : The sides of the trench are excavated back in a slope or bench to create more stability in the soil. The required angle of the slope or bench is determined by the type of soil. This method often eliminates the need for shoring equipment, but requires are large footprint to work in. It also increases the volume of earth removal and backfill required. For more information on this method of protection, see our Trench & Excavation Safety toolbox talk.
- Shoring: This method shields workers by directly supporting the sides of the trench with a protective barrier against trench wall collapses. Shored trenches are excavated with vertical sides, creating a smaller footprint. This method may be selected over benching when there is limited space to work due to nearby structures, utilities or other conflicts.. Other benefits to shoring include easier access to the work area and smaller volume of excavation. There are many types of shoring systems. The shoring system selected for a job will depend on the availability and details of the work required. Shoring systems come with data sheets showing how deep they can be installed in each soil type, but note that any trench shoring system installed more than 20 ft. deep is required to be analyzed by a licensed engineer.
Types of Shoring
- Trench Boxes: Trench Boxes are fabricated structures consisting of spreaders and shields. They are simple to assemble and able to to withstand large amounts of earth-pressure. The following are key safety items related using trench boxes:
- Tabulated Data: Every system has a tabulated data sheet for the model and configuration. This sheet indicates how deep the box can be used for each soil condition. OSHA requires that tabulated data be kept onsite. Do not use a system outside of the tabulated data parameters
- Inspection: Inspect Trench box systems daily. Look for damage that affects the structural integrity of the system.
- Hardware & Components: Do not mix and match spreaders, shields or pins for different systems. Each trench box is engineered to work as a system with the manufacturer’s components. Also, ensure retaining pins are used to secure the spreader pins. This is required by OSHA
- Hydraulic Shoring: Hydraulic shoring systems consist of hydraulic spreaders that span the width of the trench to support shields at the trench wall. They are more versatile than trench boxes because they can be assembled inside the trench around obstacles such as underground utilities. The same safety items for trench boxes apply to hydraulic shoring. Reference tabulated data to correctly install shoring systems in the proper configuration. Inspect the system daily. Only use components recommended by the manufacturer to assemble the shoring system.
- Other types of shoring: Other shoring systems can be constructed onsite without the use of pre-manufactured materials. Some examples include timber pile systems, sheet piles, beam & plate, and wire walls. Select shoring systems based on the application and materials available. Shoring systems that are constructed onsite need to be designed by a professional engineer. Any shoring system installed at depths more than 20 feet must be designed or analyzed by a professional engineer.
Examples of Shoring Systems
Key Safety Measures
- Competent Person: A trained individual should be present on-site to identify potential hazards as well as to determine appropriate protective systems.
- Trench Shoring: Install shoring or benching in all trenches deeper than 5 feet to prevent collapse.
- Utility Lines: Always locate and mark the exact location of underground utilities before beginning work to avoid damaging them.
- Atmospheric Testing: Regularly test the atmosphere in trenches for toxic gases and other hazards.
- Proper Equipment: Use the right trench shoring equipment for the job, to include trench boxes and hydraulic shoring systems.
Preventing Cave-Ins
- Sloping and Benching: Adjust the angle of trench walls to reduce the risk of collapse.
- Shoring Systems: Use hydraulic shoring or other methods to reinforce trench walls.
- Trench Shields: Employ trench boxes to protect workers within the trench.
- Regular Inspections: Conduct daily inspections of trench walls and protective systems, especially after rainstorms or other events that could affect soil stability.
Site Safety Practices
- Edge Protection: Keep heavy equipment and materials away from the edge of the trench to prevent falling loads. Keep tools, material and equipment at least 4 feet from the edge of trenches at all times.
- Worker Training: Train all employees in trench safety so they understand the risks involved.
- Emergency Response: Have a plan in place for quickly rescuing workers in the event of a cave-in or other emergency.
Conclusion
Trenching shoring is essential to maintaining safety on construction sites. By implementing protective systems, conducting regular inspections, and training workers, we can prevent cave-ins and protect the lives of those working in trenches. Always adhere to OSHA guidelines and prioritize safety in all trenching and excavation activities.