A Deep Dive into Trench Safety
Without the proper safety protections, working in a trench or excavation site can be deadly. But companies can prevent accidents, injuries, and fatalities by following safety guidelines and employing the proper protective equipment.
Trench safety refers to a series of practices that reduce the chance of worker injuries related to cave-ins, falling loads, equipment hazards, and dangerous atmospheres. Unprotected trenches are dangerous – walls can suddenly collapse – and dirt is much heavier than people think. A cubic yard of dirt can weigh as much as a small car.
Importance of Trench Safety
Unfortunately, trench-related injuries and deaths are all too common. In 2022, 39 workers died in trench or excavation work-related accidents – up from 15 in 2021. The majority of fatalities take place in the construction industry.
Trench safety will be even more important as companies gear up for the many projects expected from the Bipartisan Infrastructure Law of 2021. The law will lead to investment in roads, bridges, mass transit, water infrastructure, and broadband.
The Occupational Safety and Health Administration (OSHA) has a three-part slogan, “Slope-Shore-Shield,” to help people remember the basics of trench safety.
What this means: Make sure to slope or bench trench walls at an angle that inclines away from the excavation. Aluminum hydraulic or other types of supports should be used to shore trench walls and prevent soil from shifting. Trench boxes and other types of supports shield trench walls to prevent cave-ins.
Trench Safety Tips
Trench safety starts with proper planning.
- Identify safe locations on the job site for removed soil (spoils) and routes for heavy equipment to safely travel.
- Keep items and equipment away from the edge of a trench.
- Ensure that all workers will be within 25 feet of a ladder or exit at all times.
- Any excavated soil and other materials should be at least two feet away from the edges of the trench.
- Locate underground utilities before starting any digging, and make sure to stay at least five feet away from these spots.
- Place proper signs and protection throughout the job site.
- Create an emergency action plan.
A competent person should properly inspect a trench site daily and again after a rainstorm or if other conditions change during the day. OSHA defines a competent person as someone with the knowledge to identify hazards and unsafe conditions, as well as the authority to take corrective action. That knowledge includes soil classification, inspection of protective systems, design of structural ramps, water removal monitoring, and site inspections.
When work is underway, employees should continue to monitor conditions in the trench area to identify potential hazards, such as standing water, and to eliminate them. Trenches greater than four feet deep should be tested for airborne hazards, such as fumes, gas, or low oxygen levels.
Workers should wear visible clothing and the proper protective equipment. Employees should not work underneath materials or loads that are raised or suspended.
Protective Systems for Trenches
OSHA regulations require that five feet deep or greater trenches have a protective system in place unless the entire trench is surrounded by stable rock. A competent person must determine if a protective system is required for trenches less than five feet deep.
A registered professional engineer must design the protective system for any trenches 20 feet deep or more.
There are many different types of protective systems.
- Benching is a method that relies on creating a series of steps of levels on the vertical walls.
- Sloping involves cutting the sides at an angle inclined away from the center.
- Shoring systems use supports to brace the walls and prevent soil from shifting to create a cave-in.
- Shielding systems – which include trench boxes – protect workers in the event of a trench collapse.
Designing a protective system is a complex process. Important factors include the soil classification, trench depth, water content, climatic conditions, and surcharge loads.
OSHA Trench Box Requirements
Trench boxes – also known as trench shields – are structures made from steel or aluminum and designed to protect people who work in trenches. Trench boxes are made from different materials and various thicknesses to safely accommodate workers in varying trench conditions.
There are specific OSHA guidelines for the use of trench boxes at excavation sites. These include the following.
- Contractors must backfill the space between the trench box and the excavation walls to restrict lateral movement in the event of a cave-in or other sudden load placed on the system.
- Trench boxes should be placed no more than two feet from the bottom of the trench.
- A trench box may be used with other protective systems, such as sloping and benching. Trench boxes used in combination with other systems must extend 18 inches above the vertical part of the trench walls.
- Trench boxes must be designed for the type of soil where they will be used and must be able to handle the pressure at the given depth.
- Contractors may stack trench boxes at different depths as necessary to protect workers, but each box should be designed for pressure at the level where it is placed.
- Workers should not remain in a trench box during transportation or installation.
Trench Safety Equipment
Individuals working in trenches should have proper personal protective equipment. These include:
- A hard hat for protection against overhead impact and electrical hazards
- Goggles or other eye protection with side shields
- Gloves that are meant for the specific hazards of the given job
- Appropriate protective footwear
- Respiratory protection as necessary
Workers entering a confined footing excavation or bell-bottom pier hole should wear a harness with a lifeline, which is separate from any line used to handle materials.
In addition to personal protective equipment, workers should have appropriate safety training for the type of job site and equipment they will use.
Additional Resources on Trench Safety
Fortunately, trench safety is becoming increasingly prevalent in our industry and communities, making resources and training more widely accessible. The more you know about trench safety, the safer you will be. Check out these reliable resources for some extra reinforcement:
- NUCA’s Trench Safety Toolbox Talk (available in “General Safety” section of this web page)
- National Trench Safety’s Expert Corner
- United States Department of Labor OSHA Trenching & Excavation Resources
We care about the safety and success of our customers and employees. To learn more about the equipment and services available at Boyd CAT, please contact us.