Toolbox Topic: Trench Safety
Workers involved in trenching projects face considerable risks. Unprotected trenches can lead to injury or death. Cave-ins result in more work-related deaths than any other excavation-related incident. Additional hazards can include dangerous environments, falling loads, and dangers from mobile equipment. In today’s episode, we will discuss precautions you should take when working in or around trenches.
According to OSHA, an excavation is any man-made cut, cavity, trench, or depression in the Earth’s surface formed by earth removal. A trench is a narrow excavation (in relation to length) made below the ground’s surface. In general, the depth of a trench is greater than its width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m).
Or, to put it more simply, trenching in construction means creating a narrow excavation below the ground’s surface. Trenches are deeper than they are wide and narrower compared to their length.
The Greeks were the first to use trenching techniques to lay underground clay pipes for water and sanitation.
Around 500 B.C, the Romans used trenching to install aqueducts, indoor plumbing, wells, sewers, and fountains.
They often used the cut and cover method, which meant they would dig the trench, install pipes, and then bury the pipes by backfilling the trench with dirt.
Trenches were used early on by the military. The Cluilian trench was a vast trench surrounding ancient Rome. The army of Alba Longa dug the trench during the war between Alba Longa and Rome.
World War I
Trenches are often associated with World War I (1914–1918). During the war, thousands of miles of trenches were dug around Europe.
Today trenching is primarily used for laying communications and electrical cables, installing irrigation systems, drainage, and water/sewer lines.
Trench Safety Statistics
Between 2003 and 2017, there were over 350 trenching fatalities. 80% were in the construction sector.
Private construction fatalities took place:
- 38% at industrial locations
- 38% at private residences
- 20% on streets or roads.
Trench Safety Tips
Safety Tip #1 Preplanning
On-the-job incidents can result from inadequate planning. Gather information through Jobsite studies, observations, test borings for soil type or conditions, and consultations with local officials and utility companies. The information will help determine the equipment needed to perform the work safely.
Consider the following:
• Proximity and physical condition of nearby structures
• Soil classification
• Surface and groundwater
• Location of the water table
• Quantity of shoring or required protective systems
• Fall protection needs
• Number of ladders needed
• Overhead and underground utilities, including utility installations’ location(s) — sewer, telephone, fuel, electric, and water lines. Be sure to call 811, that’s the “Call Before You Dig” number, to establish the location of any underground utilities in the work area.
Safety Tip#2: Install Protective Systems
Protective systems are designed to protect employees from cave-ins. OSHA generally requires that employers protect workers from cave-ins by:
• Sloping and benching the sides of the excavation
• Supporting the sides of the excavation or
• Placing a shield between the side of the excavation and the work area.
Trench boxes are the most common form of trench protection.
Safety Tip #3 Support Systems
Excavation standards also require support systems, such as shoring, bracing, or underpinning, when necessary to ensure that adjacent structures (including adjoining buildings, walls, sidewalks, and pavements) remain stable. The standards also prohibit excavation below the base or footing of any foundation or retaining wall that could be reasonably expected to pose a hazard to workers unless:
• A support system is provided, such as underpinning.
• The excavation is in stable rock; or
• A registered professional engineer determines that the structure is far enough away from the excavation that it would not be affected by the excavation activity or that the excavation work will not pose a hazard to workers.
Safety Tip #4: Install and Remove Protective Systems Safely
The Excavation standards require protecting workers when installing and removing support systems. For example:
• Members of support systems must be securely connected to prevent sliding, falling, kick outs, or predictable failure. Also, support systems must not be overloaded.
• Support systems must be installed and removed to protect workers from cave-ins, structural collapses, and being struck by support system members.
• Before the temporary removal of individual members, additional precautions are required, such as installing other structural members to carry loads imposed on the support system.
• Removal must begin at and progress from the bottom of the excavation.
• Backfilling must progress together with the removal of support systems from excavations.
Safety Tip #5: Know the Dangers and Take Precautions
Working in a trench is dangerous. The walls can collapse suddenly and without warning. If this happens, you may not have time to get out. A square yard of dirt may not seem like a lot. However, that small amount can weigh more than a compact car. It weighs enough to fatally crush and suffocate you. So always take precautions when working in or around trenches:
• Keep equipment at least 2 feet away from the edge of the trench.
• Watch out for falling loads.
• Routinely inspect trenches -inspect all excavations, adjacent areas, and protective systems daily for hazardous conditions. Complete inspections at the start of work and as needed throughout the shift.
• Inspect the site following natural events, such as rainstorms, or other hazard-increasing occurrences, such as blasting work. If any unsafe conditions are discovered, workers must evacuate the site until it is made safe again.
• Check to ensure ladders, steps, ramps, or other safe means of egress are in place. When working in trench excavations of 4 feet (1.22 meters) or deeper, check that the means of egress are located so as not to require more than 25 feet of travel laterally within the trench.