Trenching and Excavation Safety
Did you know? One cubic yard of soil can weigh as much as a vehicle!
Excavation and trenching are among the most hazardous operations in the construction industry. A trench collapse can happen fast, without warning, and can be fatal. Collapses can occur even in shallow trenches. Often, trench collapses are caused by cave-ins that occur when trench walls suddenly collapse inward. In just seconds, the heavy weight of soil can cause workers to be buried, experience crushing and potentially fatal injuries, or be trapped in an oxygen-deficient environment. Beyond collapses, falls into trenches, hazardous conditions, equipment instability, and underground utility damage should all be considered in the construction planning and preparation phase.
Types of Protective Systems in Excavation Safety
To help prevent incidents and reduce the risk of trench collapse and worker injury/death, it’s critical that all trenching and excavation work be properly planned, inspected, and protected. Protective systems are designed to prevent trench collapse and protect workers should a collapse occur. OSHA requires protective systems for trenches 5 feet or deeper, unless specific requirements for soil are met. The type of protection used depends on various conditions, including soil conditions, trench depth, weather, workspace, and much more.
Among the types of Protective Systems that can aid in excavation safety:
Sloping refers to cutting back the trench wall at an angle away from the excavation to prevent a vertical collapse. The angle steepness will vary depending on the soil type. While a simple, effective method, sloping requires a significant amount of space. Benching means cutting the sides of a trench into horizontal steps to reduce pressure and lower the potential of collapse. Benching is only permitted with certain stable soil types. Shielding involves the use of a trench box or shield, and must be used according to OSHA requirements, manufacturers’ tabulated data, or an approved engineered design. Trench boxes do not prevent a trench collapse, but rather provide protection to workers if one were to occur Shoring is the use of a support system to hold back trench walls to prevent soil collapse. This requires planned coordination for installation and removal. Shoring systems can include:
- Hydraulic
- Pneumatic
- Timber
- & Other manufactured or engineered support systems
Parting Thoughts
When planning for trenching & excavation safety, it’s important to consider three additional factors: Soil Classification: The type of soil determines how likely a trench wall is to collapse, and what protective systems are required. Types of soil include:
- Stable Rock
- Type A – the most stable, cohesive soil
- Type B – medium stability
- Type C – the least stable (this could include sand, gravel, or saturated soil)
Weather Conditions: Heavy rainfall, freezing/thawing, and other conditions can destabilize the soil. Previous Soil Disturbance: Soil that has already been disturbed is more unstable than untouched soil As construction crews work to make progress on projects ahead of the fall season, it’s important to remain up to speed and vigilant on trenching and excavation safety. After all, taking the time to properly plan work, inspect conditions, and use appropriate protective systems is critical in preventing serious injuries and ensuring that employees return home safely.
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