Trench Excavation Safety: What Are OSHA Trenching Standards?
Last year saw an alarming increase in trench-related fatalities – almost twice as many construction workers died during excavation work in 2022 than the previous year.
Trench collapses are rarely survivable. It's a grim reminder that an unprotected trench is just a cave-in away from being an early grave. The good news is, we know how to prevent them.
What Is the Definition of Excavation in Construction?
In the construction industry, excavation is the process of removing soil or rock with tools, equipment, or explosives. OSHA's excavation standards define it as "any man-made cut, cavity, trench, or depression in the earth's surface formed by earth removal."
What Does the OSHA Excavation Standard Cover?
OSHA's Excavation standard, 29 CFR 1926 Subpart P, applies to all open excavations made in the Earth's surface.
There are many different types of excavation with varying degrees of risk.
Cut and fill excavation typically involves stripping layers of topsoil and grading the surface to create a level building pad, so the main hazards relate to the use of heavy equipment.
Other types of excavation involve greater depths, resulting in hazards related to cave-ins and collapses.
Trenching excavation is recognized as one of the most hazardous construction activities, which is why the OSHA Excavation standards include a special emphasis on trench safety.
What Is Trenching Safety?
Trenching is a common type of excavation, typically used to bury lines (including water, sewer, or gas) or cables (for power or telecommunications).
A trench is a narrow excavation (relative to its length) made below the ground surface. A trench's depth is generally greater than its width, but OSHA standards define the width of a trench as not greater than 15 feet across, measured at the bottom.
How Deep Can a Trench Be Without Shoring?
A protective system is required for trenches with a depth of at least 5 feet. The protective system can involve:
- Sloping: Cutting the trench wall at an angle inclining away from the excavation
- Benching: Excavating the trench walls to form one or more steps
- Shoring: Installing supports to prevent soil movement and cave-ins
- Shielding: Using trench boxes that will protect workers in the event of a collapse
The choice of protective system will depend on a few variables, including soil type, water content, weather, and more.
Shallower trenches may or may not require a protective system – if a trench is less than 5 feet deep, a competent person should inspect the site to determine if a protective system is required.
Deep trenches have extra requirements – sloping and benching are only acceptable solutions at depths less than 20 feet. Additionally, the protective system for trenches at least 20 feet deep needs to be designed or approved by a registered professional engineer.
When Should Trenches Be Inspected by the Competent Person?
OSHA standards require trenches (and protective equipment) to be inspected by a competent person for hazards on a daily basis, before worker entry. However, they may need to be inspected more often if conditions change.
You also need a competent person for trenching and excavation safety tasks like classifying soil, designing structural ramps, and monitoring water removal equipment.
What Are Common Digging Safety Hazards & Their Remedies?
Trenching and excavation safety involves multiple sets of complex hazards.
Cave-ins and Collapses
Collapses and cave-ins are one of the biggest excavation hazards. A cubic yard of soil can weigh as much as a car, crushing or trapping anyone in its way.
Collapses and cave-ins can be triggered by a few things, including:
- The weight of equipment too close to the edge
- The vibration of traffic or construction equipment
- Unstable or less-than-cohesive soil
- Precipitation or freeze/thaw cycles that compromise the structural integrity of trench walls
Some of these conditions are unavoidable, which is why protective systems are required below a certain depth. Others collapse hazards can be mitigated through measures like keeping supplies, equipment, and removed soil at least 2 feet away from the edge of a trench.
Falls or Falling Objects
Excavations are below ground, so workers need to transport themselves, their supplies, and their equipment in and out – that means the potential for falling or being struck by a falling object.
OSHA requires safe means of entry or exit in trenches 4 feet deep or more, like ladders, steps, or ramps.
Additionally, the Excavation standards address fall hazards by requiring:
- Fall protection around the edges of the excavation
- Scaling of the trench walls to remove loose material
- Keeping equipment and materials away from trench edges
- Ensuring that no one stands below a load carried by lifting or digging equipment
The air in a trench can quickly become an inhalation hazard, thanks to its confined nature, depressed elevation, and lack of elevation. The air can become oxygen-deficient or dangerous gases like carbon monoxide can accumulate.
That's why OSHA's excavation standards require atmospheric testing for trenches more than 4 feet deep.
Water ingress and accumulation is another potential hazard, whether it's through a broken water line, seepage from a nearby body of water, or heavy rain.
These hazards need to be considered during the planning phase and addressed with an emergency action plan.
Trenches can involve a myriad of other hazards too, including the risk of damaging underground utilities, the hazard of working near heavy equipment, exposure to temperature extremes, and more.
Learn More About How to Perform a Safe Excavation
To work safely in excavations or trenches, you need a whole lot more than a blog article under your belt.
While OSHA's Excavation standards don't explicitly require training on the topic, the agency holds employers responsible for training employees in all the hazards they're likely to face and methods for protecting themselves.
Online courses through an OSHA-authorized training provider like us are an effective and efficient way to ensure your people learn everything they need to know.
Our Excavation Safety in Construction course covers the hazards of working in excavations, the role of a competent person on-site, relevant safety measures, and more.