According to OSHA, a trench is any excavation longer than it is deep and less than 15 ft. wide. Trenching and excavation rank among the construction industry’s most perilous activities. Tragically, every year, lives are lost in trenching-related accidents. It’s essential to understand that appearances can be deceiving, and just because a trench “looks safe” doesn’t mean it is. Trenches can cave in suddenly, posing a grave threat to workers. Even a mere cubic yard of dirt can easily crush or engulf a worker. Educating your crews about trench safety is paramount. When working within a trench, strict adherence to OSHA regulations is the key to safeguarding yourself and your colleagues.
Trenches that are 5 ft. deep or deeper must be equipped with a protective system. For trenches reaching a depth of 20 ft. or more, a protective system must be designed and approved either by a registered professional engineer and based on PE-approved tabulated data corresponding to the system in use.
Recognize the Hazards
Never rely on appearances alone to determine whether it’s safe to work in a trench. The fact that a trench “looks safe” or resembles other trenches you’ve worked in doesn’t guarantee safety. Trench collapses can happen without warning, generating an immense force that can crush and suffocate anyone trapped inside. The pressure from a trench cave-in is so formidable that even a worker with their head and shoulders above ground can be fatally injured by the encroaching soil. The only way to work safely in a trench is by implementing the appropriate trench protection system, considering the soil type and trench depth. Establish a trench safety plan for your worksite so that workers have a clear procedure to ensure the trench they’re working in is secure.
Develop your Plan for Trench and Excavation Safety
Type A Soil
The first step in developing your protection plan is to identify the type of material you are trenching in. Material can be classified as type A, B or C. Type A soil is the most stable, with an unconfined compressive strength of at least 1.5 tons per square foot (sf). Type A soil should be free from fissures, water seepage, or prior disturbance. Examples include highly cohesive clay.
Type B Soil
Type B soil is less stable than Type A, with an unconfined strength between 0.5 and 1.5 tons per sf. Examples of Type B soil include wet or fissured clay, gravel, silt, and loam.
Type C Soil
Type C soil is the least stable, possessing an unconfined strength of less than 0.5 tons per sf. Granular soils, like sand and gravel, typically fall under Type C due to their low cohesion and inability to stick together.
How to Classify Type A,B & C Soil for Trench and Excavation Safety
There are many ways to test soil to verify its classification. One quick way to estimate a soil’s classification is the thumb penetration test. To perform this test, press your thumb into the soil. When your thumb cannot depress the material without great effort, it is type A. If your thumb sinks to the end of your thumbnail, it is type B. If your thumb easily penetrates entirely into the soil, it is type C. A more precise way to check soil classification is to use a penetrometer. A pocket penetrometer is a handy tool to quickly and accurately assess the soil you are trenching in.
After identifying the type of material you are trenching in, use that soil classification to select the type of protection you will be using. When crews use trench boxes, spreaders and trench plates, they need be sure to reference the tabulated data or design to verify that the shoring protection is rated for the material classification and depth of your trench. Trenches need to be protected via sloping or benching, reference the information below:
For a comprehensive guide to trench and excavation safety, explore OSHA’s regulations on trench safety and soil classification:
https://www.osha.gov/trenching-excavation
Enhancing Trench and Excavation Safety for Your Team
Your commitment to trench and excavation safety goes beyond regulations; it’s a fundamental duty. Plan ahead and prioritize safety during this hazardous activity to protect your team and ensure a safe and smooth operation!