Each employee who enters a trench must be protected from cave-ins by a protective system if the excavation is 5 feet or greater in depth, unless it is dug into stable rock. A support system is not required if the trench is less than 5 feet in depth and examination of the ground by a competent person provides no indication of a potential cave-in.
One cubic yard of soil can weigh as much as a car, 3,000 pounds, and comes in many varieties. Some types of soil are stable and some are not. When digging a trench, it's important to know the type of soil you're working with so you know how to properly slope, bench, or shore the trench. This can help prevent a cave-in.
OSHA requires that employers have a competent person to determine the soil type. A competent person is someone who can identify conditions that are hazardous to employees and who also has the authorization to correct these hazards. All trenches that are five feet or deeper must follow OSHA's rules. The appendices of the OSHA Excavation Standard show the various types of support systems that may be used, up to a maximum depth of 20 feet. Any excavation deeper than 20 feet must use a protective system approved by a professional engineer.
For all excavations, a competent person must conduct a full investigation every day, or when any trench conditions change, to identify and remove any potential hazards.
In this video, you will see how a visual inspection of a construction site's soil is performed. You will also see how to test the soil using three of the most common methods: the plasticity test, the thumb penetration test, and the pocket penetrometer test. For best results, OSHA recommends that the competent person use more than one of these methods to test the soil. Knowing the type of soil makes it possible to determine the right protective system to keep workers safe when they're working in an excavation.
Source: OSHA