In trenches that are ___ feet or more in depth, the hazardous atmosphere must be checked for oxygen levels?

For trenches that are 4 feet or more in depth, it is essential to check for hazardous atmospheres, including ensuring adequate oxygen levels. This requirement is in place because deeper trenches pose a greater risk of encountering conditions like low oxygen, the presence of toxic gases, or other atmospheric hazards. Understanding this regulatory standard helps ensure workers' safety by identifying potential dangers that may not be immediately visible at shallower depths. Checking the atmosphere is a critical safety measure for mitigating risks associated with working in confined or enclosed spaces.