OSHA has specific regulations for excavation work to protect employees from cave-ins and other hazards [1]. These regulations apply to all open excavations in the earth's surface, including trenches [2].

Key requirements include:

• Protective Systems: Employees in excavations must be protected from cave-ins by an adequate protective system, unless the excavation is made entirely in stable rock or is less than 5 feet deep and a competent person has examined the ground and found no indication of a potential cave-in 3, 20.
• Sloping and Benching: If sloping or benching systems are used, their design must adhere to specific requirements, such as appropriate angles for different soil types 11, 20. For example, excavations in Type C soil must have a maximum allowable slope of 1 1/2 horizontal to 1 vertical (34 degrees) 11, 19, 20.
• Support Systems: When the stability of adjacent structures is endangered by excavation operations, support systems like shoring, bracing, or underpinning must be provided 1, 18.
• Underground Installations: Before opening an excavation, the estimated location of utility installations (sewer, telephone, fuel, electric, water lines, etc.) must be determined [3]. Utility companies should be contacted to establish the exact location of these installations [3].
• Hazardous Atmospheres: Excavations greater than 4 feet in depth must be tested for oxygen deficiency or hazardous atmospheres before employees enter 6, 15. Precautions must be taken to prevent employee exposure to hazardous atmospheres, including providing proper respiratory protection or ventilation 6, 16.
• Water Accumulation: Employees should not work in excavations with accumulated water unless adequate precautions have been taken, such as special support or shield systems, water removal, or safety harnesses and lifelines 1, 16.
• Inspections: Daily inspections of excavations, adjacent areas, and protective systems must be conducted by a competent person for any evidence of potential cave-ins, failure of protective systems, hazardous atmospheres, or other hazardous conditions 3, 14. Inspections are also required after every rainstorm or hazard-increasing occurrence 3, 14.
• Access and Egress: A safe means of egress, such as a stairway, ladder, or ramp, must be located in trench excavations that are 4 feet or more in depth, requiring no more than 25 feet of lateral travel for employees 6, 15.
• Protection from Falling Loads and Equipment: Employees should not be permitted underneath loads handled by lifting or digging equipment and must stand away from vehicles being loaded or unloaded 6, 15.

It's important to consult the full OSHA regulations and any applicable state or local requirements for detailed guidance.