When working with trenches, there are several key safety requirements to ensure the safety of employees:

1. Observation and Supervision: Ensure that there is an employee on the surface who can observe the employee working in the trench. This is crucial for immediate assistance in case of an emergency [1].

2. Material Handling: Operators of powered mobile equipment or cranes should not lower materials into a trench unless they have unrestricted visibility or a signaller is used to direct the movement. Employees should not be under any material being lowered [1].

3. Illumination and Barriers: Trenches should be adequately illuminated when work is being carried out, and barriers should be set up to prevent inadvertent entry and protect workers from vehicular traffic [1].

4. Slope and Support: The walls of a trench should be sloped or supported to prevent collapse. For example, in 'hard and compact soil', walls should be sloped at an angle of not less than 30 degrees from the vertical [2]. If the trench is more than 1.2 meters deep, shoring, bracing, or caging should be used unless the trench is in solid rock [3].

5. Safe Access and Egress: Provide safe means of entering and exiting the trench, such as ladders, stairways, or ramps, located no more than 8 meters from where the worker is working [4].

6. Water and Hazardous Atmospheres: Keep trenches free of water accumulation and test for hazardous gases or oxygen deficiency before entry. Adequate ventilation should be provided to prevent the accumulation of hazardous gases [5].

7. Spoil Piles: Ensure that spoil piles are at least 1 meter away from the edge of the trench to prevent materials from falling back into the trench [2].

8. Certification and Inspection: Shoring, bracing, or caging should be certified as adequate by an engineer, and proof of certification should be available upon request [3].

By adhering to these guidelines, you can significantly reduce the risks associated with trench work and ensure a safer working environment for all employees involved.