When working with open manholes, several safety measures should be implemented to prevent accidents and protect workers. Here's a breakdown of key requirements:

1. Guarding the Opening: When manhole or vault covers are removed, the opening must be promptly guarded by a railing, temporary cover, or other suitable barrier to prevent accidental falls and protect workers from foreign objects entering the manhole [1].
2. Fall Protection: Ensure workers on walking/working surfaces are protected from falling through holes by using personal fall arrest systems, covers, or guardrail systems [2]. Covers should be secured to prevent accidental displacement and marked with "HOLE" or "COVER" to warn of the hazard [3].
3. Atmospheric Testing: Before entering a manhole, test the internal atmosphere for combustible gas and oxygen deficiency [1]. If unsafe conditions are detected, ventilate the work area to make it safe for entry [4].
4. Continuous Air Supply: Provide an adequate continuous supply of air when combustible or explosive gas vapors have been detected, when organic solvents or open flame torches are used, or when the manhole is located in a public right of way exposed to gas seepage, or if a toxic gas or oxygen deficiency is found [4].
5. Ladder Use: Use ladders to enter and exit manholes exceeding 4 feet in depth [4]. Ensure manhole steps are capable of supporting the maximum intended load and are inspected at the start of each work shift [5].
6. Emergency Assistance: While work is being performed in a manhole, a person with basic first aid training must be immediately available to render assistance if a safety hazard exists 1, 7.
7. Falling Object Protection: Implement measures to prevent objects from falling into the manhole, such as toeboards, screens, or guardrail systems [6].

It's important to remember that these are general guidelines, and specific situations may require additional precautions. Always assess the specific hazards of the worksite and adjust safety measures accordingly.