OSHA's requirements for confined space entry are detailed in the 29 CFR 1910.146 standard, which outlines the necessary precautions and procedures to ensure safety. Key requirements include:

1. Permit-Required Confined Spaces: Employers must identify and evaluate confined spaces to determine if they are permit-required. A permit-required confined space has one or more of the following characteristics: a hazardous atmosphere, potential for engulfment, an internal configuration that could trap or asphyxiate, or any other recognized serious safety or health hazard [1].

2. Atmospheric Testing: Before entry, the internal atmosphere must be tested for oxygen content, flammable gases and vapors, and potential toxic air contaminants. Continuous monitoring is required to ensure safe conditions are maintained [2].

3. Ventilation: Continuous forced air ventilation must be used to eliminate any hazardous atmosphere before entry and must continue until all employees have exited the space [2].

4. Entry Permits: A written entry permit must be issued before entry, detailing the hazards, entry conditions, and the measures taken to ensure safety. The permit must be available to all entrants [3].

5. Training and Roles: Employees must be trained for their specific roles, such as authorized entrants, attendants, and entry supervisors. The training ensures they understand the hazards and the procedures to follow [4].

6. Emergency and Rescue Procedures: Employers must develop and implement procedures for summoning rescue and emergency services, and for rescuing entrants from permit spaces. Unauthorized personnel must be prevented from attempting a rescue [5].

7. Reevaluation and Reclassification: If conditions change, the space must be reevaluated, and if necessary, reclassified as a permit-required confined space. If all hazards are eliminated, it may be reclassified as a non-permit space [6].

These requirements are designed to protect workers from the significant risks associated with confined spaces, ensuring that all necessary precautions are taken before and during entry.