OSHA's requirements for confined space entry are detailed in the 29 CFR 1910 standards. Key requirements include:

1. Atmospheric Testing: The atmosphere within the confined space must be tested periodically to ensure that continuous forced air ventilation is preventing the accumulation of hazardous atmospheres. Employees entering the space must be given the opportunity to observe this testing [1].

2. Hazardous Atmosphere Detection: If a hazardous atmosphere is detected during entry, employees must leave the space immediately, and the space must be evaluated to determine how the hazardous atmosphere developed. Measures must be implemented to protect employees before any subsequent entry [1].

3. Permit System: Employers must develop a written permit space program that includes procedures for safe entry, such as specifying acceptable entry conditions, isolating the space, and providing necessary equipment like testing and monitoring devices, ventilation, and personal protective equipment [2].

4. Training: Employers are required to provide training to ensure that all employees understand the hazards and the procedures necessary for safe entry into confined spaces [3].

5. Rescue and Emergency Services: Employers must develop and implement procedures for summoning rescue and emergency services, and for rescuing entrants from permit spaces [4].

6. Reclassification of Spaces: A permit-required confined space can be reclassified as a non-permit space if all hazards are eliminated without entry into the space. This must be documented and made available to employees [1].

These requirements are designed to ensure the safety of employees working in confined spaces by controlling potential hazards and ensuring proper procedures and equipment are in place.