Yes, respirators may be required in a confined space, especially if a safe atmosphere cannot be maintained through ventilation alone [1]. Here's a breakdown:

• Hazardous Atmosphere: If a hazardous atmosphere exists or is likely to exist, ventilation and purging should be performed before entry [2]. If this is impractical or ineffective, respiratory protective equipment is required [2].
• Specific Hazards: Respirators are needed if airborne concentrations of substances exceed permissible limits, or if there's oxygen deficiency or enrichment [1].
• IDLH Conditions: For Immediately Dangerous to Life or Health (IDLH) atmospheres, specific respirators like a full facepiece pressure demand SCBA or a combination supplied-air respirator with an auxiliary self-contained air supply are required 12, 19.
• Emergency Situations: Responders entering confined spaces for rescue must have appropriate respiratory protection, especially if calibrated direct-reading instruments are unavailable and the situation is assumed to be IDLH 1, 7.

It's also important to remember that if welding, cutting, or heating in a confined space, and sufficient ventilation can't be achieved without blocking access, air line respirators are required [3].