What does the IMO guidance on entering enclosed spaces require, and which SOLAS regulations back it?

flowchart LR
  A["Identify the enclosed spaces"] --> B["Risk assessment by a responsible officer"]
  B --> C["Entry permit, isolate, ventilate continuously"]
  C --> D["Test the atmosphere from outside at different levels: oxygen 20.9%, flammable gas 0%, H2S and CO within limits"]
  D --> E["Attendant at the entrance, communication, lifeline, rescue gear ready"]
  E --> F["Monitor during entry; evacuate if a reading goes wrong"]

• Instrument: resolution A.1050(27), Revised Recommendations for Entering Enclosed Spaces (2011), superseding MSC/Circ.744 (1996).
• Why: oxygen-deficient (below 20.9%), toxic (H2S, CO) or flammable atmospheres kill without warning, and unprotected rescuers become the next casualties.
• Procedure: identify, risk assessment, entry permit, isolate and ventilate continuously, test from outside at different levels with a calibrated instrument, attendant at the entrance, lighting, lifeline, rescue equipment ready.
• Rule of rules: never enter or attempt a rescue in an unverified atmosphere without breathing apparatus (SCBA).
• SOLAS: XI-1/7 requires a portable instrument for oxygen, flammable gases, hydrogen sulphide and carbon monoxide; III/19 requires entry and rescue drills at least once every two months.
• As Chief Engineer: most enclosed spaces are mine (boilers, crankcases, tanks, cofferdams, duct keels, scavenge spaces); no permit, no entry, and I run the two-monthly drills.