Which of the following conditions must be met before a marine chemist will issue a certificate for a compartment to be "safe for workers, safe for hot-work"?

Correct Answer: Option D — All of the above.

A Marine Chemist's certification requires a comprehensive assessment of the atmosphere. This includes verifying that toxic gas concentrations are within safe limits, combustible gas levels are below 10% of the Lower Flammable Limit (LFL), and no residues exist that could generate hazardous vapors under hot-work conditions, ensuring total worker safety.