Which statement about entering into a tank which has been sealed for a long time is TRUE?

Correct Answer: Option B — The tank must be tested at frequent intervals to ensure that hazardous gasses have not regenerated.

Atmospheric conditions in sealed tanks can change rapidly due to chemical reactions, oxidation, or the release of trapped gases from sludge. Continuous or frequent re-testing is mandatory to ensure that oxygen levels remain stable and toxic or explosive gases do not regenerate, maintaining a safe environment for personnel working inside.