🔍 Key Concepts

• Marine chemist certificates and what “Safe for Men” and “Safe for Fire” actually mean • How vapors and flammable atmospheres can change over time inside confined spaces • The effect of temperature changes and contamination on tank atmospheres

💭 Think About

• Think about what could cause the atmosphere in a certified-safe tank to become unsafe again, even without anyone entering it • Consider whether a change in contents, a change in residual material (muck/sludge/scale), or a change in conditions around the tank (like temperature) could alter vapor levels • Ask yourself: are these potential causes independent, or could more than one of them reasonably affect the safety status?

✅ Before You Answer

• Verify which options involve new or additional vapors being introduced or released into the tank • Check how temperature can influence vapor pressure and the release of flammable or toxic gases • Before choosing, ask: could each listed factor realistically change a tank from safe to unsafe after certification?