A tank or compartment is "gas free" when there is an absence of dangerous concentrations of __________.

Correct Answer: Option C — flammable or toxic gases

Gas-freeing is the process of removing flammable or toxic vapors to reach safe atmospheric levels. A space is officially gas-free when testing confirms that concentrations of these hazardous gases are below established threshold limits, ensuring the environment is safe for personnel entry or the commencement of hot work.