Which of the following indicates a properly inerted space?

• A. Oxygen concentration not more than 2%
• B. Oxygen concentration above 20%
• C. Oxygen concentration not more than 8%
• D. Oxygen concentration around 15%

Answer: (C)

Inerting a space means lowering the oxygen level so there isn’t enough oxygen to sustain a flame if flammable vapors are present. In tanker operations, you dilute the air with an inert gas like nitrogen until the oxygen concentration is low enough that ignition cannot easily occur.

Not more than 8% oxygen is the best standard because it reduces the atmosphere to a level where most hydrocarbon vapors cannot reach the flammable range and sustain combustion. Normal air is about 21% oxygen, so anything at or below 8% is significantly safer and widely used as a practical threshold for a properly inerted space.

Having oxygen near normal levels (around 20% or even around 15%) means there’s still enough oxygen to support ignition, so it isn’t inerted. Going to an extremely low level like 2% is technically possible, but it’s more stringent than needed for typical operations and can introduce other practical challenges; 8% provides a safe, workable standard for preventing ignition in many tanker contexts.