How does an inert gas system on a tanker function to prevent explosions in cargo tanks?

The function of an inert gas system on a tanker is primarily to ensure safety by preventing explosions in cargo tanks. This is accomplished by using inert gas, which is typically a mix of gases, such as nitrogen and carbon dioxide, that does not support combustion. By introducing inert gas into the cargo tanks, the system effectively dilutes the concentration of flammable vapors in the tank atmosphere.

When the concentration of flammable vapors and air is diluted below the lower explosive limit (LEL), the mixture becomes non-combustible, greatly reducing the risk of an explosion. This process is crucial for maintaining a safe environment during the carrying and loading of volatile cargoes, which is a common operation on oil and chemical tankers.

The other options do not accurately describe the essential action of inert gas systems. Maintaining a positive pressure or filtering out flammable vapors are not the primary methods employed by these systems to ensure safety against explosions in cargo tanks. Instead, the emphasis is on the inert gas's ability to create a safe atmosphere by keeping flammable substances below explosive levels.