Why do gas masks not supply oxygen to the wearer?

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Carnival mask — Mask Women wearing a mask during Carnival celebrations in Venice, Italy.

Standard gas masks are designed as filtering devices rather than life-support systems. Their primary function is to remove harmful contaminants from the existing ambient air rather than to provide a breathable atmosphere.

The device works by drawing air through filters that use fiber screens to trap solid particles and chemical compounds, such as charcoal, to capture or neutralize poisonous gases. Because these filters only clean the air already present in the environment, they do not add oxygen to the air being inhaled.1

If an environment lacks sufficient oxygen or contains contaminants that cannot be filtered, a standard gas mask is insufficient. In such cases, specialized equipment—such as a mask connected by a hose to a separate tank of oxygen—is required to ensure the wearer has a safe supply of breathable air.1