Which mode of air line respirator uses the least amount of supplied air?

The mode of air line respirator that uses the least amount of supplied air is demand flow. This system operates based on inhalation; air is supplied only when the wearer takes a breath. This efficient use of air means that it conserves the available resources because it will not continuously supply air when the user is not inhaling.

In contrast, continuous flow systems provide a constant stream of air regardless of inhalation status, leading to greater air consumption. Pressure demand systems also maintain a higher supply pressure and can deliver more air than what is typically needed, especially during periods of lower breathing rates. Static supply systems might maintain a ready supply of air but may not adjust based on the user's demand, leading to potentially more wastefulness in the usage of compressed air. Thus, demand flow represents the most efficient mode for air consumption in air line respirators.