How long will a d oxygen tank last on 3.5 liters?

The duration a D oxygen tank lasts depends on its size and the flow rate of oxygen being used. A typical D tank contains about 425 liters of oxygen. At a flow rate of 3.5 liters per minute, the tank would last approximately 121 minutes, or just over 2 hours, if fully filled. However, actual duration may vary based on tank pressure and specific usage conditions.