Air Consumption Rate
Definition
Air Consumption Rate (ACR) measures the volume of breathing gas a diver consumes per minute under specific conditions, usually surface pressure.
More on Air Consumption Rate
Air Consumption Rate is a fundamental metric for planning safe and efficient dives. It allows divers to calculate how long their breathing gas will last at different depths. The most common form of this measurement is Surface Air Consumption (SAC) rate, which normalizes gas usage to surface pressure (1 ATA). Knowing your ACR helps with dive planning, gas management, and reducing anxiety underwater. Environmental factors, workload, thermal comfort, and stress can all increase your air usage. Divers are encouraged to record and average multiple dives to find their personal SAC rate for various conditions.
Frequently Asked Questions
To calculate your ACR, record the pressure drop in your tank during a dive, multiply by tank volume to get gas used, divide by bottom time, and adjust for depth by dividing by the ambient pressure in ATA. This gives your SAC rate in liters per minute (L/min).
Several factors affect ACR, including stress, poor trim, excessive movement, cold water, and poor buoyancy control. Streamlining your gear, breathing slowly and deeply, and improving fitness can all help reduce consumption.
For recreational divers, a SAC rate between 15–25 L/min is typical. Technical divers often aim for 10–15 L/min. Training and relaxation help improve this over time.
No, SAC (Surface Air Consumption) is pressure-based, while RMV (Respiratory Minute Volume) is volume-based. RMV accounts for tank size, making it more consistent across equipment setups.
Understanding your ACR allows you to estimate how long your tank will last at a given depth, ensuring you return to the surface with a safe gas reserve. It's crucial for decompression dives and overhead environments.